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

2 Strategy of the analysis uu, dd, ss e cc from the continuum Combinatorics (correlated + uncorrelated) Fake Lepton signal background B ±  D o l ±  B ±  D o l ±   B ±  D o l ±  X B ± o  D * o ± l ±  |  D o  B ± o  D * o ± l ±  |  D o  B ± o  D * o ± l ±   |  D o  B ± o  D * o ± l ±  X |  D o  B ± o  D ** l ±  |  D *  |  D o  B ± o  D ** l ±  |  D o   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. e/  D0D0 B  K B

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

4 Plain Exclusive vs Semiexclusive analysis for the D* How It Compares Semiexclusive analysis  Several semileptonic decays of the B ->charm are selected  No slow pion related problems B o  D * l  2.47 times the B o  D * ± l statistics: B o  D * l D *  D o  B o  D * ± l D * ±  D o  ± (67.7%) B  D * o l D * o  D o  /  o B ±  D * o l D * o  D o  /  o (100%)  Needs input from MC to separate the various channels and the background Exclusive analysis  Fully reconstruct one particular channel  Must understand slow pion efficiency  Lower statistics  Use sidebands from data to reject the background

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

6 Dependence of the Variables from q 2

7 Applying The Final Cuts Cuts on the fitted variables    D o  K +  - ) < 3    D o  lepton vtx ) < 3    tag B) /N dof < 3 Cuts on the kinematical variables P CM (lepton) > 1.0 GeV P CM (D o ) > 0.4 GeV R2 < 0.5

8 Status of the Analysis  Analized MC and data (cut P lept > 1.0 GeV & )  MC: ~133x10 6 bbgeneric MC vs ~18x10 6 for the PDF determination.  Data: most of on peak (~ 90x10 6 B pairs) and ~4 fb -1 off resonance.  No B->D o  control sample for fake muons. Using only electrons.  All sources of systematic errors (except one) evaluated.

9 Binned fit results for MC (e  only) M 2 ( ) cos(  D-lept ) cos(  B-Dlept ) R2R2R2R2  All  MC B ±  D o l ±  (+  )  MC B ±  D o l ±  X  MC B ±  D * l ±  (+  )  MC B ±  D * l ±  X  MC B ±  D ** l ±   Continuum  Background

10 Binned fit results for data (e  only)  All  MC B ±  D o l ±  (+  )  MC B ±  D o l ±  X  MC B ±  D * l ±  (+  )  MC B ±  D * l ±  X  MC B ±  D ** l ±   Continuum  Background cos(  B-Dlept ) M 2 ( ) cos(  D-lept ) R2R2R2R2

11 Contour Plots

12 Performance on SP4 MC (e  only) MC TruthFit B   D o l  10.1% 9.9  0.2% B   D o l  X 2.8% 2.6  0.5% B o   D* o l  50.7% 50.5  0.5% B o   D* o l  X 1.5% 1.1  0.7% B o   D** o l  9.6% 10.2  0.7% Continuum 0% 0.0  0.01% Background 25.5% 25.7  0.2%

13 Performance on Data (e  only) Fit B   D o l  12.9  0.3% B   D o 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%

14 Efficiencies and Yields Statistical errors only Efficiency from MC B   D o l  10.2  0.1% B o   D* o l  10.8  0.1% Background 0.11  % Yield from data B   D o l  9824  230 B o   D* o l   334 Background  233

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

16 D** Modelling Study Repeating the analysis with the PDF for D** blend replaced with a single resonance All the specific channel founds in SP4: D 1, D 2 *, D(2s), D’ 1, D*(2s) both neutral and charged, decaying into D 0 or D*decays 17 SP4 collections used

17 Systematical Errors (e  only) Error% B   D o l  B o   D* o l  Track efficiency0.87% B counting1.6% Electron ID (electrons only)2% Fake lepton rate (electrons only)0.13% D o ->K  Branching Ratio 2.37% f +- /f %0.6% PDF estimation (smoothing/bin)0.45%0.3% Data selection (cuts/binnings)0.76%1.2% D** modeling0.9%0.7% MC Form Factorsno Total4.6%3.9% % % Largest contributions

18 Results (blind) B   D o e  X  2.3% (stat)  4.6 %(syst) B  o  D*  o e  X  1.0% (stat)  3.9% (syst) This analysis B   D o l  (2.15  0.22)  B o  D*  l  (4.60  0.27)  PDG

19 Conclusions Status of the analysis 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 Split background channel into two ore more sub-channels Next Systematical uncertainties related to the MC modeling of the decays (semileptonic form factors)