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Register a new userTwo-component source to explain $Lambda$ and $bar{Lambda}$ global polarization in non-central heavy-ion collisions
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Ivonne Alicia Maldonado Cervantes
Publication date
2020
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and research's language is
English
Authors
A. Ayala
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The STAR Beam Energy Scan program has found a difference in the global polarization of $Lambda$s and $bar{Lambda}$s produced in $Au+Au$ collisions. This difference is larger for lower center of mass collision energies. In this work we show that a two-component source, consisting of a high density core and a lower density corona, can describe quantitatively the $Lambda$ and $bar{Lambda}$ polarization as a function of collision energy.
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We investigate the two-particle intensity correlation function of $Lambda$ in relativistic heavy-ion collisions. We find that the behavior of the $LambdaLambda$ correlation function at small relative momenta is fairly sensitive to the interaction potential and collective flows. By comparing the results of different source functions and potentials, we explore the effect of intrinsic collective motions on the correlation function. We find that the recent STAR data gives a strong constraint on the scattering length and effective range of $LambdaLambda$ interaction as, $-1.8 mathrm{fm}^{-1} < 1/a_0 < -0.8 mathrm{fm}^{-1}$ and $3.5 mathrm{fm} < r_mathrm{eff} < 7 mathrm{fm}$, respectively,if $Lambda$ samples do not include feed-down contribution from long-lived particles. We find that feed-down correction for $Sigma^0$ decay reduces the sensitivity of the correlation function to the detail of the $LambdaLambda$ interaction. As a result, we obtain a weaker constraint $1/a_0 <-0.8$ fm$^{-1}$. Implication for the signal of existence of $H$-dibaryon is discussed. Comparison with the scattering parameters obtained from the double $Lambda$ hypernucleus may reveal in-medium effects in the $LambdaLambda$ interaction.
With a Yang-Mills flux-tube initial state and a high resolution (3+1)D Particle-in-Cell Relativistic (PICR) hydrodynamics simulation, we calculate the $Lambda$ polarization for different energies. The origination of polarization in high energy collisions is discussed, and we find linear impact parameter dependence of the global $Lambda$ polarization. Furthermore, the global $Lambda$ polarization in our model decreases very fast in the low energy domain, and the decline curve fits well the recent results of Beam Energy Scan (BES) program launched by the STAR collaboration at the Relativistic Heavy Ion Collider (RHIC). The time evolution of polarization is also discussed.
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.
We consider $Lambda$ and $bar{Lambda}$ production in a wide range of proton scattering experiments. The produced $Lambda$ and $bar{Lambda}$ may or may not contain a diquark remnant of the beam proton. The ratio of these two production mechanisms is found to be a simple universal function $r = [ kappa/(y_p - y) ]^i$ of the rapidity difference $y_p - y$ of the beam proton and the produced $Lambda$ or $bar{Lambda}$, valid over four orders of magnitude, from $r approx 0.01$ to $r approx 100$, with $kappa = 2.86 pm 0.03 pm 0.07$, and $i = 4.39 pm 0.06 pm 0.15$.
Predictions for the global polarization of $Lambda$ hyperons in Au+Au collisions at moderately relativistic collision energies, 2.4 $leqsqrt{s_{NN}}leq$ 11 GeV, are made. These are based on the thermodynamic approach to the global polarization incorporated into the model of the three-fluid dynamics. Centrality dependence of the polarization is studied. It is predicted that the polarization reaches a maximum or a plateau (depending on the equation of state and centrality) at $sqrt{s_{NN}}approx$ 3 GeV. It is found that the global polarization increases with increasing width of the rapidity window around the midrapidity.
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