International Journal of Modern Physics E

The Compressed Baryonic Matter (CBM) experiment will investigate high-energy heavy-ion collisions at the international Facility for Antiproton and Ion Research (FAIR), which is under construction in Darmstadt, Germany. The CBM research program is focused on the exploration of QCD matter at neutron star core densities, such as study of the equation-of-state and the search for phase transitions. Key experimental observables include (multi-) strange (anti-) particles, electron-positron pairs and dimuons, particle correlations and fluctuations, and hyper-nuclei. In order to measure these diagnostic probes multi-differentially with unprecedented precision, the CBM detector and data acquisition systems are designed to run at reaction rates up to 10 MHz. This requires the development of fast and radiation hard detectors and readout electronics for track reconstruction, electron and muon identification, time-of-flight (TOF) determination and event characterization. The data are read-out by ultra-fast, radiation-tolerant, and free-streaming front-end electronics, and then transferred via radiation-hard data aggregation units and high-speed optical connections to a high-performance computing center. A fast and highly parallelized software will perform online track reconstruction, particle identification and event analysis. The components of the CBM experimental setup will be discussed and results of physics performance studies will be presented.

The mission of the Compressed Baryonic Matter (CBM) experiment at the future Facility for Antiproton and Ion Research (FAIR) in Darmstadt is to explore the QCD phase diagram at high net baryon densities likely to exist in the core of neutron stars. The CBM detector system is designed to perform multi-differential measurements of hadrons and leptons in central gold-gold collisions at beam energies between 2 and 11 A GeV with unprecedented precision and statistics. In order to reduce the systematic errors of the lepton measurements, which generally suffer from a large combinatorial background, both electrons and muons will be measured with the same acceptance. Up to now, no di-muon measurements have been performed in heavy-ion collisions at beam energies below 158 A GeV. The main device for electron identification, a Ring Imaging Cherenkov (RICH) detector, can be replaced by a setup comprising hadron absorbers and tracking detectors for muon measurements. In order to obtain a complete picture of the reaction, it is important to measure simultaneously leptons and hadrons. This requirement is fulfilled for the RICH, which has a low material budget, and only little affects the trajectories of hadrons on their way to the Time-of-Flight (TOF) detector. In contrast, the simultaneous measurement of muons and hadrons within the same experimental acceptance poses a substantial challenge. This article reviews the simulated performance of the CBM experiment for muon identification, together with the possibility of simultaneous hadron measurements.

As high-intensity beams are required for various applications, high-power, high-current, continuous-wave (CW) radio-frequency quadrupole (RFQ) accelerators have become a research focus in recent years and also a direction for development in the future. To master and accumulate the advanced technology in design, fabrication and operation of high-current CW RFQs, the RFQ group at Peking University has built a window-type CW RFQ, operating at 162.5MHz, to accelerate a 50-mA deuteron beam from 50keV to 1MeV. It is the first relatively high-frequency window-type CW RFQ in the world. A ${\text{H}}_2^{+}$ ion beam extracted from an electron cyclotron resonance (ECR) ion source was used for the beam commissioning because deuteron beam acceleration will produce a serious radiation risk. We compared and analyzed the measurement results obtained during the beam commissioning with simulations. The data show good consistency in many respects. For the discrepancies, we explain the issues in detail. We achieved stable and robust acceleration of about 1.5mA CW ${\text{H}}_2^{+}$ for 1h. Finally, we discuss the differences between ${\text{H}}_2^{+}$ ion beam acceleration and deuteron beam acceleration.

Empirical formulas in determining the cross-sections play an important role at the energies of which there are no experimental data scattered about. The purpose of the present communication is to further improve the formulas of the cross-section of $(n,2n)$ reactions at the energies near 14.6MeV. A systematics for the evaluation of these cross-sections is studied. We present the empirical formulas based on the statistical theory of nuclear reactions in connection with the compound nucleus. The new empirical formulas are found by using the experimental cross-sections as a function of the reaction $Q$-value. Thus, the new formulas provide the best description of the existing measured data compared with systematics suggested earlier by other authors.

