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1. A Semi-analytical Method of Calculating Nuclear Collision Trajectory in the QCD Phase Diagram

   https://doi.org/10.31349/SuplRevMexFis.3.040920  

   Lin, Zi-Wei ; Mendenhall, Todd ( December 2022 , Suplemento de la Revista Mexicana de Física)

   The finite nuclear thickness affects the energy density (t) and conserved-charge densities such as the net-baryon density nB(t) produced in heavy ion collisions. While the effect is small at high collision energies where the Bjorken energy density formula for the initial state is valid, the effect is large at low collision energies, where the nuclear crossing time is not small compared to the parton formation time. The temperature T(t) and chemical potentials µ(t) of the dense matter can be extracted from the densities for a given equation of state (EOS). Therefore, including the nuclear thickness is essential for the determination of the T-µB trajectory in the QCD phase diagram for relativistic nuclear collisions at low to moderate energies such as the RHIC-BES energies. In this proceeding, we will first discuss our semi-analytical method that includes the nuclear thickness effect and its results on the densities є(t), nB(t), nQ(t), and nS(t). Then, we will show the extracted T(t), µB(t), µQ(t), and µS(t) for a quark-gluon plasma using the ideal gas EOS with quantum or Boltzmann statistics. Finally, we will show the results on the T-µB trajectories in relation to the possible location of the QCD critical end point. This semi-analytical model provides a convenient tool for exploring the trajectories of nuclear collisions in the QCD phase diagram. 

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2. The Golden Era of Neutron Stars: From Hadrons to Quarks

   https://doi.org/10.7566/JPSCP.26.011001  

   Baym, Gordon ( November 2019 , Proc. 8th Int. Conf. Quarks and Nuclear Physics (QNP2018))

   Neutron stars were first posited in the early thirties and discovered as pulsars in late sixties; however, only recently are we beginning to understand the matter they contain. This talk describes the continuing development of a consistent picture of the liquid interiors of neutron stars, driven by four advances: observations of heavy neutron stars with masses in the range of two solar masses; inferences of masses and radii simultaneously for an increasing number of neutron stars in low mass X-ray binaries, and ongoing determinations via the NICER observatory; the observation of the binary neutron star merger, GW170817, through gravitational waves as well as across the electromagnetic spectrum; and an emerging understanding in QCD of how nuclear matter can turn into deconfined quark matter in the interior. We describe the modern quark-hadron crossover equation of state, QHC18 and now QHC19, and the corresponding neutron stars, which agree well with current observations. 

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3. Neutron Star Radii, Deformabilities, and Moments of Inertia from Experimental and Ab Initio Theory Constraints of the 208Pb Neutron Skin Thickness

   https://doi.org/10.3390/galaxies10050099  

   Lim, Yeunhwan ; Holt, Jeremy W. ( October 2022 , Galaxies)

   Recent experimental and ab initio theory investigations of the 208Pb neutron skin thickness have the potential to inform the neutron star equation of state. In particular, the strong correlation between the 208Pb neutron skin thickness and the pressure of neutron matter at normal nuclear densities leads to modified predictions for the radii, tidal deformabilities, and moments of inertia of typical 1.4M⊙ neutron stars. In the present work, we study the relative impact of these recent analyses of the 208Pb neutron skin thickness on bulk properties of neutron stars within a Bayesian statistical analysis. Two models for the equation of state prior are employed in order to highlight the role of the highly uncertain high-density equation of state. From our combined Bayesian analysis of nuclear theory, nuclear experiment, and observational constraints on the dense matter equation of state, we find at the 90% credibility level R1.4=12.36−0.73+0.38 km for the radius of a 1.4M⊙ neutron star, R2.0=11.96−0.71+0.94 km for the radius of a 2.0M⊙ neutron star, Λ1.4=440−144+103 for the tidal deformability of a 1.4M⊙ neutron star, and I1.338=1.425−0.146+0.074×1045gcm2 for the moment of inertia of PSR J0737-3039A whose mass is 1.338M⊙. 

