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Experimental Heavy Quark Physics

Experimental Heavy Quark Physics. Fabrizio Bianchi University of Torino, Italy and INFN - Torino. Outline. Lecture 1: Big Questions in Particle Physics Goals of Heavy Quark Physics Tools for Heavy Quark Physics Lecture 2: CP Primer Observation of Direct CP Violation

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Experimental Heavy Quark Physics

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  1. Experimental Heavy Quark Physics Fabrizio Bianchi University of Torino, Italy and INFN - Torino

  2. Outline • Lecture 1: • Big 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| XXX Nathiagali Summer College

  3. Measuring a B→ p p B→ r p B→ r r (r,h) a * * Vub Vud Vtd Vtb * * Vcd Vcb Vcd Vcb g b (0,0) (0,1) XXX Nathiagali Summer College

  4. Tree decay B0B0mixing Penguin decay  The Route to sin(2a) Access to a from the interference of a b→u decay (g) with B0B0 mixing (b) Inc. penguin contribution How can we obtain α from αeff ? Time-dep. asymmetry : NB : T = "tree" amplitude P = "penguin" amplitude XXX Nathiagali Summer College

  5. Gronau and London, Phys. Rev. Lett. 65, 3381 (1990) Taming the Penguins: Isospin Analysis • The decays Bp+p-, p+p0, p0p0are related by SU(2) • Isospin relations between amplitudes A+-, A+0, A00 • Central observation is that pp states can have I = 2 or 0, but penguins only contribute to I = 0 (DI = ½ rule) • p+p0is pure I = 2, so only tree amplitude  |A+0| = |A-0| 2|-eff| XXX Nathiagali Summer College

  6. hep-ex/0501071 (submitted to PRL) CP Asymmetries in B0 →p+p- B0 B0 Kp crossfeed Ignoring penguins: XXX Nathiagali Summer College

  7. Now we needB+→p+p0 • Analysis method reconstructs and fitsB+→p+p0 andB+→K+p0 together B+→h+p0 B+→K+p0 B+→p+p0 Inserts show background components XXX Nathiagali Summer College

  8. Using isospin relations and • 3 B.F.s • B0->p+p- • B+->p+p0 • B0->p0p0 • 2 asymmetries • Cp+p- • Cp0p0 |a-aeff |< 35° Isospin analysis not currently viable in the B→ppsystem …andB0→p0p0 61±17 events in signal peak (227MBB) Signal significance = 5.0s B±→r±p0

  9. Comparison between BaBar and Belle Belle:hep-ex/0502035 Spp = - 0.67 ± 0.16(stat) ± 0.06(syst) Cpp = - 0.56 ± 0.12(stat) ± 0.06(syst). BaBar:hep-ex/0501071 Spp = - 0.30 ± 0.17(stat) ± 0.03(syst) Cpp = - 0.09 ± 0.15(stat) ± 0.04(syst). XXX Nathiagali Summer College

  10. a from B → rr P → VV decay, three possible ang mom states: • S wave (L=0, CP even) • P wave (L=1, CP odd) • D wave (L=2, CP even) Preliminary Angular analysis needed Blessing #1: r helicity angle ~100% longitudinally polarized! ~pure CP-even final state XXX Nathiagali Summer College

  11. afrom B0→ r+r- BaBar: hep-ex/0503049 Preliminary Preliminary XXX Nathiagali Summer College

  12. BaBar: Phys.Rev.Lett.94:131801,2005 Search for B0→ r0r0: Blessing #2 B (B→r+r-) = 30 x 10-6 c.f. B→p+p- B.F.= 4.7 x 10-6 and B→p0p0 B.F.= 1.2 x 10-6 Didn’t find it? Excellent! XXX Nathiagali Summer College

  13. Isospin analysis using B→rr • Taking the world average and thanks to we apply the isospin analysis to B→rr • The small rate of means • |a-aeff | is small[er] • P/T is small in the B→rrsystem (…Relative to B→ppsystem) |a-aeff |< 11° XXX Nathiagali Summer College

  14. α = (106 ± 8)o U (170 ± 9)o Combined Measurements of a a from B0→ (rp)0 Isospin analyses in pp and rr, time-dep Dalitz analysis in rp From combined pp, rp, rr results XXX Nathiagali Summer College

