arXiv subjects

J. Ranft

Publications and source records attributed to J. Ranft.

At least 37 records · Page 2Linked to original sources

arXiv2000

Hadronic collisions: physics, models and event generators used for simulating the cosmic ray cascade at the highest energies

Most hadronic event generators which can be used for simulating hadronic and nuclear collisions up to the highest energies are quite similar in their construction and in the underlying theoretical concepts. At energies, where data from accelerator and collider experiments are available the models agree rather well with each other and with the most important features of the data. As soon as we compare the extrapolations of the models at higher energy we find in spite of the similarities in the underlying theoretical concepts quite often striking differences between the predictions of the models.

hep-ph↗

arXiv2000

Baryon stopping in high energy collisions in the DPMJET-III model

A new striking feature of hadron production in nuclear collisions is the large stopping of the participating nucleons in hadron-nucleus and nucleus-nucleus collisions. This enhanced baryon stopping can be understood introducing new diquark breaking mechanisms in multistring models of hadron production. Here we discuss the implementation of these diagrams into the DPMJET-III hadronic Monte Carlo model.

hep-ph↗

arXiv2000

Baryon stopping in high energy collisions and the extrapolation of hadron production models to Cosmic Ray energies

A new striking feature of hadron production in nuclear collisions is the large stopping of the participating nucleons in hadron-nucleus and nucleus-nucleus collisions. This enhanced baryon stopping can be understood introducing new diquark breaking mechanisms in multistring models of hadron production. Here we show, that similar diquark breaking mechanisms occur at high energy even in hadron-hadron collisions. This effect leads to significant changes in the extrapolation of these models to Cosmic Ray energies.

hep-ph↗

arXiv1999

DPMJET version II.5, code manual

DPMJET samples hadron-hadron, hadron-nucleus, nucleus-nucleus and neutrino-nucleus interactions at high energies. The two-component Dual Parton Model is used with multiple soft chains and multiple minijets at each elementary interaction. Particle production is realized by the fragmentation of colorless parton-parton chains constructed from the quark content of the interacting hadrons. DPMJET-II.5 includes the cascading of secondaries within the target as well as projectile nuclei which is suppressed by the formation time concept. The excitation energy of the remaining target and projectile nuclei is calculated and using this nuclear evaporation is included into the model. It is possible to use the model up to primary energies of 10${}^{21}$ eV (per nucleon) in the lab. frame. DPMJET can also be applied to neutrino nucleus collisions. It extends the neutrino-nucleon models qel (quasi elastic neutrino interactions) and lepto (deep inelastic neutrino nucleon collisions) to neutrino collisions on nuclear targets.

hep-ph↗

arXiv1999

New features in DPMJET version II.5

DPMJET is a Monte Carlo model for sampling of hadron-hadron, hadron-nucleus, nucleus-nucleus and neutrino-nucleus interactions at accelerator and Cosmic Ray energies according to the two-component Dual Parton Model. Here we describe new features in version DPMJET-II.5: Implementation of new DPM diagrams for an improved description of baryon stopping in nuclear collisions and improvements in the calculation of Glauber cross sections. The new diagrams allow two quite different extrapolations of the model to the highest Cosmic Ray energies. The new version of the model is compared to experimental data on hadron-hadron, hadron-nucleus and nucleus-nucleus collisions.

hep-ph↗

arXiv1998

MARS Code Developments

Recent developments in the physical model of 1 MeV to 100 TeV hadron and lepton interactions with nuclei and atoms are described. These include a new nuclear cross section library, a model for soft pion production, the cascade-exciton model, the dual parton model, deuteron-nucleus and neutrino-nucleus interaction models, detailed description of muon, pion, and antiproton absorption and a unified treatment of muon and charged hadron electromagnetic interactions with matter. New algorithms are implemented into the MARS13(98)} Monte Carlo code and benchmarked against experimental data. The code capabilities to simulate cascades and generate a variety of results in complex media have been also enhanced.

nucl-th↗

arXiv1998

Rapidity gaps and the PHOJET Monte Carlo

A model for the production of large rapidity gaps being implemented in the Monte Carlo event generator PHOJET is discussed. In this model, high-mass diffraction dissociation exhibits properties similar to hadron production in non-diffractive hadronic collisions at high energies. Hard diffraction is described using leading-order QCD matrix elements together with a parton distribution function for the pomeron and pomeron-flux factorization. Since this factorization is imposed on Born graph level only, unitarity corrections lead to a non-factorizing flux function. Rapidity gaps between jets are obtained by soft color reconnection. It was previously shown that this model is able to describe data on diffractive hadron production from the CERN-SPS collider and from the HERA lepton-proton collider. In this work we focus on the model predictions for rapidity gap events in p-p collisions at \sqrt{s} = 1800 GeV and compare to TEVATRON data.

hep-ph↗

arXiv1998

Simulation of nuclear effects in quasi elastic and resonant neutrino interactions

The effects of nuclear re-interactions in quasi elastic and resonant neutrino interactions have been considered in the framework of the nuclear models of the DPMJET code. A preliminary investigation on the modifications induced on the final state has been performed. Some consequences affecting the experimental identification are discussed.

hep-ph↗

arXiv1997

Photoproduction Off Nuclei, Part II: Particle and Jet Production

High energy multiparticle photoproduction off nuclear targets is studied. The photon is assumed to interact in direct scattering processes or as a resolved $q\bar{q}$-state according to the Generalized Vector Dominance Model. In the description of resolved interactions multiple soft and hard processes in each $q\bar{q}$--nucleon interaction are taken into consideration. The model, formulated within the framework of the two-component Dual Parton Model, is shown to agree with hadron production data from real and weakly virtual photon-nucleus interactions. Differences between multiparticle production in photon-nucleus and hadron-nucleus interactions and features of jet production in photon-nucleus collisions at HERA-energies are discussed.

