1. Missing Mass Reconstruction of Ds*(2317)± in pp →Ds±Ds(2317)±
Vishwajeet Jha
PANDA Meeting : GSI March 09

2. Motivation : To determine the width of the Ds*(2317)
Present measurements put upper limit ( Γ < 4.6 MeV)
Method:
Experiment : Energy scan around the p pbar →DsDs*(2317) threshold ,
Shape of excitation function gives the width
Simulation : At energy above threshold determine the events in signal
region and from cross section dependence vs. energy
determine the excitation function shape.
Present Work : Missing mass reconstruction of Ds*(2317) for one selected
energy above threshold

3. Signal and Background :
Inclusive reconstruction of signal
ppbar →Ds Ds*(2317) via decay mode Ds→φ π± , φ→K+ K-
Signal generated at GeV ( 0.1 MeV width for Ds*(2317) state)‏
In addition, several background channels were simulated,
Background channels with important contribution in signal region are
ppbar →Ds Ds π+ π- ,
ppbar →Ds Ds 2πo ,
ppbar →Ds Ds* π0

4. Signal ( Φ and Ds candidates):
σ ~ 4 MeV
σ ~ 12 MeV

5. Missing Mass:
Mass window: φ candidates <10 MeV , Ds candidates < 30 MeV
σ ~ 6 MeV
σ ~ 15 MeV
ppbar →Ds Ds*(2317) (Signal)‏ ‏
ppbar →Ds Ds π+ π- (Background)‏

6. Correlation between reconstructed MDs and Missing mass :
ppbar →Ds Ds π+ π- (Background)‏
ppbar →Ds Ds*(2317) (Signal)‏ ‏

7. MSUM = MDs + MMISS
σ ~ 1 MeV

8. Msum‏ ( w/o Ds mass cut)‏
Reconstruction using LHETRACK:
σ ~ 2.5 MeV
σ ~ 1.8 MeV
Msum‏ ( w/o Ds mass cut)‏ ‏

9. Vertex Fitting : Vertex cuts have not been employed in analysis so far
The vertex fitter (with TPC tracks)‏
has an efficiency of ~25% for the
reconstructed Ds candidates from
the ppbar → Ds Ds*(2317) ‏
ppbar →Λ Λbar, Λ →pπ- ,
L=8.72 cm (PDG value =7.89cm)‏

10. Summary:
Simulation studies for ppbar →Ds Ds*(2317) (Signal) have been performed
Missing mass reconstruction give σ ~ 1 MeV.
Simulation for the excitation function shape near threshold
is in progress.