felix-clark / dissertation

Ph.D. dissertation on femtoscopic methods in proton-lead collisions at the LHC

Femtoscopic signatures of small QGP droplets in proton-lead collisions at the Large Hadron Collider

A PhD dissertation on the application of femtoscopic methods to proton-lead collisions at the LHC with the ATLAS detector.

Abstract

The spacetime dimensions of the particle source in proton-lead collisions at sNN = 5.02 TeV is measured with the ATLAS detector at the Large Hadron Collider. Femtoscopic measurements are made from correlation functions built with charged pions identified by their ionization energy loss. The measured HBT radii that represent the source dimensions are presented differentially as a function of centrality, transverse momentum, and rapidity. The effect of jet fragmentation on the two-particle correlation function is studied, and a method using opposite-charge pair data to constrain its contributions to the measured correlations is described. The measured source sizes are substantially larger in more central collisions and are observed to decrease with increasing pair kT. A correlation of the radii with the local charged-particle density dN/dy is demonstrated. The scaling of the extracted radii with the mean number of participating nucleons is also used to compare a parameterization of an initial-geometry model that allows for fluctuations in the proton cross-section. The cross-term Rol is measured as a function of rapidity, and a nonzero value is observed that agrees with hydrodynamic predictions. The HBT radii are also shown for central events in intervals of azimuthal angle relative to the 2nd-order event plane, pair transverse momentum, kT, and flow vector magnitude, |q2|, where the correlation functions are corrected for the event plane resolution. Significant modulations of the transverse HBT radii Rout, Rside, and Ros are observed. The orientation of this modulation is the same as that in heavy-ion collisions, in which they are attributed to hydrodynamic evolution from an elliptic initial geometry. The sign and kT dependence of these modulations are consistent with a hydrodynamic evolution of a short-lived medium.