Two-photon production of leptons at hadron colliders in semielastic and elastic cases

The mechanism of two-photon dilepton production is studied in the equivalent-photon (Weizsäcker–Williams) approximation. This approximation is shown to describe well experimental data from hadron accelerators. The respective total and differential cross sections were obtained for the LHC and for the Tevatron collider at various energies of colliding hadrons. The differential cross sections were studied versus the dilepton invariant mass, transverse momentum, and emission angle in the reference frame comoving with the center of mass of colliding hadrons. The cases of semielastic and inelastic collisions were examined.     

Kinematically complete charge exchange experiment in the Cs(+)+Rb collision system using a MOT target

Charge exchange is examined with unprecedented precision using the newly developed magneto-optical trap-target recoil ion momentum spectroscopy (MOTRIMS) technique. Initial and final state selective, charge exchange cross sections are obtained for 6 keV Cs+ colliding with rubidium in 5s and 5p states. For each charge transfer channel, cross sections differential in scattering angle are measured. These data are used to overturn previous long-standing conjecture as to the origin of oscillations seen in total charge exchange cross section measurements, and compare well with an enhanced Demkov model calculation.     

Interactions of heavy stable hadronising particles

In this article, we study the interactions of stable, hadronising new states, arising in certain extensions of the standard model. A simple model, originally intended for stable gluino hadrons, is developed to describe the nuclear interactions of hadrons containing any new colour triplet or octet stable parton. Hadron mass spectra, nuclear scattering cross sections and interaction processes are discussed. Furthermore, an implementation of the interactions of heavy hadrons in GEANT 3 is presented, signatures are studied, and a few remarks about possible detection with the ATLAS experiment are given.Received: 2 April 2004, Published online: 6 August 2004     

Soft multihadron production from partonic structure and fragmentation functions

We describe a two-chain model for soft multiparticle production in hadronic collisions. The model is formulated in a parton framework and is consistent with the dual topological scheme for the Pomeron. The sole inputs are valence quark structure functions in the colliding hadrons and parton fragmentation functions, both of which are known from “hard” processes. Our model, which contains no adjustable parameters, reproduces the shape, the energy dependence, and the normalization of inclusive spectra both in the central region and in the fragmentation region. The model provides a natural explanation for the ratio of πp topp cross sections.     

Fusion and quasifission within the dinuclear system model

The dinuclear system model considers a configuration of two touching nuclei which exchange nucleons. The microscopical justification of the model is presented. The fusion and quasifission processes are described in the reactions of synthesis of heavy and superheavy nuclei. The dependence of evaporation residue cross sections on isotopic composition of colliding nuclei is analyzed. The results agree with the available experimental data.     

Resonant charge exchange in slow collisions involving halogens and oxygen

The coupling of electron momenta is considered for the resonant charge exchange process in slow collisions. Because the electron transfer in this process occurs at large distances between the colliding atomic particles, where ion-atom interactions are relatively weak, we can separate different types of interaction and find the character of coupling of the electron momenta in the quasi-molecule, consisting of the colliding ion and its atom, for real collision pairs. Since the real number of interaction types for colliding particles exceeds that used in the classical Hund coupling scheme, there are intermediate cases of momentum coupling outside the standard Hund scheme. This occurs for the resonant charge exchange involving halogens and oxygen where the quantum numbers of the quasi-molecule in the course of the electron transfer are the total momenta J and j of the colliding ion and atom and the projection M or M_J of the atom orbital or total momentum on the quasi-molecule axis. The ion-atom exchange interaction potential is independent of the ion fine state, and under these conditions, the resonant charge exchange process is not entangled with the rotation of electron momenta, as in case “a” of the Hund coupling. The partial cross section of the resonant charge exchange process depends on quantum numbers of the colliding particles. The average cross sections depend weakly on the coupling scheme.     

Benchmarks for the forward observables at RHIC,the Tevatron-run II,and the LHC

We present predictions on the total cross sections and on the rho parameter for present and future pp and (-)pp colliders, and on total cross sections for gammap-->hadrons at cosmic-ray energies and for gammagamma-->hadrons up to sqrt[s]=1 TeV. These predictions are based on an extensive study of possible analytic parametrizations invoking the largest hadronic dataset available at t=0. The uncertainties on total cross sections reach 1.9% at the Relativistic Heavy Ion Collider, 3.1% at the Tevatron, and 4.8% at the Large Hadron Collider, whereas those on the rho parameter are, respectively, 5.4%, 5.2%, and 5.4%.     

