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Bc Meson Physics

Bc Meson Physics. Chao-Hsi Chang ( 张肇西 ) I.T.P., Chinese Academy of Sciences. 1. The meson Bc 2. Mass, lifetime & decays 3. Production (theoretical estimates) a. Production at Z 0 (at LEP-I) b. Hadronic Production (at Tevatron & LHC) 4. Experimental status

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Bc Meson Physics

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  1. Bc Meson Physics Chao-Hsi Chang (张肇西) I.T.P., Chinese Academy of Sciences 1. The meson Bc 2. Mass, lifetime & decays 3. Production (theoretical estimates) a. Production at Z0 (at LEP-I) b. Hadronic Production (at Tevatron & LHC) 4. Experimental status 5. Prospect for LHC 6. Comment on Ji’s paper Bc meson physics

  2. 1. The meson Bc Of the six quarks u c t d s b - u, d, s, light - c, b, t , heavy (top lifetime τ too short to form hadrons) Bc: double heavy explicit-flavored meson (unique) Experimental studies are at the stage: 1998-discovery, 2005 new results, …… Bc meson physics

  3. 2. Mass, lifetime & decays Bc mass: according to PM & Lattice QCD Bc lifetime: Weak decay only (no strong &EM decay) According to spectator model and B & D mesons’ lifetime: we may obtain (the earliest 1994: PRD 49 3399) More careful estimate invertex detectorability Bc meson physics

  4. 2. Mass, lifetime & decays Phys. Rev. D. 64, 014003, 2001 : : : : Bc meson physics

  5. 2. Mass, lifetime & decays Bc decays: weak decays (Mandelstam formulation & instantaneous BS equation) Bc meson physics

  6. 2. Mass, lifetime & decays Mandelstam formulation (Composite quantum field theory) Transitions (decays with great momentum recoil) Bc meson physics

  7. 2. Mass, lifetime & decays Bc meson physics

  8. 2. Mass, lifetime & decays Bc meson physics

  9. 2. Mass, lifetime & decays Bc meson physics

  10. 2. Mass, lifetime & decays The results for various decays • Pure leptonic (radiative) decays : The radiative decays escaped from chiral suppression ! Bc meson physics

  11. 2. Mass, lifetime & decays • Semileptonic decays (S-wave product): One I-W function Bc meson physics

  12. 2. Mass, lifetime & decays • Semileptonic decays (P-wave product or ): Two I-W functions Spectrum of charged lepton in the decays: Recoil one Normal one Bc meson physics

  13. 2. Mass, lifetime & decays • Nonleptonic decays (S-wave product): Bc meson physics

  14. 2. Mass, lifetime & decays • Nonleptonic decays (P-wave product or ): Bc meson physics

  15. 2. Mass, lifetime & decays • The lifetime is quite long that the vertices of • production and decay can be detected by vertex • detector experimentally (in the window). • Sizable decay channels are rich. • The branch ratio of the decay to is • quite great. • The branch ratio of decay to or is large. • Radiative pure leptonic decays escape from chiral • suppression. • ……. Bc meson physics

  16. 3. Production (theoretical estimates) • It had not expected the difficulty of Bc production • before our prediction for such `light meson’ Bc • (LUND model is not applicable): • The reliable theoretical prediction (most favorable • mechanism): • At Z0 (LEP-I) Bc can be produced marginally. • Only at very high energy hadronic colliders • (Tevatron and LHC) numerous Bc mesons can be • produced for experimental studies. Bc meson physics

  17. 3a. Production at Z0 (at LEP-I) 微扰因子 We explicitly pointed out LUND model is not applicable and the mechanism should be as the left figure. The key point is the hard gluon & it can be QCD factorized as indicated by the figure. PRD46, (1992) 3845; PLB284,(1992) 127;…… + … Z0 硬胶子 The result is that at Z0 peak for LEP-I several thousands of Bc may be produced per year ! Considering the detecting efficiency, to observe Bc at LEP-I is on the margin. Bc meson physics

  18. 3b. Hadronic Production at Tevatron & LHC 微扰因子 Gluon-gluon fusion mechanism dominant Subprocess: 硬胶子 36 Feynman diagrams for complete calculations The information about the accompany quark-jets interests experimentalists QCD factorization: Bc meson physics

