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Hadronic Moments in Semileptonic B Decays from CDFII

Hadronic Moments in Semileptonic B Decays from CDFII. Alessandro Cerri. Hep-ph/0502003 Accepted for publication in PRDRC. Analysis Strategy. Typical mass spectrum M(X 0 c ) (Monte Carlo):. D 0 and D* 0 well-known  measure only f**  only shape needed. 1) Measure f**(s H )

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Hadronic Moments in Semileptonic B Decays from CDFII

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  1. Hadronic Moments in Semileptonic B Decays from CDFII Alessandro Cerri Hep-ph/0502003 Accepted for publication in PRDRC

  2. Analysis Strategy Typical mass spectrum M(X0c)(Monte Carlo): D0 and D*0 well-known measure only f**  only shape needed 1) Measure f**(sH) 2) Correct for background, acceptances, bias  moments of D** 3) Add D and D*  M1,M2 4) Extract , 1 Alessandro Cerri CKM Workshop

  3. Channels • Possible D’D(*)contributions neglected: • No BlD’ experimental evidence so far • DELPHI limit: • We assume no D’ contribution in our sample Must reconstruct all channels to get all the D** states. • However CDF has limited capability for neutrals • B0D**-l+ always leads to neutral particlesignore it • B- D**0l- better, use isospin for missing channels: • D**0 D+- OK • D**0 D00 Not reconstructed. Half the rate of D+- • D**0 D*+- • D*+ D0+OK • D*+ D+0 Not reconstructed. Feed-down to D+- • D**0D*00 Not reconstructed. Half the rate of D*+- Alessandro Cerri CKM Workshop

  4. Event Topology Exclusive reconstruction of D**: • D**0 D+**- • K- + + (Br=9.2%) • D**0 D*+**- • D0*+ (Br=67.7%) • K- + (Br=3.8%) • K- + - + (Br=7.5%) • K- + 0 (Br=13.0%) “D+” “D*+” Alessandro Cerri CKM Workshop

  5. Backgrounds Physics background: BD(*)+Ds-, D(s)Xl  MC, subtracted Combinatorial background under the D(*) peaks:  sideband subtraction • Feed-down in signal: • D**0 D*+( D+0)- • irreducible background to • D**0 D+-. • subtracted using data: • shape from D0- in D**0 D*+( D0+)- • rate: ½ (isospin) x eff. x BR • Prompt pions faking **: • fragmentation • underlying event • separate B and primary vertices (kills also prompt charm)  use impact parameters to discriminate •  model: wrong-sign **+-combinations Alessandro Cerri CKM Workshop

  6. Lepton + D Reconstruction Total: ~ 28000 events • Lepton + D(*)+: • D vertex: • 3D • l+D(+*) vertex (“B”): • 3D • Lxy(B) > 500 m • m(B) < 5.3 GeV • Data Sample: • e/ + displaced track • ~ 180 pb-1 • ( Sept 2003) • Track Selection: • 2 GeV track (SVT leg) • e/: pT > 4 GeV • other: pT > 0.4 GeV Alessandro Cerri CKM Workshop

  7. Raw m** Distributions Measured in m**, shifted by M(D(*)+), side-band subtracted. D1,D1*,D2* Feed-down D2*,D0* Alessandro Cerri CKM Workshop

  8. Efficiency Corrections • 1) Correct the raw mass for any dependence of reco on M(D**): • Possible dependence on the D** species (spin). • Monte-Carlo for all D** (Goity-Roberts for non-resonant), cross-checked with pure phase space decays. • Detector simulation shortcomings cause residual data/MC discrepancy: derive corrections from control samples (D* and D daughters) • 2) Cut on lepton energy in B rest frame: • Theoretical predictions need well-defined pl* cut. • We can’t measure pl*, but we can correct our measurement to a given cut:  pl* > 700 MeV/c. Alessandro Cerri CKM Workshop

  9. Corrected Mass and D** Moments Results (in paper): Procedure: • Unbinned procedure using weighted events. • Assign negative weights to background samples. • Propagate efficiency corrections to weights. • Take care of the D+ / D*+relative normalization. • Compute mean and sigma of distribution. No Fit !!! Alessandro Cerri CKM Workshop

  10. Final Results (m1,m2)=0.61 (M1,M2)=0.69 Pole mass scheme 1S mass scheme Alessandro Cerri CKM Workshop

  11. Systematic Errors (from the paper) Alessandro Cerri CKM Workshop

  12. Comparison with Other Measurements Pole mass scheme Alessandro Cerri CKM Workshop

  13. First measurement at hadron machines: different environment and experimental techniques. Competitive with other experiments. Little model dependency. No assumptions on shape or rate of D** components. Through integration with other experiments and other “moments” we can seriously probe HQET/QHD Let’s do it! Summary Alessandro Cerri CKM Workshop

