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Hadronic B Decays To Double-Charm Final States

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Hadronic B Decays To Double-Charm Final States. SERGIO GRANCAGNOLO L.Lanceri – J.P.Lees BINP Novosibirsk Particle Physics Seminar. Outline. Introduction The BaBar Detector at PEP-II The D sJ observations Theoretical Interpretations of D sJ Analysis of B D (*) D sJ decays

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  1. Hadronic B DecaysTo Double-Charm Final States SERGIO GRANCAGNOLO L.Lanceri – J.P.Lees BINP Novosibirsk Particle Physics Seminar

  2. Outline • Introduction • The BaBar Detector at PEP-II • The DsJ observations • Theoretical Interpretations of DsJ • Analysis of BD(*)DsJ decays • Results: branching fractions and angular distributions • Comparison with models and conclusions Sergio Grancagnolo

  3. Introduction

  4. The Standard Model • Fundamental particles: • 6 quark , 6 leptons • 4 interactions • The model works well but there are several issues to be understood, for instance: • Higgs boson • Supersymmetry • Strong interactions W,Zbosons Sergio Grancagnolo

  5. Quantum Numbers Of The Quarks Quark Property Sergio Grancagnolo

  6. CKM Matrix and Unitary Triangle qi=u,c,t Unitary relationship CKM W+ Vij qj=d,s,b A complex phase in the V matrix can be a source of CP violation in B decays VV†=I VudVub*+VcdVcb*+VtdVtb*=0 a VtdVtb* VudVub* Unitary triangle g b VcdVcb* Sergio Grancagnolo

  7. _ _ _ _ _ Mesons in the Quark Model • Quarks exist only in baryons and mesons • Mesons are made of a quark-antiquark pair • As an example: • Mesons are not stable • Mass, charge and lifetime are main characteristics • Meson width~ 1/lifetime depends on the allowed decay modes Sergio Grancagnolo

  8. sQ sq q _ Q Heavy Quark Approximation ℓ In the heavy quark approximation mq<<mQ,, mQ sQ, j conserved However J, P good quantum numbers Sergio Grancagnolo

  9. Charmed Mesons Spectroscopy _ _ • States with ℓ=1 can decay strongly with emission of a pseudoscalar meson • j=1/2 emission in s-wave • j=3/2 emission in d-wave • D*0,D´1observed by CLEO, Focus and Belle • Broad resonances as expected ℓ=0 ℓ=1 broad ~100 MeV narrow ~10 MeV Sergio Grancagnolo

  10. _ The expected cs Meson Spectra M.Di Pierro, E.Eichten Phys. Rev. D64, 114004 (2001) 2.51 GeV 2.36 GeV States expected but not observed • Masses over threshold DK(*) • Broad states (large widths) * Sergio Grancagnolo

  11. B Meson Decay • Spectator quark model the other u,d quark enters the final state without participating to the interaction • In hadronic decays, could be tested the factorization hypothesis: the final hadrons are produced independently Since mb >>mu,d the B meson decay dominantly through the disintegration of the b quark. The main transition W* ℓn semileptonic is the weak decay bcW* where _ hadronic W* qiqj W* virtual boson Sergio Grancagnolo

  12. _ - _ _ _ _ Exclusive Hadronic B decays • In exclusive decays all particles in final state are reconstructed • Double charm decays contains two mesons with charm quarks • Examples: Ds- BDsD _ D(*)0,D(*)+ B-,B0 D(*)0 K(*)- B DDK B-,B0 D(*)0,D(*)+ Sergio Grancagnolo

  13. The BaBar Experiment

  14. The PEP-II B-factory at SLAC PEP-II is a high luminosity, asymmetric, e+e- collider Integrated luminosity Lint=254 fb-1 113fb-1 Ldesign = 3 x 1033 cm-2s-1 Lpeak = 9.21 x 1033 cm-2s-1 Sergio Grancagnolo year

