----- Begin Included Message ----- >From bjornhs@fys.uio.no Tue Jun 6 11:14 MET 2000 Date: Tue, 6 Jun 2000 11:15:19 +0200 (CEST) From: Bj|rn Hallvard Samset <b.h.samset@fys.uio.no> X-Sender: bjornhs@brahms.uio.no To: brahms-dev-l@bnl.gov cc: jhlee@sgs1.hirg.bnl.gov, bearden@hehi03.nbi.dk, hagel@comp.tamu.edu, Trine Spedstad Tveter <t.s.tveter@fys.uio.no> Subject: Vertexing MIME-Version: 1.0 Content-Transfer-Encoding: QUOTED-PRINTABLE <If this mail doesn't show up on brahms-dev-l, could someone please forward it there? Sorry about double-mailing some of you - I am trying to figure out this mailing-problem> Hello all :-) I'll try to give some comments on the issues raised in the last few e-mails on this subject. First of all, I have never suggested that BrHCVertex should be our only primary vertex-finder. The reason that I have concentrated on this method, as I said in my last mail, is that tracking has long been far from optimal and thus given JH's BrVertex too little to work with. As JH says, BrVertex is a fast method that gives the vertex quite precisely in y and z, and better the closer mid-rap is to 90 deg - but it needs enough tracks. Now that tracking has evolved quite a bit I think it will do even better than it has done before, and I would like to work a bit further with it if JH thinks this is ok. (Please note: The current CVS-version of BrVertex includes code for a "turnable plane of determination" that I made to try and get the x-coord too - I checked in the wrong version and will fix this shortly) As for BrHCVertex, this far it has given better results than BrVertex in z for all simulations I have tried but as I said this may well have changed with the improved tracking. I will look into this thorougly, and give a presentation to you (either on a web-page or when I come to BNL at the end of the month). Two points: 1) BrHCVertex will probably be able to determine y and possibly x too - I just haven't had time to test my ideas due to exams and illness. 2) Now that I am familiar with the bugs in the ROOT peak-finder (see below) I do have an uncertainty-estimate in BrHCVertex. It currently comes in the form of the sigma of the gaussian that finds z, but this will be worked on further. What I would actually like to do, is to make a module that uses both these methods plus ZDC-data etc. to double-check vertex-locations, plus do secondary tracking to possibly find secondary vertices. Plus, the methods are in fact somewhat complementary as BrVertex is at its best with mid-rap close to 90 deg. and vertex close to z=0, while BrHCVertex is slower but deals better with other angles and vertex-locations. Naming: I propose the following naming-changes: BrVertexData becomes BrVertex (I agree with Chris...) BrVertex becomes BrTPMTrackVertexModule BrHCVertex becomes BrTPMClusterVertexModule This leaves room for a common BrTPMVertexModule which could either just be a supermodule that uses the two others, or a base class from which they derive. (I'm not sure that this is a good idea in this case, since they have very little in common structurally, but it would follow our Brat conventions) A note on problems with ROOT: I have made extensive use of the ROOT fit-function (TH1->Fit()) to fit a gaussian to my data. When I do this in a macro in interactive ROOT and run the program more than one time (e.g. not restarting ROOT) the fitter does strange things. Eiher it sometimes puts a linear, diagonal background on top of my fitted data, or it fits the peak nicely but then offsets the result by exactly 3 cm. (3 units on the axis) It appears that something, somewhere is overwriting some memory (uncontrolled pointers, most likely), but after scanning my code quite a number of times I cannot find an error there. Has anyone else had these problems with the fitting-functions? Anyway, the problems seem to disappear once things are compiled so this is only a problem during coding and testing... Well - that was a long mail. To summarize: I wish to keep working with both TPM1-vertexfinders, and give you a presentation when I come to BNL. I will also, if you approve, make the above naming-changes etc. shortly - I just have to finish my exam on thursday first :-) I am sorry that the vertex-finder has not progressed quicker, but as I said this has been due to many courses and illness... Cheers ------------------------------------------------ Bjørn H. Samset Hovedfagsstudent, tungionefysikk Mob: 92 05 19 98 Lesesal: 22 85 77 62 Adr: Kri 2A709 Sognsveien 218 0864 Oslo ----- End Included Message -----
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