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Di-muon measurements in CBM
experiment at FAIR
Arun Prakash1
Partha Pratim Bhadhuri2
Subhasis Chattopadhyay2
Bhartendu Kumar Singh1
(On behalf of CBM Collaboration)
1 Department of Physics , Banaras Hindu University,Varanasi 221 005, India
2 Variable Energy Cyclotron Centre , Kolkata -700 0064, India
Outline
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Introduction
Physics Motivation
CBM Detector Concept
Feasibility Studies
R&D on Detectors
Summary
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Exploring the QCD Phase diagram
High-energy heavy-ion collision experiments:
RHIC, LHC: cross over transition, QGP at high T and low ρ
Low-energy RHIC: search for QCD-CP with bulk observables
NA61@SPS: search for QCD-CP with bulk observables
CBM@FAIR: scan of the phase diagram with bulk and rare observables
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What do we need to measure?
The equation-of-state at high B
 collective flow of hadrons
 particle production at threshold energies (open charm?)
Deconfinement phase transition at high B
 excitation function and flow of strangeness (K, , , , )
 excitation function and flow of charm (J/ψ, ψ', D0, D, c)
QCD critical endpoint
 excitation function of event-by-event fluctuations (K/π,...)
Onset of chiral symmetry restoration at high B
 in-medium modifications of hadrons (,, e+e-(μ+μ-), D)
CBM: detailed measurement over precise energy bins (pp, pA, AA)
FAIR beam energy range 2-45 AGeV (protons 90 GeV)
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Probing the quark-gluon plasma with charmonium
J/ψ
ψ'
rescaled
to
158 GeV
Quarkonium dissociation temperatures:
(Digal, Karsch, Satz)
sequential dissociation?
Measure excitation functions of J/ψ and ψ' in p+p, p+A and A+A collisions !
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In-medium modifications
mesons
Hadronic properties are expected to be affected by the enormous baryon densities
Data: In+In 158 AGeV, NA60
→ -meson is expected to melt at high baryon densities
Data: CERES
Calculations: R. Rapp
Calculations: H.v. Hees, R. Rapp
hep-ph/0604269
no ρ,ω,φ → e+e- (μ+μ-) data between 2 and 40 AGeV
no J/ψ, ψ' → e+e- (μ+μ-) data below 160 AGeV
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Multiplicity in central Au+Au collisions
W. Cassing, E. Bratkovskaya, A. Sibirtsev, Nucl. Phys. A 691 (2001) 745
Low charm multiplicity
Rare particles with high statistics
SIS
100/300
High beam intensity
Interaction rate: 10 MHz
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Fast detectors/DAQ
CBM experiment : Muon set up
TRD
MuCh
RPC (TOF)
PSD
Dipole Magnet
STS
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Muon detection system
Chambers:
high resolution gas
Fe
detectors
(major
Indian participation)
shielding
Challenges:
High Rate
High density
low-mass vector meson
measurements
(compact setup)
Large background
≡ 7.5 λI
≡ 13.5 λI
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Feasibility Studies
Simulation Framework : CBMROOT
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Event Generators : Pluto (signal) & UrQMD (background)
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Central Au+Au @ 8 AGeV, 25 AGeV & 35 AGeV
Transport : Geant-3
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Reconstruction: Segmentation(minimum pad size 2 mm x 4 mm,
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maximum pad size 3.2 cm x 3.2 cm, total number of pads: 0.5 Million
GEM avalanche and clustering not included.
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Tracking: Propagation from STS tracks using
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Cellular Automaton & Kalman Filter
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Detector acceptance
Elab = 8 GeV/n
meson
Elab = 35 GeV/n
Elab = 25 GeV/n
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Reconstructed J/
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Invariant mass spectra
Omega
J/Psi
Combinatorial background is calculated using Super Event (SE)
analysis
Tracks from different UrQMD events are combined
 Mass peaks visible for LMVM and charmonia
Excellent signal/background for J/psi
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Results of the full reconstruction
Efficiency (%)
S/B
Energy
(GeV/n)
J/ψ→ µ+ µ-
ω→ µ+ µ-
J/ψ→ µ+ µ-
ω→ µ+ µ-
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4.9
.96
3.3
1.41
25
13
1.58
7
.49
35
13
1.82
11
.34
Optimized for Segmentation :
Minm. Pad size: 4 mm. * 4mm. Maxm. Pad size: 3.2 cm. * 3.2 cm.
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Elliptic flow (v2)
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Elliptic flow parameter (v2) , signals a strong evidence for the creation of a hot
& dense system at a very early stage in the non-central collisions.
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At FAIR energy regime, charm quarks will be produced early in the reaction.
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Collectivity of charm quarks (radial & elliptic flow) in Au+Au collisions, would
indicate that early time dynamics is governed by partonic collectivity.
Simulation of v2
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A given amount of v2 is added at the input level to J/’s in Pluto.
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The J/’s are deacyed into di-muons.
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Transport through cbm muon detection set-up.
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Reconstruction & selection of single muon tracks following
standard analysis.
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Reconstruction of J/ following 4-momentum conservation.
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Calculation of J/ v2 following <cos2> method.
Reconstructed v2 vs. E Lab
J/ψ
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Experimental Challenge : High Hit Density
DATA RATE
Two numbers:
(a) number of points on MUCH layers (points/cm^2/event
(will tell the particle rate)
(b) Number of cells fired/event, will give the data rate
(Numbers below are for central events, for minb, it will be 1/4th)
Number of points/cm^2/event
For 1cm x 1cm size pad, data rate will be10
MHz (beam rate) x .12 = 1.2 MHz on first layer
So, we need to have smaller pads
Number of pads/event:
Pad sizes:
layer 1: 0.4cm x 0.4cm, 0.5cm x 0.5cm, 1cm x1cm
layer 2 onwards: 1.6cm x 1.6 cm
Maximum pad rate: .18 x10 = 1.8 MHz (2nd station)
Schematic and assembled GEM test Chambers
Readout PCB
GEMS
1 2 3
Drift plane
(inner side copper plated)
12 x cm 12 cm x 10 mm -- perspex
Chamber Gain
Energy Resolution
Efficiency
MIP spectra (cosmic test) at different HVs
MPV=24
MPV=32
HV=3600
MPV=41
MPV=60
GEM-based detector R&D for MUCH
98% efficiency achieved
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Linearity with HV
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Beam spot seen even with 1.6 mm pad width
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MIP spectra with HV
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Summary
Dimuon measurement will be important observable
in the CBM experiment
Set up is designed to measure both LMVM
and charmonium through dimuon channel
Simulation performed with full reconstruction and geometry
establishes the feasibility of the experiment
R&D on detectors is ongoing using GEM technology
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