Raj Gandhi

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}

Physics at a future Neutrino Factory and super-beam facility

The conclusions of the Physics Working Group of the International Scoping Study of a future Neutrino Factory and super-beam facility (the ISS) are presented. The ISS was carried out by the international community between NuFact05, (the 7th International Workshop on Neutrino Factories and Super-beams, Laboratori Nazionali di Frascati, Rome, 21–26 June 2005) and NuFact06 (Ivine, CA, 24–30 August 2006). The physics case for an extensive experimental programme to understand the properties of the neutrino is presented and the role of high-precision measurements of neutrino oscillations within this programme is discussed in detail. The performance of second-generation super-beam experiments, beta-beam facilities and the Neutrino Factory are evaluated and a quantitative comparison of the discovery potential of the three classes of facility is presented. High-precision studies of the properties of the muon are complementary to the study of neutrino oscillations. The Neutrino Factory has the potential to provide extremely intense muon beams and the physics potential of such beams is discussed in the final section of the report.The conclusions of the Physics Working Group of the International Scoping Study of a future Neutrino Factory and super-beam facility (the ISS) are presented. The ISS was carried out by the international community between NuFact05, (the 7th International Workshop on Neutrino Factories and Superbeams, Laboratori Nazionali di Frascati, Rome, June 21-26, 2005) and NuFact06 (Irvine, California, 2430 August 2006). The physics case for an extensive experimental programme to understand the properties of the neutrino is presented and the role of high-precision measurements of neutrino oscillations within this programme is discussed in detail. The performance of second generation super-beam experiments, beta-beam facilities, and the Neutrino Factory are evaluated and a quantitative comparison of the discovery potential of the three classes of facility is presented. High-precision studies of the properties of the muon are complementary to the study of neutrino oscillations. The Neutrino Factory has the potential to provide extremely intense muon beams and the physics potential of such beams is discussed in the final section of the report. The ISS Physics Working Group Editors: S.F. King1, K. Long2, Y. Nagashima3, B.L. Roberts4, and O. Yasuda5.

Mass Hierarchy Determination via future Atmospheric Neutrino Detectors

We study the problem of determination of the sign of {delta}m{sub 31}{sup 2}, or the neutrino mass hierarchy, through observations of atmospheric neutrinos in future detectors. We consider two proposed detector types: (a) Megaton sized water Cerenkov detectors, which can measure the event rates of {nu}{sub {mu}}+{nu}{sub {mu}} and {nu}{sub e}+{nu}{sub e} and (b) 100 kton sized magnetized iron detectors, which can measure the event rates of {nu}{sub {mu}} and {nu}{sub {mu}}. For energies and path lengths relevant to atmospheric neutrinos, these rates obtain significant matter contributions from P{sub {mu}}{sub e}, P{sub {mu}}{sub {mu}} and P{sub ee}, leading to an appreciable sensitivity to the hierarchy. We do a binned {chi}{sup 2} analysis of simulated data in these two types of detectors which includes the effect of smearing in neutrino energy and direction and incorporates detector efficiencies and relevant statistical, theoretical and systematic errors. We also marginalize the {chi}{sup 2} over the allowed ranges of neutrino parameters in order to accurately account for their uncertainties. Finally, we compare the performance of both types of detectors vis a vis the hierarchy determination.

Neutrino Mass Hierarchy and Octant Determination with Atmospheric Neutrinos

The recent discovery by the Daya-Bay and RENO experiments, that θ(13) is nonzero and relatively large, significantly impacts existing experiments and the planning of future facilities. In many scenarios, the nonzero value of θ(13) implies that θ(23) is likely to be different from π/4. Additionally, large detectors will be sensitive to matter effects on the oscillations of atmospheric neutrinos, making it possible to determine the neutrino mass hierarchy and the octant of θ(23). We show that a 50 kT magnetized liquid argon neutrino detector can ascertain the mass hierarchy with a significance larger than 4σ with moderate exposure times, and the octant at the level of 2-3σ with greater exposure.