hep-ph↗

arXiv1997

Hard diffraction and central diffraction in hadron-hadron and photon-hadron collisions

Hadron production in single and central diffraction dissociation is studied in a model which includes soft hadron interaction as controlled by a supercritical pomeron parametrization and hard diffraction. Within this model, particle production in collisions with pomerons exhibit properties like multiple soft interactions and multiple minijets, quite similar to hadron production in non-diffractive hadronic collisions at high energies. However, important differences occur in transverse momentum jet and hadron distributions. It is shown that the model is able to describe data from the CERN-SPS collider and from the HERA collider. Model predictions are presented for single and central diffraction at TEVATRON.

hep-ph↗

arXiv1997

Cosmic Ray particle production

The status of some popular models to simulate hadronic and nuclear interactions at Cosmic Ray energies is reviewed. The models predict the rise of all the hadronic and nuclear cross sections with energy and a smooth (logarithmic) rise of average multiplicities, rapidity plateaus and average transverse momenta with the energy. The importance is stressed to put more effort into the models and especially a better understanding of the minijet component at the highest energies. Likewise, experimental data on particle production are needed at the highest possible energies, to guide the models.

hep-ph↗

arXiv1997

Fusion of strings vs. percolation and the transition to the quark-gluon plasma

In most of the models of hadronic collisions the number of exchanged colour strings grows with energy and atomic numbers of the projectile and target. At high string densities interaction between them should melt them into the quark-gluon plasma state. It is shown that under certain assumptions about the the string interaction, a phase transition to the quark gluon plasma indeed takes place in the system of many colour strings. It may be of the first or second order (percolation), depending on the particular mechanism of the interaction. The critical string density is about unity in both cases. The critical density may have been already reached in central Pb-Pb collisions at 158 A GeV.

hep-ph↗

arXiv1997

Multiparticle production in high-mass diffraction dissociation and the interplay of photons and pomerons

Multiple interaction models satisfying $s$-channel unitarity predict that, in contrast to inelastic processes, factorization is violated in diffractive processes. The size of this effect can be characterized in terms of the rapidity gap survival probability. The possibility of its measurement at HERA is pointed out. Furthermore a method to measure photon diffraction dissociation at LEP2 and planned linear colliders is discussed and cross section predictions are given.

hep-ph↗

arXiv1996

Deviations from the superposition model in a Dual Parton Model with formation zone cascade in both projectile and target nuclei

A Dual Parton Model with a formation zone intranuclear cascade in the spectators of the projectile and target nuclei is studied. The hadrons produced in the formation zone cascade contribute to Feynman-$x_F$ and lab-$x$ distributions in the fragmentation regions of the target and projectile nuclei. We discuss the consequences of this model in the secondary cosmic ray production, by analyzing the calculated spectrum weighted moments for pion and kaon production. We show that the proposed model leads to significant differences with respect to a simple superposition model, where the nucleus-nucleus collision is replaced by a few corresponding nucleon-nucleus collisions.

hep-ph↗

arXiv1996

Photoproduction off Nuclei and Point-like Photon Interactions Part I: Cross Sections and Nuclear Shadowing

High energy photoproduction off nuclear targets is studied within the Glauber-Gribov approximation. The photon is assumed to interact as a $q\bar{q}$-system according to the Generalized Vector Dominance Model and as a ``bare photon'' in direct scattering processes with target nucleons. We calculate total cross sections for interactions of photons with nuclei taking into account coherence length effects and point-like interactions of the photon. Results are compared to data on photon-nucleus cross sections, nuclear shadowing, and quasi- elastic $ρ$-production. Extrapolations of cross sections and of the shadowing behaviour to high energies are given.

hep-ph↗

arXiv1996

Diffraction dissociation, an important background to photon-photon collisions via heavy ion beams at LHC

The cross sections for the production of hadrons in quasi-real photon-photon collisions in proton-proton and heavy ion interactions are compared with the corresponding cross sections for central diffraction and for photon-pomeron collisions. The signatures, heavy ions or protons with only slightly changed momenta together with two large rapidity gaps and a cluster of produced hadrons in the central region, are nearly identical in all three processes. Therefore, it will be rather difficult to distinguish the reactions experimentally. It is found, that central diffraction is the dominant process in collisions of protons, light and medium-heavy ions. The photon-pomeron and photon-photon processes have quite similar cross sections in collisions of heavy ions like lead.

hep-ph↗

arXiv1996

The production of residual nuclei in peripheral high energy nucleus-nucleus interactions

A formation zone intranuclear cascade model is applied to peripheral nucleus-nucleus collisions. We calculate the excitation energies of prefragments, treat their further nuclear disintegration and introduce a model for nuclear deexcitation by photon emission. Results are compared to data on target associated particle production in nucleus-nucleus collisions. We discuss implications of these models to the description of particle production in the fragmentation regions. Special emphasis is put on applications for air showers induced by cosmic ray nuclei and for residual nucleus production at heavy ion colliders.

nucl-th↗

arXiv1996

Gamma-Gamma Physics at LEP2

This report is an overview of the gamma-gamma physics capabilities of LEP2, and covers the following topics: structure functions, equivalent photon approximation, tagging conditions etc, soft and semihard physics, large-$p_t$ processes, heavy-quark physics, and exclusive channels.

hep-ph↗