Activities on straw tube simulation PAVIA group PANDA meeting, Jülich., 8 September 2009

Single straw simulation: remember that… -1 The position and number of electron clusters is sampled from the exponential distribution (25 cluster/cm in Argon). The number of electrons belonging to a cluster is taken from both experimental and theoretical papers. The energy lost is obtained from the mean energy spent for a ion pair (27 eV in Ar) Their position is dispersed according to the GARFIELD diffusion curves.

Single straw simulation: remember that… -2 The arrival time of each electron on the wire is derived from the GARFIELD x-t curves. The arrival of each electron gives rise to a charge, obtained by sampling from a Polya distribution with mean value given by the GARFIELD gain. The total ADC signal is obtained by summing the charge over the number of electrons. Gain: 7 104 (GARFIELD) sampled from the Polya distribution Electrons on the wire no electronics response

The formation of the signal ... Primary electrons arrival times

Recent improvements All this single straw simulation was already performed. Now, to adapt the existing simulations to the new detector parameters, we have resumed some studies with GARFIELD to make available correct distributions with our new parameters. Until now, we have reproduced the drift velocity and the x-t curves with different gas mixtures: Ar/CO2 80/20 % and 90/10% with different voltages: DV = 2150, 2300, 2500 V with magnetic field (B = 2 T). For the TDR, it could be useful to continue a systematic work with GARFIELD by testing the STT in different working conditions.

GARFIELD drift velocity: gas mixing studies Ar/CO2 90/10% Drift velocity nearly constant in a limited region around the wire Ar/CO2 80/20% Drift velocity never constant Both cases: p = 2.2 bar DV = 2150 V B = 2 T tube diameter = 1 cm anode diameter = 20 mm

GARFIELD drift velocity: voltage studies All cases: Ar/CO2 90/10% P = 2.2 bar B = 2 T 2150 V 2300 V 2500 V v (cm/ ms) v (cm/ ms) v (cm/ ms) r (cm) r (cm) r (cm) An enhancement of the voltage could slightly reduce the gap in the drift velocity

GARFIELD x-t curves for single electron Drift faster in Ar/CO2 90/10% mixture Ar/CO2 90/10% B = 2 T

Wide dynamical range “autofocus”

FT CF Signal threshold Fixed: above a static value (ex. 5% of mean value of all the signals) Constant fraction: a % of max of the signal (ex. 5% of maximum value of each signal) FT CF simulated white noise time (ns) Warning: this will lead to an offset

Single straw simulation: remember that… The shape of the electrical signal is reproduced taking into account the (gaussian) response to each charge multiplication. The time is given by a threshold on the impulse, to be determined. The cumulative of the simulated time histogram gives the response curve r(t) of the tube, and so the spatial resolution curve. Parallel illumination

Self-calibration No differences between FT and CF Significant differences between the two gas mixtures Calibration: use a parallel beam and find the time response of the tube (simulation of the calibration with cosmic rays ):

Offset correction during calibration

Offset correction during calibration

Spatial resolution curves Fixed threshold: Max 160 mm Min about 60 mm Constant fraction: Max 110 mm Min below 50 mm Residuals: S |( xrec – xtrue )| / N Curves obtained with Ar/CO2 mixing (no difference between 80/20 and 90/10 %) B = 2 T Experimental data (P.Wintz, with B=0) well reproduced Mean value (fixed threshold)

Fast simulation

ADC simulation Problem with GARFIELD

Gain measurements © Peter Wintz

Rate measurements © Peter Wintz

dE/dx performances, stt vs tpc similar results with 1 bar pressure Supposing the particles are hitting 22 tubes tpc [Panda TPR]

Summary I (from GARFIELD) With Ar/CO2 90/10 % gas mixture, compared to 80/20 % one, the drift process is faster the drift velocity is nearly constant (at least over a limited region of about 200 mm around the anode wire) A little enhancement of the drift velocity could also be obtained by increasing the voltage up to 2500 V. The GAIN calculation presents some problem, not yet fully understood

Summary II (from the simulation code) Self calibration and offset correction is important for achieving good resolution (mean value with fixed threshold: about 90 mm). The gas mixture affects the time response but does not affect the spatial resolution The spatial resolution improves by determining the signal threshold by the constant fraction method