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Search for exclusive two body decays of B→D h at Belle. * S. Thesis Defense of Luminda Kulasiri Dept. of Physics, University of Cincinnati 05.09.2005. Motivation-. *. V cs. c. c. s. s. W -. W -. b. u. b. * -. * -. u. V ub. D S. D S. *. V ub. V cs. p 0. B 0.
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Search for exclusive two body decays of B→D h at Belle * S Thesis Defense of Luminda Kulasiri Dept. of Physics, University of Cincinnati 05.09.2005
Motivation- * Vcs c c s s W- W- b u b *- *- u Vub DS DS * Vub Vcs p0 B0 B- p+ d d u u • Decay via b → u spectator Diagram • Clean measurement for Vub -No penguin terms • Model independent • Not yet seen • Importantinput for measuring Sin(2β+γ) CKM Matrix
b *+ DS * Vcb Vud s W s K- d u Motivation- • Evidence for W-exchange • First seen in B0→ Ds-K+decay • PRL 89, 231804(2002) • Not seen • Role of the final state interactions • Br can be as large as 10-4 • D+-, D00 can turn out to beDs*-K+ • (B. Block et al. PRL 78, 3999, 1997) c B0
Past Measurements & Theoretical Predictions -PDG 2004 Theoretical predictions A. Deandrea et al. Phy. Lett. B 318, 549(1993)
Theoretical predictions a1~1.0, Vub~.003, Vcs~0.97 → → D. Choudhry et al. Phy. Rev. D, 45, 217(1992)
KEKB Accelerator • Asymmetric Collider with, • 8.0 GeV e- x 3.5 GeV e+ • 22 mrad crossing angle • Lpeak = 15.33nb-1s-1 • ∫Ldt ~400 fb-1 • Ecm = 10.58 GeV operates at (4S) resonance e+e-→ (4S) →BB (4S) center of mass frame
Belle Detector Aerogel Cherenkov cnt. KL/µ Detector CsI Calorimeter 3.5 GeV e+ TOF counter SC solenoid 8GeV e- Silicon Vertex Detector (SVD) Central Drift Chamber (CDC)
Belle Detector • Silicon Vertex Detector (SVD) • Tracks low momentum particles with CDC • Vertex reconstruction, 18 µm • Central Drift Chamber (CDC)Mom. of charged particles is measured from the curvature of the track traversing in the magnetic field • PID using dE/dx - energy loss by ionization of the matter • Aerogel Cerenkov Counter (ACC) • Index of refraction ranges from 1.01 to 1.03 • K/ ID between 1.2 – 4.0 GeV/c TOF counter K/ separation using timing of plastic scintillation counters CsI Calorimeter Measure energy of e’ns and via detection of scintillation light from e.m. showers. KL/µ Detector Detect high mom.(>600 MeV) K/µ SC Solenoid Generates 1.5 T mag. field
Particle Identification (PID) at Belle • Uses information from CDC, TOF, and ACC • Combine the information using Likelihood method Pi – likelihood for signal species Pj – likelihood for background species Where i, j {e, , K, , p}
Used 250 fb-1 data at (4S) Center of Mass resonance • 274.8 million BB events Decay Chain B0→ Ds*+-, B0→ Ds*-K+, B+→ Ds*+0 Ds*+→ Ds+ Ds+ → {+, KSK+, K*K+} →K+K-, KS→+-, K*→K+- Conjugate modes are also assumed
Data Data Reconstruction of and, K*0 →K+K- Kaon ID > 0.6 1.0116 < M(KK) < 1.0272 GeV (±3 of the nominal mass) K*0→K+- K/ ID > 0.6 |M(KK) – 0.8961| < 0.060 GeV (±3 of the nominal mass)
Helicity Angle Helicity angle(θh) – Angle between momentum of DS and momentum of K in (K*) frame. • Flat dist. for background events. • Cos2(θ) dist. for signal events. • Selection requirement, • |cos(θh)| > 0.3 Bg. evts. Signal evts.
