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 gamma production from the 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 gamma rays in 124Sn + 124Sn reactions at 25 MeV/nucleon 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 gamma spectrum with isospin-dependent Boltzmann-Uehling-Uhlenbeck simulations, the high momentum tail (HMT) fraction of RHMT = (20 +/- 3)% is derived in 124Sn nuclei. This work provides a detailed and validated experimental framework for extracting SRC information from bremsstrahlung gamma-ray emission and demonstrates the feasibility of studying nucleon SRCs with high precision in low-energy heavy-ion collisions.

The Čerenkov detector has a distinct advantage in constructing the reaction vertex and incident direction of energetic particles, thereby enabling the identification of emission sources. A novel approach is proposed to measure neutrino sources by employing a modular photomultiplier tube (PMT) array, utilizing clean and transparent deep seawater as the sensitive medium. The feasibility of detecting solar neutrinos was demonstrated through extensive simulations using the Geant4 package. These simulations incorporate the production and transport of Čerenkov photons generated by electron scattering, with the Hough transform method applied to enhance the accuracy of the vertex and direction reconstruction, particularly in the presence of noisy or incomplete data. The dominant background from γ -radiation due to ^40K in seawater can be suppressed by a factor of 10^7 by introducing a threshold on the number of triggered PMTs. The total reconstruction efficiency increases with the incident energy, achieving 25

Femtoscopic interferometry is a powerful tool for probing the spatio-temporal evolution of emission sources in heavy-ion collisions. A major challenge in the field is formulating a self-consistent description of the source function, final-state interactions between the particle pair, and interactions inherent to the source itself. To address this, we have developed a novel Monte Carlo model for calculating two-particle correlation functions in a classic framework. The model incorporates self-consistently the emission source of thermal equilibrium and three-body final state interactions. Application of the model shows satisfactory fit to experimental data, revealing that the correlation function is highly sensitive to the source's spatio-temporal extent. In contrast, the temperature parameter governing the emitted particles' energy spectra has a negligible influence. Our approach offers the potential to extract the spatio-temporal information from the emission source, thereby advancing the applicability of femtoscopic interferometry in the Fermi energy domain.

Abstract This study reports on the design, simulation, construction, and testing of a full-size prototype of the multi-wire drift chamber for the CSR external-target experiment. The multi-wire drift chamber array incorporates drift cells of three different sizes: 8 $$\times $$ × 8 mm $$^{\textrm{2}}$$ 2 , 10 $$\times $$ × 10 mm $$^{\textrm{2}}$$ 2 , and 15 $$\times $$ × 15 mm $$^{\textrm{2}}$$ 2 . Simulation studies were carried out to compare their electron drift time spectra, R-T relations, and position resolution. The prototype was constructed based on the design of the multi-wire drift chamber closest to the target. Since the beam passes through the center region of the multi-wire drift chamber, the prototype features a special beam avoidance design. The design ensures that the detector is sensitive to reaction products while remaining unresponsive to heavy ion beams. The size of the prototype is 930 $$\times $$ × 1660 mm $$^{\textrm{2}}$$ 2 , comprising 960 drift cells. Testing was conducted with dedicated electronics. An energy resolution of 22% was achieved for the $$^{\textrm{55}}$$ 55 Fe source; the track residuals were approximately 300 $$\upmu $$ μ m for the cosmic rays; the detection efficiency of each layer exceeds 96% for the cosmic rays.

Heavy-ion collisions(HICs)is a unique experimental tool for investigating the properties of nuclear matter under extreme conditions in the laboratory.At HIRFL-CSR energies,HICs can create nuclear matter with 2-3 times the saturation density(ρ0).The HIRFL-CSR external-target experiment(CEE)is a large-acceptance spectrometer designed to explore frontier top-ics in high-energy nuclear physics,such as the QCD phase structure and nuclear matter equation of states.In this letter,we introduce simulation and analysis software for the CEE experiment(CeeROOT).Based on the CEE conceptual design and CeeROOT software,the configurations of its subdetectors were optimized by considering foreseeable physical constraints.The final detector layout of the CEE spectrometer and its acceptances were validated through simulations of U+U collisions at 500 MeV/u and pp collisions at 2.8 GeV,which demonstrated that the CEE experiment will serve as a detector with wide acceptance and multi-particle identification capabilities for studying high-energy nuclear physics topics at HIRFL-CSR energies with pp,pA,and AA collisions.

The Richardson-Lucy algorithm is applied to reconstruct the three-dimensional source function of identical pions from their two-particle correlation functions. The algorithm's performance is first evaluated through simulations with Gaussian-type initial source functions. Its imaging quality and robustness are further demonstrated with experimental data from Au+Au collisions at 1.23 A GeV, collected by the HADES Collaboration. Additionally, using UrQMD simulations of Pb+Pb collisions at 1.5 A GeV, we show that the deblurred source functions exhibit sensitivity to the initial neutron skin thickness of the colliding nuclei. This highlights the potential of the Richardson-Lucy algorithm as a tool for probing the neutron density distribution in heavy nuclei.

