1. Experimental Heavy Quark Physics
XXX Nathiagali Summer College
27 June - 2 July 2005
Experimental Heavy Quark Physics
Fabrizio Bianchi
University of Torino, Italy and INFN - Torino
Fabrizio Bianchi

2. XXX Nathiagali Summer College
27 June - 2 July 2005
Outline
Lecture 1:
Fundamental Questions in Particle Physics
Goals of Heavy Quark Physics
Tools for Heavy Quark Physics
Lecture 2:
CP Primer
Observation of Direct CP Violation
Measurement of sin2b
Lecture 3:
Measurement of a and g
Measurement of |Vcb| and |Vub|
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XXX Nathiagali Summer College
Fabrizio Bianchi

3. Fundamental Questions in Particle Physics: Generation and Masses
In the SM, Gauge Forces do not distinguish fermions of
different generations:
• e,µ have same electrical charge
• quarks have same color charge
Why generations ? Why 3 ? Why fermion masses are so different ?
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XXX Nathiagali Summer College

4. Fundamental Questions in Particle Physics: What happened to antimatter ?
All Matter
no Antimatter
Matter Antimatter Symmetric
Big Bang
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XXX Nathiagali Summer College

5. Fundamental Questions in Particle Physics: Baryogenesis
Sakharov criteria:
• Baryon-number violation
• CP violation
• Non-equilibrium
SM satisfies prerequisites for baryogenesis
• Baryon-number violation at high temperatures (DB=DL)
• Non-equilibrium during phase transitions (symmetry breaking)
CP violation in the quark and lepton sectors
Fundamental connection between particle physics and cosmology!
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XXX Nathiagali Summer College

6. Luminosity and Energy Frontiers
Study of Flavor Physics is complementary to the discovery of
new particles at high energy
Any extension of the SM that can solve the hierarchy problem
contains many new flavor parameters
If New Physics exists at or below a TeV, its effects should show up
in flavor physics!
Flavor and CP-violating couplings can only be studied using
precision measurements at highest luminosity
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XXX Nathiagali Summer College

7. XXX Nathiagali Summer College
Example: the top quark
Couplings ( |Vts| ~ 0.04 and |Vtd| ~ 0.003) measured in B physics.
Mass prediction based on precision electro weak measurements.
Direct production has proved existence and measured mass and spin.
Study of Flavor Physics is an essential part of the roadmap for the exploration of new energy scales, now and even in the LHC era.
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XXX Nathiagali Summer College

8. XXX Nathiagali Summer College
CKM Matrix I
SM accounts for flavor changing quark transition through the
coupling of the V-A charged current operator to a W boson:
where:
Vij are the elements of the CKM matrix
i, j run on the three quark generations
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XXX Nathiagali Summer College

9. Wolfenstein Parameterization
CKM Matrix II
CKM matrix can be regarded as a rotation from the quark mass eigenstates (d, s, b) to a set of new states (d’, s’, b’) with diagonal coupling to u, c, t
Complex matrix described by 4 independent real parameters (including one phase)
l~ 0.22
sinθC
Cabibbo angle
Wolfenstein Parameterization
2 ® 1 ~l
3 ® 2 ~l2
3 ® 1 ~l3
h changes
sign under CP
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XXX Nathiagali Summer College

10. Product of 1st and 3rd columns
Unitarity Triangle
Product of 1st and 3rd columns
(1 of 6 relations)
Can be represented as a triangle in the complex plane
a = f2
g = f3
b = f1
Dividing all sides by
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11. Normalized Unitarity Triangleh
Apex at
r, h a g b r
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12. Goals of Heavy Quark Physics
Precise determinations of the elements of the
Cabibbo-Kobayashi-Maskawa (CKM) matrix
Measure sides and angles of the Unitarity Triangle
Over constraint r and h
Tests of the CKM mechanism of flavor and CP violation
Search for deviations from the SM
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XXX Nathiagali Summer College