Data Reconstruction of K0s K0s→+- Pion ID > 0.6 0.4902 < M(+-) < 0.5051 GeV (±3 of the nominal mass) 2< 30 (vertex reconstruction fit) Other cuts: dr > 0.009 cm; d < 0.2 rad dr – smaller of dr1 and dr2, where dr1 and dr2 are the smallest approach from the IP to the two tracks in x-y plane d- angle betn. the momentum vector and decay vertex displacement vector in r- plane Signal Events Background Events dr(cm) dr(cm) d(rad) d(rad)
Photon Energy (Eg) Bg. Signal Reconstruction of DS+and DS*+ ±3 of the nominal mass (1968.5±0.6 MeV) 1.9539 < M() < 1.9833 GeV 1.9471 < M(KSK) < 1.9901 GeV 1.9495 < M(K*K) < 1.9877 GeV momentum selection 1.7< P(cms) < 2.5 GeV M = M(DS*)-M(DS) M has better resolution than mass. 0.124 < M < 0.164 GeV A large portion of the background is accounted by photons that are not really coming from DS*. E(cms) > 110 MeV 0 veto – reject if 0.12 < M() <0.15 GeV GeV
GeV GeV/c2 B→Ds*+- (Ds+→+) Selection of the B Candidate Two quantities M(B) and E are defined as, E vs. M(B) Signal MC where Ebeam = 5.29 GeV, Pi- mom. of B, Ei-energy of B Signal Region, –0.05 < E < 0.05 GeV for h {, K} –0.10 < E < 0.05 GeV for h {0} 5.27 < M(B) < 5.29 GeV/c2
Largest background source is e+e-→ qq (q{u,d,s,c}) events Fisher Discriminant is a powerful tool to discriminate signal and background Background Suppression – Fisher Discriminant (FD) • A linear combination of 9 variables • Optimized to discriminate signal from background
Cos(θth) – Angle between thrust axis of the B candidate • and the thrust axis of the remaining particles. • Cos(B) – Angle between the B momentum & beam axis • qr x (QD) – qr contains flavor information of the other B; • q = ±1; 0<r<1; QD – charge of Ds Where is a unit vector s. t. it maximizes T is the mom. of the ith particle in CM frame s s Combine all 9 variables into F Background Suppression – Fisher Discriminant (FD) (cont.)
Used Figure of Merit (FOM) vs FD plots to decide the best selection Background Suppression – Fisher Discriminant (FD) (cont.) All the parameters are optimized to get the maximum discrimination between signal and background continuum Signal Arbitrary units s - Signal b - background FD
N - inclusive Ds* yield ; - efficiency ; Reconstruction Efficiencies • First used Sig. MC – fitting M(B) • Observed inconsistency among the yields of DS sub modes • Minimized MC dependence by using inclusive M • Efficiency for mode obtained using sig. MC • Total eff. obtained by multiplying by eff. of the other cuts Following relationships can be obtained
Sideband Study • Sidebands of Ds and M used • 3 from lower and upper side of the signal region • used to compare data and MC • Background shapes were obtained Observations: • Bkg. shapes of data and MC agree each other • Observed a disagreement in bkg. levels ~12% – 22% • Bkg. of Ds not random – real Ds but not from Ds*→Ds
Simultaneous Fitting • Simultaneous fitting of 3 DS sub decay modes • Common branching fraction for all 3 DS sub-decay modes M-1D • Signal - Gaussian shape with mean & fixed to sig. MC shape • Bkg. - linear shape, by fitting data excluding the signal region E-1D • Signal - Gaussian shape with mean & fixed to sig. MC shape • Bkg. - sideband shapes of M Lmax - max. likelihood L(0) – max. likelihood if signal is zero
Simultaneous fitting - cont. Ds*+- Ds*-K+ E fit Solid line (red) – total fit dotted line (blue) - background Ds*+0
Simultaneous fitting - cont. DS*+- DS*+K- • M fit • Solid line (red) – total fit • dotted line (blue) - background DS*+0
Systematic Uncertainties Since 3 Ds modes, Total Syst. error = common syst. errors + indept. syst. errors Common Errors (%)
Systematic Uncertainties-cont. Independent Errors
RD* for Sin(21+3) D* - strong phase,c – Cabibbo angle D. Becirevic, Nucl. Phys. Proc. Suppl. 94, 337 (2001) - good agreement with the expected result which is ~0.02
Estimation of Vub -Good agreement with the world average for |Vub| which is (3.67±0.47)x10-3
Used 278.4 million events • M fits give more consistent results • Both M and E results agree within errors • Obtained estimates for Vub and RD* Summary
M and E DS*+- DS*-K+ DS*+0 (2.14 0.81)x10-5 (2.43 1.11)x10-5 (1.64 0.66)x10-5 M E
Combined yields from M fit (274.8 m evts.) DS*+- 19.0±5.7 evts DS*-K+ 11.0±4.8 evts DS*+0 9.4±5.5 evts
Combined yields from E fit (274.8 m evts.) 4.48.4 evts. 15.15.6 evts. 8.24.7 evts.
Combined yields from M(B) fit (274.8 m evts.) DS*+- 21.4±5.9 evts. DS*-K+ 10.6±4.9 evts. DS*+0 8.1±5.7 evts.