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Access Type

WSU Access

Date of Award

January 2017

Degree Type


Degree Name



Physics and Astronomy

First Advisor

Sergei Voloshin


Heavy-ion collisions at LHC energies create a hot and dense medium of deconned quarks

and gluons, known as the quark-gluon plasma (QGP) [56]. 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 [18].

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 [23]. 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 [48]. 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) [48].

Azimuthally-dierential femtoscopic measurements can be performed relative to the di100

rection of dierent harmonic event planes [25]. The harmonic event planes are determined

using the event plane method [48]. The measurements of HBT radii with respect to the first

harmonic (directed)

flow at the AGS [30] revealed that the source was tilted relative to the

beam direction [31]. 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 [55]. 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) [33]. The signs of the HBT radii relative to the third harmonic event plane angle

oscillations constrain the origin of these oscillation [33].

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