  14. BACK-UP SLIDES

  15. Motivation (I) Most precise determination of Vcb comes from sl (“inclusive” determination): (4S), LEP/SLD, CDF measurements. Experimental |Vcb|~1% Theory with pert. and non-pert. corrections. |Vcb|~2.5% Ftheory evaluated using OPE in HQET: expansion in s and 1/mB powers: O(1/mB)  1 parameter:  (Bauer et al., PRD 67 (2003) 071301) O(1/mB2)  2 more parameters: 1, 2 O(1/mB3)  6 more parameters: 1, 2,T1-4 Constrained from pseudo-scalar/vector B and D mass differences Alessandro Cerri CKM Workshop

  16. Motivation (II) Many inclusive observables can be written using the same expansion (same non-perturbative parameters).Thespectral moments: • Photonic moments: Photon energy in b  s  (CLEO) • Leptonic moments: BXcl, lepton E in B rest frame (CLEO, DELPHI, BABAR) • Hadronic moments: BXcl, recoil mass M(Xc) (CLEO, DELPHI, BABAR, CDFII) Constrain the unknown non-pert. parameters and reduce |Vcb| uncertainty. With enough measurements: test of underlying assumptions (duality…). Alessandro Cerri CKM Workshop

  17. What is Xc? Higher mass states: D** Semi-leptonic widths (PDG 04): (PDG b/B+/B0 combination, bu subtracted) • ~25% of semi-leptonic width is poorly known • Possible D’D(*)contributions neglected: • No BlD’ experimental evidence so far • DELPHI limit: • We assume no D’ contribution in our sample Alessandro Cerri CKM Workshop

  18. Take M(D0), M(D*0), sl, 0, * from PDG 2004 : sl, 0, * are obtained combining BR’s for B-, B0 and admixture, assuming the widths are identical (not the BR’s themselves), and using f-/f0 = 1.044 ± 0.05 (B-)/(B0) = 1.086 ± 0.017 Average: BR(B+ X0cl+l) = 0.1099 ± 0.0031 BR(B+ D0l+l) = 0.0223 ± 0.0015 BR(B+ D*0l+l) = 0.0604 ± 0.0023 Combination with D0, D*0 Alessandro Cerri CKM Workshop

  19. K, e K,  K,  K, e K0, e K, e Monte-Carlo Validation (I) MC vs. semileptonic sample: Matching 2 probability for those plots: Alessandro Cerri CKM Workshop

  20. ** 3D IP signif. wrt BV ** 2D IP signif. wrt PV ** Selection • Based on topology: • impact parameter significances w.r.t. primary, B and D vertices Cuts are optimized using MC and background (WS) data: Additional cuts only for D+: • pT > 0.4 GeV • R < 1.0 • |d0PV/| > 3.0 • |d0BV/| < 2.5 |d0DV/| > 0.8 Lxy BD > 500m Alessandro Cerri CKM Workshop

  21. Pl* • Theory prediction depends on Pl* cuts. We cannot do much but: • see how our efficiency as a function of Pl* looks like • Use a threshold-like correction • Evaluate systematics for different threshold values Alessandro Cerri CKM Workshop

  22. Vcb measurements • |Vcb| from exclusive B decays • Large statistics on Bd0D(*)- available and new measurements are coming • Present precision (5%) is systematics limited: • Experiments: D** states, D’s BR • Theory: form factor extrapolation, corrections to F(1)=1 can be reduced in the future |Vcb|excl=(42.1 1.1exp 1.9theo) 10-3 (PDG 2002, Vcb review) • |Vcb| from inclusive B decays • Experiment: large statistics on BR(BXc-) and tBand small systematics |Vcb|incl= (40.4 ± 0.5exp ± 0.5, ± 0.8theo) 10-3 (PDG 2002, Vcb review) Alessandro Cerri CKM Workshop

  23. D*+ Reconstruction and Yields D*+ channels:Dm* M(D0*) – M(D0) D(*)+ l- (+cc) yields: ~ 28000 events Alessandro Cerri CKM Workshop

  24. MC validation: quantitative Alessandro Cerri CKM Workshop

  25. K K ** 3D IP signif. wrt BV ** 2D IP signif. wrt PV Impact Parameters in MC Comparison data/MC for IP: (worst case) • Residual corrections: • derived from data: • * • non-SVT D daughters (pT > 1.5 GeV) • corrections from double ratios • in pT • in m** Alessandro Cerri CKM Workshop

  26. Computing the Xc Moments • The D0 and D*0 pieces have to be added to the D**0 moments, according to • where the fi are the fractions of Dil events above the pl*cut. Only ratios of fi’s enter the final result. f Alessandro Cerri CKM Workshop

  27. Pl* • Theory prediction depends on Pl* cuts. We cannot do much but: • see how our efficiency as a function of Pl* looks like • Use a threshold-like correction • Evaluate systematics for different threshold values Alessandro Cerri CKM Workshop

