NPL groups present many new results at Quark Matter Conference in Houston. Two Graduate Students win conference awards.

Using multi-particle correlations to estimate fluctuations in jet and rare probe azimuthal anisotropies, by undergrad student Abraham Holtermann 

Jets, heavy flavor, and many more “rare probes” are useful for understanding QCD processes that occur within the Quark Gluon Plasma produced in heavy ion collisions. The azimuthal anisotropies of these rare probes are often measured by correlating their angles with soft particles using differential cumulants. We introduce a more comprehensive differential multiparticle correlation framework that allows for the study of fluctuations in rare probe azimuthal anisotropy. To test this method, we show the sensitivity of three new observables to a toy model, and show their ability to isolate both fluctuations in rare probe anisotropies, and the correlations between rare probe anisotropies and the collective flow of soft, low pT particles.

arXiv: 2307.16796

Structure in the speed of sound: from neutron stars to heavy-ion collisions, by grad student Nanxi Xiao

Neutron star equations of state that can sustain heavy neutron stars over 2 Msun necessitate a large, rapid rise in the speed of sound.  In our studies, we convert equations of state with a bump in the speed of sound that are compatible with massive neutron stars to nearly symmetric nuclear matter using the nuclear symmetry energy expansion with 4 coefficients. With a range of different coefficients, we are able to obtain upper and lower bounds for converted symmetric nuclear matter with causality and stability constraints. We compare our converted equation of state with heavy-ion collision data by hadronic transport method SMASH.

Exploring neutron stars with three conserved charges in a newly optimized C++ Chiral Mean Field code, by grad student Nikolás Cruz Camacho
The Chiral Mean Field model (CMF) has been successful in describing the equation of state at large baryon densities, such as those found in neutron stars, neutron star mergers, and heavy-ion collisions. The MUSES collaboration has rewritten the zero-temperature CMF model from Fortran 77 into a parallelized modern C++20 using OpenMP, which has resulted in at least an order of magnitude improvement in runtime. We obtained equations of state across \mu_B, \mu_S and \mu_Q, and within the metastable regime around the quark deconfinement phase transition. The improved numerical resolution allows for the accurate computation of higher-order derivatives such as susceptibilities.

Investigation of initial state effects in p+Pb collisions at ATLAS via measurement of the centrality dependence of the dijet yield, by Research Scientist Riccardo Longo 

Proton-nucleus collisions at LHC energies represent an incredible source of information to further understand the building blocks of matter. The proton internal structure fluctuates, but when it collides with the nucleus, because of the very short transit time, it does it in a practically frozen configuration. By measuring dijet events using the full acceptance of the ATLAS calorimeter, we have explored how the proton configuration affects its own size and interaction strength. Our results, included in a recent ATLAS paper just submitted for publication (see arXiv 2309.00033), represent an unprecedented input towards the understanding of the proton’s size fluctuations and the associated changes in its interaction strength. 

A new approach to stochastic relativistic fluid dynamics from information flow, by Graduate Student Nicki Mullins 

The matter formed in heavy-ion collisions is well described as a viscous relativistic fluid. The fluctuation-dissipation theorem guarantees that such a theory will also experience thermal fluctuations, but these are often ignored in the modeling of the quark-gluon plasma. To better understand how these fluctuations enter in relativistic contexts, we constructed the first theory of stochastic hydrodynamics that is guaranteed to be causal, stable against fluctuations, and foliation independent. Using this theory, we constructed an effective action for fluctuating relativistic hydrodynamics and derived a symmetry of this action that can be used to implement the fluctuation-dissipation theorem. 

arXiv:2309.00512

Neutral Pion and Eta Meson Reconstruction with the sPHENIX Detector, by Post-Doctoral Research Associate Anthony Hodges 

sPHENIX is a new detector at the Relativistic Heavy-Ion Collider (RHIC) designed to make precision jet and upsilon measurements in 200 GeV p + p, p + Au, and Au + Au collisions and will begin taking data in 2023. In addition to having the first hadronic calorimeter (HCal) at mid-rapidity at RHIC, sPHENIX also contains a tungsten-scintillator based Electromagnetic Calorimeter (EMCal) for measuring the energy of photons and electrons. The EMCal absorber blocks were largely constructed by the UIUC NPL (see this Condensate article for more details). Anthony presented in his poster the performance of the calorimeter as evaluated in test beam data, as well as the first calibration data available from the first year of sPHENIX running.