Hi Jens Ivar, One things that I tried to do at some point was to check the extrapolated yield of unidentified charged particles calculated with FFS and FS to the published values. In principle this allows you to partly verify if the combination of efficiency, decays corrections etc. is correct.... There must be a power point from some colaboration meeting end of last year on the BRAHMS homepage. I found that FFS was ok, but FS was generally too low, but I think it was a premature conclusion in the sense that I should use more time on this. I think it is a good idea to do make these kind of checks, but probably you need a long time to really understand the details. To sit down and really understand the FS is still a major task for someone;) BTW it is also good to check that you have the latest greatest set of efficiencies from Pawel and remember that they are in principle related to a special set of reduced files with the tracking, geometry and magnetic fields as of that date. The bottomline is ofcourse that it is hard to say something _quick_ about the correctness of the efficiencies....... If however you want to trace the values of 100% you could start by studying the projection of the 3d efficiencies and I believe there is also a 3D count histogram. That way you might be able to identify the problems in a reasonably fast way. For me it is clear that with Pawels method you will have efficiencies that will be 0 and 1 because of the counting statistics and maybe also because of geometry/fields. This leads to the MC efficiency estimates ala Truls which is a tough way to go...... Cheers, Peter On Thu, 29 Jul 2004, Jens Ivar Jordre wrote: > Howdy Peter. > > Peter H.L. Christiansen wrote: > > Yes it is a bit strange/unphysical with the discontinuities between 100% > > and 80%. I believe that Pawel has once showed that the efficiencies works > > in the sense that FFS and FS is similar with efficiencies. I am also > > convinced that it works since Djamel and I have compared FS to FFS and > > different FS/FFS settings to each other where the efficiencies were quite > > different and found good agreement. > > Well, I'm not convinced by this argument. It may very well be that both > FS _and_ FFS effiencies are wrongly calculated. The values of 100% > effiency show up also in T1 and T2. So you could very well have nice > agreement in e.g. efficiency corrected FS and FFS spectra and both being > wrong. > > > So likely for some reason we don't quite understand the tracking "works > > better" in some part of the detector than others or the statistics is > > low or .... It is at least also somehow clear that the 3d histogram is too > > big for the low number of tracks that makes it all the way through the > > FS, and maybe you could reparamatrize this, summing over the top 0-20% > > and summing over fx the coordinate in a detector to get an efficiency > > that you can apply track by track. > > > > What Djamel and I did was to calculate the average tracking efficiency as > > a function of momentum (a profile of the single track efficiencies) and to > > use that for the correction (actually using the average where the counting > > statistics was low) - this is at least be continous. I think we got the > > same results no matter what we did, but it makes it a lot easier to > > understand what you do. > > That's what I'm doing too. But what bothers me is the dependence on > momentum, i.e. where there is significant negative slope in the > efficiency as function of momentum, as shown in some of the plots in [1]. > > Best wishes from > Jens Ivar > > [1] http://www.ift.uib.no/~jens/trackingefficiency > -- :-) --------------------------- )-: Peter H L Christiansen pchristi@nbi.dk / (+41)764870425 :-D --------------------------- \-: _______________________________________________ Brahms-dev-l mailing list Brahms-dev-l@lists.bnl.gov http://lists.bnl.gov/mailman/listinfo/brahms-dev-lReceived on Thu Jul 29 10:08:11 2004
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