Hypertriton and light nuclei production at Λ-production subthreshold energy in heavy-ion collisions

High-energy heavy-ion collisions produce abundant hyperons and nucleons. A dynamical coalescence model coupled with the ART model is employed to study the production probabilities of light clusters, deuteron (d), triton (t), helion (³He), and hypertriton (_Λ³H) at subthreshold energy of Λ production (≈ 1 GeV per nucleon). We study the dependence on the reaction system size of the coalescence penalty factor per additional nucleon and entropy per nucleon. The Strangeness Population Factor (S₃ / (³He × (Λ/p))) shows an extra suppression of hypertriton comparing to light clusters of the same mass number. This model predicts a hypertriton production cross-section of a few μb in ³⁶Ar+³⁶Ar, ⁴⁰Ca+⁴⁰Ca and ⁵⁶Ni+⁵⁶Ni in 1 A GeV reactions. The production rate is as high as a few hypertritons per million collisions, which shows that the fixed-target heavy-ion collisions at CSR (Lanzhou/China) at Λ subthreshold energy are suitable for breaking new ground in hypernuclear physics.     

Isospin Effects of Threshold Energy of Radial Flow in Heavy Ion Collisions

The threshold energies of radial flow in reactions of ^40 Ca-^40Ca and ^48Ca＋ ^48Ca in central collisions are investigated within an isospin dependent quantum molecular dynamics model by using three different forms of symmetry energy. It is found that the neutron-rich system has smaller threshold energy of radial flow and this quantity depends on the form of symmetry potential. It is indicated that the threshold energy of radial flow can provide a new method to determine the symmetry energy of asymmetric nuclear matter.     

Radial Expansion Flow in Reactions of 40Ca+58Fe and 40Ca+58Ni

By means of using an isospin-dependent Boltzmann-Langevin equation which includes isospin-dependent symmetry energy, Coulomb energy, isospin-dependent nucleon-nucleon cross sections, Pauli blocking, and initialization, the radial expansion flow of reaction systems ⁴⁰Ca+⁵⁸Ni and ⁴⁰Ca+⁵⁸Fe at 53, 100, 150, and 200 MeV/u in the central collisions were studied. It has shown that the more neutron rich system exhibits smaller radial expansion flow. It was found that the neutron rich system had smaller threshold energy which may provide a new method to determine the isospin dependent nuclear equation of state from calculated result and linear fitting result.     

Impact parameter dependence of the scaling of anisotropic flowsin intermediate energy heavy-ion collisions

The scaling behaviors of anisotropic flows of light charged particles are studied for 25 MeV/u ⁴⁰Ca+⁴⁰Ca collisions at different impact parameters by the isospin-dependent quantum molecular dynamics model. The nucleon-number scaling of elliptic flow exists and the scaling of the ratios of v₄/v₂² and v₃/(v₁v₂) is applicable to collisions at almost all impact parameters except for peripheral collisions.     

Nuclear Matter Density,Collision Number and Entropy in Dynamics Process of Intermediate High Energy Heavy Ion Collision

The nuclear matter density,collision number and entropy in the dynamic process of heavy ion collision ⁴⁰Ca+⁴⁰Ca at E_L=400MeV/A for very central collision were calculated.The results show that the nuclear spatial density distributions depend mainly on the mean field but rarely on the nucleonnucleon collisions.The density distribution in the momentum space,collision number and entropy are influenced by the mean field and nucleon-nucleon collision,especially the medium effects.     

Target Residues from the Interaction of Copper with 40MeV/u 40Ar Ions

Cross Sections and average forward recoil range FW were measured for target residues from the interaction of Cu with 40MeV/u ⁴⁰Ar ions using off-line y-ray spectroscopy.The mass yield distribution was obtained with assumption of charge distribution.The linear momentum transfer was calculated from FW values.A comparison with similar results of ¹²C+Cu and ²⁰Ne+Cu reactions indicates that the fractional linear momentum transfer,corresponding to central collisions,decreases with increasing projectile mass at the same energy per nucleon. However,the excitation energy of the composite system created from the collisions of Cu with ⁴⁰Ar ions reached the value of 5.3MeV /u and was higher than those from the collisions with ¹²C and ²⁰Ne ions.     

A Monte Carlo Study of the Fractal Property inside Jets Produced in High Energy e+e－ Collisions

The anomalous scaling property inside jets produced in e⁺e^－ Collisions at s91.2GeV is studied using Monte Carlo method. A new variable r is applied, which has very good anomalous scaling property. The relation between the scaling indices of different orders is investigated. The Lévy index for the hadronic system inside jets is obtained, which turns out to be μ=2.498±0.025, very close to the same index of hadron-hadron collisions. On the contrary, the Lévy index of e⁺e^－ collisions is 1.701±0.043, being less than 2. Since the multi-hadron production in e⁺e^－ collisions is dominated by hard gluon emission or hard parton branching, while the parton fragmentation into jet, like the multi-production in hadron-hadron collisions, is a soft process, the above results suggest that the value of Lévy index may provide another signal for the qualitative difference between hard and soft processes.     