  28. Lepton momentum cut-off • We are not “literally” cutting on Pl* (it is not accessible, experimentally) • Detector implicitly cuts on it • Assume a baseline cut-off • Vary in a reasonable range to evaluate systematics • We use f to derive f**, given f0, f* • f=f(,1) • We use experimental prior knowledge on ,1 to evaluate systematics • Effect is negligible Alessandro Cerri CKM Workshop

  29. Efficiency vs m** Alessandro Cerri CKM Workshop

  30. MC/Data corrections • Dominant source of systematics! • * reproduces ** topology but statistics too low: • Use all D* candidates • Cross check on non-triggering D0 daughters (helps for pT) Alessandro Cerri CKM Workshop

  31. Use mass side-bands to subtract combinatorial background. Use D*+[D0+] - to subtract feed-down from D*+[D+0] - to D+-. Use wrong-sign **+ l- combinations to subtract prompt background to **. Possible charge asymmetry of prompt background studied with fully reconstructed B’s: 4% contribution at most. Background Subtraction Alessandro Cerri CKM Workshop

  32. BACK-UP: details on systematics

  33. Systematics • Input parameters • D(*)+ Masses, in combining D(*) with D** mM [PDG errors] • BR (BD+/D*+mM) [PDG errors] • Experimental • Detector resolution [re-smear satellite sample by full resolution: 60MeV] • Data/MC Efficiency discrepancies [measure Pt and m dependency on control sample, probe different fit models] • Decay models in MC [full kinematic description vs pure phase space] • Pl* cut correction [repeat measurement at various Pl* thresholds] • Backgrounds • Scale [charge correlation WS/RS from fully reconstructed B: 4%] • Optimization Bias [repeat optimization procedure on bootstrap copies of the sample] • Physics background [vary 100%] • BXc [estimate / yield and kinematic differences using MC] • Fake leptons [no evidence in WS D+l+, charge-correlated negligible] Alessandro Cerri CKM Workshop

  34. Data-based study • Extract a bootstrap sample a of the data • Optimize  get new set of cuts • Evaluate bias with respect to the parent distribution (initial data) with new cuts • We can repeat this 50 times and obtain 50 independent estimates of the bias(es) • CPU intensive • [~5 hours/(bootstrap+optimization+“fit”)] • Mean of those estimates is an unbiased estimator of the bias • (as long as the data is a good • representation of the ideal distribution) •  is a convolution of: • Intrinsic fluctuation of bias • Statistical fluctuation of a after cuts Data Bootstrap a Cuts! Optimize Selection Selection m1a,m2a m1unb,m2unb - • =bias • =(bias fluctuation)(statistical uncertainty) Bias! Alessandro Cerri CKM Workshop

  35. Physics Background • Physics background studied with BD(*)+Ds- • Size wrt signal: • 100% uncertainty Other modes ~7% ~1 ~7% Alessandro Cerri CKM Workshop

  36. A problem if observed m** distributions are different! Two possible sources of difference: Kinematics: different m** distribution to begin with because m()/m(B) >> m(e/)/m(B) Different reconstruction efficiency Study with generator-level MC + smearing + trigger & reco. parameterization Conclusion: [BlD**]/[BlD**]2% Difference in m** acceptance is ~10% and mass-independentirrelevant m()/m(B) matters only for the nonresonant component which is in MC 13% of the overall distribution I.e. 13%x2% 0.003small [(m1,m2)(0.01 GeV2,0.065 GeV4)] is evaluated on the above montecarlo, the overall BKG systematics is (0.02,0.1)) BlD** Not a Significant Source of Systematics  Background Alessandro Cerri CKM Workshop

  37. Fake Correlated Leptons • For background which is sign correlated the nastiest source is D**(-)+X where we mismatch + as a fake lepton: Decreasing efficiency AND BR • Assuming: • An average efficiency equal to the one for signal • Overall BR(BD**(-)+X) is at most 3xBR(BD**(-)l+X) • From Run I + Run II studies from Masa, e+ fakes are about 1.6% in total for this trigger • We get a fake count of ~2.4% the signal • Kinematic m** bias much smaller than for the  background case • Similar fake rate • As negligible (or more favorable) than  Alessandro Cerri CKM Workshop

  38. One fit to combine them all, one fit to find them!…( ) • Fit based on Bauer et al. (hep-ph/0210027) • Fit (,1) in the pole scheme to moments vs pl* cut • Not including all the CLEO points • Including BELLE’s (thanks to the BELLE folks for privately providing the correlations) Alessandro Cerri CKM Workshop

  39. Statistical Weight All but BABAR All but BELLE All All but CDF All but CLEO All but DELPHI Alessandro Cerri CKM Workshop

  40. Statistical Weight All but BABAR All but CDF All • Same fit as previous page, but excluding single experiments • CDF contribution is significant Only BABAR Only CDF Alessandro Cerri CKM Workshop

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