Hi Bjorn et al, On Tue, 9 Jan 2001 09:18:10 -0500 (EST) Bjorn H Samset <bjornhs@rcf.rhic.bnl.gov> wrote concerning ": Re: Centrality (was: ZDC cut efficency vs multiplicity)": > I have tried to impose a vertex cut of +-30 cm on the ZDC/Mult plots, and > to my eye it makes no difference to the spectra in this case. You should also be aware of the asymmetry of the tile layout, as reported by J. H.. This makes the ADC/Vz distribution skewed to the left. Hence, a symmetric, at least one as wide as +/- 30cm will be errouneous. > Maybe the cut should be narrower - this is being tested now. The > plot I gave you is the one without a cut, since it had better > statistics Low statistics is obvious the problem of all this. If, as Flemming claims trigger 4 is really the minimum bias trigger, then one should use inclusive trigger 4 (as in the upper 8 bits of the trigger word) events to determine the centrality thresholds. However, for later runs, where the downscale factor of trigger 4 is very high ~ 100, this will pose the problem of low statistics. However, one can do the analysis on runs with a lower scale factor, and compare the threshold values with those from later runs, and my guess is that we'll find the thresholds at similar ADC values. > - for one with cut have a look at > www.fys.uio.no/~bjornhs/Run2235_25k_vtxcut.ps > This one has 25k events. The other difference is that here the top left > plot is trigger 4 mult and trigger 6 mult superimposed. As Claus pointed > out to me, we seem to have events with a high mult but no trigger 6! Any > ideas on this? No, I'm afraid not. We've seen something similar and are at least as puzzled as you. If you plot the histogram with errors, you'd be even more dazzled! If the two distributions were to overlap within errors, I'd feel comfortable in saying that is some statitical fluc, but since they don't, I'm puzzled - I said that already - hell I'll say it again: I'm puzzled! One reason could be, that trigger 6 is inefficient - that is, in some events the trigger just wasn't set, even though it should have, due to some error, either in the DAQ or the Beam-Beam counters themselves. Another possibility, would be that since the Beam-Beam arrays, in particular the big tubes, only cover a small fraction of the solid angle, and may not be hit in some event, either due to some interresting physics like fluctuations, or just because the emittion from the collision is stocastic - i.e., statistical fluctuations. But hey, I'm only speculating. Yours, Christian ----------------------------------------------------------- Holm Christensen Phone: (+45) 35 35 96 91 Sankt Hansgade 23, 1. th. Office: (+45) 353 25 305 DK-2200 Copenhagen N Web: www.nbi.dk/~cholm Denmark Email: cholm@nbi.dk
This archive was generated by hypermail 2b29 : Tue Jan 09 2001 - 09:48:24 EST