Guoji Lin

Electro-magnetic (E&M) probes such as direct photons and muons (μ) are important tools to study the properties of the extremely hot and dense matter created in heavy ion collisions at the Relativistic Heavy Ion Collider (RHIC). In this thesis, several topics of E&M physics will be addressed, including neutral pion (π⁰) production, direct photon HBT, and photon elliptic flow (v₂) in Au+Au collisions at [special characters omitted] = 200 GeV. A discussion on the simulation study of the new Muon Telescope Detector (MTD) will also be presented.

The π⁰ production is a fundamental measurement of hadron production and prerequisite for the background study of direct photons. Neutral pions are reconstructed using the photons detected by the STAR Barrel Electro-magnetic Calorimeter (BEMC) and the Time Projection Chamber (TPC). Spectra of π ⁰ are measured at transverse momentum 1 < p_T < 12 GeV/c near mid-rapidity (0 < η < 0.8) in 200 GeV Au+Au collisions. The spectra and nuclear modification factors R_CP and R_AA are compared to earlier π^± and π⁰ results.

Direct photon Hanbury-Brown and Twiss (HBT) correlations can reveal information of the system size throughout the whole collision. A first attempt of direct photon HBT study at RHIC in 200 GeV Au+Au collisions is done using photons detected by the STAR BEMC and TPC. All unknown correlation at small Q_inv is observed, whose magnitude is much larger than the expected HBT signal, and possible causes of the correlation will be discussed.

Direct photon elliptic flow (v₂) at intermediate to high p_T is sensitive to the source of direct photon production. Results of inclusive photon v₂ in 200 GeV Au+Au collisions are presented. The v₂ of π⁰ decay photons is calculated from the previously published π results. The comparison between inclusive and decay photon v ₂ indicates that direct photon v₂ is small.

A new large-area Muon Telescope Detector at mid-rapidity at RHIC is proposed and under investigation, using the Long-strip Multi-Gap Resistive Plate Chamber (Long-MRPC). Simulations indicate that the MTD can effectively identify μ and reject hadron backgrounds, and it can serve as a μ trigger. A beam test result of the Long-MRPC at Fermi National Accelerator Laboratory (FNAL) is also discussed