CBM

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CBM MUCH Simulationfor Low-mass Vector Meson

• Work done at GSI during
• June 2006

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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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• 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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Challenges Small branching ratios
signal/background
Central AuAu _at_ 25 AGeV Charged particle
multiplicity 1600 (UrQMD)
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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

STS
Target
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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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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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 -gt varied thicknesses
  of individual absorbers.
• For different geometry versions run transport and
  tracking for 1000 PLUTO events and 100
  PLUTOUrQMD (central) events.
• Studied in terms of of surviving muons and
  background tracks.

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

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cbmroot2Muons from PLUTO (rho-new version)
UrQMD Min. Bias
No. of STS hits gt6
Variations in results are not much and may be
attributed to statistical uncertainties. We
choose CV8 for further studies.
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MUCH_CV8 1k embedded eventscomparison between
rho and omega
No. of STS hits gt4
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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Muons from PLUTO - rho MUCH_CV8 1k events
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Muons from PLUTO - rho MUCH_CV8 1k events
No track below 1 GeV/c in MUCH
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Muons from PLUTO - omega MUCH_CV8
No track below 1 GeV/c in MUCH
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Muons from PLUTO - rho MUCH_CV8 1k events
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Stages where we loose PLUTO(rho) 1k events
as compared to STS - Full Mag. Field
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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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How to catch lower-p muons?
Loss may be due to absorption or bending or due
to both

• Reduce absorber thickness -gt allows more
  background.
• Reduce magnetic field strength that bends low
  momentum particles out of acceptance-gt affects
  momentum resolution.
• Improvement in track-matching.

We study effects of reducing magnetic field
strength
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• 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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Effect of reducing Mag. Field Strength
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Effect of reducing Mag. Field Strength PLUTO
omega 1k events
By reducing mag. field strength, we gain. But,
low momentum (lt1 GeV/c) muons are still missing
may be due to absorption.
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Effect of reducing Mag. Field Strength
PLUTO omega 1k events
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Effect of reducing Mag. Field Strength PLUTO
omega -1k events
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Comparison - momentum resolution full field
and 0.7 Mag. Field 10k events
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Reducing Mag. Field - effect on delta_p/p
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Effect of reducing Mag. Field Strength 1k
embedded events
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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.