CBM – MUCH Simulation for Low-mass Vector Meson

1. CBM – MUCH Simulationfor Low-mass Vector Meson Work done at GSI during June 2006 Premomoy Ghosh

2. Talk Layout Introduction Effects on track-reconstruction efficiency due to: • Variation in individual absorber thickness • Variation in strength of Magnetic Field Future plan Premomoy Ghosh

3. The Physics motivation of CBM leads to the requirement • of a Muon Chamber (MUCH) for detecting muons from • decays of low-mass vector mesons. • Simulation for such a MUCH has been initiated recently. • Studies on some the aspects will be presented here. • CBM will be equipped with Silicon Tracking Station (STS) • in magnetic field for: • Track reconstruction of all charged particles • Vertex reconstruction • Tracks reconstructed in STS have to be matched to hits in • MUCH Premomoy Ghosh

4. Challenges Small branching ratios & signal/background Central Au+Au @ 25 AGeV Charged particle multiplicity ~ 1600 (UrQMD) Premomoy Ghosh

5. CBM Much general layout Gap between two detector layers = 45 mm Gap between absorber and adjacent detector layer = 1 mm Thickness of each detector layer = 10 mm • Carbon absorber • Detector layers Target STS • 4 carbon absorbers & 13 detector layers • Three detector layers in between 2 absorbers Sliced absorbers placed in between detector layers – to facilitate efficient track matching for low momentum particles Premomoy Ghosh

6. Simulation Tools • CBM analysis framework – cbmroot and cbmroot2 • UrQMDevent generator - Au + Au events at 25 GeV/nucleon. • PLUTO event generator – Muons from light vector meson decay. • UrQMD events, embedded with PLUTO events or with generated single particle muons, were transported through STS (with magnetic field on) and MUCH. • Track reconstruction in STS in done with with the option - Ideal Tracking. Premomoy Ghosh

7. Variation in thicknesses of individual absorbers • Individual absorber-thicknesses likely to affect track matching due to: - Hit-density - Deviation due to multiple scattering • Started in cbmroot • Followed previous configuration: • Studied cases with total thickness of 180, 190 and 200 cm. • Different geometry versions -> varied thicknesses of individual absorbers. • For different geometry versions run transport and tracking for 1000 PLUTO events and 100 PLUTO+UrQMD (central) events. • Studied in terms of # of surviving muons and background tracks. Premomoy Ghosh

8. cbmrootMuons from PLUTO (rho-old version) and background tracks from UrQMD (central) Premomoy Ghosh

9. Variation of absorber thickness contd. • Switched over to new framework - cbmroot2 • Changes in software structure • MUCH-codes newly installed – not yet thoroughly tested • PLUTO for rho changed • Magnetic Field changed • Position of MUCH changed • Repeated some parts of the study. Premomoy Ghosh

10. Muons from PLUTO (rho-old version) comparison of cbmroot and cbmroot2 • Even for same geometry, results in cbmroot2 are very much different from those from cbmroot(!) • Magnetic field or some bugs in codes or something else – What is responsible? • Needs thorough investigation to understand differences in results. Premomoy Ghosh

11. cbmroot2Muons from PLUTO (rho-new version) + UrQMD Min. Bias No. of STS hits >=6 Variations in results are not much and may be attributed to statistical uncertainties. We choose CV8 for further studies. Premomoy Ghosh

12. MUCH_CV8 – 1k embedded eventscomparison between rho and omega Each PLUTO event generates 1 dimuon – 1k events corresponds to 2k tracks. Why so less reconstructed tracks and signals? No. of STS hits >=4 We look into the loss in terms of tracks. Premomoy Ghosh

13. Muons from PLUTO - rho – MUCH_CV8 – 1k events Premomoy Ghosh

14. Muons from PLUTO - rho – MUCH_CV8 – 1k events No track below 1 GeV/c in MUCH Premomoy Ghosh

15. Muons from PLUTO - omega – MUCH_CV8 No track below 1 GeV/c in MUCH Premomoy Ghosh

16. Muons from PLUTO - rho – MUCH_CV8 – 1k events Premomoy Ghosh

17. Stages where we loose – PLUTO(rho) – 1k events – as compared to STS - Full Mag. Field Premomoy Ghosh

18. After every absorber - loss in y_pt - compared to mu-tracks in STS – Full Mag. Field Major loss in MUCH acceptance Premomoy Ghosh

19. How to catch lower-p muons? Loss may be due to absorption or bending or due to both • Reduce absorber thickness -> allows more background. • Reduce magnetic field strength that bends low momentum particles out of acceptance-> affects momentum resolution. • Improvement in track-matching. • We study effects of reducing magnetic field strength Premomoy Ghosh

20. To study the effect of reducing magnetic field strength on acceptance at MUCH - selected MUCH_CV8 with PLUTO events for rho (new version) and omega. We present here the case of omega. • Run with minimal cuts at signal reconstruction (p_min = 0.5 GeV/c, OA = 120, SPd= -0.26 and Spu= 0.04) • Study with Ideal Tracking Premomoy Ghosh

21. Effect of reducing Mag. Field Strength Premomoy Ghosh

22. Effect of reducing Mag. Field Strength PLUTO omega 1k events By reducing mag. field strength, we gain. But, low momentum (<1 GeV/c) muons are still missing – may be due to absorption. Premomoy Ghosh

23. Effect of reducing Mag. Field Strength – PLUTO omega 1k events Premomoy Ghosh

24. Effect of reducing Mag. Field Strength PLUTO omega -1k events Premomoy Ghosh

25. Comparison - momentum resolution – full field and 0.7 Mag. Field –10k events Premomoy Ghosh

26. Reducing Mag. Field - effect on delta_p/p Premomoy Ghosh

27. Effect of reducing Mag. Field Strength 1k embedded events Premomoy Ghosh

28. Conclusion and Plan • Difference in results from cbmroot and cbmroot2 needs to be understood. • More systematic study on absorber thickness and strength of magnetic field is required. • Present study – singles muons and pions – varying carbon absorber thickness – different momentum (at GSI machine). • After optimizing absorber thickness and magnetic field strength, depending on the acceptable background and momentum resolution respectively, improvement in track-matching efficiency may be addressed. • Plan: • To install the codes at VECC machine and continue. Premomoy Ghosh