Recent results on 3770 production decays from BESBEPC

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 1

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

Introduction u. 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 For the evaluation of the electromagnetic coupling at the Z mass scale, . For determination of of the muon. determination of the mass of Higgs boson from the measurement of indirectly. 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 Ge. V to 35. 0 Ge. V).

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 … u (3770) production & decays It is believed to be a mixture of and states of system. It is thought to decay almost entirely to pure DDbar. However Long-standing puzzle of (3770) production and decays: before BES-II & CLEO-c Cross section at peak (PDG 04 parameters) (Mark-III) previous measurements Previously published data indicate that more than about 35% of (3770) does not decay to DD-bar ? This conflicts with theoretical 4 prediction.

u. New Measurements Recently BES and CLEO-c measured the DD and (3770) production at 3. 773 Ge. V based on the data taken below DD threshold and at 3. 773 Ge. V. To uncover the puzzle A better way: cross section scan 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 … 5

BES-II data samples u (3770) data ~17. 3 pb-1 of data taken at 3. 773 Ge. V. Equivalent to ~27 pb-1 at (3770) peak ~15 pb-1 of (cross section scan ) data taken in between 3. 665 Ge. V and 3. 878 Ge. V (Mar. 2003 data set & Dec. 2003 data set). Data taken over hundred energy points. u. Ecm= 3. 650, 3. 665 Ge. V 6. 5 pb-1 of data collected at 3. 650 Ge. V. ~1 pb-1 of data collected at 3. 665 Ge. V. 6

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

MC generator & simulation Full energy range ISR Generator Density [nb/Ge. V] Nch KNO φ cosθ Thrust Oblateness Aplanarity Sphericity BES-II (3770) and (3686) scan Jet axis cosθ x Pt η <PTin 2> Y <PTout 2> MARK-I, MARK-II, DELCO, … smooth eff. curve 8

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 Mass [Me. V] PDG 04 When scan over 3. 770 Ge. V BEPC 9

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

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

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

R values measured at three energy points ECM [Ge. V] σobshad R 3. 650 3. 665 3. 773 (preliminary !) stat. & p-to-p systematic error see before Obtained by fitting the (3770) and (3686) cross sections Obtaining by fitting to the R values measured by BES in the range from 2. 0 to 3. 0 Ge. V 13

Comparison of R measurements from different experiments 14

determined with u Taking the R for light hadron production to be a constant, then We obtain Including (3770) My calculation Preliminary It is consistent with PLB 603(2004)130 obtained based on PDG 04 (3770) resonance parameters 15

u Determination of branching fractions with and 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 Ge. V, we have Obtained from analysis of R Radiative correction Assuming that (3770) decay exclusively into PR D 62 (2000)012002 -1 Radiative correction factor Some systematic uncertainties can be canceled out Radiative correction factor obtained based on new (3770) resonance parameters measured by BES-II. 16

u Results of branching fractions With BES previously measured cross sections for DD production. PLB 603(2004) 130 These result in the non-DD branching fraction preliminary Is calculated with the (2 S) resonance parameters measured by scanning the (2 S) peak. PLB 641 (2006) 145 17

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

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

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

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

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

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. 23

(3686) (3770) 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 ke. V! Mar. 2003 data set (3686) Mainly due to vacuum polarization corrections PRL 97 (2006) 121801 After subtraction of (3686) , (3770) and J/ from the observed cross sections, one obtains the expected cross sections of the continuum hadron 24 production.

Comparison of (3770) Resonance Parameters which is consistent within error with 25 PRL 97 (2006) 121801 Mar. 2003 data set obtained based on PDG 04 parameters

Obtained based on cross section scan Comparison of (3686) Resonance Parameters experiment E 760 BES-II PDG 04 This work PRL 97 (2006) 121801 Mar. 2003 data set 26 PDG 04

u Branching fractions Obtained from fitting to the inclusive hadron and the DD-bar production cross sections simultaneously. 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 27

Search For (3770) decay to Φπ0 and Φη Ecm around 3. 773 Ge. V (L=33 pb-1) π0 Ecm=3. 65 Ge. V (L=6. 5 pb-1) π0 η η Φ Φ signal Φ sideband Φ Ecm [Ge. V] Φ π0 around 3. 773 0 3. 65 0 Φη 5. 2± 2. 5 0 28

Search For (3770) decay to Φπ+π-, ΦK+K- and Φpp Ecm around 3. 773 Ge. V (L=33 pb-1) Ecm=3. 65 Ge. V (L=6. 5 pb-1) K+ K- π + π - K+ K- K+K- pp- K+K- pp Ecm Φ π + π- ΦK+K- Around 3. 773 Ge. V 6. 0 ± 3. 5 27. 3 ± 5. 8 2 3. 65 Ge. V (L=6. 5 pb-1) 2 4. 9 ± 2. 6 0 (L=33 pb-1) Φpp 29

Search for (3770) decay to multi-body final states containing π0 or η Around 3. 773 Ge. V Ecm=3. 65 Ge. V 2(π+ π-) π0 Around 3. 773 Ge. V (L=33 pb-1) Ecm=3. 65 Ge. V (L=6. 5 pb-1) 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. 30

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. 31

BES-II (3770) p+p- J/ CLEO-c mainly (3770) p+p- J/ 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 PRL 96, 082004(2006) The two measurements are consistent within the errors. 32

SUMMARY (preliminary !) u. BES. measured the R values at 3. 773 Ge. V and around 3. 666 Ge. V with average uncertainties of Obtained from fitting to (3686) and (3770) u. 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 PDG 04. 33

SUMMARY (preliminary !) measured the branching fractions for inclusive non-DD-bar u. BES. 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. observed the first non-DD events of u. BES. (3770) p+p- J/ , and established this hadronic transition process. BES searched for some charmless final states around 3. 773 Ge. V and at 3. 65 Ge. V, but did not observe obvious cross section discrepancy at the two energy points for most decay modes. 34

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

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. 36

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: BES measured near DD-bar threshold and R at 3. 773 Ge. V 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. Use parameter Method: CLEO-c directly count the number of hadronic events observed at 3. 773 Ge. V, and subtract the backgrounds from J/ , (2 S) 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 37

Comparison with those measured by CLEO-c Discussion BES-II Method: 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 Method: CLEO-c did not consider the difference of ISR & vacuum polarization corrections for continuum hadron production at two energy points (3. 671 Ge. V and 3. 773 Ge. V) when subtracting background at 3. 773 Ge. V. PRL 97 (2006) 121801 38

Comparison of measurements of the cross sections for DD-bar production My estimation, Input with PDG 04 Br 39

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

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

Branching fraction of (3770) to non-DD-bar My estimation Which is obtained based on the DD-bar cross section measured by CLEO and PDG 06 psi(3770) resonance parameters. 42

MARK-I DELCO PRL 40 (1978) 671 PRL 39 (1977) 526 MARK-II BES-II hep-ex/0605107 43

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