Experimental Heavy Quark Physics Fabrizio Bianchi University of

Experimental Heavy Quark Physics Fabrizio Bianchi University of Torino, Italy and INFN - Torino F. Bianchi XXX Nathiagali Summer College

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 sin 2 b • Lecture 3: • Measurement of a and g • Measurement of |Vcb| and |Vub| F. Bianchi XXX Nathiagali Summer College 2

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 ? F. Bianchi XXX Nathiagali Summer College 3

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

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 undamental connection between particle physics and cosmology F. Bianchi XXX Nathiagali Summer College 5

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 Te. V, its effects should show up in flavor physics! • Flavor and CP-violating couplings can only be studied using precision measurements at highest luminosity F. Bianchi XXX Nathiagali Summer College 6

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. F. Bianchi XXX Nathiagali Summer College 7

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 F. Bianchi XXX Nathiagali Summer College 8

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 Wolfenstein Parameterization Cabibbo angle 2 ® 1 ~l 3 ® 2 ~l 2 3 ® 1 ~l 3 F. Bianchi XXX Nathiagali Summer College h changes sign under CP 9

Unitarity Triangle Product of 1 st and 3 rd columns (1 of 6 relations) Can be represented as a triangle in the complex plane a = f 2 g = f 3 b = f 1 Dividing all sides by F. Bianchi XXX Nathiagali Summer College 10

Normalized Unitarity Triangle h Apex at r, h a g F. Bianchi b XXX Nathiagali Summer College r 11

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 F. Bianchi XXX Nathiagali Summer College 12

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

Averaging Results of Different Experiments Heavy Flavor Averaging Group http: //www. slac. stanford. edu/xorg/hfag/ Averages results from different experiments. UTfit: http: //utfit. roma 1. infn. it/ Uses Bayesan approach described in: hep-ph/0012308 to makes global fits to UT CKM Fitter: http: //www. slac. stanford. edu/xorg/ckmfitter/ckm_welcome. html Uses Frequentistic approach to makes global fits to UT F. Bianchi XXX Nathiagali Summer College 14

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 0 reconstruction • capability to reconstruct neutral hadrons F. Bianchi XXX Nathiagali Summer College 15

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 Tevatron @ FNAL: CDF, D 0, BTEV LHC @ CERN: CMS, ATLAS, LHCB F. Bianchi XXX Nathiagali Summer College 16

Hadronic vs e+e- colliders II e+ e- collider at the Y(4 S) (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 F. Bianchi XXX Nathiagali Summer College 17

Hadronic vs e+e- colliders III B Physics at an e+ e- collider at the Y(4 S): • only B 0 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(4 S) rest frame. Travel ~26 mm before decaying in that frame. Solution: use beams of different energies to boost the Y(4 S) rest frame w. r. t. the lab frame increasing the spatial separation of the decays making it measurable. PEP-II @ SLAC: Ba. Bar F. Bianchi KEK-B @ KEK: Belle XXX Nathiagali Summer College 18

Hadronic vs e+e- colliders IV Others e+ e- colliders (mostly charm/t physics): CESR-c @ Cornell (3 < BEPC @ IHEP (3 < < 5 Ge. V): CLEO-c < 4 Ge. V ): BES Plan to start in 2007 with L ~ 1034 cm 2 s-1 From now on, I’ll discuss mainly b-factories F. Bianchi XXX Nathiagali Summer College 19

KEK-B vs PEP-II Both started in summer 1999. KEK-B: 8. 0 Ge. V electrons and 3. 5 Ge. V positrons bg = 0. 42 PEP-II: 9. 0 Ge. V electrons and 3. 1 Ge. V positrons bg = 0. 56 mean separation between decay vertices: 260 mm CM boost: • folds particles forward • Increases momentum range to cover with Particle ID F. Bianchi XXX Nathiagali Summer College 20

PEP-II F. Bianchi XXX Nathiagali Summer College 21

Interaction Region F. Bianchi XXX Nathiagali Summer College 22

PEP-II Luminosity F. Bianchi XXX Nathiagali Summer College 23

Trickle injection at the B Factories Best shift, no trickle Nov 2003 Best shift, LER only trickle Mar 2004 Best shift, double trickle PEP-II Lumi HER current LER current PEP-II: ~5 Hz continuous KEKB: at ~5 -10 min intervals F. Bianchi XXX Nathiagali Summer College 24

BABAR Detector F. Bianchi XXX Nathiagali Summer College 25

BABAR Detector F. Bianchi XXX Nathiagali Summer College 26

Silicon Vertex Tracker I Performance Requirements: • Single vertex resolution along z-axis better than 80 μm • Stand-alone tracking for 50 < pt < 120 Me. V/c with high efficiency PEP II Constraints: • Dipole magnets (B 1) at +/-20 cm from interaction point • Polar angle: 17. 2 o < q < 150 o • Bunch Crossing Period 4. 2 ns • Radiation exposure at innermost layer: average 33 Krad/year in beam plane: 240 Krad/year F. Bianchi XXX Nathiagali Summer College 27

Silicon Vertex Tracker II 5 layers of double-sided AC-coupled Silicon 340 Si wafers, 150 K channels Custom rad-hard readout IC (the ATo. M 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 F. Bianchi XXX Nathiagali Summer College 28

Silicon Vertex Tracker III F. Bianchi XXX Nathiagali Summer College 29

Silicon Vertex Tracker: Performances z side Phi side SVT Hit Resolution vs Incident Track Angle • Average hit efficiency ~97% • Slow pion efficiency >70 % for p. T > 50 Me. V • Average hit resolution 10 -40 μm, depending on angle of track • No change observed so far due to radiation F. Bianchi XXX Nathiagali Summer College 30

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) F. Bianchi XXX Nathiagali Summer College 31

Drift Chamber: Performances F. Bianchi XXX Nathiagali Summer College 32

Tracking s. Pt/Pt ~ 1% @ 3 Ge. V Doca resolution vs pt F. Bianchi XXX Nathiagali Summer College 33

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 b 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, 000 2. 5 cm-diameter phototubes. F. Bianchi XXX Nathiagali Summer College 34

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) F. Bianchi XXX Nathiagali Summer College 35

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

DIRC: Control samples for and K p K Projection for 2. 5 < p < 3 Ge. V/c F. Bianchi XXX Nathiagali Summer College 37

DIRC Impact on D 0 purity: Background rejection factor ~ 5 F. Bianchi XXX Nathiagali Summer College 38

Electromagnetic Calorimeter n n 6580 Cs. I(Tl) crystals with photodiode readout About 18 X 0 0 s = 5. 0% F. Bianchi XXX Nathiagali Summer College 39

Instrumented Flux Return ØUp to 21 layers of resistive-plate chambers (RPCs) between iron plates of flux return Muon identification > 800 Me. V/c o Neutral Hadrons (KL) detection; also with EMC/ECL o ØBakelite RPCs Problems with QC, dark current, and stability o Forward end cap replaced in 2003; barrel replaced with LST in 20042006 o F. Bianchi XXX Nathiagali Summer College 40

Instrumented Flux Return F. Bianchi XXX Nathiagali Summer College 41

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

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