|
반중성미자와 중성미자에 대하여
한국학중앙연구원 한국학대학원 박사과정 수료 이재유
(부산고 36회 졸업, 청조동문)
(이메일: jaeyiewlee@hanmail.net)
출처: http://cafe.daum.net/FortheKidnapped/LfAU/91
http://cafe.daum.net/FortheKidnapped/
우주를 구성하는 것을 물질과 반물질로 나눌 수 있을 것이다. 밝음과 어둠의 관계에서와 같이 힘으로 보면 작용과 반작용의 관계를 구성하는 것과 유사한 구조이다.
우주의 창조와 태초의 비밀은 이런 물질과 반물질 내지 작용과 반작용의 관계에서 풀어야 한다. 현재 밝혀진 많은 작은 발견들이 모여서 그런 물질과 반물질 혹은/ 그리고 작용과 반작용의 관계와 그 관계실현으로 인해 과학적 지식과 이론의 내용과 뼈대가 되고 있다.
우주의 진리와 진실에 보다 가까이 가기 위해 다음 가설을 세워본다.
이재유 가설: 양자, 전자, 중성미자는 모두 물질과 반물질의 근원적인 관계에서 보아야 하고 그들 간에 상대적인 작용과 반작용의 결과나 원인으로 계속 환원되든지 반환원 되든지 할 수 있고, 다시 그것은 서로의 작용과 반작용으로 인해 에너지나 힘의 준위도 교체가능하다.
태양에서 행성의 공전 이동법칙과 같이 중심핵을 중심이나 가상의 입자 질량의 중심에서 가까이 다가가면 입자의 회전은 빨라지고 멀어지면 느려지는 소립자나 입자세계에서도 케플러의 법칙(Kepler's law)이 존재한다.
두 그림 출처: http://fracton.khu.ac.kr/~comp/kepler/kepler.htm
우주에서 행성이 태양둘레를 도는 운동에서의 케플러법칙이 소립자세계에서도 작용하고 있다. 소립자들의 입자가속기에서의 가속 충돌실험이나 우주에서의 빅뱅이든 각각 소립자들의 궤도 혹은 오르빗(orbit)이 변화 중심핵을 향한 하강 다운상태나 이탈 들뜬상태는 에너지 준위나 힘의 준위 변이나 변화에 의해 이루지고 특히 그 궤도가 중심핵방향으로 안쪽 궤도로 하강 다운되면 빛이나 광자를 방출하고 바깥궤도에서보다 안쪽 궤도에서 더 빨리 이동하거나 움직인다. 이런 현상은 원형 입자가속기에서 소립자를 원형방향으로 가까이 회전하도록 각도를 꺾어서 가속시키거나 빅뱅과 같이 서로 중심핵이 궤도를 더 가까이 충돌하는 등의 경우에서와 같이 순간적으로 바깥궤도에서 궤도이동 원주거리 중심핵으로 향해 줄여지거나 작아짐에서 그 이동이나 운동에너지를 같은 상태로 보존 내지 유지하려는 항상성 내지 자체 원래 궤도에서의 관성에서의 에너지준위 유지나 보존경향에서 이탈하면서 원주상 안쪽 궤도 이동거리를 상대적으로 더 빨리 이동하거나 회전하는 경향이 있고 중심핵 쪽으로의 당겨짐에 전자기장변화, 에너지준위나 힘준위의 변화나 변이가 광자의 방출로 밝음과 광명이 나타난다. 역으로 소립자가 중심핵으로 벗어나거나 이탈하는 에너지 준위나 힘의 변화는 상대적으로 회전이나 이동이 느려지고 이는 광자의 흡수나 흡착으로 어둠과 암흑이 된다. 그런 광자의 방출이든 흡착이든 에너지준위나 힘의 준위 변화와 변이하는 그 과정에서 중성미자나 반중성미자는 어디든 나타나거나 존재할 수 있다.
양자 - 반양자, 전자 - 반전자, 중성미자 - 반중성미자 간에 상호 환원과 반환원의 변환과 작용과 반작용이 존재할 수 있다.
특히 중성미자 변환에 대해 다음 그림과 같이 어느 특정상태(에너지 준위변화에서의 불안정에서 안정상태) 변환의 가설을 세워본다.
위에서 주목하고 중시해야 할 것으로는, 어느 특정 에너지준위나 힘의 상태에서 반타우와 반뮤온 중성미자간에 변환율이 0%라고 하나 끊임없는 물질과 반물질 혹은 / 그리고 작용과 반작용으로 빅뱅이 일어나는 경우에서와 같이 에너지 준위나 힘의 준위 변화로 안정상태에서 불안정상태로 혹은 불안정상태에서 안정상태로 변동이나 변화가 가능할 것이고 변환비율도 변동할 것이다.
참고자료 및 참고문헌:
한국, 우주비밀 풀 열쇠 찾았다…세계 발칵
국내연구진, `중성미자` 마지막 변환상수 측정 성공…중국 이어 두번째
안경애 기자 naturean@dt.co.kr | 입력: 2012-04-03 19:44
[2012년 04월 04일자 15면 기사]
국내 연구진이 중국에 이어 우주 생성의 비밀을 풀 수 있는 중요한 열쇠로 꼽히는 `중성미자'의 마지막 퍼즐을 맞추는 데 성공했다.
서울대 김수봉 교수(물리천문학부ㆍ사진)는 서울대ㆍ경북대ㆍ부산대ㆍ성균관대ㆍ세종대ㆍ전북대 등 12개 대학이 참여한 `중성미자검출설비(리노ㆍRENO)' 연구진이 지금까지 풀지 못 했던 전자중성미자와 뮤온중성미자간 변환비율이 10.3%라는 결론을 내렸다고 3일 밝혔다.
연구진은 이 결과를 2일 물리학 분야의 권위지인 `피지컬리뷰레터스'에 투고하고, 3일 전국적으로 실험결과를 발표하는 세미나를 개최했다.
◇실험결과 발표 중국에 선수 빼앗겨=우리 연구진은 2006년 3월부터 영광 원자력발전소 부근에 중성미자검출설비를 짓기 시작해 지난해 5월 완공하고 8월부터 실험을 시작했다. 그러나 이번 발표는 중국 연구진에 3주 뒤졌다. 지난 3월8일 중국과 미국 연구진이 주도한 중국 다야베이 원전 중성미자 연구단은 변환상수가 9.2%라는 결론을 얻고 같은 학술지에 논문을 투고했다. 양쪽 연구진은 논문을 투고하는 동시에 실험결과를 전세계에 발표해 공개 검증절차를 거친다.
우리 연구진은 중국에 비해 3주 늦게 결과를 내놨지만 대형 검출시설을 이용한 연구결과는 통상 한달 내의 시간간격이 있어도 동등한 업적으로 취급받는 만큼 과학적 발견의 업적은 동등하게 평가받을 것으로 기대하고 있다. 특히 우리의 측정 신뢰도가 6.3시그마(6시그마=10억회 중 2회 틀릴 가능성)로, 중국의 5.2시그마(5시그마=1000만회 중 6회 틀릴 가능성)에 비해 높다는 설명이다. 통상 3∼5시그마의 신뢰도는 틀림없는 결과이자 과학적 발견으로 받아들여진다.
학술지를 발간하는 미국물리학회측은 두 연구진의 실험결과를 심사해 게재 여부를 결정할 예정이다. 중요한 과학적 발견을 담은 논문이 연이어 투고될 경우 같은 호에 묶어 소개하는 경우가 많다.
김수봉 교수는 "두 팀이 얻은 변환상수는 오차범위 내에 있어 결국 같은 결과라고 볼 수 있다"고 말했다.
◇우주 비밀 한 걸음 다가가=중성미자의 마지막 남은 변환상수를 밝힌 것은 물리학계의 대사건으로 받아들여진다.
중성미자는 우주에 광자 다음으로 많은 입자지만 질량이 거의 없고 물질과 상호작용을 하지 않아 `유령입자'로 알려져 있다. 빅뱅 직후 만들어져 전 우주에 퍼져 있으며, 핵융합이나 핵분열 시에도 만들어지지만 질량이나 특성이 베일에 가려져 있었다.
중성미자는 뮤온ㆍ타우ㆍ전자 등 3가지가 있는데, 뮤온과 타우, 타우와 전자, 전자와 뮤온중성미자가 시간이 가면 서로 자유롭게 형태를 바꾼다. 지금까지 뮤온-타우중성미자 변환 비율이 100%, 타우-전자중성미자 80%로 밝혀졌고, 이번에 전자-뮤온중성미자가 10.3%의 비율로 바뀐다는 사실이 확인됐다.
출처:
http://www.dt.co.kr/contents.html?article_no=2012040402011557650002&ref=naver
우주 생성의 비밀, 전남대에서 밝혀
[노컷뉴스] 2012년 04월 04일(수) 오후 03:57 |
[광주CBS 권신오 기자]
노벨 물리학상 주제로 세번이나 오를 정도로 물리학의 핵심 연구분야인 중성미자 연구에서 전남대학교 연구진이 중국에 이어 세계 두 번째로 중성미자의 세 가지 변환상수 중 마지막 남은 상수를 풀었다.
전남대 우주소립자연구소(소장 김재률, 임인택,주경광 교수)는 서울대 등 국내 10여 개 대학과 함께 지난 3일 “오랫동안 측정하지 못했던 마지막 중성미자 변환상수가 10.3%임을 확인했다”고 밝혔다.
연구진은 “이 결과는 10억번에 2번 정도 틀릴 확률로 정확도가 높아 중국의 연구결과보다 더 믿을 만한 수치다”며 관련 연구논문을 미국 물리학회의 ‘피지컬 리뷰 레터스(Physical Review Letters)’지에 제출했다고 밝혔다.
중성미자는 우주를 구성하는 기본 입자 중 하나로 양성자나 전자보다도 훨씬 더 작은 소립자의 일종으로 질량이 워낙 작은 데다 빛의 속도로 움직이며 다른 물질과 반응하지 않아 ‘유령입자’로 불리기도 한다.
현재까지 밝혀진 중성미자의 종류는 전자,뮤온,타우 중성미자 등 세가지며, 이들 중성미자는 전자에서 뮤온으로, 뮤온에서 타우로, 타우에서 전자로 서로 자유롭게 형태를 바꾸는 것으로 알려져 있다.
과학자들은 그동안 뮤온-타우 간 변환비율(진동변환상수)이 100%, 타우-전자 간 변환비율이 80%임을 밝혔으나 전자-뮤온 간 변환비율은 측정하지 못했다.
따라서 이번 연구결과는 중성미자의 성질과 기본입자의 원리를 규명하고 교과서를 새로 써야 할 만큼 획기적인 발견을 거듭할 것으로 기대하고 있다.
김재률 교수(물리학과, 사진 아래 왼쪽에서 두번째)는 “중성미자로 물질의 기원을 찾는 후속 연구에서 선도적 위치에 설 수 있게 됐다”며 “우리 순수 기술로 만들어진 국내시설을 기반으로 우리나라 전문 인력의 역량이 뛰어남을 입증하기도 했다”고 밝혔다.
