MC Simulation of Micromegas Chambers Trigger Studies on NSW Theodoros Alexopoulos, Venetios Polychronakos, George Iakovidis MAMMA Group - Dec. 2011

How Our Simulation Looks Like ? 2019 events, 2020 events....were I was? 4ns....10ns....1000ns whatever .... I missed the last 10 numbers....!!!

No.....it’s something like that .... !

Main Aspects - goals ! Timing Response of a Micromegas Detector for different chips (mainly focus on BNL). APV timing simulation, BNL Chip response function integrated (three techniques). Gas properties fully simulated with Garfield and reproduced with Garfield++. Multiple Applications, eg Micromegas with strip pitch 250um 500um, driftGap 5mm, 9mm, different geometries ex ‘level arm’ 300mm, plain separation..etc ‘Back to Back’ Geometry simulation Multiple Gas Mixtures, Ar:CO2 93:7, 80:20, 85:15, Ar:CF4 90:10, 95:15 and many more with diffusion analytically calculated. (Penning effects taken into account). Theta resolution calculation Trigger Pattern simulation, hits within 1-4 BXs, lookup tables etc. Describe as much as possible the ionization, primary cluster, secondary electrons. whatever else comes with it....

Garfield ++ http://garfieldpp.web.cern.ch/garfieldpp/ List of Gases Garfield++ is a toolkit for the detailed simulation of particle detectors that use gas and semi- conductors as sensitive medium. The main area of application is currently in micropattern gaseous detectors.Garfield++ shares functionality with Garfield. The main differences are the more up-to-date treatment of electron transport the user interface, which is derived from ROOT. List of Gases ar_45_co2_15_cf4_40.gas ar_50_ic4h10_50.gas ar_80_co2_20.gas ar_90_cf4_10_penning.gas ar_90_cf4_10.gas ar_93_co2_7.gas ar_95_ch4_5.gasar_100.gas ch4_100.gas dme_50_ic4h10_50.gas dme_90_co2_10.gas xe_80_co2_20.gas http://garfieldpp.web.cern.ch/garfieldpp/

Single Chamber MC Ionization Collisions - Probability of a Poisson-like Statistics Cluster Size Secondary Electrons Avalanche Fluctuations Cross Talk between strips from Maxwell Simulation. Chamber Efficiency ~ 98% as measured from test beams Electronics response

Ionizing Collisions A charged particle that traverses the gas of a drift chamber leaves a track of ionization along its trajectory. The encounters with the gas atoms are purely random and are characterised by a mean free flight path λ between ionizing encounters given by the ionization cross-section per electron σ and the density N of electrons. λ=1/(Νσ) Therefore, the number of encounters along any length L has a mean of L/λ, and the frequency distribution is the Poisson distribution Measured numbers of ionizing collisions per centimeter of track length in various gases at normal density

Ionization Energy Loss Of Charged Particles in Gas Ar:CO2 Number of Primary Electrons not easily calculated, taken from experimental plots (linear correlation of nprim and the average atomic number. Secondary Electrons calculated analytically. Minimum ionizing particles in Argon NTP: Minimum ionizing particles in CO2 NTP:

Primary ionization Encounters Small number of independent events following the Poisson-like statistics. Experimental cluster-size distributions P(k) in per cent

Avalanche Fluctuations Ar:CO2 probability distribution of the total number of electrons and ions in the avalanche chain which develops in a low pressure gas in a high electric field when single avalanches generate successors by photoelectric effect at the cathode.

Cross Talk Maxwell Software, calculation signal cross-talk between first and second strip. strip distance = 0.100 mm strip width=0.150 mm strip pitch = 0.250 mm CrossTalks - 1-2strip = 16%, 1-3 = 6% strip distance = 0.100 mmstrip width=0.400 mmstrip pitch = 0.500 mmCrossTalks - 1-2strip = 9.5%, 1-3 = 3.2%

Theta Reconstruction Effect on single chamber 100 300 pitch 250 um 300 600 pitch 500 um Δθ as measured per event from a single chamber with least squares for 10k of events with the same angle.

Theta Reconstruction Effect on single chamber large angles Charge at first strips and especially on bigger angles is concentrated at left side of strip. Unfortunately when we reconstruct the track we take as points the center of the strips. This results in different angles. Of course only relevant on the ‘single’ chamber track reconstruction.

Theta Reconstruction Effect on single chamber - small angles Charge at first strips and especially on bigger angles is concentrated at left side of strip. Unfortunately when we reconstruct the track we take as points the center of the strips. This results in different angles. Of course only relevant on the ‘single’ chamber track reconstruction.

