SEARCH FOR THE CHIRAL MAGNETIC EFFECT BY EVENT SHAPE ENGINEERING DIFFERENTIALLY IN INVARIANT MASS IN AU+AU COLLISIONS AT 200 GEV FROM STAR

<p dir="ltr">It has been predicted by quantum chromodynamics (QCD) that vacuum fluctuations can result in gluon fields of non-zero topological charges (Chern-Simons winding numbers) in local metastable domains. Interactions of quarks with such gluon fields can cause chirality imbalance, breaking the parity and charge-parity symmetries in those domains. Such chirality imbalance, under a strong magnetic field, can result in charge separation along the magnetic field, a phenomenon called chiral magnetic effect (CME). Relativistic heavy ion collisions, where a high-temperature quark-gluon plasma and a strong magnetic field are produced, are an ideal place to search for the CME. A commonly used observable is the CME-sensitive observable, charge-dependent three-point azimuthal correlator ∆γ. However, this correlator, being parity even, is contaminated by a major physics background proportional to the particle elliptic flow (v2), an azimuthal anisotropy due to a global correlation to the initial collision geometry. In this thesis, we present a new analysis from the STAR experiment on charge separation using the event-shape engineering (ESE) approach, projecting ∆γ to zero v2 to obtain the intercept ∆γese in which the flow-induced background is largely suppressed. The ESE variable selecting/characterizing events is calculated using particles separated from the particles of interest (POIs), so the resultant variation in v2 of these events arises from dynamical fluctuations. The reaction plane, to which the magnetic field is perpendicular on average, is proxied by the event plane reconstructed from the time projection chamber (or using the three-particle cumulant method) and by the spectator plane reconstructed from the zero degree calorimeters. We apply the ESE method differentially as a function of the pair invariant mass of POIs because CME is a low-pT phenomenon and hence may be more sensitive to the lower mass region. We investigate remaining contamination from nonflow correlations (those unrelated to the collision geometry) in the extracted ESE intercept. Results are reported for Au+Au collisions at nucleon-nucleon center-of-mass energy √sNN = 200 GeV at STAR experiment.</p><p dir="ltr">We further investigate the robustness of our ESE approach using several dynamical and phenomenological models as well as a toy model. We discuss a new CME observable, similar to the ∆γ correlator, in the context of these model studies.</p>