전남대 연구진은 국내 대학들과 함께 2011년 8월 전남 영광 원자력발전소 부근에 세계에서 가장 성능이 뛰어난 중성미자 검출 설비를 갖추고 우주생성의 비밀을 풀기 위한 실험에 본격 착수했다.
특히 전남대는 영광 현지 지반 및 지질 조사, 액체섬광검출용액 R&D, 중성미자 신호 추출을 위한 데이터 분석 등 실험의 중추적인 역할을 담당했다.
ppori5@hanmail.net
출처:
전남대 연구진, 우주생성 비밀 캐냈다
[뉴시스] 2012년 04월 04일(수) 오후 03:29 |
공유하기
FacebookTwitter가 가| 이메일| 프린트 【광주=뉴시스】구용희 기자 = 전남대학교 연구진이 중국에 이어 세계 두 번째로 중성미자의 세 가지 변환상수 중 마지막 남은 상수를 풀었다.전남대 우주소립자연구소는 서울대 등 국내 10여 개 대학과 함께 지난 3일 오랫동안 측정하지 못했던 마지막 중성미자 변환상수가 10.3%임을 확인했다고 4일 밝혔다.
연구진은 "이 결과는 10억번에 2번 정도 틀릴 확률로 정확도가 높아 중국의 연구결과보다 더 믿을 만한 수치다"며 관련 연구논문을 미국 물리학회의 '피지컬 리뷰 레터스'(Physical Review Letters)지에 제출했다고 덧붙였다.
중성미자는 우주를 구성하는 기본 입자 중 하나로 양성자나 전자보다도 훨씬 더 작은 소립자의 일종으로 질량이 워낙 작은 데다 빛의 속도로 움직이며 다른 물질과 반응하지 않아 '유령입자'로 불리기도 한다.
현재까지 밝혀진 중성미자의 종류는 전자·뮤온·타우 중성미자 등 세가지며 이들 중성미자는 전자에서 뮤온으로, 뮤온에서 타우로, 타우에서 전자로 서로 자유롭게 형태를 바꾸는 것으로 알려져 있다.
과학자들은 그 동안 뮤온-타우 간 변환비율(진동변환상수)이 100%, 타우-전자 간 변환비율이 80%임을 밝혔으나 전자-뮤온 간 변환비율은 측정하지 못했다.
따라서 이번 연구결과는 중성미자의 성질과 기본입자의 원리를 규명하고 교과서를 새로 써야 할 만큼 획기적인 발견을 거듭할 것으로 기대하고 있다.
김재률 교수(물리학과)는 "중성미자로 물질의 기원을 찾는 후속 연구에서 선도적 위치에 설 수 있게 됐다"며 "순수 우리 기술로 만들어진 국내시설을 기반으로 우리나라 전문 인력의 역량이 뛰어남을 입증하기도 했다"고 말했다.
전남대 연구진은 국내 대학들과 함께 지난해 8월 전남 영광 원자력발전소 부근에 세계에서 가장 성능이 뛰어난 중성미자 검출 설비를 갖추고 우주생성의 비밀을 풀기 위한 실험에 본격 착수했다.
특히 전남대는 영광 현지 지반 및 지질 조사, 액체섬광검출용액 R&D, 중성미자 신호 추출을 위한 데이터 분석 등 실험의 중추적인 역할을 담당했다.
persevere9@newsis.com
<저작권자ⓒ 공감언론 뉴시스통신사. 무단전재-재배포 금지.>
구용희(기자)
출처:
‘우주기원 열쇠’ 중성미자 질량 밝혀졌다
글씨크기URL단축목록메일인쇄태양을 비롯한 별의 중심부에서 핵융합 반응이 일어날 때 발생하는 중성미자(뉴트리노)의 질량이 밝혀졌다. 우주 탄생의 비밀과 별의 내부 활동, 우주 구성 물질의 실체를 밝히는 열쇠를 제공하는 획기적인 성과로 평가된다.
▲ 입자물리학의 표준모형. 원자를 구성하는 6개의 쿼크 입자(붉은색 그룹) 6종류와 가벼운 6개의 경입자(초록색 그룹)는 세상 만물의 가장 작은 구성단위다. 초록색 그룹의 아래 세 입자는 전자·뮤온·타우 중성미자로 이번에 처음으로 질량이 밝혀졌다. 보라색 그룹은 각 입자간 힘을 나타내며, 가운데의 힉스 입자는 각 입자의 질량을 결정한다.
물리학연구그룹 ‘슈퍼B’ 홈페이지
영국 유니버시티칼리지 런던(UCL)의 오퍼 라하프 교수 연구팀은 22일(현지시간) 물리학 저널 ‘피지컬 리뷰 레터스’에 게재한 논문에서 “중성미자의 질량은 0.28전자볼트(eV) 이내”라고 밝혔다. 이는 중성미자의 질량이 원자 가운데 가장 가벼운 수소원자의 10억분의1에 불과하다는 뜻이다.
라하프 교수 연구팀은 직접적인 실험 대신 우주의 3차원 지도를 그리는 국제 공동연구 ‘슬론 전천 탐사’의 결과물을 이용해 중성미자의 질량을 쟀다. 우주 지도를 그린 뒤 은하계 행성들의 분포와 상호 역학관계를 분석해 중성미자의 질량을 추정해낸 것이다. 라하프 교수는 “2002년 이론적인 중성미자 질량 최대치가 1.8eV 이내라는 분석을 내놓은 바 있다.”면서 “이번 연구로 중성미자의 정확한 질량을 측정한 것은 놀라운 일”이라고 설명했다.
현대 물리학에서 정설로 받아들여지고 있는 입자물리학 표준모형에 따르면 만물을 구성하는 기본 입자는 원자 핵을 만드는 6개의 무거운 중입자 ‘쿼크’와 6개의 가벼운 경입자 ‘랩턴’으로 구성돼 있다. 경입자 중 전자·뮤온·타우 등 세 종류의 중성미자는 한때 질량이 없는 것으로 알려질 정도로 작고 가볍다. 엄지손가락 하나를 들고 있으면 1초 동안 태양에서 발생한 중성미자 수백억개가 손톱 부분을 통과할 정도로 많은 양이 존재하지만 지나는 물체와 상호작용을 전혀 일으키지 않아 ‘유령입자’로 불려 왔다.
물리학자들이 중성미자의 실체에 대해 큰 관심을 갖는 것은 중성미자가 우주 전체의 25% 정도를 차지하고 있는 암흑물질의 주요 구성요소인 데다 우주 탄생과 별 활동의 핵심 부산물이기 때문이다. 물리학자들은 중성미자의 정확한 역할을 알면 빅뱅(대폭발) 직후 별과 은하가 어떻게 생성됐는지는 물론 태양을 비롯한 별 내부에서 어떤 일이 벌어지고 있는지를 알 수 있을 것으로 기대하고 있다. 이 같은 중요성 때문에 1930년 물리학자 볼프강 파울리가 중성미자의 존재를 이론적으로 입증한 뒤 관련 연구에서만 8명의 노벨물리학상 수상자가 나오기도 했다.
박건형기자 kitsch@seoul.co.kr
2010-06-24 20면
출처: http://www.seoul.co.kr/news/newsView.php?id=20100624020012
중성미자 위키백과, 우리 모두의 백과사전.이동: 둘러보기, 찾기 중성미자
구성 기본입자
가족 페르미온
무리 렙톤
반입자 반중성미자
이론 볼프강 파울리(1930)
발견 프레더릭 라이너스 등(1956)
기호 νe, νμ, ντ
전하 0
스핀 1/2
중성미자(中性微子) 또는 뉴트리노[1](neutrino)는 약력과 중력에만 반응하는, 아주 작은 질량을 가진 기본입자로, 스핀은 1/2인 페르미온과, 렙톤이며, 약 아이소스핀이 -1/2으로 전하를 띠지 않는다. 1990년대 말까지 질량이 없다고 생각했으나, 1999년 슈퍼 카미오칸데 실험 이후 여러 실험을 통해 미세하지만, 질량이 있다고 밝혀졌다(중성미자 진동). 그러?나 질량이 너무 작아 아직 직접적으로 질량을 측정하지 못하고 있다.
볼프강 파울리가 처음이 이 입자를 '중성자(neutron)'라고 부르기로 제안하였지만, 몇 년 후인 1932년에 채드윅이 지금의 중성자를 발견하고 그 입자를 중성자(neutron)라고 불렀다. 이로 말미암아 서로 다른 두 입자에 같은 이름이 붙게 되었다. 엔리코 페르미가 다음 해인 1933년에 베타 붕괴의 이론을 발표하며, 파울리의 '중성자(neutron)'에 '작다.'라는 이탈리아어의 접미어 '-ino'를 붙여서, '뉴트리노(neutrino)'로 부르게 되었다.
2011년 9월 22일 유럽 입자 물리 연구소(CERN)의 공식 발표에 의하면, 732km 떨어진 두 도시를 대상으로 뉴트리노 1만 5,000개를 쏘아 보낸 결과, 평균적으로 빛보다 60나노초 더 빨리 도달하였다고 한다. 이는 같은 해 11월 20일 CERN의 재실험에서도 확인되었다.[2]
그런데 2012년 2월 말 오페라 연구진은 실험 과정의 오류 가능성을 하였다. 오페라 소속 연구자들 가운데 몇 명이 팀을 이뤄 실험 과정을 전면 재검토했고 그 결과 그동안 간과해왔던 오류 가능성을 두 가지 발견했다. 연구자들은 광섬유케이블과 GPS 위성을 씀으로써 시간 측정 오차를 2.3나노초 이내로 정밀하게 보정했다고 주장했다.[3]
목차 [숨기기]
1 역사
2 종류
3 유도 베타 붕괴를 통한 직접검출
4 실험
5 주석
6 같이 보기
[편집] 역사1930년대의 베타 붕괴 실험에서, 기존의 물리학으로 설명할 수 없는 붕괴 에너지 스펙트럼을 발견하였다. 스펙트럼의 연속성에서 착안하여, 볼프강 파울리는 에너지 스펙트럼에 맞추기 위해 질량이 아주 작은 (또는 0인) 입자를 가정하여 중성미자라는 입자를 도입하였고, 이후에 실험적으로 발견되었다.
[편집] 종류오른쪽의 표와 같이 중성미자는 3세대로 되어 있다. 이들은 총 렙톤 수를 보존하지만, 중성미자 진동으로 인해 각 맛깔의 렙톤 수는 보존하지 않는다.