13. What you want to achieve…
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XXX Nathiagali Summer College

14. Averaging Results of Different Experiments
Heavy Flavor Averaging Group
Averages results from different experiments.
UTfit:
Uses Bayesan approach described in: hep-ph/
to makes global fits to UT
CKM Fitter:
Uses Frequentistic approach to makes global fits to UT
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XXX Nathiagali Summer College

15. To do Heavy Quark Physics…
XXX Nathiagali Summer College
27 June - 2 July 2005
To do Heavy Quark Physics…
You need:
To produce a lot of b & c hadrons
Hadrons vs. e+e- machines
To build a detector with:
high tracking efficiency
good tracking and vertexing to have good mass resolution
good particle identification capability to distinguish among
different modes and reject background
good g and p0 reconstruction
capability to reconstruct neutral hadrons
F. Bianchi
XXX Nathiagali Summer College
Fabrizio Bianchi

16. Hadronic vs e+e- colliders I
Hadronic machines:
• enormous production of c and b-hadrons (sbb ~ 50 mb)
• all b-hadrons can be produced
• trigger is challenging
• complicated many-particles events
• incoherent production of B mesons
FNAL: CDF, D0, BTEV
CERN: CMS, ATLAS, LHCB
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XXX Nathiagali Summer College

17. Hadronic vs e+e- colliders II
e+ e- collider at the Y(4S) (b-factory):
• Trigger is moderately easy.
• Simpler events, easier to reconstruct.
Copious production of b, c and t.
sbb = 1.05 nb
scc = 1.30 nb
stt = 0.94 nb
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XXX Nathiagali Summer College

18. Hadronic vs e+e- colliders III
B Physics at an e+ e- collider at the Y(4S):
• only B0 and B+ can be produced.
all the final state particles come from B decays.
• coherent production of B mesons in a L=1 state.
• B are produced almost at rest in the Y(4S) rest frame.
Travel ~26 mm before decaying in that frame.
Solution: use beams of different energies to boost the Y(4S)
rest frame w.r.t. the lab frame increasing the spatial separation
of the decays making it measurable.
SLAC: BaBar KEK: Belle
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XXX Nathiagali Summer College

19. Hadronic vs e+e- colliders IV
XXX Nathiagali Summer College
27 June - 2 July 2005
Hadronic vs e+e- colliders IV
Others e+ e- colliders (mostly charm/t physics):
Cornell (3 < < 5 GeV): CLEO-c
IHEP (3 < < 4 GeV ): BES
Plan to start in 2007 with L ~ 1034 cm2 s-1
From now on, I’ll discuss mainly b-factories
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XXX Nathiagali Summer College
Fabrizio Bianchi

20. XXX Nathiagali Summer College
KEK-B vs PEP-II
Both started in summer 1999.
KEK-B:
8.0 GeV electrons and 3.5 GeV positrons
bg = 0.42
PEP-II:
9.0 GeV electrons and 3.1 GeV positrons
bg = 0.56
mean separation between decay vertices: 260 mm
CM boost:
• folds particles forward
• Increases momentum range to cover with Particle ID
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XXX Nathiagali Summer College

21. XXX Nathiagali Summer College
PEP-II
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22. XXX Nathiagali Summer College
Interaction Region
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23. XXX Nathiagali Summer College
PEP-II Luminosity
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24. Trickle injection at the B Factories
XXX Nathiagali Summer College
27 June - 2 July 2005
Trickle injection at the B Factories
Best shift, no trickle
Best shift, LER only trickle
Nov 2003
Best shift, double trickle
Mar 2004
PEP-II: ~5 Hz continuous
KEKB: at ~5-10 min intervals
PEP-II Lumi
HER current
LER current
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XXX Nathiagali Summer College
Fabrizio Bianchi

25. XXX Nathiagali Summer College
BABAR Detector
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26. XXX Nathiagali Summer College
BABAR Detector
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XXX Nathiagali Summer College

