Statistical and Dynamic Models of Charge Balance Functions

Charge balance functions, which identify balancing particle-antiparticle pairs on a statistical basis, have been shown to be sensitive to whether hadronization is delayed by several fm/c in relativistic heavy ion collisions. Results from two classes of models are presented here, microscopic hadronic models and thermal models. The microscopic models give results which are contrary to recently published pi+pi- balance functions from the STAR collaboration, whereas the thermal model roughly reproduce the experimental results. This suggests that charge conservation is local at breakup, which is in line with expectations for a delayed hadronization. Predictions are also presented for balance functions binned as a function of Q_inv.Comment: 12 pages 6 figure

Forward-backward multiplicity correlations for identified particles at STAR

Kinematic observables of charged particles from relativistic heavy-ion collisions are measured in search of quark-gluon degrees of freedom. Long-Range Forward-Backward multiplicity correlations (LRC) may be a signal for multiple partonic interactions in dense matter, as predicted by the Dual Parton Model (DPM), Color String Percolation Model (CSPM), and the Color Glass Condensate (CGC) picture. Previously, a strong LRC for inclusive charged hadrons was measured as a function of pseudorapidity gap (Δη) in Au+Au collisions at [special characters omitted] = 200 GeV, and were shown to decrease with decreasing centrality. In this dissertation, the forward-backward correlation strength is studied with respect to its particle species dependence (pions, kaons, protons and anti-protons), and is measured as a function of rapidity gap (Δy) in Au+Au collisions at [special characters omitted] = 200 GeV. The CGC picture, which describes particle sources as longitudinal flux tubes, predicts that the correlation will grow with centrality. Furthermore, fluctuations in the number of gluons at early times will produce a long range correlation strength significantly larger for pions than for baryons. A strong, long-range (Δy \u3e 1.0) correlation is measured for pions in central Au+Au collisions at [special characters omitted] = 200 GeV, which decreases with decreasing centrality. The measured small short-range correlation compared to pions for protons and antiprotons suggests their long-range component will also be small. The forward-backward multiplicity correlation measurements for identified particles indicate multiple partonic interactions in high-energy, central Au+Au collisions, and the possible formation of the quark-gluon plasma

Hyperon Polarization along the Beam Direction Relative to the Second and Third Harmonic Event Planes in Isobar Collisions at <math display="inline"><mrow><msqrt><mrow><msub><mrow><mi>s</mi></mrow><mrow><mi>N</mi><mi>N</mi></mrow></msub></mrow></msqrt><mo>=</mo><mn>200</mn><mtext> </mtext><mtext> </mtext><mi>GeV</mi></mrow></math>

The polarization of Λ and Λ¯ hyperons along the beam direction has been measured relative to the second and third harmonic event planes in isobar Ru+Ru and Zr+Zr collisions at sNN=200  GeV. This is the first experimental evidence of the hyperon polarization by the triangular flow originating from the initial density fluctuations. The amplitudes of the sine modulation for the second and third harmonic results are comparable in magnitude, increase from central to peripheral collisions, and show a mild pT dependence. The azimuthal angle dependence of the polarization follows the vorticity pattern expected due to elliptic and triangular anisotropic flow, and qualitatively disagrees with most hydrodynamic model calculations based on thermal vorticity and shear induced contributions. The model results based on one of existing implementations of the shear contribution lead to a correct azimuthal angle dependence, but predict centrality and pT dependence that still disagree with experimental measurements. Thus, our results provide stringent constraints on the thermal vorticity and shear-induced contributions to hyperon polarization. Comparison to previous measurements at RHIC and the LHC for the second-order harmonic results shows little dependence on the collision system size and collision energy.The polarization of $\Lambda$ and $\bar{\Lambda}$ hyperons along the beam direction has been measured relative to the second and third harmonic event planes in isobar Ru+Ru and Zr+Zr collisions at $\sqrt{s_{NN}}$ = 200 GeV. This is the first experimental evidence of the hyperon polarization by the triangular flow originating from the initial density fluctuations. The amplitudes of the sine modulation for the second and third harmonic results are comparable in magnitude, increase from central to peripheral collisions, and show a mild $p_T$ dependence. The azimuthal angle dependence of the polarization follows the vorticity pattern expected due to elliptic and triangular anisotropic flow, and qualitatively disagree with most hydrodynamic model calculations based on thermal vorticity and shear induced contributions. The model results based on one of existing implementations of the shear contribution lead to a correct azimuthal angle dependence, but predict centrality and $p_T$ dependence that still disagree with experimental measurements. Thus, our results provide stringent constraints on the thermal vorticity and shear-induced contributions to hyperon polarization. Comparison to previous measurements at RHIC and the LHC for the second-order harmonic results shows little dependence on the collision system size and collision energy