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Subnuclear Physics in the 1970s

Subnuclear Physics in the 1970s. IFIC Valencia. 4-8 November 2013 Lecture 6 The 2 nd and 3 rd families Three neutrinos Tau November revolution Hidden beauty Reaching the top. Neutrino flavours. Neutrinos cannot be directly detected

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Subnuclear Physics in the 1970s

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  1. Subnuclear Physics in the 1970s IFIC Valencia. 4-8 November 2013 Lecture 6 The 2nd and 3rd families Three neutrinos Tau November revolution Hidden beauty Reaching the top

  2. Neutrino flavours Neutrinos cannot be directly detected The charged lepton produced by the neutrino interaction in the detector identifies the neutrino flavour

  3. Neutrino flavour CHANGES In the last 15 years we learnt that neutrino change flavour, provided time (flight distance) is given them to do so Oscillations and flavour conversion in matter, prove that neutrinos, contrary to the Standard model have non-zero mass flavour states are superposition (mixing) of mass eigenstates

  4. Electron and pion showers Hadrons are produced much more frequently than leptons. Need discrimination power electron Detector should look at and enhance the difference Main difference in the “nose” pion

  5. Signature of nm The world’s first muon neutrino observation in a 12-foot hydrogen bubble chamber at Argonne. muon = long, non interacting track

  6. Tau HL/tlifetime is short, 0.29 ps  O(100 µm) length Nagoya Emulsion Cloud Chamber

  7. The 2nd and 3rd lepton family 1937. J. Street and E. Stevenson; C. Anderson and S. Neddermeyer: discover the penetrating component of cosmic rays (the µ) 1947. M. Conversi, E. Pancini, O. Piccioni: discover in cosmic rays the leptonic character of the µ (I. I. Rabi will later ask: “Who ordered that?”) 1956. F. Reines and C. Cowan. Discovery of the (electron-)anti neutrino with a reactor 1962. M. Schwartz, L. Lederman , J. Steinberger et al. discover the muon-neutrino at BNL AGS proton accelerator 1960. A. Zichichi proposal at CERN PS of the PAPLEP (Proton-AntiProton into LEpton Pairs) initiating the search for the 3rd sequential lepton family, a replica of the first two the “Heavy Lepton and its neutrino” Searching for acoplanar lepton pairs of opposite charges

  8. PAPLEP. The two-arm electron & muon spectrometer • Experimental challenges • Large solid angle • Discriminate (rare) electrons from the (dominant) hadrons • Early shower development [CERN-63-26. Nuclear Physics Division, June 27, 1963] • Discriminate (rare) muon from (dominant) hadrons • Fe hadron absorber • “Punch through” [Nuovo Cimento 35 (1965) 759] Massam, T. A new electron detector with high rejection power against pions. Nuovo Cimento39 (1965) 464. See also CERN-63-26. Nuclear Physics Division, June 27, 1963

  9. PAPLEP. The two-arm electron & muon spectrometer Lepton-Antilepton Pairs = e+e–, µ+µ–, eµ 1963 camera camera Pb Pb Pb Pb camera camera camera camera beam

  10. PAPLEP. The two-arm electron & muon spectrometer

  11. Preshower CERN-63-26. Nuclear Physics Division, June 27, 1963 Nuov Cim 29 (1965) 464 Accurately sample the “nose” of the shower Control early development with Z and thicknesses of detector elements Combine visual and non-visual approaches (each 10–2 rejection) Tracking with thin plate (Al) spark chambers Energy sampling with Pb-scintillator sandwiches e/π separation 4 x 10–4 Heavy lepton not found Final paper N. Cim. 40 (1965) 690 reported the discovery of the “time-like” nucleon form factor

  12. The search at ADONE 1967. Zichichi proposes the search for the HL at the ADONE e+e– collider at Frascati [M. Bernardini et al. INFN/AE-67/3, 20 March 1967] Electron and positrons, differently from protons and antiprotons are pointlike. May give a better chance

  13. The limit HL is here The maximum ADONE energy was however √s=3 GeV, below the threshold for t+t– production √s=3.554 GeV A lower limit for the HL mass was obtained [V. Alles Borelli et al. Lett. Nuov. Cim. 4 (1970) 1156] Simplfied from Nuovo Cimento 17A (1973) 383

  14. MARK I @ SPEAR e+e– √s=6 GeV The search for the 3rd lepton looking for eµ pairs was repeated by Perl et al. Poor lepton identification Electron = 4 x min. ionisation in Pb-scintillator detectors 18% of hadrons in the electron sample Muon= penetration of 20 cm of Fe (1.7l) 20% of hadrons in the muon sample Analysis had to rely statistically on acoplanarity selection MARK I 1974 The general purpose detector M. L. Perl et al. Phys. Rev. Lett. 35 (1975) 1489 . Evidence for anomalous lepton production in e+e– annihilation “We have found 64 events of the form for which we have no conventional explanation”

