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

Fabrizio Salvatore, Royal Holloway College Outline The search for CP violation with asymmetric e+e- collider PEPII and the BaBar Experiment sin2b measurement: The golden modes: b -> ccs The Cabibbo-suppressed modes: b -> ccd The pure penguin modes: b -> sss sin2aeff measurement: CP asymmetries in p+p- and K+p- p+p0 and p0p0 decay rates CP asymmetries in r+p- and r+K- Future: g and sin(2b +g ) Asymmetry in B ->D0(CP)K decay B0 ->D* (n)p decays Conclusions - - September 26, 2002 Fabrizio Salvatore, Royal Holloway College

Physics principles: CP violation in the SM The only source of CP violation in the SM is the KM phase that appears in the CKM matrix Unitarity Triangle comes from the unitarity of the matrix f1 f2 f3 a, b and g constrained by CP asymmetries in B decays CP from complex component of Vub and Vtd September 26, 2002 Fabrizio Salvatore, Royal Holloway College

Time-dependent CP violation from B0-B0 mixing fCP b d u,c,t top quark box introduces: Vtb Vtd* Dmd = mH - mL W Direct CP violation if multiple amplitudes with different phases Purely CP violation in interference of decays with and without mixing September 26, 2002 Fabrizio Salvatore, Royal Holloway College

Fabrizio Salvatore, Royal Holloway College 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 Run 1 20.7 on peak 2a 9.0 2b 26.7 2c 25.0 81.4 800 bunches E+ 1775 mA E- 1060 mA IP 147 micron x 5 micron September 26, 2002 Fabrizio Salvatore, Royal Holloway College

Fabrizio Salvatore, Royal Holloway College BABAR Detector Svt 5 layer double sided strips DCH 40 stereo layers DIRC: 144 quart bars, 11000 PMTS EMC 6580 crystals IFR: 19 layers 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 % September 26, 2002 Fabrizio Salvatore, Royal Holloway College

B0-B0 events at the (4S) resonance Z m- K- Flavour tag and vertex reconstruction Boost: bg = 0.55 (4S) Btag Brec m- Exclusive B meson and vertex reconstruction p+ p- KS m+ Coherent BB pair B0 Start the Clock Compute f+ (Dt) September 26, 2002 Fabrizio Salvatore, Royal Holloway College

Vertexing and tagging algorithms Beam spot Interaction Point BREC Vertex BREC daughters BREC direction BTAG direction TAG Vertex TAG tracks, V0s z 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 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 Use per-event estimate sigma_delta_Z Empirical model to correct it Q = 28.1 + 0.7 % (~7% improvement) PRL87 (Aug01) September 26, 2002 Fabrizio Salvatore, Royal Holloway College

sin2b from charmonium states (b  ccs) Tree level dominates and CP only from B 0-B 0 mixing B0 K0 lf = hf e-i2b, hf=±1 B0 -> J/Y Ks B0 -> Y(2S) Ks B0 -> cc1 Ks B0 -> hc Ks hf = -1 hf = 1 B0 -> J/Y KL hf = 1- 2RT B0 -> J/Y K*0 (K*0 -> Ks p0) RT = 16.0 + 3.5 % (PRL87) September 26, 2002 Fabrizio Salvatore, Royal Holloway College

Event yields and purity Event Sample Ntag Purity J/y Ks(p+p-) 974 97% J/y Ks(p0p0) 170 89% y(2S) Ks 150 c1 Ks 80 95% hc Ks 132 73% Total (hf = -1) 1506 92% J/y KL 988 55% J/y K*0 (Ks p0) 147 81% All CP modes 2641 78% Eta_c KS has more peaking background than other modes 15% Psi KS 13% Peaking background Recent addition: B0 hc Ks where hc  K+K-p0 or K+Ks p- Energy-substituted mass: Energy difference: September 26, 2002 Fabrizio Salvatore, Royal Holloway College

Fabrizio Salvatore, Royal Holloway College sin2b result 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) hf =-1 hf =+1 sin2b = 0.755  0.074 sin2b = 0.723  0.158 sin2b = 0.741  0.067 (stat)  0.033 (sys) September 26, 2002 Fabrizio Salvatore, Royal Holloway College (hep-ex/0207042)

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 September 26, 2002 Fabrizio Salvatore, Royal Holloway College

sin2b fit results by decay mode Consistency of CP Channels: P(c2) = 57% September 26, 2002 Fabrizio Salvatore, Royal Holloway College

