טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentPanikashvili Natalia
SubjectLow pt Muon Identification for B Physics in the ATLAS
Detector
DepartmentDepartment of Physics
Supervisor Professor Shlomit Tarem


Abstract

The B production cross section at the LHC is very high, but it is a small fraction of the total inelastic cross section (0.7%), so the trigger for B physics has to be very selective. The LVL1 trigger for B physics will be an inclusive muon trigger with a transverse momentum threshold pT>6GeV/c1. This is well matched to the physics, because at lower pT, backgrounds from decays in flight of pions and kaons and from punch-through-hadrons will dominate. But the pT spectrum of muons from B decays is such that this threshold causes a big loss of efficiency.


Although the large number of B events produced at the LHC could lead to excellent measurements, actual accuracy will depend crucially on the trigger efficiency. The trigger for B physics is typically based on the leptons from semileptonic B decay or a J/y decay. Once triggered, the obtainable precision depends on the reconstruction and identification accuracy and efficiency of relatively low pT muons such as a second muon from J/y. For instance, the expected error on sin2b is reduced from 0.015 to 0.010, if a second muon can be reconstructed down to pT of 3GeV instead of 5GeV. The main goal of this work is the development of an algorithm that increases the efficiency of identifying low pT muons with high purity.


Prompt J/y production is also of importance as a background to CP-violation studies based on B meson decays into J/yX, with X being K0s, f etc. We present the first preliminary results of separating the direct J/y from J/y which decayed from B hadrons.



1 Throughout this work, the symbol pT is used for the transverse momentum with respect to the beam direction, and η for the pseudorapidity, h=-ln(tg(q/2)).