1. 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,

2. 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 July 19th,2012

3. 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 July 19th,2012

4. 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 July 19th,2012

5. Construct it with two pions
Stage One (finished)
Construct it with two pions
Yi July 19th,2012

6. 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 July 19th,2012

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

8. Enjoy
Yi July 19th,2012