Ina Sarcevic

Ultrahigh-energy neutrino interactions

Abstract Cross sections for the interactions of ultrahigh-energy neutrinos with nucleons are evaluated in the light of new information about nucleon structure functions. For 10 2 eV neutrinos, the cross section is about 2.4 times previous estimates. We also review the cross sections for neutrino interactions with atomic electrons. Some consequences for interaction rates in the Earth and for event rates from generic astrophysical sources in large-scale detectors are noted

Neutrino interactions at ultrahigh energies

We report new calculations of the cross sections for deeply inelastic neutrino-nucleon scattering at neutrino energies between 10{sup 9}thinspeV and 10{sup 21}thinspeV. We compare with results in the literature and assess the reliability of our predictions. For completeness, we briefly review the cross sections for neutrino interactions with atomic electrons, emphasizing the role of the W-boson resonance in {bar {nu}}{sub e}e interactions for neutrino energies in the neighborhood of 6.3 PeV. Adopting model predictions for extraterrestrial neutrino fluxes from active galactic nuclei, gamma-ray bursters, and the collapse of topological defects, we estimate event rates in large-volume water {hacek C}erenkov detectors and large-area ground arrays. {copyright} {ital 1998} {ital The American Physical Society}

Prompt neutrino fluxes from atmospheric charm

We calculate the prompt neutrino flux from atmospheric charm production by cosmic rays, using the dipole picture in a perturbative QCD framework, which incorporates the parton saturation effects present at high energies. We compare our results with the next-to-leading order perturbative QCD result and find that saturation effects are large for neutrino energies above 10^6 GeV, leading to a substantial suppression of the prompt neutrino flux. We comment on the range of prompt neutrino fluxes due to theoretical uncertainties.

Jet quenching in the direction opposite to a tagged photon in high-energy heavy-ion collisions

We point out that events associated with large {ital E}{sub {ital T}} direct photons in high-energy heavy-ion collisions can be used to study jet energy loss in dense matter. In such events, the {ital p}{sub {ital T}} spectrum of charged hadrons from jet fragmentation in the direction opposite to the tagged photon is estimated to be well above the background which can be reliably subtracted at moderately large {ital p}{sub {ital T}}. We demonstrate that comparison between the extracted fragmentation function in {ital AA} and {ital pp} collisions can be used to determine the jet energy loss and the interaction mean free path in the dense matter produced in high-energy heavy-ion collisions. {copyright} {ital 1996 The American Physical Society.}

Propagation of muons and taus at high energies

The photonuclear contribution to charged lepton energy loss has been reevaluated taking into account DESY HERA results on real and virtual photon interactions with nucleons. With large Q{sup 2} processes incorporated, the average muon range in rock for energies of 10{sup 9} GeV is reduced by only 5% compared with the standard treatment. We have calculated the tau energy loss for energies up to 10{sup 9} GeV taking into consideration the decay of tau. A Monte Carlo evaluation of tau survival probability and range shows that at energies below 10{sup 7}--10{sup 8} GeV, depending on the material, only tau decays are important. At higher energies the tau energy losses are significant, reducing the survival probability of the tau. We show that the average range for tau is shorter than its decay length and reduces to 17 km in water for an incident tau energy of 10{sup 9} GeV, as compared with its decay length of 49 km at that energy. In iron, the average tau range is 4.7 km for the same incident energy.

Analysis of multiplicity moments for hadronic multiparticle data

Abstract We show that rapidity-bin factorial moments contain a large combinatoric contribution from two-particle correlations. In addition, the higher-order correlations are nonnegligible and increase with energy. The analysis is completely general and also applies for the case where the moments scale. We find that the linked-pair approximation (LPA) for higher correlations is valid for UA1 and UA5 data, with coefficients that are approximately independent of energy and somewhat smaller than for the negative binomial distribution.

String-gauge dual description of deep inelastic scattering at small-x

The AdS/CFT correspondence in principle gives a new approach to deep inelastic scattering as formulated by Polchinski and Strassler. Subsequently Brower, Polchinski, Strassler and Tan (BPST) computed the strong coupling kernel for the vacuum (or Pomeron) contribution to total cross sections. By identifying deep inelastic scattering with virtual photon total cross section, this allows a self consistent description at small-x where the dominant contribution is the vacuum exchange process. Here we formulate this contribution and compare it with HERA small-x DIS scattering data. We find that the BPST kernel along with a very simple local approximation to the proton and current “wave functions” gives a remarkably good fit not only at large Q2 dominated by conformal symmetry but also extends to small Q2, supplemented by a hard-wall cut-off of the AdS in the IR. We suggest that this is a useful phenomenological parametrization with implications for other diffractive processes, such as double diffractive Higgs production.

Reconciling neutrino flux from heavy dark matter decay and recent events at IceCube

A bstractThe IceCube detector has recently reported the observation of 28 events at previously unexplored energies. While the statistics of the observed events are still low, these events hint at the existence of a neutrino flux over and above the atmospheric neutrino background. We investigate the possibility that a significant component of the additional neutrino flux originates due to the decay of a very heavy dark matter (VHDM) particle via several possible channels into standard model particles. We show that a combination of a power law astrophysical neutrino spectrum and the neutrino flux from the decay of a DM species of mass in the range 150 − 400 TeV improves the fit to the observed neutrino events than that obtained from a best-fit astrophysical flux alone. Assuming the existence of an astrophysical background described by the IC best-fit, we also show that, for the decay of even heavier DM particles (mDM ~ 1 PeV), the same observations impose significant constraints on the decay lifetimes. Allowing the astrophysical flux normalization to vary leads to modifications of these limits, however, there is still a range of dark matter mass and lifetime that is excluded by the IC results.

Lepton fluxes from atmospheric charm

We reexamine the charm contribution to atmospheric lepton fluxes in the context of perturbative QCD. We include next-to-leading order corrections and discuss theoretical uncertainties due to the extrapolations of the gluon distributions at small {ital x}. We show that the charm contribution to the atmospheric muon flux becomes dominant over the conventional contribution from {pi} and {ital K} decays at energies of about 10{sup 5} GeV. We compare our fluxes with previous calculations. {copyright} {ital 1999} {ital The American Physical Society}

Perturbative charm production and the prompt atmospheric neutrino flux in light of RHIC and LHC

A bstractWe re-evaluate the prompt atmospheric neutrino flux, using the measured charm cross sections at RHIC and the Large Hadron Collider to constrain perturbative QCD parameters such as the factorization and renormalization scales, as well as modern parton distribution functions and recent estimates of the cosmic-ray spectra. We find that our result for the prompt neutrino flux is lower than previous perturbative QCD estimates and, consequently, alters the signal-to-background statistics of the recent IceCube measurements at high energies.