Niels Bohr hypothesized the existence of quantum mechanical restrictions on the principle of energy conservation, but Pauli couldn’t buy that:

Wolfgang Pauli1900-1958

Dear Radioactive Ladies and Gentlemen, as the bearer of these lines, to whom I graciously ask you to listen, will explain to you in more detail, how because of the "wrong" statistics of the N and Li6 nuclei and the continuous beta spectrum, I have hit upon a desperate remedy to save the "exchange theorem" of statistics and the law of conservation of energy. Namely, the possibility that there could exist in the nuclei electrically neutral particles, that I wish to call neutrons, which have spin 1/2 and obey the exclusion principle and which further differ from light quanta in that they do not travel with the velocity of light. The mass of the neutrons should be of the same order of magnitude as the electron mass and in any event not larger than 0.01 proton masses. The continuous beta spectrum would then become understandable by the assumption that in beta decay a neutron is emitted in addition to the electron such that the sum of the energies of the neutron and the electron is constant...

I agree that my remedy could seem incredible because one should have seen those neutrons much earlier if they really exist. But only the one who dare can win and the difficult situation, due to the continuous structure of the beta spectrum, is lighted by a remark of my honoured predecessor, Mr Debye, who told me recently in Bruxelles: "Oh, It's well better not to think to this at all, like new taxes". From now on, every solution to the issue must be discussed. Thus, dear radioactive people, look and judge. Unfortunately, I cannot appear in Tubingen personally since I am indispensable here in Zurich because of a ball on the night of 6/7 December. With my best regards to you, and also to Mr Back. Your humble servant . W. Pauli, December 1930

"I have done a terrible thing. I have postulated a particle that cannot be detected."

1936 Millikan’s group shows at earth’s surface cosmic ray showers are dominated by electrons, gammas, and

X-particles capable of penetrating deep underground (to lake bottom and deep tunnel experiments) and yielding isolated single cloud chamber tracks

Primary proton

1937 Street and Stevenson1938 Anderson and Neddermeyer determine X-particles

•are charged•have 206× the electron’s mass•decay to electrons with a mean lifetime of 2sec

0.000002 sec

1947 Lattes, Muirhead, Occhialini and Powell observe pion decay

Cecil Powell (1947)Bristol University

Nature 163, 82 (1949)

C.F.Powell, P.H. Fowler, D.H.PerkinsNature 159, 694 (1947)

Consistently ~600 microns (0.6 mm)

+ energy always

predictably fixedby E

Under the influence of a magnetic field

simple 2-body decay!

+ + + neutrino?charge +1 +1 ?spin 0 ½ ?

0½

n p + e + neutrino?

+ + + neutrino?Then

- e- + neutrino????

As in the case of decaying radioactive isotopes, the electrons’s energy varied, with a maximum cutoff (whose value was the 2-body prediction)

3 body decay!

p

e

e

2 neutrinos

1953, 1956, 1959Savannah River (1000-MWatt) Nuclear Reactor in South Carolinalooked for the inverse of the process

n p + e + neutrino

Cowan & Reines

also looked forn + neutrino p + e

but never observed!

observed2-3 p + neutrino events/hour

with estimate flux of 51013 neutrinos/cm2-sec

p + neutrino n + e+?

1967 •built at Brookhaven labs•615 tons of tetrachloroethylene•Neutrino interaction 37Cl37Ar(radioactive isotope, ½ = 35 days)Chemically extracting the 37Ar, its radioactivity gives the number of neutrino interactions in the vat(thus the solar neutrino flux). Results: Collected data 1969-1993 (24 years!!) gives a mean of 2.5±0.2 SNU while theory predicts 8 SNU (1 SNU = 1 neutrino interaction per second for 10E+36 target atoms). This is a neutrino deficit of 69%.

Homestake MineExperiment

Underground Neutrino Observatory

The proposed next-generation underground water Čerenkov detector

to probe physics beyond the sensitivity of the highly successful Super-Kamiokande detector in Japan

The SuperK detector is a

water Čerenkov detector

40 m tall40 m diameter

stainless steel cylinder

containing 50,000 metric tons of ultra pure water

The detector is located 1 kilometer below Mt. Ikenoyama inside the Kamioka zinc mine.

The main sensitive region is 36 m high, 34 m in dia viewed by 11,146 inward facing Hamamatsu photomultiplier tubes surrounding 32.5 ktons of water

Underground Neutrino Observatory

• 650 kilotons

• active volume: 440 kilotons

20 times larger than Super-Kamiokande

major components: photomultiplier tubes, excavation, water purification system.

$500M The optimal detector depth to perform the full proposed scientific program ofUNO 4000 meters-water-equivalent

or deeper

1953 Konopinski & Mahmoudintroduce LEPTON NUMBER to account for which decays/reactions are possible,which not

e, ( ) assigned L = +1e+, + ( +) assigned L =1

n p + e + neutrino

_

p + neutrino n + e+

_

n + e+ _

n + p + e?? ??

1962 Lederman,Schwartz,Steinberger Brookhaven National Laboratory

using a as a source of antineutrinos

and a 44-foot thick stack of steel (from a dismantled warship hull) to shield everything but the ’s

found 29 instances of

+ p + + n

but none of

+ p e+ + n

1988 Nobel Prize in Physics

"for the neutrino beam method and the demonstration of the doublet structure of the leptons through the discovery of the muon neutrino"

So not just ONE KIND of neutrino, the leptons are associated into “families”

ee

n

p

e

e

e

e