  19. 3b. Hadronic Production at Tevatron & LHC • The lowest order calculations: • uncertainties from Bc meson physics

  20. 3b. Hadronic Production at Tevatron & LHC Tevatron LHC Bc meson physics

  21. 3b. Hadronic Production at Tevatron & LHC and Bc meson physics

  22. 3b. Hadronic Production at Tevatron & LHC Uncertainties:quite great; sensitive to Q2, mc high order calculation can suppress them but too complicated. Bc meson physics

  23. 3b. Hadronic Production at Tevatron & LHC P-wave excited state production To match the wave functions correctly (special attention on the spin structure), we start with the Mandelstam formulation on BS solution: Bc meson physics

  24. LHC TEVATRON 3P2 1P1 1P1 3P1 3P1 3P0 3P2 3P0 3b. Hadronic Production at Tevatron & LHC Bc meson physics

  25. 3b. Hadronic Production at Tevatron & LHC Color octet may be comparable with that of color singlet Color-singlet (P-wave): Color-octet (S-wave): Bc meson physics

  26. 3b. Hadronic Production at Tevatron & LHC LHC Tevatron Bc meson physics

  27. 3b. Hadronic Production at Tevatron & LHC Color octet may be comparable with that of color singlet Color-singlet (P-wave): Color-octet (S-wave): Bc meson physics

  28. 3b. Hadronic Production at Tevatron & LHC Intrinsic charm & bottom mechanisms: Intrinsic charm mechanism (general-mass variable-flavor-number GM-VFN scheme): Gluon-gluon fusion mechanism (in fixed flavor number FFN scheme and in GM-VFN scheme): There is a ‘double counting’ (in GM-VFN scheme) due to structure functions, so one must deduct it when summing up the contributions from the two mechanisms. Bc meson physics

  29. 3b. Hadronic Production at Tevatron & LHC Bc meson physics

  30. 3b. Hadronic Production at Tevatron & LHC LHC: Tevatron: Bc meson physics

  31. 3b. Hadronic Production at Tevatron & LHC GM-VFN intrinsic + gg-fusion LHC: FFN gg-fusion Tevatron: Intrinsic charm and bottom in GM-VFN scheme makes difference from general FFN scheme only at very small Pt region. Bc meson physics

  32. 3b. Hadronic Production at Tevatron & LHC • The cross section of Bc at LHC is greater than that • at Tevatron by one or two order of magnitude • The uncertainties are quite big at LO QCD • The cross section is at the order 10-3 of B meson • production Experimental needs of the M.C. generator: Difficulties of the experiments in Hadronic Collider High efficiency for the generator Signals for feasibility studies Generator: BCVEGPY1.0 (S-wave, helicity techniques ) BCVEGPY2.0 (S,P-wave, Color-octet,…) CPC Lib. & hppt://www.itp.ac.cn/~zhangzx/ Bc meson physics

  33. 4. Experimental status We predicted LEP-I may and may not observe Bc meson. LEP-I (at Z0 peak): ALAPH DELPHI OPAL tried to observe Bc seriously The result: Cannot conclude:`discovery of Bc meson’ due tosmall `statistics’ but itconsists with the prediction ! Bc meson physics

  34. Chicago  Booster CDF DØ Tevatron p source Main Injector (new) Discovery of Bc meson (CDF at Tevatron) Bc meson physics

  35. - The only previous evidence by CDF RunI CDF discovery (1998 Observation) - 110 Pb-1 data PRD 58 (1998) 112004 Bc±  J/y(m+m-) m± n -- Br~2.4% + trilepton final state + easy to trigger Bc meson physics

  36. Experimental progress (D0 result) D0 result (ObservationINew, 2004) Events Selection: ICHEP'04 & Fermilab 4539-conf - 210pb-1 data - di-muon triggered - M(m+m-)within 0.25 GeV of J/y - a third track (pT>1.5) with best common vertex fit to J/y(mm) : “J/y+1 track” data control sample - The third “+1” track should be muon, with M(J/ym) ＜8 GeV After Selection: • due to missing neutrals, the select samples are polluted by background severely • use (ym) invariant mass and pseudo proper time distributions to fit Bc meson physics

