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CBM

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Low-mass Vector Meson. Work done at GSI during. June 2006. CBM ... Effects on track-reconstruction efficiency due to: Variation in individual absorber thickness ... – PowerPoint PPT presentation

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Title: CBM


1
CBM MUCH Simulationfor Low-mass Vector Meson
  • Work done at GSI during
  • June 2006

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

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

4
Challenges Small branching ratios
signal/background
Central AuAu _at_ 25 AGeV Charged particle
multiplicity 1600 (UrQMD)
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

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
6
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.

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 -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.

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

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.

11
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.
12
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.
13
Muons from PLUTO - rho MUCH_CV8 1k events
14
Muons from PLUTO - rho MUCH_CV8 1k events
No track below 1 GeV/c in MUCH
15
Muons from PLUTO - omega MUCH_CV8
No track below 1 GeV/c in MUCH
16
Muons from PLUTO - rho MUCH_CV8 1k events
17
Stages where we loose PLUTO(rho) 1k events
as compared to STS - Full Mag. Field
18
After every absorber - loss in y_pt - compared to
mu-tracks in STS Full Mag. Field
Major loss in MUCH acceptance
19
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
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

21
Effect of reducing Mag. Field Strength
22
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.
23
Effect of reducing Mag. Field Strength
PLUTO omega 1k events
24
Effect of reducing Mag. Field Strength PLUTO
omega -1k events
25
Comparison - momentum resolution full field
and 0.7 Mag. Field 10k events
26
Reducing Mag. Field - effect on delta_p/p
27
Effect of reducing Mag. Field Strength 1k
embedded events
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.
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