LHCb Analysis of Xi - → Lambda + Pi- + Pr channe

Alexandra Raborn Anderson High School

Will Beckes Summit Country Day School

Dr. Mike Sokoloff Mentor

Xi-  Pi+  Invariant Mass
For my research, I analyzed a data set from the Large Hadron Collider Beauty (LHCb) experiment, specifically the Xi - → Lambda + Pi- + Pr channel. To begin, I chose selection criteria that would allow me to view a defined signal region on the plot of invariant mass. This included a tight cut on the Lambda mass, which I chose to fit between 1110 and 1120 MeV, as well as the Xi- mass, between 1310 and 1335 MeV. I also made cuts using the ProbNN(particle) variables to values that made sense, such as a higher probability that a particle is detected correctly and a lower probability that a particle is detected incorrectly. From there, I adjusted the values to those which would provide the best signal to background ratios. While inspecting these histograms, I deduced that the data only manipulated a signal around the 1530 resonance, giving me a more specific point to analyze rather than the entire range.  After analyzing how well the selection criteria allowed for a defined signal at 1530, I chose to make a corrected Xi- mass. In order to do this, I first subtracted the Lambda mass given in the data from the Xi- mass given in the data. To then shift the Xi- mass to a more accurate placement, I added back the average Lambda mass from PDG Live, 1115.683 MeV.  Using this corrected Xi- mass, I applied the previously used cuts and analyzed how they affected this new histogram. As assumed, the data was more accurate and a slightly more precise signal region was outlined. I found that the invariant mass of a Xi- Pi+ decay was best analyzed using logical particle detection probabilities and a corrected Xi- mass.