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Simulation of Muons in the Fe-DHCAL

Simulation of Muons in the Fe-DHCAL. Jos é Repond Argonne National Laboratory. (S)DHCAL Meeting Lyon, France January 15, 2014. Monte Carlo Simulation Strategy. Experimental set-up Beam (E,particle,x,y,x’,y’). Measured signal Q distribution. Points (E depositions in gas gap: x,y,z ).

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Simulation of Muons in the Fe-DHCAL

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  1. Simulation of Muons in the Fe-DHCAL JoséRepond Argonne National Laboratory (S)DHCAL Meeting Lyon, France January 15, 2014

  2. Monte Carlo Simulation Strategy Experimental set-up Beam (E,particle,x,y,x’,y’) Measured signal Q distribution Points (E depositions in gas gap: x,y,z) GEANT4 RPC response simulation Hits Parameters Distance cut dcut (within which only 1 avalanche) Charge adjustment Q0 (if needed) Exponential slopes a1, a2 (of signal spread in pad plane) Ratio R (between 2 exponentials) Threshold T (of discriminator) Hits Comparison DATA With muons – tune a1, a2, R, T, (dcut), and Q0 With positrons – tune dcut Pions – no additional tuning

  3. Geometrical setup 38 layers interleaved with Steel absorber plates Large 1 x 1 m2 Scintillator paddles in front of DHCAL and back of TCMT +32 GeV/c secondary beam plus 3m Fe blocker Spill of 3.5 seconds DAQ rate typically 500 – 1000/spill Muon simulation GEANT4 Physics list – QGSP_Bert (believed to be irrelevant) Range cut 0.005 mm Muons of 32 GeV (no difference if 10 or 20 GeV) Trigger DHCAL TCMT 1 x 1 m2 Scintillator Paddle A 1 x 1 m2 Scintillator Paddle B

  4. Event selection Tracks at least 3 active layers (this requirement is to safe time, otherwise irrelevant) < 2 clusters per layer (otherwise don’t reconstruct track for that layer) at least 4 tracking layers (again to safe time, otherwise irrelevant) Only use clusters with less than 5 hits (but keep the event if more than 4 hits) (in more recent analysis of run 650265 reject track if any tracking cluster has more than 4 hits) Look for clusters in investigated layer within 2.5 cm Clean tracks Reduced chi2 < 1.0 At least 11/38 tracking layers Slope less than 3 degrees

  5. RPC_sim Generate a total charge Charge generated according to our own measurement with analog system In reality the charge depends on distance of first ionization from anode This approach is correct in average, but ignores higher ionization probabilities of non-MIPs Burak is currently trying to implement something more sophisticated into his simulation → see later Ignore close by avalanches An avalanche will deplete the electric field and so a second avalanche within a small radius (parameter of simulation) is unlikely

  6. RPC_sim Spread of charge on anode surface Use of different functions with 1 – 3 parameters Determine charge on each pad (using MC method) Add charge from different avalanches This takes care of simulating showers properly Apply a threshold This is also a parameter of the simulation

  7. RPC_sim_3 Parameters Distance dcut Distance under which there can be only one avalanche (one point of a pair of points randomly discarded if closer than dcut) Charge Q0 Shift applied to charge distribution to accommodate possible differences in the operating point of RPCs Slope a1 Slope of exponential decrease of charge induced in the readout plane Slope a2 Slope of 2nd exponential, needed to describe tail towards larger number of hits Ratio R Relative contribution of the 2 exponentials Threshold T Threshold applied to the charge on a given pad to register a hit Only used in 2 exponential parameterization

  8. Strategy for tuning RPC_sim Ensure proper simulation of impact point and angular spread Use only first 10 layers to determine track parameters Define ‘clean’ regions To be used to determine calibration factors To first order independent of local beam intensity in detector plane Tune parameters in ‘clean’ regions This takes a long time Then look at entire plane Modify charge at borders to simulate loss of efficiency/multiplicity Recheck ‘clean’ regions To make sure they are still well simulated

  9. RPC_sim Programs Measure ‘Response per layer’ and not ‘sum of hits’ This has reduced dependence on beam’s angular distribution Note Applied to positron/pion data we observe large differences in shower shapes Uncertainty in digitization will be packed into systematic error of simulation → see later

  10. Distribution of charge on anode Done with MC technique Only add up charges within a maximum radius = 4 cm n_int = number of throws →n_int = 50,000 (unfortunately, slows program down significantly)

  11. Muon response in ‘clean’ regions • Dead ASICs (cut away an area of 8 x 8 cm2 plus a rim of 1 cm) • Edges in x (cut away 6.0 cm from the 2 edges in x) • Edges in y (cut away 6.0 cm from the 6 edges in y) • Fishing lines (cut away ±1 cm around fishing line) • Layer 27 (which showed unusually high pad multiplicity) J. Repond - The DHCAL

  12. Comparison of different RPC_sim programs In ‘clean’ regions only RPC_sim_4 1 exponential Can’t do the tail RPC_sim_3 2 exponentials Core not as good

  13. RPC_sim_5 2 Gaussians Bin 4 a problem RPC_sim_6 ‘Function’ Tail no good My preference goes to RPC_sim_5

  14. RPC_sim_5 in ‘entire’ plane

  15. Systematic effect in upper/lower RPC (will be corrected with calibration)

  16. Backup

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