1 Semiexclusive semileptonic Bcharm decays C Gatto INFN

1 Semiexclusive semileptonic B->charm decays C. Gatto - INFN Napoli A. Mazzacane - Universita’ di Napoli April 10, 2003

Strategy of the analysis B± Do l± 2 § Reconstruct a D 0 and associated to a lepton from a common vertex § Reconstruct the vtx of the other B § Reconstruct the neutrino § Apply loose kinematic cuts to reduce the background. B± Do l± g B± Do l± X B±o D*o± l± | Do K B±o D*o± l± D 0 | Do g B B±o D*o± l± g e/m | Do B B±o D*o± l± X | Do B±o D** l± | D* signal uu, dd, ss e cc from the continuum | o D Combinatorics (correlated + B±o D ** l± background uncorrelated) | o D Fake Lepton

Which Physics can you do with the D 3 o and D* channels Divide the Channels Ø Gets insights on the Form Factors Add the Channels Ø Measure Vcb with increased statistics and smaller systematic errors (than adding 2 separate measurements)

How It Compares n 4 Plain Exclusive vs Semiexclusive analysis for the D* Semiexclusive analysis Exclusive analysis Ø Several semileptonic decays of the B - Ø Fully reconstruct one particular >charm are selected channel Ø No slow pion related problems Ø Must understand slow pion efficiency Ø 2. 47 times the Bo D*± l statistics: Bo D*± l D*± Do p ± (67. 7%) Ø Lower statistics B± D*o l D*o Do g/po (100%) Ø Needs input from MC to separate the Ø Use sidebands from data to reject the background various channels and the background

5 Discriminating Among the Various Channels n Use a Discriminant Analysis with: 2 n M ( ) invariant B missing mass squared n cos(q. B-Dlept) cosine of the angle between the B meson and the D-lepton system n cos(q. D-lept) cosine of the angle between the D meson and the leptone n R 2 Fisher discriminant n Use MC and control samples to obtain the PDF’s n Perform c 2 fits to extract the fractions

6 Dependence of the Variables from q 2

Applying The Final Cuts n n n Cuts on the fitted variables c 2 (Do K+ - ) < 3 c 2 (Do - lepton vtx ) < 3 c 2(tag B) /Ndof < 3 Cuts on the kinematical variables PCM(lepton) > 1. 0 Ge. V PCM(Do) > 0. 4 Ge. V R 2 < 0. 5 7

Status of the Analysis Ø Analized MC and data (cut Plept > 1. 0 Ge. V & ) v MC: ~133 x 106 bbgeneric MC vs ~18 x 106 for the PDF determination. v Data: most of 2000+2001+2002 on peak (~ 90 x 106 B pairs) and ~4 fb-1 off resonance. Ø No B->Do control sample for fake muons. Using only electrons. Ø All sources of systematic errors (except one) evaluated. 8

9 Binned fit results for MC (e only) M 2( ) cos(q. D-lept) cos(q. B-Dlept) R 2 § All § MC B± Do l± (+g) § MC B± Do l± § MC B± D** l± § Continuum § Background X (+g) X

10 Binned fit results for data (e only) M 2( ) cos(q. D-lept) cos(q. B-Dlept) R 2 § All § MC B± Do l± (+g) § MC B± Do l± § MC B± D** l± § Continuum § Background X (+g) X

Contour Plots 11

Performance on SP 4 MC (e only) MC Truth Fit B Do l 10. 1% 9. 9 0. 2% B Do l X 2. 8% 2. 6 0. 5% B o D*o l 50. 7% 50. 5% B o D*o l X 1. 5% 1. 1 0. 7% B o D**o l 9. 6% 10. 2 0. 7% 0% 0. 01% 25. 5% 25. 7 0. 2% Continuum Background 12

13 Performance on Data (e only) Fit B Do l 12. 9 0. 3% B Do l X 0. 0 0. 1% B o D*o l 42. 6 0. 4% B o D*o l X 0. 0 0. 2% B o D**o l 8. 7 0. 3% Continuum 11. 5 0. 2% Background 24. 3 0. 3%

Efficiencies and Yields Efficiency from MC B Do l 10. 2 0. 1% B o D*o l 10. 8 0. 1% Background 0. 11 0. 001% Yield from data B Do l 9824 230 B o D*o l 32447 334 Background 19280 233 Statistical errors only 14

15 Systematical Uncertainties Study n Cuts: n n Histogram binnings: n n Varying the binning of the fitted histos: 22 changes PDF smoothing: n n Varying the cuts applied at the final stage: 37 changes Varying the parameter of the fitted PDF’s by 1 s: 10 changes PDF binning: n Varying the binning of the fitted PDF’s: 11 changes

16 D** Modelling Study n n Repeating the analysis with the PDF for D** blend replaced with a single resonance All the specific channel founds in SP 4: D 1, D 2*, D(2 s), D’ 1, D*(2 s) both neutral and charged, decaying into D 0 or D*decays n 17 SP 4 collections used

Systematical Errors (e only) B o D*o l B Do l Error% Track efficiency 0. 87% B counting 1. 6% Electron ID (electrons only) 4. 43. 7% 2% Fake lepton rate (electrons only) 0. 13% Do->K Branching Ratio 2. 37% f+-/f 00 2. 6% 0. 6% PDF estimation (smoothing/bin) 0. 45% 0. 3% Data selection (cuts/binnings) 0. 76% 1. 2% D** modeling 0. 9% 0. 7% no no 4. 6% 3. 9% MC Form Factors Total Largest contributions 17 1. 31. 4%

Results (blind) This analysis B Do e X 2. 3% (stat) 4. 6 %(syst) B o D* o e X 1. 0% (stat) 3. 9% (syst) PDG B Do l (2. 15 0. 22) ´ 10 -2 Bo D* l (4. 60 0. 27) ´ 10 -2 18

Conclusions n Status of the analysis n n Fit machinery is working in a consistent manner New smoothing for the PDF used since last SLAC meeting Systematical uncertainties study is almost complete Eventual improvements n n 19 Split background channel into two ore more sub-channels Next n Systematical uncertainties related to the MC modeling of the decays (semileptonic form factors)