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Recent Results from B A B AR

Recent Results from B A B AR. P.-Fabrizio Salvatore Royal Holloway College, University of London For the B A B AR Collaboration. Measurement of sin2 b Measurement of sin2 a eff Future: g and sin (2 b + g ). Hadron Structure 2002, Herl’any 22-27 September 2002. Outline.

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Recent Results from B A B AR

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  1. Recent Results from BABAR P.-Fabrizio Salvatore Royal Holloway College, University of London For the BABARCollaboration Measurement of sin2b Measurement of sin2aeff Future:g and sin (2b + g ) Hadron Structure 2002, Herl’any 22-27 September 2002

  2. Outline • The search for CP violation with asymmetric e+e- collider • PEPII and the BaBar Experiment • sin2bmeasurement: • The golden modes: b -> ccs • The Cabibbo-suppressed modes: b -> ccd • The pure penguin modes: b -> sss • sin2aeffmeasurement: • CP asymmetries in p+p- and K+p- • p+p0 and p0p0decay rates • CP asymmetries in r+p- and r+K- • Future:g and sin(2b +g ) • Asymmetry inB ->D0(CP)Kdecay • B0 ->D* (n)p decays • Conclusions - - Fabrizio Salvatore, Royal Holloway College

  3. Physics principles: CP violation in the SM Unitarity Triangle comes from the unitarity of the matrix f2 f3 f1 a, b and g constrained by CP asymmetries in B decays CP from complexcomponent ofVubandVtd The only source of CP violation in the SM is the KM phase that appears in the CKM matrix Fabrizio Salvatore, Royal Holloway College

  4. Time-dependent CP violation fromB0-B0mixing fCP u,c,t d b u,c,t b d top quark box introduces: VtbVtd* W W Dmd = mH - mL Direct CP violation if multiple amplitudes with different phases Purely CP violation in interference of decays with and without mixing Fabrizio Salvatore, Royal Holloway College

  5. PEPII performances Peak luminosity: 4.60 x 1033cm-2s-1 (exceeded design goal 3.0 x 1033) PEP-II delivered 99 fb-1 BaBar recorded 94 fb-1 For sin2b and sin2a used: On peak 81 fb-1 88M BB pairs Off peak 10 fb-1 Fabrizio Salvatore, Royal Holloway College

  6. BABAR Detector SVT: 5 double side layers. 97% efficiency, 15 mm z hit resolution (inner layers, perp. tracks) Momentum resolution (SVT+DCH): (pT)/pT= 0.13 %  pT+0.45 % DIRC: 144 quartz bars. Provide K- separation 4.2  @ 3.0 GeV/c  2.5  @ 4.0 GeV/c EMC: 6580 CsI(Tl) crystals. Energy resolution: E/E = 2.3 %E-1/4 1.9 % Fabrizio Salvatore, Royal Holloway College

  7. B0-B0events at the (4S) resonance m- K- Flavour tag and vertex reconstruction (4S) Btag m- Brec m+ B0 KS B0 p+ Coherent BB pair p- Exclusive B meson and vertex reconstruction Compute f+ (Dt) Z Boost: bg= 0.55 Start the Clock Fabrizio Salvatore, Royal Holloway College

  8. Vertexing and tagging algorithms z BREC direction BREC Vertex BREC daughters Interaction Point Beam spot TAG Vertex BTAG direction TAG tracks, V0s • 5 mutually exclusive categories: • Lepton - isolated high-momentum leptons; • kaon I – high quality K, correlated K and slow p; • kaon II – low quality K or slow p; • Inclusive – unidentified leptons, low quality K, high-momentum tracks; • Untagged Q = 28.1 + 0.7 % (~7% improvement) PRL87 (Aug01) • Brec vertex from charged Brec daughters • BTag vertex from: • All charged tracks not in Brec,constrain with Brec vertex, beam spot, and (4S) momentum • High efficiency: 95% • Average Dz resolution ~ 180 mm (measured from data) • New tagging algorithm based on neural networks: • inputs: leptons, K, slow p (D*decay) and high-momentum tracks Fabrizio Salvatore, Royal Holloway College

