STAR-SSD-Fast Simulator description

General plots		STAR SSD	- OFFLINE
		Fast Simulator plots description

Recently a Fast Simulator was implemented and is now available in CVS.
Basically we take the hits from Geant, smear the local coordinates according to the hits resolution in r/&phi and then write them to the SsdHitCollection.

To use it, instead of the slow simulator, you have to replace in your bfc chain option "ssd" by "ssdfast".

We write 5 histograms, that can be retrieved using the ".hist.root" of your process.
From this ".hist.root" file :

open root4star
type .x bfcread_hist_extract.C("my_file.hist.root","SsdFastSim")
the last argument is the name of the branch to the histos
it then creates a root file : my_file_SsdFastSim.hist.root

The hits resolution are :

in transverse plan : &sigma_r/&phi = 24 &mu m
in Z : &sigma_Z = 700 &mu m

General plots

dX Distribution of the X global coordinate before and after the smearing Eplanation of the peak at 0 : here
dY Distribution of the Y global coordinate before and after the smearing
dZ Distribution of the Z global coordinate before and after the smearing
HitsMap HitsMap Distribution of the number of hits per wafer. In this example, 10 events were process ; assuming #hits/wafer ~ 10 and knowing the active area of a wafer, it leads us to a hit density : &epsilon ~ 0.30 hits /cm² Here is a plot of the density : here
Wafer Id Wafer Id The numbering is : id_wafer = 7000 + (wafer*100) + (ladder), where wafer goes from 1 to 16 and ladder from 1 to 20.

Updates

2 methods are implemented in order to remove hits from the dead and from the inactive areas for each wafer.

Figure : ssd wafer

IsOnWafer():removes hits after smearing if they don't match the requirement to belong in the active area
RemoveTriangle() : removes hits from the triangle area.

The 2 next pictures show the local (x-y) position of hits :


Figure : local position of hits before the 2 methods	Figure : local position of hits after the removal of hits

The 2 next pictures show the ratio between the number of hits written in StEvent after the application of the 2 methods with the geant ssd hit table.
Without the methods, the ratio is 1.
I run the fast simulator over 100 events in this exemple.


Figure : before the 2 methods	Figure : after the removal of hits

The 2 next pictures show the efficiency of tracking as a function of momentum.


Figure : before the 2 methods	Figure : after the removal of hits

Jonathan.Bouchet

General plots

STAR SSD

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Fast Simulator plots description

General plots

Updates