Yi Bao Supervisor: Rolf Oldeman July 19th, 2012 @CERN Feasibility study of the measurement of absolute branching fractions of the Λc baryon Yi Bao Supervisor: Rolf Oldeman July 19th, 2012 @CERN

Brief Intro Motivation: All decays of the heavy baryons Λc + and Λb are presently affected by a large uncertainty of 22% in the decay of . Investigate whether the decay chain of the Λc (2595) + (an excited state of Λc) can provide a tag that is precise enough and has a low enough background to count the total number of Λc + baryons in the data sample. Estimate the precision that can be obtained in the LHCb experiment and identify possible backgrounds. My work is doing Monte Carlo simulation to find an effective way to select Λc. Yi Bao@CERN, July 19th,2012

A Little Theory Decay chain: M=2455 Λc (2595) + →Σc0,++ π+,- M=2286 r-φ view of the decay (from CDF Collaboration) M=2455 Λc (2595) + →Σc0,++ π+,- M=2286 Impact Parameter (IP) Yi Bao@CERN, July 19th,2012

Three Stages Python Raw random number to simulate Still Python Fast MC Python Raw random number to simulate Complete MC Still Python Using events generated by Pythia Real Data? Introduce the method I used Branching ratio? We will see… Almost all information of events are accessive Depend on how much cheating Yi Bao@CERN, July 19th,2012

Construct it with two pions Stage One (finished) Construct it with two pions Yi Bao@CERN, July 19th,2012

Progress at Stage Two Several improvements (use generated events): Less “cheating”: visible quantity (e.g. Impact parameter (IP)) Pointing value: <primvtx → secondvtx, p(μ Λc + estimated) > Consider more background (e.g. muon + prompt pions which have IP=0) And more potential physical quantity to make it clean Problem: How to distinguish two pions? Cannot only rely on Pt and pointing value Better way to select muons Candidates are rare → time consuming Yi Bao@CERN, July 19th,2012

Progress at Stage Two “Right” combination: blue “Wrong” combination: red M(Λb 0)≈5619 Yi Bao@CERN, July 19th,2012

Enjoy Yi Bao@CERN, July 19th,2012