  9. sin2b from charmonium states (b  ccs) B0 K0 B0 -> J/Y Ks B0 -> Y(2S) Ks B0 -> cc1 Ks B0 -> hc Ks hf= 1 B0 -> J/Y KL hf= -1 hf= 1- 2RTB0 -> J/Y K*0(K*0 -> Ksp0) RT = 16.0 + 3.5 %(PRL87) Tree level dominates and CP only from B 0-B 0mixing lf = hfe-i2b, hf=±1 Fabrizio Salvatore, Royal Holloway College

  10. Event yields and purity • Energy-substituted mass: • Energy difference: Recent addition: B0 hc Ks where hc K+K-p0 or K+Ks p- Fabrizio Salvatore, Royal Holloway College

  11. sin2b result hf =-1 hf =+1 sin2b = 0.741  0.067 (stat)  0.033 (sys) • Unbinned maximum likelihood fit: • 34 parameters: sin2b, mistag fract. (8), Dt resolution funct. (8), bkgnd (17) • tB = 1.542 ps, Dmd = 0.489 ps-1 fixed (PDG 2002) sin2b = 0.755  0.074 sin2b = 0.723  0.158 Fabrizio Salvatore, Royal Holloway College (hep-ex/0207042)

  12. Asymmetry in b  ccs modes with lepton tag Golden mode (cc) Ks with lepton tag only Ntagged = 220 Purity = 98% Mistag fraction 3.3% sDt 20% better than other tag categories sin2b = 0.79  0.11 Fabrizio Salvatore, Royal Holloway College

  13. sin2b fit results by decay mode Consistency of CP Channels: P(c2) = 57% Fabrizio Salvatore, Royal Holloway College

  14. Constraints in the (r,h) plane r = r (1-l2/2) h = h (1-l2/2) Method as in Höcker et al, Eur.Phys.J.C21:225-259,2001 One solution for b is in excellent agreement with measurements of unitarity triangle apex Fabrizio Salvatore, Royal Holloway College

  15. Search for new physics in (cc)KS events In the measurement of sin2b we have assumed |lf | = 1 (SM expectation) Sf - hf sin2bCf0 If another amplitude that contributes with a different phase: | lf| = 0.948  0.051 (stat)  0.017 (syst) Sf = 0.759  0.074 (stat)  0.032 (syst) Fit |lf| and Sf using the clean (cc)Ksmodes (hf =-1, Ntagged = 1506, Purity = 92%): Consistent with the Standard Model expectation of |lf|=1 and nominal fit sin2b = 0.755  0.074 for (cc)Ks modes alone. Fabrizio Salvatore, Royal Holloway College

  16. The Cabibbo-suppressed modes (b ccd ) (I) D* - Vcd D* + B0 D* - B0 D* + • B0D*+D*-: same weak phase as b  ccs (tree level); • small penguin contribution (<0.1 Tree); • not CP eigenstate (needs angular analysis) |l+|= 0.98  0.25 (stat)  0.09 (syst) Im(l+)= 0.31  0.43 (stat)  0.10 (syst) RT = 0.07+0.06+0.03 + Ntagged= 102 Purity = 82% Parameterize l in terms of CP-odd (l) and CP-even (l+) components and use: |l |= 1, Im(l) = -0.741 (hep-ex/0207072) Im(l+)measurement ~2.7s from BaBar sin2bin charmonium, assuming no penguins. If penguins are negligible, then Im(l+) = - sin2b Fabrizio Salvatore, Royal Holloway College

  17. The Cabibbo-suppressed modes (b ccd) (II) Comparable tree and penguin contribution ~ O(l3) Vcd Penguin:~VcbVcd* + VubVud* Tree: ~VcbVcd* • B0J/yp0 : also color-suppressed Ntagged = 49 Purity = 59% hf = + 1 (hep-ex/0207058) Fabrizio Salvatore, Royal Holloway College

  18. sin2b from penguin mode B0fKS Same Weak phase as b  ccs, but sensitive to new physics in loops Ntagged = 66 Purity = 50% hf = - 1 |lfK| = 1 fixed SfK = -0.19 (stat)  0.09 (syst) +0.52 - 0.50 Dominated by b sss gluonic penguins • Small branching fraction O(10-5) • Significant background from qq continuum • Using only fK+K- (hep-ex/0207070) Cross check on B+fK +: SfK = 0.26  0.27 Analysis of B0h’KS in progress If no new physics, SfK = sin2b Fabrizio Salvatore, Royal Holloway College

