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H. J. Drescher

Publications and source records attributed to H. J. Drescher.

At least 19 recordsLinked to original sources
arXiv2007

Toward an effective centrality trigger in pp collisions at LHC

We investigate the impact of very strong small x gluon fields in colliding nucleons at LHC energies on the interaction of valence quarks. We find that in the range of small impact parameters, which contribute significantly to the production of heavy new particles, several of the valence quarks receive large transverse momenta, exceeding 1 GeV/c. This results in a suppression of leading baryon production and consequently in an additional energy flow to smaller rapidities. We suggest several triggers for centrality in pp collisions which allow one to study the propagation of partons through gluon fields of a strength comparable to the ones encountered in heavy ion collisions at the LHC.

hep-ph↗
arXiv2007

Remnant Break-up and Muon Production in Cosmic Ray Air Showers

We discuss the relation between remnant fragmentation in inelastic high-energy hadronic interactions and muon production in extensive cosmic ray air showers. Using a newly developed tool, a simple and flexible hadronic event generator, we analyze the forward region of hadronic interactions. We show that measurements of the Feynman-x distribution in the beam fragmentation region at LHCf will be key to understanding muon production in air showers quantitatively.

hep-ph↗
arXiv2005

Air Shower Properties with the Gluon Saturation Model BBL

The hadronic interaction model BBL implements the ideas of gluon saturation due to large densities. When approaching the black body limit at high energies, leading partons acquire large transverse momenta which breaks up their coherence. This leads to a suppression of forward scattering, and is therefore important for air showers. We discuss some general aspects of this new approach and their influence on air shower properties as seen by fluorescence and surface detectors: The position of the shower maximum is reduced due to stronger absorption in the atmosphere. The lateral distribution functions become flatter for the same reason. Muons are produced abundantly due to high multiplicities in the mid-rapidity region. The response of water Cherenkov detectors and comparisons to other interaction models are shown.

astro-ph↗
arXiv2005

High Energy Cosmic Ray Air Showers and small-x QCD

We discuss that hadron-induced atmospheric air showers from ultra-high energy cosmic rays are sensitive to QCD interactions at very small momentum fractions x where nonlinear effects should become important. The leading partons from the projectile acquire large random transverse momenta as they pass through the strong field of the target nucleus, which breaks up their coherence. This leads to a steeper x_F-distribution of leading hadrons as compared to low energy collisions, which in turn reduces the position of the shower maximum Xmax. We argue that high-energy hadronic interaction models should account for this effect, caused by the approach to the black-body limit, which may shift fits of the composition of the cosmic ray spectrum near the GZK cutoff towards lighter elements. We further show that present data on Xmax(E) exclude that the rapid ~ 1/x^0.3 growth of the saturation boundary (which is compatible with RHIC and HERA data) persists up to GZK cutoff energies. Measurements of pA collisions at LHC could further test the small-x regime and advance our understanding of high density QCD significantly.

hep-ph↗
arXiv2004

The QCD Black Disk Limit in Cosmic Ray Air Showers

We discuss particle production in the high energy limit of QCD. Due to a large gluon density, the interaction reaches the black disk limit and the projectile is resolved into its partonic structure at the saturation scale. This leads to suppression of forward particle production and hereby to a faster absorption of cosmic ray air showers. This property is most suitable for the distinction of evolution scenarios for the saturation scale, e.g. fixed and running coupling BFKL, the latter of which is favored by air shower measurements.

astro-ph↗
arXiv2004

Hybrid Simulation of Cosmic Ray Air Showers

Air shower simulations are essential for interpreting data from cosmic ray experiments. At highest energies though, a microscopic treatment of a whole shower is not possible any more, since it would require a huge amount of CPU-time. We review hybrid approaches of air shower simulation which try to overcome this problem without giving rise to artificial fluctuations as generated by the thinning algorithm.

astro-ph↗
arXiv2004

High-density QCD and Cosmic Ray Air Showers

We discuss particle production in the high-energy, small-x limit of QCD where the gluon density of hadrons is expected to become nonperturbatively large. Strong modifications of the phase-space distribution of produced particles as compared to leading-twist models are predicted which reflect in the properties of cosmic ray induced air showers in the atmosphere. Assuming hadronic primaries, our results suggest a light composition near GZK cutoff energies. We also show that cosmic ray data discriminate among various QCD evolution scenarios for the rate of increase of the gluon density at small x, such as fixed-coupling and running-coupling BFKL evolution. There are clear indications for a slower growth of the gluon density as compared to RHIC and HERA, due e.g. to running-coupling effects.

hep-ph↗
arXiv2003

High PT Suppression without Jet Quenching in Au+Au Collisions in NEXUS

Problem of high PT suppression in RHIC data is generally associated to jet quenching in a dense medium. We recently proposed a new approach to high energy nuclear scattering, which treats the initial stage of heavy ion collisions in a sophisticated way, and whose numerical solution is the model NEXUS. Within this model, there is no jet quenching, but the explicit energy conservation leads to similar results. RHIC high PT ratio between AA and pp results can be reproduced for different centrality bins.

hep-ph↗
arXiv2002

New results for hadronic collisions in the framework of the Parton-Based Gribov-Regge Theory

We recently proposed a new approach to high energy nuclear scattering, which treats hadronic collisions in a sophisticated way. Demanding theoretical consistency as a minimal requirement for a realistic model, we provide a solution for the energy conservation, screening problems and identical elementary interactions, the so-called "Parton-Based Gribov-Regge Theory" including enhanced diagrams. We can now present some of our results for SPS and RHIC energies.

