From ryu@rcf2.rhic.bnl.gov Mon Sep 10 10:38:52 MDT 2001 ... Date: Mon, 10 Sep 2001 12:38:34 -0400 (EDT) From: Sangsu Ryu To: "John P. Sullivan" cc: , , , , Subject: Re: Mvd vertex In-Reply-To: <1223.130.199.98.185.1000135048.squirrel@rcf.rhic.bnl.gov> Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Status: RO Dear all, Yes I talked to a Bbc expert. Bbc calibration is up to date except Z offset. I should have been more careful when calculating efficiency. Here is more accurate number. If my understanding is correct Mvd is supposed to do vertexing within +-3*31.8 where 31.8 is half Z of Mvd. So let me include only events with Bbc vertex in this range. That counts 3071 events out of total 7489 events in this run. Sigma of gaussian fit (p2) is ~0.48 which is similar to Bbc-PC vertex width. Gaussian mean is 0.64 so the count of events within -2*0.49+0.64 and 2*0.49+0.64 is 278. Efficiency is 278/3071=9.05%. This is best I get till now. With Bbc cut +-31.5 the number is 230/1312=17.5%. No multiplicity cut was applied to these numbers. Best regards, Sangsu If you take close look at second plot On Mon, 10 Sep 2001, John P. Sullivan wrote: > Hi Sangsu, > > I'm glad to see the progress you are making. > > Last week you did not want to send these to phenix-mvd-l > because you were not sure about the BBC calibrations. Have you > checked that? > > What cuts do you apply to the 3000 events you use to calculate an > efficiency. Are the BBC vertex cuts, multiplicity cuts, or anything else? > > Thanks, > John > > > Dear all, > > > > Here is an update on vertex. > > Over the weekend I made a scan over a few offset values of barrel > > detectors. Take look at > > http://www.phenix.bnl.gov/~ryu/public/mvd/vertexstudy.html > > The first 2 plots are the best I can get up to now. 0.5cm offset > > and 0.6mm bin size. > > I made fits on vertex_mvd-vertex_bbc with "gaussian+const". > > Meanings of parameters are: > > > > p0 : constant for gaussian > > p1 : mean for gaussian > > p2 : sigma for gaussian > > p3 : constant > > > > Third plot shows p0 distribution over assumed offsets. It is > > clear that peak is around 0.4~0.5cm. The next plot is p2 distribution. > > Again minimum is around 0.5cm. Based on fit parameters, number of good > > events were calculated for each offset. I counted events good when mvd > > and bbc vertices fall within 2*p2. Never mind that 0.8cm offset has > > most good events. That is because p2 is so large. > > So I would conclude that combination of sag and bow amounts about > > 0.5cm. > > However efficiency is not very good. The numbers are from about > > 3000+ (very rough) events with meaningful bbc vertex. That means > > 205/3000=6.8%. > > The last 3 plots were made with 0.3mm bin size. I tried 0.6mm bin > >size and it improves efficiency a little. 269/3000=9.0%. The first 2 > >plots were obtained with 0.6mm bin size. > > > > Best regards, > > Sangsu > >