  19. Summary of sin2b results Results have been improving by more than just luminosity gain July 00 Feb 01 July 01 Mar 02 July 02 Million BB pairs • New measurement of sin2b from charmonium modes (88 x106BB) Submitted to PRL July 17, 2002 (hep-ex/0207042) sin2b = 0.741 ± 0.067 (stat) ± 0.033 (syst) • Interesting new measurements are being obtained on the open charm modes: B0D*+D*-(hep-ex/0207072) and b penguin modes: B0J/ p0(hep-ex/0207058) B0f K0S(hep-ex/0207070) No hints of physics beyond the Standard Model yet, but lots of opportunities to challenge the theory with the increasing event statistics in BaBar Fabrizio Salvatore, Royal Holloway College

  20. sin2a from charmless B decays measure sin2aeff Penguin contribution is non-negligible mixing + decay Penguin (P) Tree (T) need BF from B-> p+p-,p+p0 and p0p0 and isospin analysis to obtain a from aeff B0p+p- Fabrizio Salvatore, Royal Holloway College

  21. sin2a : B → pp, Kp, KK modes lots of data needed • Small branching ratios (10-5-10-6) Data sample: 88M BB events use kinematic and topology of events to separate signal from light-quark bg • Large background from continuum (qq) events Fisher discriminant: p* q* p- • Ambiguity between p and K needs excellent particle ID (DIRC) p+ Fabrizio Salvatore, Royal Holloway College

  22. K/p separation using the DIRC phypothesis Khypothesis • For e=85%: • P(K->p) = 1.7% • P(p->K) = 2.7 % • Identification of h+h’- tracks as p or K using the angle qc measured in the DIRC • Double-gaussian PDFs built from the difference (qc – qcexp)/s(qc) • K/p separation and PDF parameters measured using fully reconstructed data Fabrizio Salvatore, Royal Holloway College

  23. Event yields and Kp asymmetry no tagging or vertexing needed Direct CP Preliminary • Time-independent maximum likelihood fit to extract event yields and Kp asymmetry Submitted to Phys Rev (hep-ex/0207055) Fabrizio Salvatore, Royal Holloway College

  24. mES and DE distributions same as for sin2b measurement Preliminary Signal events are selected in the (mES,DE) plane Bo -> pp Bo -> pp Kp Fabrizio Salvatore, Royal Holloway College

  25. Spp and Cpp measurement Projection in sample of pp-selected events qq+ Kp 1 ps Preliminary Spp = 0.02 + 0.34 + 0.05 Cpp = -0.30 + 0.25 + 0.04 Submitted to Phys Rev (hep-ex/0207055) • Time-dependent unbinned maximum likelihood fit • Same tagging and vertexing procedure as for sin2b Fabrizio Salvatore, Royal Holloway College

  26. Extraction of a from aeff • B ->p+p-,p+p0 and p0p0 decays related by isospin • (gluonic) penguins contribute only to I=0 • p+p0 has I=2 only tree amplitude only • (|A+0|= |A-0|) Need to measure: B+ ->p+p0, B0 ->p0p0, B0 ->p0p0 2aeff = 2a + kpp Isospin analysis Gronau and London, Phys.Rev.Lett 65, 3381 (1991) Grossman-Quinn bound • Otherwise, put limit on BR(B0 ->p0p0): Fabrizio Salvatore, Royal Holloway College

  27. B+->p+p0and B+->K+p0branching ratio B+->p+p0 has pure tree amplitude and no CP expected Fit region r+p- Simultaneous fit to pp0/Kp0 e+e- → qq Preliminary • Usual charmless two-body analysis • B0-> r+p- bg reduced by a tight cut on DE hep-ex/0207065 Fabrizio Salvatore, Royal Holloway College

  28. B0->p0p0branching ratio • Small signal expected • Flavour tagging and event topology used to reduce qq bg • B+->r+p0 bg reduced using a cut on m(p+p0) and DE @ 90% CL |a – aeff| < 510 Central value for BR: Preliminary B0->p0p0 yield determined by unbinned ML fit: hep-ex/0207063 If BR as high as its central value, Grossman-Quinn bound not adequateisospin analysis is necessary Fabrizio Salvatore, Royal Holloway College

  29. B0->rh:direct and indirect CP measurement NOT CP eigenstate  BR = (28.9+5.4+4.3)x10-6 CP CP  insensitive to CP rK self tagging Direct CP ACP and C = 0 Indirect CP S = 0 Fabrizio Salvatore, Royal Holloway College

