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A. Ringwald

Publications and source records attributed to A. Ringwald.

84 records · Page 5Linked to original sources
arXiv1998

Instanton-Induced Cross-Sections in Deep-Inelastic Scattering

We present our results for inclusive instanton-induced cross-sections in deep-inelastic scattering, paying in particular attention to the residual renormalization-scale dependencies. A ``fiducial'' kinematical region in the relevant Bjorken variables is extracted from recent lattice simulations of QCD. The integrated instanton-contribution to the cross-section at HERA corresponding to this fiducial region is surprisingly large: It is in the O(100) pb range, and thus remarkably close to the recently published experimental upper bounds.

hep-ph↗
arXiv1998

QCD-Instantons at HERA

A ``fiducial'' kinematical region for our calculations of instanton (I)-induced processes at HERA within I-perturbation theory is extracted from recent lattice simulations of QCD. Moreover, we present the finalized I-induced cross-sections exhibiting a strongly reduced residual dependence on the renormalization scale.

hep-ph↗
arXiv1996

Instanton-Induced Processes in Deep-Inelastic Scattering

We present a status report of our systematic theoretical and phenomenological study of QCD-instanton induced processes in deep-inelastic scattering. We show that this regime plays a distinguished role for studying manifestations of QCD-instantons, since the typical hard momentum scale $Q$ provides a dynamical infrared cutoff for the instanton size $ρ\lwig O(1/Q)$. For deep-inelastic scattering at HERA, we present a preliminary theoretical estimate of the total instanton-induced cross-section (subject to appropriate kinematical cuts). It is surprisingly large, in the $ O(1-100)$ pb range, albeit still uncertain. We report on our investigation of the discovery potential for instanton-induced events at HERA by means of a Monte Carlo event generator. It is based on a detailed study of the characteristic signatures of the final state, like a large total transverse energy, $E_{T}= O(20)$ GeV, a large multiplicity, $n= O(25)$, and a flavour-democratic production of hadrons. A combination of event shape information with searches of $K^{0}$ mesons, muons, and multiplicity cuts might help to discriminate further the QCD-instanton induced processes from the standard perturbative QCD background.

hep-ph↗
arXiv1996

Instantons in Deep-Inelastic Scattering - The Simplest Process -

Instanton calculations in QCD are generically plagued by infrared divergencies associated with the integration over the instanton size $ρ$. Here, we demonstrate explicitly that the typical inverse hard momentum scale ${\mathcal Q}^{-1}$ in deep-inelastic scattering provides a dynamical infrared cutoff for the size parameter $ρ$. Hence, deep-inelastic scattering may be viewed as a distinguished process for studying manifestations of QCD-instantons. For clarity, we restrict the explicit discussion to the simplest chirality-violating process, $γ^{\ast}+{\rm g}\rightarrow \overline{{\rm q}_{L}}+{\rm q}_{R}$. We calculate the corresponding fixed angle cross-section as well as the contributions to the gluon structure functions, ${\mathcal F}_{2g}$ and ${\mathcal F}_{Lg}$, within standard instanton perturbation theory in leading semi-classical approximation. To this approximation, fixed-angle scattering processes at high $Q^2$ are reliably calculable. In the Bjorken limit, the considered instanton-induced process gives a scaling contribution to ${\mathcal F}_{2g}(x,Q^{2})$ and the Callan-Gross relation holds.

hep-ph↗
arXiv1995

QCD--Instanton Induced Final States in Deep Inelastic Scattering

We report briefly on a broad and systematic study of possible manifestations of QCD-instantons at HERA. We concentrate on the high multiplicity final state structure, reminiscent of an isotropically decaying ``fireball''. First results of a Monte Carlo simulation are presented, with emphasis on the typical event-structure and the transverse energy, muon and $K^0$ flows.

hep-ph↗
arXiv1994

Towards the Phenomenology of QCD-Instanton Induced Particle Production

We present a first status report on a broad and systematic study of possible manifestations of QCD-instantons at HERA. Considerable motivation comes from the close analogy between instanton-induced $B+L$ violation in electroweak processes and effects of QCD-instantons in deep inelastic scattering. We concentrate on the high multiplicity final state structure, reminiscent of an isotropically decaying ``fireball''. A set of experimental isolation criteria is proposed. They serve to further enhance the striking event signature without significantly suppressing the expected rates.

hep-ph↗
arXiv1994

Monte Carlo simulation of baryon and lepton number violating processes at high energies

We report results obtained with the first complete event generator for electroweak baryon and lepton number violating interactions at supercolliders. We find that baryon number violation would be very difficult to establish, but lepton number violation can be seen provided at least a few hundred L violating events are available with good electron or muon identification in the energy range 10 GeV to 1 TeV.

hep-ph↗
arXiv1994

Astrophysical Searches For Exotic Phenomena In Ultrahigh Energy Neutrino-Nucleon Scattering

We investigate the potential of near-future neutrino telescopes like NESTOR for searches for exotic processes in ultrahigh energy neutrino-quark scattering. (NESTOR is the acronym for NEutrinos, from Supernovae and TeV sources, Ocean Range ... a water Cherenkov detector to be constructed in the Mediterranean off the coast of Greece). We consider signatures such as muon bundles and/or contained cascades from the nonperturbative production of multiple weak gauge bosons in the Standard Model, compositeness and leptoquark production.

hep-ph↗
arXiv1993

Phenomenology of Multi-W Processes in Cosmic Rays

We report on a study of the potential of various cosmic ray physics experiments to search for Standard Model processes involving the nonperturbative production of O(30) weak gauge bosons. Whereas present and near-future experiments are insensitive to proton-induced processes, neutrino-induced processes give rise to promising signatures and rates in AMANDA, DUMAND, MACRO and NESTOR provided that a cosmic neutrino flux exists at levels suggested by recent models of active galactic nuclei. The Fly's Eye currently constrains the largest region of parameter space characterizing multi-W phenomena.

hep-ph↗
arXiv1993

Multiple Muons From Neutrino-Initiated Multi-W(Z) Production

Current underground detectors can search for multiple muons from multi-W(Z) production initiated by ultrahigh energy neutrinos from active galactic nuclei. O($μ$b) cross sections give rise to downward going muon bundles whose features differ from those of atmospheric muon bundles.

hep-ph↗
arXiv1993

Cosmic Ray Signatures of Multi-W Processes

We explore the discovery potential of cosmic ray physics experiments for Standard Model processes involving the nonperturbative production of O(30) weak gauge bosons. We demonstrate an experimental insensitivity to proton-induced processes and emphasize the importance of neutrino-induced processes. The Fly's Eye currently constrains the largest region of parameter space characterizing multi-W phenomena if a cosmic neutrino flux exists at levels suggested by recent models of active galactic nuclei. MACRO (DUMAND) can constrain or observe additional regions by searching for 1-100 (1-10) characteristic near-vertical (near-horizontal) spatially compact energetic muon bundles per year.

hep-ph↗