  15. B-factory Cross Sections E(e+) = 3.1 GeV E(e-) = 9.0 GeV The boost allows a separation of the two B vertices. boost: bg=0.56 Ecm=10.58 GeV _ _ U(4S)BB _ _ _ s[e+e- hadrons](nb) _ √s(GeV) _ _ e+e- bb on-resonance BB _ “coontinuum”e+e- cchigh momentum charmed particles Sergio Grancagnolo

  16. BABAR Detector 1.5 T solenoid Electromagnetic Calorimeter e+ (3.1 GeV) Cerenkov Detector (DIRC) e-(9 GeV) Drift Chamber Silicon Vertex Tracker Instrumented Flux Return Sergio Grancagnolo

  17. The DsJ observations

  18. DsJ(2317) Discovery * + • BaBar discovered a new particle decaying into Dsp0 • c and s quarks • Mass < DK threshold • Width < 10 MeV • Seen by Belle and CLEO • Is this the expected Ds0? BaBar collaboration Phys.Rev.Lett. 90, 242001 (2003) + _ Dsp0Invariant mass + *+ m=2.317GeV GeV Inclusive selection of high momentum charmed meson from coontinuume+e- cc _ Sergio Grancagnolo

  19. DsJ(2460) Discovery + • CLEO observed another state decaying to Ds p0! • c and s quarks • Mass < (DK)* threshold • Width < 10 MeV • Observed also decay modes: • Dsg, Dsp+p- • Is this the expected Ds1? CLEO collaboration Phys. Rev. D68, 032002 (2003) *+ _ Ds p0Invariant mass *+ 80 60 m=2.460 GeV Events/7 MeV/c2 40 20 0 + + 2.25 2.5 2.75 GeV + Seen by BaBar and Belle Sergio Grancagnolo

  20. _ The Observed cs Meson Spectra 2.51 GeV 2.36 GeV New states observed • Masses below threshold DK(*) • Narrow states * Sergio Grancagnolo

  21. Isospin Violation in These Decays • Isospin symmetry is not exact • Violation already observed in Ds* Dsp0 decay _ _ _ _ _ _ _ DsJ Dsp0 Invoked hp oscillation P.L.Cho, M.B.Wise Phys.Rev.D49: 6228-6231,1994 Sergio Grancagnolo

  22. Theoretical Interpretations of DsJ Standard interpretations Exotic interpretations

  23. Standard interpretations Entia non sunt multiplicanda praeter necessitatem (G.Occam) • Quark models • Potential: coulombian • (0-,1-),(0+,1+) chiral partners • doublets mass splitting via chiral symmetry breaking • transitions via scalar meson + linear Cahn, Jackson + spherical not linear Lucha, Schoberl need to adjust a posteriori input parameters, predict mass higher than observed or not reproduce non-strange charmed mesons spectra Bardeen, Eichten, Hill hyperfine splitting for charmed mesons (D, D*, etc.) marginally compatible with experiments Sergio Grancagnolo

  24. Standard interpretations • Unitarized chiral models • generalization replacing a light quark with an heavy quark • Non-perturbative methods • lattice QCD • QCD sum rules Beveren, Rupp several new mesons predicted not observed Bali initial difficulties to reproduces masses, reproduces mass splitting Dai, Huang, Liu, Zhu low accuracy Sergio Grancagnolo

  25. D K Ds p Exotic Interpretations Barnes, Close, Lipkin Dsp molecule cs  DK  4-q mixing DK molecule Szczepaniak Browder, Pakvasa, Petrov D _ _ _ _ qq qqqq K di-quark pairs _ qq Maiani, Piccinini, Polosa, Riquer _ qq Sergio Grancagnolo

  26. Analysis of BD(*)DsJ decays Branching ratios: Method Event selection Signal and Backgrounds Efficiency and “cross-feed”

  27. BD(*)DsJ Decays • ExclusiveDsJ production: expected to be dominant • Allow to measure DsJquantum numbers • In principle, allow to discriminate between conventional and multi-quark scenarios compared with other B decays such as BD(*)Dsand BD(*)D(*)K • If the DsJ is the conventional cs state should be produced in the following graph: _ _ Weak external W emission DsJ- - _ _ _ _ _ D(*)0,D(*)+ B-,B0 Same graph as BD(*)Ds similar branching ratios could be expected Sergio Grancagnolo