Hadron diffractive processes: the structure of soft pomeron and colour screening

On the basis of the experimental data on diffractive processes in πp, pp and pˉp collisions at intermediate, moderately high and high energies, we restore the scattering amplitude related to the t-channel exchange by vacuum quantum numbers by taking account of the diffractive s-channel rescatterings. At intermediate and moderately high energies, the t-channel exchange amplitude turns, with a good accuracy, into an effective pomeron which renders the results of the additive quark model. At superhigh energies the scattering amplitude provides a Froissart-type behaviour, with an asymptotic universality of cross sections such as σ^tot _πp/σ^tot _pp→ 1 at s→∞. The quark structure of hadrons being taken into account at the level of constituent quarks, the cross sections of pion and proton (antiproton) in the impact parameter space of quarks, σ_π(r _1⊥, r _2⊥; s) and σ_p(r _1⊥, r _2⊥, r _3⊥; s), are found as functions of s. These cross sections implicate the phenomenon of colour screening: they tend to zero at |r _i⊥−r _k⊥|→ 0. The effective colour screening radius for pion (proton) is found for different s. The predictions for the diffractive cross sections at superhigh energies are presented. Received: 15 December 1998     

Semihard hadron processes and the quark-gluon string model

A new approach to the analysis of soft and semihard hadron processes is suggested. In the framework of the Quark-Gluon String Model, the interaction of quarks from colliding hadrons is calculated as the exchange by nonperturbative gluons, for which the cut-off parameter in the gluonic propagator is included. This modification has allowed us to analyse the inclusive hadron spectra in hadron collisions at transverse momenta up to 3–4 GeV/c.     

Resonant charge exchange with the p-electron transition

The asymptotic resonant charge exchange theory is developed for slow collisions of atoms and ions with valent p-electrons. Because of a small rotation angle of the molecular axis in the course of the p-electron transition, the resonant charge exchange cross section is not sensitive to the rotational energy of colliding particles, and the cross sections are nearly equal for cases “a”, “b”, and “d” of the Hund coupling, and also for cases “c” and “e” of the Hund coupling. The cross sections of the resonant charge exchange process are evaluated under various conditions and for various elements of the periodical table with p-electron shells of atoms and ions.     

EMC effect and breaking of additivity of nucleons in the high-energy hadron-nucleus interactions

The EMC effect implies a strong violation of additivity of nucleons in the absorption of virtual photons by atomic nuclei. In this paper we analyze the experimental data on the hadron-nuclei interaction cross sections in search for similar effects in the scattering of hadrons on nuclei. Specifically, we look for deviations from predictions of the multiple scattering theory. We formulate, and make extensive use of the Glauber-Bribov universality of the hadron-nucleus interaction cross sections, which makes it possible to check in a unique way a consistency of the experimental data on the total, inelastic and absorption cross sections for all the incident hadrons. We find evidence for the effective cross section of interaction with bound nucleons being 5–15% larger than with free nucleons. We comment on implications of this observation for models of the EMC effect.     

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.     

Hadron scattering in an additive eikonal quark model

Total and differential cross sections for p?p, pp, π^±p, K^+-p and Ψp at high energies are analysed in an additive eikonal quark model. It is shown that the exceptionally small Ψp slope contradicts the Chou-Yang model at present energies but can be accounted for by a quark-quark potential with different ranges for different pairs of quarks. This leads to smaller rms radii for hadrons than those derived from e.m. formfactors, implying that the constituent quarks have formfactors. Predictions for hadron-neutron and strange and charmed hadron-nucleon scattering are derived.     

Meson exchange interactions at low and intermediate energies: colour screening effects

We consider the colour screening effects of constituent quarks and the exchange of effective gluons in the interaction of hadrons. To this end we propose two different processes derived from fundamental properties of the underlying microscopic theory (QCD). Sum rules for diagrams providing colour screening are also given.     

On the hadron-parton reciprocity relation

The possibility of an equality between the distributions of partons inside hadrons and the distributions of hadrons in parton fragmentation is studied. It is consistent with existing electroproduction data when the momentum fractions involved are not too small. Implications for current-hadron interactions, large p_T hadronic cross sections and heavy lepton pair production in hadron-hadron collisons are discussed.     

Charge exchange of a polar molecule at its cation

The Landau-Herring method is used to derive an analytic expression for the one-electron exchange interaction of a polar molecule with its positively charged ion, induced by a σ-electron. Analogously to the classical Van der Pole method, the exchange interaction potential is averaged over the rotational states of colliding particles. The resonant charge-transfer cross section is calculated, and the effect of the dipole moments of the core on the cross section is analyzed. It is shown that allowance for the dependence of the exchange potential on the orientation of the dipole moments relative to the molecular axis may change the dependence of the cross section on the velocity of colliding particles, which is typical of the resonant charge exchange, from the resonance to the quasi-resonance dependence.     

Ionization of heavy ions in collisions with neutral atoms at relativistic energies

Ionization processes of heavy ions colliding with atoms and ions at relativistic energies are considered. Formulaes for calculating ionization cross sections in the Born approximation using momentum-transfer representation without regard to magnetic interactions are given as well as those in dipole and impulse approximations. Using the LOSS-R [25] and HERION codes, calculations of relativistic cross sections are performed for H-like multiply changed ions with the nuclear charge Z ≈ 80?90, colliding with neutral atoms and for multiply changed uranium ions colliding with protons and carbon atoms. The results of calculations are compared with available experimental data and calculations performed by other authors.     

The interaction and fusion of arbitrarily oriented deformed nuclei

The fusion/capture cross sections between various deformed nuclei are calculated. It is shown that quadrupole and hexadecapole deformations of heavy nuclei are important for evaluating the barrier height, capture well depth, and fusion/capture cross sections of heavy nuclei. It is found that calculations of the capture cross section of two heavy deformed nuclei must be performed with averaging over all possible mutual orientations of the colliding nuclei.