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Production and decay of the meson Bc

Production and decay of the meson Bc. —— A brief review of theoretical studies ——. Chao-Hsi Chang ( 张肇西 Zhao-XiZhang) zhangzx@itp.ac.cn I.T.P., Chinese Academy of Sciences. Introduction (the meson Bc & its mass) Decay (lifetime, …) Production (Tevatron vs LHC) Outlook.

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Production and decay of the meson Bc

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  1. Production and decay of the meson Bc —— A brief review of theoretical studies —— Chao-Hsi Chang (张肇西 Zhao-XiZhang) zhangzx@itp.ac.cn I.T.P., Chinese Academy of Sciences • Introduction (the meson Bc & its mass) • Decay (lifetime, …) • Production (Tevatron vs LHC) • Outlook (Based on the collaboration with Y.-Q. Chen, X.-Q. Li, C.-D. Lu, C.-F. Qiao, G.-L. Wang, J.-X. Wang, X.-G. Wu, et al) C.H. Chang, ITP, AS Beijing

  2. 1. Introduction (the meson Bc & its mass) 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-flavor mesons (unique in SM) (weak decay only) Very similar to, and very different from, hidden flavored heavy quarkonium J/ψ, ηc, …,Υ,ηb…. Good and new object for tests of PM, NRQCD, Lattice results etc. C.H. Chang, ITP, AS Beijing

  3. 1. Introduction (the meson Bc & its mass) Bc mass : Lattice QCD : I.F. Allisonet al, PRL 94 172001. PM: Y.Q. Chen &Y.P. Kuang, PRD 46, 1165; Eichten & C.Quigg, PRD 49, 5845;….: A. Kronfeld’s talk C.H. Chang, ITP, AS Beijing

  4. 1. Introduction (the meson Bc & its mass) The “early” day’s results Theoretical estimate at Z resonance (LEP-I) : OPAL result PLB 420, 157: Theoretical estimate & LEP-I (ALAPH, PLB 402, 213; DELPHI PLB 398, 207): experimental studies of Bc can be carry out at Tevatron and LHC only! C.H. Chang, ITP, AS Beijing

  5. - The only previous evidence by CDF RunI 1. Introduction (the meson Bc & its mass) Present experimental status: • CDF discovery (1998 Observation) PRD 58, 112004 - 110 Pb-1 data ECM=1.8 TeV RunI Bc±  J/y(m+m-) m± n - Br~2.4% + trilepton final state + easy to trigger • CDF new Observation hep-ex/0505076 - 360 Pb-1 data ECM=1.96 TeV,RunII Bc±  J/y(m+m-) ± mBc=6287.0±4.8(stat)±1.1(syst) MeV/c2, 18.9±5.7 events Note: even Br(Bc±  J/y(m+m-) ± )/Br(Bc±  J/y(m+m-) m± n) not available ! • D0 new Observation ICHEP-04 & Fermilab 4539-CONF - 200 Pb-1 data ECM=1.96 TeV,RunII Bc±  J/y(m+m-) m± n +0.14 Mass: 5.95 ± 0.34 GeV/c2 Events: 95 ± 12±11 -0.13 Lifetime: 0.448 +0.123 ± 0.121 ps -0.096 C.H. Chang, ITP, AS Beijing

  6. 2. Decay Bc lifetime: weak decay only (no strong &EM direct decay) according to spectator model and B & D mesons’ lifetime and annihilation: one may estimate More careful estimate: vertex detector is useful in observation Decay: Pure (radiative) leptonic Semoleptonic Nonleptonic C.H. Chang, ITP, AS Beijing

  7. 2. Decay Bc lifetime (non-spectator effects involved) : : : : In comparison with D & B mesons (input), we obtain: ( ) C.H. Chang, ITP, AS Beijing

  8. 2. Decay • Pure leptonic (radiative) decay • (about measurement of the decay constant fBc): Pure leptonic (tree) decay: (chiral suppression) Radiative leptonic decay (decay constant): (escaped from chiral suppression) QED corrections (one-loop): C.H. Chang, ITP, AS Beijing

  9. 2. Decay Radiative leptonic decay (QED correction to the tree level) in total: Photon spectrum: It is quite difficult for hadronic expt. to measure the decay constant! C.H. Chang, ITP, AS Beijing

  10. 2. Decay • Leptonic decay with light hadrons (color-singlet vs color-octet): Color-singlet: Short distance: Long distance: Charge lepton spectrum: In the decay C.H. Chang, ITP, AS Beijing

  11. 2. Decay Color-octet: Charged lepton spectrum: Color-singlet S-wave (color-octet) P-wave (color-octet) Near the endpoint of the charged lepton in the decay to observe the color-octet components! C.H. Chang, ITP, AS Beijing

  12. 2. Decay • Semileptonic decays : Transitions (decays with great momentum recoil) The key factor: C.H. Chang, ITP, AS Beijing

  13. 2. Decay The ‘wave function’ of bound state equation: To cover a great range of momentum transfer (recoil), BS equation seems to be one of good choices for the problem. Mandelstam formulation(or say composite quantum field theory)to deal with the recoil effects in transitions: C.H. Chang, ITP, AS Beijing

