Chen Jiangchuan (for BES Collaboration) Institute of High Energy Physics, Beijing 100039, P.R. C.

1. Recent Results on (3770) Resonance and D Mesons Production & Decays from BES Chen Jiangchuan (for BES Collaboration) Institute of High Energy Physics, Beijing 100039, P.R. C. The International Conference on QCD and Hadronic Physics June 16—20, 2005

2. Outline (3770) production & decays D0 & D+Meson Decays Summary

3. BES (3770) data Sample ~18 pb-1 of data taken at 3.773 GeV ~7 pb-1 of data taken at the region from 3.768 GeV to 3.778 GeV ~8 pb-1 of data taken in the energy region from 3.665 to 3.878 GeV about 33 pb-1 of data collected around 3.773 GeV in total. 2004 Jan.5 BES completed total (3770) data collection.

4. (3770) production & decays (3770) resonance parameters DD-bar cross cection at 3.773 GeV Search for charmless decays of Evidence for

5. Puzzle of (3770) production and decays (3770) is believed to be a mixture of and states of system Since its mass is above open charm-pair threshold and its width is two order of magnitude larger than that of , (3770) is thought to decay almost entirely to pure DD-bar. (3770) production cross section at peak Using mass and branching fraction (PDG02): (Mark-III) Non-saturate decay ? About39%of(3770)does not decay to DD-bar ?

6. Theoretical prediction There are some theoretical arguments about decays (3770) Lipkin pointed out that could decay to non-DD-bar final states with a large branching fraction. (3770) There are some theoretical calculations about non-DD-bar decays Added all above numbers up !

7. (3770) resonance parameters To understand this long-standing puzzle, (3770) and production cross section should be measured more precisely. The cross section of (3770) can be obtained based on the (3770) resonance parameters. (3770) resonance parameters can be extracted from a fit to the observed hadonic cross sections in the energy range which cover (3770) resonance (-- scan experiment).

8. Events collected at BESII N N Events Recorded by BESII Cosmic-ray and beam associated background Distributions of the vertex of events physics background could be estimated based on cross sections, luminosities and acceptances

9. Monte Carloproduction The ISR (Initial State Radiation) return. The histogram show the hadronic event production due to ISR when nominal center-of-mass energy at 3.78 GeV.

10. Monte Carloproduction Shadows are experimental data, lines are MC sample, (Ecm= 3.773 GeV). (Nch, KNO, Thrust, Sphericity, Aplanarity, xp, η, <pTin>, <pTout> distributions)

11. Hadron efficiency vs C.M. energy Observed cross section (Kuraev and Fadin)

12. BEPC energy calibration Just before the scan experiment EBEPC is the energy of BEPC set in the experiment, Etrue is the true energy When scan over 3.770GeV

13. (3770) production To get right resonance parameters, the two resonance productions and decays should be considered simultaneously. In this way the “correct” QED background( ) can be determined correctly ! BES-II Preliminary !

14. Comparison of (3770) Resonance Parameters (preliminary !)

15. Comparison of (2s) Resonance Parameters Using a constant for vacuum polarization correction

16. DD-bar Cross Section at 3.773 GeV • BES-II: of data @ 3.773 GeV Single tag method Using kinematical fit method to improve momentum resolution and select the singly tagged D meson K- D π+ tag π+ D+ Single tag analysis e+ e- D D- From Monte Carlo Requiring PDG02 Br

17. Observed cross sections for DD-bar production at 3.773 GeV

18. DD-bar Cross Section at 3.773 GeV • BES-II: of data @ 3.773 GeV Using ‘double tag’ method, pioneered by MARK-III Double tag method Near DD-bar production threshold region Singly tagged D sample K- K- D D π+ tag tag π+ π+ D0 D+ e+ e- e+ e- D0 D D- D Doubly tagged D

19. 绝对测量 Preliminary !

20. Radiative correction Assuming that decay exclusively into (3770) PR D62 (2000)012002-1 Initial State Radiation correction factor

21. Obtained based on PDG02 (3770) resonance parameters: Radiative correction factor Due to the uncertainties in resonance parameters and vaccum polarization

22. and Squares are the BES-II direct R measurements by counting inclusive hadronic events The open square is charm counting method of R measurement (3770) Assuming that decays exclusively into DD-bar or The contribution to R in the charm threshold region from the light quarks is estimated to be , which is obtained by fitting to the R values from 2.0 to 3.0 GeV measured by BES-II. The theoretical expectation is that is approximately independent of center of mass energy in this region. yielding which is obtained in measurement of (3770) resonance parameters

23. Search for charmless decays of 4-prong with net charge zero Selection criteria Data taken around (3770) peak Neutral mode Charged mode

24. Check if there are continuum production ? Normalized to the luminosity and phase space of ψ(3770) production Data taken off-resonance (@ 3.65 GeV)

25. Charmless final states observed Resonance productions and decays QED process Three gluon annihilation process Observed in experiment around 3.77 GeV