hep-ph↗
arXiv2002

The Nexus Model

The interpretation of experimental results at RHIC and in the future also at LHC requires very reliable and realistic models. Considerable effort has been devoted to the development of such models during the past decade, many of them being heavily used in order to analyze data. There are, however, serious inconsistencies in the above-mentioned approaches. In this paper, we will introduce a fully self-consistent formulation of the multiple-scattering scheme in the framework of a Gribov-Regge type effective theory.

hep-ph↗
arXiv2002

A Novel Mechanism of H^0 Di-baryon Production in Proton-Proton Interactions from Parton Based Gribov-Regge Theory

A novel mechanism of H^0 and strangelet production in hadronic interactions within the Gribov-Regge approach is presented. In contrast to traditional distillation approaches, here the production of multiple (strange) quark bags does not require large baryon densities or a QGP. The production cross section increases with center of mass energy. Rapidity and transverse momentum distributions of the H^0 are predicted for pp collisions at E_lab = 160 AGeV (SPS) and \sqrt s = 200 AGeV (RHIC). The predicted total H^0 multiplicities are of order of the Omega-baryon yield and can be accessed by the NA49 and the STAR experiments.

hep-ph↗
arXiv2002

Screening Corrections In Simulating Heavy Ion Collisions

One year ago, we presented a new approach to treat hadronic interactions for the initial stage of nuclear collisions. It is an effective theory based on the Gribov-Regge formalism, where the internal structure of the Pomerons at high energies is governed by perturbative parton evolution, therefore the name "Parton-Based Gribov-Regge Theory". The main improvement compared to models used so-far is the appropriate treatment of the energy sharing between the different elementary interactions in case of multiple scattering. It is clear that the above formalism is not yet complete. At high energies (RHIC, LHC), the multiple elementary interactions (Pomerons) can not be purely parallel, they interact. So we introduce multiple Pomeron vertices into the theory.

hep-ph↗
arXiv2002

Initial Condition for QGP Evolution from NEXUS

We recently proposed a new approach to high energy nuclear scattering, which treats the initial stage of heavy ion collisions in a sophisticated way. We are able to calculate macroscopic quantities like energy density and velocity flow at the end of this initial stage, after the two nuclei having penetrated each other. In other words, we provide the initial conditions for a macroscopic treatment of the second stage of the collision. We address in particular the question of how to incorporate the soft component properly. We find almost perfect "Bjorken scaling": the rapidity coincides with the space-time rapidity, whereas the transverse flow is practically zero. The distribution of the energy density in the transverse plane shows typically a very "bumpy" structure.

hep-ph↗
arXiv2001

Consistent Treatment of Soft and Hard Processes in Hadronic Interactions

The QCD improved parton model is a very successful concept to treat processes in hadronic interactions, whenever large partonic transverse momenta are involved. However, cross sections diverge in the limit p_T -> 0, and the usual treatment is the definition of a lower cutoff p_T_min, such that processes with a smaller p_T -- so-called soft processes -- are simply ignored, which is certainly not correct for example at RHIC energies. A more consistent procedure amounts to introduce a technical parameter Q_0^2, referred to as soft virtuality scale, which is nothing but an artificial borderline between soft and hard physics. We will discuss such a formalism, which coincides with the improved parton model for high p_T processes and with the phenomenological treatment of soft scattering, when only small virtualities are involved. The most important aspect of our approach is that it allows to obtain a smooth transition between soft and hard scattering, and therefore no artificial dependence on a cutoff parameter should appear.

hep-ph↗
arXiv2001

Inconsistencies in Models for RHIC and LHC

The interpretation of experimental results at RHIC and in the future also at LHC requires very reliable and realistic models. Considerable effort has been devoted to the development of such models during the past decade, many of them being heavily used in order to analyze data. It is the purpose of this paper to point out serious inconsistencies in the above-mentioned approaches. We will demonstrate that requiring theoretical self-consistency reduces the freedom in modeling high energy nuclear scattering enormously. We will introduce a fully self-consistent formulation of the multiple-scattering scheme in the framework of a Gribov-Regge type effective theory. In addition, we develop new computational techniques which allow for the first time a satisfactory solution of the problem in the sense that calculations of observable quantities can be done strictly within a self-consistent formalism.

hep-ph↗
arXiv2001

Models for RHIC and LHC: New Developments

We outline inconsistencies in presently used models for high energy nuclear scattering, which make their application quite unreliable. Many "successes" are essentially based on an artificial freedom of parameters, which does not exist when the models are constructed properly. The problem is the fact that any multiple scattering theory requires an appropriate treatment of the energy sharing between the individual interactions, which is technically very difficult to implement. Lacking a satisfying solution to this problem, it has been simply ignored. We introduce a fully self-consistent formulation of the multiple-scattering scheme. Inclusion of soft and hard components - very crucial at high energies - appears in a "natural way", providing a smooth transition from soft to hard physics. We can show that the effect of appropriately considering energy conservation has a big influence on the results, and MUST therefore be included in any serious calculation.

hep-ph↗
arXiv2001

Nuclear Scattering at Very High Energies

We discuss the current understanding of nuclear scattering at very high energies. We point out several serious inconsistencies in nowadays models, which provide big problems for any interpretation of data at high energy nuclear collisions. We outline how to develop a fully self-consistent formalism, which in addition uses all the knowledge available from studying electron-positron annihilation and deep inelastic scattering, providing a solid basis for further developments concerning secondary interactions.

hep-ph↗