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

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Outline

IntroductionPhysics MotivationCBM Detector ConceptFeasibility StudiesR&D on DetectorsSummary

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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