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Charm Physics Potential at BESIII

Charm Physics Potential at BESIII. Kanglin He Jan. 2004, Beijing hekl@ihep.ac.cn. Outline. Charm physics at threshold Absolute Branching Ratio Leptonic Decay and Decay Constant Semileptonic Decay and CKM Matrix Physics Beyond Standard Model D 0 D 0 Mixing CP violation

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Charm Physics Potential at BESIII

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  1. Charm Physics Potential at BESIII Kanglin He Jan. 2004, Beijing hekl@ihep.ac.cn

  2. Outline • Charm physics at threshold • Absolute Branching Ratio • Leptonic Decay and Decay Constant • Semileptonic Decay and CKM Matrix • Physics Beyond Standard Model • D0D0 Mixing • CP violation • Rare Charm Decay • Summary

  3. Charm Physics at Threshold • Charm threshold • D physics @3.77GeV • Ds physics @4.03GeV and @4.14GeV • Why charm threshold • Pair production of charmed D and Ds mesons • With less or without background • Take the advantage of BEPCII and BESIII • Large data sample • Better mass resolution and particle identification

  4. Charm Cross Section and Event Number for 1 yr running

  5. Absolute Branching Ratio • Precision of Br(D0→Kπ), Br(D+→Kππ), Br(Ds→φπ) are normalization constants for • Precision D, Ds physics • Precision B physics • Precision of Br(D0→Kπ), Br(D+→Kππ) , Br(Ds→φπ) are needed for • Decay constants • Precision of CKM elements • Model independent measurements at BESIII

  6. Tagging Technology(1) • Pair Production of D and Ds mesons • Large Brs (1~10%) of hadronic decay modes • High tagged efficiency • ~5M D tags, >0.2M Ds tags

  7. Tagging Technology(2)Beam Constrain Mass GeV/c2 D+→Kππ Mode

  8. Tagging Technology(3)Kinematic constrain for Double tags D0 Double Tags D+ Double Tags 80 pb-1 Monte Carlo DATA @3.77GeV

  9. Number of observed double tagsin 5fp-1 Ds Data at 4.03GeV ~7000 double tags

  10. Tagging Technology(4) Number of expected single tags Number of expected double tags Combining the single tags and double tags

  11. Precision of Absolute Branching Ratio Improvement after BESIII

  12. Leptonic Decay and Decay Constant

  13. Take the advantage of running at charm threshold Pair production →Double tag method, model independent Take the advantage of BESIII detector High muon identification efficiency →suppress background Take the advantage of BEPCII Large data sample →reduce statistic error Information on the meson wave function Test lattice QCD Extract CKM elements |Vcd|, |Vcs| Theory→ extract |Vtd|, |Vts| Measurement of Decay constantsat BESIII

  14. Analysis Technique • Double tag measurements • Tagged D(s) with hadronic decay modes • muon identification • Absent of isolated photons • Reconstruction of missing mass square →0

  15. Measurement of fDs

  16. Precision of fD(s) (1) Major Uncertainty

  17. Precision of fD(s) (2) Great improvement after BESIII

  18. Semileptonic decay and CKM Matrix D(s) Form Factor p

  19. Measurement of CKMat BESIII • Good performance of BESIII detector • e/π/μ identification • mass resolution • Extract |Vcd|, |Vcs| • Form factor shape and normalization • Γ(q2) describe the contribution of form factor, it was calculated from lattice QCD. • The shape of form factor are helpful to theory. • Extract the ratio of |Vcd/Vcs| • Extract |Vub| from B physics →Theory

  20. Analysis Technique • Hadronic tag • PID • Umiss Signal Background Signal Background (GeV/c)

  21. Precision of Branching Ratioof D0, D+ Semileptonic Decay

  22. Precision of CKM Form factor term ΔΓ/Γ，come from theory (Lattice QCD). Supposing ΔΓ/Γ ~3% , BESIII will get

  23. Form Factors From semileptonic decay of charm meson, dN/dq2 will provide information on form factors (under studying)

  24. Physics Beyond Standard Model • D0D0 Mixing at ψ(3770) • In SM, mixing is very small(10-6). • BESIII is sensitive to 10-4 • Possible to measure the phase shift • CP violation in charm decays • SM predicts the ACP may be as big as 10-3. • BESIII is sensitive to ACP >10-2 • Rare Charm Decay

  25. D0D0 Mixing D0 decays as D0 Separate Mixing from DCS

  26. Mixing Phenomenology(1) Like the K0K0 mixing, constructing DS and DL

  27. 0.1 y 0 -0.1 0 0.2 0.1 x Experimental Situation x and y are in the orders of 10-2─10-1

  28. Mixing Phenomenology(2) Mixing Measuring the Asymmetry of CP eigenstate (K+K-(+), Ksρ0(-)…) DCS CF Supposing CP violation is small Possible to measure the phase shift

  29. Mixing at ψ(3770) • The D0 and D0 are produced coherently in JPC=1-- state • DCSD (Double Cabbibo Suppressed Decay) contribution is 0 at ψ(3770) • D0 produced ~at rest, cannot measure ΔΓ (y) directly by using lifetime difference Useful for measuring rD

  30. Experimental Searching forD0D0 Mixing • Big challenge to PID (Kπchannel) • Main backgrounds come from the double miss-PID • Searching in semi-leptonic decay modes are experimental difficulty with 2 missing neutrino (hard to reduce background contribution to 10-4) • Monte Carlo study with different PID (TOF resolution)

  31. Detection efficiency vs TOF resolution

  32. Background rates vsTOF resolution

  33. Probing New Physics to rD~10-4 • The detection efficiency is ~40%, ~20K events with D0→K+π- are expected to be found in 5fb-1ψ(3770) data • The background contamination rate is 0.1─0.5x10-4 while the TOF resolution varies from 65ps to 100ps • BESIII is sensitive to 10-4 for the mixing rate if the TOF resolution is designed to be around 100ps.

  34. CP Violation at ψ(3770) Suppose Both D0 decay to CP eigenstate f1 and f2 . Any oberservations of CP(f1)=CP(f2) at ψ(3770) are the direct evidence of CP Violation Several hundreds events with 100% CP eigenstate will be found in 5fb-1ψ(3770) data. The sensitivity of direct CP violation is ACP~10-2─10-1

  35. Rare Charm Decay The Up limit for most modes listed above are estimated in the range of 10-6─10-5, will update PDG data.

  36. Summary BESIII contributes to charm physics on • Precision absolute branching ratio of charm mesons (<1% for D, <2% for Ds) • Precision decay constants (2~3%) • Precision CKM Matrix (<2%) • Sensitive to rD~10-4 for mixing • Sensitive to ACP~10-2─10-1 for CP violation • Set the up limit of branching ratio for most rare charm decays to 10-6─10-5 range • And more, more,……

  37. Comparison of BES3, CLEO-c and B-factories On Charm physics topics * D/Ds cross section over estimated by a factor of 2this number need confirming

  38. Thank you ! 谢谢

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