표준모형의 왼손 중성미자 이름 기호 질량
1세대 (전자-)
전자 중성미자 < 2.5 eV
전자 반중성미자 < 2.5 eV
2세대 (뮤온)
뮤온 중성미자 < 170 keV
뮤온 반중성미자 < 170 keV
3세대 (타우온)
타우 중성미자 < 18 MeV
타우 반중성미자 < 18 MeV
[편집] 유도 베타 붕괴를 통한 직접검출중국의 왕칸창(Kan-Chang Wang)은 1942년 중성미자의 실험적 검출방법으로 베타포획의 사용을 처음으로 제안하였다[4]. 이에 1946년 코웬 클라이드(Clyde Cowan) 과 라이너스 프레드릭(Frederick Reines) 외 그의 동료( 해리슨 F. B.(F. B. Harrison), 크루스 H. W.(H. W. Kruse), 그리고 맥과이어 A. D(A. D. McGuire)) 은 이 과정을 통해 실제로 중성미자를 검출하였다[5]. 이후 이 실험은 코웬-레인스 중성미자 실험으로 알려지게 되며, 이들에게 중성미자 검출의 공로로써 1995년의 노벨 물리학상이 주어졌다.
[편집] 실험CHORUS(CERN Hybrid Oscillation Research apparatUS), DONuT(Direct Observation of Neutrino Tau), OPERA(Oscillation Project with Emulsion-tRacking Apparatus)등의 실험에서 중성미자에 대한 많은 연구가 진행되었다. 현재 OPERA 실험에 대한 결과 데이터 분석이 진행중이며 한국의 국립경상대학교 고에너지 물리실험실팀이 참가 중이다.
[편집] 주석1.↑ http://www.ps.uci.edu/~superk/neutrino.html
2.↑ “빛 보다 빠른 중성미자, 2차 실험서도 빛보다 빨라”, 《서울경제신문》, 2011년 11월 20일 작성. 2011년 11월 23일 확인.
3.↑ “빛보다 빠른 물질 있나? 없나?”, 《THE SCIENCE》, 2012년 4월 4일 작성. 2012년 4월 4일 확인.
4.↑ K.-C. Wang (1942). A Suggestion on the Detection of the Neutrino. Physical Review 61 (1?2): 97. doi:10.1103/PhysRev.61.97.
5.↑ C.L Cowan Jr., F. Reines, F.B. Harrison, H.W. Kruse, A.D McGuire (July 20, 1956). Detection of the Free Neutrino: a Confirmation. Science 124 (3212): 103?4. PMID 17796274. doi:10.1126/science.124.3212.103.
http://ko.wikipedia.org/wiki/%EC%A4%91%EC%84%B1%EB%AF%B8%EC%9E%90
중성미자 진동 위키백과, 우리 모두의 백과사전.이동: 둘러보기, 찾기 중성미자 진동(中性微子振動, neutrino oscillation)은 중성미자의 맛깔이 시간이 흐름에 따라 변하는 양자 역학 현상이다. 이는 브루노 폰테코르보(Bruno Pontecorvo)가 예측하였다. 어떤 한 중성미자가 특정 맛깔을 가질 확률은 중성미자가 전파해 나감이 따라서 달라진다. 중성미자 진동은 이론과 실험에서 큰 관심의 대상이다. 이 현상의 관측은 중성미자가 질량을 가지고 있다는 것을 의미하며, 이것은 입자 물리학에서 기존의 표준 모형에서 고려하지 않았던 부분이다.
목차 [숨기기]
1 관측
1.1 태양 중성미자 진동
1.2 대기 중성미자 진동
1.3 원자로 중성미자 진동
1.4 빔을 이용한 중성미자 진동
1.5 붕괴 진동
2 주석
[편집] 관측중성미자 진동에 대한 많은 증거들이 다양한 출처로부터, 다양한 측정기술로, 넓은 중성미자 에너지 범위에 대해서 수집되었다.
[편집] 태양 중성미자 진동중성미자 진동 현상을 측정한 최초의 실험은 1960년대 후반에 레이먼드 데이비스가 행한 홈스테이크 실험(Homestake Experiment)이다. 데이비스는 염소 기반의 검출기로 태양에서 나오는 중성미자들의 흐름의 결함을 관측하고, 이론과 어긋나는 결과를 얻었다. 이를 태양 중성미자 문제라로 부른다. 이어 방사능 물질이나 물을 이용한 체렌코프 검출기들에 의해 결함이 확인되었으나, 2001년 서드버리 중성미자 관측소(Sudbury Neutrino Observatory)가 중성미자의 맛깔이 변한다는 사실을 증명하기 전까지는 중성미자 진동이 태양 중성미자 결함의 원인으로 단정지을 수 없었다.
태양 중성미자는 에너지가 20MeV 이하이며, 태양에서 검출기까지 1AU를 날아온다. 태양 내부에서 MSW 효과라고 알려진 공명을 통해서 5 MeV 이상의 에너지에서 태양 중성미자 진동이 일어나며, 진공에서의 중성미자 진동은 다른 과정이다.
[편집] 대기 중성미자 진동뮤온이 대기중에서 붕괴하여 전자 중성미자를 만들어 내므로, IMB, MARCO 와 카미오칸데 II 같은 대형 검출기로 뮤온과 전자 중성미자의 비율이 맞지않는것이 관측되었다. 슈퍼 카미오칸데실험은 수백 MeV에서 수 TeV 에너지 범위에서 지구 반경을 고려하여 매우 정밀한 중성미자 진동을 측정하였다.
[편집] 원자로 중성미자 진동많은 실험들이 원자로에서 나오는 전자 반중성미자의 진동을 측정하려고 하고 있다. 원자로에서 만들어지는 중성미자는 태양 중성미자와 갈이 수 MeV의 에너지를 갖는다.
[편집] 빔을 이용한 중성미자 진동입자 가속기에서 만들어지는 중성미자 빔은 연구하는 데 있어서 중성미자를 통제할 수 있다는 큰 이점이 있다. 대기 중성미자를 관측 해왔던 곳들에서 수 GeV의 에너지를 갖는 중성미자로 많은 실험들이 수행되었다.
[편집] 붕괴 진동2008년, 독일 다름슈타트의 GSI 헬름홀츠 중이온연구소는 프라세오디뮴-140와 프로메튬-142의 방사성 붕괴를 연구하여 원자 붕괴에서 중첩된 진동을 발견하였고, 이를 중성미자 진동과 관련지었다.[1][2]. 그러나 이 현상을 중성미자 진동으로 기술하기위한 이론적 설명에는 아직 의견이 분분하며, 그럴듯한 명확한 이론이 아직없다. [3].
[편집] 주석1.↑ 중성미자를 측정하는 새로운 방법
2.↑ Nuclear physics: A neutrino's wobble?
3.↑ Hendrik Kienert et al., The GSI anomaly, arXiv:0808.2389와 그 안의 참고 문헌들을 참고.
http://ko.wikipedia.org/wiki/%EC%A4%91%EC%84%B1%EB%AF%B8%EC%9E%90_%EC%A7%84%EB%8F%99
Neutrino
From Wikipedia, the free encyclopedia
Jump to: navigation, search
For other uses, see Neutrino (disambiguation).
The first use of a hydrogen bubble chamber to detect neutrinos, on November 13, 1970. A neutrino hit a proton in a hydrogen atom. The collision occurred at the point where three tracks emanate on the right of the photograph.
Composition
Elementary particle
Statistics
Fermionic
Generation
First, second and third
Interactions
Weak interaction and gravitation
Symbol
νe, νμ, ντ, νe, νμ, ντ
Antiparticle
Antineutrinos are possibly identical to the neutrino (see Majorana fermion).
Theorized
νe (Electron neutrino): Wolfgang Pauli (1930)νμ (Muon neutrino): Late 1940s
ντ (Tau neutrino): Mid 1970s
Discovered
νe: Clyde Cowan, Frederick Reines (1956)νμ: Leon Lederman, Melvin Schwartz and Jack Steinberger (1962)ντ: DONUT collaboration (2000)
Types
3 ? electron neutrino, muon neutrino and tau neutrino
Mass
Small, but non-zero. See the mass section.
Electric charge
0?e
Spin
1?2
Weak hypercharge
?1
B ? L
?1
X
?3
A neutrino (?/njuː?triːno?/; Italian pronunciation:?[neu?triːno]) is an electrically neutral, weakly interacting elementary subatomic particle[1] with half-integer spin. The neutrino (meaning "small neutral one" in Italian) is denoted by the Greek letter ν (nu). All evidence suggests that neutrinos have mass but that their mass is tiny even by the standards of subatomic particles. Their mass has never been measured accurately.
Neutrinos do not carry electric charge, which means that they are not affected by the electromagnetic forces that act on charged particles such as electrons and protons. Neutrinos are affected only by the weak sub-atomic force, of much shorter range than electromagnetism, and gravity, which is relatively weak on the subatomic scale. They are therefore able to travel great distances through matter without being affected by it.
Neutrinos are created as a result of certain types of radioactive decay, or nuclear reactions such as those that take place in the Sun, in nuclear reactors, or when cosmic rays hit atoms. There are three types, or "flavors", of neutrinos: electron neutrinos, muon neutrinos and tau neutrinos. Each type also has a corresponding antiparticle, called an antineutrino with an opposite chirality.
Most neutrinos passing through the Earth emanate from the Sun. About 65?billion (6.5×1010) solar neutrinos per second pass through every square centimeter perpendicular to the direction of the Sun in the region of the Earth.[2]
Contents
?[hide]?
? 1History
? 1.1Pauli's proposal
? 1.2Direct detection
? 1.3Neutrino flavor
? 1.4Solar neutrino problem
? 1.5Oscillation
? 1.6Supernova neutrinos
? 2Properties and reactions
? 2.1MSW effect
? 2.2Nuclear reactions
? 2.3Alteration of nuclear decay rate
? 2.4Induced fission
? 2.5Types
? 2.6Antineutrinos
? 2.7Flavor oscillations
? 2.8Speed
? 2.9Mass
? 2.10Size
? 2.11Handedness
? 3Sources
? 3.1Artificial
? 3.2Geologic
? 3.3Atmospheric
? 3.4Solar
? 3.5Supernovae
? 3.6Supernova remnants
? 3.7Big Bang
? 4Detection
? 5Motivation for scientific interest
? 6See also
? 7Notes
? 8References
? 9Bibliography
? 10External links
[edit]History
[edit]Pauli's proposal
The neutrino[nb 1] was postulated first by Wolfgang Pauli in 1930 to explain how beta decay could conserve energy, momentum, and angular momentum (spin). Pauli hypothesized an undetected particle that he called a "neutron" in keeping with convention employed for naming both the proton and the electron, which in 1930 were known to be respective products for alpha and beta decay:[3][nb 2]
n0→ p++ e?+ νe
James Chadwick discovered a much more massive nuclear particle in 1932 and also named it a neutron, leaving two kinds of particles with the same name. Enrico Fermi, who developed the theory of beta decay, coined the term neutrino (the Italian equivalent of "little neutral one") in 1933 as a way to resolve the confusion.[4][nb 3] Fermi's paper, written in 1934, unified Pauli's neutrino with Paul Dirac's positron and Werner Heisenberg's neutron-proton model and gave a solid theoretical basis for future experimental work. However the journal Nature rejected Fermi's paper, saying that the theory was "too remote from reality". He submitted the paper to an Italian journal, which accepted it, but the general lack of interest in his theory at that early date caused him to switch to experimental physics.[5][6]
[edit]Direct detection
Clyde Cowan conducting the neutrino experiment c. 1956
In 1942 Kan-Chang Wang first proposed the use of beta-capture to experimentally detect neutrinos.[7] In the July 20, 1956 issue of Science, Clyde Cowan, Frederick Reines, F. B. Harrison, H. W. Kruse, and A. D. McGuire published confirmation that they had detected the neutrino,[8][9] a result that was rewarded almost forty years later with the 1995 Nobel Prize.[10]
In this experiment, now known as the Cowan?Reines neutrino experiment, antineutrinos created in a nuclear reactor by beta decay reacted with protons producing neutrons and positrons:
νe + p+→ n0+ e+
The positron quickly finds an electron, and they annihilate each other. The two resulting gamma rays (γ) are detectable. The neutron can be detected by its capture on an appropriate nucleus, releasing a gamma ray. The coincidence of both events ? positron annihilation and neutron capture ? gives a unique signature of an antineutrino interaction.
