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Recent results on (3770) production & decays from BES/BEPC

Recent results on (3770) production & decays from BES/BEPC. Gang RONG. (for BES Collaboration). Institute of High Energy Physics, Beijing 100049, P.R. China. CNHEP’06. 27 -- 31 October, 2006, Guilin. Outline. Introduction. Measurement of R values. values and.

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Recent results on (3770) production & decays from BES/BEPC

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  1. Recent results on (3770) production & decays from BES/BEPC Gang RONG (for BES Collaboration) Institute of High Energy Physics, Beijing 100049, P.R. China CNHEP’06 27 -- 31 October, 2006, Guilin

  2. Outline Introduction Measurement of Rvalues values and Resonance parameters of (3770) and (3686)& Search for decays of (3770) Summary

  3. Introduction • Why are we interested in R(s) ? Vacuum polarization correction (in the photon propagator ) needs the R(s) values, which plays an important role in the precision test of the Standard Model. affects the determination of the mass of Higgs boson from the measurement of indirectly. For the evaluation of the electromagnetic coupling at the Z mass scale, . For determination of of the muon. The R values at all energies is needed to calculate the effects of vacuum polarization on the parameters of Standard Model. [ for example, and ]. A large uncertainty in this calculation arises from the uncertainties in the measured R values in the open charm threshold region (3.7 GeV to 5.0 GeV).

  4. Introduction Precision measurements of R values in open charm region are also important in understanding 1-- resonance production, for searching for new states, study of dynamics … • (3770) production & decays It is believed to be a mixture of and states of system. It is thought to decay almost entirely to pure DD-bar. However Cross section at peak (PDG04 parameters) Long-standing puzzle of (3770) production and decays: (Mark-III) before BES-II & CLEO-c previous measurements Previously published data indicate that more than about 35%of(3770)does not decay to DD-bar ? This conflicts with theoretical prediction.

  5. New Measurements Recently BES and CLEO-c measured the DD and (3770) production at 3.773 GeV based on the data taken below DD threshold and at 3.773 GeV. A better way: cross section scan To uncover the puzzle A better way to measure the cross sections, the widths of the resonance and the DD branching fractions of (3770) is to analyze the line-shapes of (3770), (3686) and DD production simultaneously. BES made a fine cross section scan covering boththe(3686) and (3770) to measure the resonance parameters, branching fractions and search for non-DD decays …

  6. BES-II data samples • (3770) data ~17.3 pb-1 of data taken at 3.773 GeV. Equivalent to ~27 pb-1 at (3770)peak ~15 pb-1 of (cross section scan ) data taken in between 3.665 GeV and 3.878 GeV (Mar. 2003 data set & Dec. 2003 data set) . Data taken over hundred energy points. • Ecm= 3.650, 3.665 GeV 6.5 pb-1 of data collected at 3.650 GeV. ~1 pb-1 of data collected at 3.665 GeV.

  7. Measurements of Rvalues pQCD calculates the R ratio in continuum region Experimentally, one measures : # of hadronic events : Luminosity : Effs. : radiative correction factor Have to be determined precisely !

  8. MC generator & simulation Full energy range ISR Generator KNO Nch φ Density [nb/GeV] cosθ Thrust Oblateness Aplanarity Sphericity Jet axis cosθ x Y η BES-II(3770) and (3686) scan Pt <PTin2> <PTout2> MARK-I, MARK-II, DELCO, … smooth eff. curve

  9. BEPC energy calibration During the cross section experiment, we performed 4 fast cross section scans over J/ and ’ resonances to calibrate the BEPC energy. 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

  10. Events collected at BESII N N Radiative correction could remove the effects of high order processes from the observed cross section, and gives Events Recorded by BESII The events observed in the experiment Cosmic-ray and beam associated background The distributions of the averaged Z of events could be estimated based on cross sections, luminosity and acceptance

  11. ISR corrections Effective c.m. energy Moninal c.m. energy Kuraev & Fadin the electron equivalent radiator thickness

  12. Vacuum polarization correction Vacuum polarization change the photon propagator results in Radiative correction factor

  13. Rvalues measured at three energy points stat. & p-to-p systematic error (preliminary !) Obtaining by fitting to the R values measured by BES in the range from 2.0 to 3.0 GeV Obtained by fitting the (3770) and (3686) cross sections see before

