### Browsing by Author "Kolbe, Isobel"

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- ItemOpen AccesspQCD energy loss and thermal field theory in small systems(2019) Kolbe, Isobel; Horowitz, William A.In recent years, experiments at the Large Hadron Collider and the Relativistic Heavy Ion Collider have discovered that many of the signatures that are traditionally ascribed to the presence of a quark-gluon plasma (QGP) in central heavy-ion collisions also manifest in certain classes of peripheral heavy-ion collisions as well as in smaller colliding systems. The glaring exception to this list of observations of QGP signatures in small systems is the partonic energy loss. However, current theoretical descriptions of partonic energy loss are ill-adapted to small systems. This thesis first presents a numerical analysis of an analytical small system extension of a standard energy loss formula, and finds that major inconsistencies in the description of small system energy loss persist, motivating a need for a first principles calculation of the properties of a small droplet of QGP. Thereafter, a first step toward such a calculation is presented by considering a single, massless, scalar field that has been geometrically confined by means of Dirichlet boundary conditions. This toy model reveals, via thermal field theoretic techniques, that quantum fields are very sensitive to the presence of a boundary, presenting significant deviations from the Stefan-Boltzmann limit and revealing a geometrically driven phase transition at the scale of the medium.
- ItemOpen AccessShort path length pQCD corrections to energy loss in the quark gluon plasma(2015) Kolbe, Isobel; Horowitz, W ARecent surprising discoveries of collective behaviour of low-pT particles in pA collisions at LHC hint at the creation of a hot, uid-like QGP medium. The seemingly conflicting measurements of non-zero particle correlations and RpA that appears to be consistent with unity demand a more careful analysis of the mechanisms at work in such ostensibly minuscule systems. We study the way in which energy is dissipated in the QGP created in pA collisions by calculating, in pQCD, the short separation distance corrections to the well-known DGLV energy loss formulae that have produced excellent predictions for AA collisions. We find that, shockingly, due to the large formation time (compared to the 1/μ Debye screening length) assumption that was used in the original DGLV calculation, a highly non-trivial cancellation of correction terms results in a null short path length correction to the DGLV energy loss formula. We investigate the e ect of relaxing the large formation time assumption in the final stages of the calculation - doing so throughout the calculation adds immense calculational complexity - and find, since the separation distance between production and scattering centre is integrated over from 0 to ∞, ≿ 100% corrections, even in the large path length approximation employed by DGLV.