  15. Measuring g B±→ D(*)K(*) GLW, ADS and D0-Dalitz methods (r,h) a * * Vub Vud Vtd Vtb g * * Vcd Vcb Vcd Vcb b (0,0) (0,1) XXX Nathiagali Summer College

  16. Measuringgin B → DK In general: need ≥ 2 amplitudes with different weak and strong phases leading to the same final state Relative amplitude rB, weak phase g and strong phase dB Critical parameter: • Use additional dof in D decay to determine simultaneously rB, g, dB • Three methods on the market: • GLW, ADS, D0 Dalitz XXX Nathiagali Summer College

  17. The GLW Method: choose D → fCP 4 observables (ACP+-,RCP+-) to determine rB, g, dB • Theoretically clean • B → Dp background • Limited statistics No useful constraints yet. Need more data! XXX Nathiagali Summer College

  18. The ADS method: choose D → Kp suppressed favored Interference favored suppressed Strong phase dD unknown → scan all values Phys.Rev.Lett.91:171801,2003 XXX Nathiagali Summer College

  19. The ADS Method: results = no signal! hep-ex/0408028 It’s a hard road ahead… XXX Nathiagali Summer College

  20. g from B → D(*)0K, D0→ KSp+p- Interference r (770) Use the phase information across the Dalitz plane to determine rB, g, dB K*DCS XXX Nathiagali Summer College

  21. K*(892) r (770) K*DCS The D0→KS p+p-Dalitz model • Determine on clean, high statistics sample of 81500 D*+→D0p+ events • ASSUME no D-mixing or CP violation in D decays • Build model from 15 known resonances (+2 unidentified scalar pp resonances) c2/ d.o.f. = 3824/(3054-32) = 1.27 XXX Nathiagali Summer College

  22. B- B+ B- B+ B+ B- K* DCS D0 Dalitz method : B→D(*)0K (227 MBB) Maximum likelihood fit extracts rB(*),g, d(*) from a fit to mES, DE, Fisher and the D0→KS p+p- Dalitz model. 282 ± 20 89 ± 11 44 ± 8 XXX Nathiagali Summer College

  23. D0 Dalitz method : B→D(*)0K : result BaBar:hep-ex/0408088 γ = (70 ± 26 ± 10 ± 10)o Belle: hep-ex/0411049 γ = (68 ± 15 ± 13 ± 11)o DK : rB < 0.19 (90% C.L.) dB = 114°±41°±8°±10° (+np) +0.070 D*K : rB = 0.155 ± 0.040 ± 0.020 -0.077 dB = 303°±34°±14°±10° (+np) Belle:hep-ex/0504013 B+→D0K*+ γ = (112 ± 35 ± 9 ± 11 ± 8)o XXX Nathiagali Summer College

  24. Combined measurement of g Measurement of g : twofold ambiguity in g extraction γ = 64.0 ± 18.2 ([30.1,99.8] @ 95% CL)γ = -116.0 ± 18.2 ([-149.7,-80.4] @ 95% CL) Belle B+→D0K*+ γ = (112 ± 35 ± 9 ± 11) not used XXX Nathiagali Summer College 3rd error is due attributed to the Dalitz model

  25. Putting the Angles Together… XXX Nathiagali Summer College

  26. Measuring the sides of the UT • Sides of Unitarity Triangle related to CKM matrix elements. • |Vub| and |Vcb| constrain the distance of the apex of the triangle from the origin. • Vub| and |Vcb| measurement complementary to sin2b • |Vub| and |Vcb| measured in semileptonic B decays XXX Nathiagali Summer College

  27. Semileptonic B decays plep • Inclusive: B→ Xcℓv or Xuℓv • Tree-level rates are • QCD corrections must be calculated • Operator Product Expansion (OPE) • How do we separate Xu from Xc? • Gc = 50 × Gu Much harder problem for |Vub| • Exclusive: B→ D*ℓv, Dℓv, pℓv, rℓv, etc. • Need form factors to relate the rate to |Vcb|, |Vub| |Vcb| , |Vub| q Mx XXX Nathiagali Summer College

  28. Understanding inclusive SL decays • The Operator Product Expansion provides a systematic method of separating perturbative from non-perturbative scales • OPE + Heavy Quark symmetry  HQE • Heavy Quark Expansion now calculated to αs2, mB-3 Essentially all we need to know for bcℓν • Coefficients of operators calculated perturbatively (EW and QCD); non-perturbative physics enters through matrix elements of operators XXX Nathiagali Summer College

