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Physics of Hadron Colliders: Lecture 4 – Heavy Flavors

Physics of Hadron Colliders: Lecture 4 – Heavy Flavors. Joseph Kroll University of Pennsylvania 21 June 2004. Tevatron Makes Progress Every Week. Another Record Store: CDF: 9.0 £ 10 31 cm -2 s -1 D Ø: 7.5 £ 10 31 cm -2 s -1. The Competition for B Physics. KEK. Context.

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Physics of Hadron Colliders: Lecture 4 – Heavy Flavors

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  1. Physics of Hadron Colliders:Lecture 4 – Heavy Flavors Joseph Kroll University of Pennsylvania 21 June 2004

  2. Tevatron Makes Progress Every Week Another Record Store: CDF: 9.0 £ 1031 cm-2s-1 DØ: 7.5 £ 1031 cm-2s-1 Joseph Kroll University of Pennsylvania

  3. The Competition for B Physics KEK Joseph Kroll University of Pennsylvania

  4. Context You have all heard this before: “The SM is very successful, but…” • Three of the outstanding issues are • Electroweak symmetry breaking (why MW,MZ≠ 0) • does the Higgs exist? • is there supersymmetry? • if neither, what is the mechanism? • The flavor problem • are there 3 & only 3 families? • why masses of fundamental fermions so different? • what set values & hierarchy of flavor parameters (quarks & leptons very different) • Violation ofCP Symmetry • why does matter dominate antimatter in Universe? • is mechanism in SM correct, is it enough? Lecture 3 addressed issues related to EW symmetry breaking Today we will talk about addressing the flavor problem and CP violation Joseph Kroll University of Pennsylvania

  5. The Flavor Parameters (CKM Matrix) mass eigenstates ≠ weak eigen. related by Cabibbo-Kobayashi-Maskawa Matrix weak mass V is unitary: VyV = 1 Measurements + Unitarity assuming 3 generations Ranges are 90% CL PDG: K. Hagiwara et al., Phys. Rev. D66 010001 (2002) Joseph Kroll University of Pennsylvania

  6. Different Parameterizations of CKM Matrix 3 £ 3 complex unitary matrix: 3 real & 1 imag. parameters ≡ 3 angles, 1 phase L. L. Chau, W. Y. Keung Phys. Rev. Lett. 53, p. 1802 (1984) - used by PDG notation: cij´ cosij & sij´ sinij, i, j = 1st, 2nd, 3rd generation • Advantages of this parameterization: • Satisfies unitarity exactly • If ij= 0, generations i & j decouple • If 13= 23= 0, 3rd generation decouples, 12 is Cabibbo angle • Same formulation used for lepton mixing matrix U with (£ diag[ei1/2,ei2/2, 1]) Joseph Kroll University of Pennsylvania

  7. Wolfenstein Parametrization Illustrates Hierarchy Original reference: L. Wolfenstein, PRL, 51, p. 1945 (1983) Reference for this slide: A. Höcker et al., Eur. Phys. J. C21, p. 225 (2001); ibid, hep-ph/0406184 Define: valid to O(6) ¼ 0.01%,  = Vus = sinCabibbo» 0.2 from hep-ph/0406184 Joseph Kroll University of Pennsylvania

  8. New Measurement of Vus from KTeV The KTeV Collaboration, T. Alexopoulos et al., hep-ex/0406001 (sub. to PRL) – and references there in 1st row of CKM matrix provides the most stringent test of unitarity: PDG 2002 New results from KTeV These results from measured KL semileptonic decays: f+(0) is the l form factor at q2=0 } Vus = 0.2252 § 0.0008KTeV§ 0.0021external } Unitarity now satisfied: 0.0018 § 0.0019 Moral: well measured parameters can change Joseph Kroll University of Pennsylvania

  9. Im Vi3V*k3 Vi2V*k2 Re Vi1V*k1 The Unitarity Triangles i = 1 is previous page V is unitarity  geometric representation: triangle in complex plane There are 6 triangles flat Kaon UT n.b. these triangles are rescaled by one of the sides Beauty UT Joseph Kroll University of Pennsylvania

  10. of Chau & Keung parametrization is  The Beauty Unitary Triangle Joseph Kroll University of Pennsylvania

