Hadron Performance in BES III detector

1. Hadron Performance in BES III detector Ji X.B., Li G., Sun S.S., Wang L.L. IHEP Jan. 10 – 12, 2006

2. Outline • Reconstruction efficiency of hadron • PID & its efficiency • J/ physics ( ) • Summary All works are based on BOSS 5.0.0 BES III meeting

3. Reconstruction efficiency • is used to get the efficiency of proton, anti-proton and pion • is used to get the efficiency of pion and kaon and KS • is used to measure the soft pion efficiency BES III meeting

4. Method • Good hardron selection(Very loose cut criteria ) Rxy < 1 cm, Z < 5 cm|cos\theta| < 0.93probPID > 0.001 (combined probability of dE/dx, TOF1, TOF2) • Event Selection At lease 3 particles should be reconstructed and identified • Efficiency BES III meeting

5. Advantage: • Large Branch ratio (6.0  0.5)x 10-3 • No neutral tracks • Momentum range is wide • Low background Total 50,000 MC events are used. BES III meeting

6. Momentum distribution pi P (0.0, 0.8) Range: (0.0, 1.1) BES III meeting

7. Missing mass P AP - + BES III meeting

8. Match criteria • The missing direction |cos < 0.8| • The angle between the expected direction and the measured direction  < 15o cos BES III meeting

9.  distribution AP P + - BES III meeting

10. Reconstruction efficiency P AP - + BES III meeting

11. (Sun S.S.) • 100,000 MC sample is used • is used to get the efficiency of pion and kaon • is used to get the efficiency of KS BES III meeting

12. Missing mass mK2 m2 BES III meeting

13. Reconstruction efficiency + - K+ K- BES III meeting

14. Reconstruction efficiency of KS mKs2 BES III meeting

15. (Li G.) • The decay mode of J/+- is used to reconstruct the J/  • The particle with momentum less than 0.5 GeV/c is regarded as pion BES III meeting

16. Tracking efficiency of pion BES III meeting

17. Charged Particle Identification • Method:  of dE/dx, Tof after reconstruction should obey standard normal distribution for a certain charged track: χdEdx=((dEdx)measured -(dEdx)exp)/(dEdx)exp χTof=((TOF)measured -(TOF)exp)/(TOF)exp So χ2= χ2dEdx+χ2TOF1+χ2TOF2 (+χ2EMCE+χ2TOF1Q+……) should obey χ2distribution. We use quantity CL(χ2measured→+∞) of χ2distribution to identify charged particles. BES III meeting

18. Charged Particle Identification • Distribution of CL ( sample) BES III meeting

19. Rec & PID efficiency( ) Prob>0.001 P AP - + BES III meeting

20. Rec &PID efficiency( ) rec. only rec. & PID K- K+ Prob>0.001 - + BES III meeting

21. J/ygpp M=1859 MeV/c2 G < 30 MeV/c2 (90% CL) 0.2 0 0.1 0.3 M(pp)-2mp (GeV) MC Study of . • Motivation • “Observation of a near-threshold enhancement in the ppbar mass spectrum from radiative J/ppbar decays” BES II, 2003 • JPC maybe 0-+ or 0++ • High precision measurement is important to determine the properties of the structure BES III meeting

22. MC Study of . (Only very preliminary results) • The mainly background is • MC used(all generated by HOWL) : BES III meeting

23. Event Selection • Two good charged tracks with opposite charge • At least one good photon • Umiss < 0.02, Ptr < 0.001Umiss = Emiss – PmissPtr = 4Pmiss2sin2(/2) BES III meeting

24. Umiss Ptr signal background BES III meeting

25. Normalized according to their Br J/X BES III meeting

26. Summary • The tracking efficiency and PID efficiency of hardrons are measured from different decay modes • A rough estimation of proton anti-proton threshold enhancement • Many works should be done in the future BES III meeting

27. Thank You! BES III meeting

28. Rec and PID BES III meeting

29. 1M BES III meeting

30. Different pid BES III meeting

31. Chi BES III meeting

32. angle BES III meeting