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Register a new userQuasielastic lepton scattering and back-to-back nucleons in the short-time approximation
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Understanding quasielastic electron- and neutrino-scattering from nuclei has taken on new urgency with current and planned neutrino oscillation experiments, and with electron scattering experiments measuring specific final states, such as those involving nucleon pairs in ``back-to-back configurations. Accurate many-body methods are available for calculating the response of light ($A leq 12$) nuclei to electromagnetic and weak probes, but they are computationally intensive and only applicable to the inclusive response. In the present work we introduce a novel approach, based on realistic models of nuclear interactions and currents, to evaluate the short-time (high-energy) inclusive and exclusive response of nuclei. The approach accounts reliably for crucial two-nucleon dynamics, including correlations and currents, and provides information on back-to-back nucleons observed in electron and neutrino scattering experiments. We demonstrate that in the quasielastic regime and at moderate momentum transfers both initial- and final-state correlations, and two-nucleon currents are important for a quantitatively successful description of the inclusive response and final state nucleons. Finally, the approach can be extended to include relativistic---kinematical and dynamical---effects, at least approximately in the two-nucleon sector, and to describe the response in the resonance-excitation region.
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The article of Pastore et al, while proposing an interesting and potentially useful approach for the generalisation of Quantum Monte Carlo techniques to the treatment of the nuclear electromagnetic response, features an incorrect and misleading discussion of y-scaling. The response to interactions with transversely polarised virtual photons receives sizeable contributions from non-scaling processes, in which the momentum transfer is shared between two nucleons. It follows that, contrary to what is stated by the the authors, y-scaling in the transverse channel is accidental.
Quasielastic scattering excitation function at large backward angle has been measured for the weakly bound system, $^{7}$Li+$^{159}$Tb at energies around the Coulomb barrier. The corresponding quasielastic barrier distribution has been derived from the excitation function, both including and excluding the $alpha$-particles produced in the reaction. The centroid of the barrier distribution obtained after inclusion of $alpha$-particles was found to be shifted higher in energy, compared to the distribution excluding the $alpha $-particles. The quasielastic data, excluding the $alpha$-particles, have been analyzed in the framework of continuum discretized coupled channel calculations. The quasielastic barrier distribution for $^{7}$Li+$^{159}$Tb, has also been compared with the fusion barrier distribution for the system.
Back-to-Back Correlations of particle-antiparticle pairs are related to the in-medium mass-modification and squeezing of the quanta involved. They are predicted to appear when hot and dense hadronic matter is formed in high energy nucleus-nucleus collisions. The survival and magnitude of the Back-to-Back Correlations of boson-antiboson pairs generated by in-medium mass modifications are studied here in the case of a thermalized, finite-sized, spherically symmetric expanding medium. We show that the BBC signal indeed survives the finite-time emission, as well as the expansion and flow effects, with sufficient intensity to be observed at RHIC.
$textbf{Background:}$ The chiral magnetic effect (CME) is extensively studied in heavy-ion collisions at RHIC and LHC. In the commonly used reaction plane (RP) dependent, charge dependent azimuthal correlator ($Deltagamma$), both the close and back-to-back pairs are included. Many backgrounds contribute to the close pairs (e.g. resonance decays, jet correlations), whereas the back-to-back pairs are relatively free of those backgrounds. $textbf{Purpose:}$ In order to reduce those backgrounds, we propose a new observable which only focuses on the back-to-back pairs, namely, the relative back-to-back opposite-sign (OS) over same-sign (SS) pair excess ($r_{text{BB}}$) as a function of the pair azimuthal orientation with respect to the RP ($varphi_{text{BB}}$). $textbf{Methods:}$ We use analytical calculations and toy model simulations to demonstrate the sensitivity of $r_{text{BB}}(varphi_{text{BB}})$ to the CME and its insensitivity to backgrounds. $textbf{Results:}$ With finite CME, the $varphi_{text{BB}}$ distribution of $r_{text{BB}}$ shows a clear characteristic modulation. Its sensitivity to background is significantly reduced compared to the previous $Deltagamma$ observable. The simulation results are consistent with our analytical calculations. $textbf{Conclusions:}$ Our studies demonstrate that the $r_{text{BB}}(varphi_{text{BB}})$ observable is sensitive to the CME signal and rather insensitive to the resonance backgrounds.
We show that the quasielastic (QE) response calculated with the SuSAv2 (superscaling approach) model, that relies on the scaling phenomenon observed in the analysis of (e,e) data and on the relativistic mean-field theory, is very similar to that from a relativistic distorted wave impulse approximation model when only the real part of the optical potentials is employed. The coincidence between the results from these two completely independent approaches, which satisfactorily agree with the inclusive data, reinforces the reliability of the quasielastic predictions stemming from both models and sets constraints for the QE response. We also study the low energy and momentum transfer region of the inclusive response by confronting the results of the relativistic mean-field model with those of the Hartree-Fock continuum random-phase approximation model, which accounts for nuclear long-range correlations. Finally, we present a comparison of our results with the recent JLab (e,e) data for argon, titanium and carbon, finding good agreement with the three data sets.
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