[edit]Neutrino flavor
In 1962 Leon M. Lederman, Melvin Schwartz and Jack Steinberger showed that more than one type of neutrino exists by first detecting interactions of the muon neutrino (already hypothesised with the name neutretto),[11] which earned them the 1988 Nobel Prize in Physics. When the third type of lepton, the tau, was discovered in 1975 at the Stanford Linear Accelerator Center, it too was expected to have an associated neutrino (the tau neutrino). First evidence for this third neutrino type came from the observation of missing energy and momentum in tau decays analogous to the beta decay leading to the discovery of the neutrino. The first detection of tau neutrino interactions was announced in summer of 2000 by the DONUT collaboration at Fermilab, making it the latest particle of the Standard Model to have been directly observed; its existence had already been inferred by both theoretical consistency and experimental data from the Large Electron?Positron Collider.
[edit]Solar neutrino problem
Starting in the late 1960s, several experiments found that the number of electron neutrinos arriving from the Sun was between one third and one half the number predicted by the Standard Solar Model. This discrepancy, which became known as the solar neutrino problem, remained unresolved for some thirty years. It was resolved by discovery of neutrino oscillation and mass. (The Standard Model of particle physics had assumed that neutrinos are massless and cannot change flavor. However, if neutrinos had mass, they could change flavor, or oscillate between flavors).
[edit]Oscillation
A practical method for investigating neutrino oscillations was first suggested by Bruno Pontecorvo in 1957 using an analogy with kaonoscillations; over the subsequent 10 years he developed the mathematical formalism and the modern formulation of vacuum oscillations. In 1985 Stanislav Mikheyev and Alexei Smirnov (expanding on 1978 work by Lincoln Wolfenstein) noted that flavor oscillations can be modified when neutrinos propagate through matter. This so-called Mikheyev?Smirnov?Wolfenstein effect (MSW effect) is important to understand because many neutrinos emitted by fusion in the Sun pass through the dense matter in the solar core (where essentially all solar fusion takes place) on their way to detectors on Earth.
Starting in 1998, experiments began to show that solar and atmospheric neutrinos change flavors (see Super-Kamiokande and Sudbury Neutrino Observatory). This resolved the solar neutrino problem: the electron neutrinos produced in the Sun had partly changed into other flavors which the experiments could not detect.
Although individual experiments, such as the set of solar neutrino experiments, are consistent with non-oscillatory mechanisms of neutrino flavor conversion, taken altogether, neutrino experiments imply the existence of neutrino oscillations. Especially relevant in this context are the reactor experiment KamLAND and the accelerator experiments such as MINOS. The KamLAND experiment has indeed identified oscillations as the neutrino flavor conversion mechanism involved in the solar electron neutrinos. Similarly MINOS confirms the oscillation of atmospheric neutrinos and gives a better determination of the mass squared splitting.[12]
[edit]Supernova neutrinos
See also: Supernova Early Warning System
Raymond Davis Jr. and Masatoshi Koshiba were jointly awarded the 2002 Nobel Prize in Physics; Davis for his pioneer work on cosmic neutrinos and Koshiba for the first real time observation of supernova neutrinos. The detection of solar neutrinos, and of neutrinos of the SN 1987Asupernova in 1987 marked the beginning of neutrino astronomy.
[edit]Properties and reactions
The neutrino has half-integer spin (½ħ) and is therefore a fermion. Neutrinos interact primarily through the weak force. The discovery of neutrino flavor oscillations implies that neutrinos have mass. The existence of a neutrino mass strongly suggests the existence of a tiny neutrino magnetic moment[13] of the order of 10?19?μB, allowing the possibility that neutrinos may interact electromagnetically as well. An experiment done by C. S. Wu at Columbia University showed that neutrinos always have left-handed chirality.[14] It is very hard to uniquely identify neutrino interactions among the natural background of radioactivity. For this reason, in early experiments a special reaction channel was chosen to facilitate the identification: the interaction of an antineutrino with one of the hydrogen nuclei in the water molecules. A hydrogen nucleus is a single proton, so simultaneous nuclear interactions, which would occur within a heavier nucleus, don't need to be considered for the detection experiment. Within a cubic metre of water placed right outside a nuclear reactor, only relatively few such interactions can be recorded, but the setup is now used for measuring the reactor's plutonium production rate.
[edit]MSW effect
Main article: MSW effect
Neutrinos traveling through matter, in general, undergo a process analogous to light traveling through a transparent material. This process is not directly observable because it doesn't produce ionizing radiation, but gives rise to the MSW effect. Only a small fraction of the neutrino's energy is transferred to the material.
[edit]Nuclear reactions
Neutrinos can interact with a nucleus, changing it to another nucleus. This process is used in radiochemical neutrino detectors. In this case, the energy levels and spin states within the target nucleus have to be taken into account to estimate the probability for an interaction. In general the interaction probability increases with the number of neutrons and protons within a nucleus.
[edit]Alteration of nuclear decay rate
A Russian study suggests that the decay rate of radioactive isotopes is not constant as is commonly believed,[15] and a recent study[16] also finds this, and says it appears to be affected by the rate of neutrinos emitted by the Sun.
[edit]Induced fission
Very much like neutrons do in nuclear reactors, neutrinos can induce fission reactions within heavy nuclei.[17] So far, this reaction has not been measured in a laboratory, but is predicted to happen within stars and supernovae. The process affects the abundance of isotopes seen in the universe.[18] Neutrino fission of deuterium nuclei has been observed in the Sudbury Neutrino Observatory, which uses a heavy water detector.
[edit]Types
Fermion
Symbol
Mass[nb 4]
Generation 1
Electron neutrino
νe
< 2.2 eV
Electron antineutrino
νe
< 2.2 eV
Generation 2
Muon neutrino
νμ
< 170 keV
Muon antineutrino
νμ
< 170 keV
Generation 3
Tau neutrino
ντ
< 15.5 MeV
Tau antineutrino
ντ
< 15.5 MeV
There are three known types (flavors) of neutrinos: electron neutrino νe, muon neutrino νμ and tau neutrino ντ, named after their partner leptons in the Standard Model (see table at right). The current best measurement of the number of neutrino types comes from observing the decay of the Z boson. This particle can decay into any light neutrino and its antineutrino, and the more types of light neutrinos[nb 5] available, the shorter the lifetime of the Z boson. Measurements of the Z lifetime have shown that the number of light neutrino types is 3.[13] The correspondence between the six quarks in the Standard Model and the six leptons, among them the three neutrinos, suggests to physicists' intuition that there should be exactly three types of neutrino. However, actual proof that there are only three kinds of neutrinos remains an elusive goal of particle physics.
The possibility of sterile neutrinos?relatively light neutrinos which do not participate in the weak interaction but which could be created through flavor oscillation (see below)?is unaffected by these Z-boson-based measurements, and the existence of such particles is in fact hinted by experimental data from the LSND experiment. However, the currently running MiniBooNE experiment suggested, until recently, that sterile neutrinos are not required to explain the experimental data,[19] although the latest research into this area is on-going and anomalies in the MiniBooNE data may allow for exotic neutrino types, including sterile neutrinos.[20] A recent re-analysis of reference electron spectra data from the Institut Laue-Langevin[21] has also hinted at a fourth, sterile neutrino.[22]
Recently analyzed data from the Wilkinson Microwave Anisotropy Probe of the cosmic background radiation is compatible with either three or four types of neutrinos. It is hoped that the addition of two more years of data from the probe will resolve this uncertainty.[23]
[edit]Antineutrinos
Antimatter
Annihilation
Devices[show]
? Particle accelerator
? Penning trap
? Wilson chamber
Antiparticles[show]
? Positron
? Antiproton
? Antineutron
Uses[show]
? Positron emission tomography
? Fuel
Bodies[show]
? ALPHA Collaboration
? ATHENA
? ATRAP
? CERN
? RHIC
People[show]
? Paul Dirac
? Carl David Anderson
? Andrei Sakharov
? v
? t
? e
Antineutrinos are the antiparticles of neutrinos, which are neutral particles produced in nuclearbeta decay. These are emitted in beta particle emissions, where a neutron turns into a proton. They have a spin of ½, and are part of the lepton family of particles. The antineutrinos observed so far all have right-handed helicity (i.e. only one of the two possible spin states has ever been seen), while the neutrinos are left-handed. Antineutrinos, like neutrinos, interact with other matter only through the gravitational and weak forces, making them very difficult to detect experimentally. Neutrino oscillation experiments indicate that antineutrinos have mass, but beta decay experiments constrain that mass to be very small. A neutrino-antineutrino interaction has been suggested in attempts to form a composite photon with the neutrino theory of light.
Because antineutrinos and neutrinos are neutral particles it is possible that they are actually the same particle. Particles which have this property are known as Majorana particles. If neutrinos are indeed Majorana particles then the neutrinoless double beta decay process is allowed. Several experiments have been proposed to search for this process.
