Branching Fraction and Direct CP Violation in B K 0 0 and B h Alfio Lazzaro Dipartimento di Fisica and INFN, Milan on behalf of the BaBar Collaboration American Physical Society 2003, Philadelphia Meeting BaBar Italia, Capri 10/04/03 Alfio Lazzaro 1 Overview Physics Motivation Analysis Strategy: Samples, Event Selection, ML fits Results on Branching Fractions and Charge asymmetries Conclusion Meeting BaBar Italia, Capri 10/04/03 Alfio Lazzaro 2 Physics Motivation • Measurements of Branching Fractions allow constraints on phenomenological models • Charge asymmetries (Ach) expected large (>20%) in B K (Soni, PRL 43, 242 (1979)) and B p (Gronau, PRL 79, 4333 (1997)) Previous Measured Branching Fractions (106): Need precise measurements Meeting BaBar Italia, Capri 10/04/03 Alfio Lazzaro 3 Data Samples and Sub-channels We have used 81.9 fb1 on-resonance _ (88.9 millions of BB pairs) We considered 3 channels: Reconstructed in (23%) Meeting BaBar Italia, Capri 10/04/03 Alfio Lazzaro (39%) 4 Event selection • Beam energy to constraint B mass and energy: • Event shapes to distinguish B events from continuum udsc: Fisher discriminant combining 4 variables: •direction of B thrust axis wrt beam direction •direction of B momentum wrt beam direction •2 Legendre moments of the energy flow of rest of event wrt B thrust axis |cos (qthrust)| < 0.9 • Loose cuts based on shapes variables, PID and kinematical quantities of secondary daughters, Cherenkov angle cut for h selection. We prepare the input to Meeting BaBar Italia, Capri 10/04/03 Maximum Likelihood Fit Alfio Lazzaro 5 Observables • Two types of background: _ qq (continuum ) dominant _ bb (non continuum ) ~ 1% – 2% • Observables: E, mES , Fisher, mass We use Unbinned Extended Maximum Likelihood (ML) Fit to extract signal yields and charge asymmetries Meeting BaBar Italia, Capri 10/04/03 Alfio Lazzaro 6 Results for 0 K and h First observation Meeting BaBar Italia, Capri 10/04/03 Alfio Lazzaro 7 Negative logLikelihood Dashed blue line: Dotted red line: Solid black line: Meeting BaBar Italia, Capri 10/04/03 Alfio Lazzaro 8 mES and E projections Shaded histograms represent gg Meeting BaBar Italia, Capri 10/04/03 Alfio Lazzaro 9 Systematics on BF and Ach Sources Error on yields • Systematics due to ML fit efficiency and bias • Daughter Branching fractions • Reconstruction efficiencies (, p0, KS, charged tracks) • Other sources: BB Number, MC statistics, PID, … 0.3 - 0.5 0.03 - 0.4 0.3 - 2.0 0.03 - 0.6 Total systematic error on BF: 7.1% (h +) 7.7% (K 0) Charge Asymmetries Systematic on charge dependence bias Meeting BaBar Italia, Capri 10/04/03 Alfio Lazzaro 1.1% 10 K0, K • Branching Fraction for BK larger than initially expected by theory • Tree diagrams are Cabibbo suppressed: • Interference between two penguin diagrams and the known – mixing angle conspire to greatly enhance B K and suppress B K (Lipkin, Phys. Lett. B 254, 247 (1991)) Meeting BaBar Italia, Capri 10/04/03 Alfio Lazzaro 11 Results for K0 and K BF Ach Meeting BaBar Italia, Capri 10/04/03 See also talk by Fred Blanc, Session T11 Alfio Lazzaro 12 mES and E Projections Shaded histograms represent pp Meeting BaBar Italia, Capri 10/04/03 Alfio Lazzaro 13 Conclusion We have presented the following preliminary results: First observation Suppressed B K Enhanced B K 2.5s Meeting BaBar Italia, Capri 10/04/03 Alfio Lazzaro 14 Altre Analisi in Corso B–> ' • BAD-462 Supporting Document BAD-605 Physics Note _ g _ t Risultati di CLEO Meeting BaBar Italia, Capri 10/04/03 d Alfio Lazzaro _ s b B0 s _ d W+ d 15 B–> ' • Analisi finita da tempo • Yields negativi • Quindi abbiamo fatto una analisi di tipo Bayesiano • Si sta ancora discutendo con i referee (Bob Cahn) ed altri esperti sul modo piu’ appropriato di presentare i risultati Meeting BaBar Italia, Capri 10/04/03 Alfio Lazzaro 16 B–> ’KL • Supporting document : BAD-591 • Scopo : Misura di BR e Time-Dependent CP-Violating Asymmetries ( analogo a quanto abbiamo fatto con •Attualmente usiamo il sotto-decadimento un prossimo futuro verra’ aggiunto °g KS) pp ma in •Statistica usata : RUN 1 + RUN 2 Meeting BaBar Italia, Capri 10/04/03 Alfio Lazzaro 17 B–> ’KL • Funzioni di likelihood per la identificazione delle KL (Antimo) • Constraint su MB e sulle direzioni per la ricostruzione cinematica • Analisi ML con le variabili: Mse , M , M , Fisher • Forte presenza di fondo comporta tagli su cos qT bassa ( 6 % ) Meeting BaBar Italia, Capri 10/04/03 Alfio Lazzaro 18 B–> ’KL • Ora stiamo cercando di aumentare l’efficienza di ricostruzione sostituendo alcuni tagli e il discriminante di Fisher con una rete neurale (NN). Uscita della rete usata come taglio per input ML • Analisi ML utilizzando le variabili : • Analisi cut & count nel piano : E , M , M ( NN , ) • Control Sample : e+e- g ( KS KL ) Meeting BaBar Italia, Capri 10/04/03 Alfio Lazzaro 19 B–> ’KS • Stiamo misurando il BR di questo canale nel sottodecadimento p p e 3 p KS p+ p- • Stiamo aggiornando l’analisi a tutta la statistica (Run1 + Run2) • Useremo questi dati nella prossima analisi CP-time dependent • Supporting Document : BAD-488 Meeting BaBar Italia, Capri 10/04/03 Alfio Lazzaro 20 B–> , , , • Stiamo misurando il BR di B nei sottodecadimenti con g e p p ( gg) • Per i canali , , stiamo usando le varie combinazioni dei sottodecadimenti con gg e 3p, g e pp . In queste analisi siamo ancora agli inizi! Meeting BaBar Italia, Capri 10/04/03 Alfio Lazzaro 21