26. A detailed maximum likelihood analysis based on above observed event numbers gives giving a significance of

27. Those yield the branching fraction and upper limit to be and partial width to be (preliminary !)

28. Evidence for Decay it is an interesting question if transitions inside the charmonium system exist.

29. Evidence for (cont’d) • Examine the recoil mass of Projecting the events on to the vertical scale (recoil mass of ), the evidence for is observed Due to ISR (mainly)

30. Evidence for (cont’d) Analysis of the recoil mass 20 times large than the data and Data MC signal events out of events in total

31. Evidence for (cont’d) analysis of the fitted dilepton masses of Open histogram is for e+e- channel, histogram in yellow is for mu+mu- channel 20 times large than the data The histogram is psi(3686), while error bars are the psi(3686) + psi(3770) mainly data MC signal events obtained out of signal events

32. Paper published in PLB605 (2005)63 Before BES-II one knows the decays (3770) It has been quoted 21 times. Comments by Referees of the paper It is an interesting question if transitions inside the charmonium system exist. (3770) It is very important in elucidating the exact nature of the(3770) and help us understand why the (3770) does not seem to be saturated by DD-bar decays. BES-II established the transition at level !

33. D0 & D+Meson Decays (3770) is a good laboratory for study D meson decays Singl tag samples Exclusive Semileptonic D Decays Purely Leptonic D+ Decay D absolute hadronic decay branching fractions

34. Singly tagged D samples Invariant mass distribution for tags Invariant mass distribution for tags

35. Semileptonic D Decays K- K- Singly tagged D sample D π+ tag π+ π+ D tag D0 D+ e+ e- D D- e+ D0 e- D

36. Motivation • Branching fractions for and To measure the standard model parameters Vcs, Vcd Probing the hadronic current Understand the dynamics of semileptonic decays As an example Where is a vector form factor, and are the four momenta of the initial and final mesons, respectively, and is the squared mass of the virtual W. (“nearest pole dominance”)

37. Longstanding Puzzle in charm decay Motivation and • Branching fraction for To test if the Isospin conservation is still held in D semileptonic decays. Isospin conservation requires Is isospin conservation held in the D semileptonic decays? From PDG Br It is called “Longstanding puzzel” in Charm decay !

38. Distribution of the Inv. masses of Combinations for the events in which the are observed in the recoil side Distribution of the momentum of the electron from the events of

39. Results Phy. Let. B597(2004)39-46 Phy. Let. B608(2005)24-30

40. Form factors Different theoretical predictions Phys.Rev.D66,114002,2000 Nucl.Phys.Prog.Suppl.83,286,2000 Nucl.Phys.B619,565,2001 inserting Average MARK-III and CLEO gives PDG04 Theoretical predictions are in the range from 0.7 to 1.4. See J.D. Richman et al., Rev. Mod. Phys., Vol. 67, No 4, 1995

41. CKM matrix elements Input theoretical predictions for the form factors Input

42. Ratio of partial width Obtained based on the branching fractions quoted from PDG02 BES-II results support isospin conservation is held in the D semileptonic decays! Solve the longstanding puzzle in Charm decays !

43. Purely Leptonic D+ Decay K- D π+ tag π+ D+ Phy. Let. B610(2005)183-191 e+ e- D D-

44. Motivation The effect of strong interaction can be parameterized by Lattice gauge, potential models bag model, QCD sum rule …, calculation predict the value of It is very difficult to measure the fD due to |Vcd| is small The fD measurement will allow comparison with the theoretical calculation to improve the theory. Mixing experiment Lattice predicts fB/fD with small errors. Precision measurement of fD precision estimate of fB and precision determination of Vtd

45. Previous measurements MARK-III set an upper limit of fD < 290 MeV BES-I observed 1 event for and measured Physics Letters B 429(1998) 188-194

46. K+ • Fully reconstruct one D D π- tag π- D- e+ e- D D+ • Require one additional charged track and no additional photons Neutrino carries energy and momentum away Total Should be around zero

47. 3 events in the signal region Monte Carlo simulation Monte Carlo sample 150 times more than data

48. 1 muon is fund in the recoil of the tags, and the events satisfied the requirements for selection of Estimation of background • Method 3 • Method 1 The main background are 3 X 100 times more Monte Carlo samples for each of the modes  Nb = 0.22 1 hadronic track in the recoil of the tags • Method 2 13 events in the tagged D- mass region Analysis of 320 pb-1 Monte Carlo sample  Nb = 0.33+/-0.11 Nb=0.31±0.09

49. 2.67±1.74 Events Singly tagged D- K+ π- D tag π- D- Search for the decay e+ e- D D+ Candidate νe

50. D absolute hadronic decay branching fractions K- K- Singly tagged D sample D π+ π+ D tag π+ tag D0 D+ e+ e+ e- D0 e- D- D D Double-tag