  29. Inclusive bcℓν • Measure electron momentum spectrum and mass of hadronic system in SL decay • Determine moments to allow comparison with parton-level calculations (duality assumed) • Calculations exist for the following: • Strategy: measure spectrum + as many moments as possible • Fit for HQE parameters and |Vcb| Lepton energy spectrum Mass of hadronic system XXX Nathiagali Summer College

  30. Observables • Define 8 moments from inclusive Eℓ and mX spectra • Integrations are done for Eℓ > Ecut, with Ecut varied in 0.6–1.5 GeV Partial branching fraction Lepton energymoments Hadron massmoments XXX Nathiagali Summer College

  31. BABAR PR D69:111104 Unlike-sign BABAR Like-sign Electron Energy Spectrum • BABAR data, 47.4 fb-1 at U(4S) + 9.1 fb-1 off-peak • Select events with an electronhaving p*>1.4 GeV; study spectrum of 2nd electron for p* > 0.5 GeV as f n of charge • Unlike-sign events dominated by B Xcev • Like-sign events from D Xev,B0 mixing • As done by ARGUS, CLEO… XXX Nathiagali Summer College

  32. BABAR PR D69:111104 BABAR Electron Energy Spectrum • Determine Ee spectrum • Subtract B Xueυ • Correct for efficiency • Correct for the detectormaterial (Bremsstrahlung) • Move from U(4S) to B rest frame • Correct for the final state radiation using PHOTOS • Calculate 0th-3rdEe moments for Ecut = 0.6 … 1.5 GeV All but ~few % can be measured Ee (GeV) XXX Nathiagali Summer College

  33. BABAR PR D69:111103 Hadron Mass Moments Fully reconstructedB hadrons • BABAR data, 81 fb-1 on U(4S) resonance • Select events with a fully-reconstructed B meson • Use ~1000 hadronic decay chains • Rest of the event contains one “recoil” B • Flavor and momentum known • Find a lepton with E > Ecut in the recoil-B • Lepton charge consistent with the B flavor • mmiss consistent with a neutrino • All left-over particles belong to Xc • Improve mX with a kinematic fit s = 350 MeV • 4-momentum conservation; equal mB on both sides; mmiss = 0 v lepton Xc XXX Nathiagali Summer College

  34. BABAR PR D69:111103 BABAR Hadron Mass Moments Validation: • Unmeasured particles  measured mX < true mX • Calibrate using simulation • Depends (weakly) on decaymultiplicity and mmiss • Validate in MC after applyingcorrection • Validate on data using partiallyreconstructed D*±  D0p±, tagged by the soft p± and lepton • Calculate 1st-4th mass moments with Ecut = 0.9 … 1.6 GeV XXX Nathiagali Summer College

  35. BABAR PRL 93:011803 Inputs to OPE Fit Error bars are stat. & syst.with comparable sizes mX moments BABAR Eℓmoments XXX Nathiagali Summer College

  36. BABAR PRL 93:011803 OPE Fit Parameters • Calculation by Gambino & Uraltsev (hep-ph/0401063,0403166) • Kinetic mass scheme to • Eℓ moments • mX moments • 8 parameters to determine • 8 moments available with several E0 • Sufficient degrees of freedom to determineall parameters without external inputs • Fit quality tells us how well OPE works kinetic chromomagnetic spin-orbit Darwin XXX Nathiagali Summer College

  37. BABAR PRL 93:011803 Fit Results ● = used, ○ = unusedin the nominal fit mX moments BABAR c2/ndf = 20/15 Eℓmoments Red line: OPE fitYellow band: theory errors XXX Nathiagali Summer College

  38. BABAR PRL 93:011803 Fit Results precision on |Vcb| = 2% • Impressive agreement between data and theory • ≈ identical results obtained in another renorm. scheme: Bauer, Ligeti, Luke, Manohar, Trott in hep-ph/0408002 Uncalculatedcorrections to G precision on mb = 1.5% • kinetic mass scheme with μ=1 GeV • Fitted values consistent with external knowledge c2/ndf = 20/15 XXX Nathiagali Summer College

