Charm production in a string model of proton-proton collisions

Using a simple string fragmentation model, with charm pair production in the string, in conjunction with a Drell-Yan type mechanism of string hadroproduction, many features of charm particle production in proton-proton collisions are described. While the normalisation of cross-sections is arbitrary, the relative normalisation of Λ_c andD production is well described by the model. This normalisation is related to previous results of the model and the running coupling α_s of QCD via a plausibility argument. It is argued that other approaches, which dismiss the possibility of charm pair production in the string, are rather pessimistic in this respect. Brief comments about testing this hypothesis through polarization measurements are made.     

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.     

Midrapidity production of secondaries in pp collisions at RHIC and LHC energies in the quark–gluon string model

We consider the phenomenological implications of the assumption that baryons are systems of three quarks connected through a gluon string junction. The transfer of baryon number in rapidity space due to the string junction propagation is considered in detail. At high energies this process leads to a significant effect on the net baryon production in hN collisions at midrapidities. The numerical results for midrapidity inclusive densities of different secondaries in the framework of the quark–gluon string model are in reasonable agreement with the experimental data. One universal value, λ≃0.25, for the strangeness suppression parameter correctly describes the yield ratios of Λ/p, Ξ/Λ, and Ω/Ξ. The predictions for pp collisions at LHC energies are also presented. PACS 25.75.Dw     

Near-threshold production of phi mesons in pp collisions

The pp-->ppphi reaction has been studied at the Cooler Synchrotron COSY-Jülich, using the internal beam and ANKE facility. Total cross sections have been determined at three excess energies epsilon near the production threshold. The differential cross section closest to threshold at epsilon=18.5 MeV exhibits a clear S wave dominance as well as a noticeable effect due to the proton-proton final-state interaction. Taken together with data for ppomega production, a significant enhancement of the phi/omega ratio of a factor 8 is found compared to predictions based on the Okubo-Zweig-Iizuka rule.     

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.     

Scaling behaviour and correlations in the string fusion model for heavy ion collisions

The KNO scaling, the scaling of multiplicities, the behaviour of fluctuations in the transverse momentum as a function of the multiplicity and the long range correlations in nucleus-nucleus collisions are studied by a Monte Carlo code based on the string fusion model. It is shown that the fusion of strings produces a strong reduction of the long range correlations at high multiplicities, which could be detected experimentally. On the contrary the KNO scaling, the scaling of multiplicities and the behaviour of fluctuations in the transverse momentum are not modified when string fusion is included.On leave of absence from the Department of High Energy Physics, University of St. Petersburg, 198904 St. Petersburg, Russia     

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.     

Destruction of a metastable string by particle collisions

We calculate the probability of destruction of a metastable string by collisions of the Goldstone bosons, corresponding to the transverse waves on the string. We find a general formula that allows to determine the probability of the string breakup by a collision of arbitrary number of the bosons. We find that the destruction of a metastable string takes place only in collisions of even number of the bosons, and we explicitly calculate the energy dependence of such process in a two-particle collision for an arbitrary relation between the energy and the largest infrared scale in the problem, the length of the critical gap in the string.     

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.     

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.     

Dirac magnetic monopole production from photon fusion in proton collisions

We calculate the lowest-order cross-section for Dirac magnetic monopole production from photon fusion ( in p collisions at = 1.96 TeV, pp collisions at = 14 TeV, and we compare with Drell-Yan (DY) production. We find the total cross-section is comparable with DY at = 1.96 TeV and dominates DY by a factor > 50 at = 14 TeV. We conclude that both the and DY processes allow for a monopole mass limit m > 370 GeV based upon the null results of the recent monopole search at the Collider Detector at Fermilab (CDF). We also conclude that production is the leading mechanism to be considered for direct monopole searches at the Large Hadron Collider (LHC).