Researchers around the world have begun to investigate the possibility of using antineutrinos for reactor monitoring in the context of preventing the proliferation of nuclear weapons.[24][25][26]
Antineutrinos were first detected as a result of their interaction with protons in a large tank of water. This was installed next to a nuclear reactor as a controllable source of the antineutrinos. (See: Cowan?Reines neutrino experiment)
[edit]Flavor oscillations
Main article: Neutrino oscillation
Neutrinos are most often created or detected with a well defined flavor (electron, muon, tau). However, in a phenomenon known as neutrino flavor oscillation, neutrinos are able to oscillate between the three available flavors while they propagate through space. Specifically, this occurs because the neutrino flavor eigenstates are not the same as the neutrino mass eigenstates (simply called 1, 2, 3). This allows for a neutrino that was produced as an electron neutrino at a given location to have a calculable probability to be detected as either a muon or tau neutrino after it has traveled to another location. This quantum mechanical effect was first hinted by the discrepancy between the number of electron neutrinos detected from the Sun's core failing to match the expected numbers, dubbed as the "solar neutrino problem". In the Standard Model the existence of flavor oscillations implies nonzero differences between the neutrino masses, because the amount of mixing between neutrino flavors at a given time depends on the differences in their squared-masses. There are other possibilities in which neutrino can oscillate even if they are massless. If Lorentz invariance is not an exact symmetry, neutrinos can experience Lorentz-violating oscillations.[27]
It is possible that the neutrino and antineutrino are in fact the same particle, a hypothesis first proposed by the Italian physicist Ettore Majorana. The neutrino could transform into an antineutrino (and vice versa) by flipping the orientation of its spin state.[28]
This change in spin would require the neutrino and antineutrino to have nonzero mass, and therefore travel slower than light, because such a spin flip, caused only by a change in point of view, can take place only if inertial frames of reference exist that move faster than the particle: such a particle has a spin of one orientation when seen from a frame which moves slower than the particle, but the opposite spin when observed from a frame that moves faster than the particle.
[edit]Speed
Main article: Measurements of neutrino speed
Before neutrinos were found to oscillate, they were generally assumed to be massless, propagating at the speed of light. According to the theory of special relativity, the question of neutrino velocity is closely related to their mass. If neutrinos are massless, they must travel at the speed of light. However, if they have mass, they cannot reach the speed of light.
In addition there are some speculative models in which Neutrinos have a tachyonic nature and travel faster than light (see Tachyon#Neutrinos). Also some Lorentz violating variants of quantum gravity might allow faster-than-light neutrinos. A comprehensive framework for Lorentz violations is the Standard-Model Extension (SME).
In the early 1980s, first measurements of neutrino speed were done using pulsed pion beams (produced by pulsed proton beams hitting a target). The pions decayed producing neutrinos, and the neutrino interactions observed within a time window in a detector at a distance were consistent with the speed of light. This measurement was repeated in 2007 using the MINOS detectors, which found the speed of 3?GeV neutrinos to be 1.000051(29)?c at 68% confidence level, and at 99% confidence level a range between 0.999976?c to 1.000126?c. The central value is higher than the speed of light and is consistent with superluminal velocity; however, the uncertainty is great enough that the result also does not rule out speeds less than or equal to light at this high confidence level. This measurement set an upper bound on the mass of the muon neutrino of 50?MeV at 99% confidence.[29][30] The detectors for the project are being upgraded, and new results are not expected until at least 2012.
The same observation was made, on a somewhat larger scale, with supernova 1987A (SN 1987A). 10-MeV antineutrinos from the supernova were detected within a time window that was consistent with a speed of light for the neutrinos. So far, the question of neutrino masses cannot be decided based on measurements of the neutrino speed.
In September 2011, the OPERA collaboration released calculations showing velocities of 17-GeV and 28-GeV neutrinos exceeding the speed of light in their experiments (see Faster-than-light neutrino anomaly). In November 2011, OPERA repeated its experiment with changes so that the speed could be determined individually for each detected neutrino. The results showed the same faster-than-light speed. However, in February 2012 reports came out that the results may have been caused by a loose fiber optic cable attached to one of the atomic clocks which measured the departure and arrival times of the neutrinos. The cable is going to be fixed and the experiment will be run again to see if the same results are found.[31] An independent recreation of the experiment in the same laboratory by ICARUS found no discernible difference between the speed of a neutrino and the speed of light.[32][33][34]
[edit]Mass
The Standard Model of particle physics assumed that neutrinos are massless, although adding massive neutrinos to the basic framework is not difficult.[clarification needed] Indeed, the experimentally established phenomenon of neutrino oscillation requires neutrinos to have nonzero masses.[19] This was originally conceived by Bruno Pontecorvo in the 1950s.
The strongest upper limit on the masses of neutrinos comes from cosmology: the Big Bang model predicts that there is a fixed ratio between the number of neutrinos and the number of photons in the cosmic microwave background. If the total energy of all three types of neutrinos exceeded an average of 50?eV per neutrino, there would be so much mass in the universe that it would collapse.[citation needed] This limit can be circumvented by assuming that the neutrino is unstable; however, there are limits within the Standard Model that make this difficult. A much more stringent constraint comes from a careful analysis of cosmological data, such as the cosmic microwave background radiation, galaxy surveys, and the Lyman-alpha forest. These indicate that the summed masses of the three neutrino varieties must be less than 0.3?eV.[35]
In 1998, research results at the Super-Kamiokande neutrino detector determined that neutrinos can oscillate from one flavor to another, which requires that they must have a nonzero mass.[36] While this shows that neutrinos have mass, the absolute neutrino mass scale is still not known. This is because neutrino oscillations are sensitive only to the difference in the squares of the masses.[37] The best estimate of the difference in the squares of the masses of mass eigenstates 1 and 2 was published by KamLAND in 2005: Δm221?=?0.000079?eV2.[38] In 2006, the MINOS experiment measured oscillations from an intense muon neutrino beam, determining the difference in the squares of the masses between neutrino mass eigenstates 2 and 3. The initial results indicate |Δm232|?=?0.0027?eV2, consistent with previous results from Super-Kamiokande.[39] Since |Δm232| is the difference of two squared masses, at least one of them has to have a value which is at least the square root of this value. Thus, there exists at least one neutrino mass eigenstate with a mass of at least 0.04?eV.[40]
In 2009 lensing data of a galaxy cluster were analyzed to predict a neutrino mass of about 1.5?eV.[41] All neutrino masses are then nearly equal, with neutrino oscillations of order meV. They lie below the Mainz-Troitsk upper bound of 2.2?eV for the electron antineutrino.[42] The latter will be tested in 2015 in the KATRIN experiment, that searches for a mass between 0.2?eV and 2?eV.
A number of efforts are under way to directly determine the absolute neutrino mass scale in laboratory experiments. The methods applied involve nuclear beta decay (KATRIN and MARE) or neutrinoless double beta decay (e.g. GERDA, CUORE/Cuoricino, NEMO-3 and others).
On 31 May 2010, OPERA researchers observed the first tau neutrino candidate event in a muon neutrino beam, the first time a transformation in neutrinos had been observed, giving evidence that they have mass. [43]
In July 2010 the 3-D MegaZ experiment reported that they had measured the upper limit of the combined mass of the three neutrino varieties to be less than 0.28?eV.[44]
[edit]Size
The physical size of neutrinos can be defined using their electroweak radius (apparent size in electroweak interaction). The average electroweak characteristic size is ?r²? = n × 10-33 cm² (n × 1 nanobarn), where n = 3.2 for electron neutrino, n = 1.7 for muon neutrino and 1.0 for tau neutrino; it depends on no other properties than mass.[45]
[edit]Handedness
Experimental results show that (nearly) all produced and observed neutrinos have left-handed helicities (spins antiparallel to momenta), and all antineutrinos have right-handed helicities, within the margin of error. In the massless limit, it means that only one of two possible chiralities is observed for either particle. These are the only chiralities included in the Standard Model of particle interactions.
It is possible that their counterparts (right-handed neutrinos and left-handed antineutrinos) simply do not exist. If they do, their properties are substantially different from observable neutrinos and antineutrinos. It is theorized that they are either very heavy (on the order of GUT scale?see Seesaw mechanism), do not participate in weak interaction (so-called sterile neutrinos), or both.
The existence of nonzero neutrino masses somewhat complicates the situation. Neutrinos are produced in weak interactions as chirality eigenstates. However, chirality of a massive particle is not a constant of motion; helicity is, but the chirality operator does not share eigenstates with the helicity operator. Free neutrinos propagate as mixtures of left- and right-handed helicity states, with mixing amplitudes on the order of mν/E. This does not significantly affect the experiments, because neutrinos involved are nearly always ultrarelativistic, and thus mixing amplitudes are vanishingly small. For example, most solar neutrinos have energies on the order of 100?keV?1?MeV, so the fraction of neutrinos with "wrong" helicity among them cannot exceed 10?10.[46][47]
[edit]Sources
[edit]Artificial
Nuclear reactors are the major source of human-generated neutrinos. Antineutrinos are made in the beta-decay of neutron-rich daughter fragments in the fission process. Generally, the four main isotopes contributing to the antineutrino flux are 235U, 238U, 239Pu and 241Pu (i.e. via the antineutrinos emitted during beta-minus decay of their respective fission fragments). The average nuclear fission releases about 200?MeV of energy, of which roughly 4.5% (or about 9?MeV)[48] is radiated away as antineutrinos. For a typical nuclear reactor with a thermal power of 4,000?MW, meaning that the core produces this much heat, and an electrical power generation of 1,300?MW, the total power production from fissioning atoms is actually 4,185?MW, of which 185?MW is radiated away as antineutrino radiation and never appears in the engineering. This is to say, 185?MW of fission energy is lost from this reactor and does not appear as heat available to run turbines, since the antineutrinos penetrate all building materials essentially without any trace, and disappear.[nb 6]
The antineutrino energy spectrum depends on the degree to which the fuel is burned (plutonium-239 fission antineutrinos on average have slightly more energy than those from uranium-235 fission), but in general, the detectable antineutrinos from fission have a peak energy between about 3.5 and 4?MeV, with a maximum energy of about 10?MeV.[49] There is no established experimental method to measure the flux of low energy antineutrinos. Only antineutrinos with an energy above threshold of 1.8?MeV can be uniquely identified (see neutrino detection below). An estimated 3% of all antineutrinos from a nuclear reactor carry an energy above this threshold. Thus, an average nuclear power plant may generate over 1020 antineutrinos per second above this threshold, but also a much larger number (97%/3% = ~30 times this number) below the energy threshold, which cannot be seen with present detector technology.
Some particle accelerators have been used to make neutrino beams. The technique is to smash protons into a fixed target, producing charged pions or kaons. These unstable particles are then magnetically focused into a long tunnel where they decay while in flight. Because of the relativistic boost of the decaying particle the neutrinos are produced as a beam rather than isotropically. Efforts to construct an accelerator facility where neutrinos are produced through muon decays are ongoing.[50] Such a setup is generally known as a neutrino factory.
Nuclear bombs also produce very large quantities of neutrinos. Fred Reines and Clyde Cowan considered the detection of neutrinos from a bomb prior to their search for reactor neutrinos; a fission reactor was recommended as a better alternative by Los Alamos physics division leader J.M.B. Kellogg.[51]
[edit]Geologic
Neutrinos are part of the natural background radiation. In particular, the decay chains of 238U and 232Th isotopes, as well as40K, include beta decays which emit antineutrinos. These so-called geoneutrinos can provide valuable information on the Earth's interior. A first indication for geoneutrinos was found by the KamLAND experiment in 2005. KamLAND's main background in the geoneutrino measurement are the antineutrinos coming from reactors. Several future experiments aim at improving the geoneutrino measurement and these will necessarily have to be far away from reactors.
