Spectral ratio: an observable to determine K+K^{+} nucleus potential and K+K^{+} N scattering cross section

Here we aim to show that the ratio of the momentum spectra of $K^{+}$ at small transverse momentum measured for symmetric systems of different sizes can be such an observable.Comment: 3 pages, 2 figs, DAE BRNS Symposium on Nuclear Physics Dec 26-30, (2011), Visakhapatnam A.P. INDI

In-medium effects on K+K^{+} and K−K^{-} spectra in lighter systems

We aim to explore the in-medium effects on the transverse momentum ($p_{T}$) spectra of $K^{+}$ and $K^{-}$ in lighter mass system $^{12}C+^{12}C$.Comment: 3 pages, 1 fig. DAE BRNS Symposium on Nuclear Physics Dec 26-30, (2011), Visakhapatnam A.P. INDI

The multifragmentation of spectator matter

We present the first microscopic calculation of the spectator fragmentation observed in heavy ion reactions at relativistic energies which reproduces the slope of the kinetic energy spectra of the fragments as well as their multiplicity, both measured by the ALADIN collaboration. In the past both have been explained in thermal models, however with vastly different assumptions about the excitation energy and the density of the system. We show that both observables are dominated by dynamical processes and that the system does not pass a state of thermal equilibrium. These findings question the recent conjecture that in these collisions a phase transition of first order, similar to that between water and vapor, can be observed.Comment: 7 page

Transverse flow of nuclear matter in collisions of heavy nuclei at intermediate energies

The Quantum Molecular Dynamics Model (IQMD) is used to investigate the origin of the collective transverse velocity observed in heavy ion experiments. We find that there are three contributions to this effect: initial-final state correlations, potential interactions and collisions. For a given nuclear equation of state (eos) the increase of the transverse velocity with increasing beam energy is caused by the potential part. For a given beam energy the collective transverse velocity is independent of the nuclear eos but the relative contributions of potential and collisions differ. In view of the importance of the potential interactions between the nucleons it is not evident that the similarity of the radial velocities measured for fragments at beam energies below 1 AGeV and that for mesons at beam energies above 2 AGeV is more than accidental.Comment: 5 pages, 5 figures, revtex, OASIS ref PLB1700

Beyond Mean Field Confrontation of Different Models with High Transverse Momentum Proton Spectra

Several models have been proposed to simulate heavy ion reactions beyond the mean field level. The lack of data in phase space regions which may be sensitive to different treatments of fluctuations made it difficult to judge these approaches. The recently published high energy proton spectra, measured in the reaction 94 AMeV Ar + Ta, allow for the first time for a comparison of the models with data. We find that these spectra are reproduced by Quantum Molecular Dynamics (QMD) and Boltzmann Uehling Uhlenbeck (BUU) calculations. Models like Boltzmann Langevin (BL) in which additional fluctuations in momentum space are introduced overpredict the proton yield at very high energies. The BL approach has been successfully used to describe the recently measured very subthreshold kaon production assuming that the fluctuations provide the necessary energy to overcome the threshold in two body collisions. Our new findings suggest that the very subthreshold kaon production cannot be due to two body scattering and thus remains a open problem.Comment: 5 pages, 3 figures (eps), revte

Isospin effects on the energy of vanishing flow in heavy-ion collisions

Using the isospin-dependent quantum molecular dynamics model we study the isospin effects on the disappearance of flow for the reactions of $^{58}Ni$ + $^{58}Ni$ and $^{58}Fe$ +$^{58}Fe$ as a function of impact parameter. We found good agreement between our calculations and experimentally measured energy of vanishing flow at all colliding geometries. Our calculations reproduce the experimental data within 5%(10%) at central (peripheral) geometries

On the elliptical flow in asymmetric collisions and nuclear equation of state

We here present the results of elliptical flow for the collision of different asymmetric nuclei (10Ne20 +13 Al27, 18Ar40 +21 Sc45, 30Zn64 +28 Ni58, 36Kr86 +41 Nb93) by using the Quantum Molecular Dynamics (QMD) model. General features of elliptical flow are investigated with the help of theoretical simulations. The simulations are performed at different beam energies between 40 and 105 MeV/nucleon. A significant change can be seen from in-plane to out-of-plane elliptical flow of different fragments with incident energy. A comparison with experimental data is also made. Further, we predict, for the first time that, elliptical flow for different kind of fragments follow power law dependence ? C(Atot)? for asymmetric systems

Hadronic Matter Is Soft

The stiffness of the hadronic equation of state has been extracted from the production rate of K mesons in heavy-ion collisions around 1 AGeV incident energy. The data are best described with a compression modulus K around 200 MeV, a value which is usually called ''soft.'' This is concluded from a detailed comparison of the results of transport theories with the experimental data using two different procedures: (i) the energy dependence of the ratio of K from Au Au and C C collisions and (ii) the centrality dependence of the K multiplicities. It is demonstrated that input quantities of these transport theories which are not precisely known, such as the kaon-nucleon potential, the N ! NK cross section, or the lifetime of the in matter, do not modify this conclusion. DOI: 10.1103/PhysRevLett.96.012302 PACS numbers: 25.75.Dw, 21.65.+f For many years one of the most important challenges in nuclear physics has been to determine E=A; T, the energy/nucleon in nuclear matter in thermal equilibrium as a function of the density and the temperature T. Only at equilibrium density, 0 , do we know the energy per nucleon E=A 0 ; T 0 ÿ16 MeV by extrapolating the Weizsäcker mass formula to infinite matter. This quest has been dubbed ''search for the nuclear equation of state (EoS).'' Modeling of neutron stars or supernovae has not yet constrained the nuclear equation of state [1]; therefore, the most promising approach in extracting E=A; T is to use heavy-ion reactions in which the density of the colliding nuclei changes significantly. Three principal experimental observables have been suggested in the course of this quest which carry -according to theoretical calculations -information on the nuclear EoS: (i) the strength distribution of the giant isoscalar monopole resonances (i) The study of monopole vibrations has been very successful, but the variation in density is minute; therefore, giant monopole resonances are sensitive to the energy which is necessary to change the density of a cold nucleus close to the equilibrium point 0 . According to theory the vibration frequency depends directly on the force that counteracts any deviation from the equilibrium and therefore the potential energy. The careful analysis of the isoscalar monopole strength in nonrelativistic [2] and relativistic mean field models has recently converged which measures the curvature of E=A; T at the equilibrium point. is the compressibility. The values found are around K 240 MeV and therefore close to what has been dubbed a ''soft equation of state.'' (ii) If the overlap zone of projectile and target becomes considerably compressed in semicentral heavy-ion collisions, an in-plane flow is created due to the transverse pressure on the baryons outside of the interaction region with this flow being proportional to the transverse pressure. In order to obtain a noticeable compression, the beam energy has to be large compared to the Fermi energy of the nucleons inside the nuclei and hence a beam energy of at least 100 AMeV is necessary. Compression goes along with excitation and therefore the compressional energy of excited nuclear matter is encoded in the in-plane flow. It has recently been demonstrated [6] that transport theories do not agree quantitatively yet and therefore conclusions (iii) The third method is most promising for the study of nuclear matter at high densities and is the subject of this Letter. K mesons produced far below the NN threshold cannot be created in first-chance collisions between projectile and target nucleons. They do not provide sufficient energy even if one includes the Fermi motion. The effective energy for the production of a K meson in the NN center of mass system is 671 MeV as, in addition to the mass of the kaon, a nucleon has to be converted into a to conserve strangeness. Before nucleons can create a K at these subthreshold energies, they have to accumulate en-PRL 96