subnuclear physics in the 1970s

1A. Bettini LSC, Padova University and INFN

Subnuclear Physics in the 1970s

21 Apr 2023

IFIC Valencia. 4-8 November 2013Lecture 6

The 2nd and 3rd familiesThree neutrinos

TauNovember revolution

Hidden beautyReaching the top


Neutrino flavours

21 Apr 2023

Neutrinos cannot be directly detected

The charged lepton produced by the neutrino interaction in the detector identifies the neutrino flavour


Neutrino flavour CHANGES

21 Apr 2023

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 modelhave non-zero massflavour states are superposition (mixing) of mass eigenstates


Electron and pion showers

21 Apr 2023

electron

pion

Main difference in the “nose”

Hadrons are produced much more frequently than leptons. Need discrimination power

Detector should look at and enhance the difference


Signature of

21 Apr 2023

muon = long, non interacting track

The world’s first muon neutrino observation in a 12-foot hydrogen bubble chamber at Argonne.


Tau

21 Apr 2023

HL/ lifetime is short, 0.29 ps O(100 µm) length Nagoya Emulsion Cloud Chamber


The 2nd and 3rd lepton family

21 Apr 2023

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 twothe “Heavy Lepton and its neutrino”Searching for acoplanar lepton pairs of opposite charges

HL

HL

⎛⎝⎜

⎞⎠⎟


PAPLEP. The two-arm electron & muon spectrometer

21 Apr 2023

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 Cimento 39 (1965) 464. See also CERN-63-26. Nuclear Physics Division, June 27, 1963



21 Apr 2023

PbPb

Pb

Pb

cameracamera

camera camera

camera camera

beam

Lepton-Antilepton Pairs = e+e–, µ+µ–, eµ

1963



21 Apr 2023


Preshower

21 Apr 2023

Accurately sample the “nose” of the showerControl 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 chambersEnergy sampling with Pb-scintillator sandwiches

e/π separation 4 x 10–4

CERN-63-26. Nuclear Physics Division, June 27, 1963Nuov Cim 29 (1965) 464

Heavy lepton not foundFinal paper N. Cim. 40 (1965) 690 reported the discovery of the “time-like” nucleon form factor


The search at ADONE

21 Apr 2023

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


The limit

21 Apr 2023

The maximum ADONE energy was however √s=3 GeV, below the threshold for – production √s=3.554 GeVA 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

HL is here


MARK I @ SPEAR e+e– √s=6 GeV

21 Apr 2023

MARK I 1974The general purpose detector

The search for the 3rd lepton looking for eµ pairs was repeated by Perl et al. Poor lepton identificationElectron = 4 x min. ionisation in Pb-scintillator detectors

18% of hadrons in the electron sampleMuon= penetration of 20 cm of Fe (1.7l)

20% of hadrons in the muon sampleAnalysis had to rely statistically on acoplanarity selection

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”


MARK I improve µ and e discrimination

21 Apr 202321 April 2023 A. Bettini. Padova University and INFN; LSC 15

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

e +e−→ e+ +missingenergy

“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”

1976? HL is called from, the third (P. Rapidis)

1977. PLUTO and DASP @ DESY confirm the observation


DONUT @ Fermilab 2000

21 Apr 2023


Discovery of

21 Apr 2023

www-donut.fnal.gov/web pages/

2001. K. Niwa et al. DONUT-E872 at Fermilab


GIM

21 Apr 2023

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

Γ K + → π +νν( ) / Γ K + → π 0e+ν e( ) < 1.2 ×10–5

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–, e), (–,) 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

Q f =−1−1+ 3 −13

⎛⎝⎜

⎞⎠⎟+ 3

23

⎛⎝⎜

⎞⎠⎟+ 3 −

13

⎛⎝⎜

⎞⎠⎟=−2


Cabibbo mixingAnalysing 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 C

W couples tod’ = d cosC + s sinC

cosC = 0.974sinC = 0.221

S=0

S|=1

€

n → pe−ν e

€

Λ→ pe−ν e

C = 12.8˚

M ∝GF ⋅eRγαeL ⋅d'RγαuL

M ∝GF cosC ⋅eRγαeL ⋅dRγαuL

M ∝GF sinC ⋅eRγαeL ⋅sRγαuL


Strangness changing neutral currentsImmediate consequence of the Cabibbo theory is the existence of the neutral current

should have similar rates. But

€

Γ K + → π +νν ( )

Γ K + → π 0e+ν e( )<1.2 ×10–5

strangness changing neutral currents are strongly suppressed

Consequently the two decays

d 'R γαd'L =cos2CdRγαdL +sin2CsRγαsL +cosC sinC dRγαsL + sRγαdL⎡⎣ ⎤⎦


GIM mechanismd’= d cosC + s sinC is a member of the doublet

€

c

s'

⎛

⎝ ⎜

⎞

⎠ ⎟

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’)

u

d '

⎛⎝⎜

⎞⎠⎟

GIM shown that to be true at all orders

2nd is

d '

s '

⎛⎝⎜

⎞⎠⎟=

cosC sinC

–sinC cosC

⎛⎝⎜

⎞⎠⎟

ds

⎛⎝⎜

⎞⎠⎟

d 'R γαd'L =cos2CdRγαdL +sin2CsRγαsL +cosC sinC dRγαsL + sRγαdL⎡⎣ ⎤⎦

s 'R γαs'L =sin2CdRγαdL +cos2CsRγαsL −cosC sinC dRγαsL + sRγαdL⎡⎣ ⎤⎦

Now there are two terms

s 'R γαs'L+d'Rγαd'L =dRγαdL + sRγαsLSumming The strangeness changing neutral currents are cancelled, at the 1st order.