  14. Comparison of R measurements from different experiments

  15. determined with Taking the R for light hadron production to be a constant, then Including (3770) We obtain Preliminary It is consistent with My calculation obtained based on PDG04 (3770) resonance parameters PLB 603(2004)130

  16. Determination of branching fractions with Assuming that there are no other new structures and effects except (3770) and continuum hadron production in the energy region from 3.70 to 3.87 GeV, we have and Obtained from analysis of R Radiative correction Some systematic uncertainties can be canceled out Assuming that decay exclusively into (3770) Radiative correction factor obtained based on new (3770)resonance parameters measured by BES-II. PR D62 (2000)012002-1 Radiative correction factor

  17. Results of branching fractions With BES previously measured cross sections for DD production. PLB603(2004) 130 These result in the non-DD branching fraction preliminary Is calculated with the (2S)resonance parameters measured by scanning the (2S)peak. PLB 641 (2006) 145

  18. If we consider the possible interference … • Results of branching fractions Considering the possible interference between the two amplitudes … Is calculated with the (2S)resonance parameters measured by scanning the (2S)peak. PLB 641 (2006) 145

  19. Resonance parameters of (3770) , (3686) and branching fractions • Observed cross section The distribution of event vertex in Z (Kuraev and Fadin) Fitting the distribution of the event vertex gives the number of hadronic events nhad. For (3770), we use energy-dependent total width

  20. DD-bar production • Energy dependent cross sections Distributions of invariant masses of combinations at different c.m. energies Mar. 2003 data set

  21. Observed cross sections Inclusive hadrons (3686) resonance region Observed cross section for hadron production [nb] Inclusive hadrons (3770) resonance region Mar. 2003 data set

  22. Fit to the observed cross sections Fitting the observed inclusive hadron and DD-bar cross sections to the theoretical cross sections, we obtain the branching fractions The total energy dependent width has three components: momentum of D at peak threshold function momentum of D (3770)total width Blatt-Weisskopf penetration factor

  23. Independent hadron and DD-bar data sample Branching fraction for the singly tagged D channel These relations remove those hadronic events which also appear in the DD-bar samples, so that the inclusive hadronic and DD-bar samples are independent.

  24. To measure the resonance parameters of (3770) or (3686), one had better to simultaneously fit (3686) and (3770) resonances, since there are strong correlations between the fitted parameters of the two resonances. (3686) (3770) If one do not consider the effects of vacuum polarization corrections on the observed cross sections in the data reduction, the total width of (3686) would decrease by about 40 keV! Mar. 2003 data set (3686) Mainly due to vacuum polarization corrections After subtraction of (3686) , (3770) and J/  from the observed cross sections, one obtains the expected cross sections of the continuum hadron production. PRL 97 (2006) 121801

  25. Comparison of (3770) Resonance Parameters which is consistent within error with Mar. 2003 data set PRL 97 (2006) 121801 obtained based on PDG04 parameters

  26. Obtained based on cross section scan Comparison of (3686) Resonance Parameters Mar. 2003 data set PDG04 PRL 97 (2006) 121801

  27. Obtained from fitting to the inclusive hadron and the DD-bar production cross sections simultaneously. • Branching fractions Inclusive hadrons where the first error is statistical and second systematic, which arises from the un-canceled systematic uncertainties in hadron cross sections (~4.4 %), neutral DD-bar cross sections (~4.5 %) and charged DD-bar cross sections (~7.4 %). PRL 97 (2006) 121801 Mar. 2003 data set

  28. Search For (3770) decayto Φπ0 and Φη Ecm=3.65GeV (L=6.5 pb-1) Ecm around 3.773 GeV (L=33 pb-1) π0 η π0 η Φ Φ Φ signal Φ sideband

  29. Search For (3770) decayto Φπ+π-,ΦK+K- andΦpp Ecm around 3.773 GeV (L=33 pb-1) Ecm=3.65GeV (L=6.5 pb-1) K+K- π+ π- K+K- π+ π- K+K- K+ K- K+ K- K+K- - K+K- pp K+K- pp

  30. Search for (3770) decayto multi-body final states containing π0 or η Around 3.773GeV Ecm=3.65GeV Around 3.773GeV (L=33 pb-1) Ecm=3.65GeV (L=6.5 pb-1) 2(π+ π-)π0 2(K+K-)π0 KKπ+ π-π0 ppπ0 3(π+ π-)π0 ppπ+ π-π0 2(π+ π-)η DD-bar events have been removed.

