Disappearance of Transverse Flow in Central Collisions for Heavier Nuclei

For the first time, mass dependence of balance energy only for heavier systems has been studied. Our results are in excellent agreement with the data which allow us to predict the balance energy of U+U, for the first time, around 37-39 MeV/nucleon. Also our results indicate a hard equation of state along with nucleon-nucleon cross-section around 40 mb.Comment: 4 pages, 3 figures, submitted to Phys. Rev. Let

On the sensitivity of the energy of vanishing flow towards mass asymmetry of colliding nuclei

We demonstrate the role of the mass asymmetry in the energy of vanishing flow by studying asymmetric reactions throughout the periodic table and over entire colliding geometry. Our results, which are almost independent of the system size and as well as of the colliding geometries indicate a sizable effect of the asymmetry of the reaction on the energy of vanishing flow

Particle-particle correlations and the space-time structure of heavy ion collisions

The present status of the use of two-particle intensity interferometry as a diagnostic tool to study the space-time dynamics of intermediate energy heavy ion collisions is examined. Calculations for the two-proton and two-pion correlation functions are presented and compared to experiment. The calculations are based on the nuclear Boltzmann-Uehling-Uhlenbeck transport theory.Comment: 20 pages, Preprint MSUCL-864 (to be published in Progress in Particle and Nuclear Physics, Vol. 30

Influence of momentum-dependent interactions on balance energy and mass dependence

We aim to study the role of momentum-dependent interactions in transverse flow as well as in its disappearance. For the present study, central collisions involving mass between 24 and 394 are considered. We find that momentum-dependent interactions have different impact in lighter colliding nuclei compared to heavier colliding nuclei. In lighter nuclei, the contribution of mean field towards the flow is smaller compared to heavier nuclei where binary nucleon-nucleon collisions dominate the scene. The inclusion of momentum-dependent interactions also explains the energy of vanishing flow in $^{12}C+^{12}C$ reaction which was not possible with the static equation of state. An excellent agreement of our theoretical attempt is found for balance energy with experimental data throughout the periodic table

Isospin dependence of collective flow in heavy-ion collisions at intermediate energies

Within the framework of an isospin-dependent Boltzmann-Uehling-Uhlenbeck (BUU) model using initial proton and neutron densities calculated from the nonlinear relativistic mean-field (RMF) theory, we compare the strength of transverse collective flow in reactions $^{48}Ca+^{58}Fe$ and $^{48}Cr+^{58}Ni$, which have the same mass number but different neutron/proton ratios. The neutron-rich system ($^{48}Ca+^{58}Fe$) is found to show significantly stronger negative deflection and consequently has a higher balance energy, especially in peripheral collisions. NOTE ADDED IN PROOF: The new phenomenon predicted in this work has just been confirmed by an experiment done by G.D. Westfall et al. using the NSCL/MSU radioactive beam facility and a spartan soccer. A paper by R. Pak et al. is submitted to PRL to report the experimental result.Comment: Latex file, 9 pages, 4 figures availabe upon request; Phys. Rev. Lett. (June 3, 1996) in pres

Neutrons from multiplicity-selected Au-Au collisions at 150, 250, 400, and 650 AMeV

We measured neutron triple-differential cross sections from multiplicity-selected Au-Au collisions at 150, 250, 400, and 650 \AMeV. The reaction plane for each collision was estimated from the summed transverse velocity vector of the charged fragments emitted in the collision. We examined the azimuthal distribution of the triple-differential cross sections as a function of the polar angle and the neutron rapidity. We extracted the average in--plane transverse momentum $\langle P_x\rangle$ and the normalized observable $\langle P_x/P_\perp\rangle$, where $P_\perp$ is the neutron transverse momentum, as a function of the neutron center-of-mass rapidity, and we examined the dependence of these observables on beam energy. These collective flow observables for neutrons, which are consistent with those of protons plus bound nucleons from the Plastic Ball Group, agree with the Boltzmann--Uehling--Uhlenbeck (BUU) calculations with a momentum--dependent interaction. Also, we calculated the polar-angle-integrated maximum azimuthal anisotropy ratio R from the value of $\langle P_x/P_\perp\rangle$.Comment: 20 LaTeX pages. 11 figures to be faxed on request, send email to sender's addres

