6453654
Photoproduction of charmonia and total charmonium proton cross-sections
Elastic virtual photoproduction cross sections ${\ensuremath{\gamma}}^{*}\stackrel{\ensuremath{\rightarrow}}{p}J/\ensuremath{\psi}({\ensuremath{\psi}}^{\ensuremath{'}})p$ and total charmonium-nucleon cross sections for $J/\ensuremath{\psi}, {\ensuremath{\psi}}^{\ensuremath{'}},$ and $\ensuremath{\chi}$ states are calculated in a parameter-free way with the light-cone dipole formalism and the same input: factorization in impact parameters, light-cone wave functions for the ${\ensuremath{\gamma}}^{*}$ and the charmonia, and the universal phenomenological dipole cross section which is fitted to other data. The charmonium wave functions are calculated with four known realistic potentials, and two models for the dipole cross section are tested. Very good agreement with data for the cross section of charmonium photoproduction is found in a wide range of s and ${Q}^{2}.$ The inclusion of the Melosh spin rotation increases the ${\ensuremath{\psi}}^{\ensuremath{'}}$ photoproduction rate by a factor of 2\char21{}3 and removes previously observed discrepancies in the ${\ensuremath{\psi}}^{\ensuremath{'}}$ to $J/\ensuremath{\psi}$ ratio in photoproduction. We also calculate the charmonium-proton cross sections whose absolute values and energy dependences are found to correlate strongly with the sizes of the states.
119138207
Lepton flavor violating photoleptonic effect
We study lepton flavor violating analogs of the photoelectric effect, with a final μ or T instead of an electron: γe → μ and γe → T. On the basis of the general parametrization of the matrix element of the electromagnetic current we estimate the upper limits for the cross sections and event rates of these processes, imposed by the current experimental bounds on μ → ey and T → eγ decays.
182432079
SPECTRALITY OF GELL-MANN-LOW FUNCTION
896237
Electroproduction of charmonia off nuclei
In a recent publication we have calculated elastic charmonium production in ep collisions employing realistic charmonia wave functions and dipole cross sections and have found good agreement with the data in a wide range of s and Q^2. Using the ingredients from those calculations we calculate exclusive electroproduction of charmonia off nuclei. Here new effects become important, (i) color filtering of the c-cbar pair on its trajectory through nuclear matter, (ii) dependence on the finite lifetime of the c-cbar fluctuation (coherence length) and (iii) gluon shadowing in a nucleus compared to the one in a nucleon. Total coherent and incoherent cross sections for C, Cu and Pb as functions of s and Q^2 are presented together with some differential cross sections. The results can be tested with future electron-nucleus colliders or in peripheral collisions of ultrarelativistic heavy ions.
117509698
QCD NUCLEON MODEL WITH RELATIVISTIC OSCILLATOR INTERACTION BETWEEN CONSTITUENT QUARK
118014393
QCD analysis of deep inelastic lepton-scattering data
We have carried out a QCD analysis of data on deep inelastic lepton-scattering (using data of the collaborations BCDMS, EMC, and CDHS) in the leading and next-to-leading orders in the coupling constant ..cap alpha../sub s/. We have considered the effect of the sea quarks and gluons. We discuss the dependence of our results for ..lambda.. on effects of twist corrections, nuclear target effects, and heavy-quark production thresholds.
120068071
Partial-transparency effects in heavy-ion collisions at energies of the order of 1 GeV/nucleon
Abstract A model of heavy-ion collisions at energies E lab ∼ 1 GeV/nucleon taking into account the effects of incomplete statistical equilibrium in highly-excited nuclear matter is presented. The collision process is considered as the interaction of two flows of nucleons decelerating each other. This process is described within the framework of a relativistic kinetic approach employing the Fokker-Planck approximation. Assuming two-flow nonequilibrium the momentum distribution function is represented as a sum of two maxwellian distributions displaced by the average relative velocity of flows. Equations for time evolution of space-averaged velocities and internal energies of flows are derived. These equations contain a single model parameter, i.e. the effective deceleration length λ d . Using the firestreak model geometry inclusive cross sections of protons and composite particles (d, t) in the reactions Ne + NaF, Ar + KCl and Ar + Pb are calculated at various values of E lab . In contrast to the firestreak model, a complete stopping of colliding tubes in the centre-of-mass frame was not assumed in the present calculation. Composite particle spectra are calculated on the basis of the coalescence model. The theory is thoroughly compared with the experimental data. The approach suggested allows us to reproduce a two-humped structure in the rapidity distributions of the secondary particles. The experimental data analysis leads to the value λ d = 8 fm for E lab = 0.8 GeV/nucleon, which is in good agreement with the estimation based on experimental NN cross sections.
