sPHENIX tracking discussion

[Christof Roland <christof.roland AT cern.ch>]

Hi Everybody, 

i am in the process of producing the new error parameterizations so we can 
swith to TrkrClusterv4. 

Looking at the MVTX residuals I see distibutions that are way to narrow, as 
far as I understand. 
Here is a list of the observed RMS of the residual (cluster phi position - 
track phi position) distribution.
There is the residual with respect to the truth track and the reco track as 
well as the a selection for cluster width in phi ==1 or bigger than one.
 
truth layer 0 phisize = 1 RMS: 0.000122
truth layer 0 phisize > 1 RMS: 0.000164
truth layer 1 phisize = 1 RMS: 0.000090
truth layer 1 phisize > 1 RMS: 0.000126
truth layer 2 phisize = 1 RMS: 0.000072
truth layer 2 phisize > 1 RMS: 0.000102
trk layer 0 phisize = 1 RMS: 0.000133
trk layer 0 phisize > 1 RMS: 0.000143
trk layer 1 phisize = 1 RMS: 0.000110
trk layer 1 phisize > 1 RMS: 0.000123
trk layer 2 phisize = 1 RMS: 0.000124
trk layer 2 phisize > 1 RMS: 0.000134

In general we see a residual width fo ~1.2 micron. The error assigned by the 
MVTX clusterizer is ~2.6 micron. 
How is this possible? the pixel pitch of the MVTX is ~30um and the intrisic 
resolution according to ALICE specs should be ~5um. 
Especially for phi size  = 1 clusters we should see something like 
30/sqrt(12) ~ 9um

Does anybody have an idea how to make sense of this?

Thanks 

    Christof