  14. 2. Decay Carry out the contour integrations & : C.H. Chang, ITP, AS Beijing

  15. 2. Decay The semileptonic decays (S-wave) : One I-W function C.H. Chang, ITP, AS Beijing

  16. 2. Decay The semileptonic decays (P-wave or ) : Two I-W functions Spectrum of charged lepton in the decays: Recoil one Normal one C.H. Chang, ITP, AS Beijing

  17. 2. Decay EFT+Factorrization Nonleptonic decays (S-wave product): C.H. Chang, ITP, AS Beijing

  18. 2. Decay Nonleptonic decays (P-wave product or ): C.H. Chang, ITP, AS Beijing

  19. 2. Decay • The lifetime is ‘quite long’ that the vertices of • production and decay can be measured by vertex • detector experimentally • Sizable decay channels are rich • The branch ratio of the decay to is • quite great (form factors) • The branch ratio of decay to or is very large • Study two flavor ‘simultaneously’ (Vcb & Vcs) • Radiative pure leptonic decays escape from chiral • suppression, but to measure the decay constant is • still difficult • The color-octet component might be observable • through • ……. C.H. Chang, ITP, AS Beijing

  20. 3. Production (Tevatron & LHC) Gluon-gluon fusion mechanism dominant Subprocess: ‘Complete LO computation’:information about the accompany quark-jets is kept 36 Feynman diagrams for complete calculations QCD factorization: C.H. Chang, ITP, AS Beijing

  21. 3. Production (Tevatron & LHC) S-wave state production • The lowest order calculations: • uncertainties from The cross-section at LHC is greater than that at Tevatron C.H. Chang, ITP, AS Beijing

  22. 3. Production (Tevatron & LHC) Uncertainty from mC Tevatron LHC C.H. Chang, ITP, AS Beijing

  23. 3. Production (Tevatron & LHC) Uncertainty from PDFs and C.H. Chang, ITP, AS Beijing

  24. 3. Production (Tevatron & LHC) Uncertainty from Uncertainties:quite great; sensitive to Q2, mc . High order calculation can suppress them but it is too complicated. C.H. Chang, ITP, AS Beijing

  25. 3. Production (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: C.H. Chang, ITP, AS Beijing

  26. LHC TEVATRON 3P2 1P1 1P1 3P1 3P1 3P0 3P2 3P0 3. Production (Tevatron & LHC) To see the contributions to Bc & the P-wave characters P-wave production ( color-singlet) C.H. Chang, ITP, AS Beijing

  27. 3. Production (Tevatron & LHC) Color octet may be comparable with that of color singlet Scaling rule of NRQCD: Color-singlet (P-wave) M.E. | |2 | |2 Color-octet (S-wave) M.E. | |2 C.H. Chang, ITP, AS Beijing

  28. 3. Production (Tevatron & LHC) P-wave production color-singlet vs color-octet Color-octet Color-singlet 3P1 LHC Color-singlet 3P2 Color-singlet 3P0 Color-singlet 1P1 Tevatron Color-octet 3S1 Color-octet 1S0 C.H. Chang, ITP, AS Beijing

  29. 3. Production (Tevatron & LHC) • The cross section of Bc at LHC is greater than that • at Tevatron by one and more order of magnitude • The uncertainties are quite big for LO PQCD • The cross section is at the order 10-3 (less) 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,…& Mixture) CPC Lib. & hppt://www.itp.ac.cn/~zhangzx/ C.H. Chang, ITP, AS Beijing

  30. 3. Production (Tevatron & LHC) The generator is tested by comparing with PYTHIA (ours) another The generator is proved to be suitable for the original purpose. C.H. Chang, ITP, AS Beijing

  31. 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 3. Production (Tevatron & LHC) To be a possible source for tagged Bs (at LHC) ? - Bc  Bs + h+ + X? - Bc Bsassociated h+(as a tag for Bs). - Br[ BcBs +h++X ]asBs CP violation source ? Bc decay vertex is crucial . C.H. Chang, ITP, AS Beijing

  32. K+ 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 oscillation (13%) p+ ※ Bc: 140mm 6.4GeV (36%) ※ beam PV beam b-jet (B0,B+) m (pT>1) Br~10%! 3. Production (Tevatron & LHC) - Bs p decay: the Bc decay vertex might be fixed with soft h+ tracks, Br increases by 50% • Them from the other side b-quark fragmentation  Muon + opposite 2nd VTX (on Ds) under feasibility investigation ! C.H. Chang, ITP, AS Beijing

  33. 4. Outlook • Experimental studies on Bc meson have been started at Tevatron • already, and fresh results will be issued ‘from time to time’. • The production cross-section at LHC is greater than that at • Tevatron, so further experimental studies at LHC can be expected. • Some model predictions will be tested. • Theoretical estimates are requested to decrease the uncertainties • and to increase the precision with data being accumulated. • Bc studies may solve some puzzles relating to charmonium • e.g. the observation may clarify up some of contents • in , in meson there are more charm quarks than in meson. • andsome ‘unexpected things’ might be found. • …… C.H. Chang, ITP, AS Beijing

  34. Thanks C.H. Chang, ITP, AS Beijing

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