Earth Matter Effects at Very Long Baselines and the Neutrino Mass Hierarchy

We study matter effects which arise in the muon neutrino oscillation and survival probabilities relevant to atmospheric neutrino and very long baseline beam experiments. The inter-relations between the three probabilities P_{\mu e}, P_{\mu \tau} and P_{\mu \mu} are examined. It is shown that large and observable sensitivity to the neutrino mass hierarchy can be present in P_{\mu \mu} and P_{\mu \tau}. We emphasize that at baselines of > 7000 Km, matter effects in P_{\mu \tau} can be large under certain conditions. The muon survival rates in experiments with very long baselines thus depend on matter effects in both P_{\mu \tau} and P_{\mu e}. We indicate where these effects are sensitive to \theta_{13}, and identify ranges of E and L where the event rates increase with decreasing \theta_{13}, providing a handle to probe small \theta_{13}. The effect of parameter degeneracies in the three probabilities at these baselines and energies is studied in detail. Realistic event rate calculations are performed for a charge discriminating 100 kT iron calorimeter which demonstrate the possibility of realising the goal of determining the neutrino mass hierarchy using atmospheric neutrinos. It is shown that a careful selection of energy and baseline ranges is necessary in order to obtain a statistically significant signal, and that the effects are largest in bins where matter effects in both P_{\mu e} and P_{\mu \tau} combine constructively. Under these conditions, upto a 4\sigma signal for matter effects is possible (for \Delta_{31}>0) within a timescale appreciably shorter than the one anticipated for neutrino factories.Comment: 40 pages, 27 figures, version to match the published versio

Lowering solar mixing angle in inverted hierarchy without charged lepton corrections

In the present work, the inverted hierarchical neutrino mass model which is characterised by opposite CP parity in the first two mass eigenvalues $(m_1,-m_2,m_3)$, is studied in order to lower the predicted value of solar mixing angle $\tan^2\theta_{12}$, from the tri-bimaximal mixing (TBM), without sacrificing the conditions of maximal atmospheric mixing angle and zero reactor angle. The present attempt is different from the earlier approach where the correction from the charged lepton mass matrix is included in the leptonic mixing matrix to lower the prediction on solar mixing angle. The lowering of the solar mixing angle without charged lepton correction, can be obtained through the variation of the input value of a flavour twister term present in the texture of neutrino mass matrix having a 2-3 symmetry. The present analysis agrees with the latest experimental bounds on neutrino mass parameters and also represents an important result on the survival of the inverted hierarchical neutrino mass models having opposite CP parity in the first two eigenvalues.Comment: 10 pages, two figures. Accepted for publication in Journal of Physics G:Nuclear and Particle Physic

Physics Potential of the ICAL detector at the India-based Neutrino Observatory (INO)

The upcoming 50 kt magnetized iron calorimeter (ICAL) detector at the India-based Neutrino Observatory (INO) is designed to study the atmospheric neutrinos and antineutrinos separately over a wide range of energies and path lengths. The primary focus of this experiment is to explore the Earth matter effects by observing the energy and zenith angle dependence of the atmospheric neutrinos in the multi-GeV range. This study will be crucial to address some of the outstanding issues in neutrino oscillation physics, including the fundamental issue of neutrino mass hierarchy. In this document, we present the physics potential of the detector as obtained from realistic detector simulations. We describe the simulation framework, the neutrino interactions in the detector, and the expected response of the detector to particles traversing it. The ICAL detector can determine the energy and direction of the muons to a high precision, and in addition, its sensitivity to multi-GeV hadrons increases its physics reach substantially. Its charge identification capability, and hence its ability to distinguish neutrinos from antineutrinos, makes it an efficient detector for determining the neutrino mass hierarchy. In this report, we outline the analyses carried out for the determination of neutrino mass hierarchy and precision measurements of atmospheric neutrino mixing parameters at ICAL, and give the expected physics reach of the detector with 10 years of runtime. We also explore the potential of ICAL for probing new physics scenarios like CPT violation and the presence of magnetic monopoles.Comment: 139 pages, Physics White Paper of the ICAL (INO) Collaboration, Contents identical with the version published in Pramana - J. Physic

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