  28. BD(*)DsJ Decays (II) • We search for DsJ particles looking at the 12 combinations: • With DsJ decays: • We measure branching ratios, quantum numbers JP Sergio Grancagnolo

  29. Subdecay Modes Intermediate particles are reconstructed in the following modes: Green::clean modes Total: 60 different submodes combined to give the 12 combinations Sergio Grancagnolo

  30. Analysis Goal and Method • We aim to measure branching ratiosBri (i=1…12) of the exclusive double charm two body production of DsJ(2317)+and DsJ(2460)+in B0and B+ • nisignumber of signal candidates for mode i • after combinatorial background subtraction • nixfdnumber of crossfeed events for mode i • contains background from other signal modes • eireconstruction efficiency from simulation • NBB= [122.0 ± 0.6(stat) ± 1.3(syst)]  106 (113 fb-1) * _ Sergio Grancagnolo

  31. _ D0 Ds + DsJ(2460)+ * A specific example: B0D*-DsJ(2460)+ * • Reconstruct the chain: • Reconstruct tracks (K,p) and photons (g) • Select D0, Ds , f, p0computing invariant masses • Use beam energykinematicconstraint • Fit nisig in Dsg invariant mass distribution K+ K+ p- f D*- p- K- p+ B0 g Sergio Grancagnolo

  32. Event Selection: Invariant Masses Invariant mass: D0 Kp Dsfp D* D0p fKK 40000 20000 0 0.99 1.02 1.04 m(f)(GeV/c2) Particles masses are set to their nominal values (mass constraint) Sergio Grancagnolo

  33. Event Selection: B candidates • Compute p*B and E*Bfrom selected D*, Ds, g • Use the B-factory constraint E*beam to compute: 5.272<mES<5.288 GeV mES “Signal box”: |DE|<32MeV Use of beam kinematic variables better resolution ΔE uncorrelation Sidebandsto estimate background outside signal box Sergio Grancagnolo

  34. DE resolution • Same resolution for all the submodes • A systematic error will take in account differences between data and simulation Simulation of signal events Data candidates in mES signal region s(DE)=16.1 s(DE)=18.9 Cross-hatched background from sidebands Missing energy effect Sergio Grancagnolo

  35. DE resolution (II) Final values used in selection (MeV) Better resolution for modes with a p0 (mass constraint) Sergio Grancagnolo

  36. Background Rejection • Reduction of the combinatorial background • Simulated signal events selected in signal region • Background from data events selected in DsJ mass sideband region • Curves represent fraction of events cut by m(D0g)> mcut(D0g) • Optimal cut set at the maximum separation between two samples m(D*g) cut Events rejected: 25% signal 75% backgrd m(D*g)>2.4GeV/c2 Gev/c2 Sergio Grancagnolo

  37. Optimization • Maximized the significance ratio: S = simulated signal events in signal region B = background from data in m(DsJ) sidebands Tried different cut levels for D and Dsusing PID, vertexing and helicity cut f cos(qhel) f mass 5000 40000 2500 20000 Tried different numbers of s cut for variables: DE, m(Ds), m(D) -1 1 1.94 2.0 cos(qhel) m(f) Cleaner modes require less stringent cuts Sergio Grancagnolo

  38. Fit nisig in DsJ(2460)+Ds+g m(Dsg) • Finally, in selected candidates: m(Dsg) • Fit the background shape with a polynomial • Fit the signal peak with a Gaussianof fixed width • s=12 MeV • estimated in data • Events in the signal peak: Entries/10 Mev/c2 GeV/c2 significance=11.7 nisig = 53.0±7.7 Sergio Grancagnolo

  39. Efficiency and Cross-feed • From gi=60k simulated signal events for each mode i • Efficiency: nisim= number of B0D*-DsJ(2460)+ events reconstructed in the corresponding simulated sample • Total cross-feed: nijsim= number of B0D*-DsJ(2460)+ events reconstructed in the simulated sample (mode j) fij= cross-feed from the mode j to the mode i Typical efficiency range: 1-10% depending on the presence of photons, soft tracks, stringent cuts, etc. ; Sergio Grancagnolo

