Recent results on D meson decays from BES

1. Recent results on D meson decays from BES 陈江川(for BES Collaboration) Institute of High Energy Physics, Beijing China 高能物理学会第七届全国会员代表大会暨学术年会 广西 桂林 2006年10月27日-11月1日

2. Outline • Introduction • Semileptonic decays of D mesons • Inclusive decays of D mesons • Summary

3. The Beijing Electron Positron Collider (BEPC) L ~ 11031 /cm2sat(3770)peak Ecm~2-5 GeV

4. BESII Detector VC: xy = 100 m TOF: T = 180 ps  counter: r= 3 cm MDC: xy = 220 m BSC: E/E= 22 % z = 5.5 cm dE/dx= 8.5 %  = 7.9 mr B field: 0.4 T p/p=1.7%(1+p2) z = 3.1 cm

5. Muon identification can be done by the Muon Counter for the charged track with momentum of great than 0.55 GeV/c dE/dx TOF

6. (3770) data sample ~18 pb-1 data taken at 3.773 GeV ~7 pb-1 data taken at the region from 3.768 GeV to 3.778 GeV ~8 pb-1 data taken in the energy region from 3.665 to 3.878 GeV The total Luminosity is about 33 pb-1.

7. Absolute Measurements With the singly tagged D sample, we can do some absolute measurements Singly tagged D sample Near DD-bar production threshold region K+ K+ D D π– tag tag π– π– D- e+ e- e+ e- D D D+

8. Semileptonic D Decays (1) K+ K+ D D π- tag tag π- π- D- e+ e- e+ e- D0 D+ D D

9. It is called “Longstanding puzzle” in Charm decay ! Motivation Isospin conservationrequires From PDG Br Is isospin conservation held in the D semileptonic decays? Recently: BES-II published on Phys. Let. B608(2005)24-30 Solved the puzzle in Charm decays ! CLEO-c contributed paper at LP05 reports:

10. Motivation Branching fractions * From PDG04 Br CKM matrix elements & * Form factors& *

11. Good track selection Charged track with good helix fit To be consistent with originating from the primary events vertex Vxy <0.02 m & |z| < 0.2 m > 0.1 GeV < 0.08 m & |z| < 0.2 m

12. Singly tagged D sample Singly tagged modes , , , , , , , , , , , (Throughout the talk, charge conjugation is implied.) PID made by combining TOF, dE/dx & BSC information K : : CL > 0.1% ; CL > CL prob ( , n ) >0.1%, n = 1, 2, 3 1C kinematic fit (mKnπ)

13. 9 modes Invariant mass distribution for tags Invariant mass distribution for tags

14. Double-tagged D decays (1) Candidate modes , ; Nγ=0 (on recoil side of the D tag) K+ Combined TOF , dE/dx & BSC information D π- π: tag π- K : D- e+ e- μ: D D+ (or Nhit > 2 on μ counter) Missing energy and momentum selection Should be around zero

15. data Bckgrd DD-bar Data (subtracted bck) MC

16. Distribution of the Inv. masses of combinations for the events for which the and are observed in the recoil side Preliminary

17. Results hep-ex/0610019 & 0610020 • Branching fraction An up limit at 90% C.L is set to be <0.89% Preliminary

18. Ratio of partial width Preliminary Obtained based on the branching fractions quoted from PDG04 The ratio of Br. for D0 decaysto K(π)μν is:

19. Semileptonic D Decays (2) K+ K+ D D π- tag tag π- π- D- e+ e- e+ e- D0 D+ D D

20. Double-tagged D decays (2) Candidate modes Combined TOF and dE/dx information π: K+ K : D π- tag KS0: π- D- Combined TOF , dE/dx & BSC information e+ e- e: D D+ Missing energy and momentum selection νe Should be around zero

21. Events found in REC. of Dtag

22. Results: Published in Eur. Phys. J. C47 (2006) 31

23. Results: Published in Eur. Phys. J. C47 (2006) 31 With the measured branching fractions in this work and quoted from BES-II earlier work, we obtain:

24. Comparison uncertainty of theoretical prediction

25. Inclusive Decay Branching Fractionsfor K+ K+ D D π- tag tag π- π- D- e+ e- e+ e- D0 D+ D D K– π – π+ X X=any particles

26. Motivation • Serving as a check on the sum of the branching fractions for the exclusive D decay. • Providing information about the relative strength of Cabibbo-favored and Cabibbo suppressed D decays.

27. Double-tagged D decays Candidate modes Combined TOF and dE/dx information K+ π: D π- K : tag π- KS0: D- e+ e- e- D+ D e+ K– D0 D π+ X=any particles π – X The Kπ with maximum CL(K)•CL(π) retained in an event

28. D0 signal region D0 sideband K+π – K–π+ D– signal region D– sideband K+π – K–π+ K +π – Cabibbo suppressed decay Cabibbo favored decay

29. Results Published in PLB625 (2005) 196 Cabibbo favored decay: Cabibbo suppressed decay:

30. Neutral K decay of D: Charged K* Decay of D: KS0 3σ K+ D tag π+π – e+ e- D0 D Removing double counting with sideband background. π – X

31. Preliminary D0 signal region D+ signal region D0 sideband D+ sideband π+π – π+π –

32. Preliminary D0 signal region D– signal region D0 sideband D– sideband KS0π – Mass(GeV/c2) KS0π – Mass(GeV/c2) KS0π + KS0π + Mass(GeV/c2) Mass(GeV/c2)

33. Results The results submitted to PLB Cabibbo favored decay: Cabibbo suppressed decay (at 90% C.L.):

34. Comparison

35. Summary hep-ex/0610019 & 0610020 BES measured semileptonic D decay branching fractions • . Preliminary • . The ratio of branching fractions is • .

36. Summary Published in Eur. Phys. J. C47 (2006) 31 Measured semileptonic D decay branching fractions • . With the measured branching fractions in this work and quoted from BES-II earlier work, we obtain: • .

37. Summary Published in PLB 625(2005)196 Measured branching fractions for inclusive Cabibbo favored and suppressed decays of D mesons: • . Cabibbo favored decay: Cabibbo suppressed decay:

38. Summary The results submitted to PLB Cabibbo favored decay: • . Cabibbo suppressed decay (at 90% C.L.): • . Branching fractions of inclusive neutral K decay of D • .

39. 谢 谢！ Thank You！