CSC Simulated Charge Tim Cox, Jay Hauser, Greg Rakness, Rick Wilkinson CSC Charge Simulation1

The Problem Simulated charge distributions are narrower than in data CSC Charge Simulation2

Our Simulation GEANT gives us an entry & exit point in the gas volume. We need to simulate the drift electrons: –How many –Where along the line they happen –Include delta ray electrons Presented by Tim in more detail here: – – CSC Charge Simulation3

Modeling the Energy Loss Particle Velocity (  ) 24 bins,  = E  = 0.1 – 5 TeV Energy Threshold 63 bins 11 eV – 8 keV Avg # of collisions over threshold per cm CSC Charge Simulation Used GEANT3 to construct a table of collisions Use the velocity and lowest threshold to generate a mean free path for a step Throw a random number between 0 and Ncollisions to get a “percentile” energy loss for that step 4

Energy Loss CSC Charge Simulation Line is GEANT4 energy loss per gap Triangle is our simulation 5

Modeling the Ionization We use two parameters to convert energy loss to some number of ionizations –Ionization energy Minimum energy to produce ionization ~10 eV –Effective work function Average energy loss per ionization ~ tens of eV Any deposit with two or more ionizations is considered a delta ray –We check range to see if it leaves gas volume CSC Charge Simulation6

Comparison with Sauli We create, on average, 72 primary ionizations per gas gap, and 91 total. Compare with Sauli’s 1977 paper on multiwire proportional chambers – He expects 34 primary ionizations per cm in CO2, 91 total, and 29 primary & 94 total for Ar. Could this explain our charge distribution? CSC Charge Simulation7

Toy Monte Carlo CSC Charge Simulation Line is 80 primary ionization, 91 total Triangle is 34 primary, 91 total Fewer collisions and bigger delta rays lead to bigger fluctuations in charge 8

Ionization Parameters Sauli’s paper uses different ionization parameters than we do. CSC Charge Simulation Ionization Energy (eV)Effective Work Function (eV) Our Sim Sauli CO Sauli Ar Using these parameters (weighted average) will lead to fewer primary ionizations, but bigger delta rays. Maybe 10.4 eV was an excitation energy, not ionization? 9

Comparison with Data CSC Charge Simulation10 OldNew Data includes Greg’s gain corrections

Electron Attachment We had been modeling this by attenuating the signal by 50%. Changed to using a 50% chance of killing the electron –Doesn’t broaden the distribution much. Is attachment a function of drift time? CSC Charge Simulation11

Charge vs. Drift Time CSC Charge Simulation12 More at Data Sim No obvious attenuation due to attachment Don’t understand structure in far tails of timing

Conclusions Simulation of energy loss looks good. Going to standard ionization parameters gives much better agreement with data charge distributions. Electron attachment is still an open question. CSC Charge Simulation13