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Date of Award
Physics and Astronomy
Heavy-ion collisions at LHC energies create a hot and dense medium of deconned quarks
and gluons, known as the quark-gluon plasma (QGP) . The QGP reball rst expands,
cools and then freezes out into a collection of nal-state hadrons. Correlations between the
free particles carry information about the space-time extent of the emitting source, and are
imprinted on the nal-state spectra due to a quantum-mechanical interference eect .
The correlation of two identical particles at small relative momentum, commonly known as
intensity, or Hanbury Brown-Twiss (HBT), interferometry, is an eective tool to study the
space-time structure of the emitting source in relativistic heavy-ion collisions . Due to
the position-momentum correlations in particle emission, the HBT radii become sensitive
to the collective velocity fields, from which information about the dynamics of the system
evolution can be extracted. The spatial anisotropies in the initial state are converted, via
pressure gradients and interactions between constituents, to momentum anisotropies, leading
to anisotropic particle flow. Anisotropic flow is usually characterized by the Fourier
decomposition of the particle azimuthal distribution and quantied by the flow harmonic
strength vn and the event plane angle . Elliptic flow is dened by the second flow
harmonic strength (n = 2), whereas triangular flow is dened by the third flow harmonic
strength (n = 3) .
Azimuthally-dierential femtoscopic measurements can be performed relative to the di100
rection of dierent harmonic event planes . The harmonic event planes are determined
using the event plane method . The measurements of HBT radii with respect to the first
flow at the AGS  revealed that the source was tilted relative to the
beam direction . In particular, measurements of the HBT radii relative to the second
harmonic event plane angle ( 2) provide information on the nal shape of the system, which
is expected to become more spherical compared to the initial state due to stronger in-plane
expansion . In contrast, hydrodynamics model studies have shown that the azimuthal
dependence of the HBT radii relative to the third harmonic event plane angle can originate
from the anisotropies in collective velocity gradients or the initial spatial anisotropy
(triangular) . The signs of the HBT radii relative to the third harmonic event plane angle
oscillations constrain the origin of these oscillation .
Saleh, Mohammad, "Azimuthally-Differential Pion Femtoscopy Relative To The Second And Third Harmonic In Pb-Pb Collisions" (2017). Wayne State University Dissertations. 1868.