[Brahms-dev-l] FS tracking efficiency with the reference method.

Hello out there.

Here comes a long mail from the northern part of the collaboration. I'm
fiddling with the FS tracking efficiency calculated for the 2001 AuAu in
hope that this is the end of the analysis for my thesis. Those
interested better get a big cup of coffee before proceeding. :)

I still have problems figuring out how to interpret the efficiency as
calculated in the reference track method output file. Mine is called
"Effic5361_5972.root" which I assume other people are using too.

First, let me describe how I extract _each_detector's_ efficiency from
the file. It is close to identical to the way done in the
EfficiencyCalculator and the BdstFsAna classes for those using any of
these. The code for this functions is in the attached file. There is,
however, one important difference to note. In the case the reference
track efficiency could not be determined, the function _does_not_ return
efficiency of 1.

The other differences in my function relates to particular treatment of
the 12 degrees 1692 settings, i.e. both A and B polarity. The statistics
is too low to require a count of 6 or more for each efficiency bin in T4
and T5. Thus, so far, I require 5 counts or more. Also, what I've seen
in the EfficiencyCalculator and BdstFsAna analogies is that they allow
use of efficiency found in the underrun and overrun bins of the
efficiency histograms. My function doesn't.

(Hope you follow so far. If not get some more coffee. ;) )

Next, I run over the available DSTs from 2001 AuAu. For each FS track I
calculate the tracking detectors' efficiencies in terms of centrality
and the tracks' x position and slope in each detector, again in close
analogy with what's done in the before mentioned classes. I then fill
histograms with the distribution of each tracking detector's efficiency.
I've limited myself to the 10% most central events.

These distribution histograms are at the core of my puzzle. The reason
is the great number of entries with efficiency of 1. I.e in the
"eff_dist_<setting>" histograms in [1] they show up with large counts in
the 100% bin on the far right. (Note the log scale.) Looking in
particular at the settings with a lot of statistics, e.g. at 3 and 4
degrees there seems to be nice (more or less) continuous distributions
of tracking efficiency with peaks in the 80 or 90% range. In addition
the bin for 100% is filled and clearly separated from the "continuum".

To me this indicates that tracking efficiency of 100% is _wrong_ and
should _not_be_used_. IS THIS THE CASE?

(More coffee anyone?)

I then try to construct a combined tracking efficiency multiplying the
individual efficiencies of T1, T2, T4 and T5 in full FS mode and only T1
and T2 in FFS mode. I've done this in 2 ways. One is to make profile
histograms for each detector and multiply these histograms together. I
refer to this method as method 1. The "method1_<setting>" histograms in
[1] are _not_ filled if the return value of GetDetectorEfficiency() is
1. (The FFS histograms for 20 and 30 degrees comes from parameterizing
Truls' simulation results, and thus T1 and T2 histograms are empty.)

Also I try a second method, method 2, in which I calculate the
efficiency while looping over the tracks in the DSTs. In the
"method2_<setting>" figures in [1] the upper panel is a profile requiring
(t1Eff != 1.) && (t2Eff != 1.) && (t4Eff != 1.) && (t5Eff != 1.)
in FS mode and
(t1Eff != 1.) && (t2Eff != 1.)
in FFS mode for the histogram to be filled. The profile in the middle
panel is filled _including_ individual efficiencies of 1. And the lower
panel is simply the momentum distribution of the particles in the setting.

Method 2 causes lower statistics in the FS tracking efficiency profile,
and therefore does not work well e.g. at the low statistics sample at 12
degrees and magnet current of 1692. But where there is good statistics
it is in fairly good agreement with method 1.

Note however that some FS settings show tracking efficiency of 30 and
40%, e.g. 8 degrees at A676 and 3 degrees at A1124. It is consistently
smaller than what I've seen for tracking efficiency in other analyzes.
Also the shape as function of momentum seems peculiar. Is there any
reason for our efficiency to be decrease with increasing momentum which
looks like being the case for many settings?

I therefore wonder if anyone has some feed back on this issue. In
particular, is tracking detector efficiency of 1 a default and/or
erroneous value which should be omitted when parameterizing the
efficiency e.g. as function of momentum.

Best wishes from
Jens Ivar

[1] http://www.ift.uib.no/~jens/trackingefficiency

-- 
           _____________________________________________________
  ________|                  Jens Ivar Jørdre                   |_______
  \       | Dept. of Physics                        Office: 521 |      /
   \      | Allégt 55                    Phone: +47 55 58 27 92 |     /
    \     | 5007 Bergen                    Fax: +47 55 58 94 40 |    /
    /     | Norway           E-mail: jensivar.jordre@ift.uib.no |    \
   /      |_____________________________________________________|     \
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                          "To be or not to bop"
                            (Dizzy Gillespie)


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