  39. Inclusive |Vcb| in Perspective XXX Nathiagali Summer College

  40. Inclusive |Vub| • |Vub| can be measured from • The problem: b → cℓv decay • Use mu << mc difference in kinematics • Maximum lepton energy 2.64 vs. 2.31 GeV • First observations (CLEO, ARGUS, 1990)used this technique • Only 6% of signal accessible • How accurately do we know this fraction? How can we suppress50× larger background? XXX Nathiagali Summer College

  41. b → uℓv Kinematics • There are 3 independent variables in B→Xℓv • Take Eℓ, q2 (lepton-neutrino mass2), and mX (hadronic mass) 6% 20% 70% Where does it come from? XXX Nathiagali Summer College

  42. m= scale which separates effects from long- and short-distance dynamics AEW = EW corrections; Apert = pert. corrections (asj, askb0) Starting point: HQE • Just like bcℓν…, and with similar accuracy • …until limited expt’l acceptance is considered • Poor convergence of OPE in region where bcℓν decays are kinematically forbidden • Non-perturbative Shape Function must be used to calculate partial rates XXX Nathiagali Summer College

  43. Shape Function – what is it? • light-cone momentum distribution of b quark: F(k+) • Property of a B meson; universal...but new “sub-leading” SFs arise at each order in 1/mb • Consequences: changes effective mb, smears spectra Rough features (mean Λ, r.m.s. λ1) are known Detailed shape, and especially the low tail, are not constrained XXX Nathiagali Summer College

  44. Shape Function – What to Do? • Measure: Same SF affects (to the first order)b→ sg decays • Caveat: whole Eg spectrum is needed • Only Eg > 1.8 GeV has been measured • Background overwhelms lower energies • Compromise: assume functional forms of f(k+) • Example: • Fit b→ sg spectrum to determine the parameters • Try different functions to assess the systematics Predict Eℓspectrum inb → uℓv Measure Egspectrum inb → sg Extract f(k+) 1.8 2 parameters(L and a) to fit XXX Nathiagali Summer College

  45. CLEO hep-ex/0402009 Belle hep-ex/0407052 SF from b→ sg • CLEO and Belle has measured the b→ sg spectrum • BABAR result on the way Belle 3 models tried Fit XXX Nathiagali Summer College

  46. Theory input for |Vub| • At present, all |Vub| measurements based on inclusive SL decays use fully differential SL rate calculated to O(αS, mb-2) (DeFazio and Neubert, JHEP 06:017 (1999)) • Input required includes values for the mean and r.m.s. of the Shape Function. • In what follows we use as input the parameters determined by a fit (hep-ex/0407052) to the Belle bsγ spectrum:Λ = 0.66 GeV, λ1 = -0.40 GeV2 + associated covariance; δΛ ~ δmb ≈ 80 MeV XXX Nathiagali Summer College

  47. Measurements • BABAR has measured |Vub| using four different approaches • Statistical correlations are small • Different systematics, different theoretical errors Inclusive B→ Xev sample.High statistics, low purity. Recoil of fully-reconstructed B.High purity, moderate statistics. XXX Nathiagali Summer College

  48. BABARhep-ex/0408075 Lepton Endpoint Data (continuum sub) • BABAR data, 80 fb-1 on U(4S) resonance • Select electrons in 2.0 < Eℓ < 2.6 GeV • Push below the charm threshold Larger signal acceptance Smaller theoretical error • Accurate subtraction of backgroundis crucial! • Data taken below the U4S resonancefor light-flavor background • Fit the Eℓ spectrum with b→ uℓv,B → Dℓv, B → D*ℓv, B → D**ℓv,etc. to measure MC for BB background Data (eff. corrected) MC XXX Nathiagali Summer College

  49. BABARhep-ex/0408075 CLEOPRL 88:231803 Lepton Endpoint BELLE-CONF-0325 • Translate DB into |Vub| • Compare results with different Eℓ cut • Theoretical error reduced with lower Eℓ cut XXX Nathiagali Summer College

  50. BABARhep-ex/0408075 BABARhep-ex/0408045 Inclusive |Vub| Results BABARhep-ex/0408068 • Summary of BABAR |Vub| results • Statistical correlation between the mX andmX-q2 results is 72%. Others negligible • Theoretical error of the mX-q2 result is different from the rest Negligible SF dependence How much |Vub| moves if the SF is determined by the CLEO data XXX Nathiagali Summer College

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