Dynamic Model Study of Fusion Reactions for 40,48Ca+90,96Zr

Based on the Improved Quantum Molecular Dynamics Model the fusion reactions of ^40,48Ca+^90,96Zr are studied by making a more rigorous treatment of the initial condition. The study shows that:(1) the calculated fusion cross sections for all four reactions of ^40,48Ca+^90,96Zr are in good agreement with experiment data; (2) the sub-barrier fusion for the neutron-rich reaction ⁴⁰Ca+⁹⁶Zr is ubstantially enhanced as compared with the other three reactions. In order to understand the reason why the sub-barrier fusion of the neutron-rich reaction ⁴⁰Ca+⁹⁶Zr is enhanced as compared with the non-neutron-rich reaction ⁴⁰Ca+⁹⁶Zr and that of the neutron-rich reaction ⁴⁸Ca+⁹⁶Zr is not enhanced, the further investigations are carried out, those are: the dynamic fusion barriers for four reactions, the relation between dynamic fusion barrier and nucleon transfer and the relation between nucleon transfer and corresponding reaction Q value. It has been found that positive Q value leads to the strong nucleon transfer which reduces the dynamic fusion barrier and enhances the sub-barrier fusion cross section.     

An Investigation of Relativistic Microscopic Optical Potential in Terms of Relativistic Brueckner-Bethe-Goldstone Equation

Relativistic microscopic optical potential of nucleon-nucleus is derived from the relativistic Brueckner-Bethe-Goldstone (RBBG) equation.The complex effective mass of a nucleon is determined by a fit to 200MeV p-⁴⁰Ca scattering data.The relativistic microscopic optical potentials with this effective mass are obtained from RBBG for p-¹⁶O,⁴⁰Ca,⁹⁰Zr and ²⁰⁸Pb scattering in energy range from 160 to 180MeV.The microscopic optical potential is used to study the proton-⁴⁰Ca scattering problem at 200MeV.The results,such as defferential cross section,analyzing power and spin rotation function are compared with those calculated from phenomenological relativistic optical potential.     

A DYNAMICAL METHOD IN DEEP IN ELASTIC COLLISION OF HEAVY IONS

A method correlating the dynamical equations with the diffusion equations is developed in this paper to explain the dissipations and fluctuations of heavy ion collisions. Considering the degrees of freedom about the relative motion, rotation and asymmetric mass, the relation between the frictional and diffusion tensors is obtained.
Some imformations of deep inelastic collisions in three reaction systems are obtained by solving coupling equations numerically. The calculated results show that there are orbiting effects in the reaction systems of ⁸⁶Kr(8.18MeV/A)+¹⁶⁶Er and ⁸⁴Kr(8.5MeV/A)+¹⁶⁵Ho and there is strong focusing effect in the reaction system of ¹³⁶Xe(8.31MeV/A)+²⁰⁹Bi. But the calculated results are in agreement with the experimental data only for larger partial waves. The nuclear force and diffusion coefficients must be studied further.     

＂Neck＂ formation and Fragmentation in Intermediate Energy Heavy-Lon Collisions

Under different impact parameters, the collision system of 30MeV/u ⁴⁰Ca+⁴⁰Ca is investigated in terms of QltllD model. It is .shown that the number of IMFs is the largest at impact pararneter b=6fm, which is due to the formation of ＂neck＂ in collision process. Meanwhile, it is found the. in the process of fonmadon of ＂neck＂, the growth of the relative density fluctuation of the reaction system is very slow and the saturation value is small, which imply the character of shape instability.     

Quantum Degenerate Fermi--Bose Mixtures of 40K and 87Rb Atoms in a Quadrupole-Ioffe Configuration Trap

We report on the attainment of quantum degeneracy of 40^K by means of efficient thermal collisions with the evaporatively cooled 87^Rb atoms. In a quadrupole-Ioffe configuration trap, potassium atoms axe cooled to 0.5 times the Fermi temperature. We obtain up to 7.59 × 10^5 degenerate fermions 40^K.     

ELASTIC SCATTERING OF K± MESONS BY 40—48Ca AND THE ANALYSIS OF NEUTRON DISTRIBUTIONS

The differential cross sections of the elastic scattering of K^±on ^40—48Ca are calculated in the framework of eikonal approximation. The theoretical values obtained by using different parameters are compared. Through adjusting the parameters of the neutron distribution, the improvement of the coincidence between the theoretical values and the experimental data is arrived. The result shows that the r.m.s radius of the neutron distribution of ⁴⁰Ca is smaller than that of the proton. (about 0.15fm smaller) and the surface thickness of the neutron distribution of ⁴⁰Ca is thinner than that of proton. This is consistent with the results of computation made by H.F. method and agrees with the analysis of elastic scaatering of protons in the mediate energy on ⁴⁰Ca by other authors.     

