Di-muon measurements in CBM experiment at FAIR Arun Prakash 1 Partha Pratim Bhadhuri 2 Subhasis Chattopadhyay 2 Bhartendu Kumar Singh 1 (On behalf of CBM Collaboration) 1 Department of Physics, Banaras Hindu University,Varanasi , India 2 Variable Energy Cyclotron Centre, Kolkata , India

2 Outline Introduction Physics Motivation CBM Detector Concept Feasibility Studies R&D on Detectors Summary

3 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 search for QCD-CP with bulk observables scan of the phase diagram with bulk and rare observables Exploring the QCD Phase diagram

4 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', D 0, 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?

5 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/ψ ψ' sequential dissociation?

6 hep-ph/ 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: CERES Calculations: R. Rapp Data: In+In 158 AGeV, NA60 Calculations: H.v. Hees, R. Rapp  mesons

7 SIS 100/300 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

8 Dipole Magnet MuCh TRDRPC (TOF) PSD STS CBM experiment : Muon set up

9 Muon detection system low-mass vector meson measurements (compact setup) ≡ 7.5 λ I ≡ 13.5 λ I shielding Fe cm Chambers: high resolution gas detectors (major Indian participation) Challenges: High Rate High density Large background

10 Feasibility Studies  Simulation Framework : CBMROOT  Event Generators : Pluto (signal) & UrQMD (background) Central 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

11 Detector acceptance E lab = 25 GeV/n E lab = 35 GeV/n  meson E lab = 8 GeV/n

12 Reconstructed J/ 

13 Invariant mass spectra  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 OmegaJ/Psi

14 Energy (GeV/n) J/ψ→ µ + µ - ω→ µ + µ - J/ψ→ µ + µ - ω→ µ + µ 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 (v 2 ) Elliptic flow parameter (v 2 ), 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 v 2 A given amount of v 2 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/  v 2 following method.

17 Reconstructed v 2 vs. E Lab J/ψ

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 1/4 th ) 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 cm Maximum pad rate:.18 x10 = 1.8 MHz (2 nd 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 cm Maximum pad rate:.18 x10 = 1.8 MHz (2 nd station) Experimental Challenge : High Hit Density

Schematic and assembled GEM test Chambers GEMS Drift plane (inner side copper plated) 12 x cm 12 cm x 10 mm -- perspex Readout PCB

Chamber Gain Energy Resolution Efficiency

HV=3600 MPV=24 MPV=32 MPV=41 MPV=60 MIP spectra (cosmic test) at different HVs

22 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

23 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