Constraints in the (r,h) plane 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 2 sigma errors r = r (1-l2/2) h = h (1-l2/2) September 26, 2002 Fabrizio Salvatore, Royal Holloway College

Search for new physics in (cc)KS events In the measurement of sin2b we have assumed |lf | = 1 (SM expectation) Sf  - hf sin2b Cf  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)Ks modes (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. September 26, 2002 Fabrizio Salvatore, Royal Holloway College

The Cabibbo-suppressed modes (b  ccd ) (I) B0  D*+D*-: same weak phase as b  ccs (tree level); small penguin contribution (<0.1 Tree); not CP eigenstate (needs angular analysis) B0 D* - D* + Vcd 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 |l+| = 0.98  0.25 (stat)  0.09 (syst) Im(l+) = 0.31  0.43 (stat)  0.10 (syst) (hep-ex/0207072) Im(l+) measurement ~2.7s from BaBar sin2b in charmonium, assuming no penguins. If penguins are negligible, then Im(l+) = - sin2b September 26, 2002 Fabrizio Salvatore, Royal Holloway College

The Cabibbo-suppressed modes (b  ccd) (II) B0  J/y p0 : also color-suppressed Vcd Tree: ~VcbVcd* Penguin:~VcbVcd* + VubVud* Comparable tree and penguin contribution ~ O(l3) Ntagged = 49 Purity = 59% hf = + 1 (hep-ex/0207058) September 26, 2002 Fabrizio Salvatore, Royal Holloway College

sin2b from penguin mode B0  f KS Dominated by b  sss gluonic penguins Same Weak phase as b  ccs, but sensitive to new physics in loops Small branching fraction O(10-5) Significant background from qq continuum Using only f  K+K- Ntagged = 66 Purity = 50% hf = - 1 (hep-ex/0207070) |lfK| = 1 fixed SfK = -0.19 (stat)  0.09 (syst) +0.52 - 0.50 Cross check on B+  f K +: SfK = 0.26  0.27 Analysis of B0  h’ KS in progress If no new physics, SfK = sin2b September 26, 2002 Fabrizio Salvatore, Royal Holloway College

Summary of sin2b results New measurement of sin2b from charmonium modes (88 x106 BB) Submitted to PRL July 17, 2002 (hep-ex/0207042) Results have been improving by more than just luminosity gain sin2b = 0.741 ± 0.067 (stat) ± 0.033 (syst) July 00 Feb 01 July 01 Mar 02 July 02 Interesting new measurements are being obtained on the open charm modes: B 0D*+D*- (hep-ex/0207072) and b penguin modes: B 0J/ p 0 (hep-ex/0207058) B 0f K0S (hep-ex/0207070) Million BB pairs No hints of physics beyond the Standard Model yet, but lots of opportunities to challenge the theory with the increasing event statistics in BaBar September 26, 2002 Fabrizio Salvatore, Royal Holloway College

sin2a from charmless B decays Penguin contribution is non-negligible measure sin2aeff mixing decay + Tree (T) Penguin (P) B0  p+p- need BF from B -> p+p-, p+p0 and p0p0 and isospin analysis to obtain a from aeff September 26, 2002 Fabrizio Salvatore, Royal Holloway College

needs excellent particle ID (DIRC) sin2a : B → pp, Kp, KK modes Small branching ratios (10-5-10-6) lots of data needed Data sample: 88M BB events Large background from continuum (qq) events use kinematic and topology of events to separate signal from light-quark bg Fisher discriminant: q* p+ p- p* Ambiguity between p and K needs excellent particle ID (DIRC) September 26, 2002 Fabrizio Salvatore, Royal Holloway College

K/p separation using the DIRC 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) p hypothesis K hypothesis K/p separation and PDF parameters measured using fully reconstructed data For e=85%: P(K->p) = 1.7% P(p->K) = 2.7 % September 26, 2002 Fabrizio Salvatore, Royal Holloway College

