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Experimental Study of Bremsstrahlung Gamma Ray Emission and Short-Range Correlations in $^{124}$Sn+$^{124}$Sn Collisions at 25 MeV/u

Junhuai Xu, Qinglin Niu, Yuhao Qin, Dawei Si, Yijie Wang, Sheng Xiao, Baiting Tian, Zhi Qin, Haojie Zhang, Boyuan Zhang, Dong Guo, Minxue Fu, Xiaobao Wei, Yibo Hao, Zengxiang Wang, Tianren Zhuo, Chunwang Ma, Yuansheng Yang, Xianglun Wei, Herun Yang, Peng Ma, Limin Duan, Fangfang Duan, Kang Wang, Junbing Ma, Shiwei Xu, Zhen Bai, Guo Yang, Yanyun Yang, Mengke Xu, Kaijie Chen, Zirui Hao, Gongtao Fan, Hongwei Wang, Chang Xu, Zhigang Xiao

Abstract

Short-range correlation (SRC) in nuclei refers to nucleons forming temporally correlated pairs in close proximity, giving rise to the high momentum of the nucleons beyond the Fermi surface. It has been reported that bremsstrahlung $γ$ production from neutron-proton process in heavy-ion reactions provides a potential probe to the SRC abundance in nuclei. In this paper, we present in detail the precision measurement of bremsstrahlung $γ$-rays in $\rm ^{124}Sn$+$\rm ^{124}Sn$ reactions at 25 MeV/u using the Compact Spectrometer for Heavy IoN Experiment (CSHINE). A comprehensive experimental and analysis framework is established to ensure the reliability and robustness of the extracted results. Background contributions are evaluated and subtracted using independent methods, and the consistency of the analysis is systematically validated. By comparing the experimental $γ$ spectrum with the Isospin-dependent Boltzmann-Uehling-Uhlenbeck simulations, the high momentum tail (HMT) fraction of $R_{\rm HMT}=(20 \pm 3)\%$ is derived in $^{124}$Sn nuclei. This work provides a detailed and validated experimental framework for extracting SRC information from bremsstrahlung $γ$-ray emission and demonstrates the feasibility of studying nucleon SRCs with high precision in low-energy heavy-ion collisions.

Experimental Study of Bremsstrahlung Gamma Ray Emission and Short-Range Correlations in $^{124}$Sn+$^{124}$Sn Collisions at 25 MeV/u

Abstract

Short-range correlation (SRC) in nuclei refers to nucleons forming temporally correlated pairs in close proximity, giving rise to the high momentum of the nucleons beyond the Fermi surface. It has been reported that bremsstrahlung production from neutron-proton process in heavy-ion reactions provides a potential probe to the SRC abundance in nuclei. In this paper, we present in detail the precision measurement of bremsstrahlung -rays in + reactions at 25 MeV/u using the Compact Spectrometer for Heavy IoN Experiment (CSHINE). A comprehensive experimental and analysis framework is established to ensure the reliability and robustness of the extracted results. Background contributions are evaluated and subtracted using independent methods, and the consistency of the analysis is systematically validated. By comparing the experimental spectrum with the Isospin-dependent Boltzmann-Uehling-Uhlenbeck simulations, the high momentum tail (HMT) fraction of is derived in Sn nuclei. This work provides a detailed and validated experimental framework for extracting SRC information from bremsstrahlung -ray emission and demonstrates the feasibility of studying nucleon SRCs with high precision in low-energy heavy-ion collisions.

Paper Structure

This paper contains 14 sections, 25 equations, 13 figures, 1 table.

Table of Contents

  1. Introduction
  2. Experimental Setup
  3. IBUU-MDI Model Description
  4. IBUU-MDI Model Overview
  5. Sensitivity to Model Parameters
  6. Experimental $\gamma$-Ray Spectra
  7. Analysis of Systematic Uncertainty
  8. Experimental $\gamma$ spectrum in slow coincidence
  9. Experimental $\gamma$ spectrum in fast coincidence
  10. Reconstruction of the Original $\gamma$ Spectrum
  11. Unfolding Method and Detector Response
  12. Original $\gamma$-Ray Spectrum
  13. Direct Comparison with IBUU-MDI Calculations
  14. Conclusion and Outlook

Figures (13)

  • Figure 1: (Color Online) Experimental setup of CSHINE. The $\gamma$ hodoscope is located at $\theta_{\rm lab}=110^\circ$ to measure the bremsstrahlung $\gamma$-rays from the collisions of the $^{124}$Sn projectile on the $^{124}$Sn target.
  • Figure 3: (a) The double differential photon production calculated by varying impact parameters. The impact parameters are taken to be $b=0\sim5\,\rm{fm}$, $b=0\sim9\,\rm{fm}$ and fixed values $b=0, 5, 9\,\rm{fm}$. The results using $b=0\sim9, 0, 5, 9\,\rm{fm}$ are normalized to the $b=0\sim5\,\rm{fm}$ case. (b) The double differential photon production calculated by varying the choice of nuclear mean-field potentials. We compare the results from the MDI potential with those from the momentum-independent SBKD potential. The results from the SBKD potential are normalized to the MDI results. (c) The double differential photon production calculated by varying symmetry energy parameters. Three different $x$ parameters are employed in the simulations, namely $x=-1$, $x=0$ and $x=1$. The results using $x=0$ and $x=1$ are normalized to the $x=-1$ case.
  • Figure 4: (Color Online) (a) Total energy Spectrum of beam-on (black) in all trigger conditions and beam-off measurement (red). (b) The $\gamma$ energy spectrum after subtracting the background.
  • Figure 5: (Color Online) Comparison of the rebinned experimental $\gamma$ spectrum (black dots) with statistical uncertainties (error bars) and systematic uncertainties (gray shaded areas) in the c.m. frame. Several key theoretical curves with different $R_{\rm HMT}$, processed with the detector filter, are overlaid for comparison.
  • Figure 6: The likelyhood function values of different $R_{\text{HMT}}$ and the corresponding quadratic fitting in the energy range of $35~\rm MeV$ to $100~\rm MeV$.
  • ...and 8 more figures