Dynamics of diffractive dissociation

We describe a QCD based model which incorporates the main properties of the inclusive particle distributions expected for diffractive processes, including the diffractive dissociation at high energies. We study, in turn, the total cross section, $$\sigma _\mathrm{tot}$$ σ tot , the differential elastic, $$d\sigma _\mathrm{el}/dt$$ d σ el / d t , cross section, the dependence of the single proton dissociation cross section, $$\xi d\sigma ^\mathrm{SD}/d\xi $$ ξ d σ SD / d ξ , on the momentum fraction, $$\xi =1-x_L$$ ξ = 1 - x L , lost by the leading proton, the multiplicity distributions in inelastic (non-diffractive) collisions and in the processes of dissociation. Besides this we calculate the mean transverse momenta of the ‘wee partons’ (secondaries) produced in the case of dissociation (that is in the processes with a large rapidity gap) and compare it with that in inelastic interactions.

A new approach to modelling elastic and inelastic photon-initiated production at the LHC: SuperChic 4

We present the results of the new Monte Carlo implementation of photon-initiated production in proton–proton collisions, considering as a first example the case of lepton pair production. This is based on the structure function calculation of the underlying process, and focusses on a complete account of the various contributing channels, including the case where a rapidity gap veto is imposed. We provide a careful treatment of the contributions where either (single dissociation), both (double dissociation) or neither (elastic) proton interacts inelastically and dissociates, and interface our results to for showering and hadronization. The particle decay distribution from dissociation system, as well the survival probability for no additional proton–proton interactions, are both fully accounted for; these are essential for comparing to data where a rapidity gap veto is applied. We present detailed results for the impact of the veto requirement on the differential cross section, compare to and find good agreement with ATLAS 7 TeV data on semi-exclusive production, and provide a new precise evaluation of the background from semi-exclusive lepton pair production to SUSY particle production in compressed mass scenarios, which is found to be low.

Evidence of forward–backward multiplicity correlation at SPS energy

In this paper, a detailed study of two-particle rapidity correlation has been presented by measuring the dynamical fluctuation variable [Formula: see text] in forward and backward pseudo-rapidity window of shower particles produced in the relativistic heavy ion collision, [Formula: see text]O–AgBr interactions at 60[Formula: see text]AGeV and [Formula: see text]S–AgBr interactions at 200[Formula: see text]AGeV. Variations of [Formula: see text] with rapidity gap between forward and backward zones and with the width of each zone have been studied. For both cases, [Formula: see text] increase with increasing either width of the zone or gap between the zones. Our findings show the presence of strong long-range correlation. Comparison of experimental results with MC-RAND events confirms the present correlation to be dynamical in nature. We have also compared our results with FRITIOF and UrQMD events. Such events also show the presence of correlation, but found to fail to reproduce the experimental results both quantitatively and qualitatively. Strength of correlation is dependent on the centrality of collision for experimental events, it decreases with centrality.