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Precision measurements of jet quenching in relativistic heavy ion collisions at the LHC

Havener, Laura

Jets are a useful probe of the hot, dense medium produced in heavy ion collisions since partons are expected to lose energy in interactions with the medium through a phenomena called jet quenching. Recent results studying jet quenching in relativistic heavy ion collisions at the LHC with the ATLAS detector are presented here. The jets are reconstructed using the anti-kt algorithm with a background subtraction that removes the large underlying event. A fully unfolded measurement of the dijet asymmetry in Pb+Pb and pp collisions with an integrated luminosity of 0.14 nb^−1 and 4.0 pb^−1, respectively, at √sNN =2.76 TeV is shown. The dijets are found to be highly asymmetric in central Pb+Pb collisions and become more symmetric, or like pp, in more peripheral collisions. A strong p_T dependence to the asymmetry is also observed. This measurement is shown to have similar qualitative features at jet radii of R=0.3 and R=0.4, implying that the underlying event is under control. Measurements of the nuclear modification factor, R_AA, for R=0.4 jets in Pb+Pb and pp collisions with an integrated luminosity of 0.49 nb^−1 and 25 pb^−1, respectively, at √sNN = 5.02 TeV are also presented. The R_AA shows the strongest suppression in central collisions and the least suppression in peripheral collisions. It shows a slight increase with jet p_T and a decrease with increasing rapidity at high p_T. Finally, the dijet asymmetry for R=0.4 jets is also reported in Xe+Xe collisions at √sNN = 5.44 TeV compared to Pb+Pb and pp collisions at √sNN = 5.02 TeV. No difference is observed between Pb+Pb and Xe+Xe collisions, within the uncertainties of the measurement, as a function of the number of participants or the collision centrality.

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More About This Work

Academic Units
Physics
Thesis Advisors
Cole, Brian A.
Degree
Ph.D., Columbia University
Published Here
November 16, 2018
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