A Search for Rare Decay D0 --> mu+mu - High Energy Physics UPRM

4.8 Optimization of the Selection Criteria 78In order to take into consideration the probability of the decay products being”misidentified as muons, the background ratio was determined from weighted histograms.Each entry in the dimuonic invariant mass histograms of the SS2 data (such as Figure 4.8)was weighted with the product of the momentum-dependent MisID probabilities for eachof the two decay products. Events with two muons were eliminated from the sample butevents with one muon were allowed in order to include semimuonic background. Theweight was calculated as follows:Ü —žÝ Þ¥ß}Ý4à (4.10)where Ýi—á£for muons, and Ýi—for non-muons. Then, we have that¿ÀÎãâ?äeå&æÎãâ?äeå&æΞâêäeåÕæ— çèÜÎãâ?äeå&æ— çèÜ£éߥ if neither decay product is identified as a muon.if one of the two decay products is identified as a muon.Results from this procedure are presented in Chapter 5. A value for the backgroundratio (• ) was obtained for each of the sets of cuts considered.4.8 Optimization of the Selection CriteriaThe optimization procedure of our selection criteria was the longest and mosttiresome phase of this effort. It established the final criteria for the selection of muoncandidate events. The aspect that was constantly kept in mind was to eliminate a largenumber of background events maintaining high efficiency values.