Proton–nucleus (p+A) collisions have long been recognized as a crucial component of the physics program with nuclear beams at high energies, in particular for their reference role to interpret and understand nucleus–nucleus data as well as for their potential to elucidate the partonic structure of matter at low parton fractional momenta (small-x). Here, we summarize the main motivations that make a proton–nucleus run a decisive ingredient for a successful heavy-ion program at the Large Hadron Collider (LHC) and we present unique scientific opportunities arising from these collisions. We also review the status of ongoing discussions about operation plans for the p+A mode at the LHC.

/pdf/proton-nucleus-collisions-at-the-lhc-scientific-3z8tkguwkn.pdf

Proton–nucleus collisions at the LHC: scientific opportunities and requirements

A hybrid simulation code is developed that is suited for fast one-dimensional simulations of shower profiles, including fluctuations It combines the Monte Carlo simulation of high energy interactions with a fast numerical solution of cascade equations for the resulting distributions of secondary particles Results obtained with this new code, called conex, are presented and compared to corsika predictions

First results of fast one-dimensional hybrid simulation of EAS using CONEX

The model dependence of the development of extensive air showers generated by high-energy cosmic-ray particles in the atmosphere is studied. The increase of proton-proton and proton-air inelastic cross sections and valuesfor the elasticity are varied in the hadronic interaction model QGSJET. Using the CORSIKA simulation program, the impact of these changes is investigated on air shower observables such as the average depth of the shower maximum X m a x and the number of muons and electrons at ground level. Calculating the mean logarithmic mass from experimental X m a x values, it is found that a moderate logarithmic increase of the proton-proton inelastic cross section from σ p p inel = 51 mb at E 0 = 10 6 GeV to σ p p inel = 64 mb at E 0 = 10 8 GeV, and an elasticity, additionally increased by 10%-15%, describe the data best. Using these parameters, the mean logarithmic mass derived from X m a x measurements is compatible with the extrapolations of the results of direct measurements to high energies using the poly-gonato model.

/pdf/on-total-inelastic-cross-sections-and-the-average-depth-of-49ftit2ftj.pdf

On total inelastic cross sections and the average depth of the maximum of extensive air showers

A new hybrid approach to air shower simulations is described. At highest energies, each particle is followed individually using the traditional Monte Carlo method; this initializes a system of cascade equations which are applicable for energies such that the shower is one dimensional. The cascade equations are solved numerically down to energies at which lateral spreading becomes significant; then, their output serves as a source function for a three-dimensional Monte Carlo simulation of the final stage of the shower. This simulation procedure reproduces the natural fluctuations in the initial stages of the shower, gives accurate lateral distribution functions, and provides detailed information about all low energy particles on an event-by-event basis. It is quite efficient in computation time.

http://export.arxiv.org/pdf/astro-ph/0212018

Air shower simulations in a hybrid approach using cascade equations

http://people.na.infn.it/~pmiglioz/AcademicTraining/BiblioCosmicRay/EAS_phenomenology.pdf

High energy physics in the atmosphere: phenomenology of cosmic ray air showers

The purpose of this paper is twofold: first we want to introduce a new type of hadronic interaction model (NEXUS), which has a much more solid theoretical basis than, for example, presently used models such as QGSJET and VENUS, and ensures therefore a much more reliable extrapolation towards high energies. Secondly, we want to promote an extensive air shower (EAS) calculation scheme, based on cascade equations rather than explicit Monte Carlo simulations, which is very accurate in calculations of main EAS characteristics and extremely fast concerning computing time. We employ the NEXUS model to provide the necessary data on particle production in hadron-air collisions and present the average EAS characteristics for energies ${10}^{14}\ensuremath{-}{10}^{17}$ eV. The experimental data of the CASA-BLANCA group are analyzed in the framework of the new model.

G. Bossard

Papers

Cosmic ray air shower characteristics in the framework of the parton-based Gribov-Regge model NEXUS