The Japanese perspective

21 Apr 2023

The true ones

1956 Sakata model. Fundamental particles are p, n and Λ

1957-8 Parity violation. V–A structure

1959 Gamba, Marshak and Okubo baryon-lepton fundamental symmetry (, e, µ) - (p, n, Λ )

1960 Maki et al. Nagoya model. “Ur” matter B+ and p=B n=e−B Λ =−B

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

2. only 2, 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

1962 Lipkin et al. notice that the observation of at rest falsifies Sakata modelpp→ KL0KS

0

N.B. If it were true neutrino and quark (Cabibbo) mixing angles would have to be equal


Discovery of charm

21 Apr 2023

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 γ enrgy

Measure of momenta in the TeV region via multiple scattering

High altitudes exposures with balloonsDevelop automatic scanning and measurement devices1971. Observation of one event produced by a TeV-energy primary

Associated production of two particles decaying in several 10–14 s weak decayTracks 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 foundBut in the West the discovery was ignored


Discovery of the J

21 Apr 2023

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 i accepting momentum pi (i=1,2). Mass of the pair

•to decouple the 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. • ee/ ππ < 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

m2 ee−( ) =2me2 +2E1E2 +2p1p2 cos 1 +2( )


Discovery of the J

21 Apr 2023

The resonance peak at m(e+e–)=3100 MeV is extremely narrow, narrower than the experimental resolution Γ< 5 MeV

Cannot be understood if only u, d and s exist

The decay in e+e–, through a photon JPC = 1– –


Discovery of and ’

21 Apr 2023

Richter and collaborators observed the resonance at SPEAR contemporarily and independently, and called it


’

21 Apr 2023

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

' → ψ + π + + π −

→ e+ + e−


Open charm

21 Apr 2023

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 statesMass =1865 MeV, width < experimental resolution

D0 → K−π D0 → K π−

The charged D-mesons were observed in the channels No resonance in the channels Mass =1869 MeV

D → K –π π D−→ K π−π−

D → K π π− D−→ K−π π−


Hidden and open charm

21 Apr 2023

(3100) and (3686) are very narrow. Why?Masses >> many more open decay channels width should be large(3100) and (3686) contain a charm antcharm pairIn 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 ”(3770) on are wide


The two arms muon spectrometer

21 Apr 2023

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 filteringof 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

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 filteringof 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


The two arms muon spectrometer

21 Apr 2023

Fermilab 1977


The Y’s and the 5th quark

21 Apr 2023

By September, with 30,000events, the enhancement was resolved into three clearly separated peaks, the third “peak” being a well-defined shoulder. SeeThese states were called , ’, ’’Simplest assumption JPC=1– –

In a month of data taking in the spring of 1977, some 7000 pairs wererecorded with masses greater than 4 GeV and a curious, asymmetric, andwide bump appeared to interrupt the Drell-Yan continuum near 9.5 GeV


The ’s and the 5th quark

21 Apr 2023

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

m 13S1( ) =9460MeV Γ 13S1( ) =53keV

m 23S1( ) =10023MeV Γ 23S1( ) =43keV

m 33S1( ) =10352MeV Γ 33S1( ) =26keV

mB++m

B−=10558MeV

2mBd0 =10558MeV

2mBs0 =10740MeV

m 43S1( ) =10580MeV; Γ 43S1( ) =20MeV → Bd0 +Bd

0; → BB−


Top

21 Apr 2023

Searched at hadrons colliders for more than a decennimDifficult due to its very large mass mt=173 GeV=173 GeV

Need CoM energy > 400 GeVNeed CoM energy > 400 GeVIn a collision In a collision pppp at at √s√s = 2 TeV a top antitop pair is produced every = 2 TeV a top antitop pair is produced every 1010 collisionsLifetime <10–24 sThere are no hadrons containing top

p + p→ t+ t + X; t→ W +b; t → W−+b

W → eeo→ µµ

t → W +b→ W + jet(b); t → W−+b→ W−+ jet(b)W→ eeo→ µµ eW→ qq'→ jet+ jet

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


Discovery of top

21 Apr 2023

Discoveres in 1995 by CDF Tevatron pp collider at Fermilab, √s=2000 GeVImportant detector elements• Si microstrip high spatial resolution vertex detector•Tracking detectors•Hermetic calorimetry (in the transversal plane) missing momenum, neutrinos

mt=173±3 GeV


Top at LHC

21 Apr 2023

Top production cross section copared to QCD calculations

Invariant mass of the jets selected as compatible with all hadronic decay of top

subnuclear physics in the 1970s

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