HEAVY ION COLLISION DYNAMICS IN FERMI DOMAIN (I) DYNAMICS DEPENDENCE OF ENERGY

In the case of central collisions,the collision mechanism of complete,incomplete fusion,and fragmentation were systematically studied via the Boltzmann-Uehling-Uhlenbeck theory which included the nuclear mean field dynamics,two-body collisions,and Pauli blocking between 5 and 150MeV/u for ²⁰Ne+²⁰Ne collision system.How the mean field,Pauli blocking of the two-body collisions were affected by bombarding energy and their effect on the reaction mechanism was discussed.     

THE l-FORBIDDEN M1 TRANSITIONS AND EFFECTIVE g-FACTORS IN 40Ca±1 NUCLEI

The B (M1) value of the l-forbidden M1 transition of ⁴⁰Ca ±1 nuclei were calculatedwith the effective g-factors in ⁴⁰Ca region. The results give a explanation of strong l-forbidden M1 transitions of ³⁹K, ⁴¹K. A qualitative explanation for the reason of largedifference of B(M1) value of l-forbidden M1 transition between ³⁹K, ⁴¹K and ³⁹Ca, ⁴¹Cais given also.     

Phenomenological Scaling of Rapidity Dependence for Anisotropic Flows in 25 MeV/nucleon Ca＋Ca by Quantum Molecular Dynamics Model

Anisotropic flows （v1, v2, v3 and v4） of light fragments up to the mass number 4 as a function of rapidity are studied for 25 MeV/nucleon ^40Ca ＋ ^40Ca at large impact parameters by a quantum molecular dynamics model. A phenomenological scaling behaviour of rapidity dependent flow parameters vn （n = 1, 2, 3 and 4） is found as a function of mass number plus a constant term, which may arise from the interplay of collective and random motions. In addition, v4/v2^2 keeps to be almost independent of rapidity and remains a rough constant of 1/2 for all light fragments.     

Diffractive production of charm in DIS and gluon nuclear shadowing

We evaluate nuclear shadowing of the total cross section of charm particles production in DIS within the framework of Gribov theory of nuclear shadowing generalized to account for the QCD evolution. We use as an input the recent QCD Pomeron parton density analysis of the HERA diffractive data. Assuming that the QCD factorization theorem is applicable to the charm production off nuclei we also calculate shadowing of the gluon densities in nuclei and find it sufficiently large for heavy nuclei: G_A~200(x,Q²)/AG_N(x,Q²) ~ 0.45 m 0.5 · (A/200)^т.15 for x ~ 10^х1ц, Q² ~ 20 1 40 GeV² to influence significantly the physics of heavy ion collisions at LHC. We evaluate also suppression of minijet and hidden charm production in the central AA collisions. We also discuss some properties of the final states for %^*A processes dominated by the scattering off small x gluons like the high p_t jet and charm production.     

Symmetric splitting of very light systems in the coalescence and reseparation model

The coalescence and reseparation model has been used to calculate trajectories of the ¹²C + ⁴⁰Ca, ⁹Be + ⁴⁰Ca and ⁶Li + ⁴⁰Ca collisions which lead to symmetric splitting. A fusion-fission mechanism is suggested by the model. Comparison with experimental data locates the reaction angular momentum window in the region of superdeformed nuclei.     

(EC+β+) Decay of 133Sm and 1.1s Isomer of 133Pr

By irradiation of an enriched target of ⁹⁶Ru with ⁴⁰Ca and using a helium-jet fast tape transport system in combination with X-γ and γ-γ coincidence measurements,the very neutron deficient isotope ¹³³Sm was produced and studied. A simple(EC+β⁺) decay scheme of Sm is proposed for the first time. A by product ¹³³Pr was produced simultaneously because of the ^98－102Ru contents of the ruthenium target. The half-life of an 11/2^－ low-lying isomeric state in ¹³³Pr has been measured to be (1.1±0.2)s. Using single-particle model,the reduced transition probabilities of the 11/2^－ isomers in ^{131,133,135,137}Pr are extracted from their experimental half-lives and compared with the Weisskopf estimate.     

New Nuclide 129Pm Near the Proton Drip Line

The very neutron-deficient nuclide ¹²⁹Pm was produced via the ⁹²Mo(⁴⁰Ca, p2n) reaction and identified for the first time by using the X-γ coincidence in combination with a He-jet tape transport system. From the decay of a 99keV γ ray which corresponds to the 5/2^－→1/2^－ transition in the daughter nucleus ¹²⁹Nd following the (EC+β⁺) decay of ¹²⁹Pm, the half-life of ¹²⁹Pm was determined to be 2.4(6)s.