  11. How Do Measurements Constrain Triangle? Figure courtesy of CKM Fitter group: ckmfitter.in2p3.fr – as were all of the formulas on previous slides B0 flavor oscillations (md) constrains one side How do B0s oscillations (ms) fit in this picture? Why is ms considered one of the most important Run II measurements? Aside: a key issue is to pick experimental quantities that can be related to CKM para. without large theory errors Joseph Kroll University of Pennsylvania

  12. Neutral Meson Flavor Oscillations Joseph Kroll University of Pennsylvania

  13. Neutral B Meson Flavor Oscillations Flavor oscillations occur through 2nd order weak interactions e.g. Same diagrams and formula for ms for Bs except replace “d” with “s” From measurement of md derive |V*tbVtd|2 All factors known well except “bag factor” £ “decay constant” md = 0.489 § 0.008 ps-1 (2%) (PDG 2002) from Lattice QCD calculations – see hep-ph/0406184 Joseph Kroll University of Pennsylvania

  14. B Meson Flavor Oscillations (cont) If we measure ms then we would know the ratio ms/md Many theoretical quantities cancel in this ratio, we are left with from Lattice QCD calculations – see hep-ph/0406184 This is why ms is high priority in Run II Since Vts ¼ Vcb this gives us our side Rt Joseph Kroll University of Pennsylvania

  15. Current Status of ms ms > 14.5 ps-1 95% CL Results from LEP, SLD, CDF I Amplitude method: H-G. Moser, A. Roussarie, NIM A384 p. 491 (1997) see http://www.slac.stanford.edu/xorg/hfag/osc/winter_2004/index.html Joseph Kroll University of Pennsylvania

  16. CP Violation Through Mixing in B Decays Examples yields sin2 Weak phase in Vts very small  very small SM CP asymmetry Large asymmetry unambiguous evidence of new physics (B0 !  K0) must know ms to observe Joseph Kroll University of Pennsylvania

  17. Strong interaction produces bb pairs B Physics at Hadron Machines Example of lowest order (LO) s2 called “flavor creation” Example of next leading order (NLO) s3 b pairs produced close in y “flavor excitation” “gluon splitting” see P. Nason, S. Dawson, R. K. Ellis Nucl. Phys. B273, p. 49 (1988) NLO contribution comparable to LO contribution Joseph Kroll University of Pennsylvania

  18. B Physics at Hadron Machines (cont.) b quarks then fragment to B hadrons fragmentation is hard: B hadron gets large fraction of b quark E B factories running on Y(4S) only produce lightest B mesons Hadron colliders (and e+e- colliders running above Y(4S)) produce other B’s Many unique B measurements at hadron colliders e.g.,ms, Bs rare decays, observation Bc, b lifetime Joseph Kroll University of Pennsylvania

  19. B Production at Tevatron The inclusive b cross-section is enormous: on the order of 100b For L = 1031 cm-2s-1 (1032)  £L = 1kHz (10kHz) Much of this not useful (trigger, acceptance, analysis selection criteria) The useful cross-section is order 10b £L» 100 Hz The CDF Collaboration, D. Acosta et al., Phys. Rev. D65, 052005 (2002) This is still well above production cross-section at B Factories, Z pole B factory rate: L = 1034 cm-2s-1 £L = 10 Hz Joseph Kroll University of Pennsylvania

  20. B Production Tests QCD Measurement of B production an extremely interesting test of QCD There is an outstanding disagreement between theory and data The CDF Collaboration, D. Acosta et al., Phys. Rev. D65, 052005 (2002) Data factor 2 – 3 above theory Recent theoretical work has reduced discrepancy: b ! B frag. model Measurement of production fractions (fd, fu, fs, fbaryon, fB**) interesting too Also necessary for absolute branching fractions & other studies Joseph Kroll University of Pennsylvania

  21. Characteristics of B Production and Decay b large, but inelastic» 103 larger Trigger & analysis strategy: Exploit unique aspects b production & decay UA1 showed it was possible: b! X, b! X, b mixing Then CDF fully reconstructed B CDF “Run 0” 2.6§0.2 pb-1 B-! J/ K-, J/!+- F. Abe et al., PRL 68, 3403 (1992) Joseph Kroll University of Pennsylvania

