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The Discovery of Neutrinos A Historical Review

The Discovery of Neutrinos A Historical Review. Sandip Pakvasa University of Hawaii. A Short Prehistory of Particle Physics. The discovery of electron: In the period 1850’s, cathode ray tubes were popular and prevalent. In. Outline: History of Invention/Discovery of Neutrino(1895-1930)

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The Discovery of Neutrinos A Historical Review

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  1. The Discovery of NeutrinosA Historical Review SandipPakvasa University of Hawaii 2017

  2. A Short Prehistory of Particle Physics The discovery of electron: In the period 1850’s, cathode ray tubes were popular and prevalent. In

  3. Outline: • History of Invention/Discovery of Neutrino(1895-1930) • Associated History of Elementary Particle Physics • Discovery of the neutrino (1956) Discovery of the second neutrino(inferred in 1943, observed in 1962) Discovery of the third neutrino(inferred in 1975, observed in 2000)

  4. In 1990, at the Neutrino ‘90 conference, Leon Lederman complained that theorists are always lionized, whereas experimentalists are short-changed and not given enuf credit! As an example, he cited Pauli getting a lot of credit for the invention of the neutrino in 1930, but the very hard work of Charles Drummond Ellis and his collaborators as well as Lise Meitner who labored hard from 1920 to 1929 to firmly establish that the beta decay spectrum is truly continuous , which made Pauli’s hypothesis necessary , were hardly acknowledged by the community….! I try to redress this iniquity as much as possible ……

  5. Early History: November 1895 :William Roentgen discovers X-rays from Cathode Ray Tubes (Wuerzburg) • January 1896: Henri Becquerel (Paris) hears about the X-rays in a lecture by Poincare • February 1896: H.B. discovers Radioactivity(in Uranium ore) while trying to find natural sources for X-rays! • 1898: Ernest Rutherford and Marie (and Pierre) Curie start working on Radioactivity and studying its properties • Rutherford found: (a) the exponential decay law; (b) three types of Activity. Alpha (deflected by magnetic field and easily stopped in matter)a little)Beta (penetrating and easily deflected by m.f.) and Gamma (undeflected and most penetrating). Thus alphas and betas were charged and gammas were neutral. • Curies found other stronger radioactive substances( Thorium, Radium, Polonium etc) and showed alphas were much heavier than betas(turned out to be electrons). deflected in magnetic fields, Alpha (“stoppable” and deflected not

  6. November 1895: Roentgen discovers X-rays, emitted from walls of Cathode ray tubes when the beam hits the wallsJanuary 1986: Henri Becquerel hears of this in a lecture by Poincare .He thinks there may be some naturally occurring florescent materials which might also emit X-rays….Tries using Uranium(occurring naturally in Pitchblende). Exposes plates over a weekend .Scheduled to give a talk on mar.1(1896) and impatient for results, develops plates wrapped in black paper(lying inside a closed drawer!) on feb 25 and finds them blackened The name “radioactivity” was given to the phenomenon 4 years later by Marie Curie. 1898: Ernest Rutherford(Cambridge) and the Curies, Marie and Pierre(Paris) start their work on radioactivity…..

  7. All this happened rather quickly, Between 1896 and 1900…….. Rutherford: u Found penetrating Radiation: beta rays Found “stoppable” radiation: Alpha rays B Beta and alpha rays D deflected in magnetic Ii fiield, not gamma rays. r

  8. The Curies found alpha rays can be slowed down in matter, hence they are heavy material particles Also discovered other radioactive elements with stronger activity making further detailed experiments possible

  9. Life and Times of Charles Drummond Ellis:- Beta spectrum very rich & complicated: Lines +Continuum………- Chadwick, Ellis and Wooster in Berlin and Cambridge(1914 - 1929)- After some confusion and controversy with Lise Meitner, they finally showed convincingly that electron energy spectrum in beta decay is continuous rather than discrete.-Ellis deserves much credit for proving beyond a shadow of a doubt that the beta decay energy spectrum is continousIn fact Mott said:”Ellis practically discovered the neutrino”

  10. Three-types of radioactivity: a, b, g Both a, gdiscrete spectrum because Ea, g= Ei – Ef But b spectrum continuous F. A. Scott, Phys. Rev.48, 391 (1935) Puzzle with Beta Spectrum Bohr: At the present stage of atomic theory, however, we may say that we have no argument, either empirical or theoretical, for upholding the energy principle in the case of b-ray disintegrations

  11. Desperate Idea of Pauli

  12. proton neutron e n December 4, 1930 b decay Dear radioactive ladies and gentlemen, ...I have hit upon a ‘desperate remedy’ to save...the law of conservation of energy. Namely the possibility that there exists in the nuclei electrically neutral particles, that I call neutrons...I agree that my remedy could seem incredible...but only the one who dare can win... Unfortunately I cannot appear in person, since I am indispensable at a ball here in Zurich. Your humble servant W. Pauli Note: this was before the discovery of the real neutron

  13. December 1933: Enrico Fermisubmits a paper to Nature: “Tentativo di Una Teoria Della Emissione di raggi Beta” It was rejected:”speculations too remote from reality to be of interest to the readers”. Eventually published in Nuovo Cimento This paper laid out the essential theory of beta decay that has survived almost unchanged until now, with “small” modifications. It predicted the spectrum, obtained the correct value for the coupling etc………In the meantime back in Osaka, Japan, Hideyuki Yukawa was busy…………….

