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Register a new userExamination of the observability of a chiral magnetically-driven charge-separation difference in collisions of the $mathrm{^{96}_{44}Ru +, ^{96}_{44}Ru}$ and $mathrm{^{96}_{40}Zr +, ^{96}_{40}Zr}$ isobars at energies available at RHIC
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Niseem Magdy
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Anomalous Viscous Fluid Dynamics (AVFD) model calculations for $mathrm{^{96}_{44}Ru +, ^{96}_{44}Ru}$ and $mathrm{^{96}_{40}Zr +, ^{96}_{40}Zr}$ collisions ($sqrt{s_{rm NN}} = 200$ GeV) are used in concert with a charge-sensitive correlator, to test its ability to detect and characterize the charge separation difference expected from the Chiral Magnetic Effect (CME) in these isobaric collisions. The tests indicate a larger charge separation for $mathrm{^{96}_{44}Ru +, ^{96}_{44}Ru}$ than for $mathrm{^{96}_{40}Zr +, ^{96}_{40}Zr}$ collisions, and a discernible CME-driven difference of $sim 10$% in the presence of realistic non-CME backgrounds. They also indicate a strategy for evaluating the relative influence of the background correlations, present for each isobar. These results suggest that charge separation measurements for these isobaric species could serve to further constrain unambiguous identification and characterization of the CME in upcoming measurements at RHIC.
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The production of $rm{^3_Lambda H}$ and $rm{{^3_{overline Lambda}overline H}}$, as well as $rm{^3H}$, $rm{{^3overline H}}$, $rm{^3He}$, and $rm{{^3overline {He}}}$ are studied in central collisions of isobars $^{96}_{44}$Ru+$^{96}_{44}$Ru and $^{96}_{40}$Zr+$^{96}_{40}$Zr at $sqrt{s_{rm{NN}}}=200$ GeV, using the dynamically constrained phase-space coalescence model and the {footnotesize PACIAE} model with chiral magnetic effect. The yield, yield ratio, coalescence parameters, and strangeness population factor of (anti-)hypertriton and (anti-)nuclei produced in isobaric $^{96}_{44}$Ru+$^{96}_{44}$Ru and $^{96}_{40}$Zr+$^{96}_{40}$Zr collisions are predicted. The (anti-)hypertriton and (anti-)nuclei production is found to be insensitive to the chiral magnetic effects. Experimental data of Cu+Cu, Au+Au and Pb+Pb collisions from RHIC, LHC, and the results of {footnotesize PACIAE+DCPC} model are presented in the results for comparison.
In the hydrodynamic model description of heavy ion collisions, the elliptic flow $v_2$ and triangular flow $v_3$ are sensitive to the quadrupole deformation $beta_2$ and octupole deformation $beta_3$ of the colliding nuclei. The relations between $v_n$ and $beta_n$ have recently been clarified and were found to follow a simple parametric form. The STAR Collaboration have just published precision $v_n$ data from isobaric $^{96}$Ru+$^{96}$Ru and $^{96}$Zr+$^{96}$Zr collisions, where they observe large differences in central collisions $v_{2,mathrm{Ru}}>v_{2,mathrm{Zr}}$ and $v_{3,mathrm{Ru}}<v_{3,mathrm{Zr}}$. Using a transport model simulation, we show that these orderings are a natural consequence of $beta_{2,mathrm{Ru}}ggbeta_{2,mathrm{Zr}}$ and $beta_{3,mathrm{Ru}}llbeta_{3,mathrm{Zr}}$. We are able to reproduce the centrality dependence of the $v_2$ ratio qualitatively and $v_3$ ratio quantitatively, and extract values of $beta_2$ and $beta_3$ that are consistent with those measured at low energy nuclear structure experiments. STAR data provide the first direct evidence of strong octupole correlations in the ground state of $^{96}$Zr in heavy ion collisions. Our analysis demonstrates that flow measurements in high-energy heavy ion collisions, especially using isobaric systems, are a new precision tool to study nuclear structure physics.
Fusion data for $^{40}$Ca+$^{96}$Zr are analyzed by coupled-channels calculations that are based on a standard Woods-Saxon potential and include couplings to multiphonon excitations and transfer channels. The couplings to multiphonon excitations are the same as used in a previous work. The transfer couplings are calibrated to reproduce the measured neutron transfer data. This type of calculation gives a poor fit to the fusion data. However, by multiplying the transfer couplings with a $sqrt{2}$ one obtains an excellent fit. The scaling of the transfer strengths is supposed to simulate the combined effect of neutron and proton transfer, and the calculated one- and two-nucleon transfer cross sections are indeed in reasonable agreement with the measured cross sections.
The nature of $J^{pi}=1^-$ levels of $^{96}$Zr below the $beta$-decay $Q_{beta}$ value of $^{96}$Y has been investigated in high-resolution $gamma$-ray spectroscopy following the $beta$ decay as well as in a campaign of inelastic photon scattering experiments. Branching ratios extracted from $beta$ decay allow the absolute $E1$ excitation strength to be determined for levels populated in both reactions. The combined data represents a comprehensive approach to the wavefunction of $1^-$ levels below the $Q_{beta}$ value, which are investigated in the theoretical approach of the Quasiparticle Phonon Model. This study clarifies the nuclear structure properties associated with the enhanced population of high-lying levels in the $^{96}$Y$_{gs}$ $beta$ decay, one of the three most important contributors to the high-energy reactor antineutrino spectrum.
Lighter heavy elements beyond iron and up to around silver can form in neutrino-driven ejecta in core-collapse supernovae and neutron star mergers. Slightly neutron-rich conditions favour a weak r-process that follows a path close to stability. Therefore, the beta decays are slow compared to the expansion time scales, and ($alpha$,n) reactions become critical to move matter towards heavier nuclei. The rates of these reactions are calculated with the statistical model and their main uncertainty, at energies relevant for the weak r-process, is the $alpha$+nucleus optical potential. There are several sets of parameters to calculate the $alpha$+nucleus optical potential leading to large deviations for the reaction rates, exceeding even one order of magnitude. Recently the $^{96}$Zr($alpha$,n)$^{99}$Mo reaction has been identified as a key reaction that impacts the production of elements from Ru to Cd. Here, we present the first cross section measurement of this reaction at energies (6.22 MeV $leq$ E$_mathrm{c.m.}$ $leq$ 12.47 MeV) relevant for the weak r-process. The new data provide a stringent test of various model predictions which is necessary to improve the precision of the weak r-process network calculations. The strongly reduced reaction rate uncertainty leads to very well-constrained nucleosynthesis yields for $Z = 44 - 48$ isotopes under different neutrino-driven wind conditions.
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