  30. Event yields and charge asymmetry B0/B0->r-p+ B0/B0->r+p- hep-ex/0207068 Preliminary tB = (1.540 + 0.014) ps Dmd = (0.503 + 0.006) ps-1 World Average Clear B0->rpsignal • Maximum likelihood fit to extract yields and charge asymmetry: • Validation test: fit tB and Dmd using data Fabrizio Salvatore, Royal Holloway College

  31. Time-dependent asymmetry expected ~0.4 (from naïve factorization) sensitive to strong phase differences hep-ex/0207068 Preliminary dominated by uncertainties on B background components Fabrizio Salvatore, Royal Holloway College

  32. Direct CP violation Direct CP can be expressed using the asymmetries: r meson from spectator quark p meson from spectator quark A+- = - 0.82+0.31(stat)+0.16(syst) A-+ = - 0.11+0.16(stat)+0.09(syst) Using previous results and their correlations: Fabrizio Salvatore, Royal Holloway College

  33. Summary of sin2a and direct CP violation results • Charmless two-body decays: • branching ratios and CP asymmetries in B0->p+p-, K+p- and K+K-(hep-ex/0207055) no evidence for large direct or indirect CP violation in p+p- • branching fractions needed to extract a from aeff computed: upper limit on BR(B0->p0p0) (hep-ex/0207063) B+->p+p0and K+p0branching ratios(hep-ex/0207065) still too early for significant constraint: • Charmless three-body decays: • first CP asymmetry measurement for B0->rpand B0->rK(hep-ex/0207068) |a – aeff| < 510 A+- = - 0.82+0.31(stat)+0.16(syst) A-+ = - 0.11+0.16(stat)+0.09(syst) Fabrizio Salvatore, Royal Holloway College

  34. Future: g and sin(2b+g) (I) Colour allowed Vus u K+ W+ s b B+ Vcb * c u D0 Colour suppressed u u D0 c b B+ Vub * W+ Vcs s u K+ u Preliminary g with B ->D0(CP)K hep-ex/0207087 data sample 75 fb-1 Fabrizio Salvatore, Royal Holloway College

  35. Future: g and sin(2b+g) (II) Cabibbo suppressed Cabibbo allowed Vcd Vud c u h+ W+ W+ D*+ d d b b B0 B0 Vcb Vub * * c u d d h- D*- d d P*(p,r,a1) P*p P*B P*D0 Preliminary B ->D*p/r/a1 Time evolution of B0->D*-h+ and B0->D*+h-related to sin(2b +g ) • For precise measurement, need many events • D*a1 mode has the largest BR (~1.3%) • use partial reconstruction: • Only the slow p from D*->D0p decay and the p/r/a1 (a1->r0p) are reconstructed • If only the D0 is missing, in the (4S) frame the B direction lies on the surface of a cone • Averaging over this surface,the missing mass mmisscan be defined Signal: mmiss peaks to D0 mass Bg events: broader distribution Fabrizio Salvatore, Royal Holloway College

  36. First steps: B0lifetime using D*p and D*r decays B ->D* r Nsig = 5521+251 B ->D* p Signal Peak. BB Comb. BB Continuum Dt(ps) tB = 1.616+0.064(stat)+0.075(syst) ps Nsig = 6971+241 tB = 1.510+0.040(stat)+0.038(syst) ps World Average hep-ex/0203036 tB = (1.540 + 0.014) ps hep-ex/0203038 Validation for the partial reconstruction technique tB extracted using an unbinned maximum likelihood fit data sample 20.7 fb-1 Fabrizio Salvatore, Royal Holloway College

  37. D*a1 branching fraction measurement • Continuum background rejected using a neural networktechnique • exploit the different topologies between qq events (jet structure) and B events (spherical) • mmiss distribution obtained from off-reso data subtracted from that obtained on on-reso • result fitted with a combination of: • BB Monte Carlo events • signal Monte Carlo events • data on-reso (off-reso subtr.) • signal+BB bg MC • BB bg MC only Signal yield: 18400+1200 Preliminary hep-ex/0207085 BF = (1.20+0.07+0.14)% PDG: (1.30+0.27)% B ->D*a1 data sample 20.7 fb-1 Fabrizio Salvatore, Royal Holloway College

