Search for (3770) non-DD-bar Decays Dahua Zhang (for BES Collaboration) Institute of High Energy Physics, Beijing 100039, P.R. China QWG’ 04 October 12—15, 2004

Outline Introduction Search for Evidence of Summary

Introduction (3770) resonance Theoretical arguments It 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. Theoretical arguments 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)

Study of exclusive decays of ψ(3770) Experimental study or search for some exclusive decay modes can be used to check the potential models of quarkonium and the hadronic transition mechanism of quarkonium states. To understand the long standing ρ-π puzzle in charmonium decays, the measurement of the partial width of V-P channels in ψ(3770) decay is necessary and is very interesting. Also see (hep-ph/0105327, J.L. Rosner)

Theoretical prediction J.L. Rosner predicts There are some theoretical calculations about non-DD-bar decays Added all above numbers up !

(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.

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

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

Charmless final states observed Resonance productions and decays QED process Observed in experiment around 3.77 GeV

giving a significance of A detailed maximum likelihood analysis based on above observed event numbers gives is the phase difference between and giving a significance of

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

Evidence for 4 good charged tacks per event data @ around 3.773 GeV 4 good charged tacks per event are identified by combining dE/dx, TOF, BSC & Muon Search for in two different ways

Evidence for (cont’d) Nominal c.m. energy of 3.773 GeV Main source of background is produced around nominal center-of-mass energy due to Breit-Wigner tail and ISR solid line dotted line Nominal c.m. energy Actual c.m. energy and productions generated at different actual energy after ISR

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

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

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) signal events mainly data MC

Check for other background Two photon events Analysis of 100000 two-photon Monte Carlo events, no “ ” “signal” events are found from analyzing the Monte Carlo events (~4 times larger than the data) events Analysis of 50000 events, no “ ” “signal” events are found from analyzing the Monte Carlo events (~4 times large than the data)

Analysis of the data taken at 4.03 GeV with BES-I events where the D or D-bar auto-decay to all possible final states Analysis of the MC events of 13 times large than the data, no “ ” “signal” events are found from analyzing the Monte Carlo events Generated with Lund generator (JETSET74) events Analysis of the MC events of 1.6 times large than the data, no “ ” “signal” events are found from analyzing the Monte Carlo events Analysis of the data taken at 4.03 GeV with BES-I Analysis of 22.3 pb-1 of data (@4.03 GeV), no significant “ ” “signal” events are found from analyzing the Monte Carlo events

Evidence for (cont’d) Number of Signal significance The probability that the 17.8 events observed are due to a fluctuation of the events is . Number of Efficiency (for analysis of pi+pi- recoil mass) (for analysis of the fitted dilepton masses)

Evidence for (cont’d) Branching fraction Partial width (recoil mass) (K.F.)

SUMMARY BES searched for the charmless decay events of . BES searched for the charmless decay events of measured the partial width of (preliminary !) and set its upper limit to be (preliminary !) . BES observed hadronic transition of to and measured the partial width to be (3770)

谢 谢！ Thank You！

Backup slides Assuming the continuum as CLEO-c observed, then giving a significance of 2.6 σ