Event yields and Kp asymmetry Preliminary no tagging or vertexing needed Time-independent maximum likelihood fit to extract event yields and Kp asymmetry Direct CP Submitted to Phys Rev (hep-ex/0207055) Mode Yield BR (10-6) ACP(Kp) B0 → p+p- 157 + 19 4.7 + 0.6 + 0.2 B0 → K+p- 589 + 30 17.9 + 0.9 + 0.7 -0.102 + 0.050 + 0.016 B0 → K+K- 1 + 8 < 0.6 (90% C.L.) September 26, 2002 Fabrizio Salvatore, Royal Holloway College

mES and DE distributions Preliminary Signal events are selected in the (mES,DE) plane same as for sin2b measurement Bo -> pp Bo -> pp Kp September 26, 2002 Fabrizio Salvatore, Royal Holloway College

Spp and Cpp measurement Time-dependent unbinned maximum likelihood fit Same tagging and vertexing procedure as for sin2b 1 ps Projection in sample of pp-selected events qq+ Kp Spp = 0.02 + 0.34 + 0.05 Cpp = -0.30 + 0.25 + 0.04 Preliminary Submitted to Phys Rev (hep-ex/0207055) September 26, 2002 Fabrizio Salvatore, Royal Holloway College

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|) 2aeff = 2a + kpp Need to measure: B+ ->p+p0, B0 ->p0p0, B0 ->p0p0 Isospin analysis Gronau and London, Phys.Rev.Lett 65, 3381 (1991) Otherwise, put limit on BR(B0 ->p0p0): Grossman-Quinn bound September 26, 2002 Fabrizio Salvatore, Royal Holloway College

B+->p+p0 and B+->K+p0 branching ratio Preliminary B+->p+p0 has pure tree amplitude and no CP expected Fit region e+e- → qq r+p- Usual charmless two-body analysis B0-> r+p- bg reduced by a tight cut on DE Simultaneous fit to pp0/Kp0 Mode Yield BR (10-6) ACP B+ →p+p0 B+ →K+p0 hep-ex/0207065 September 26, 2002 Fabrizio Salvatore, Royal Holloway College

B0->p0p0 branching ratio Preliminary 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 B0->p0p0 yield determined by unbinned ML fit: @ 90% CL |a – aeff| < 510 hep-ex/0207063 Central value for BR: If BR as high as its central value, Grossman-Quinn bound not adequate isospin analysis is necessary September 26, 2002 Fabrizio Salvatore, Royal Holloway College

B0->rh: direct and indirect CP measurement  CP NOT CP eigenstate BR = (28.9+5.4+4.3)x10-6 insensitive to CP rK self tagging Direct CP ACP and C = 0 Indirect CP S = 0 September 26, 2002 Fabrizio Salvatore, Royal Holloway College

Event yields and charge asymmetry B0/B0->r-p+ B0/B0->r+p- Clear B0->rp signal Maximum likelihood fit to extract yields and charge asymmetry: Preliminary hep-ex/0207068 Validation test: fit tB and Dmd using data tB = (1.540 + 0.014) ps Dmd = (0.503 + 0.006) ps-1 World Average September 26, 2002 Fabrizio Salvatore, Royal Holloway College

Time-dependent asymmetry hep-ex/0207068 Preliminary expected ~0.4 (from naïve factorization) sensitive to strong phase differences dominated by uncertainties on B background components September 26, 2002 Fabrizio Salvatore, Royal Holloway College

Using previous results and their correlations: Direct CP violation Direct CP can be expressed using the asymmetries: r meson from spectator quark p meson from spectator quark Using previous results and their correlations: A+- = - 0.82+0.31(stat)+0.16(syst) A-+ = - 0.11+0.16(stat)+0.09(syst) September 26, 2002 Fabrizio Salvatore, Royal Holloway College

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+p0 and K+p0 branching ratios (hep-ex/0207065) still too early for significant constraint: Charmless three-body decays: first CP asymmetry measurement for B0->rp and 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) September 26, 2002 Fabrizio Salvatore, Royal Holloway College

Future: g and sin(2b+g) (I) Preliminary g with B ->D0(CP)K W+ B+ b u s c K+ D0 Vus Vcb * Colour allowed Vcs Vub Colour suppressed hep-ex/0207087 data sample 75 fb-1 September 26, 2002 Fabrizio Salvatore, Royal Holloway College

Future: g and sin(2b+g) (II) Preliminary B ->D*p/r/a1 h+ W+ B0 b d u c D*- Vud Vcb * Cabibbo allowed W+ B0 b d c u h- Vcd Vub * Cabibbo suppressed D*+ 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 mmiss can be defined P*(p,r,a1) P*p P*D0 P*B Signal: mmiss peaks to D0 mass Bg events: broader distribution September 26, 2002 Fabrizio Salvatore, Royal Holloway College