  22. Muon systems Iron shielding Hadronic Calorimetry Electromagnetic Calorimetry Lumi monitor Silicon tracking Solenoid and TOF Drift chamber CDF II New Front-end elec. & DAQ: 7.6 MHz clock (132 ns) Joseph Kroll University of Pennsylvania

  23. Some Key Detector Features for B Physics Resolution pT/pT = (0.15%) pT (in GeV/c) Central Outer Tracker (COT) • Immersed in 1.4 T axial field; covers R = 0.4 m to 1.4 m; full coverage ||<1 • High redundancy drift chamber: 4 axial & 4 stereo (2o) layers – 12 wires each • Particle ID with dE/dx from time over threshold Particle separation power from dE/dx K/ separation > 1.4 for pT>2 GeV e/ separation = 3 for pT=1 GeV e K   Joseph Kroll University of Pennsylvania

  24. Some Key Detector Features for B Physics Silicon Tracking – 3 separate detectors Online impact parameter resol. 47m best wedges 55m average of all wedges includes » 30m from beam 1. Layer 00: (single sided) • attached to beampipe • 1.4 to 1.6cm from beam line •axial only 2. SVXII: (double sided) • 87 cm length, 12 wedges in azimuth • 5 layer with 3D track reconstruction • axial+small angle stereo or axial+90o • 3 barrels (6 half barrels in trigger) • 2.4 cm inner radius, 10.6 cm outer 3. ISL: (double sided) • 1 layer at 22 cm in ||<1 • 2 layers (20 & 28 cm) 1<||<2 • axial+small angle stereo SVT online @ L2 Joseph Kroll University of Pennsylvania

  25. Time of Flight Detector (TOF) Kaon ID for B physics • 216 Scintillator bars, 2.8 m long, 4 £ 4 cm2 • located @ R=140 cm • read out both ends with fine mesh PMT • (operates in 1.4 T B field – gain down ~ 400) • anticipated resolution TOF=100 ps • (limited by photostatistics) Measured quantities: s = distance travelled t = time of flight p = momentum Derived quantities: v = s/t m = p/v Joseph Kroll University of Pennsylvania

  26. Detector Hardware tracking for pT1.5 GeV 1.7 MHz bunch crossing rate Muon-track matching 46 L1 buffers L1 trigger Electron-track matching Missing ET, sum-ET 30 kHz L1 accept Silicon tracking for pT>2 GeV 4 L2 buffers L2 trigger Jet finding Refined electron/muon/photon finding 300 Hz L2 accept L3 trigger 300 CPU’s Full event reconstruction 70 Hz L3 accept tape >100Hz with data compression CDF II Trigger System (XFT) (SVT) courtesy E. Thomson (OSU/Penn) Joseph Kroll University of Pennsylvania

  27. K- K+ - D-s + B0s d0 Trigger Strategy for B Physics Exploit the characteristics of B production and decay 1. B mass relatively large  decay products have relatively high pT require pT > 1.5 – 2.0 GeV/c or larger 2. B decay produces high pT leptons (electron and muon) B! X, e X & B! J/ X, J/!+- 3. B’s have long decay distance trigger on displaced tracks 4. Combine lepton & displaced track Joseph Kroll University of Pennsylvania

  28. Example of Specific Trigger for B Physics Level 1 - 2 XFT tracks with pT > 1.5 GeV - opposite charge -  < 135o - |pT1| + |pT2| > 5.5 GeV Hadronic Path – designed for B0s! D-s+ At Level 3 using trigger criteria Level 2 - confirm L1 requirements - both XFT tracks - SVT 2<15 - 120 m< |d0| <1mm - 2o <  < 90o - Decay length Lxy > 200 m Level 3 - confirm L2 with COT & SVX “offline” quality track reco. Joseph Kroll University of Pennsylvania

  29. CDF = “Charm Detector @ Fermilab” Most of that charm is prompt charm, i.e., not from B ! DX We proved that using the D impact parameter - prompt charm points back to the PV (within resolution) - charm from B do not point to PV Prompt B ! D Measure d0 resolution in prompt peak apply to model of B! DX Prompt fraction: (86.6 § 0.4 (stat.))% Systematic error 3-4% CDF II, D. Acosta et al., PRL 91, 241804 (2003) & C. Chen (UPenn) Ph. D. Dissertation, fermilab-thesis-2003-14 Joseph Kroll University of Pennsylvania

