On Mon, 5 Jun 2000, J. H. Lee wrote: > About BrHCVertex: (mainly to Bjorn) > =========================== > I understand that finding a vertex using a histogramming > method (BrHCVertex) is supposed to be fast and reliable. > But still I am not 100% convinced that that's the best way to > calculate production vertices for BRAHMS. Somewhat I still > believe that using track parameters rather than hits would do > a better job to calculate a vertex position except for events > which have too few reconstructed tracks. Before we declare > "BrHCVertex" as "the" vertex finder, I would like to see more > systematic comparisons between two methods with code > optimizations. I don't think that anyone has declared BrHCVertex to be "the" vertex finder. Rather, it seems to be the one which has gotten the most work, and thus is maybe a bit more polished. Of course we do need to compare the various methods in detail, but it seems to me that this task is only made easier by having code which works (and which several people know about) in BRAT. I also am not sure which optimizations you are speaking of, do you mean that there are parameters within the code that have to be tuned? >I also would like to mentioned that it's quite > important to be able to calculate "3-dimensional" vertex > positions (x,y,z) without assuming x=y=0 especially for the > calibration purpose. Is this possible? I thought that for most cases even the "rich man's" vertex method (using tracks in MTPC1) does not give a good measure of x and y. We should, of course, try to determine x and y. We should NOT avoid BrHCVertex just because it explicitly assumes x=y=0. I suppose that x and y can be determined, but do not know how well. In any event, my guess is that the "known" x and y position from RHIC will be better than we can determine with any method, but this is just a guess and may be wrong. Has anyone any idea how well this will be known and how well we can measure it? > > About BrVertex Module: (mainly to Kris) > ============================== > I think it's okay to have a general vertex module to include > vertex information from the BB's and ZDC's. But I also think > that it might not be a bad idea to distinguish (separate) > the "vertices" calculated using timing information in the global > detectors from the vertices calculated using spatial information in Has anyone ever suggested that we not keep the information about the method used to determine the vertex? It seems we *must* know how the vertex is determined as well as the errors associated with the determination. That is my 17oere worth. Cheers, Ian
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