Solar neutrinos (proton-proton chain) in the Standard Solar Model
[edit]Atmospheric
Atmospheric neutrinos result from the interaction of cosmic rays with atomic nuclei in the Earth's atmosphere, creating showers of particles, many of which are unstable and produce neutrinos when they decay. A collaboration of particle physicists from Tata Institute of Fundamental Research (India), Osaka City University (Japan) and Durham University (UK) recorded the first cosmic ray neutrino interaction in an underground laboratory in Kolar Gold Fields in India in 1965.
[edit]Solar
Solar neutrinos originate from the nuclear fusion powering the Sun and other stars. The details of the operation of the Sun are explained by the Standard Solar Model. In short: when four protons fuse to become one helium nucleus, two of them have to convert into neutrons, and each such conversion releases one electron neutrino.
The Sun sends enormous numbers of neutrinos in all directions. Every second, about 65 billion (6.5×1010) solar neutrinos pass through every square centimeter on the part of the Earth that faces the Sun.[2] Since neutrinos are insignificantly absorbed by the mass of the Earth, the surface area on the side of the Earth opposite the Sun receives about the same number of neutrinos as the side facing the Sun.
[edit]Supernovae
SN 1987A
In 1966 Colgate and White[52] calculated that neutrinos carry away most of the gravitational energy released by the collapse of massive stars, events now categorized as Type Ib and Ic and Type IIsupernovae. When such stars collapse, matter densities at the core becomes so high (1017?kg/m3) that the degeneracy of electrons is not enough to prevent protons and electrons from combining to form a neutron and an electron neutrino. A second and more important neutrino source is the thermal energy (100 billion kelvins) of the newly formed neutron core, which is dissipated via the formation of neutrino-antineutrino pairs of all flavors.[53]
Colgate and White’s theory of supernova neutrino production was confirmed in 1987, when neutrinos from supernova 1987A were detected. The water-based detectors Kamiokande II and IMB detected 11 and 8 antineutrinos of thermal origin,[53] respectively, while the scintillator-based Baksan detector found 5 neutrinos (lepton number = 1) of either thermal or electron-capture origin, in a burst lasting less than 13 seconds. The neutrino signal from the supernova arrived at earth several hours before the arrival of the first electromagnetic radiation, as expected from the evident fact that the latter emerges along with the shock wave. The exceptionally feeble interaction with normal matter allowed the neutrinos to pass through the churning mass of the exploding star, while the electromagnetic photons were slowed.
Because neutrinos interact so little with matter, it is thought that a supernova's neutrino emissions carry information about the innermost regions of the explosion. Much of the visible light comes from the decay of radioactive elements produced by the supernova shock wave, and even light from the explosion itself is scattered by dense and turbulent gases. Neutrinos, on the other hand, pass through these gases, providing information about the supernova core (where the densities were large enough to influence the neutrino signal). Furthermore, the neutrino burst is expected to reach Earth before any electromagnetic waves, including visible light, gamma rays or radio waves. The exact time delay depends on the velocity of the shock wave and on the thickness of the outer layer of the star. For a Type II supernova, astronomers expect the neutrino flood to be released seconds after the stellar core collapse, while the first electromagnetic signal may emerge hours later. The SNEWS project uses a network of neutrino detectors to monitor the sky for candidate supernova events; the neutrino signal will provide a useful advance warning of a star exploding in the Milky Way.
[edit]Supernova remnants
The energy of supernova neutrinos ranges from a few to several tens of MeV. However, the sites where cosmic rays are accelerated are expected to produce neutrinos that are at least one million times more energetic, produced from turbulent gaseous environments left over by supernova explosions: the supernova remnants. The origin of the cosmic rays was attributed to supernovas by Walter Baade and Fritz Zwicky; this hypothesis was refined by Vitaly L. Ginzburg and Sergei I. Syrovatsky who attributed the origin to supernova remnants, and supported their claim by the crucial remark, that the cosmic ray losses of the Milky Way is compensated, if the efficiency of acceleration in supernova remnants is about 10 percent. Ginzburg and Syrovatskii's hypothesis is supported by the specific mechanism of "shock wave acceleration" happening in supernova remnants, which is consistent with the original theoretical picture drawn by Enrico Fermi, and is receiving support from observational data. The very high energy neutrinos are still to be seen, but this branch of neutrino astronomy is just in its infancy. The main existing or forthcoming experiments that aim at observing very high energy neutrinos from our galaxy are Baikal, AMANDA, IceCube, ANTARES, NEMO and Nestor. Related information is provided by very high energy gamma ray observatories, such as VERITAS, HESS and MAGIC. Indeed, the collisions of cosmic rays are supposed to produce charged pions, whose decay give the neutrinos, and also neutral pions, whose decay give gamma rays: the environment of a supernova remnant is transparent to both types of radiation.
Still higher energy neutrinos, resulting from the interactions of extragalactic cosmic rays, could be observed with the Pierre Auger Observatory or with the dedicated experiment named ANITA.
[edit]Big Bang
Main article: Cosmic neutrino background
It is thought that, just like the cosmic microwave background radiation left over from the Big Bang, there is a background of low energy neutrinos in our Universe. In the 1980s it was proposed that these may be the explanation for the dark matter thought to exist in the universe. Neutrinos have one important advantage over most other dark matter candidates: we know they exist. However, they also have serious problems.
From particle experiments, it is known that neutrinos are very light. This means that they easily move at speeds close to the speed of light. Thus, dark matter made from neutrinos is termed "hot dark matter". The problem is that being fast moving, the neutrinos would tend to have spread out evenly in the universe before cosmological expansion made them cold enough to congregate in clumps. This would cause the part of dark matter made of neutrinos to be smeared out and unable to cause the large galactic structures that we see.
Further, these same galaxies and groups of galaxies appear to be surrounded by dark matter that is not fast enough to escape from those galaxies. Presumably this matter provided the gravitational nucleus for formation. This implies that neutrinos make up only a small part of the total amount of dark matter.
From cosmological arguments, relic background neutrinos are estimated to have density of 56 of each type per cubic centimeter and temperature 1.9?K (1.7×10?4?eV) if they are massless, much colder if their mass exceeds 0.001?eV. Although their density is quite high, due to extremely low neutrino cross-sections at sub-eV energies, the relic neutrino background has not yet been observed in the laboratory. In contrast, boron-8 solar neutrinos?which are emitted with a higher energy?have been detected definitively despite having a space density that is lower than that of relic neutrinos by some 6 orders of magnitude.
[edit]Detection
Main article: Neutrino detector
Neutrinos cannot be detected directly, because they do not ionize the materials they are passing through (they do not carry electric charge and other proposed effects, like the MSW effect, do not produce traceable radiation). A unique reaction to identify antineutrinos, sometimes referred to as inverse beta decay, as applied by Reines and Cowan (see below), requires a very large detector in order to detect a significant number of neutrinos. All detection methods require the neutrinos to carry a minimum threshold energy. So far, there is no detection method for low energy neutrinos, in the sense that potential neutrino interactions (for example by the MSW effect) cannot be uniquely distinguished from other causes. Neutrino detectors are often built underground in order to isolate the detector from cosmic rays and other background radiation.
Antineutrinos were first detected in the 1950s near a nuclear reactor. Reines and Cowan used two targets containing a solution of cadmium chloride in water. Two scintillation detectors were placed next to the cadmium targets. Antineutrinos with an energy above the threshold of 1.8?MeV caused charged current interactions with the protons in the water, producing positrons and neutrons. This is very much like β+decay, where energy is used to convert a proton into a neutron, a positron (e+) and an electron neutrino (νe) is emitted:
From known β+decay:
Energy + p → n + e++ νe
In the Cowan and Reines experiment, instead of an outgoing neutrino, you have an incoming antineutrino (νe) from a nuclear reactor:
Energy (>1.8?MeV) + p + νe → n + e+
The resulting positron annihilation with electrons in the detector material created photons with an energy of about 0.5?MeV. Pairs of photons in coincidence could be detected by the two scintillation detectors above and below the target. The neutrons were captured by cadmium nuclei resulting in gamma rays of about 8?MeV that were detected a few microseconds after the photons from a positron annihilation event.
Since then, various detection methods have been used. Super Kamiokande is a large volume of water surrounded by photomultiplier tubes that watch for the Cherenkov radiation emitted when an incoming neutrino creates an electron or muon in the water. The Sudbury Neutrino Observatory is similar, but uses heavy water as the detecting medium, which uses the same effects, but also allows the additional reaction any-flavor neutrino photo-dissociation of deuterium, resulting in a free neutron which is then detected from gamma radiation after chlorine-capture. Other detectors have consisted of large volumes of chlorine or gallium which are periodically checked for excesses of argon or germanium, respectively, which are created by electron-neutrinos interacting with the original substance. MINOS uses a solid plastic scintillator coupled to photomultiplier tubes, while Borexino uses a liquid pseudocumene scintillator also watched by photomultiplier tubes and the proposed NOνA detector will use liquid scintillator watched by avalanche photodiodes. The IceCube Neutrino Observatory uses 1?km3 of the Antarctic ice sheet near the south pole with photomultiplier tubes distributed throughout the volume.
[edit]Motivation for scientific interest
Neutrinos' low mass and neutral charge mean they interact exceedingly weakly with other particles and fields. This feature of weak interaction interests scientists because it means neutrinos can be used to probe environments that other radiation (such as light or radio waves) cannot penetrate.
Using neutrinos as a probe was first proposed in the mid 20th century as a way to detect conditions at the core of the Sun. The solar core cannot be imaged directly because electromagnetic radiation (such as light) is diffused by the great amount and density of matter surrounding the core. On the other hand, neutrinos pass through the Sun with few interactions. Whereas photons emitted from the solar core may require 40,000 years to diffuse to the outer layers of the Sun, neutrinos generated in stellar fusion reactions at the core cross this distance practically unimpeded at nearly the speed of light.[54][55]
Neutrinos are also useful for probing astrophysical sources beyond our solar system because they are the only known particles that are not significantly attenuated by their travel through the interstellar medium. Optical photons can be obscured or diffused by dust, gas, and background radiation. High-energy cosmic rays, in the form of swift protons and atomic nuclei, are unable to travel more than about 100 megaparsecs due to the Greisen?Zatsepin?Kuzmin limit (GZK cutoff). Neutrinos, in contrast, can travel even greater distances barely attenuated.[citation needed]
The galactic core of the Milky Way is fully obscured by dense gas and numerous bright objects. Neutrinos produced in the galactic core should be measurable by Earth-based neutrino telescopes in the next decade.[citation needed]
Another important use of the neutrino is in the observation of supernovae, the explosions that end the lives of highly massive stars. The core collapse phase of a supernova is an extremely dense and energetic event. It is so dense that no known particles are able to escape the advancing core front except for neutrinos. Consequently, supernovae are known to release approximately 99% of their radiant energy in a short (10-second) burst of neutrinos.[56] These neutrinos are a very useful probe for core collapse studies.