  14. Fermi’s pioneering paper • Had many innovations and new idea. • He was the first one to apply the newly developed quantum field theory to fermions and the idea of creating neutrino and electron at the instaant of decay and not pre-existing in the nucleus….. • He worked out the spectrum for massless as well as massive neutrinos…..

  15. Yukawa’s Brainwave:In 1934, Yukawa proposed a π meson as a carrier of the nuclear force, and from the known range of about 10^-13 cm, deduced a mass of about 100 MeV.Immediate confirmation(1938-9) in cosmic rays when charged particles of such a mass were seen. But soon it was found to behave strangely and not at all like Yukawa’s π meson was supposed to; wrong lifetime, no strong coupling etc………..It was proposed by Shoichi Sakata(1943)(with Inoue) that the funny particle was not π but μ, and that π decayed into μ + νμ and the μ decayed into e + νμ + νe. At the time, it was not clear if the two neutrinos, from beta decay and from π decay were the same or different……..

  16. The Sakata Scheme of pi-mu decay was completely confirmed in 1947-8 by Powell et al (Bristol).Anti-νe Detection Reines-Cowan(1956): Idea was to use the radioactive Beta decays of fission products of Uranium:U + n → X + Y + neutronsX and Y are neutron rich and beta decay: X → Z + e- + anti-νeFor detection they used liquid scintillator and the reaction:anti-νe + p → n + e+

  17. neutrino g e+ H2O + CdCl2 Cd n p+ g Project Poltergeist 1956 Signal 2g, then several g ~few ms later Reines Cowan Experiment attempted at Hanford in 1953, too much background. Repeated at Savannah River in 1955. [Flux: 1013 neutrinos/(cm2 s)]

  18. Neutrinos are Left-handed

  19. This result that neutrino is left-handed is exactly what was expected in the 1957 V - A theory of Sudarshan and Marshak(and Feynman and Gell-Mann) and in the two component theory of Lee, Yang and Landau and Salam, so this was a confirmation of it. The fact that weak interactions are V – A was crucial in constructing the Standard Model of electroweak interactions a la Glashow, Salam and Weinberg.

  20. Confirmation that the second neutrino is different from the first!Brookhaven 1962

  21. m± p± p+ Tons of steel Detector n n More than one kind of neutrino? Date: 1962 Intent: Measure weak force at high energies Expectation: Since neutrinos are created with muons and electrons, the neutrino beam should create both electrons and muons in the detector. Result: No electrons produced, only muons Conclusion: There must be two kinds of neutrinos. Mel Schwartz

  22. In 1975 Martin Perl et al. observed events at SLAC in e+-e- collisions which suggested the existence of a third charged lepton, christened the Tau(τ). There was a third neutrino expected to be associated with this charged lepton. It took 25 years (2000) to confirm the existence of ντ by direct detection (Fermilab)! The process was production of charmed-strange meson then called F (csbar) by PP->F + Λ + K +x… with F decaying into τ + ντ with an expected BR of 5.5%

  23. Observation of the third neutrino FermiLab 2000

  24. Neutrino masses, mixings andOscillations • When neutrinos have masses, the “flavor” states, such as e and  • do NOT have well defined masses, • So the production is of these states, whereas the propagation afterwards is in terms of states with well defined masses. • Z. Maki, M. Nakagawa and S. Sakata (1962) • V. Gribov and B. Pontecorvo (1968)

  25. Flavor Basis Mass Basis Important!

  26. Flavor Oscillations (Naïve Treatment) • Let νµ be produced in π decay at t=0.Then Ψ(0) = νµ = sν1 + cν2 , at a later time t Ψ(t) = -sν1exp(-iE1t) + cν2exp(-iE2t) In the ultra-rel. approx, and assuming plane waves (with equal momentum p): Ei = p+ mi2/2p; then Ψ(t) becomes: Ψ(t) = exp(-ipt) [ s ν1exp{(-im12/2p)t} + c ν2exp{(-im22/2p)t}] Hence, the amplitude to find νµ is: Aµ = <νµǀΨ(t)> = s2exp{(-im12/2p)t} + c2exp{(-im22/2p)t} after removing the overall phase. Here s = sin(θ) and c = cos(θ)

  27. Hence the survival Probability for νµ is: Pμ(L)= c4 + s4 + 2 c2 s2 cos{δm2L/2E}, where δm2 = m22 – m12; this can be written as: Pμ(L) = 1 – sin2(2θ) sin2{δm2L/4E} and Obviously, the conversion probability is: Pμe(L) = 1-Pμ(L) = sin2(2θ) sin2{δm2L/4E} Here we have replaced t by distance travelled by the neutrino beam L = ct =t.

