Simulation studies of the isovector reorientation effect of deuteron scattering on heavy target

TL;DR

The study tackles constraining the density dependence of the nuclear symmetry energy $E_{ m sym}( ho)$ by exploiting the isovector reorientation (IVR) effect in deuteron scattering on heavy targets. It combines a transport-model ($ ext{ImQMD}$) event generator with GEANT4-based detector simulations of the SAMURAI setup to forecast how the IVR-induced angular correlations in deuteron breakup reflect the isovector potential $U_{ m sym}( ho,k)$, parameterized by the stiffness exponent $ extgamma$ in $E_{ m sym}( ho)=rac{C_{ m s,k}}{2}( ho/ ho_0)^{2/3}+rac{C_{ m s,p}}{2}( ho/ ho_0)^{ extgamma}$. The results show that the observable $R=rac{N(P_x^{ m p}>P_x^{ m n})}{N(P_x^{ m p}<P_x^{ m n})}$ is highly sensitive to $ extgamma$, with stronger effects in neutron-rich targets like $^{124}$Sn and clearer signals for $p_{zz}$ (z'-polarization) than for $p_{yy}$. The simulations demonstrate feasible extraction of IVR signals at SAMURAI with realistic beam intensities and polarization levels, offering a robust path to tighten constraints on $E_{ m sym}( ho)$ at sub-saturation densities and decouple isovector information from isoscalar contributions.

Abstract

The isovector reorientation (IVR) effect of deuteron scattering on heavy target provides a novel means to probe the nuclear isovector potential, which gives rise to the nuclear symmetry energy. The simulation studies on the experimental measurement of IVR effect using the SAMURAI terminal at RIKEN Nishina center have been performed to demonstrate the feasibility of the experiment. By introducing a well-designed polarimeter to detect the $\mathrm{p}(\vec{\mathrm{d}}, \mathrm{d})\mathrm{p}$ elastic scattering, monitoring of the tensor polarization of the deuteron beam can be implemented. The protons and neutrons produced by the breakup of polarized deuterons scattering off heavy targets are designed to be measured by proton drift chamber (PDC) combined with the SAMURAI magnet and NEBULA detector, respectively. The detector responses are simulated using Geant4 framework, where the events of the deuteron elastic breakup are generated by an Improved Quantum Molecular Dynamics model. The results of reconstructing the deuteron breakup events demonstrate the feasibility of detecting the IVR effect at SAMURAI with both longitudinal and transverse tensor polarized deuteron beams with a polarization degree of approximately 80\%.

Figures (13)

• Figure 1: The schematic view of the isovector reorientation effect of a polarized deuteron scattering on a $^{124}$Sn target, followed by the elastic breakup. The inset presents the momentum vectors to be used in the following analysis.
• Figure 2: The bird's-eye view of the experiment. The AVF (Azimuthally Varying Field Ring Cyclotron), RRC (Riken Ring Cyclotron) and SRC (Superconducting Ring Cyclotron) are used to produce, accelerate and transport the polarized deuteron beam to 190 MeV/u. Beam trigger (SBT) is to provide the ount number of beam and determine start timing to calculate the time of flight(TOF). The Polarimeter monitors the tensor polarization of the deuteron beam before it reaches the target. The target is positioned at the entrance of the SAMURAI spectrometer, which is a large-acceptance superconducting dipole magnet for momentum analysis of charged particles. The PDC (Proton Drift Chamber) detects breakup protons downstream of the target, while NEBULA is used to detect neutrons.The VD (veto detector) is to veto the central collision based on the multiplicity.
• Figure 3: Reference frame. The red axes represent the projectile helicity frame, with the $xoz$ plane defined as the reaction plane.
• Figure 4: The relationship between the analyzing power and the center-of-mass scattering angle $\theta_{\mathrm{c.m.}}$, data taken from SekiguchiK.
• Figure 5: The correlation between the (a) energy and (b) scattering angle of the deuteron and the recoil proton. The location and the angular coverage of the detectors are represented by the colored squares.