The rest mass of the neutrino (see above) is an important test of cosmological and astrophysical theories (see Dark matter). The neutrino's significance in probing cosmological phenomena is as great as any other method, and is thus a major focus of study in astrophysical communities.[57]
The study of neutrinos is important in particle physics because neutrinos typically have the lowest mass, and hence are examples of the lowest energy particles theorized in extensions of the Standard Model of particle physics. For example, one would expect that if there is a fourth class of fermions beyond the electron, muon, and tau generations of particles, then the fourth generation neutrino would be the easiest to generate in a particle accelerator.[citation needed]
[edit]See also
Science portal
Physics portal
Book: Leptons
Book: Particles of the Standard Model
Wikipedia books are collections of articles that can be downloaded or ordered in print.
? Cowan?Reines neutrino experiment
? IceCube Neutrino Observatory
? List of neutrino experiments
? Neutrino astronomy
? Neutrino oscillations
? Seesaw mechanism
? Sterile neutrino
? Supernova Early Warning System
[edit]Notes
1. ^More specifically, the electron neutrino.
1. ^Niels Bohr was notably opposed to this interpretation of beta decay and was ready to accept that energy, momentum and angular momentum were not conserved quantities.
2. ^It is a pun on the Italian word for neutron, neutrone, the -one ending being (though not in this case) an augmentative in Italian, so neutrone could be read as the "large neutral one".
3. ^Since neutrino flavor eigenstates are not the same as neutrino mass eigenstates (see neutrino oscillation), the given masses are actually mass expectation values. If the mass of a neutrino could be measured directly, the value would always be that of one of the three mass eigenstates: ν1, ν2, and ν3. In practice, the mass cannot be measured directly. Instead it is measured by looking at the shape of the endpoint of the energy spectrum in particle decays. This sort of measurement directly measures the expectation value of the mass; it is not sensitive to any of the mass eigenstates separately.
4. ^In this context, "light neutrino" means neutrinos with less than half the mass of the Z boson.
5. ^Typically about one third of the heat which is deposited in a reactor core is available to be converted to electricity, and a 4,000?MW reactor would produce only 2,700?MW of actual heat, with the rest being converted to its 1,300?MW of electric power production.
[edit]References
6. ^"Neutrino". Glossary for the Research Perspectives of the Max Planck Society. Max Planck Gesellschaft. http://www.mpg.de/12928/Glossary. Retrieved 2012-03-27.?
7. ^ abJ. Bahcall et al. (2005). "New solar opacities, abundances, helioseismology, and neutrino fluxes". The Astrophysical Journal621: L85?L88. arXiv:astro-ph/0412440. Bibcode2005ApJ...621L..85B. doi:10.1086/428929.?
8. ^Improved understanding between 1930 and 1932 led Viktor Ambartsumian and Dmitri Ivanenko to propose the existence of the more massive neutron as it is now known, subsequently demonstrated by James Chadwick in 1932. These events necessitated renaming Pauli's less massive, momentum-conserving particle. Enrico Fermi coined "neutrino" in 1933 to distinguish between the neutron and the much lighter neutrino. K. Riesselmann (2007). "Logbook: Neutrino Invention". Symmetry Magazine4 (2). http://www.symmetrymagazine.org/cms/?pid=1000450.?
9. ^M.F. L'Annunziata (2007). Radioactivity. Elsevier. p.?100. ISBN?9780444527158. http://books.google.com/books?id=YpEiPPFlNAAC&pg=PA100.?
10. ^F. Close (2010). Neutrino. Oxford University Press.?
11. ^E. Fermi (1934). "Versuch einer Theorie der β-Strahlen. I". Zeitschrift f?r Physik A88 (3?4): 161. doi:10.1007/BF01351864.? Translated in F.L. Wilson (1968). "Fermi's Theory of Beta Decay". American Journal of Physics36 (12): 1150. Bibcode1968AmJPh..36.1150W. doi:10.1119/1.1974382. http://microboone-docdb.fnal.gov/cgi-bin/RetrieveFile?docid=953;filename=FermiBetaDecay1934.pdf;version=1.?
12. ^K.-C. Wang (1942). "A Suggestion on the Detection of the Neutrino". Physical Review61 (1?2): 97. Bibcode1942PhRv...61...97W. doi:10.1103/PhysRev.61.97.?
13. ^C.L Cowan Jr., F. Reines, F.B. Harrison, H.W. Kruse, A.D McGuire (1956). "Detection of the Free Neutrino: a Confirmation". Science124 (3212): 103?4. Bibcode1956Sci...124..103C. doi:10.1126/science.124.3212.103. PMID?17796274.?
14. ^K. Winter (2000). Neutrino physics. Cambridge University Press. p.?38ff. ISBN?9780521650038. http://books.google.com/?id=v_tiL2NlfvMC&pg=PA38.?This source reproduces the 1956 paper.
15. ^"The Nobel Prize in Physics 1995". The Nobel Foundation. http://nobelprize.org/nobel_prizes/physics/laureates/1995/. Retrieved 29 June 2010.?
16. ^I.V. Anicin (2005). "The Neutrino ? Its Past, Present and Future". arXiv:physics/0503172?[physics].?
17. ^M. Maltoni et al. (2004). "Status of global fits to neutrino oscillations". New Journal of Physics6: 122. arXiv:hep-ph/0405172. Bibcode2004NJPh....6..122M. doi:10.1088/1367-2630/6/1/122.?
18. ^ abS. Eidelman et al. (Particle Data Group) (2004). "Leptons in the 2005 Review of Particle Physics". Physics Letters B592 (1): 1?5. arXiv:astro-ph/0406663. Bibcode2004PhLB..592....1P. doi:10.1016/j.physletb.2004.06.001. http://pdg.lbl.gov/2005/listings/lxxx.html.?
19. ^S.M. Caroll (25 March 2009). "Ada Lovelace Day: Chien-Shiung Wu". Discover Magazine. http://blogs.discovermagazine.com/cosmicvariance/2009/03/25/ada-lovelace-day-chien-shiung-wu/. Retrieved 2011-09-23.?
20. ^S.E. Shnoll, K.I. Zenchenko, I.I. Berulis, N.V. Udaltsova, I.A. Rubinstein (2004). "Fine structure of histograms of alpha-activity measurements depends on direction of alpha particles flow and the Earth rotation: experiments with collimators". arXiv:physics/0412007?[physics.space-ph].?
21. ^D. Stober (August 2010). The strange case of solar flares and radioactive elements. . Stanford Report (Stanford University). http://news.stanford.edu/news/2010/august/sun-082310.html.?
22. ^E. Kolbe, G.M. Fuller (2004). "Neutrino-Induced Fission of Neutron-Rich Nuclei". Physical Review Letters92 (11): 1101. arXiv:astro-ph/0308350. Bibcode2004PhRvL..92k1101K. doi:10.1103/PhysRevLett.92.111101.?
23. ^A. Kelic, K.-H. Schmidt (2005). "Cross sections and fragment distributions from neutrino-induced fission on r-process nuclei". Physics Letters B616 (1?2): 48?48. arXiv:hep-ex/0312045. Bibcode2005PhLB..616...48K. doi:10.1016/j.physletb.2005.04.074.?
24. ^ abG. Karagiorgi et al. (2007). "Leptonic CP violation studies at MiniBooNE in the (3+2) sterile neutrino oscillation hypothesis". Physical Review D75 (13011): 1?8. arXiv:hep-ph/0609177. Bibcode2007PhRvD..75a3011K. doi:10.1103/PhysRevD.75.013011.?
25. ^M. Alpert (2007). "Dimensional Shortcuts". Scientific American. http://www.sciam.com/article.cfm?chanID=sa006&colID=5&articleID=B5CB9C67-E7F2-99DF-3BF7368614D46C5D. Retrieved 2009-10-31.?[dead link]
26. ^Th. A. Mueller et al. (2011). "Improved Predictions of Reactor Antineutrino Spectra". Physical Review C83 (5): 054615. arXiv:1101.2663. doi:10.1103/PhysRevC.83.054615.?
27. ^G. Mention et al. (January 2011). "The Reactor Antineutrino Anomaly". Physical Review D83 (7): 073006. arXiv:1101.2755. doi:10.1103/PhysRevD.83.073006.?
28. ^R. Cowen (2 February 2010). "Ancient Dawn's Early Light Refines the Age of the Universe". Science News. http://www.sciencenews.org/view/generic/id/55957/title/Ancient_dawns_early_light_refines_age_of_universe. Retrieved 2010-02-03.?
29. ^neutrinos.llnl.gov "LLNL/SNL Applied Antineutrino Physics Project. LLNL-WEB-204112". 2006. http://neutrinos.llnl.gov/ neutrinos.llnl.gov.?
30. ^apc.univ-paris7.fr "Applied Antineutrino Physics 2007 workshop". 2007. http://www.apc.univ-paris7.fr/AAP2007/ apc.univ-paris7.fr.?
31. ^"New Tool To Monitor Nuclear Reactors Developed". ScienceDaily. 13 March 2008. http://www.sciencedaily.com/releases/2008/03/080313091522.htm. Retrieved 2008-03-16.?
32. ^V.A. Kostelecky, M. Mewes (2004). "Lorentz and CPT violation in neutrinos". Physical Review D69 (1): 016005. arXiv:hep-ph/0309025. doi:10.1103/PhysRevD.69.016005.?
33. ^C. Giunti, C.W. Kim (2007). Fundamentals of neutrino physics and astrophysics. Oxford University Press. p.?255. ISBN?0198508719. http://books.google.com/?id=SdAcSwTR0CgC&lpg=PA255&dq=majorana%20neutrino%20helicity&pg=PA255.?
34. ^P. Adamson et al. (MINOS Collaboration) (2007). "Measurement of neutrino velocity with the MINOS detectors and NuMI neutrino beam". Physical Review D76 (7): 072005. arXiv:0706.0437. Bibcode2007PhRvD..76g2005A. doi:10.1103/PhysRevD.76.072005.?
35. ^D. Overbye (22 September 2011). "Tiny neutrinos may have broken cosmic speed limit". New York Times. http://www.nytimes.com/2011/09/23/science/23speed.html. "That group found, although with less precision, that the neutrino speeds were consistent with the speed of light."?
36. ^J. Timmer (22 February 2012). "Faster Than Light Neutrino Result Apparently a Mistake Due to Loose Cable". Ars Technica. http://arstechnica.com/science/news/2012/02/faster-than-light-neutrino-result-apparently-a-mistake-due-to-loose-cable.ars.?
37. ^M. Antonello et al. (2012). "Measurement of the neutrino velocity with the ICARUS detector at the CNGS beam". arXiv:1203.3433?[hep-ex].?
38. ^Associated Press (16 March 2012). "Einstein Proved Right in Retest of Neutrinos' Speed". New York Times. http://www.nytimes.com/2012/03/17/science/einstein-proved-right-in-retest-of-neutrinos-speed.html. Retrieved 2012-03-17.?