  40. Narrow Cross-feed Efficiency Reconstructed mode: B0D*0Ds1- [Ds-g] m(DsJ) Generated mode: B0D*0Ds1- [Ds-g] nisim= 2778 gi=60000 ei=(4.63±0.08)% Cross-feed Generated mode: B0D*+Ds1- [Ds+g] nijsim= 24 gj=60000 fij=(0.82±0.04)% Narrow: sxfdssig Sergio Grancagnolo GeV/c2

  41. Wide Cross-feed Efficiency Reconstructed mode: B0D0Ds1- [Ds-g] m(DsJ) Generated mode: B0D0Ds1- [Ds*-p0] nisim= 1350 gi=60000 Cross-feed ei=(2.25±0.07)% Generated mode: B0D*+Ds0- [Ds-p0] nisim= 144 gi=60000 fij=(0.24±0.02)% Cross-feed nisim= 162 gi=60000 Generated mode: B0D*0Ds0- [Ds-p0] fij=(0.27±0.02)% Wide: sxfd 2.5 ssig Sergio Grancagnolo GeV/c2

  42. Branching Ratios and Cross-feed An iterative procedure is needed: • Compute for each mode i without considering cross-feed • Estimate nixfdusing Brj and the cross-feed fij from all the modes • Subtract the number of cross-feed events • Compute the corrected branching ratio • Recompute the cross-feed iterating point 2-4 until convergence. __ Sergio Grancagnolo

  43. Results

  44. Fit Results And Significance s=5.5 s=4.2 s=5.0 s=5.2 s=7.4 s=11.7 s=3.1 s=5.1 s=4.3 s=6.0 s=7.7 s=2.5 Sergio Grancagnolo

  45. Main Systematic Errors Depends on the tracks or photons number • Tracking efficiency 9% • g/p0 efficiency 5% • Background fitting model5% • Tried exponential instead of polynomial to fit background • DE width 5% • Changed the width of the DE signal region by ±3 MeV • DsJ width 3% • Varied by ±1 MeV the s of the Gaussian (12 MeV) that fit the signal Modes with D*0 more affected Sergio Grancagnolo

  46. Branching Ratios Results Phys.Rev.Lett.93:181801,2004 NEW! NEW! NEW! NEW! NEW! NEW! Sergio Grancagnolo Measurements with significance>5

  47. DsJ(2460)+ Angular Analysis (I) _ • Use B0DsJ+D-and B+DsJ+D0 with DsJ+Dsg • B DDsJ+is a transition 0- 0- JP so DsJis polarized • Compute the helicity angleqh of DsJ+Dsgand compare with the predictions for JP=1+ and JP=2+(0+forbidden) Sergio Grancagnolo

  48. DsJ(2460)+ Angular Analysis (II) DsJ events are fitted separately in 5cos(qh) bins not used cut m(Dg)>2.3 Sergio Grancagnolo Simulation is used to correct for detector acceptance

  49. DsJ(2460)+ Angular Analysis (III) • Expected distribution for JP=1+ is: 1-cos2(qh) • Distribution compatible with this case • c2/d.o.f.=3.9/4 • Supporting the Ds1+ hypothesis for this state • Comparison with JP=2+ hypothesis is also provided • c2/d.o.f.=34.5/4   Sergio Grancagnolo

  50. Some Comparisons With Models • Branching ratios smaller than the corresponding BD(*)Ds(*) • Factorization effects could be important and could not cancel in the ratios RD0,1 • support a multiquark hypothesis • Observation of electromagnetic DsJ(2460)+ decay • supports a conventional cs picture • In agreement with prediction from chiral multiplets we measure: Colangelo, De Fazio, Ferrandes: Mod.Phys.Lett. A19:2083,2004 Godfrey Phys.Lett. B568:254,2003 _ Bardeen, Eichten, Hill: Phys.Rev. D68:054024,2003 Sergio Grancagnolo