On Wed, 21 Mar 2001, Flemming Videbaek wrote: > Bjorrn, > > Your plots are interesting in more ways than indicated below. > > a) Why is the p1 coeef in the first plot .93 +-.002 It really should be one > since it is a > distance beasured both places. Since the ZDC time calibration is probably > known to better the 7% (I assume) > it sounds like a problme in the tracking - What pad pitch did you use? At > some earlier stages we have also seen > a small change in the projected y-pos with 'z' so maybe some small geometry > problem still exsists? You're right... I thought this was an effect from low-statistics bins at the edges, but I have now removed them and the result is the same. My pad-pitch was 0.4 - I guess that could cause this effect. I'll try a run tonight with another value - is 0.39 the "best guess"? I have now also tried the same for BB vs TPM1, and the result is the same: p1=0.912+-0.001. Clearly a tracking problem. > b) Is the deviation in the ZDC-TPM1 vs mult similar to that of the BB? This > could help isolate the problem. In fact it is - have a look at www.fys.uio.no/~bjornhs/ZDCBBvsTPM1.ps ZDC is deviating slightly more than BB, bit the trend is really the same. This reco-run includes the BB cosmetic factor that Yury introduced around QuarkMatter. It really looks like there is a problem somewhere in either the tracking or in the TPC vertexing. I cannot say that I see any clear way that the ClusterVertex could contain any mult-dependence, especially not on the order of several centimeters, but that may only mean that I have missed something... I'll try to go through it again. As for tracking, I'll try a reco-run with another pad-pitch to see what that may change - if I can remove the first of the above problems and still see the second I'll start looking even harder. A third possibility is of course that there is some additional geometry problem that we haven't seen yet - if you saw a problem with the y-proj I'd say the assumed angle of the TPC is a good place to start. Has this been (re-)checked? > c) You would probably be better off making a cut on ZDC energies + a rough > BB cut to resolve the double > value problem. THis should be mainly for conformation. I know - the problem is the info I have in my trakc tree. (It was made for dNdEta, not vertex calibrations.) I'll put this in for my test runs. Oche - back to work. Gotta figure this one out... ------------------------------------------------ Bjorn H. Samset Master-student in Heavy Ion physics Mob: +47 92 05 19 98 Office: +47 22 85 77 62 Adr: Kri 2A709 Sognsveien 218 0864 Oslo
This archive was generated by hypermail 2b29 : Wed Mar 21 2001 - 09:26:59 EST