details of SMD simulator, simu shower zoom-in


Fig 1. Geant simu of EM shower of one electron with ET=10 GeV at eta=0.


  • one phi-strip is parallel to cavities, extends over 1/10 of the cavity length, and integrates over 2 consecutive cavities.
  • one eta-strip is perpendicular to cavities, extends over 1/150 of the cavity length, and integrates over all 30 cavities in the module.

 Hi Jan,

the only documentation I know of is the code itself --  
hopefully you'll consider it human-readable.  Look at  
StEmcSimpleSimulator::makeRawHit() in StEmcSimulatorMaker.  We use the  
kSimpleMode case.  The GEANT energy deposition is multiplied by a  
sampling fraction that's a second-order polynomial in pseudorapidity,  
and then we take pedestals, calibration jitter, etc. into account.   
The exact parameters of the sampling fraction are defined in the  
constructor for StEmcSimpleSimulator.  I don't remember how they were  

 also meant to add that the width broadening is OFF by  
default.  To turn it on one needs to do

emcSim->setMaxCrossTalkPercentage(kBarrelEtaStripId, aNumber);

 The "width broadening" only occurs  

for eta strips and was implemented by Mike Betancourt in  
StEmcSimulatorMaker::makeCrossTalk().  He wrote a blog post about it:




Maybe I should note that the cross talk I implemented was to account  
for the capacitive cross talk between the cables carrying the eta  
strip signals to the readout, and not for any effects related to the  
energy deposition.


Hi Jan,
Well, Oleg should probably make the definitive reply, but I think it is like this:
The amplification happens only at the wire, it is independent of the positions of the primary ionization. Of course, there is a little effect from a small amount of recombination or capture of the charge on impurities, and there must be a (hopefully small) effect from the dependence of the mean pulse shape on the position of the ionization and the dependence of the effective gain of the electronics on the mean pulse shape. But these things can't amount to much, I would think. (Of course, I don't want to discourage you from looking in the data to confirm it!)


 These are all quite true, small effects which will be difficult 
 to see. The bigger effect is reading out one time bucket.
 I have made some estimates before test run 98 (?) or so, see this PS

 if you look at numbers still very small effect which is unpractical
 to measure.

Hi, Yes indeed, I don't know why I neglected to think of the simple effect of drift time, but it is certainly going to be a much bigger effect (~10% if I read your fig.3 correctly?) than the other two. (Perhaps still too small to see in the data, I don't know...). Anyway, given the data volume and already limited readout speed of the BSMD I am pretty sure there is no prospect to ever read more than the one fixed time sample from BSMD; this is probably something to live with. [But it is not impossible to have 2 or 3 point readout, and if we want to seriously consider it it should be brought up ~now, well that is in case we are given the green light to work on BSMD readout "mini-upgrade". If not, well it will just wait until then. But keep in mind, more points readout would offer slightly better gain accuracy but will complicate offline and calibrations too, probably you really don't want it anyway!]


p.s. Jan I don't know if it adds anything to the wider discussion on BSMD gain/cal but if you feel so you may surely post to hn.

p.p.s. Oleg, an important question - in your note you don't specify exactly how you obtain the drift time... I mean, yes you show a drift velocity curve, but really of course you must mean there was a calculation such as with garfield to get a drift time out of this... _So_, was that calculation done with the magnetic field on? [The wires are parallel to the magnetic field, right? So it will make possibly a very big difference in drift times.] Jan, do you/others realize the BSMD gain will probably have some systematic dependence on the magnetic field, including the sign thereof? So if you care about gain calibration it should be separated out according to the state of STAR magnet, fortunately there are only a few running states, right?