  15. MARK I improve µ and e discrimination Summer 1974. Add thick absorbers to filter muons added in the upper part 1976. Add Pb glass wall (A. Galtieri) M. L. Perl et al. Phys. Lett. 63B (1976) 466. Properties of anomalous eµ events produced in e+e– annihilation “We present the properties of 105 events of the form The simplest hypothesis compatible with all data is that these events come from the production of a pair of heavy leptons, the mass of the lepton being in the range 1.6 to 2.0 GeV” 1977. PLUTO and DASP @ DESY confirm the observation 1976? HL is called t from trton, the third (P. Rapidis) 16 September 2014 A. Bettini. Padova University and INFN; LSC 15

  16. DONUT @ Fermilab 2000

  17. Discovery of nt 2001. K. Niwa et al. DONUT-E872 at Fermilab www-donut.fnal.gov/web pages/

  18. GIM Existence and properties of “charmed” hadrons was predicted on theoretical grounds 1. 1970. GIM mechanism: Glashow, Iliopoulos and Maiani introduced a new quark flavour, charm, to explain the suppression of weak neutral current processes between quarks of different flavour, which otherwise should have been orders of magnitude larger than observed 2. 1972‘t Hooft showed that EW theory can be “renormalised” (infinite terms can be subtracted in a coherent manner) if the sum of the electric charged of the fermions is zero With 4 leptons (e–, ne), (m–,nm) and 3 quark (d,u) and s, each with 3 colours (1973) • Need another quark, in three colours, with charge 2/3, similar to u • Charmed particles should have been • masses  2 GeV • produced in pair • short lifetimes  0.1 ps and should decay more often in “strange” final states than not • But in 1974, charm, strongly wanted by theorists, had not been found. Or at least so it was thought in the West

  19. Cabibbo mixing Analysing the decay rates of the strange hyperons and mesons shows that the decays with ∆S = 1 are suppressed by an order of magnitude to those with ∆S=0 In addition the decay rate of the n is suppressed a bit with respect to the µ Cabibbo showed that universality is recovered assuming that the quarks that couple to the W are not in the basis d and s, but in one rotated by an angle qC DS=0 |DS|=1 W couples to d’ = d cosqC + s sinqC cosqC = 0.974 sinqC = 0.221 qC = 12.8˚

  20. Strangness changing neutral currents Immediate consequence of the Cabibbo theory is the existence of the neutral current Consequently the two decays should have similar rates. But strangness changing neutral currents are strongly suppressed

  21. GIM mechanism d’= d cosqC + s sinqC is a member of the doublet In 1970 Glashow, Iliopoulos and Maiani (GIM) suggested the existance of a new flavour called charm that makes a doublet with s’ (the state ortogonal to d’) Now there are two terms The strangeness changing neutral currents are cancelled, at the 1st order. Summing GIM shown that to be true at all orders 2nd is

  22. The Japanese perspective 1956 Sakata model. Fundamental particles are p, n and L 1957-8 Parity violation. V–A structure 1959 Gamba, Marshak and Okubo baryon-lepton fundamental symmetry (n, e, µ) - (p, n, L ) 1960 Maki et al. Nagoya model. “Ur” matter B+ and 1962 Second neutrino, lepton-baryon symmetry lost Try to recover: Katayama et al. and Maki et al. advanced two hypothesis 1. are not the "true" neutrinos, but linear mixtures, of them The true ones 2. only n2, for not explained reasons, couples to the B+ Maki et al.mentioned also the possibility of “transmutation” between neutrino flavours Katayama et al. advanced the hypothesis that a 4th “Sakaton” might exist N.B. If it were true neutrino and quark (Cabibbo) mixing angles would have to be equal 1962 Lipkin et al. notice that the observation of at rest falsifies Sakata model

  23. Discovery of charm The emulsion technique, abandoned in the West had made much progress in Japan Niu and collaborators developed in Nagoya the“emulsion chamber”, made of two main parts several emulsion layers perpendicular to tracks sandwitch of emulsions and Pb sheets (t=1 mm)  identification of e, measure g enrgy Measure of momenta in the TeV region via multiple scattering High altitudes exposures with balloons Develop automatic scanning and measurement devices 1971. Observation of one event produced by a TeV-energy primary Associated production of two particles decaying in several 10–14 s  weak decay Tracks OB, BB and π˚ are coplanar. Particle h decaying at B is in a hadronic shower  is a hadron; mass mx=1.5 -3.5 GeV depending on the nature of BB’) With this mass cannot be strange. 1972. Final confirmation that it has the characteristics of charm. Research was intensified. By 1975 a dozen of events were found But in the West the discovery was ignored

