Hyperon production in pp collisions

We report on a study of the proton induced hyperon production reactions. We discuss the theoretical efforts made towards understanding the existing data and the uncertainties involved in the calculations. Our recent calculations of the missing mass spectra for the pp → K ⁺ Λp reaction which involve a proper coupled channel treatment of the final state Λp interaction are presented. Significant differences in the results using different models of the hyperon-nucleon interaction are found.     

Universality of identified hadron production in pp collisions

The shapes of invariant differential cross section for identified $\pi ^{\pm },K^{\pm }, p$ and $\overline{p}$ production as a function of transverse momentum measured in $pp$ collisions by the PHENIX detector are analyzed in terms of a recently introduced approach. Simultaneous fits of these data to the sum of exponential and power-law terms show a significant difference in the exponential term contributions. This effect qualitatively explains the observed shape of the experimental $K/\pi $ and $p/\pi $ yield ratios measured as a function of transverse momentum of produced hadrons. A picture with two types of mechanisms for hadron production is presented. Universality of the power-law term behavior for $\pi ^{\pm },K^{\pm }, p$ , and $\overline{p}$ production is shown.     

Exclusive production of heavy mesons in photon-photon collisions: The double scattering mechanism

We present two mechanisms which can compete with constituent interchange in the exclusive production at wide angle of heavy mesons in photon-photon collisions. We show that they have the same energy behaviour as constituent interchange, and that their amplitudes are free from large logarithms. We exploit this to calculate the double-scattering diagrams numerically. We find that while constituent interchange dominates at 90°, double scattering becomes dominant for angles less than about 45°.     

Production of unusual mesons in photon-photon collisions

The cross-section for the production of unusual mesons, such as (bc?) or (b?c), in photon-photon collisions is obtained in a high energy approximation. For a 100 + 100 GeV e⁺e^? collider, the cross section is estimated to be about one unit of R for (bc?) and (b?c).     

Resonance model study of strangeness production in pp collisions

Results for the energy dependence of the elementary kaon production cross sections in proton-proton collisions are reported. Calculations are performed within an extended version of the resonance model which was used for the previous studies of elementary kaon production in pion-nucleon and pion-Δ collisions. Although the model treatment is within theempirical tree level (observed widths for the resonances are used), it is fully relativistic, and includes all relevant baryon resonances up to 2 GeV. One of the purposes of this study is to provide the results for the simulation codes of subthreshold kaon production in heavy ion collisions. This is the first, consistent study of the elementary kaon production reactions including both πB and BB (B = N,Δ) collisions on the same footing. Comparisons are made between the calculated results and the existing semi-empirical parametrizations which are widely used for the simulation codes, as well as the experimental data.     

Seeing the B mesons in hadronic collisions

The weak decays B→ψ(J) + X are investigated. It is argued that these decays are dominated by B→ψ(J)Kπ (branching ratio of about 1%). Detailed predictions for these decays are made.     

Inclusive jet production in pp(macro) collisions

We report a new measurement of the pseudorapidity (eta) and transverse-energy ( E(T)) dependence of the inclusive jet production cross section in pp(macro) collisions at square root of s = 1.8 TeV using 95 pb(-1) of data collected with the D0 detector at the Fermilab Tevatron. The differential cross section d(2)sigma/(dE(T)d eta) is presented up to eta = 3, significantly extending previous measurements. The results are in good overall agreement with next-to-leading order predictions from QCD and indicate a preference for certain parton distribution functions.     

Dilepton production in pp and CC collisions with HADES

e ⁺ e ^- production was studied using the High Acceptance DiElectron Spectrometer (HADES). In pp collisions at 2.2GeV kinetic beam energy, the exclusive η production and the Dalitz decay η→γe ⁺ e ^- have been reconstructed. The electromagnetic form factor of the latter decay was found to be in good agreement with the existing theoretical predictions. In addition, an inclusive e ⁺ e ^- invariant-mass spectrum from the ¹²C + ¹²C reaction at 2AGeV is presented and compared with a simplified thermal model.     

The photon structure and exclusive production of vector mesons in \gamma\gamma collisions

The process of exclusive vector meson production, , is studied for almost real photons. This process may be reduced to the photoproduction of off the meson. We discuss the possibility of extracting the gluon distribution of and of the photon from such a measurement. Predictions are also given for the reaction for various cms energies typical for LEP and for the future linear colliders. Received: 13 December 2000 / Revised version: 6 January 2001/ Published online: 6 April 2001     

Properties of light mesons in ultrarelativistic nucleus-nucleus collisions

The PHENIX experiment at the Relativistic Heavy Ion Collider is designed for studying the new state of nuclear matter, which is presumably created in central ultrarelativistic collisions of heavy nuclei: the so-called quark-gluon plasma. Light mesons are an important tool in this research. This paper reviews the recent experimental results on the light meson invariant yields, nuclear modification factors, and the yield ratios for the vector and pseudoscalar mesons in the p + p, d + Au, and Au + Au collisions at the energy of √s _NN = 200 GeV.     

Study of ω-meson production in pp collisions at ANKE

The production of ω-mesons in the pp → ppω reaction has been investigated with the COSY-ANKE spectrometer for excess energies of 60 and 92MeV by detecting the two final protons and reconstructing their missing mass. The large physical background was subtracted using an event-by-event transformation of the proton momenta between the two energies. Differential distributions and total cross-sections were obtained after careful studies of possible systematic uncertainties in the overall ANKE acceptance. The results are compared with the predictions of theoretical models. Combined with data on the φ-meson, a more refined estimate is made of the Okubo-Zweig-Iizuka rule violation in the φ/ω production ratio.     

The QCD pomeron in ultraperipheral heavy ion collisions: IV. Photonuclear production of vector mesons

The photonuclear production of vector mesons in ultraperipheral heavy-ion collisions is investigated within the QCD color dipole picture, with particular emphasis on the saturation model. The integrated cross section and the rapidity distribution for the ( ) process are computed and theoretical estimates for scattering on both light and heavy nuclei are given for the energies of RHIC and LHC. A comparison with the recent STAR data on coherent production of mesons is also presented. Furthermore, we calculate the photoproduction of vector mesons in proton-proton collisions at RHIC, Tevatron and LHC energies.Received: 12 January 2005, Revised: 2 February 2005, Published online: 9 March 2005