Searching for QGP droplets with high-<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>p</mml:mi><mml:mi>T</mml:mi></mml:msub></mml:math> hadrons and heavy flavor
Weiyao Ke, Ivan Vitev
Abstract
The search for the smallest quark-gluon plasma (QGP) droplets in nature has motivated recent small collisions system programs at the BNL Relativistic Heavy Ion Collider (RHIC) and the CERN Large Hadron Collider (LHC). Unambiguous identification of jet quenching due to final-state interactions is key to confirming quark-gluon plasma (QGP) formation in these reactions. We compute the nuclear modification factors ${R}_{AA}$ and ${R}_{p(d)A}$ of charged hadrons and heavy flavor mesons in large (Au-Au, Xe-Xe, Pb-Pb) and small ($d\text{\ensuremath{-}}\mathrm{Au}$, $p\text{\ensuremath{-}}\mathrm{Pb}$, O-O) colliding systems, respectively. Our results include the Cronin effect and initial-state parton energy loss in cold nuclear matter. In the final state, hard partons undergo collisional energy loss and branching that was recently derived using soft-collinear-effective-theory with Glauber gluons (${\mathrm{SCET}}_{\mathrm{G}}$). In large colliding systems, medium-modified quantum chromodynamics evolution of the fragmentation functions dominates the nuclear correction. As the system size decreases, we find that cold nuclear matter effects, collisional energy loss, and QGP-induced radiations can become equally important. A systematic scan over the medium size and mass or flavor dependence of ${R}_{AA}$ provides the opportunity to separate these individual contributions and identify QGP signatures in small systems. Predictions for ${R}_{AA}^{h}$, ${R}_{AA}^{D}$, ${R}_{AA}^{B}$ in O-O collisions at $\sqrt{s}=0.2$ and 7 TeV are presented with and without the formation of a QGP and contrasted with the corresponding ${R}_{p(d)A}$ calculations. Single-hadron measurements at RHIC and the LHC will not only test the O-O predictions for both light and heavy flavor production but also shed light on the possibly very different dynamics of $p\text{\ensuremath{-}}A$ and $A\text{\ensuremath{-}}A$ reactions at similar soft particle production multiplicities.