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## ) motivation, CKM mass resolution ) SELEX, three aspects ) radius distributions & tails

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**Radial Tail Resolution in the SELEX RICHA. Morelos,**P.Cooper, J.Mata, J.EngelfriedUsing a 7 Million data sample of 600 GeV/c single track pion events, where the pion track is reconstructed upstream and downstream the SELEX RICH, a circle fit on the phototubes ring is performed. From the fit we get three parameters, the radius, and the center coordinates plus their statistical errors. Applying modest cuts on track and circle fit uncertainties we build the radius histogram distribution and count the tail the events that fall outside 5s from the b=1 radius, giving a fraction of 4x10-5 events outside the gaussian tails. This control of events stablish the ability of using the RICH as velocity spectrometers for high precession search of the K+ p+n anti(n) experiments like CKM.**outline**) motivation, CKM mass resolution ) SELEX, three aspects ) radius distributions & tails ) a look into simulation ) summary**PNN1**PNN2**Número de planos prendidos Npl**Beam Transition Radiation Detector BTRD**Ring Imaging Cherenkov**beam event at 600 GeV/c**Beam**Vertex M1 M2 RICH Vdc-a Vdc-b Downstream track**Track existence**Select PMT´s around +- 1.27 cm From SELEX standard radius ring fit soft cuts on center and radius uncertainties**Mean radius dispersion by run**Dispersion 0.009 cm s radius 0.15 cm single track 0.18 cm multi-track**s C2n by run**Single hit 0.55 0.47 cm in agreement no track uncertainty**Ring Radius distribution**upstream track existence dowstream track existence**5s tail (CKM < 3 x10-5)**upstream existence downstream existence**A model**for decay events in RICH blind Rich blind downstream existence**Events are left in the tails**“ C “ type: either close or opens the radius**A look into**random PMT simulation no PMT efficiency no individual noise**“ C “ event like events**radian radian maximum angle between two consecutive PMT´s per event ( radians ) data broadness: improve lowering noise and better efficiency**Summary**) downstream track existence eliminated decay events which were in the tail region ) With 5 s tail analysis we are in a region of 3.9 x10-5 events, close to CKM requirements (less than 3 x10-5 ) ) Still: a completely stand alone algorithm, work is being done, and include noise and efficiency per tube in simulation

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