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4. Calculating QCD Phase Diagram Trajectories of Nuclear Collisions using a Semi-analytical Model

   https://doi.org/10.1051/epjconf/202327601012  

   Mendenhall, Todd ; Lin, Zi-Wei ( January 2023 , EPJ Web of Conferences)

   Kim, Y. ; Moon, D.H. (Ed.)

   At low to moderate collision energies where the parton formation time τ F is not small compared to the nuclear crossing time, the finite nuclear thickness significantly affects the energy density ϵ( t ) and net conserved-charge densities such as the net-baryon density n B ( t ) produced in heavy ion collisions. As a result, at low to moderate energies the trajectory in the QCD phase diagram is also affected by the finite nuclear thickness. Here, we first discuss our semi-analytical model and its results on ϵ( f ), n R ( t ), n Q ( t ), and n s ( t ) in central Au+Au collisions. We then compare the T ( t ), μ B ( t ), μ Q ( t ), and μ S ( t ) extracted with the ideal gas equation of state (EoS) with quantum statistics to those extracted with a lattice QCD-based EoS. We also compare the T -μ B trajectories with the RHIC chemical freezeout data. Finally, we discuss the effect of transverse flow on the trajectories. 

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5. A nuclear physics example of statistical bootstrap is used on the MARATHON nucleon structure function ratio data in the quark momentum fraction regions xB → 0 and xB → 1. The extrapolated F2 ratio as quark momentum fraction xB → 1 is Fn 2 F p 2 → 0.4 ± 0.05 and this value is compared to theoretical predictions. The extrapolated ratio when xB → 0 favors the simple model of isospin symmetry with the complete dominance of sea quarks at low momentum fraction. At high-xB, the proton quark distribution function ratio d/u is derived from the F2 ratio and found to be d/u → 1/6. Our extrapolated values for both the Fn 2 F p 2 ratio and the d/u parton distribution function ratio are within uncertainties of perturbative QCD values from quark counting, helicity conservation arguments, and a Dyson-Schwinger equation with a contact interaction model. In addition, it is possible to match the statistical bootstrap value to theoretical predictions by allowing two compatible models to act simultaneously in the nucleon wave function. One such example is nucleon wave functions composed of a linear combination of a quark-diquark state and a three-valence quark correlated state with coefficients that combine to give the extrapolated F2 ratio at xB = 1.

   https://doi.org/10.1103/PhysRevC.107.065203  

   Valenty, Hannah ; West, Jennifer Rittenhouse ; Benmokhtar, Fatiha ; Higinbotham, Douglas W. ; Parker, Asia ; Seroka, Erin ( June 2023 , Physical Review C)

   A nuclear physics example of statistical bootstrap is used on the MARATHON nucleon structure function ratio data in the quark momentum fraction regions xB → 0 and xB → 1. The extrapolated F2 ratio as quark momentum fraction xB → 1 is Fn 2 F p 2 → 0.4 ± 0.05 and this value is compared to theoretical predictions. The extrapolated ratio when xB → 0 favors the simple model of isospin symmetry with the complete dominance of sea quarks at low momentum fraction. At high-xB, the proton quark distribution function ratio d/u is derived from the F2 ratio and found to be d/u → 1/6. Our extrapolated values for both the Fn 2 F p 2 ratio and the d/u parton distribution function ratio are within uncertainties of perturbative QCD values from quark counting, helicity conservation arguments, and a Dyson-Schwinger equation with a contact interaction model. In addition, it is possible to match the statistical bootstrap value to theoretical predictions by allowing two compatible models to act simultaneously in the nucleon wave function. One such example is nucleon wave functions composed of a linear combination of a quark-diquark state and a three-valence quark correlated state with coefficients that combine to give the extrapolated F2 ratio at xB = 1. 

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