Hi all, Thanks to Peter I realized that it's maybe not so clever to calculate the mass from the RICH rings (some may even say that it's a bit stupid). One should rather calculate the mass^2 (like for the time-of-flight walls). The RICH mass is calculated from the momentum and the radius of the reconstructed rings (or the cherenkov angle theta). The mass is calculated from m = p sqrt( (n*cos(theta))^2 - 1 ) The problem is just that (n*cos(theta))^2 - 1) can be negative, if the measured theta/radius is bigger than the theoretical maximum theta/radius. Fortunately the resolution of the RICH is so good that this does not happen very often - we loose approx 3% of the calculated masses in the high field runs (1/2 field), and probably much less in the lower field runs. The right way to do it, is to use mass^2 all the way (as for the time-of-flight walls): m^2 = p^2 * (n*cos(theta))^2 - 1) If you use the RichPid objects the radius should be ok, but if you make cuts in mass I guess you will loose the few cases where (n*cos(theta))^2)>1. I would like to make the changes in brat soon - that is introduce mass2 instead of mass in the BrRichPid class. This will of course cause some trouble for those that use the mass from the BrRichPid objects. If there are no strong objections I will commit the changes one of these days. Comments and suggestions are welcome! Claus +-------------------------------------------------------------+ | Claus Jørgensen | | Cand. Scient. Phone : (+45) 33 32 49 49 | | Cell : (+45) 27 28 49 49 | | Niels Bohr Institute, Ta-2, Office : (+45) 35 32 53 07 | | Blegdamsvej 17, DK-2100, E-mail : ekman@nbi.dk | | University of Copenhagen Home : www.nbi.dk/~ekman/ | +-------------------------------------------------------------+
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