We study the hadronic yields produced in two small collision systems $d-\mathrm{\text{Au}}$ at $\sqrt{s_{NN}}=0.2$TeV and $p-\mathrm{\text{Pb}}$ at $\sqrt{s_{NN}}=5.02$TeV, and extracted the chemical freeze-out (CFO) parameters. The CFO parameters are obtained using a hadron resonance gas (HRG) model and in this study present the system size dependence of the parameters. We observe that with the strangeness suppression factor ${\gamma }_S$ included in the model, a single freeze-out scenario can describe hadronic yields for all the centralities of $d-\mathrm{\text{Au}}$ collision at $\sqrt{s_{NN}}=0.2$TeV, indicating that the strange hadrons have not reached full equilibrium. On the other hand, for small average charged particle multiplicity ($〈d{N}_{ch}/d\eta 〉$) bins of $p-\mathrm{\text{Pb}}$ collision at $\sqrt{s_{NN}}=5.02$TeV strangeness is not fully equilibrated whereas strangeness equilibration seems to be reached in large $〈d{N}_{ch}/d\eta 〉$. For both the collision systems, no significant system volume dependence of the temperature has been observed. However, in comparable $〈d{N}_{ch}/d\eta 〉$ values, temperatures are 10–20MeV larger for $d-\mathrm{\text{Au}}$ collision compared to $p-\mathrm{\text{Pb}}$ collision. We observe that the volume of the system at the CFO increases with increase of charge multiplicity for both the collisions. The increase is much steeper in $p-\mathrm{\text{Pb}}$ collision at $\sqrt{s_{NN}}=5.02$TeV than $d-\mathrm{\text{Au}}$ collision at $\sqrt{s_{NN}}=0.2$TeV. Further, we analyze the transverse momentum ($p_T$) spectra of different hadrons produced in $d-\mathrm{\text{Au}}$ collision at $\sqrt{s_{NN}}=0.2$TeV in a combined freeze-out scenario. We show the $〈d{N}_{ch}/d\eta 〉$ dependence of freeze-out parameters. It is observed that with ${\gamma }_S$ included in the model, a single freeze-out scheme can describe the $p_T$ spectra. For similar $〈d{N}_{ch}/d\eta 〉$ values, ${\gamma }_S$ in both the collision systems are close to each other and overall values of ${\gamma }_S$ increase with increase of $〈d{N}_{ch}/d\eta 〉$. Unlike CFO scenario using the produced hadron yields only, freeze-out temperature in combined scenario of chemical and kinetic freeze-out, obtained from $p_T$ spectra, increases with increase of $〈d{N}_{ch}/d\eta 〉$. For smaller $〈d{N}_{ch}/d\eta 〉$ values, the temperature in $d-\mathrm{\text{Au}}$ collision at $\sqrt{s_{NN}}=0.2$TeV is similar to that of $p-\mathrm{\text{Pb}}$ collision at $\sqrt{s_{NN}}=5.02$TeV. However, temperatures are larger in $d-\mathrm{\text{Au}}$ collision than $p-\mathrm{\text{Pb}}$ collision at larger $〈d{N}_{ch}/d\eta 〉$ values.

A stochastic approach based on four-dimensional (4D) dynamical model has been used to simulate the fission process of the excited compound nuclei ${}^{213}$Fr, ${}^{215}$Fr and ${}^{217}$Fr produced in fusion reactions. Effects of isospin and dissipation coefficient of the $K$ coordinate, ${\gamma }_k$, on estimation of the evaporation residue (ER) cross-section, the prescission neutron multiplicity, the variance of the mass and energy distributions of fission fragments and the anisotropy of fission fragments angular distribution have been investigated for the excited compound nuclei ${}^{213}$Fr, ${}^{215}$Fr and ${}^{217}$Fr. Three collective shape coordinates $(c,h,\alpha )$ plus the projection of total spin of the compound nucleus to the symmetry axis, $K$, were considered in the 4D dynamical model. In the 4D dynamical model, the magnitude of the dissipation coefficient of $K$, ${\gamma }_k$, was considered as a free parameter and its magnitude inferred by fitting measured data on the ER cross-section. Results of the extracted dissipation coefficients of $K$ for different isotopes of Fr were shown that the magnitude of the dissipation coefficient of $K$ increases with decreasing isospin of fissioning compound nucleus. It was also shown that the prescission neutron multiplicity and the anisotropy of fission fragments angular distribution increase with increasing isospin whereas the variance of the mass and energy distributions of fission fragments decrease with increasing isospin of fissioning compound nucleus. Furthermore, it was shown that the calculated values of prescission neutron multiplicity and the variance of the mass distribution of fission fragments for the excited compound nuclei ${}^{213}$Fr, ${}^{215}$Fr and ${}^{217}$Fr decrease with the dissipation strength of $K$, whereas the variance of the energy distribution of fission fragments and the anisotropy of fission fragments angular distribution increase with the dissipation strength of $K$.

The half-life of a parent nucleus of Astatine isotopes $191\le =A\le =219$ decaying via alpha emission is investigated by employing Coulomb and proximity potential model (CPPM) using the WKB barrier penetration probability and other different analytical and semiempirical formulae of Royer, AKRE, Akrawy, RoyerB, MRoyerB, MRenB, SemFIS, VS and SLB. In the calculation of Alpha decay (AD) half-life the available experimental and theoretical $Q$-values with the total alpha kinetic energy have been considered. The behavior of hindrance factor with the variation of mass numbers of parent nuclei for isotopes in the range $191\le =A\le =219$ and the effect of magic number at closed shells were investigated. Through the comparison of obtained results from the systematics with the experimental data, the prediction of SemFIS formula was the best among the studied ones where it shows the minimum standard deviation of 0.829881.

The energy dependence of the effective temperatures of charged kaons, $\varphi$ and $\mathrm{\Omega }$ produced in Au$+$Au collisions at the Relativistic Heavy Ion Collider (RHIC) Beam Energy Scan (BES) energies are presented. At energies around $\sqrt{s_{NN}}\sim 8$GeV, there is a sudden change in the energy dependence of $K^{\pm }$ and $\varphi$ effective temperatures, while at higher energies a slower, continuous rise up to $\sqrt{s_{NN}}=2.76$TeV is observed. This behavior is similar with previous SPS results and could indicate the onset of deconfinement in this energy range. The $\mathrm{\Omega }$ effective temperatures increase with energy and no plateau-like behavior is evidenced by the data.