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

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

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. 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). For the evaluation of the electromagnetic coupling at the Z mass scale,. For determination of of the muon. affects the determination of the mass of Higgs boson from the measurement of indirectly.

4 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 … Introduction   (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. Long-standing puzzle of  (3770) production and decays: Previously published data indicate that more than about 35% of  (3770) does not decay to DD-bar ? This conflicts with theoretical prediction. Cross section at peak (PDG04 parameters) (Mark-III) before BES-II & CLEO-c However previous measurements

5  New Measurements Recently BES and CLEO-c measured the DD and  (3770) production at GeV based on the data taken below DD threshold and at GeV. 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 both the  (3686) and  (3770) to measure the resonance parameters, branching fractions and search for non-DD decays … A better way: cross section scan To uncover the puzzle

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

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

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

9 When scan over GeV Just before the scan experiment Mass [MeV] PDG04 BEPC BEPC energy calibration E BEPC is the energy of BEPC set in the experiment, E true is the true energy During the cross section experiment, we performed 4 fast cross section scans over J/  and  ’ resonances to calibrate the BEPC energy.

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

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

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

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

14 Comparison of R measurements from different experiments

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

16 Assuming that decay exclusively into  (3770) Radiative correction PR D62 (2000) Radiative correction factor Obtained from analysis of R  Determination of branching fractions with and Some systematic uncertainties can be canceled out Radiative correction factor obtained based on new  (3770) resonance parameters measured by BES-II. 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

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

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

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

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

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

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

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 Mainly due to vacuum polarization corrections  (3770)  (3686) 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. 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! PRL 97 (2006) After subtraction of  (3686),  (3770) and J/  from the observed cross sections, one obtains the expected cross sections of the continuum hadron production. Mar data set

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

26 experiment E760 BES-II PDG04 This work Comparison of  (3686) Resonance Parameters PDG04 Obtained based on cross section scan Mar data set PRL 97 (2006)

27 Inclusive hadrons  Branching fractions Obtained from fitting to the inclusive hadron and the DD-bar production cross sections simultaneously. 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 %). Mar data set PRL 97 (2006)

28 Φ π0π0 η Φ signal Φ sideband Ecm [GeV]Φ π 0 Φη around ± Search For  (3770) decay to Φπ 0 and Φη Φ π0π0 η Ecm around GeV (L=33 pb -1 ) Ecm=3.65GeV (L=6.5 pb -1 )

29 Ecm Φ π + π - ΦK + K - Φpp Around GeV (L=33 pb -1 ) 6.0 ± ± GeV (L=6.5 pb -1 ) ±2.6 0 K + K - π + π - K + K - pp Search For  (3770) decay to Φπ + π -, ΦK + K - and Φpp Ecm around GeV (L=33 pb -1 )Ecm=3.65GeV (L=6.5 pb -1 ) K + K - π + π - K + K - K + K - pp -

30 2(π + π -) η 2(π + π - ) π 0 KKπ + π - π 0 ppπ + π - π 0 ppπ 0 2(K + K - )π 0 3(π + π - ) π 0 DD-bar events have been removed. Search for  (3770) decay to multi-body final states containing π 0 or η Around 3.773GeVEcm=3.65GeV Around 3.773GeV (L=33 pb -1 ) Ecm=3.65GeV (L=6.5 pb -1 )

31 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. Search for charmless decays of  (3770)

32 BES-II observed the first non-DD events of  (3770) decays. CLEO-c conformed the BES observation of the non-DD decay. CLEO-c BES-II CLEO-c PRL96,082004(2006) PLB 605 (2005)63 The two measurements are consistent within the errors.       J/  mainly BES-II

33 SUMMARY BES measured the R values at GeV and around GeV with average uncertainties of 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. . (preliminary !) Obtained from fitting to  (3686) and  (3770)

34 BES measured the branching fractions for inclusive non-DD-bar decays of  (3770) using two different data samples and two different methods . (preliminary !) SUMMARY 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       J/ , and established this hadronic transition process. BES searched for some charmless final states around GeV and at 3.65 GeV, but did not observe obvious cross section discrepancy at the two energy points for most decay modes.

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

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

37 BES-IICLEO-c Based on measured R values. Comparison with those measured by CLEO-c Method: BES measured near DD-bar threshold and R at 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 the efficiency for e + e -  hadrons. Method: CLEO-c directly count the number of hadronic events observed at GeV, and subtract the backgrounds from J/ ,  (2S) radiative tails and continuum QED background. CLEO-c used the efficiency for the decay  (3770)  J/  π + π - to estimate the efficiency for e + e -  hadrons. Use parameter Assuming that there are interference between the two amplitudes of continuum and resonance

38 BES-IICLEO-c Comparison with those measured by CLEO-c Method: Discussion 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 CLEO-c did not consider the difference of ISR & vacuum polarization corrections for continuum hadron production at two energy points (3.671 GeV and GeV) when subtracting background at GeV. PRL 97 (2006)

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 weighted average My estimation

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

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

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

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