39. ^J. Palmer (16 March 2012). "Neutrinos clocked at light-speed in new Icarus test". BBC. http://www.bbc.co.uk/news/science-environment-17364682. Retrieved 17 March 2012.?
40. ^A. Goobar, S. Hannestad, E. M?rtsell, H. Tu (2006). "The neutrino mass bound from WMAP 3 year data, the baryon acoustic peak, the SNLS supernovae and the Lyman-α forest". Journal of Cosmology and Astroparticle Physics606 (6): 19. arXiv:astro-ph/0602155. Bibcode2006JCAP...06..019G. doi:10.1088/1475-7516/2006/06/019.?
41. ^Fukuda, Y., et al (1998). "Measurements of the Solar Neutrino Flux from Super-Kamiokande's First 300 Days". Physical Review Letters81 (6): 1158?1162. arXiv:hep-ex/9805021. Bibcode1998PhRvL..81.1158F. doi:10.1103/PhysRevLett.81.1158.?
42. ^R.N. Mohapatra et al. (APS neutrino theory working group) (2007). "Theory of Neutrinos: A White Paper". Reports on Progress in Physics70 (11): 1757. arXiv:hep-ph/0510213. Bibcode2007RPPh...70.1757M. doi:10.1088/0034-4885/70/11/R02.?
43. ^T. Araki et al. (KamLAND Collaboration) (2005). "Measurement of Neutrino Oscillation with KamLAND: Evidence of Spectral Distortion". Physical Review Letters94 (8): 081801. arXiv:hep-ex/0406035. Bibcode2005PhRvL..94h1801A. doi:10.1103/PhysRevLett.94.081801. PMID?15783875.?
44. ^"MINOS experiment sheds light on mystery of neutrino disappearance" (Press release). Fermilab. 30 March 2006. http://www.fnal.gov/pub/presspass/press_releases/minos_3-30-06.html. Retrieved 2007-11-25.?
45. ^C. Amsler et al. (Particle Data Group) (2008). "The Review of Particle Physics: Neutrino Mass, Mixing, and Flavor Change". Physics Letters B667: 1. Bibcode2008PhLB..667....1P. doi:10.1016/j.physletb.2008.07.018. http://pdg.lbl.gov/2008/reviews/rpp2008-rev-neutrino-mixing.pdf.?
46. ^Th. M. Nieuwenhuizen (2009). "Do non-relativistic neutrinos constitute the dark matter?". Europhysics Letters86 (5): 59001. Bibcode2009EL.....8659001N. doi:10.1209/0295-5075/86/59001.?
47. ^"The most sensitive analysis on the neutrino mass [...] is compatible with a neutrino mass of zero. Considering its uncertainties this value corresponds to an upper limit on the electron neutrino mass of m <2.2 eV/c2 (95% Confidence Level)" The Mainz Neutrino Mass Experiment
48. ^N. Agafonova et al. (OPERA Collaboration) (2010). "Observation of a first ντ candidate event in the OPERA experiment in the CNGS beam". Physics Letters B691 (3): 138?145. arXiv:1006.1623. Bibcode2010PhLB..691..138A. doi:10.1016/j.physletb.2010.06.022.?
49. ^S. Thomas, F. Abdalla, O. Lahav (2010). "Upper Bound of 0.28?eV on Neutrino Masses from the Largest Photometric Redshift Survey". Physical Review Letters105 (3): 031301. doi:10.1103/PhysRevLett.105.031301.?
50. ^J. Lucio, A. Rosado, A. Zepeda (1985). "Characteristic size for the neutrino". Physical Review D31 (5): 1091. doi:10.1103/PhysRevD.31.1091.?
51. ^B. Kayser (2005). "Neutrino mass, mixing, and flavor change". Particle Data Group. http://pdg.lbl.gov/2006/reviews/numixrpp.pdf. Retrieved 2007-11-25.?
52. ^S.M. Bilenky, C. Giunti (2001). "Lepton Numbers in the framework of Neutrino Mixing". International Journal of Modern Physics A16 (24): 3931?3949. arXiv:hep-ph/0102320. Bibcode2001IJMPA..16.3931B. doi:10.1142/S0217751X01004967. http://www.nu.to.infn.it/pap/0102320/.?
53. ^"Nuclear Fission and Fusion, and Nuclear Interactions". NLP National Physical Laboratory. 2008. http://www.kayelaby.npl.co.uk/atomic_and_nuclear_physics/4_7/4_7_1.html. Retrieved 2009-06-25.?
54. ^A. Bernstein et al. (2002). "Nuclear reactor safeguards and monitoring with antineutrino detectors". Journal of Applied Physics91 (7): 4672. arXiv:nucl-ex/0108001. Bibcode2002JAP....91.4672B. doi:10.1063/1.1452775.?
55. ^A. Bandyopadhyay et al. (ISS Physics Working Group) (2007). "Physics at a future Neutrino Factory and super-beam facility". Reports on Progress in Physics72 (10): 6201. arXiv:0710.4947. Bibcode2009RPPh...72j6201B. doi:10.1088/0034-4885/72/10/106201.?
56. ^F. Reines, C. Cowan Jr. (1997). "The Reines-Cowan Experiments: Detecting the Poltergeist". Los Alamos Science25: 3. http://library.lanl.gov/cgi-bin/getfile?25-02.pdf.?
57. ^S. A. Colgate and R. H. White (1966). "The Hydrodynamic Behavior of Supernova Explosions". The Astrophysical Journal143: 626. Bibcode1966ApJ...143..626C. doi:10.1086/148549.?
58. ^ abA.K. Mann (1997). Shadow of a star: The neutrino story of Supernova 1987A. W. H. Freeman. p.?122. ISBN?0716730979. http://www.whfreeman.com/GeneralReaders/book.asp?disc=TRAD&id_product=1058001008&@id_course=1058000240.?
59. ^J.N. Bahcall (1989). Neutrino Astrophysics. Cambridge University Press. ISBN?052137975X.?
60. ^D.R. David Jr. (2003). "Nobel Lecture: A half-century with solar neutrinos". Reviews of Modern Physics75 (3): 10. Bibcode2003RvMP...75..985D. doi:10.1103/RevModPhys.75.985.?
61. ^"Error: no |title= specified when using {{Cite web}}". http://focus.aps.org/story/v24/st4.?
62. ^G.B. Gelmini, A. Kusenko, T.J. Weiler (May 2010). "Through Neutrino Eyes". Scientific American302 (5): 38?45. Bibcode2010SciAm.302e..38G. doi:10.1038/scientificamerican0510-38. http://www.scientificamerican.com/article.cfm?id=through-neutrino-eyes.?
[edit]Bibliography
? Tammann, G.A.; Thielemann, F.K.; Trautmann, D. (2003). "Opening new windows in observing the Universe". Europhysics News. http://www.europhysicsnews.com/full/20/article8/article8.html. Retrieved 2006-06-08.?
? Bahcall, John N. (1989). Neutrino Astrophysics. Cambridge University Press. ISBN?0-521-35113-8.?
? Close, Frank (2010). Neutrino. Oxford University Press. ISBN?978-0-19-957459-9.?
? Griffiths, David J. (1987). Introduction to Elementary Particles. John Wiley &Sons. ISBN?0-471-60386-4.?
? Perkins, Donald H. (1999). Introduction to High Energy Physics. Cambridge University Press. ISBN?0-521-62196-8.?
? Riazuddin (2005). "Neutrinos". National Center for Physics. http://www.ncp.edu.pk/docs/12th_rgdocs/Riazuddin.pdf. Retrieved 2010.?
? Povh, Bogdan (1995). Particles and Nuclei: An Introduction to the Physical Concepts. Springer-Verlag. ISBN?0-387-59439-6.?
? Tipler, Paul; Llewellyn, Ralph (2002). Modern Physics (4th ed.). W.H. Freeman. ISBN?0-7167-4345-0.?
? Alberico, W.M. Bilenky, S.M.; Bilenky (2003). "Neutrino Oscillations, Masses And Mixing". Phys.Part.Nucl. 35 (2004) 297-323; Fiz.Elem.Chast.Atom.Yadra 35 (2004) 545-596: 6239. arXiv:hep-ph/0306239. Bibcode2003hep.ph....6239A.?
? Bumfiel, Geoff (1 October 2001). "The Milky Way's Hidden Black Hole". Scientific American. http://www.sciam.com/article.cfm?id=the-milky-ways-hidden-bla. Retrieved 2010-04-23.?
? Zuber, Kai (2003). Neutrino Physics. Institute of Physics Publishing. ISBN?978-075-030-750-5.?
? Measurement of the neutrino velocity with the OPERA detector in the CNGS beam. 2011. http://static.arxiv.org/pdf/1109.4897.pdf.?
[edit]External links
? "What's a Neutrino?", Dave Casper (University of California, Irvine)
? Aspera European network portal
? www.astroparticle.org: all about astroparticle physics...
? Neutrino unbound: On-line review and e-archive on Neutrino Physics and Astrophysics
? Nova: The Ghost Particle: Documentary on US public television from WGBH
? SNEWS: Using neutrino detectors to receive early warning of supernovae
? Measuring the density of the earth's core with neutrinos
? John Bahcall Website
? Universe submerged in a sea of chilled neutrinos, New Scientist, 5 March 2008
? Neutrinos caught in the act, "R&D" July 24, 2009 By Tia Jones
? What's a neutrino?
? Search for neutrinoless double beta decay with enriched 76Ge in Gran Sasso 1990?2003
? Neutrino caught in the act of changing from muon-type to tau-type, CERN press release
? Neutrino 'ghost particle' sized up by astronomers BBC News 22 June 2010
? Pillar of physics challengedNeutrinos in the Standard Modelof elementary particlesNeutrino/Antineutrino
The first use of a hydrogen bubble chamber to detect neutrinos, on November 13, 1970. A neutrino hit a proton in a hydrogen atom. The collision occurred at the point where three tracks emanate on the right of the photograph.
Composition
Elementary particle
Statistics
Fermionic
Generation
First, second and third
Interactions
Weak interaction and gravitation
Symbol
νe, νμ, ντ, νe, νμ, ντ
Antiparticle
Antineutrinos are possibly identical to the neutrino (see Majorana fermion).
Theorized
νe (Electron neutrino): Wolfgang Pauli (1930)νμ (Muon neutrino): Late 1940s
ντ (Tau neutrino): Mid 1970s
Discovered
νe: Clyde Cowan, Frederick Reines (1956)νμ: Leon Lederman, Melvin Schwartz and Jack Steinberger (1962)ντ: DONUT collaboration (2000)
Types
3 ? electron neutrino, muon neutrino and tau neutrino
Mass
Small, but non-zero. See the mass section.
Electric charge
0?e
Spin
1?2
Weak hypercharge
?1
B ? L
?1
X
?3
Neutrino/Antineutrino
Source: http://en.wikipedia.org/wiki/Neutrino
|