Elliptic flow studies using the CMS detector

The azimuthal anisotropy of charged particles in heavy ion collisions is an important probe of quark-gluon plasma evolution at early stages. The nuclear reaction plane can be determined independently by different detector subsystems and using different analysis methods. This paper reports the capability of the CMS detector at the LHC to reconstruct the reaction plane of the collision and to me asure elliptic flow with calorimetry and a tracking system. The analysis is based on a full CMS detector simulation of \rm{Pb+Pb} events with the HYDJET event generator

Gamow-Teller strength distributions for nuclei in pre-supernova stellar cores

Electron-capture and $\beta$-decay of nuclei in the core of massive stars play an important role in the stages leading to a type II supernova explosion. Nuclei in the f-p shell are particularly important for these reactions in the post Silicon-burning stage of a presupernova star. In this paper, we characterise the energy distribution of the Gamow-Teller Giant Resonance (GTGR) for mid-fp-shell nuclei in terms of a few shape parameters, using data obtained from high energy, forward scattering (p,n) and (n,p) reactions. The energy of the GTGR centroid $E_{GT}$ is further generalised as function of nuclear properties like mass number, isospin and other shell model properties of the nucleus. Since a large fraction of the GT strength lies in the GTGR region, and the GTGR is accessible for weak transitions taking place at energies relevant to the cores of presupernova and collapsing stars, our results are relevant to the study of important $e^-$-capture and $\beta$-decay rates of arbitrary, neutron-rich, f-p shell nuclei in stellar cores. Using the observed GTGR and Isobaric Analog States (IAS) energy systematics we compare the coupling coefficients in the Bohr-Mottelson two particle interaction Hamiltonian for different regions of the Isotope Table.Comment: Revtex, 28 pages +7 figures (PostScript Figures, uuencoded, filename: Sutfigs.uu). If you have difficulty printing the figures, please contact [email protected]. Accepted for publication in Phys. Rev. C, Nov 01, 199

Nuclear Flow Excitation Function

We consider the dependence of collective flow on the nuclear surface thickness in a Boltzmann--Uehling--Uhlenbeck transport model of heavy ion collisions. Well defined surfaces are introduced by giving test particles a Gaussian density profile of constant width. Zeros of the flow excitation function are as much influenced by the surface thickness as the nuclear equation of state, and the dependence of this effect is understood in terms of a simple potential scattering model. Realistic calculations must also take into account medium effects for the nucleon--nucleon cross section, and impact parameter averaging. We find that balance energy scales with the mass number as $A^{-y}$, where $y$ has a numerical value between 0.35 and 0.5, depending on the assumptions about the in-medium nucleon-nucleon cross section.Comment: 11 pages (LaTeX), 7 figures (not included), MSUCL-884, WSU-NP-93-

Near-threshold production of the multi-strange Ξ−\Xi^- hyperon

The yield for the multi-strange $\Xi^{-}$ hyperon has been measured in 6 AGeV Au+Au collisions via reconstruction of its decay products $\pi^{-}$ and $\Lambda$, the latter also being reconstructed from its daughter tracks of $\pi^{-}$ and p. The measurement is rather close to the threshold for $\Xi^{-}$ production and therefore provides an important test of model predictions. The measured yield for $\Xi^{-}$ and $\Lambda$ are compared for several centralities. In central collisions the $\Xi^{-}$ yield is found to be in excellent agreement with statistical and transport model predictions, suggesting that multi-strange hadron production approaches chemical equilibrium in high baryon density nuclear matter.Comment: Submitted to PR