A. SarratILC TPC meeting, DESY, 15/02/06 Simulation Of a TPC For T2K Near Detector Using Geant 4 Antony Sarrat CEA Saclay, Dapnia

A. SarratILC TPC meeting, DESY, 15/02/06 Introduction T2K near detector will have 3 TPCs for PID and momentum measurement. A TPC equipped with Micromegas detector was tested at CERN in Nov –> Monte Carlo simulation of these tests Useful for resolution study (vs pad size, magnetic field, gas properties, …)

A. SarratILC TPC meeting, DESY, 15/02/06 T2K Near Detector Magnet + Side-MRD P0D TPC FGD Pb-P0D EM calorimeter FGD+H 2 O beam

A. SarratILC TPC meeting, DESY, 15/02/06 CERN Setup (HARP TPC) Micromegas End-plate ~ 52 cm ~ 26 cm HARP TPC ~ 154 cm ~ 1300 cm 2 instrumented ~1.5m drift length

A. SarratILC TPC meeting, DESY, 15/02/06 The Monte Carlo Simulation

A. SarratILC TPC meeting, DESY, 15/02/06 Flow Chart Geant 4 used for the tracking. Everything else done manually (through Geant user’s routine)

A. SarratILC TPC meeting, DESY, 15/02/06 Detector Simulation Magnet (Fe) B = 0.0, 0.2 and 0.4T TPC’s body (Al) Drift volume (gas) Ar + CF 4 + IsoC 4 H 10 (3%) (2%) or e.g. Ar + CO 2

A. SarratILC TPC meeting, DESY, 15/02/06 Primary Events Cosmic spectrum Vertex generated on the top trigger plane - Flat in (x,z) - Fixed y = +100 cm or 55 Fe source (5.9 keV  ) –z = +154 cm –x,y = 0 Vertex X vs Z Distribution Primary Spectrum (GeV) X Z PP

A. SarratILC TPC meeting, DESY, 15/02/06 Track Generation Use GEANT 4 simulation package to do the tracking inside the TPC gas volume. Physics processes: –> standard EM processes –> transportation –> delta-rays production Save step information (energy loss and pre-step time-space position) during the tracking.

A. SarratILC TPC meeting, DESY, 15/02/06 Ionization E loss in a step is used to generate the ionization electrons. W I = 26 eV (Sauli) Step limited to 1mm (≤ 1mm)  = Peak ~ 8é / step 8 é / step 80 cm -1

A. SarratILC TPC meeting, DESY, 15/02/06 Drift And Diffusion From Magboltz: Drift speed V drift = 6.5 cm.  s -1 Diffusion coefficient  L =  z = 290  m.cm -1/2  T = 310  m.cm -1/2 (0.0T) 240  m.cm -1/2 (0.2T) 160  m.cm -1/2 (0.4T) Use 2D Gaussian for  x &  y  = B = 0.2T

A. SarratILC TPC meeting, DESY, 15/02/06 Track After Drift Y X Z Vertex

A. SarratILC TPC meeting, DESY, 15/02/06 Digitization Use the same layout than during data taking at CERN 8*8 mm 2 pads with 0.1 mm pitch and 4 mm staggering. 2 detectors, 1024 pads each (768 active pads per detector during data taking because of electronic/DAQ troubles) Transverse (x,y) view

A. SarratILC TPC meeting, DESY, 15/02/06 Electronic Signal Charge (ADC) Time (tick=100ns) G = 6000 Gain 4 th order semi-gaussian filter: (X e -X ) 4 with X = (T - T 0 ) /  and  = 190 ns Gain fluctuations with an exponential distribution.

A. SarratILC TPC meeting, DESY, 15/02/06 Digitized Event Q > 160 Q > 300 Q > 800 Q < 160 (ADC)

A. SarratILC TPC meeting, DESY, 15/02/06 Noise Simulation Electronic noise: Gaussian with:  = 0,  ~ 2.0 ADC unit (same as in data) With 2048 pixels and 400 time bins per pixel: ~ 800k noise generated / event Save only the noise above 4  = 8.0 ADC (in bins without signal)

A. SarratILC TPC meeting, DESY, 15/02/06 MC Event With Noise 4  Hits 5  threshold Q > 160 Q > 300 Q > 800 Q < 160 (ADC)

A. SarratILC TPC meeting, DESY, 15/02/06 Output Text file –Primary info. (X,Y,Z) and (Px, Py, Pz) –Number of pads with hit –For each pad with at least one hit: Number of hits Time and charge of each hit Root file with histograms for debugging

A. SarratILC TPC meeting, DESY, 15/02/06 Data / MC Comparison

A. SarratILC TPC meeting, DESY, 15/02/06 Gain Tuning Using 55 Fe Run Run with 55 Fe radioactive sourceSimulation of 5.89 keV photons Larger  in data: channel to channel fluctuations ?

A. SarratILC TPC meeting, DESY, 15/02/06 Number of Pad Fraction Fraction of number of pad per cluster vs drift length MC B = 0.2 TData B = 0.2 T 1 pad 2 pads 50% 25% 75% (cm)

A. SarratILC TPC meeting, DESY, 15/02/06 Resolution vs Z at B=0.2T

A. SarratILC TPC meeting, DESY, 15/02/06 Resolution vs Z at B=0

A. SarratILC TPC meeting, DESY, 15/02/06 Resolution vs Z at B=0.4T

A. SarratILC TPC meeting, DESY, 15/02/06 Conclusion / To Do A Monte Carlo simulation of a TPC was written for T2K near detector, using Geant 4 package. The method and C++ code are simple. Work needs to be done to understand some distributions that do not agree with data Comparison with data gives good agreement for resolution versus drift length

A. SarratILC TPC meeting, DESY, 15/02/06 Transverse Diffusion B = 0.2T  = B = 0.2T  = 0.024

A. SarratILC TPC meeting, DESY, 15/02/06 B = 0.4T  = B = 0.4T  = Distribution of  x/y / √ (drift length) Transverse Diffusion

A. SarratILC TPC meeting, DESY, 15/02/06 Comparison Data/MC

A. SarratILC TPC meeting, DESY, 15/02/06 Estimated Track Width Estimated track width vs time MC B = 0.2 T  ~ 2.5mm z = 1m Data B = 0.2 T z = 1m  ~ 2.8mm