High-energy photons function as effective indicators across several physical processes, including ultra-relativistic heavy-ion (URHI) collisions and astrophysical events like solar flares, both fields depend on photons to investigate the underlying dynamics of energetic systems under severe conditions.

In solar particle events, photons provide insights into particle acceleration and magnetic reconnection. In high-energy nuclear collisions, direct photons serve as crucial probes for investigating the first phases of quark-gluon plasma (QGP) formation, due to their ability to escape the medium without strong interactions. This conceptual overlap motivates the investigation presented in this thesis, which focuses on direct photon and neutral pion production in relativistic heavy-ion collisions as a window into quantum chromodynamics (QCD) and parton energy loss.

The Standard Model is a theoretical framework in modern particle physics that explains the behavior and interactions of Elementary particles, including quarks, leptons, and gauge bosons, that are fundamental components in the study of QCD, which is the theoretical framework that clarifies the mechanisms behind the powerful interactions between quarks and gluons. QCD exhibits two fundamental characteristics: The terms "color confinement" and "asymptotic freedom" pertain to distinct topics within the field of physics. Quarks as well as the gluons exhibit color properties which usually restricted to exist within hadrons as color-singlet states. However, the strong coupling constant (αs) decreases when this momentum transfer increases in high-energy reactions or in settings characterized by an exceedingly high temperature or density. Therefore, when the temperature of either density of a many-body hadronic structure rises, it is anticipated that it undergoes a phase transition through an individual type of existence in which both gluons and quarks become no longer contained. The state referred to here is commonly referred to QGP.

A state of matter is expected to be formed in ultra-relativistic collisions. Several tests with heavy ions were recently performed to identify distinctive indications of this state. The RHIC at Brookhaven National Laboratory (BNL) in the USA conducted Au+Au collisions at a center-of-mass energy for each nucleon (sNN) of 200 GeV. This thesis reports preliminary findings on a study that measured neutrality pions and direct photons during high-speed collisions between gold nuclei using the RHIC-PHENIX spectrometer. Both the pions and direct photons are observed at mid-rapidity with high transverse momentum (pT) values of up to 20 GeV/c. The pion and direct photon production in Au+Au collisions are examined by comparing these results with run 4 data obtained from the same experiment.

During high-energy gold-gold collisions, an impressive drop in neutral pion formation at high transverse momentum (pT) is observed compared to the yield in proton proton collisions at identical centers of mass energy (s), adjusted to the number of interactions between nucleons during gold-gold collisions. This suppression is significant, approximately five times, and remains nearly changing within the range of transverse momentum from around 5 to approximately 20 GeV/c. However, direct photon production in Au+Au collisions lines up with the p+p results scaled with the number of binary collisions. Considering how many high-pT direct photon come from early hard scatterings, the suppression is understood as a result of parton energy exhaustion resulting from gluon bremsstrahlung in the dense medium. The neutral pion suppression pattern was compared to a theoretical calculation by I. Vitev using the GLV energy loss formalism. This comparison allowed for a quantitative estimation of the effective gluon density (dNgeff/dy) during this high-density substance produced in sNN=200 GeV when two gold particles collide, which is approximately 1300−100+300. As a plasma dominated by gluons forms within a time frame of 0.6 femtoseconds, the resulting energy density is 18 ((\text{GeV/fm}^3)).

This thesis examines the unique variables affecting photon generation and behavior across multiple fields, including electromagnetic processes in solar environments and partonic interactions in the quark-gluon plasma produced during heavy-ion collisions.