First steps: B0 lifetime using D*p and D*r decays Validation for the partial reconstruction technique tB extracted using an unbinned maximum likelihood fit B ->D* r Nsig = 5521+251 B ->D* p Dt(ps) Continuum Comb. BB Peak. BB Signal Nsig = 6971+241 data sample 20.7 fb-1 tB = 1.616+0.064(stat)+0.075(syst) ps hep-ex/0203036 tB = (1.540 + 0.014) ps World Average tB = 1.510+0.040(stat)+0.038(syst) ps hep-ex/0203038 September 26, 2002 Fabrizio Salvatore, Royal Holloway College

D*a1 branching fraction measurement B ->D*a1 data sample 20.7 fb-1 Continuum background rejected using a neural network technique 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 PDG: (1.30+0.27)% BF = (1.20+0.07+0.14)% Signal yield: 18400+1200 Preliminary hep-ex/0207085 September 26, 2002 Fabrizio Salvatore, Royal Holloway College

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 of B0 -> D*a1 decay channel (hep-ex/0207085) R= (8.31+0.35+0.20)% ACP= (0.17+0.23 ) +0.09 -0.07 BF = (1.20+0.07+0.14)% tB = (1.533+0.034+0.038) ps Combined measurement: Analyses just begun, still lot of work to do ! September 26, 2002 Fabrizio Salvatore, Royal Holloway College

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) BaBar and Belle’s sin2b results have convinced the physics community that CKM is the dominant source of CP violation 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) 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/0207063) CP asymmetry in B0/B0->r+p+ decay (hep-ex/0207068) (hep-ex/0207055) Extremely productive time for B physics with BaBar ! More still to come ! BUT September 26, 2002 Fabrizio Salvatore, Royal Holloway College

More exciting physics results are on their way ! 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 higher precision in the sin2b measurement measurement of a and g better knowledge of |Vub| and |Vcb| rare decays (possibility to probe new physics) Charm physics (D0 mixing, CP, ….) tau results other very interesting physics results: More exciting physics results are on their way ! September 26, 2002 Fabrizio Salvatore, Royal Holloway College

Fabrizio Salvatore, Royal Holloway College Tagging performance Category Efficiency (e) Mistag Fr. (w) d Mistag Q=e(1-2w)2 Lepton 9.1  0.2 3.3  0.6 -1.4  1.1 7.9  0.3 KPiorK 16.7  0.2 9.9  0.7 -1.1  1.1 10.7  0.4 KorPi 19.8  0.3 20.9  0.8 -4.2  1.1 6.7  0.4 Inclusive 20.0  0.3 31.6  0.9 -2.0  1.2 2.7  0.3 Total 65.6  0.5 28.1  0.7 September 26, 2002 Fabrizio Salvatore, Royal Holloway College

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 CP content of argus background taken to be -1 to 1! Resolution model (3 gaussians or 2?gaussians plus exponential) Error reduction Switched PDG2002 from 2000 Split peaking background per mode Increased MC stastics by factor of 7 Steadily reducing systematic error: July 2002 = 0.033 July 2001 = 0.05 September 26, 2002 Fabrizio Salvatore, Royal Holloway College

Fabrizio Salvatore, Royal Holloway College sin2b in subsamples September 26, 2002 Fabrizio Salvatore, Royal Holloway College

Cross-check on data control samples Observed no asymmetry as expected September 26, 2002 Fabrizio Salvatore, Royal Holloway College

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) September 26, 2002 Fabrizio Salvatore, Royal Holloway College

The Cabibbo-suppressed modes (b  ccd) B0  D*+D- : D* _ D+ B0 D*+ D _ CP conjugation strong phase Not a CP eigenstate possible strong phase contributions; different decay time distributions for : B0  D- D*+ B0  D*- D+ D*D 56 fb-1 Ntagged= 85 Purity = 52% 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 September 26, 2002 Fabrizio Salvatore, Royal Holloway College

Validation of tagging, vertexing and fit procedure 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 tB = (1.56 + 0.07) ps Dmd = (0.52 + 0.05) ps-1 tB = (1.540 + 0.014) ps Dmd = (0.503 + 0.006) ps-1 World Average September 26, 2002 Fabrizio Salvatore, Royal Holloway College