Muon detection in the CBM experiment at FAIR Andrey Lebedev 1,2 Claudia Höhne 1 Ivan Kisel 1 Anna Kiseleva 3 Gennady Ososkov 2 1 GSI Helmholtzzentrum für Schwerionenforschung GmbH, Darmstadt, Germany 2 Laboratory of Information Technologies, Joint Institute for Nuclear Research, Dubna, Russia 3 Frankfurt University, Germany DPG 2010 March 15-19, 2010 Bonn

2/10 A.Lebedev et al. Muon detection in the CBM Experiment at FAIR The CBM experiment at FAIR exploration of the QCD phase diagram in regions of high baryon densities and moderate temperatures comprehensive measurement of hadron and lepton (vector mesons  μ + μ - ) production in pp, pA and AA collisions for 8-45 AGeV beam energy fixed target experiment beam STS track, vertex and momentum reconstruction MUCH muon identification TRD in case of muons only tracking TOF time of flight measurement

3/10 A.Lebedev et al. Muon detection in the CBM Experiment at FAIR Challenges for μ identification Peculiarities for CBM: large track multiplicities ‒ up to 800 charged particles per reaction in +/- 25˚ high reaction rate ‒ up to 10 MHz reconstruction of low momentum muons (p> 1 GeV/c) measurement of rare probes  fast and efficient trigger and tracking algorithms major background of muons from pion and kaon decay punch through of hadrons, track mismatches huge amount of data : foreseen are currently 1Gb/s archiving rate (600Tb/week) Central Au+Au collision at 25 AGeV (UrQMD + GEANT3) → clean μ identification → absorber-detector layers for continues tracking and variable μ ID for different momentum ranges → fast tracking algorithms are essential standard: muon identification by absorber technique

4/10 A.Lebedev et al. Muon detection in the CBM Experiment at FAIR The Muon detector (MUCH) 3 detector stations between the absorbers Low mass vector mesons 5 Fe absorbers (125 cm) 7.5 I, p> 1 GeV/c Charmonium 6 Fe absorbers (225 cm) 13.5 I, p> 2.8 GeV/c Measurements of: Alternating detector-absorber layout for continuous tracking of muons through the absorber Detector challenges: High hit density (up to 1 hit per cm 2 per event) High event rates (up to 10 7 events/s) Position resolution < 300 μm → consider GEMs (minimum pad size 2.8x2.8 mm 2 ) for first stations → for the last stations straw tubes are under investigation

5/10 A.Lebedev et al. Muon detection in the CBM Experiment at FAIR Track reconstruction algorithm Two main steps: – Tracking – Global track selection Track propagation Inhomogeneous magnetic field: ‒ solution of the equation of motion with the 4 th order Runge-Kutta method Large material budget: ‒ Energy loss (ionization: Bethe-Bloch, bremsstrahlung: Bethe-Heitler, pair production) ‒ Multiple scattering (Gaussian approximation) Tracking is based on Track following Initial seeds are tracks reconstructed in the STS (fast Cellular Automaton (CA), I.Kisel) Kalman Filter Validation gate Hit-to-track association techniques ‒ nearest neighbor: attaches the closest hit from the validation gate Global track selection aim: remove clone and ghost tracks tracks are sorted by their quality, obtained by chi-square and track length Check for shared hits

6/10 A.Lebedev et al. Muon detection in the CBM Experiment at FAIR Optimization and parallelism Parallel programming is mainstream! SIMD: Single Instruction Multiple Data Multithreading make use of many core CPUs Algorithm optimization Minimize access to global memory: approximation of the MF map Simplification of the detector geometry Computational optimization of the Kalman Filter float precision Time [ms/event]Speedup Initial730- Optimization SIMDization Multithreading Final Computer with 2xCPUs Intel Core i7 (8 cores in total) at 2.67 GHz Parallel tracking performance Minor loss in tracking efficiency: 94.7%  94.0% Significant speedup of the track finder:

7/10 A.Lebedev et al. Muon detection in the CBM Experiment at FAIR Tracking performance Simulation: UrQMD events at 25 AGeV AuAu collisions + 5 μ + and 5 μ - Tracking efficiency vs. momentum 225 cm Fe 125 cm Fe

8/10 A.Lebedev et al. Muon detection in the CBM Experiment at FAIR Reconstructed background per central Au+Au collision at 25 AGeV beam energy select primary vertex tracks (impact parameter) cut on  2 of reconstructed MUCH tracks Cuts: Muon identification Rejection of muons from pion and kaon decays in STS applying different cuts 125 cm Fe

9/10 A.Lebedev et al. Muon detection in the CBM Experiment at FAIR Physics feasibility study for low-mass vector mesons and J/  reconstruction in central Au+Au collisions at 25 AGeV beam energy signals  J/ψ  Ψ'  background signals  ρ  ω  φ  η  η Dalitz  background Signal-to- Background (S/B) ratio Efficiency (%) Mass resolution (MeV)ω φ J/ψ Ψ' Muon identification

10/10 A.Lebedev et al. Muon detection in the CBM Experiment at FAIR Summary Succesful demonstration of track reconstruction in the proposed muon detector: – 95% tracking efficiency for muons passing the absorber; even in the high track density environment – low rate of ghosts, clones and track mismatches Physics feasibility studies on J/  and low-mass vector meson reconstruction promising Preparation of fast reconstruction algorithms ‒ Optimization and parallelization of algorithms: speedup factor of 2400 for track fit; factor 487 for track finder → Develop fast trigger algorithms → Use established tracking routines for layout optimization → Investigate new parallel languages (CUDA, OpenCL)

11/10 A.Lebedev et al. Muon detection in the CBM Experiment at FAIR Backup

12/10 A.Lebedev et al. Muon detection in the CBM Experiment at FAIR Acceptance for vector mesons Rho acceptanceJ/psi acceptance

13/10 A.Lebedev et al. Muon detection in the CBM Experiment at FAIR Absorption of particles Absorption of particles vs. absorber length

14/10 A.Lebedev et al. Muon detection in the CBM Experiment at FAIR Efficiency Rho efficiency LMVM: Pt vs. invariant mass