We have developed a systematic approach to calculate the correlation function for spin-1/2 particles, incorporating both central and noncentral components of the interparticle interaction. This is achieved by extending the variable phase method to accommodate noncentral potentials and numerically solving the Schrödinger equation. Within this framework, the partial-wave contributions to the nucleon-nucleon correlation functions adopting the Reid soft-core potential are evaluated. The resulting correlation functions are then compared for Gaussian sources of different sizes.

New liquid drop model with the isospin-square dependence of the volume and surface energy terms is applied to reproduce experimentally known masses of nuclei with number of protons and neutrons larger or equal to twenty. The ground-state microscopic energy corrections are taken into account. In spite of the fact that the model contains only six adjustable parameters, the quality of mass reproduction is good, and it is comparable with other contemporary mass models. Also, the fission barrier heights of actinide nuclei evaluated using the topographical theorem of Myers and Swiatecki are close to the data.

The neutron-neutron (nn) correlation function has been measured in 25  MeV/u ^{124}Sn+^{124}Sn reactions. Using the Lednický-Lyuboshitz approach, the nn scattering length and effective range (f_{0}^{nn}, d_{0}^{nn}), as well as the reduced space-time size R^{(0)} of the neutron emission source are simultaneously extracted as (18.9_{-1.2}^{+1.3}  fm, 1.9_{-1.0}^{+1.3}  fm) and 4.12±0.12  fm, respectively. The measured nn scattering length is consistent with the results obtained in the low-energy scattering ^{2}H(π^{-},γ)2n, indicating heavy-ion collisions can serve as an effective approach for measuring nn interactions and further investigating the charge symmetry breaking of nuclear force. The space-time size extracted from momentum-gated correlation functions exhibits clear dependence on the pair momentum, with R^{(0)}=2.8±0.1  fm and 4.9±0.2  fm being determined for the high and low momentum neutrons, respectively.

By combining femtoscopic interferometry with an optical deblurring algorithm, we present a novel method to image the source in heavy-ion collisions (HICs), while simultaneously determining the interaction strength between particle pairs. The spatial distribution of the emission source has been reconstructed for protons (p) and antiprotons ( p ) from the respective pp and pp correlation functions in Au+Au collisions at SNN=200 GeV. Within experimental uncertainties, protons and antiprotons share the same freeze-out distribution showing higher density in the center compared to the widely assumed Gaussian shape. The results evidence the matter-antimatter symmetry in coordinate space at the freeze-out moment before the nucleons are fully randomized in the collisions.

Electron–positron colliders operating in the GeV center-of-mass range, or tau-charm energy region, have been proved to enable competitive frontier research due to several unique features. With the progress of high-energy physics in the last two decades, a new-generation Tau-Charm factory, called the Super Tau-Charm Facility (STCF), has been actively promoted by the particle physics community in China. STCF has the potential to address fundamental questions such as the essence of color confinement and the matter–antimatter asymmetry within the next decades. The main design goals of the STCF are a center-of-mass energy ranging from 2 to 7 GeV and a luminosity surpassing 5 × 1034 cm−2 s−1 that is optimized at a center-of-mass energy of 4 GeV, which is approximately 50 times that of the currently operating Tau-Charm factory—BEPCII. The STCF accelerator has two main parts: a double-ring collider with a crab-waist collision scheme and an injector that provides top-up injections for both electron and positron beams. As a typical third-generation electron–positron circular collider, the STCF accelerator faces many challenges in both accelerator physics and technology. In this paper, the conceptual design of the STCF accelerator complex is presented, including the ongoing efforts and plans for technological research and development, as well as the required infrastructure. The STCF project aims to secure support from the Chinese central government for its construction during the 15th Five-Year Plan (2026–2030).

A half-size prototype of the multi wire drift chamber for the cooling storage ring external-target experiment (CEE) was assembled and tested in the 350 MeV/u Kr + Fe reactions at the heavy-ion research facility in Lanzhou. The prototype consists of six sense layers, where the sense wires are stretched in three directions X, U, and V; meeting 0^∘ , 30^∘ , and -30^∘ , respectively, with respect to the vertical axis. The sensitive area of the prototype is 76 cm× 76 cm . The amplified and shaped signals from the anode wires were digitized in a serial capacity array. When operating at a high voltage of 1500 V on the anode wires, the efficiency for each layer is greater than 95 301 ± 2 μm . This performance satisfies the requirements of CEE.

The emission of neutrons from heavy ion reactions is an important observable for studying the asymmetric nuclear equation of state and the reaction dynamics. A 20-unit neutron array has been developed and mounted on the compact spectrometer for heavy ion experiments (CSHINE) to measure the neutron spectra, neutron- neutron and neutron-proton correlation functions. Each unit consists of a 15 x 15 x 15 cm3 plastic scintillator coupled to a cent = 52 mm photomultiplier. The Geant4 simulation with optical process is performed to investigate the time resolution and the neutron detection efficiency. The inherent time resolution of 212 ps is obtained by cosmic ray coincidence test. The n-y discrimination and time-of-flight performance are given by 252 Cf radioactive source test and beam test. The neutron energy spectra have been obtained in the angular range 30 degrees <= B lab <= 51 degrees in the beam experiment of 124 Sn + 124 Sn at 25 MeV/u with CSHINE.