  28. Sources of Neutrinos: Natural: (i) Atmospheric (10 -4 s), (ii) Solar (8 min), (iii) Supernova (>104 yr), (iv) Other astrophysical sources (GRB, AGN) (106 yr), (v) Early Universe (1012 yr), (vi) Earth’s Interior (0.01 s). • Artificial (Man-made): • (i)Reactors (10-4 s) • (ii)Accelrators (0.001 s)

  29. The first observations of Atmospheric Neutrinos made in Kolar Gold Fields near Bangalore,and in South Africa in 1965. • The Indian team was led by M. G. K. Menon et al • The South African team was led by F. Reines et al.

  30. KGF – The 1st reported Atmospheric n Several detectors in KGF mine at various depths. 3 n evts published 15 Aug 65 7600 MWE

  31. CWI – The 1st recorded Atmospheric n First n February 29, 1965 Recorded 100 (1/month)

  32. 1998: The Super-Kamiokande Announces observation of Neutrino Oscillations

  33. pe+p0, K+n, etc So far not seen Atmospheric neutrino main background Cosmic rays isotropic Atmospheric neutrino up-down symmetric Super-KamiokandeNucleon Decay Experiment

  34. Super-Kamiokande 11 stories high 1,000 meters underground 50,000 tons of water 22,500 tons fiducial volume 11,200 photomultipliers 0.5 meter photomultiplier diameter (old copper and zinc mine)

  35. Half of nm lost!

  36. K2K First Long Baseline Experiment

  37. Veto Shield Coil Fermilab Cross check with man-made ’s from Fermilab: MINOS

  38. Good consistency with SK! • MINOS result 2006

  39. What we learnt from Atmospheric Neutrino Observations: • νµ = (ν2 + ν3)/√2 • νт = (ν2 - ν3)/√2 This corresponds to a mixing angle θ of 45 deg. We also learnt that the squared mass difference is dm232= 2.5 x 10-3 eV2

  40. Solar Neutrinos:How the Sun burns • The Sun emits light because nuclear fusion produces a lot of energy Pioneers: Ray Davis and John Bahcall, starting in ’60’s

  41. The Sun seen in Neutrinos from SuperK Bob Svoboda Th

  42. Homestake Gold Mine 100,000 gallons of cleaning fluid C2Cl4 Expected 1.5 interactions per day Measured 0.5 interactions per day Sensitive to 8B solar neutrinos only ne + 37Cl  e- + 37Ar 1968! Ray Davis John Bahcall

  43. Soviet-American Gallium Experiment SAGE 71Ga + n  71Ge + e- Sensitive to pp fusion in sun. 50 metric tons of Gallium They extract a few tens of atoms of Germanium Measured: 77 6  3 SNU Predicted: 123 + 9 -7 SNU

  44. Solar NeutrinoSummary Different experiments are sensitive to different solar processes. But all experiments show a marked deficit of electron neutrinos. Could reflect ignorance of how the sun works? Except.....

  45. SNO Sudbury Neutrino Observatory In Sudbury, Ontario • Cerenkov detector • Heavy water (can do solar model independent measurements) • 6800 feet underground • 9600 PMTs

  46. Charged interactions convert neutron to proton. Sensitive only to ne. 30 events/day SNO Physicsand Results Neutral interactions disassociate deuteron into neutron and proton. Sensitive to ne, nm, nt. 30 events/day Announcement: June 18, 2001 Comparison of SNO results with Super K indicates that the neutrino flux from the sun contains muon neutrinos, supporting neutrino oscillations. Electron scattering mostly sensitive to ne, with small contribution from nm , nt . 3 events/day

  47. SNO clinches case for solar neutrino problem as , not due to solar model

  48. KamLAND 1kt Terrestrial “Solar Neutrino” • Can we convincingly verify oscillation with man-made neutrinos? • Hard for low Dm2 • To probe LMA, need L~100km, 1kt • Need low En, high Fn • Use neutrinos from nuclear reactors

  49. KamLAND:Reactor Anti-neutrinos do oscillate! First clear demonstration of oscillations… ~2005 Proper time  L0=180 km And ~ same as solar neutrinos

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