122100360
Kaon production in intermediate-energy nuclear collisions
Abstract Production of positive kaons in nuclear collisions at intermediate energies (∼1–2 GeV/nucleon) is studied within the 3-dimensional fluid dynamics combined with the hadrochemical kinetics for strangeness production. Sensitivity of the kaon probe to a form of the nuclear equation of state is analyzed. The model reproduces total and differential cross sections of Ne + NaF → K + + X and Ne + Pb → K + + X reactions at E lab = 2.1 GeV/nucleon, provided a soft equation of state is used. The pion-production data are also well described employing the same equation of state. Predictions are made for the current experiment on kaon production at the SIS accelerator. The obtained results are compared with the predictions of other models.
9999495
Relativistic heavy-ion collisions within three-fluid hydrodynamics : Hadronic scenario
A three-fluid hydrodynamic model for simulating relativistic heavy-ion collisions is introduced. Along with two baryon-rich fluids, the new model considers the time-delayed evolution of a third, baryon-free (i.e., with zero net baryonic charge) fluid of newly produced particles. Its evolution is delayed because of a formation time {tau}, during which the baryon-free fluid neither thermalizes nor interacts with the baryon-rich fluids. After the formation it starts to interact with the baryon-rich fluids and quickly gets thermalized. Within this model with pure hadronic equation of state, a systematic analysis of various observables at incident energies between few and about 160A GeV has been done as well as a comparison with results of transport models. We have succeeded in reasonably reproducing a great body of experimental data in the incident energy range of E{sub lab}{approx_equal} (1-160)A GeV. The list includes proton and pion rapidity distributions, proton transverse-mass spectra, rapidity distributions of {lambda} and {lambda} hyperons, elliptic flow of protons and pions (with the exception of proton v{sub 2} at 40A GeV), multiplicities of pions, positive kaons, {phi} mesons, hyperons, and antihyperons, including multistrange particles. This agreement is achieved on the expense of substantial enhancement of the interflow friction as compared to thatmore » estimated proceeding from hadronic free cross sections. However, we have also found out certain problems. The calculated yield of K{sup -} is approximately higher than that in the experiment by a factor of 1.5. We have also failed to describe directed transverse flow of protons and pion at E{sub lab}{>=}40A GeV. This failure apparently indicates that the used EOS is too hard and thereby leaves room for a phase transition.« less
117037776
Dynamical instabilities in hadron plasma:: Filamentation
Abstract In the framework of a relativistic kinetic model with mean σ- and ω-fields possible instabilities of hadron plasma are studied under the conditions arising in heavy nucleus collisions at energies of tens GeV/nucleon. A general dispersion equation is derived. It is shown that in a two-flux regime the filamentation mode resulting in the system stratification into separate current filaments turns out to be most unstable. Time scale estimates suggest that this instability should be expected in heavy nucleus collisions. A collective filamentation deceleration mechanism which can considerably increase the stopping power of nuclear matter is discussed. A method of detecting the filamentation instability by a characteristic angular distribution of hard electromagnetic radiation is proposed.
123021094
Analysis of intermediate-energy heavy-ion collisions within relativistic mean-field two-fluid model
A three-dimensional realization of the relativistic mean-field two-fluid model is described. First results of analyzing the inclusive data on the yield of nuclear fragments and pions, as well as the Plastic-Ball rapidity distributions of nuclear fragments are presented. For comparison, calculations within the conventional relativistic hydrodynamical model with the same mean fields are also performed. In spite of a pronounced sensitivity of the nuclear dynamics to the nuclear equation of state (more precisely, to the form of the mean fields), it is found that all the analyzed observables, except the pion spectra, appear to be fairly insensitive to it. The sensitivity to the nuclear stopping power is slightly higher. The original sensitivity of the rapidity distributions to the stopping power is smeared out by the Plastic-Ball filter and selection criterion. Nevertheless, one can conclude that the stopping power induced by the Cugnon parametrization of the nucleon-nucleon cross sections is not quite sufficient for a more adequate reproduction of the experimental data.