Massive Dirac neutrinos and the SN1987A signal

Abstract We present results of calculations which incorporate the effect of massive Dirac neutrinos in numerical models for the cooling of the neutron star associated with SN1987A. In the Weinberg-Salam standard model, minimally extended to include Dirac neutrino masses, the production of sterile (positive helicity) neutrinos via neutral-current neutrino-nucleon scattering proceeds at a rate that significantly affects the energetics of cooling. We determine the expected number of events, total energy in neutrinos and the burst duration for both Kamiokande II and Irvine-Michigan-Brookhaven detectors. Due to an increase in the cooling rate caused by sterile neutrinos, we find that for m ν μ,τ = m ν μ 2 +m ν τ 2 ⩾14 keV , the expected neutrino burst is shortened to a duration that is inconsistent with the observations reported by both detectors. The calculations incorporate the feedback effects of the cooling due to sterile neutrinos in a self-consistent manner and the mass limit obtained is found to be largely insensitive to the equation of state used.

Resolving the mass hierarchy with atmospheric neutrinos using a liquid argon detector

We explore the potential offered by large-mass liquid argon detectors for determination of the sign of {delta}m{sub 31}{sup 2}, or the neutrino mass hierarchy, through interactions of atmospheric neutrinos. We give results for a 100 kT sized magnetized detector which provides separate sensitivity to {nu}{sub {mu}}, {nu}{sub {mu}} and, over a limited energy range, to {nu}{sub e}, {nu}{sub e}. We also discuss the sensitivity for the unmagnetized version of such a detector. After including the effect of smearing in neutrino energy and direction and incorporating the relevant statistical, theoretical, and systematic errors, we perform a binned {chi}{sup 2} analysis of simulated data. The {chi}{sup 2} is marginalized over the presently allowed ranges of neutrino parameters and determined as a function of {theta}{sub 13}. We find that such a detector offers superior capabilities for hierarchy resolution, allowing a >4{sigma} determination for a 100 kT detector over a 10-year running period for values of sin{sup 2}2{theta}{sub 13}{>=}0.05. For an unmagnetized detector, a 2.5{sigma} hierarchy sensitivity is possible for sin{sup 2}2{theta}{sub 13}=0.04.

Atmospheric neutrinos as a probe of CPT and Lorentz violation

Abstract We show that atmospheric neutrinos can provide a sensitive and robust probe of CPT violation (CPTV). We perform realistic event-rate calculations and study the variations of the ratio of total muon to antimuon survival rates with L / E and L ( L ≡ baseline length, E ≡ neutrino energy) in a detector capable of identifying the muon charge. We demonstrate that measurements of these ratios when coupled with the significant L and E range which characterizes the atmospheric neutrino spectrum provides a method of both detecting the presence of such violations and putting bounds on them which compare very favorably with those possible from a future neutrino factory.

Testing nonstandard neutrino matter interactions in atmospheric neutrino propagation

We study the eects of non-standard interactions on the oscillation pattern of atmospheric neutrinos. We use neutrino oscillograms as our main tool to infer the role of non-standard interactions (NSI) parameters at the probability level in the energy range, E 2 [1; 20] GeV and zenith angle range, cos 2 [ 1; 0]. We compute the event rates for atmospheric neutrino events in presence of NSI parameters in the energy range E2 [1; 10] GeV for two dierent detector congurations - a magnetized iron calorimeter and an unmagnetized liquid

Large matter effects in nu(mu) ---> nu(tau) oscillations

We show that matter effects change the numu-->nutau oscillation probability by as much as 70% for certain ranges of energies and path lengths. Consequently, the numu-->nutau survival probability also undergoes large changes. A proper understanding of numu survival rates must consider matter effects in Pmutau as well as Pmue. We comment on (a) how these matter effects may be observed and the sign of Delta31 determined in atmospheric neutrino measurements and at neutrino factories, and (b) how they lead to heightened sensitivity for small theta13.