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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
2
Outline
IntroductionPhysics MotivationCBM Detector ConceptFeasibility StudiesR&D on DetectorsSummary
3
High-energy heavy-ion collision experiments:
RHIC, LHC: cross over transition, QGP at high T and low ρLow-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
Exploring the QCD Phase diagram
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Onset of chiral symmetry restoration at high B
in-medium modifications of hadrons (,, e+e-(μ+μ-), D)
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)
The equation-of-state at high B
collective flow of hadrons
particle production at threshold energies (open charm?)
QCD critical endpoint
excitation function of event-by-event fluctuations (K/π,...)
CBM: detailed measurement over precise energy bins (pp, pA,
AA) FAIR beam energy range 2-45 AGeV (protons 90 GeV)
What do we need to measure?
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Quarkonium dissociation temperatures:
(Digal, Karsch, Satz)
Measure excitation functions of J/ψ and ψ' in p+p, p+A and A+A collisions !
rescaled
to
158 GeV
Probing the quark-gluon plasma with charmonium
J/ψψ'
sequential dissociation?
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hep-ph/0604269
Hadronic properties are expected to be affected by the enormous baryon densities
→ -meson is expected to melt at high baryon densities
In-medium modifications
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
Data: CERESCalculations: R. Rapp
Data: In+In 158 AGeV, NA60
Calculations: H.v. Hees, R. Rapp
mesons
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SIS100/300
Multiplicity in central Au+Au collisions
W. Cassing, E. Bratkovskaya, A. Sibirtsev, Nucl. Phys. A 691 (2001) 745
Rare particles with high statistics
High beam intensity
Interaction rate: 10 MHz
Fast detectors/DAQ
Low charm multiplicity
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Dipole Magnet
MuChTRD RPC (TOF) PSD
STS
CBM experiment : Muon set up
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Muon detection system
low-mass vector mesonmeasurements
(compact setup) ≡ 7.5 λI ≡ 13.5 λI
shielding
Fe20 2
0 20
30 35
100 cm
Chambers:
high resolution gas
detectors
(major Indian participation)
Challenges:
High Rate
High density
Large background
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Feasibility Studies
Simulation Framework : CBMROOT
Event Generators : Pluto (signal) & UrQMD (background)
Central Au+Au @ 8 AGeV, 25 AGeV & 35 AGeV
Transport : Geant-3
Reconstruction: Segmentation(minimum pad size 2 mm x 4 mm,
maximum pad size 3.2 cm x 3.2 cm, total number of pads: 0.5 Million
GEM avalanche and clustering not included.
Tracking: Propagation from STS tracks using
Cellular Automaton & Kalman Filter
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Detector acceptance
Elab = 25 GeV/n Elab = 35 GeV/n meson
Elab = 8 GeV/n
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Reconstructed J/
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Invariant mass spectra
Combinatorial background is calculated using Super Event (SE) analysisTracks from different UrQMD events are combined Mass peaks visible for LMVM and charmoniaExcellent signal/background for J/psi
Omega J/Psi
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Energy (GeV/n)
J/ψ→ µ+ µ- ω→ µ+ µ- J/ψ→ µ+ µ- ω→ µ+ µ-
8 4.9 .96 3.3 1.41
25 13 1.58 7 .49
35 13 1.82 11 .34
Efficiency (%) S/B
Optimized for Segmentation : Minm. Pad size: 4 mm. * 4mm. Maxm. Pad size: 3.2 cm. * 3.2 cm.
Results of the full reconstruction
Elliptic flow (v2)
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.
At FAIR energy regime, charm quarks will be produced early in the reaction.
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
A given amount of v2 is added at the input level to J/’s in Pluto.
The J/’s are deacyed into di-muons.
Transport through cbm muon detection set-up.
Reconstruction & selection of single muon tracks following
standard analysis.
Reconstruction of J/ following 4-momentum conservation.
Calculation of J/ v2 following <cos2> method.
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Reconstructed v2 vs. E Lab
J/ψ
DATA RATETwo 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 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 cmMaximum pad rate: .18 x10 = 1.8 MHz (2nd station)
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 cmMaximum pad rate: .18 x10 = 1.8 MHz (2nd station)
Experimental Challenge : High Hit Density
Schematic and assembled GEM test Chambers
GEMS
1 2 3
Drift plane
(inner side copper plated)
12 x cm 12 cm x 10 mm -- perspex
Readout PCB
Chamber Gain
Energy ResolutionEfficiency
HV=3600
MPV=24MPV=24 MPV=32MPV=32
MPV=41MPV=41 MPV=60MPV=60
MIP spectra (cosmic test) at different HVs
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MIP spectra with HV
GEM-based detector R&D for MUCH
•98% efficiency achieved
•Linearity with HV
•Beam spot seen even with 1.6 mm pad width
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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