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Re: Weird STT reconstruction: efficiency depends on charge [message #5693 is a reply to message #5673] Wed, 23 January 2008 17:07 Go to previous messageGo to previous message
Pablo Genova is currently offline  Pablo Genova
Messages: 32
Registered: May 2007
continuous participant
From: *PV.INFN.IT
Dear Andrew,

the errow was really stupid i. e. in the line 914 of PndSttHelixTrackFitter

if(a<0.000001) return 0;

to protect the division by zero was cutting away the a<0 i. e. the positive tracks, with

if(fabs(a)<0.000001) return 0;

it's now OK.

So try to svn-update the PndSttHelixTrackFitter and do again the reconstruction.

Other observations:

->cross check of the variables

1. fParamLast.fTx*0.006 <--------> transverse momentum

[i. e. cbmsim->Draw("(fParamLast.fTx*0.006)"]

2.fParamLast.fTx*0.006*sqrt(1+fParamLast.fTy**2)) <------> total momentum

Do you agree?

->importance of fFlag==3 parameter

when you are looking at total reco, to get the only the events with the full reconstruction succeeded do like this:

cbmsim->Draw("(fParamLast.fTx*0.006)>>h2","fFlag==3")

in this way you select the events with fFlag==3 i. e. full success of the whole reconstructed procedure.
You should not see any more the 90 degree values (algorithm failure). Of course I expect that the reconstruction is not perfect when you go to small theta angles, since you are using only the stt with lower number of hits.

It's certainly an interesting and not yet done study that of STT resolution at small theta angles, with or without MVD.

MVD + STT integration is also an interesting issue not yet tackled.

########################################
If you need better explanation of the variables and the fitting procedure etc etc I can send you the presentations I made in the past and Lia's Phd Thesis (which, among other things, describes in detail the algorithm).
########################################
I'll soon clean the code and put into the repository a better commented version of PndSttHelixTrackFitter


LET ME KNOW IF IT'S OK AND ANY QUESTION ON YOUR SIDE!!


ciao, Pablo





 
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