Ph.D Thesis
Ph.D Student Kopeliansky Revital Search for Charged Long-Lived Particles with the ATLAS Detector in pp Collisions at s=8TeV Department of Physics Professor Shlomit Tarem

Abstract

Searches for heavy charged long-lived particles (LLPs) were performed under the Supersymmetry (SUSY) theory using data sample of 19.1 fb-1 from proton-proton collisions at center-of-mass energy  collected by the ATLAS detector at the Large-Hadron-Collider (LHC).

When traveling with a speed measurably lower than the speed of light, charged particles can be identified and their mass (m) determined from their measured speed (b) and momentum (p), using the relation: m , where the momentum p can be deduced from the particle’s track in the detector, g is the Lorenz factor, and the velocity b can be estimated from the measured Time-of-Flight (ToF) and from specific ionization energy loss  that measures bg.

The searches are based almost entirely on the characteristics of the LLP itself, but are further optimized for the different experimental signatures of sleptons, charginos and composite colorless states of a squark or gluino together with light Standard Model (SM) quarks or gluons, called R-hadrons.

No excess was observed above the estimated background and limits were placed on the mass of long-lived particles in various supersymmetric models. Long-lived tau sleptons in models with gauge-mediated SUSY breaking are excluded up to masses between 440 and 385 GeV for tan b between 10 and 50, with a 290 GeV limit in the case where only direct tau slepton production is considered. In the context of LeptoSUSY models, where sleptons are stable and have a mass of 300 GeV, squark and gluino masses are excluded up to a mass of 1500 and 1360 GeV, respectively. Directly produced stable charginos, that are nearly degenerate to the lightest neutralino, are excluded up to a mass of 620 GeV. R-hadrons, composites containing a gluino, bottom squark and top squark, are excluded up to a mass of 1270, 845 and 900 GeV, respectively, using the full detector.