  30. Measurement of Prompt Charm Production Data above theory – much less discrepancy than Run I B cross-section vs. theory 1st PRL from Tevatron in Run II CDF II, D. Acosta et al., PRL 91, 241804 (2003) & C. Chen (UPenn) Ph. D. Dissertation, fermilab-thesis-2003-14 Joseph Kroll University of Pennsylvania

  31. CDF II B Cross-section from B! J/ X Measure (B) down to pT(B) = 0 Use B! J/ X, J/!+- - Trigger on dimuon - Get clean J/ signal - Use t (Lxy) to separate B from prompt - B fraction varies from 10 – 40% Agreement with theory has improved - CDF II data consistent with Run I - theory changed - updated parton distribution functions - updated b quark fragmentation Joseph Kroll University of Pennsylvania

  32. Experimental Steps for Measuring Bs Mixing 1. Extract B0s signal – decay mode must identify b-flavor at decay (TTT) Examples: 2. Measure decay time (t) in B rest frame (L = distance travelled) (L00) 3. Determine b-flavor at production “flavor tagging” (TOF) “unmixed” means production and decay flavor are the same “mixed” means flavor at production opposite flavor at decay Flavor tag quantified by dilution D = 1 – 2w, w = mistag probability Joseph Kroll University of Pennsylvania

  33. Measuring Bs Mixing (cont.) 4. Measure asymmetry Asymmetry is conceptual: actually perform likelihood fit to expected “unmixed” and “mixed” distributions these formulas assume perfect resolution for t Joseph Kroll University of Pennsylvania

  34. Comment on : Time Integrated Mixing is the time integrated mixing probability In principle, a measurement of  determines  m - the first Bd mixing measurements were  measurements - d = 0.181 § 0.004 (PDG 2002) - this does not work for Bs: s = 0.5 (the limit as x!1) A measurement of is very interesting Joseph Kroll University of Pennsylvania

  35. Example of Bs Oscillations Example of Asymmetry with lots of statistics ms = 20 ps-1 Illustrated are - tagging reduces statistics dilution reduces amplitude - decay length resolution damps amplitude further - momentum uncertainty damps amplitude more as decay time t increases Large ms: Bs! Ds l  no good need fully reconstructed decays e.g., Bs! Ds Figures courtesy M. Jones (Penn/Purdue) Joseph Kroll University of Pennsylvania

  36. B+, Bd, Bs Signals I. K. Furic Ph. D. Dissertation MIT (2004) We see signals with good S/B: rate is about 1/10th expected Results of this analysis Joseph Kroll University of Pennsylvania

  37. Common B Meson Selection Criteria slide courtesy of I. K. Furic (MIT/EFI Chicago) Joseph Kroll University of Pennsylvania

  38. Background Dominated by Heavy Flavor Extensive simulation required to study complex background shape Peaked structure in B+ background is due to D* polarization Very little of the reflections/partially reconstructed decays leak into signal Joseph Kroll University of Pennsylvania

  39. What About Measuring B Lifetimes? Lifetime bias from trigger complicates lifetime measurement in B ! D Must solve this problem eventually for the Bs mixing analysis – in progress Have measured lifetimes in B! J/ K (dimuon trigger – no bias) Fit mass and lifetime distribution simultaneously B+ = 1.662 § 0.033 (stat) § 0.008 (syst) ps Example: B+! J/ K+ 240 pb-1 Joseph Kroll University of Pennsylvania

  40. 240 pb-1 Bs! J/ Decay interesting for CP Violation and search for new physics CP analysis requires knowing CP composition (% even) Preliminary tranversity analysis indicates predominantly CP even in agreement with Bd! J/ K* K. Anikeev, MIT, Ph. D. Thesis, in preparation Joseph Kroll University of Pennsylvania

  41. B Flavor Tagging We quantify performance with efficiency and dilution D = fraction of signal with flavor tag D = 1-2w, w = probability that tag is incorrect (mistag) Statistical error A on asymmetry A (N is number of signal) statistical error scales with D2 Joseph Kroll University of Pennsylvania

