Pion emission in 2H, 12C, 27Al, gamma pi+ reactions at threshold

The first data from MAX-lab in Lund, Sweden on pion production in photonuclear reactions at threshold energies, is presented. The decrease of the total yield of pi+ in gamma + 12C, 27Al reactions below 200 MeV as well as differential, dsigma/dOmega, cross sections follow essentially predictions from an intranuclear cascade model with an attractive potential for pion-nucleus interaction in its simplest form. Double differential, d2sigma/dOmegadT, cross sections at 176 MeV show, however, deviations from the model, which call for refinements of nuclear and Coulomb potentials and possibly also for coherent pion production mechanisms.Comment: 19 pages, 7 figure

Inclusive meson production in peripheral collisions of ultrarelativistic heavy ions

There exist several proposals to use Weizs\"{a}cker-Williams photons generated by ultrarelativistic heavy ions to produce exotic particles in $\gamma\gamma$ fusion reactions. To estimate the background conditions for such reactions we analyze various mechanisms of meson production in very peripheral collisions of ultrarelativistic heavy ions at RHIC and LHC energies. Besides $\gamma\gamma$ fusion they include also electromagnetic $\gamma A$ interactions and strong nucleon-nucleon interactions in grazing $AA$ collisions. All these processes are characterised by low multiplicities of produced particles. $\gamma A$ and $AA$ events are simulated by corresponding Monte Carlo codes, RELDIS and FRITIOF. In each of these processes a certain fraction of pions is produced close to the mid-rapidity region that gives a background for the $\gamma\gamma$ events. The possibility of selecting mesons produced in $\gamma\gamma$ fusion events via different $p_t$ cut procedures is demonstrated.Comment: 27 pages with 4 eps-figures included, uses axodraw.sty Tab.2 and 3 correcte

Comparison of exact and approximate cross-sections in relativistic Coulomb excitation

We present a new method of obtaining time-dependent matrix elements of the electromagnetic pulse produced by a highly-relativistic projectile. These matrix elements are used in a coupled-channel calculation to predict the cross-sections for population of 1- and 2-phonon states of the giant dipole resonance. Comparisons are made with the predictions of the long-wavelength and Born approximations.Comment: 26 pages, LaTex2

Long-range Angular Correlations On The Near And Away Side In P-pb Collisions At √snn=5.02 Tev

7191/Mar294

Electromagnetically-induced nuclear-charge pickup observed in ultra-relativistic Pb collisions

A strong increase of inclusive nuclear-charge pickup cross sections, forming _8_3Bi from 158 A GeV _8_2Pb ions, is observed in comparison to similar measurements at 10.6 A GeV. From the dependence of these cross sections on target atomic number, this increase is attributed to the electromagnetic process of pion production by equivalent photons. The observed cross sections can be reproduced quantitatively using the recently developed RELDIS code. (orig.)Available from TIB Hannover: RO 801(2002-02) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Emission of forward neutrons by 158A GeV indium nuclei in collisions with Al, Cu, Sn and Pb

The cross sections of forward emission of one, two and three neutrons by 158A GeV 115In nuclei in collisions with Al, Cu, Sn and Pb targets are reported. The measurements were performed in the framework of the ALICE-LUMI experiment at the SPS facility at CERN. Various corrections accounting for the absorption of beam nuclei and produced neutrons in target material and surrounding air were introduced. The corrected cross section data are compared with the predictions of the RELDIS model for electromagnetic fragmentation of 115In in ultraperipheral collisions, as well as with the results of the abrasion-ablation model for neutron emission in hadronic interactions. The measured neutron emission cross sections well agree with the RELDIS results, with the exception of In-Al collisions where the measured cross sections are larger compared to RELDIS. This is attributed to a relatively large contribution of hadronic fragmentation of In on Al target with respect to electromagnetic fragmentation, on the contrary to similar measurements performed earlier with 30A GeV 208Pb colliding with Al.Comment: 14 pages, 9 figures, 11 tables: updates to the paper structure, typos fixed in version