1 straw tube signal simulation A. Rotondi PANDA meeting, Stockolm 15 June 2010

STT FZJ Designed for COSY-TOF and PANDA (P. Wintz) DESIGN 4 x (16 x 2) = 128 straws (4 self-supporting double-layers, 32 tubes each) 1.5 m long 30  m wall thickness (aluminised mylar) 20  m anode wire Different gas mixtures (ArCO 2 (90/10) - ArC 2 H 6 (80/20)) Operating at about 2 bar overpressure ELECTRONICS ELECTRONICS: Standard existing electronics 64 channels with CMP16 + F1-TDC 64 channels with Fast QDC (160 MHz, 240 MHz in prep) from COSY S. Costanza PANDA Collaboration Meeting – GSI, 9/03/2010

3 © Peter Wintz Gain measurements

4 © Peter Wintz Rate measurements

Results from COSY-TOF 5

Straw Tube output Signal calculation 6 To start from the charged particle-nucleus cross sections to calculate the energy lost by the projectile and the ionization Alternatively, one can start from the number of free electrons created by the projectile and from the mean energy lost per primary electron. These data are available both for Argon and C02 theoretically and experimentallly. Then, electrons per cluster Energy loss  = cluster electrons per cluster W AR = 26 eV CO2 = 33 eV

7 Single straw simulation 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.

8 Single straw simulation Electrons on the wire no electronics response 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 (26 eV in Ar) Their position is dispersed according to the GARFIELD diffusion curves.

GARFIELD drift velocity: gas mixing studies 9 Ar/CO 2 80/20% Drift velocity never constant Ar/CO 2 90/10% Drift velocity nearly constant in a limited region around the wire Both cases: p = 2.2 bar  V = 2150 V B = 2 T tube diameter = 1 cm anode diameter = 20  m

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

11 Gain: (GARFIELD) sampled from Polya distribution 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.

12 The signal for each electron... Sampled from Polya..... is summed-up for each primary electron..... Average gain: 30000

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

14 SIGNAL TRESHOLD Warning: this will lead to an offset simulated white noise time (ns) Preamp + fixed threshold + TDC

15 Wide dynamical range “autofocus”

Signal threshold 16 simulated white noise time (ns) 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

17 Self-Calibration: first step… 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: starting curve Calibration: use a parallel beam and find the time response of the tube (simulation of the calibration with cosmic rays ): No differences between FT and CF Significant differences between the two gas mixtures 18

19 Spatial sim resolution curves Fixed threshold: Max 160  m Min about 60  m Constant fraction: Max 110  m Min below 50  m Curves obtained with Ar/CO 2 mixing (no difference between 80/20 and 90/10 %) B = 2 T Experimental data (P.Wintz, with B=0) well reproduced Residuals:  |( x rec – x true )| / N Mean value (fixed threshold)

Experimental calibration PREFIT: minimization of the perpendicular distances of a set of N points (x i, y i ) from the best-fit line The function to be minimized is: where (x i, y i ) = centres of the firing tubes Since the absolute value function does not have continuous derivatives, minimizing R is not amenable to analytic solution. square of the perpendicular distances The square of the perpendicular distances is minimized instead: S. Costanza PANDA Collaboration Meeting – GSI, 9/03/2010

21 Self-calibration: procedure

22 Exp result: preliminary

Mean residuals exp distribution S. Costanza PANDA Collaboration Meeting – GSI, 9/03/2010  =  m  =  m  =  m  =  m

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

The ATLAS experience NIM A 474(2001)172 25

26 pions

27 Pion/electrons 0.4 GeV ns Pion/protons 0.4 GeV ns Pion/kaons 0.4 GeV Pion/protons 0.4 GeV CF Discri mination

28 Pion/electrons 1.0 GeV Pion/kaons 1.0 GeV Pion/protons 1.0 GeV

Summary (from the simulation code) 29 Self calibration 90  m Self calibration is important for achieving good resolution (mean value with fixed threshold: the limit seems about 90  m). gas mixture time response The gas mixture affects the time response spatial resolution but does not affect the spatial resolution spatial resolution constant fraction method The spatial resolution improves by determining the signal threshold by the constant fraction method ToT technique No separation above 1 sigma with the ToT technique

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Straws considered Diameter 10 mm Length: cm Wire diameter 20  m Absolute pressure: about 2 bar Gas mixtures: Ar/C02 90/10 and (80/20) Mylar wall thickness: about 23  m 33