  31. Search for charmless decays of (3770) Observed Cross Sections Preliminary ! No obvious cross section discrepancy at the two energy points is observed. However, to extract the non-DD-bar branching fractions of (3770) decays, one needs to consider the interference between the two amplitudes of the continuum and the resonances, and to consider the difference of ISR & vacuum polarization corrections at two energy points.

  32. BES-II CLEO-c y(3770) p+p-J/y mainly y(3770) p+p-J/y BES-II observed the first non-DD events of (3770) decays. CLEO-c conformed the BES observation of the non-DD decay. BES-II PLB 605 (2005)63 CLEO-c PRL96,082004(2006) The two measurements are consistent within the errors.

  33. SUMMARY (preliminary !) BES measured the R values at 3.773 GeV and around 3.666 GeV with average uncertainties of • . Obtained from fitting to (3686) and (3770) • . BES measured the resonance parameters of (3770) and (3686) with the improved precision on (3770) resonance parameters and with precision in measuring leptonic width of (3686) comparable to the current PDG04.

  34. SUMMARY (preliminary !) BES measured the branching fractions for inclusive non-DD-bar decays of (3770) using two different data samples and two different methods • . Determined from analysis of R values and DD-bar cross sections Obtained from fitting to the inclusive hadron and the DD-bar production cross sections simultaneously. BES observed the first non-DD events of y(3770) p+p-J/y, and established this hadronic transition process. BES searched for some charmless final states around 3.773 GeV and at 3.65 GeV, but did not observe obvious cross section discrepancy at the two energy points for most decay modes. • .

  35. Backup slides Gang RONG (for BES Collaboration) Institute of High Energy Physics, Beijing 100049, P.R. China

  36. Comparison with those measured by CLEO-c BES-II CLEO-c (hep-ex/0512038); PRL 96 (2006) 092002 Based on analysis of inclusive hadron and DD-bar cross section scan data. PLB 141 (2006) 145 Actually, considering the errors, the two results are not in contradiction.

  37. Comparison with those measured by CLEO-c BES-II CLEO-c Assuming that there are interference between the two amplitudes of continuum and resonance Based on measured R values. Method: Method: BES measured near DD-bar threshold and R at 3.773 GeV with traditional method, then calculate the Born order cross section for (3770) production. By comparing the cross sections for DD-bar and (3770) production, BES obtained the branching fraction. BES used an ISR generator to simulate the decay e+e- hadrons and obtain theefficiency for e+e- hadrons. CLEO-c directly count the number of hadronic events observed at 3.773 GeV, and subtract the backgrounds from J/, (2S) radiative tails and continuum QED background. CLEO-c used the efficiency forthe decay (3770) J/ π+ π-to estimate the efficiency for e+e- hadrons. Use parameter Use parameter

  38. Comparison with those measured by CLEO-c BES-II CLEO-c Discussion Method: Method: CLEO-c did not consider the difference of ISR & vacuum polarization corrections for continuum hadron production at two energy points (3.671 GeV and 3.773 GeV) when subtracting background at 3.773 GeV. if we use to calculate the ISR & vacuum polarization correction factor, and assuming that there are interference between the two amplitudes of the continuum and the resonance, we would obtain PRL 97 (2006) 121801

  39. Comparison of measurements of the cross sections for DD-bar production My estimation, Input with PDG04 Br

  40. Comparison of measurements of the cross sections for DD-bar production My estimation weighted average My estimation

  41. Branching fraction of (3770)to non-DD-bar My estimation Which is obtained based on the data from MARK-I, MARK-II, MARK-III, BES-II and CLEO-c.

  42. Branching fraction of (3770)to non-DD-bar My estimation Which is obtained based on the DD-bar cross section measured by CLEO and PDG06 psi(3770) resonance parameters.

  43. MARK-I DELCO PRL40 (1978) 671 PRL39 (1977) 526 MARK-II BES-II hep-ex/0605107

  44. Branching fraction of (3770)to non-DD-bar My estimation Which is obtained based on the data from MARK-I, MARK-II, MARK-III, BES-II and CLEO-c.

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