The isospin-dependent nuclear equation of state, i.e. symmetry energy E-sym(rho) plays an important role in the study of nuclear physics and astrophysics. In terrestrial lab, heavy-ion reaction provides a unique way to constrain E-sym(rho). So a compact spectrometer for heavy ion experiment (CSHINE) is built and particle correlation functions are measured. The HBT correlation function method is applied as an chronometer to extract the emission timescale and determine the emission order of hydrogen isotopes from the intermediate velocity source formed in 30MeV/u(40)Ar +(197) Au. The proton emission timescale tau(p) approximate to 100 fm/c is extracted by the fit of Koonin-Pratt equation with correlation after burner (CRAB) code. And the dynamic emission order of tau(p) > tau(d)> tau(t) is evidenced via the correlation functions of nonidentical particle pairs, indicating that the neutron rich particles are emitted earlier. Meanwhile, transport model simulations demonstrate that the emission timescale of isospin dependent particles depends on the density slope parameter of the nuclear symmetry energy. And the isospin chronology provides a promising route to study the symmetry energy and isospin relaxation.

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 p(d⃗, d)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 (Neutron-detection system for Breakup of Unstable-Nuclei with Large Acceptance) 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

Silicon (Si) detectors are extensively used for the detection of charged particles in nuclear and particle physics experiments. To achieve position-sensitive charged-particle detection with a relatively low cost, a mosaic- type array based on off-the-shelf Si photodiodes was developed. The high granularity allows the geometric configuration of the array to be modified according to the requirements of specific experiments. In this article, the results of an investigation of the photodiode characteristics using a sources are presented together with the results of an a-decay spectroscopy experiment performed using the constructed array.

In heavy-ion collision experiments, the global collectivity of final-state particles can be quantified by anisotropic flow coefficients (nu(n)). The first-order flow coefficient, also referred to as the directed flow (nu(1)), describes the collective sideward motion of produced particles and nuclear fragments in heavy-ion collisions. It carries information on the very early stage of the collision, especially at large pseudorapidity (eta), where it is believed to be generated during the nuclear passage time. Directed flow therefore probes the onset of bulk collective dynamics during thermalization, providing valuable experimental guidance to models of the pre-equilibrium stage. In 2018, the Event Plane Detector (EPD) was installed in STAR and used for the Beam Energy Scan phase-II (BES-II) data taking. The combination of EPD (2.1 < |eta| < 5.1) and high-statistics BES-II data enables us to extend the nu(1) measurement to the forward and backward eta regions. In this paper, we present the measurement of nu(1) over a wide. range in Au+Au collisions at root s(NN) = 19.6 and 27 GeV using the STAR EPD. The results of the analysis at root s(NN) = 19.6 GeV exhibit excellent consistency with the previous PHOBOS measurement, while elevating the precision of the overall measurement. The increased precision of the measurement also revealed finer structures in heavy-ion collisions, including a potential observation of the first-order event-plane decorrelation. Multiple physics models were compared to the experimental results. Only a transport model and a three-fluid hybrid model can reproduce a sizable nu(1) at large. as was observed experimentally. The model comparison also indicates nu(1) at large. might be sensitive to the QGP phase transition.

The linear response of CsI(Tl) crystals to γ-rays plays a crucial role in their calibration, as any deviation from linearity can introduce systematic errors not negligible in the measurement of γ energy spectra, particularly at high energies. In this study, the responses of CsI(Tl) crystals to high-energy photons up to 20 MeV are investigated using quasi monochromatic γ beam provided by the Shanghai Laser Electron Gamma Source. The spectra are folded using a detector filter implemented by Geant4. Both quadratic and linear fits to six energy points are used to assess the linearity of the CsI(Tl) detector. The results demonstrate that the difference between the linear and non-linear fits is at the level of 4%. Applying these findings to the γ hodoscope of the Compact Spectrometer for Heavy Ion Experiment (CSHINE), the potential systematic uncertainties caused by CsI(Tl) non-linearity are evaluated. This work provides a comprehensive calibration methodology for employing CsI(Tl) crystal to detect high energy γ-rays.

Revealing the neutron density distribution in the nucleus is one of the crucial tasks of nuclear physics. Within the framework of the ultrarelativistic quantum molecular dynamic model followed by a correlation afterburner program, we investigate the effects of the initial neutron density distribution on the charged-pion yield ratio π−/π+, the two-pion momentum correlation function, and the emission source dimension. It is found that the π−/π+ ratio is sensitive to the initial neutron density distribution and the impact parameter, especially for collisions at large impact parameter. However, the charge splitting in the correlation functions between positively π+π+ and negatively π−π−, as well as the source radii and volumes extracted exhibit a stronger dependence on the initial neutron density distribution, but a weaker dependence on the impact parameter. The present study highlights that π+π+ and π−π− correlation functions in heavy-ion collisions could be used to probe the initial neutron density distribution of nuclei.