  42. Some More Detail Aside: Total  D2¼ 30% at the B factories Joseph Kroll University of Pennsylvania

  43. Produce bb pairs: find 2nd b, determine flavor, infer flavor of 1st b Two Types of Flavor Tags Opposite side + Applicable to both B0 and B0s −other b not always in the acceptance Same side Based on fragmentation tracks or B** + better acceptance for frag. tracks than opp. side b −Results for B+ and B0not applicable to B0s Reminder: for limit on ms must know D Joseph Kroll University of Pennsylvania

  44. jet from b (b) has negative (positive) charge on average Types of Opposite Side Flavor Tags Lepton tags low  high D mistags from Run II: for muons: D2 = (0.66 § 0.19)% expect comparable for elec. Jet charge tag Run II: D2 = (0.419 § 0.024)% high , low D Kaon tag Run II: no useful tag yet (have seen D,  too low) Largest D2 @ B factories TOF Joseph Kroll University of Pennsylvania

  45. Also opposite-side B hadron can mix: D = 1 – 2 = 0.76 Performance of OST’s is Poor – Why? Part of the problem is acceptance of opposite side b Generator Level study from K. Lannon, Ph. D. Dissertation, Illinois, 2003 Joseph Kroll University of Pennsylvania

  46. Same Side Flavor Tags Based on correlation between charge of fragmentation particle and flavor of b in B meson Decay of P-wave mesons B** also contributes to B0, B+ (not B0s) Expected correlations different for B+, B0, B0s TOF Joseph Kroll University of Pennsylvania

  47. Results on Same Side Flavor Tag Apply to B0! J/ K*0, D-+ Select track in R = 0.7 around B with minimum pT(rel) wrt B + track Run II: measure D and md simultaneously md = 0.55 § 0.10 Find  = 66.0 § 0.6 D = 12.4 § 3.3 D2 = 1.0 § 0.5 (all in %, stat error only) Joseph Kroll University of Pennsylvania

  48. Run I: Understood SST Well MC explained D+ vs. D0 F. Abe et al., PRD 58, 032001 (1999) Data vs. Tuned MC Excellent Agreement We have to use MC for D of SSKT for limit Joseph Kroll University of Pennsylvania

  49. Summary: Bs Flavor Oscillations We have a long way to go - rates are far below expectations - tagging is far below expectations - lifetime resolution not as good as expected – not as critical yet BUT we are making progress and there is plenty of reason to be optimistic The potential significance of a measurement can be estimated using the following formula Joseph Kroll University of Pennsylvania

  50. Acknowledgements Thanks to organizer Xin Wu (Geneva) & to co-lecturer Paris Sphicas (Athens) Special thanks to Marjorie Shapiro (Berkeley) for a copy of her 1999 CERN Academic Lectures & to Evelyn Thomson (OSU/Penn) for discussions on Tevatron top physics Many of my colleagues in CDF provided information including Konstantin Anikeev (MIT), David Ambrose (Penn), Chunhui Chen (Maryland), Frank Chlebana (FNAL), Nathan Eddy (FNAL), Stefano Giagu (INFN-Roma), Chris Hays (Duke), Beate Heinemann (Liverpool), Matt Herndon (JHU), Joey Huston (MSU), Jaco Konigsberg (Florida), Ashutosh Kotwal (Duke), Stephanie Menzemer (MIT), Rolf Oldeman (INFN-Roma), Manfred Paulini (CMU), Kevin Pitts (Illinois), Sal Rappoccio (Harvard), Marco Rescigno (INFN-Roma), Rob Roser (FNAL), Rick Snider (FNAL), Brian Winer (OSU), Peter Wittich (Penn), Kohei Yorita (Waseda) also Paul Derwent (FNAL), Jens Erler (UNAM), Paul Keener (Penn), Paul Langacker (Penn), Michelangelo Mangano (CERN), Jackie Mileski (Penn), Ron Moore (FNAL), Mary Scott Thomas (Penn) Finally, special thanks to my wife Monica Kroll for her support Joseph Kroll University of Pennsylvania

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