טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentBen-Ami Sagi
SubjectExperimental B Physics at ATLAS
DepartmentDepartment of Physics
Supervisor Professor Yoram Rozen
Full Thesis textFull thesis text - English Version


Abstract

The Large Hadron Collider  at CERN (LHC) will be the most powerful accelerator in the world. Starting in 2008 it will produce proton-proton collisions at a center of mass energy of ECM=14TeV and luminosity of L=1034cm-2s-1. Experimental data using the higher energies reached by the LHC can push knowledge forward, challenging those who seek confirmation of established knowledge, as well as open new frontiers in particle physics.

ATLAS is a general-purpose experiment designed to fully exploit the LHC discovery potential and make new discoveries, as well as measure known phenomena precisely.


In the Standard Model of particle physics, the Cabibo-Kobayashi-Maskawa matrix is a unitary matrix which contains information on the strength of the flavour-changing weak decays. Technically, it specifies the mismatch of quantum states of quarks when they propagate freely and when they take part in the weak interactions. Because the CKM matrix is a unitary matrix, we can illustrate different relations between the matrix elements as a set of triangles, one of them known as the unitary triangle. Measuring the angles of the unitarity triangle will give us valuable information regarding the CP-symmetry violation in the Standard Model, as well as possible hints regarding new physics.


The work presented here is a feasibility study for measuring one of the unitarity triangle’s angles, namely Gamma, in the ATLAS experiment, by using two techniques which involve the measurements of branching ratios of rare B-decays. The feasibility study was done by reconstructing B meson candidates by combining tracks using different selection criteria based on event variables measured by the detector.


We reach the conclusion that both of the two proposed measurements will be feasible in the ATLAS experiment under certain assumptions of signal to background ratio, while for low signal to background ratios only one of the proposed methods is feasible, when using the full discovery potential of the experiment.

Final conclusions regarding the feasibility of the methods can be deduced only when further knowledge regarding the background in the experiment will be available. We expect such information will be available as the ATLAS experiment begin collecting data later this year.