APV 25ns trigger window (example for qThr = 2e) First Time Above threshold of Event for 10k events before the APV 25 ns trigger window First Time Above threshold of Event for 10k events after the APV 25 ns trigger window

BNL chip Signal simulation (qThr = 2e, intTime = 25ns, eThr = 0.45) First Peak Time above Threshold Maximum Peak Time # of e ns First Time Above Electronics Threshold Double_t qThreshold=1; //qThreshold=2e, we accept a good strip if the charge is >=2e Double_t alpha = 1.25;// power of response function Double_t RC = 20;// time constant of response function Double_t electronicsThreshold = qThreshold * (TMath::Power(alpha,alpha)*TMath::Exp(-alpha));

BNL chip Signal simulation (qThr = 1e, intTime = 50ns) First Times for the Maximum Peak of amplitude of Event for 10k events ns First Times for the First Peak above threshold of amplitude of Event for 10k events ns

Several ‘quality’ plots

Small Wheel Simulation

Small Wheel Simulation Four trigger techniques, first above threshold, first peak above threshold, maximum peak above threshold, mixed technique CSC-EIL trigger. Geometry flexibility Back to back geometry simulation Mixed geometries and Gases Separation 2 Drift Gaps 2 Drift Gaps 2 Drift Gaps 2 Drift Gaps Plain Separation Plain Separation

Trigger Simulation - Back To Back Chambers MM Times References eg 300 1 BC 1 2 3 4

Angle Generation Random Generation of eta from ~1.3 to ~ 2.9

Micromegas Potential timings with Ar:CO2 93:7, 50ns, 1e

Micromegas Potential timings with Ar:CF4 90:10

Micromegas Potential timings with Ar:CH4 50:50

Angular resolution Random Generation of eta from ~1.3 to ~ 2.9

Trigger Schema Simulation

Trigger Simulation - Proposal V. Polychronakos NSW Upgrade September 2011

Trigger Simulation - Proposal V. Polychronakos NSW Upgrade September 2011

Trigger Simulation - Track Reconstruction within 4 BCs - Hit Patterns Hits on SW Pattern for LUT

Trigger Simulation - Track Reconstruction within 4 BCs - 2MMegas 50ns, qthr 1e 77.9 % of events 99.9 % of events 1.35 mrad 1.00 mrad 100 % of events 100 % of events 0.90 mrad 0.88 mrad

Trigger Simulation - Track Reconstruction within 4 BCs - 2MMegas (one each side) - 50ns, qthr 1e 82.3 % of events 99.9 % of events 1.37 mrad 1.03 mrad 100 % of events 100 % of events 0.94 mrad 0.93 mrad

Distance from points of fit to the line (not perpendicular) mm

Backup Slides

Avalanche Fluctuations The dependence on N can be explained as follows. If the first ionization occurs after the electron has traveled a distance larger than the mean free path for ionization, the ionization probability per unit path length increases. Oppositely, fluctuations at larger N in the early stages of the avalanche will reduce the rate of development in the latter stages. The net effect is a reduction of the gain fluctuations. The Polya distribution treats electrons starting the avalanche differently than the ones subsequently produced and therefore misses a clear physical interpretation. Yet, it fits the measurements of single electron response in parallel-plate detectors remarkably well. Also, measurements of very good energy resolution with detectors of different geometries can only be explained if the gain fluctuations are Polya-like. G= 3.7 104 G= 5.0 104 G= 6.0 104 VMesh <500V θ = 2.3 ± 0.1 f = 0.30 ± 0.01 θ = 2.2 ± 0.1 f = 0.31 ± 0.01 θ = 2.3 ± 0.1 f = 0.30 ± 0.01

Penning Effect Ar:CO2

micromegas

Crosstalk Studies 3 strips 3 resistives res1 res2 res3 strip1 strip2 strip3 14.887 pf/m 8.657 pf/m 14.702 pf/m 103.11 pf/m 88.656 pf/m 101.98 pf/m 22.481 pf/m 22.589 pf/m 29.693 pf/m 29.634 pf/m Maxwell Table Pulse - 5μΑ , width 10 ns)

Timing Distribution: Why has this shape ?

References F.Sauli, CERN 77-09, 1977, Principles of Operation of Multiwire Proportional and Drift Chambers Sahin, O et al. Penning transfer in argon-based gas mixtures, J. Instrum. 5 (2010) P05002 , 1748-0221/5/05/P05002 Instrumentation in high energy physics By Fabio Sauli Particle detection with drift chambers - W.Blum, W. Riegler, L. Rolandi L. G. Christophorou, D. L. McCorkle, D. V. Maxey, and J. G. Carter, "Fast gas mixtures for gas- filled particle detectors Jul.1979 T. Zerguerras et al. NIM A 608 (2009) 397. J. Byrne, The statistical distribution of particle number in an avalanche chain, Physica, Volume 47, Issue 1, 29 April 1970, Pages 38-44, ISSN 0031-8914, 10.1016/0031-8914(70)90097-2.