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

2. Outline
Introduction
Search for
Evidence of
Summary

3. 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)

4. 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/ , J.L. Rosner)

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

6. (3770) data sample ~18 pb-1 of data taken at 3.773 GeV
~7 pb-1 of data taken at the region from GeV to GeV
~8 pb-1 of data taken in the energy region from to GeV
about 33 pb-1 of data collected around GeV in total.

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

8. 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)

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

10. 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

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

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

13. 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

14. 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)

15. 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

16. 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

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

18. 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 GeV), no significant “ ” “signal” events are found from analyzing the Monte Carlo events

19. 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)

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

21. 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)

22. 谢 谢！
Thank You！

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