  37. Bc mass log likelihood Background shape (data): • Divided into 2 subsets: • 1) “prompt” J/y（T<0) • 2) “heavy flavor” from B (T>0) • Cross-checked with • y(2S) + 1 track bkg dominated data • Use J/y+1 track control data sample Signal shape (MC): Bc Fit: - MC templates of MBc 5.5 – 6.7 with 0.1GeV interval - Full detector smearing + Selection Extract signal from a combined unbinned likelihood fit to J/ym invariant mass and proper time 5.95 ±0.34 GeV +0.14 -0.13 Experimental progress (D0 result) Bc meson physics

  38. Number of events Total 231 Signal 95.5±11.8 Prompt 66.0 Heavy F69.5 Experimental progress (D0 result) “Floating” fit signal + bkg distributions: With significance SB in excess of 5 standard deviations Bc meson physics

  39. Simple counting analysis - normalize background J/y+1 track sample to selected sample with T>2 - check excess consistency with data Experimental progress (D0 result) Consistency check: Fit w/o signal D2log(likelihood)=60 for 5 degrees of freedom Bc meson physics

  40. Mass: 5.95 ±0.34 GeV/c2 +0.14 -0.13 Lifetime: 0.448 ±0.121 ps +0.123 -0.096 Experimental progress (D0 result) D0 results: • Preliminary results on Bc with significantly more statistics Events: 95 ± 12±11 in some 200pb-1 Bc meson physics

  41. Experimental progress (CDF result) CDF result (Observation IINew, 2005) hep-ex/0505076 The observation II ofBc  J/y(m+m-) p+ Exclusive process (mass measurement) Theor. Refs.: BCVEGPY CPC 159 192, (2004) Uncertainties Eur. Phys. J. C. 38 267, (2004) Special Acknowledgement (to us) Bc meson physics

  42. Experimental progress (CDF result) 360 pb from the `` '' -trigger stream The significance function (score function ) S = Monte Carlo signal B = measured background The control sample (important): Bc meson physics

  43. Experimental progress (CDF result) Bc meson physics

  44. Experimental progress (CDF result) Bc meson physics

  45. Experimental progress (CDF result) vs (m-100MeV~m+200MeV) Bc meson physics

  46. Experimental progress (CDF result) The mass of Bc (mBc) Bc meson physics

  47. Experimental progress (CDF result) Summary(CDF RUN-II, ECM=1.96 TeV, 360pb-1) 18.9±5.7 events New Result (version 2) mBc=6285.7±5.3(stat)±1.2(syst) MeV/c2 Bc meson physics

  48. 5. Prospect for LHCb i).Repeat Tevatron results (mass, lifetime etc) P+P→ Bc+… Bc → J/ψ+ l++ν J/ψ+ π (ρ) ii). New decay chennals (relative branching ratios) P+P→ Bc+… Bc → χC (hC) + l++ν χC (hC) + π(ρ) Bs (Bs *)+ l++ν Bs (Bs *) + π(ρ) etc Bc meson physics

  49. 5. Prospect for LHC iii). Deeper studies (with profound understanding the beam and your detector) Precise measurements of the production: The mechanisms (NRQCD) Excited Bc (P-wave) production etc. (potential model) Form factor measurements in semileptonic decays etc Study of the ‘self-tag’ of Bs ( for mixing) Bc → Bs (Bs *)+ l++ν Bs (Bs *) + π(ρ, a1) etc Something else Bc → light hadrons+ l++ν (color octet in Bc) Bc meson physics

  50. K+ m+ h+: p, r,m,e(n) tracks: pT~100-500MeV, too soft, off-line only p- (100%) K0* ※ K- (3.3%) Ds-: 147mm 1.968GeV ※ Bs: 438mm 5.4GeV Oscilla. (8%) ? nm Bc: 140mm 6.4GeV (36%) ※ beam PV beam About the source for tagged Bs - Bc  Bs + h+ + X? - associated h+ + Bs(m)  Bc tag, e.g. open angle, invariant mass in Bc window,common vertex? Br ~ 36%×8%×3.3%×100%~1×10-3 - Br[ BcBs +h++X ]or/andBs CP violation source? motivation and detail crucial to Bc decay vertex, namely no n in Bs decay Bc meson physics

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