  38. Summary: B ->D0(CP)K and B0 ->D*(n)p • B -> D0(CP)K mode: • ratio of branching fraction for B->D0K and B->D0p modes • first measurement of CP asymmetry in B->D0 (CP)K(hep-ex/0207087) • B -> D*(n)p mode : • B0 lifetime using D*p and D*r decays (hep-ex/0203038, hep-ex/0203036) • branching fraction ofB0 -> D*a1decay channel(hep-ex/0207085) R= (8.31+0.35+0.20)% +0.09 -0.07 ACP= (0.17+0.23 ) tB = (1.533+0.034+0.038) ps Combined measurement: BF = (1.20+0.07+0.14)% Analyses just begun, still lot of work to do ! Fabrizio Salvatore, Royal Holloway College

  39. Conclusions (I) • New measurement of sin2b from charmonium modes Submitted to PRL July 17, 2002 (hep-ex/0207042) sin2b = 0.741 ± 0.067 (stat) ± 0.033 (syst) • No evidence for large direct or indirect CP violation in B0->p+p- • Measurement of the branching ratios for B+-> p+p0,K+p0(hep-ex/0207065) • Upper limit on BR(B0-> p0p0) and constraint on |a -aeff| (hep-ex/0207055) (hep-ex/0207063) • CP asymmetry in B0/B0->r+p+decay (hep-ex/0207068) • First steps to analyze decay modes related to g and sin(2b +g ) • first measurement of CP asymmetry in B->D0K(hep-ex/0207087) • B0 lifetime with D*p and D*r decays (hep-ex/0203038, hep-ex/0203036) • branching fraction of B0->D*a1 decay (hep-ex/0207085) Extremely productive time for B physics with BaBar ! BUT More still to come ! BaBar and Belle’s sin2b results have convinced the physics community that CKM is the dominant source of CP violation Fabrizio Salvatore, Royal Holloway College

  40. Conclusions (II) A lot more to do with the 100 fb-1 of data already recorded and those still to come in the next run starting this fall • better knowledge of |Vub| and |Vcb| • rare decays (possibility to probe new physics) • Charm physics (D0 mixing, CP, ….) • tau results • higher precision in the sin2bmeasurement • measurement of a and g • other very interesting • physics results: More exciting physics results are on their way ! Fabrizio Salvatore, Royal Holloway College

  41. Tagging performance Fabrizio Salvatore, Royal Holloway College

  42. Sources of Systematic Error s(sin2b) Description of background events 0.017 CP content of background components Background shape uncertainties Composition and content of J/y KL background 0.015 Dt resolution and detector effects 0.017 Silicon detector alignment uncertainty Dt resolution model Mistag differences between BCP and Bflav samples 0.012 Fit bias correction 0.010 Fixed lifetime and oscillation frequency 0.005 TOTAL 0.033 Steadily reducing systematic error: July 2002 = 0.033 July 2001 = 0.05 Fabrizio Salvatore, Royal Holloway College

  43. sin2b in subsamples Fabrizio Salvatore, Royal Holloway College

  44. Cross-check on data control samples Observed no asymmetry as expected Fabrizio Salvatore, Royal Holloway College

  45. CP composition of B0D*+D*- • We measure CP odd fraction (corrected for acceptance) to be small: R = 0.07  0.06 (stat) 0.03 (syst) Fabrizio Salvatore, Royal Holloway College

  46. The Cabibbo-suppressed modes (b ccd) D+ D*+ D _ B0 D*_ CP conjugation strong phase Not a CP eigenstate D _ D*_ D*+ D+ B0 • possible strong phase contributions; • different decay time distributions for : B0D-D*+ B0D*- D+ D*D 56 fb-1 Ntagged= 85 Purity = 52% • B0D*+D- : S+- = - 0.43  1.41  0.20 C+- = 0.53  0.74  0.13 S-+ = 0.38  0.88  0.05 C-+ = 0.30  0.50  0.08 Update to full data set in progress Fabrizio Salvatore, Royal Holloway College

  47. Validation of tagging, vertexing and fit procedure tB = (1.56 + 0.07) ps Dmd = (0.52 + 0.05) ps-1 World Average tB = (1.540 + 0.014) ps Dmd = (0.503 + 0.006) ps-1 Projection in sample of K-selected events • Use B0 ->Kp events: T=tag charge, Q=K charge • same sample as for CP asymmetries • tB and Dmd floating in the fit Fabrizio Salvatore, Royal Holloway College

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