M.Sc Thesis
M.Sc Student Hershenhorn Alon David Bc Lifetime Measurements Using the ATLAS Detector Department of Physics Professor Yoram Rozen

Abstract

The Large Hadron Collider located at CERN, near Geneva, Switzerland is the most energetic accelerator in the world. It is currently working at a center of mass energy of s2=49 TeV2/c4 and is designed to reach s2=196 TeV2/c4. ATLAS is a multi purpose detector located on the LHC ring. One of the main goals of the ATLAS detector is to find the Higgs particle, the only unobserved particle in the standard model of particle physics. It is also used to search for new physics beyond the standard model.

The Bc meson is a bound state of the b and c quarks. It was discovered by CDF in 1998. The Bc meson is unique in that it is the only known meson with two heavy quarks of different flavor. As such, it is a good candidate to test heavy quark theories. An accurate measurement of the Bc lifetime might constrain some of the parameters that are used in the theoretical calculations of these theories.

This work presents a measurement method of the Bc lifetime using the decay Bc into a J/Psi, a muon and a neutrino. The J/Psi subsequently decays into two muons. The missing neutrino momentum prevents the measurement of the Bc momentum. The distribution of the measurable quantity t' is learned from monte carlo samples and is used in an unbinned maximum likelihood fit to find the Bc lifetime. The resulting statistical error on the lifetime, corresponding to an integrated luminosity of 86 pb-1 is -0.116.128 ps .