Inclusive. measurement

Transcription

1 V b Inclsive V b measrement V b V b of V b at V b V b V b V b V b CKM 2005 Workshop on the Unitarity Triangle March 18, San Diego V b V b I. Bizjak, J. Stefan Institte V b for Belle collaboration

2 Belle KEK-B Record vales 5 years of data taking: L max = cm -2 s -1 L int = 381fb > 400 million B meson events Beam energies e + (HER): 8.0 GeV e - (LER): 3.5 GeV E CM =10.58 GeV Belle Detector covers large part of solid angle

3 New inclsive V b reslts from Belle Using endpoint of momentm spectrm for e ± with 27 fb -1 Endpoint of momentm spectrm region above 1.9 GeV/c Measre partial branching fraction + obtain V b Using fll reconstrction tagging with 253 fb -1 3 kinematical selections where b c decays are sppressed 1) Mx<1.7 GeV/c 2 / q 2 >8 GeV 2 /c 2 2) Mx<1.7 GeV/c 2 / no q 2 ct 3) P + analysis : P + <0.66 GeV Measre partial branching fractions + obtain V b

4 Electron spectrm endpoint: the method Measrement region: Backgrond estimation region: 1.9 GeV/c < p e* < 2.6 GeV/c (CMS) N/N B X c l ν B X l ν BB backgronds B X c lν Leptons from other decays (J/ψ, ψ (2S), γ conv.) Fake electrons 1.5 GeV/c < p e* < 1.9 GeV/c (CMS) Deal with large backgronds: MC simlation: D**eν (ISGW2) D*eν (HQET) Deν (ISGW2) Veto on invariant mass Estimated sing K s π + π QED radiative corrections inclded Fit (D*+ D)lν/ D** lν relative contribtions GeV/c

5 How to deal with large non-bb backgrond Non BB backgronds Continm (e + e - qq ) QED processes Visible energy Charged mltiplicity Fox-Wolfram moments Fisher discriminant: Energy flow variables Thrst axis Rare B decay tag + Sbtraction of continm (8.8fb -1 of offresonance data) Energy flow variable Rare B decay tag Acceptance of selection reqirements as a fnct. of q 2

6 Electron spectrm endpoint: the reslt ( 27 fb -1 ) BB backgrond (b c MC expectation) continm backgrond Systematic ncertainty: Model dependent signal efficiency % B X c lν backgrond estimation... 17% b MC expected shape Br(X lν ) = N(X 2N BB lν ) ε MC Br (1.9 GeV/c < p e * < 2.6 GeV/c) = (8.47 ± 0.37 ± 1.53) 10-4 stat syst

7 Standard V b method Br(X DFN lν ) = (1 + δ ) Br(X lν )/f f ( m 4. 62, µ 2 = 0 40) rad De Fazio&Nebert, JHEP 9906,017 (1999) b= π. spectral distortion de to final state radiation Belle measrement of m b and µ π 2 Limosani&Nozaki : hep-ex/ Belle Collaboration,Phys. Rev. Lett (2004) ( X lν ) Br 1.61ps Vb = ( 1 ± λ ± , τ B 1 mb ) 1.9 GeV/c <p e < 2.6 GeV/c : V b = (5.01 ± 0.47 ± 0.17 ± 0.32 ± 0.24) 10-3 exp stat/sys theo Br Vb f error Total error onv b... 13% V b vs. lower m. ct

8 New V b method An improved treatment of shape fnction effects + Bosch, Lange, Nebert, Paz, Ncl.Phys. B699 (2004) weak annihilation effect estimated Calclation of V b directly from the partial fraction Br V b = (1 + δ ) rad τ Br B ( X lν) 1 R SF parameters (shape fnction scheme) ( m (SF) 4. 63, µ 2 (SF) = 0 20) b = π. 1.9 GeV/c <p e < 2.6 GeV/c : V b = (4.50 ± 0.42 ± 0.32 ± 0.21) 10-3 exp SF theo Total error onv b... 13%

9 Analysis on a flly reconstrcted sample Flly reconstrct the event 4-momenta of both B s are known: p(b sig )= Y(4S) p(b reco ) On signal side identify the lepton from B Xlν Use Particle ID: calclate P + and M x (= p x2 : p x =Σp sig.rec p lept ) Calclate q 2 distribtion q 2 = (p(b sig ) p x ) 2 b c reconstrcted P(B reco ) P(B sig ) Calclate M miss2 distribtion M 2 miss = (q p lept ) 2 Use different cts to sppress large B X c lν p x l ± ν q Try to estimate no. of B X lν X or X c Interpret the reslt in terms of V b