27. Silicon Vertex Tracker I
Performance Requirements:
• Single vertex resolution along z-axis better than 80 μm
• Stand-alone tracking for 50 < pt < 120 MeV/c with high
efficiency
PEP II Constraints:
• Dipole magnets (B1) at +/-20 cm from interaction point
• Polar angle: 17.2o < q < 150o
• Bunch Crossing Period 4.2 ns
• Radiation exposure at innermost layer:
average 33 Krad/year
in beam plane: 240 Krad/year
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XXX Nathiagali Summer College

28. Silicon Vertex Tracker II
5 layers of double-sided AC-coupled Silicon
340 Si wafers, 150K channels
Custom rad-hard readout IC (the AToM chip)
Stand-alone tracking for slow particles:
• inner 3 layers for angle and impact parameter measurement
• outer 2 layers for pattern recognition and low pt tracking
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XXX Nathiagali Summer College

29. Silicon Vertex Tracker III
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XXX Nathiagali Summer College

30. Silicon Vertex Tracker: Performances
z side
Phi side
SVT Hit Resolution vs Incident Track Angle
Average hit efficiency ~97%
Slow pion efficiency >70 % for pT > 50MeV
Average hit resolution μm, depending on angle of track
No change observed so far due to radiation
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XXX Nathiagali Summer College

31. XXX Nathiagali Summer College
Drift Chamber I
40 layers of wires (7104 cells)
Helium:Isobutane 80:20 gas, Al field wires, Beryllium inner wall,
and all readout electronics mounted on rear endplate
Particle identification from ionization loss (7% resolution)
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XXX Nathiagali Summer College

32. Drift Chamber: Performances
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XXX Nathiagali Summer College

33. XXX Nathiagali Summer College
Tracking
sPt/Pt ~ 3 GeV
Doca resolution vs pt
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XXX Nathiagali Summer College

34. Detection of Internally Reflected Cherenkov light I
Ring imaging Cherenkov detector based on total internal
reflection.
Uses long, rectangular bars made from synthetic fused silica
("quartz") as both radiator and light guide.
A charged particle traversing a DIRC quartz bar with velocity
produces Cherenkov light if nb > 1.
Through internal reflections, the Cherenkov light from the passage of a particle is carried to the ends of the bar and to an
array of 11, cm-diameter phototubes.
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XXX Nathiagali Summer College

35. Detection of Internally Reflected Cherenkov light II
The high optical quality of the quartz preserves the angle of the
emitted Cherenkov light. The measurement of this angle, in
conjunction with knowing the track angle and momentum from
the drift chamber, allows a determination of the particle mass.
qc = arcos (1/nb)
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XXX Nathiagali Summer College

36. Detection of Internally Reflected Cherenkov light III
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XXX Nathiagali Summer College

37. DIRC: Control samples for p and K
Projection for
2.5 < p < 3 GeV/c
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38. XXX Nathiagali Summer College
DIRC Impact
Impact on D0 purity:
Background rejection factor ~ 5
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XXX Nathiagali Summer College

39. Electromagnetic Calorimeter
6580 CsI(Tl) crystals with photodiode readout
About 18 X0 0
s = 5.0%
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XXX Nathiagali Summer College

40. Instrumented Flux Return
Up to 21 layers of resistive-plate
chambers (RPCs) between iron
plates of flux return
Muon identification > 800 MeV/c
Neutral Hadrons (KL) detection;
also with EMC/ECL
Bakelite RPCs
Problems with QC, dark current,
and stability
Forward end cap replaced in 2003;
barrel replaced with LST in 2004-
2006
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XXX Nathiagali Summer College

41. Instrumented Flux Return
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XXX Nathiagali Summer College

42. Electron and Muon ID Muon ID Efficiency & Electron ID Efficiency
p Mis-ID Probability
Electron ID Efficiency
&
p Mis-ID Probability
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XXX Nathiagali Summer College

43. XXX Nathiagali Summer College
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XXX Nathiagali Summer College