The History of Neutrinos, 1930 − 1985. What have we Learned About Neutrinos? What have we Learned Using Neutrinos?

J. Steinberger Prepared for “25th International Conference On Neutrino Physics and Astrophysics”, Kyoto (Japan), June 2012

1 2 3 4 The detector of the experiment of Conversi, Pancini and Piccioni, 1946, 5 which showed that the mesotron is not the Yukawa particle. Detector with 80 Geiger counters. The muon decay spectrum is continuous. My thesis experiment, under Fermi, which showed that the muon decays into two neutral particles, plus the electron.

Fermi, myself and others, in 1954, at a summer school in Varenna, lake Como, a few months before Fermi’s untimely disappearance.

6 Demonstration of the Neutrino

In 1956 Cowan and Reines detected antineutrinos from a nuclear reactor, reacting with protons in liquid scintillator which also contained cadmium, observing the positron as well as the scattering of the neutron on cadmium.

7 The Electron and Muon Neutrinos are Different. 1. G. Feinberg, 1958. 2. B. Pontecorvo, 1959. 3. M. Schwartz (T.D. Lee), 1959 4. Higher energy accelerators, Courant, Livingston and Snyder.

Pontecorvo

8 9 A C

B D

Spark chamber and counter arrangement. A are triggering counters, Energy spectra of neutrinos B, C and D are anticoincidence counters from pion and kaon decays.

10 Event with penetrating muon and hadron shower 11 The group of the 2nd neutrino experiment in 1962: J.S., Goulianos, Gaillard, Mistry, Danby, technician whose name I have forgotten, Lederman and Schwartz. 12 Same group, 26 years later, at Nobel ceremony in Stockholm.

13 Discovery of partons, nucleon structure, scaling, in deep inelastic scattering of electrons on protons at SLAC in 1969.

• Panofsky responsible for 24 GeV electron linear accelerator. • Experiment of J. Friedman, H. Kendall, R. Taylor and colleagues.

Discovery of nucleon structure at SLAC in 1969. The cross-section, for different masses of the final hadronic state, is, in first approximation, independent of q2.

14 Gargamelle Experiment Discovery of Neutral Currents, confirming E-W theory Demonstration that partons are Gell-Mann - Zweig quarks

Higher Intensity neutrino beams made possible by extracted proton beams and vanderMeer horns

Simon vanderMeer A vanderMeer Horn 15 The Gargamelle bubble chamber, 6 m long, 2 m diam., filled with freon.

16

Muon-less event in Gargamelle. Neutrino beam enters from left, produces a lambda (on top), and a K+ (on bottom).

17 Distributions along the neutrino beam axis a) Neutral current events in ν. b) Charged Current events in ν. c) NC/CC, ν. _ d) Neutral Current events in ν_ . e) Charged_ current events in ν . f) NC/CC, ν . g) Neutron stars, 100 < E < 500 MeV. h) Computed distributions of neutron stars from Monte Carlo.

Events identified as neutron interactions are attenuated along the beam direction, events identified as neutrino interactions are not.

18 Gargamelle collaboration, Deden et al. 1974. First quantitative confirmations of predictions of the Gell-Mann – Zweig proposal of quarks as partons, comparison

of the F2(x) structure functions for neutrinos on protons with those of SLAC for electrons. Agreement with the predicted factor, 18/5. 19 Deep Inelastic Scattering at higher Energies.

Physics aims: • Precise checks of quark parton model. 2 • Checks on E-W model, measurement of sin θW. • Determination of nuclear structure functions. • Checks on QCD. The measurement of scaling violations in the Q2 dependence of structure function gave the first quantitative confirmation of QCD.

Deep inelastic neutrino detectors: Fermilab Tevatron: HPWF -- (Harvard, Pennsylvania, Wisconsin, Fermilab), liquid scintillator target. CCFR – (Caltech, Columbia, Fermilab, Rochester), iron target. 15 foot hydrogen, deuterium bubble chamber.

CERN SPS CDHS – (CERN, Dortmund, Heidelberg, Saclay). Iron target. CHARM – (CERN, Hamburg, Amsterdam, Moscow). Marble target. BEBC 35m3 Big European hydrogen, deuterium Bubble Chamber.

20 Beam layout at SPS

_ ν and ν beam energy spectra The lower, flat spectra are the narrow band beams

21 Narrow band beam, CC events, energy vs. radius in CDHS detector. Top group from kaon decay, bottom group from pion decay.

CDHS Detector

22 CDHS detector

Charged current event in CDHS detector 23 Results on Weinberg angle, using neutral-charged current ratio.

In E-W theory:

2 Original Gargamelle result (1973): sin θW = 0.3 - 0.4 Early CDHS result (1977), 2 with r= .48±.02 and sin θW = 0.24 ± 0.02

Late CDHS result (1986), NC,ν CC,ν 2 with r = .39±.01 and σ /σ = .3059±.0035 sin θW = 0.227 ± 0.007

2 For comparison, the present value of sin θW = 0.23116 ± 0.00013

24 _ ν Structure functions

2 x = Q /2mpEν = parton mass fraction; y = Ehad/Eν 0 ≤ x ≤ 1; 0 ≤ y ≤ 1;

2 2 2 2 Three structure functions, functions of x and Q : F2(x,Q ), 2xF1(x,Q ) and xF3(x,Q ); Cross-sections for neutrinos and anti-neutrinos are:

The charged lepton cross-section depends only on two structure functions:

In the parton model:

Relationship of structure functions_ to parton distributions: _ F2(x) and 2xF1(x) = q(x) + q (x), xF3(x) = q(x) – q (x) 25 Scaling. The total cross-section divided by neutrino energy, in energy range 30 – 270 Gev.

CDHS results for y distribution of cross-sections, in agreement with quark-parton model.

26 CDHS_ results for the F2(x) and xF3(x) structure functions, and q (x), one-half of their difference, the quark sea structure function. xF3(x) is the structure function of the valence quarks. 27

CDHS result for the gluon structure function. Gluons don’t interact with neutrinos, but do interact with quarks.

G(x) can be obtained from scaling violations in F2(x).

28 CDHS result for the longitudinal structure function, FL(x) = F2(x) – 2xF1(x).

29 QCD asymptotically free predictions of Q2 scaling violations. First quantitative confirmation of QCD predictions , in 1979.

First result (CDHS, 1979), showing quantitative Final CDHS result,1983, showing agreement of observation with QCD. good agreement with QCD, with

Fit to asymptotic freedom prediction gives ΛQCD= .25 ± .12 ΛQCD = .5 ± .2 30 Structure functions in hydrogen

Expected to be approximately equal for protons, neutrons and nuclei .

CDHS measurements of the valence up quark (left) and valence down quark (right) structure functions of the proton.

31 Ratios of F2 structure functions in iron and hydrogen. Left: neutrinos, CDHS at CERN; center: electrons at SLAC; right: muons, EMC at CERN.

32 Demonstration that there are three neutrino families. LEP 1989, using width and height of Z0 resonance.

Aleph result, 1989, Final LEP result, Aleph, Delphi, Nν = 3.27 ± .30 L3 and Opal, Nν = 2.987 ± .008

33 Detection of tau neutrino, Fermilab, Donut experiment, 2001.

Donut , layout. Beam dump neutrino production target, emulsion target, silicon fiber tracker, magnetic spectrometer, muon detector.

Two events. Neutrino enters from left, produces a tau in emulsion, tau track observed, muon detected and momentum is measured. 34