  24. Discovery of the J 1974 Sam Ting and coll. protonsincrotron AGS at BNL: spctrometer to search for “heavy photons”, particles with JP = 1, narrow, decaying in e+e– through the reaction p+N e+e–+ X (X = anything) Two arm spectrometer. Each at the production angle qi accepting momentum pi (i=1,2). Mass of the pair • to decouple the q and p magnet deflect in the vertical plane • range of search in m variable, by varying acceptance in p1 and p2 • e+e– are produced in EM processes. • see/ sππ < 10–6 very high rejection power necessary>>108 • Threshold Cherenkov sees only e, not π, K. knok-on electron produced in the first one are bent out by B and do not reach the second • calorimeters give shower profile • must cope with high flux 1012 protons/s

  25. Discovery of the J The resonance peak at m(e+e–)=3100 MeV is extremely narrow, narrower than the experimental resolution G< 5 MeV Cannot be understood if only u, d and s exist The decay in e+e–, through a photonJPC = 1– –

  26. Discovery of y and y’ Richter and collaborators observed the resonance at SPEAR contemporarily and independently, and called it y

  27. Y’ The systematic search for more narrow resonances followed 10 days after the second (and last) was found at M=3686 MeV, the y’

  28. Open charm The Mark I detector started the search of the charmed pseudoscalar mesons at √s=4.02 GeV in 1976, after having improved its K to π discrimination ability, in the channels The mesons appear as resonances in the final state. Neutral D were observed decaying in the final states Mass =1865 MeV, width < experimental resolution The charged D-mesons were observed in the channels No resonance in the channels Mass =1869 MeV

  29. Hidden and open charm y(3100) and y(3686) are very narrow. Why? Masses >> r, w, f many more open decay channels width should be large y(3100) and y(3686) contain a charm antcharm pair In spectroscopic notation are 13S1 and 23S1 They would like to decay in charmed mesons, but this is not energetically possible. 2 mD˚ = 3730 MeV; 2 mD± = 3738 MeV cfr y”(3770) on are wide

  30. The two arms muon spectrometer When the new proton accelerator became operational at Fermilab, in 1972, the Columbia-Fermilab-Stony Brook submitted a proposal to search for new heavy vector bosons with a single arm lepton spectrometer, using a combination of magnetic measurement and lead-glass photon detectors to identify electrons with a pion contamination of <10-5 . Such rejection is needed when only one particle is involved. Lederman in the Nobel lecture says: “The single-lepton effects turned out to be relatively unfruitful, and the originally proposed pair experiment got underway in 1975. In a series of runs the number of events with pair masses above 4 GeV gradually increased and eventually grew to a few hundred... The group was learning how to do those difficult experiments. In early 1977, the key to a vastly improved dilepton experiment was finally discovered. The senior Ph. D.s on the collaboration, Steve Herb, Walter Innes, Charles Brown, and John Yoh, constituted a rare combination of experience, energy, and insight. A new rearrangement of target, shielding, and detector elements concentrated on muon pairs but with hadronic absorption being carried out in beryllium, actually 30 feet of beryllium. The decreased multiple scattering of the surviving muons reduced the mass resolution to 2%, a respectable improvement over the 10 - 15 % of the 1968 BNL experiment. The filtering of all hadrons permitted over 1000 times as many protons to hit the target as compared to open geometry. …Recall that this kind of observation can call on as many protons as the detector can stand,... Muon-ness was certified before and after bending in iron toroids to redetermine the muon momentum and discourage punchthroughs

  31. The two arms muon spectrometer Fermilab 1977

  32. The Y’s and the 5th quark In a month of data taking in the spring of 1977, some 7000 pairs were recorded with masses greater than 4 GeV and a curious, asymmetric, and wide bump appeared to interrupt the Drell-Yan continuum near 9.5 GeV By September, with 30,000 events, the enhancement was resolved into three clearly separated peaks, the third “peak” being a well-defined shoulder. See These states were called , ’, ’’ Simplest assumption JPC=1– –

  33. The  ’s and the 5th quark The  are beauty-antibeauty bound states observed at the e+e– colliders at DESY (Hamburg) and afterward at Cornell JPC=1– –, I=0. They are 3S1 with principal quantum number n=1, 2, 3 Cannot decay, for energy conservation, in states with explicit beuaty, hence they are narrow

  34. Top Searched at hadrons colliders for more than a decennim Difficult due to its very large mass mt=173 GeV Need CoM energy > 400 GeV In a collision pp at √s = 2 TeV a top antitop pair is produced every 1010 collisions Lifetime <10–24 s There are no hadrons containing top Look in the “clean” channels W decays most often in quark antiquark, but background is huge due to strong interactions Good tag: detect a b in the hadronic jet

  35. Discovery of top • Discoveres in 1995 by CDF Tevatron pp collider at Fermilab, √s=2000 GeV • Important detector elements • Si microstrip high spatial resolution vertex detector • Tracking detectors • Hermetic calorimetry (in the transversal plane)  missing momenum, neutrinos mt=173±3 GeV

  36. Top at LHC Top production cross section copared to QCD calculations Invariant mass of the jets selected as compatible with all hadronic decay of top

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