Probing Properties of Nuclear Matter with Heavy-Ion Collisions

Date of Award

8-2025

Degree Name

Doctor of Philosophy

Department

Physics

First Advisor

Zbigniew Chajecki, Ph.D.

Second Advisor

Giuseppe Verde, Ph.D.

Third Advisor

Elena Litvinova, Ph.D.

Fourth Advisor

Asghar Kayani, Ph.D.

Keywords

Correlation function, nuclear equation of state, nuclear physics, transport model

Abstract

Understanding the equation of state (EoS) of nuclear matter is central to bridging nuclear physics with astrophysical phenomena. The EoS describes how matter behaves under extreme conditions of density, temperature, and isospin asymmetry, providing a crucial link between the microscopic interactions among nucleons and the macroscopic properties of compact stellar objects such as neutron stars. Observables from both laboratory experiments, such as heavy-ion collisions, and astrophysical measurements, including gravitational wave signals from neutron star mergers, mass-radius relationships, and pulsar timing, offer complementary constraints on the nuclear EoS. By integrating insights from these diverse domains, our goal is to construct a unified and consistent model of dense matter, advancing our understanding of the universe’s most extreme environments and the fundamental behavior of nuclear interactions.

In addition to the bulk properties encoded in the equation of state, theoretical models used to interpret laboratory and astrophysical data must incorporate detailed physical inputs, such as in-medium nucleon-nucleon cross sections (˜σNN) and particle production mechanisms. These components are critical for accurately describing the transport properties and reaction dynamics in nuclear collisions and modeling the dense, hot environments in supernovae and neutron star mergers. Without a robust understanding of how these quantities evolve under extreme conditions—such as changes in density, temperature, and isospin asymmetry— the predictive power of EoS models remains limited. Consequently, constraining these microscopic inputs through experimental measurements and theoretical developments is a necessary step toward reliably connecting nuclear physics to the astrophysical behavior of compact objects.

To investigate the properties of nuclear matter at extreme conditions, a dedicated heavyion collision (HIC) experiment was conducted at the National Superconducting Cyclotron Laboratory (NSCL) at Michigan State University. Primary beams of 40,48Ca at 56 and 140 AMeV were impinged on targets of 58,64Ni, creating nuclear reactions across a range of densities and isospin asymmetries. Using the upgraded High Resolution Array (HiRA10), light charged particles including protons (p), deuterons (d), tritons (t), 3He and 4He, were identified with high statistics.

Transverse momentum (pT) spectra were constructed for mid-rapidity light charged particles from central collisions. These spectra were analyzed using a BlastWave model to extract the kinetic freeze-out temperature (Tkin) and collective radial flow velocity (βcoll). To study medium effects, experimental spectra were compared with Antisymmetrized Molecular Dynamics (AMD) calculations incorporating a screened parameterization of ˜σNN. The results indicate a more significant reduction of ˜σNN at 56 AMeV than at 140 AMeV.

To probe the space-time structure of the emission source, two-particle correlation functions (CFs) were measured. A novel, model-independent technique based on the Richardson- Lucy deblurring algorithm with maximum entropy regularization was developed to extract source functions directly from CFs. This method demonstrated robustness against noise and was successfully applied to p–p and d–α correlation functions.

The experimental p–p and d–α CFs were compared with a Monte Carlo model incorporating thermal emission and collective expansion. Simulations used source parameters guided by the BlastWave fit to pT spectra. The resulting CF line shapes were consistent with emission sizes of Rd = Rα ≈ 5.1 fm and Rp = 10.1 fm. The larger p–p emission radius is consistent with expectations: deuterons and alpha particles are primarily emitted during early, instantaneous processes such as multifragmentation, whereas protons also originate from later, evaporative emission stages.

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Dissertation-Abstract Only

Restricted to Campus until

8-1-2027

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