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Charmless Hadronic B Decays at BaBar

Charmless Hadronic B Decays at BaBar. XXXVI Rencontres de Moriond March 17 th -24 th , 2001 Gianluca Cavoto Università di Roma La Sapienza & INFN on behalf of BaBar Collaboration. Charmless Decays. Preliminary Branching Fraction measurements

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Charmless Hadronic B Decays at BaBar

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  1. Charmless Hadronic B Decays at BaBar XXXVI Rencontres de Moriond March 17th-24th, 2001 Gianluca Cavoto Università di Roma La Sapienza & INFN on behalf of BaBar Collaboration Gianluca Cavoto - Roma

  2. Charmless Decays PreliminaryBranchingFraction measurements ( and upper limit ) with BaBar at PEP-II • p+p-, K+p-, K+K- (h+h-) • p0 p+, p0 K+ (p0h+) • K0 p+, K0 K+ (K0h+) • K0p0 • fK*+ • fK+,fp+ • fK0 • Data from 1999-2000 run • 20.7 fb-1 on-resonance • N((4S)) = 22.74 ±0.36 million • 2.6fb-1 off-resonance Gianluca Cavoto - Roma

  3. Physics Target d u • B mesons : dominant decay : b  c (Vcb) • Charmless decays: • Direct CP search • Time-dependent CP asymmetry • p+p-  sin(2a),fK0 sin(2b) • Theoretical model validation Vtd,s u u Vub Vtb Vud,s d u Cabibbo-suppressed tree diagrams penguin diagrams Gianluca Cavoto - Roma u p+, K+ Vtb Vtd,s d,s b W d,s p+, K+ W Vub Vud,s u b u t u p- B0 d d p- d d Cabibbo-suppressed tree diagrams penguin diagrams

  4. BaBar detector EMC 6580 CsI(Tl) crystals DIRC (PID) 144 fused silica bars 11000 PMs 1.5T solenoid Instrumented Flux Return iron / RPCs (muon / neutral hadrons) Drift Chamber 40 axial/stereo layers e+ (3.1GeV) Silicon Vertex Tracker 5 double sided layers e- (9GeV) • SVT: z resolution ~70 microns • Tracking: (pT)/pT = 0.13%  pT 0.45% • DIRC: K- separation > 3.4 for P<3.5GeV • EMC: E/E = 1.33%E-1/4  2.1% Gianluca Cavoto - Roma

  5. DIRCherenkov qC measurement Pion-Kaon separation at high momenta Detector of Internally Reflected Cherenkov light. 144 fused silica bars (1.7 cm thick) 11000 PMTs, 25-50 p.e./particle, 10 mrad single photon resolution Gianluca Cavoto - Roma

  6. B Candidate selection • Initial state kinematic constraint: K0 as KS to p+p- fK+K- K*+ K+p0,KS p+ energy substitued (constrained) mass Fully reconstructed decays Efficiency (with daughter BF) K0p0,h+p0,h+K0,h+h: 10-45% fK*+,fK0,fK+ :3-20% energy difference DE signal sideband mES Gianluca Cavoto - Roma unknown polarization in fK*+ select

  7. Composite particles s=4.3 MeV < E > ~ 3 GeV s=8.5 MeV loose Kaon PID requirements onf/K* daugheters f mass KS mass p0 mass Additional cuts: KS:decay time significance p0: photoncos(q*), cluster lateral shape Gianluca Cavoto - Roma

  8. Background suppression Jet-like topology • Background dominated by continuum quark-antiquark production (u,d,s,c) • cos(qTh) = • cosine of angle between thrust axes of B and rest of the event • Fisher discriminant: • Linear combination of event-shape variables cos qTh background Loose Cut on cos(qTh) to suppress bkg Fisher signal (dots) B- D0p- (histo)h+h- MC background signal h+h-DE sideband (dots) continuum h+h- MC (histo) Gianluca Cavoto - Roma

  9. Likelihood fit analysis • Use an extendedglobal likelihood fit to extract different signal yields (NS) in each topology • mES, DE, Fisher(cosqTh), (f mass), qC • Independent control sample to study Probability Density Function for both BKG and SIG h+h- DE sideband B- Dop- Gaussian s 2.6 MeV ARGUS function

  10. Critical Kaon ID • Why critical?: • Separate channels with same decay topology • Use as control sample: D*+ D0p+K-p+ PDF in momentum bins qC p qC - qC (K) distribution for true Kaon Gianluca Cavoto - Roma

  11. Systematic Uncertainties • Vary PDF parameters • alternative PDF • Other systematics (% variation on BF): • track finding efficiency: 1.2% per track • p0 (KS ) efficiency 5(4)% • B meson counting 1.6% Variation in yield Gianluca Cavoto - Roma

  12. B0p+p-, K+p-, K+K- cut-based analysis distributions for consistency check • 2 charged particles in the final state Gianluca Cavoto - Roma

  13. B+K0p+, K0 K+B0K0p0 KSp+ KSp0 KSK+ Cut based analysis cross-checks KS to p+p- ML fit results Gianluca Cavoto - Roma

  14. B+p0p+, p0 K+ Max likelihood fit projection p0 p+ BB background investigated: ML fit allows for rp component < 9.0(UL 90%CL) p0 K+ Gianluca Cavoto - Roma

  15. B fK(*) Max likelihood fit projection fK0 fK*+(K+p0) fK*+(K0p+) fK- Gianluca Cavoto - Roma

  16. Summary • BaBar has recorded • 20.7 fb-1 last year • Expect to collect additional ~30 fb-1 in 2001 • Next targets : • Direct CP asymmetry in these and other channels • Time-dependent CP asymmetry ( p+p-) Gianluca Cavoto - Roma

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