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Meeting BaBar Italia, Capri 10/04/03 Alfio Lazzaro1 Branching Fraction and Direct CP Violation in B 0 K 0 and B h B 0 K 0 and B h Branching Fraction and.

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Presentazione sul tema: "Meeting BaBar Italia, Capri 10/04/03 Alfio Lazzaro1 Branching Fraction and Direct CP Violation in B 0 K 0 and B h B 0 K 0 and B h Branching Fraction and."— Transcript della presentazione:

1 Meeting BaBar Italia, Capri 10/04/03 Alfio Lazzaro1 Branching Fraction and Direct CP Violation in B 0 K 0 and B h B 0 K 0 and B h Branching Fraction and Direct CP Violation in B 0 K 0 and B h B 0 K 0 and B h Alfio Lazzaro Dipartimento di Fisica and INFN, Milan on behalf of the BaBar Collaboration American Physical Society 2003, Philadelphia

2 Meeting BaBar Italia, Capri 10/04/03 Alfio Lazzaro2 Physics Motivation Analysis Strategy: Samples, Event Selection, ML fits Results on Branching Fractions and Charge asymmetries ConclusionOverview

3 Meeting BaBar Italia, Capri 10/04/03 Alfio Lazzaro3 Measurements of Branching Fractions allow constraints on phenomenological models Charge asymmetries (A ch ) expected large (>20%) in B K (Soni, PRL 43, 242 (1979)) and B (Gronau, PRL 79, 4333 (1997)) Physics Motivation Need precise measurements Previous Measured Branching Fractions ( 10 6 ):

4 Meeting BaBar Italia, Capri 10/04/03 Alfio Lazzaro4 Data Samples and Sub-channels We considered 3 channels: Reconstructed in We have used 81.9 fb on-resonance (88.9 millions of BB pairs) _ (23%)(39%)

5 Meeting BaBar Italia, Capri 10/04/03 Alfio Lazzaro5 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 ( thrust )| < 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 Maximum Likelihood Fit

6 Meeting BaBar Italia, Capri 10/04/03 Alfio Lazzaro6 Two types of background: qq (continuum ) dominant bb (non continuum ) ~ 1 % – 2 % Observables: E, m ES, Fisher, mass ObservablesObservables _ _ We use Unbinned Extended Maximum Likelihood (ML) Fit to extract signal yields and charge asymmetries

7 Meeting BaBar Italia, Capri 10/04/03 Alfio Lazzaro7 Results for K 0 and h Results for K 0 and h First observation Preliminary

8 Meeting BaBar Italia, Capri 10/04/03 Alfio Lazzaro8 Negative logLikelihood Dashed blue line: Dotted red line: Solid black line:

9 Meeting BaBar Italia, Capri 10/04/03 Alfio Lazzaro9 m ES and E projections m ES and E projections Shaded histograms represent

10 Meeting BaBar Italia, Capri 10/04/03 Alfio Lazzaro10 Systematics on BF and A ch Sources Error on yields Systematics due to ML fit efficiency and bias Daughter Branching fractions Reconstruction efficiencies (, 0, K S, charged tracks) Other sources: BB Number, MC statistics, PID, … Total systematic error on BF: Charge Asymmetries Systematic on charge dependence bias 7.1% ( h + ) 7.7% ( ) 1.1%

11 Meeting BaBar Italia, Capri 10/04/03 Alfio Lazzaro11 K 0, K K 0, K Branching Fraction for B K 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))

12 Meeting BaBar Italia, Capri 10/04/03 Alfio Lazzaro12 Results for K 0 and K Results for K 0 and K BF A ch Preliminary See also talk by Fred Blanc, Session T11

13 Meeting BaBar Italia, Capri 10/04/03 Alfio Lazzaro13 m ES and E Projections m ES and E Projections Shaded histograms represent

14 Meeting BaBar Italia, Capri 10/04/03 Alfio Lazzaro14Conclusion We have presented the following preliminary results: First observation 2.5 Suppressed B K Enhanced B K

15 Meeting BaBar Italia, Capri 10/04/03 Alfio Lazzaro15 Altre Analisi in Corso B–> ' B–> ' BAD-462 Supporting Document BAD-605 Physics Note Risultati di CLEO B0B0 d b _ W+W+ t _ d d _ g s s _

16 Meeting BaBar Italia, Capri 10/04/03 Alfio Lazzaro16 B–> ' 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

17 Meeting BaBar Italia, Capri 10/04/03 Alfio Lazzaro17 B–>K L Supporting document : BAD-591 Scopo : Misura di BR e Time-Dependent CP-Violating Asymmetries ( analogo a quanto abbiamo fatto con S ) Attualmente usiamo il sotto-decadimento ma in un prossimo futuro verra aggiunto ° Statistica usata : RUN 1 + RUN 2

18 Meeting BaBar Italia, Capri 10/04/03 Alfio Lazzaro18 B–> K L Funzioni di likelihood per la identificazione delle K L ntimo Constraint su M B e sulle direzioni per la ricostruzione cinematica Analisi ML con le variabili: M se, M, M, Fisher Forte presenza di fondo comporta tagli su cos T bassa ( 6 % )

19 Meeting BaBar Italia, Capri 10/04/03 Alfio Lazzaro19 B–> K L Ora stiamo cercando di aumentare lefficienza di ricostruzione sostituendo alcuni tagli e il discriminante di Fisher con una rete neurale (NN). Uscita della rete usata come taglio per input ML E, M, M Analisi ML utilizzando le variabili : Analisi cut & count nel piano : ( NN, ) Control Sample : e+e- ( S L )

20 Meeting BaBar Italia, Capri 10/04/03 Alfio Lazzaro20 B–> K S Stiamo misurando il BR di questo canale nel sottodecadimento e S + - Stiamo aggiornando lanalisi a tutta la statistica (Run1 + Run2) Useremo questi dati nella prossima analisi CP-time dependent Supporting Document : BAD-488

21 Meeting BaBar Italia, Capri 10/04/03 Alfio Lazzaro21 B–> Stiamo misurando il BR di B nei sottodecadimenti con e ( Per i canali stiamo usando le varie combinazioni dei sottodecadimenti con e 3, e In queste analisi siamo ancora agli inizi!


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