Non-photonic electron distributions at pseudo-rapidities between 1.1 and 1.5 in proton-proton collisions at √s=200 GeV at Relativistic Heavy Ion Collider.

Naresh Subba

Department of Physics

Kent State University

This Dissertation project involved using the Endcap Electro-Magnetic Calorimeter (EEMC) to try to measure charm quark production in proton-proton (p+p) collisions at √s=200 GeV. This was performed by identifying electrons produced in the decay of charm D⁰ mesons. This project included testing and calibration of elements used in the installation of the EEMC on the Solenoidal Tracker At RHIC (STAR) detector on the Relativistic Heavy Ion Collider (RHIC) accelerator at Brookhaven National Laboratory (BNL). These measurements provided an upper limit for non-photonic electron production at pseudo-rapidities (η) between 1.1 and 1.5 in p+p collisions at √s=200 GeV using the EEMC as the main detector in conjunction with the Time Projection Chamber (TPC) in STAR. Non-photonic electrons are the electrons from the semi-leptonic decay of charm D⁰ mesons.

Ionization energy loss, dE/dx, of a charged particle in the TPC and the associated momentum (p) of the particle are two important observables that help identify electrons from hadrons, mainly in the mid-rapidity region. In the forward rapidity region, where the TPC tracking resolution is poor, energy deposit (E) information in the pre-shower, post-shower and shower maximum detectors (SMD) in the EEMC provide additional power in distinguishing electrons from hadrons. A combination of dE/dx and p/E cuts provide electrons with purity > 92% and an acceptance efficiency of 52% for electrons incident upon the EEMC.

The hadron-corrected inclusive electron spectrum is contaminated by photonic background electrons. The major sources of this photonic background are electrons from photon conversions and π⁰ Dalitz decays. We make use of the invariant mass technique to reconstruct photonic background electrons, taking advantage of the fact that electron-positron pairs from conversion photons or π⁰ Dalitz decays have a small invariant mass and small opening angles in φ and θ, while there is no such correlation for non-photonic electrons. Reconstruction efficiency of photonic electrons is obtained from simulations.

Our calculations provide an upper limit for the non-photonic electron yield and consequently an upper limit for the total quark charm production. In this dissertation, we present the methods and procedures adopted to obtain these results.