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CBM-Meet, VECC July 21, 2006 1Premomoy Ghosh CBM – MUCH Simulation for Low-mass Vector Meson Work done at GSI during June 2006
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CBM-Meet, VECC July 21, 2006 2Premomoy Ghosh Talk Layout Introduction Effects on track-reconstruction efficiency due to: Variation in individual absorber thickness Variation in strength of Magnetic Field Future plan
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CBM-Meet, VECC July 21, 2006 3Premomoy Ghosh 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
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CBM-Meet, VECC July 21, 2006 4Premomoy Ghosh Challenges Small branching ratios & signal/background Vector meson Mass MeV/c 2 MeV Multiplicity 25 AGeV Au+Au (central) Branching Ratio ρ 770 149.2 224.6 * 10 -5 ω 7828.49 0.99389 * 10 -5 Central Au+Au @ 25 AGeV Charged particle multiplicity ~ 1600 (UrQMD)
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CBM-Meet, VECC July 21, 2006 5Premomoy Ghosh CBM Much general layout Carbon absorber Detector layers STSTarget Gap between two detector layers = 45 mm Gap between absorber and adjacent detector layer = 1 mm Thickness of each detector layer = 10 mm 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
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CBM-Meet, VECC July 21, 2006 6Premomoy Ghosh Simulation Tools CBM analysis framework – cbmroot and cbmroot2 UrQMD event 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.
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CBM-Meet, VECC July 21, 2006 7Premomoy Ghosh 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.
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CBM-Meet, VECC July 21, 2006 8Premomoy Ghosh cbmroot Muons from PLUTO (rho-old version) and background tracks from UrQMD (central) Much versionSTS+CV8STS+CV20STS+CV9STS+CV12STS+CV18 Absorber thickness 30,40,50,80 =200 cm 80,50,40,30 =200 cm 30,40,50,60 =180 cm 60,50,40,30 =180 cm 45,45,45,45 =180 cm Reconstructed background tracks per 100 events 513493588652574 Reconstructed muon tracks per 1000 events 919908951946951
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CBM-Meet, VECC July 21, 2006 9Premomoy Ghosh 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.
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CBM-Meet, VECC July 21, 2006 10Premomoy Ghosh 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. Muons from PLUTO (rho-old version) comparison of cbmroot and cbmroot2 MUCH_CV8cbmrootcbmroot2 # of reconstructed tracks919558 # of tracks on the 1 st MUCH-detector 11201320
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CBM-Meet, VECC July 21, 2006 11Premomoy Ghosh cbmroot2 Muons from PLUTO (rho-new version) + UrQMD Min. Bias Much versionSTS+CV8STS+CV20STS+CV9STS+CV12STS+CV18 Absorber thickness 30,40,50,80 =200 cm 80,50,40,30 =200 cm 30,40,50,60 =180 cm 60,50,40,30 =180 cm 45,45,45,45 =180 cm Reconstructed background tracks per 1000 events 307243415427455 Reconstructed Muon tracks per 1000 events 404363443396402 Reconstructed Invariant mass (%) 1.40.71.50.90.7 No. of STS hits >=6 Variations in results are not much and may be attributed to statistical uncertainties. We choose CV8 for further studies.
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CBM-Meet, VECC July 21, 2006 12Premomoy Ghosh PLUTO + UrQMD (Min. Bias) 1k events Au+Au 25 AGeV # of muon tracks in STS # of muon tracks in MUCH % of reconstructed signal rho 13904181.8 omega13525932.8 MUCH_CV8 – 1k embedded events comparison between rho and omega No. of STS hits >=4 Each PLUTO event generates 1 dimuon – 1k events corresponds to 2k tracks. Why so less reconstructed tracks and signals? We look into the loss in terms of tracks.
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CBM-Meet, VECC July 21, 2006 13Premomoy Ghosh Muons from PLUTO - rho – MUCH_CV8 – 1k events
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CBM-Meet, VECC July 21, 2006 14Premomoy Ghosh Muons from PLUTO - rho – MUCH_CV8 – 1k events No track below 1 GeV/c in MUCH
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CBM-Meet, VECC July 21, 2006 15Premomoy Ghosh Muons from PLUTO - omega – MUCH_CV8 No track below 1 GeV/c in MUCH
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CBM-Meet, VECC July 21, 2006 16Premomoy Ghosh Muons from PLUTO - rho – MUCH_CV8 – 1k events
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CBM-Meet, VECC July 21, 2006 17Premomoy Ghosh Stages where we loose – PLUTO(rho) – 1k events – as compared to STS - Full Mag. Field
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CBM-Meet, VECC July 21, 2006 18Premomoy Ghosh After every absorber - loss in y_pt - compared to mu-tracks in STS – Full Mag. Field Major loss in MUCH acceptance
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CBM-Meet, VECC July 21, 2006 19Premomoy Ghosh How to catch lower-p muons? –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 Loss may be due to absorption or bending or due to both
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CBM-Meet, VECC July 21, 2006 20Premomoy Ghosh 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
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CBM-Meet, VECC July 21, 2006 21Premomoy Ghosh PLUTO – omega 1k events Au+Au 25 AGeV # of muon tracks in STS # of muon tracks in MUCH % of reconstructed signal omega Full Field 13455953.9 omega.7*Field 13386705.7 Effect of reducing Mag. Field Strength
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CBM-Meet, VECC July 21, 2006 22Premomoy Ghosh 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.
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CBM-Meet, VECC July 21, 2006 23Premomoy Ghosh Effect of reducing Mag. Field Strength – PLUTO omega 1k events
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CBM-Meet, VECC July 21, 2006 24Premomoy Ghosh Effect of reducing Mag. Field Strength PLUTO omega -1k events
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CBM-Meet, VECC July 21, 2006 25Premomoy Ghosh Comparison - momentum resolution – full field and 0.7 Mag. Field –10k events
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CBM-Meet, VECC July 21, 2006 26Premomoy Ghosh Reducing Mag. Field - effect on delta_p/p PLUTO – omega – 10k events Full MF0.9*MF0.8*MF0.7*MF0.6*MF # of muons detected in STS 1349313482134241345313570 # of muons detected in MUCH 60166233636166176819 Mom. Resolution (muons at MUCH) sigma (dp/p)*10 -2 0.57310.61720.71480.79670.9444
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CBM-Meet, VECC July 21, 2006 27Premomoy Ghosh PLUTO (omega) + UrQMD (Min. Bias) 1k events Au+Au 25 AGeV # of muon tracks in STS # of muon tracks in MUCH % of reconstructed signal omega Full Field 13525932.8 omega.7*Field 13415834.8 Effect of reducing Mag. Field Strength 1k embedded events
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CBM-Meet, VECC July 21, 2006 28Premomoy Ghosh 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.
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