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 Moriond QCD 2001 Gianluca Cavoto - Roma

Charmless Decays Preliminary Branching Fraction 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 2.6 fb-1 off-resonance Moriond QCD 2001 Gianluca Cavoto - Roma

Cabibbo-suppressed tree diagrams Cabibbo-suppressed tree diagrams Physics Target 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 d u Vtd,s u u Vub Vtb Vud,s d u Cabibbo-suppressed tree diagrams penguin diagrams Moriond QCD 2001 Gianluca Cavoto - Roma u p+, K+ Vtb Vtd,s b W d,s d,s p+, K+ W Vub Vud,s u b u t p- u B0 d d p- d d Cabibbo-suppressed tree diagrams penguin diagrams

Instrumented Flux Return Silicon Vertex Tracker 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% Moriond QCD 2001 Gianluca Cavoto - Roma

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 Moriond QCD 2001 Gianluca Cavoto - Roma

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 Moriond QCD 2001 Gianluca Cavoto - Roma unknown polarization in fK*+ select

Composite particles f mass s= 4.3 MeV s= 8.5 MeV loose Kaon PID < E > ~ 3 GeV s= 8.5 MeV loose Kaon PID requirements on f/K* daugheters f mass KS mass p0 mass Additional cuts: KS :decay time significance p0 : photon cos(q*), cluster lateral shape Moriond QCD 2001 Gianluca Cavoto - Roma

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) Moriond QCD 2001 Gianluca Cavoto - Roma

Likelihood fit analysis Use an extended global 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

Critical Kaon ID Use as control sample: D*+  D0p+  K-p+ 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 Moriond QCD 2001 Gianluca Cavoto - Roma

Systematic Uncertainties Vary PDF parameters alternative PDF Variation in yield Other systematics (% variation on BF): track finding efficiency: 1.2% per track p0 (KS ) efficiency 5(4)% B meson counting 1.6% Moriond QCD 2001 Gianluca Cavoto - Roma

B0  p+p-, K+p-, K+K- 2 charged particles in the final state cut-based analysis distributions for consistency check 2 charged particles in the final state Moriond QCD 2001 Gianluca Cavoto - Roma

B+ K0p+, K0 K+ B0  K0p0 KSp+ KSp0 KSK+ Cut based analysis cross-checks KS to p+p- ML fit results Moriond QCD 2001 Gianluca Cavoto - Roma

B+ p0p+, p0 K+ p0 p+ p0 K+ Max likelihood fit projection < 9.0 (UL 90%CL) p0 K+ BB background investigated: ML fit allows for rp component Moriond QCD 2001 Gianluca Cavoto - Roma

B  fK(*) Max likelihood fit projection fK0 fK*+(K+p0) fK*+(K0p+) fK- Moriond QCD 2001 Gianluca Cavoto - Roma

Summary Next targets : Direct CP asymmetry in these and other channels 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-) Moriond QCD 2001 Gianluca Cavoto - Roma