10 Flly reconstrcted sample Flly reconstrcted sample Clean environment bt small sample: ε reco Exclsive method: 180 decay channels Reconstrcted channels: B 0 D (*) π + /D (*) ρ + /D (*) a 1 + /D (*) D s (*)+ B + D (*)0 π + /D (*)0 ρ + /D (*)0 a 1 + /D (*)0 D s (*)+ D *0 D 0 π 0 D * D 0 π/ Dπ 0 D s* D s γ D 0 Kπ/Kππ 0 /Kπππ/K s π 0 /K s ππ/k s πππ 0 /KK D Kππ/Kπππ 0 /K s π/k s ππ 0 /K s πππ/kkπ D s K s Kπ/KKπ B fb -1 B + Fit by Args and Crystal Ball fnctions Signal bkgd prity Signal bkgd prity

11 Selection of B X lν events 1 From reconstrcted events select events with high momentm leptons 2 p* >1GeV/c Charged B tag: + reqire charge consistency sample of semileptonic decays Additional selection criteria: Reqire only one lepton ΣQ=0 1GeV 2 <M miss2 < 0.5GeV 2 No(K + )=0, No(K 0 S)=0 cosϑ MM < Constrct kinematical variable distribtions by obtaining the yield in each bin by M bc fit 4 Fit the kinematical variable distribtion with expected distribtions from b and b c and sbtract the fitted b c contribtion 5 Calclate the partial branching fraction

12 Branching fraction calclation Nmber of excess events Unfolding factor F Br(X lν ) Br(Xlν ) = N b N sl ε F sel ε ε b frec sl frec ε b l sl ε l Nmber of semileptonic events Ratio of efficiencies for b and sl selection efficiency Use PDG vale for Br (Xlν)= ± Br (X lν) New V b method V b directly from Br (X lν)

13 M x analysis M x <1.7 GeV/c 2 / q 2 >8 GeV 2 /c 2 Total error onv b... 12% 253 fb -1 V b = (4.34 ± 0.22 ± 0.19 ± 0.13 ± 0.12 ± 0.33 ) 10-3 stat syst b b c model dep SF theo M x <1.7 GeV/c 2 / no q 2 ct : total error onv b... 11% 253 fb -1 V b = (3.80 ± 0.17 ± 0.13 ± 0.12 ± 0.04 ± ) 10-3 stat syst b b c model dep SF theo

14 P + analysis New proposed kinematical variable Bosch, Lange, Nebert, Paz, Phys Rev Lett 93, (2004) P + P + =E x p x P =E x + p x (M x 2 = P + P ) 253 fb -1 V b = (3.87 ± 0.18 ± 0.18 ± 0.12 ± 0.17 ± ) 10-3 stat syst b c b model dep SF theo Total error onv b... 13%

15 Sbtracted shapes of M x and q 2 no q 2 ct M x <1.7GeV/c 2

16 Partial branching fractions (What is actally being measred) V b Reslts V b vales are 10% lower with new method... ncorrelated correlated Br (M x <1.7, q 2 >8, p* >1) = (8.41 ± 1.14 ± 0.69) 10-4 Br (M x <1.7, p* >1) = (1.24 ± 0.15 ± 0.08) 10-3 Br (P + <0.66, p* >1) = (1.10 ± 0.15 ± 0.12) 10-3 Lepton endpoint (p* > 1.9 GeV/c ) V b = (4.50 ± 0.15 ± 0.55) 10-3 Fll reconstrction tagging V b = (4.34 ± 0.29 ± 0.43) 10-3 V b = (3.80 ± 0.21 ± 0.35) 10-3 V b = (3.87 ± 0.25 ± 0.43) % M x / q 2 12% M x 11% P + 13%

17 Lepton endpoint measrement with lowest ct (1.9 GeV/c) V b error 13%, a competitive reslt Conclsions V b errors for M X (/q 2 ) with 253fb -1 : 11% / 12% Fll reconstrction tagging P + sable (bt with largest error) Mainly de to SF par. determination It seems avoiding SF region does not bring mch profit...? error (M X,q 2 ) > error (M X ) What can we expect from 500 fb -1? Fll recon. tagging + Improve S/B x 1.3 frec. eff. x 1.5 Lmi scale x 2 SF error -10% V b error = 2% stat syst SF other total M x /q 2 5.0% 4.4% 7.5% 6.2% 12% M x 4.6% 3.5% 7.7% 4.7% 11% P + 4.7% 4.6% 9.1% 6.3% 13% stat syst SF other total M x /q 2 1.5% 3.7% 6.8% 6.2% 10% M x 1.6% 3.1% 6.9% 4.7% 9% P + 1.6% 3.8% 8.2% 6.3% 11%

18 backp slides

19 Appendix I Analysis on a flly reconstrcted sample The endpoint analysis Breakdown of errors on V b for different lower momentm ctoffs detected generated M x For events with M x >1.7 GeV/c 2 : M x resoltion σ 115 MeV/c 2