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Open Access Publications from the University of California

Scholarly Works (7 results)

  • Article
  • Peer Reviewed
Research Grants Program Office (RGPO) Funded Publications (2020)
Abstract: We study the energy loss of a heavy quark slowly moving through an evolving strongly coupled plasma. We use the linearized fluid/gravity correspondence to describe small perturbations of the medium flow with general spacetime dependence. This all order linearized hydrodynamics results in a drag force exerted on a heavy quark even when it is at rest with the fluid element. We show how the general contribution to the drag force can be derived order by order in the medium velocity gradients and provide explicit results valid up to the third order. We then obtain an approximate semi-analytic result for the drag force to all orders in the gradient expansion but linearized in the medium velocity. Thus, the effects of a class of hydrodynamic gradients on the drag force are re-summed, giving further insight into the dissipative properties of strongly coupled plasmas. The all order result allows us to study the drag force in the non-hydrodynamic regime of linear medium perturbations that vary rapidly in space and time.
    Cover page: Drag force to all orders in gradients
    • Thesis
    • Peer Reviewed
    UCLA Electronic Theses and Dissertations (2023)

    Jets comprise a rich class of emergent phenomena stemming the underlying theory of the strong nuclear force, Quantum Chromodynamics. As jets are produced in copious quantities in hadron colliders, understanding their internal structure and evolution is of the utmost importance for modern particle physics. In this thesis, we study various aspects of a special class of jets---that is, jets containing heavy quarks, such as charm, bottom and top---which can all be understood from a statistical point of view. In the first part, we consider situations in which the observation of back-to-back heavy-quark dijet pairs shed light on key physics governing the final and initial states of high-energy particle collisions---from the modification of dijet mass spectra by the quark-gluon plasma created in the collisions of heavy ions to the probing of the Sivers spin asymmetry in deep inelastic scattering. In the second part, we analyze the internal landscapes of jets initiated by heavy quarks and demonstrate how the so-called ``dead-cone'' effect manifests in the cumulants of jet substructure distributions. In the third and final part, we adapt concepts from the machine learning community to tag top jets from a background of jets initiated by light quarks and gluons as well develop a novel data type that is particularly well-suited to exposing the characteristic angular structure of top decay products.

      Cover page: Statistical Aspects of Jets Containing Heavy Quarks
      • Article
      • Peer Reviewed
      Research Grants Program Office (RGPO) Funded Publications (2021)
        • Article
        • Peer Reviewed
        Research Grants Program Office (RGPO) Funded Publications (2021)
        Abstract: Using Soft-Collinear Effective Theory, we develop the transverse-momentum-dependent factorization formalism for heavy flavor dijet production in polarized-proton-electron collisions. We consider heavy flavor mass corrections in the collinear-soft and jet functions, as well as the associated evolution equations. Using this formalism, we generate a prediction for the gluon Sivers asymmetry for charm and bottom dijet production at the future Electron-Ion Collider. Furthermore, we compare theoretical predictions with and without the inclusion of finite quark masses. We find that the heavy flavor mass effects can give sizable corrections to the predicted asymmetry.
          • Article
          • Peer Reviewed
          Research Grants Program Office (RGPO) Funded Publications (2019)
          Back-to-back light and heavy flavor dijet measurements are promising experimental channels to accurately study the physics of jet production and propagation in a dense QCD medium. They can provide new insights into the path length, color charge, and mass dependence of quark and gluon energy loss in the quark-gluon plasma produced in reactions of ultra-relativistic nuclei. To this end, we perform a comprehensive study of both light and heavy flavor dijet production in heavy ion collisions. We propose the modification of dijet invariant mass distributions in such reactions as a novel observable that shows enhanced sensitivity to the QGP transport properties and heavy quark mass effects on in-medium parton showers. This is achieved through the addition of the jet quenching effects on the individual jets as opposed to their subtraction. The latter drives the subtle effects on more conventional observables, such as the dijet momentum imbalance shifts, which we also calculate here. Results are presented in Pb+Pb collisions at $\sqrt{s_{NN}}$ = 5.02 TeV for comparison to data at the Large Hadron Collider and in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV to guide the future sPHENIX program at the Relativistic Heavy Ion Collider.
            Cover page: Light and heavy flavor dijet production and dijet mass modification in heavy ion collisions
            • Article
            • Peer Reviewed
            UC Berkeley Previously Published Works (2017)
            The design of low temperature bolometric detectors for rare event searches necessitates careful selection and characterization of structural materials based on their thermal properties. We measure the thermal conductivities of polytetrafluoroethylene (PTFE) and Al2O3 ceramic (alumina) in the temperature ranges of 0.17–0.43 K and 0.1–1.3 K, respectively. For the former, we observe a quadratic temperature dependence across the entire measured range. For the latter, we see a cubic dependence on temperature above 0.3 K, with a linear contribution below that temperature. This paper presents our measurement techniques, results, and theoretical discussions.
              Cover page: Thermal conductivity measurements of PTFE and Al2O3 ceramic at sub-Kelvin temperatures
              • Article
              • Peer Reviewed
              Research Grants Program Office (RGPO) Funded Publications (2020)
              In these proceedings, we review the production of both light and heavy flavor dijets in heavy ion collisions and highlight a promising observable to expose their distinct signatures. We propose the modification of dijet invariant mass distributions in heavy ion collisions as a new observable that exhibits striking sensitivity to the heavy quark mass dependence of in-medium parton showers. This observable has the advantage of amplifying the effects of jet quenching in contrast to conventional observables, such as the dijet momentum imbalance shift, which involve cancellations of such effects and, hence, result in less pronounced signals. Predictions are presented for Au+Au collisions at √SNN = 200 GeV to guide the future sPHENIX program at the Relativistic Heavy Ion Collider.
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