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
31-Jul-17
A. Bettini LSC, Padova University and INFN
1
Neutrino flavours
Neutrinos cannot be directly detected
The charged lepton produced by the
neutrino interaction in the detector
identifies the neutrino flavour
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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
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Electron and pion showers
Hadrons are produced much more frequently than leptons. Need discrimination power
electron
Main difference
in the “nose”
Detector should look at and
enhance the difference
pion
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Signature of nm
The world’s first muon neutrino observation in a 12-foot hydrogen bubble chamber at Argonne.
muon = long, non interacting track
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Tau
HL/t lifetime is short, 0.29 ps  O(100 µm) length 
Nagoya Emulsion Cloud Chamber
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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
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 n HL 
 HL 
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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 Cimento 39
(1965) 464. See also CERN-63-26. Nuclear Physics Division, June 27, 1963
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PAPLEP. The two-arm electron & muon spectrometer
Lepton-Antilepton Pairs = e+e–, µ+µ–, eµ
1963
camera
camera
Pb
camera
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camera
Pb
camera
camera
bea
m
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PAPLEP. The two-arm electron & muon spectrometer
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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 “timelike” nucleon form factor
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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
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The limit
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
HL is here
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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 Pbscintillator 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
e+ + e  e + m m+  2 undetected particles
for which we have no conventional explanation”
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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
e+ + e  e + m m + missing energy
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)
31
July 2017
31-Jul-17
A.A.Bettini.
Padova
INFN; LSCand INFN
Bettini
LSC,University
Padovaand
University
1515
DONUT @ Fermilab 2000
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Discovery of nt
2001. K. Niwa et al. DONUT-E872 at Fermilab
www-donut.fnal.gov/web pages/
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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

 

 K +   +nn /  K +   0 e+n 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–, ne), (m–, nm) and 3 quark (d,u) and s, each with 3 colours (1973)
 1
 2
 1
Q f  1 1+ 3    + 3   + 3     2
 3
 3
 3
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
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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
n  pene
DS=0
M 
 GF cosq C  eR  n eL  d R  u L
M  GF  eR n eL  d ' R   u L
W couples to
d’ = d cosqC + s sinqC
qC = 12.8˚
cosqC = 0.974
sinqC = 0.221
|DS|=1

  pene
M  GF sin q C  eR n eL  sR  u L
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Strangness changing neutral currents
Immediate consequence of the Cabibbo theory is the existence of the neutral current
d ' R   d ' L  cos2 qC dR  dL + sin 2 qC sR  sL + cosqC sinqC  dR  sL + sR  dL 
Consequently the two decays
should have similar rates. But

 1.2 10 –5
K +   0e+n e 
 K +   +nn
strangness changing neutral currents are strongly suppressed

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GIM mechanism
d’=
d cosqC + s sinqC is a member of the doublet
 u
 d '
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
 d '  cosqC
 s '    – sinq
C
sinqC   d 
cosq   s 
c 
 
s' 
C

d ' R   d ' L  cos qC dR  dL + sin qC sR  sL + cosqC sinqC  dR  sL + sR  dL 
2
2
s ' R   s ' L  sin 2 qC dR  dL + cos2 qC sR  sL  cosqC sinqC  dR  sL + sR  dL 
Summing
s ' R   s ' L + d ' R   d ' L  d R  d L + sR  sL
The strangeness changing neutral
currents are cancelled, at the 1st order.
GIM shown that to be
true at all orders
2nd is
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The Japanese perspective
1956 Sakata model. Fundamental particles are p, n and 
1957-8 Parity violation. V–A structure
1959 Gamba, Marshak and Okubo baryon-lepton fundamental symmetry (n, e, µ) - (p, n,  )
p  n B+
1960 Maki et al. Nagoya model. “Ur” matter B+ and
n  e B+
  m  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
n1  n e cos  + n m sin 
n 2  n e cos   n m sin 
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
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pp  K L0 K S0
at rest falsifies Sakata model
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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
1.several emulsion layers perpendicular to tracks
2. sandwitch of emulsions and Pb sheets (t=1 mm) 
identification of e, measure  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 TeVenergy 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
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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
m 2 e+ e  2m 2 + 2E E + 2 p p cos q + q
 
e
1
2
1
2
1
2

•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
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31-Jul-17
Discovery of the J
The resonance peak at m(e+e–)=3100 MeV is extremely narrow, narrower than the
experimental resolution  < 5 MeV
Cannot be understood if only u, d and s exist
The decay in e+e–, through a photon JPC = 1– –
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Discovery of yand y’
Richter and collaborators observed
the resonance at SPEAR
contemporarily and independently,
and called it y
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Y’
The systematic search for more narrow
resonances followed 10 days after the
second (and last) was found at M=3686
MeV, the y’
y 'y ++ +
y  e+ + e
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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
e+ + e–  D0 + D0 + X
e+ + e–  D+ + D_ + X
The mesons appear as resonances in the final state. Neutral D were observed decaying in the final
states
D0  K +  D0  K  +
Mass =1865 MeV, width < experimental resolution
The charged D-mesons were observed in the channels D+  K –  + +
No resonance in the channels D+  K + + 
D  K  + 
Mass =1869 MeV
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D  K +  
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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
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The two arms muon spectrometer
When the new proton accelerator became operational at Fermilab, in 1972, the ColumbiaFermilab-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
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The two arms muon spectrometer
Fermilab 1977
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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
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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– –
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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
 
m 2 S   10023 MeV
m 3 S   10352 MeV
m 13 S1  9460 MeV
3
1
3
1


m 4 3 S1  10580 MeV;
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 
 2 S   43 keV
 3 S   26 keV
 13 S1  53 keV
m B+ + m B  10558 MeV
1
2m B0  10558 MeV
1
2m B0  10740 MeV
3
3


 4 3 S1  20 MeV
d
s
 Bd0 + Bd0 ;
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 B+ B
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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
p + p  t + t + X; t  W + + b;
t W +b
W  en e o  µn µ
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
t  W + + b  W + + jet(b);
W  en e o  µn µ e
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t  W  + b  W  + jet(b )
W  qq '  jet + jet
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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
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Top at LHC
Top production cross section copared to
QCD calculations
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Invariant mass of the jets selected
as compatible with all hadronic
decay of top
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