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Register a new userInvestigating Local Parity Violation in Heavy-Ion Collisions Using Lambda Helicity
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We propose the measurement of net $Lambda$ and $bar{Lambda}$ helicity, correlated event-by-event with the magnitude and sign of charge separation along the events magnetic field direction, as a probe to investigate the Chiral Magnetic Effect in Heavy-Ion Collisions. With a simple simulation model of heavy-ion events that includes effects of Local Parity Violation, we estimate the experimental correlation signal that could be expected at RHIC given the results of previous measurements that are sensitive to the CME.
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Parity-odd domains, corresponding to non-trivial topological solutions of the QCD vacuum, might be created during relativistic heavy-ion collisions. These domains are predicted to lead to charge separation of quarks along the orbital momentum of the system created in non-central collisions. To study this effect, we investigate a three particle mixed harmonics azimuthal correlator which is a P-even observable, but directly sensitive to the charge separation effect. We report measurements of this observable using the STAR detector in Au+Au and Cu+Cu collisions at $sqrt{s_{NN}}$=200 and 62~GeV. The results are presented as a function of collision centrality, particle separation in rapidity, and particle transverse momentum. A signal consistent with several of the theoretical expectations is detected in all four data sets. We compare our results to the predictions of existing event generators, and discuss in detail possible contributions from other effects that are not related to parity violation.
We discuss the helicity polarization which can be locally induced from both vorticity and helicity charge in non-central heavy ion collisions. Helicity charge redistribution can be generated in viscous fluid and contributes to azimuthal asymmetry of the polarization along global angular momentum or beam momentum. We also discuss on detecting the initial net helicity charge from topological charge fluctuation or initial color longitudinal field by the helicity polarization correlation of two hyperons and the helicity alignment of vector mesons in central heavy ion collisions.
The three-dimensional pion and kaon emission source functions are extracted from the HKM model simulations of the central Au+Au collisions at the top RHIC energy $sqrt{s_{NN}}=200$ GeV. The model describes well the experimental data, previously obtained by the PHENIX and STAR collaborations using the imaging technique. In particular, the HKM reproduces the non-Gaussian heavy tails of the source function in the pair transverse momentum (out) and beam (long) directions, observed in the pion case and practically absent for kaons. The role of the rescatterings and long-lived resonances decays in forming of the mentioned long range tails is investigated. The particle rescatterings contribution to the out tail seems to be dominating. The model calculations also show the substantial relative emission times between pions (with mean value 14.5 fm/c in LCMS), including those coming from resonance decays and rescatterings. The prediction is made for the source functions in the LHC Pb+Pb collisions at $sqrt{s_{NN}}=2.76$ TeV, which are still not extracted from the measured correlation functions.
We investigate the measurement of Hanbury Brown-Twiss (HBT) photon correlations as an experimental tool to discriminate different sources of photon enhancement, which are proposed to simultaneously reproduce the direct photon yield and the azimuthal anisotropy measured in nuclear collisions at RHIC and the LHC. To showcase this, we consider two different scenarios in which we enhance the yields from standard hydrodynamical simulations. In the first, additional photons are produced from the early pre-equilibrium stage computed from the textit{bottom-up} thermalization scenario. In the second, the thermal rates are enhanced close to the pseudo-critical temperature $T_capprox 155,text{MeV}$ using a phenomenological ansatz. We compute the correlators for relative momenta $q_o, ,q_s$ and $q_l$ for different transverse pair momenta, $K_perp$, and find that the longitudinal correlation is the most sensitive to different photon sources. Our results also demonstrate that including anisotropic pre-equilibrium rates enhances non-Gaussianities in the correlators, which can be quantified using the kurtosis of the correlators. Finally, we study the feasibility of measuring a direct photon HBT signal in the upcoming high-luminosity LHC runs. Considering only statistical uncertainties, we find that with the projected $sim 10^{10}$ heavy ion events a measurement of the HBT correlations for $K_perp<1, text{GeV}$ is statistically significant.
We report predictions for the suppression and elliptic flow of the $Upsilon(1S)$, $Upsilon(2S)$, and $Upsilon(3S)$ as a function of centrality and transverse momentum in ultra-relativistic heavy-ion collisions. We obtain our predictions by numerically solving a Lindblad equation for the evolution of the heavy-quarkonium reduced density matrix derived using potential nonrelativistic QCD and the formalism of open quantum systems. To numerically solve the Lindblad equation, we make use of a stochastic unraveling called the quantum trajectories algorithm. This unraveling allows us to solve the Lindblad evolution equation efficiently on large lattices with no angular momentum cutoff. The resulting evolution describes the full 3D quantum and non-abelian evolution of the reduced density matrix for bottomonium states. We expand upon our previous work by treating differential observables and elliptic flow; this is made possible by a newly implemented Monte-Carlo sampling of physical trajectories. Our final results are compared to experimental data collected in $sqrt{s_{NN}} = 5.02$ TeV Pb-Pb collisions by the ALICE, ATLAS, and CMS collaborations.
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