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Neutron-proton bremsstrahlung from intermediate energy heavy-ion reactions as a probe of the nuclear symmetry energy?  [PDF]
Gao-Chan Yong,Bao-An Li,Lie-Wen Chen
Physics , 2007, DOI: 10.1016/j.physletb.2008.02.013
Abstract: Hard photons from neutron-proton bremsstrahlung in intermediate energy heavy-ion reactions are examined as a potential probe of the nuclear symmetry energy within a transport model. Effects of the symmetry energy on the yields and spectra of hard photons are found to be generally smaller than those due to the currently existing uncertainties of both the in-medium nucleon-nucleon cross sections and the photon production probability in the elementary process $pn\to pn\gamma$. Very interestingly, nevertheless, the ratio of hard photon spectra $R_{1/2}(\gamma)$ from two reactions using isotopes of the same element is not only approximately independent of these uncertainties but also quite sensitive to the symmetry energy. For the head-on reactions of $^{132}Sn+^{124}Sn$ and $^{112}Sn+^{112}Sn$ at $E_{beam}/A=50$ MeV, for example, the $R_{1/2}(\gamma)$ displays a rise up to 15% when the symmetry energy is reduced by about 20% at $\rho=1.3\rho_0$ which is the maximum density reached in these reactions.
Azimuthal asymmetry of direct photons in intermediate energy heavy-ion collisions  [PDF]
G. H. Liu,Y. G. Ma,X. Z. Cai,D. Q. Fang,W. Q. Shen,W. D. Tian,K. Wang
Physics , 2007, DOI: 10.1016/j.physletb.2008.04.037
Abstract: Hard photon emitted from energetic heavy ion collisions is of very interesting since it does not experience the late-stage nuclear interaction, therefore it is useful to explore the early-stage information of matter phase. In this work, we have presented a first calculation of azimuthal asymmetry, characterized by directed transverse flow parameter $F$ and elliptic asymmetry coefficient $v_2$, for proton-neutron bremsstrahlung hard photons in intermediate energy heavy-ion collisions. The positive $F$ and negative $v_2$ of direct photons are illustrated and they seem to be anti-correlated to the corresponding free proton's flow.
Multipole Expansion for Relativistic Coulomb Excitation  [PDF]
H. Esbensen,C. A. Bertulani
Physics , 2001, DOI: 10.1103/PhysRevC.65.024605
Abstract: We derive a general expression for the multipole expansion of the electro-magnetic interaction in relativistic heavy-ion collisions, which can be employed in higher-order dynamical calculations of Coulomb excitation. The interaction has diagonal as well as off-diagonal multipole components, associated with the intrinsic and relative coordinates of projectile and target. A simple truncation in the off-diagonal components gives excellent results in first-order perturbation theory for distant collisions and for beam energies up to 200 MeV/nucleon.
Bremsstrahlung Pair Production In Relativistic Heavy Ion Collision  [PDF]
H. Meier,K. Hencken,D. Trautmann,G. Baur
Physics , 1997, DOI: 10.1007/s100520050178
Abstract: We calculate production of electron- and muon-pairs by the bremsstrahlung process in hadron collisions and compare it with the dominant two-photon process. Results for the total cross section are given for proton-proton and heavy-ion collisions at energies of the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC).
Bremsstrahlung from Electrons and Positrons in Peripheral Relativistic Heavy Ion Collisions  [PDF]
Kai Hencken,Dirk Trautmann,Gerhard Baur
Physics , 1999, DOI: 10.1103/PhysRevC.60.034901
Abstract: We study the spectrum of the bremsstrahlung photons coming from the electrons and positrons, which are produced in the strong electromagnetic fields present in peripheral relativistic heavy ion collisions. We compare different approaches, making use of the exact pair production cross section in heavy ion collisions as well as the double equivalent photon approximation.
Bremsstrahlung from a Microscopic Model of Relativistic Heavy Ion Collisions  [PDF]
S. M. H. Wong,M. Belkacem,J. I. Kapusta,S. A. Bass,M. Bleicher,H. St?cker
Physics , 2000, DOI: 10.1103/PhysRevC.63.014903
Abstract: We compute bremsstrahlung arising from the acceleration of individual charged baryons and mesons during the time evolution of high-energy Au+Au collisions at the Relativistic Heavy Ion Collider using a microscopic transport model. We elucidate the connection between bremsstrahlung and charge stopping by colliding artificial pure proton on pure neutron nuclei. From the intensity of low energy bremsstrahlung, the time scale and the degree of stopping could be accurately extracted without measuring any hadronic observables.
Thermal Bremsstrahlung photons probing the nuclear caloric curve  [PDF]
D. G. d'Enterria,G. Martínez,L. Aphecetche,H. Delagrange,F. Fernández,H. L?hner,R. Ortega,R. W. Ostendorf,Y. Schutz,H. W. Wilschut
Physics , 2001, DOI: 10.1016/S0370-2693(02)01973-1
Abstract: Hard-photon (E$_{\gamma}>$ 30 MeV) emission from second-chance nucleon-nucleon Bremsstrahlung collisions in intermediate energy heavy-ion reactions is studied employing a realistic thermal model. Photon spectra and yields measured in several nucleus-nucleus reactions are consistent with an emission from hot nuclear systems with temperatures $T\approx$ 4 - 7 MeV. The corresponding caloric curve in the region of excitation energies $\epsilon^\star\approx$ 3{\it A} - 8{\it A} MeV shows lower values of $T$ than those expected for a Fermi fluid.
Probing the Space-Time evolution of Heavy Ion Collisions with Bremsstrahlung  [PDF]
J. I. Kapusta,S. M. H. Wong
Physics , 1999,
Abstract: We examine the bremsstrahlung photons emitted in the central collisions of two gold nuclei at the Relativistic Heavy Ion Collider. While the measurements of the final hadrons can reveal only the amount of stopping, they tell us very little about the space-time evolution of the bulk matter in the collisions. By using two extreme collision scenarios, we argue that the low and medium energy bremsstrahlung photons can, not only reveal the amount of stopping, but also the finer details of the space-time evolution of the charges.
Dilepton production by bremsstrahlung of meson fields in nuclear collisions  [PDF]
I. N. Mishustin,L. M. Satarov,H. Stoecker,W. Greiner
Physics , 1997, DOI: 10.1103/PhysRevC.57.2552
Abstract: We study the bremsstrahlung of virtual omega mesons due to the collective deceleration of nuclei at the initial stage of an ultrarelativistic heavy-ion collision. It is shown that electromagnetic decays of these mesons may give an important contribution to the observed yields of dileptons. Mass spectra of positron-electron and muon pairs produced in central Au+Au collisions are calculated under some simplifying assumptions on the space-time variation of the baryonic current in a nuclear collision process. Comparison with the CERES data for 160 AGev Pb+Au collisions shows that the proposed mechanism gives a noticeable fraction of the observed lepton pairs in the intermediate region of invariant masses. Sensitivity of the dilepton yield to the in-medium modification of masses and widths of vector mesons is demonstrated.
Multipole decomposition of potentials in relativistic heavy ion collisions  [PDF]
A. Isar
Physics , 2006,
Abstract: In relativistic heavy ion collisions an exact multipole decomposition of the Lorentz transformed time dependent Coulomb potentials in a coordinate system with equal constant, but opposite velocities of the ions, is obtained for both zero and different from zero impact parameter. The case of large values of $\gamma$ and the gauge transformation of the interaction removing both the $\gamma$ dependence and the $\ln b$ dependence are also considered.
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