Srubabati Goswami

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.

Update of the solar neutrino oscillation analysis with the 766 Ty KamLAND spectrum

Abstract We investigate the impact of the 766.3 Ty KamLAND spectrum data on the determination of the solar neutrino oscillation parameters. We show that the observed spectrum distortion in the KamLAND experiment firmly establishes Δ m 21 2 to lie in the low-LMA solution region. The high-LMA solution is excluded at more than 4σ by the global solar neutrino and KamLAND spectrum data. The maximal solar neutrino mixing is ruled out at 6σ level. The 3σ allowed region in the Δ m 21 2 – sin 2 θ 12 plane is found to be remarkably stable with respect to leaving out the data from one of the solar neutrino experiments from the global analysis. We perform a three flavor neutrino oscillation analysis of the global solar neutrino and KamLAND spectrum data as well. The 3σ upper limit on sin 2 θ 13 is found to be sin 2 θ 13 0.055 . We derive predictions for the CC to NC event rate ratio and day–night (D–N) asymmetry in the CC event rate, measured in the SNO experiment, and for the suppression of the event rate in the BOREXINO and LowNu experiments. Prospective high precision measurements of the solar neutrino oscillation parameters are also discussed.

Implications of the first neutral current data from SNO for solar neutrino oscillation

Abstract We perform model independent and model dependent analyses of solar neutrino data including the neutral current event rate from SNO. The inclusion of the first SNO NC data in the model independent analysis determines the allowed ranges of 8 B flux normalisation and the ν e survival probability more precisely than what was possible from the SK and SNO CC combination. We perform global ν e –ν active oscillation analyses of solar neutrino data using the NC rate instead of the SSM prediction for the 8 B flux, in view of the large uncertainty in the latter. The LMA gives the best solution, while the LOW solution is allowed only at the 3σ level.

Invited review: 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.

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.

Impact of the first SNO results on neutrino mass and mixing

Abstract We investigate the implications of the SNO charged-current (CC) and electron scattering (ES) measurements of solar 8 B neutrino fluxes for neutrino mass and mixing parameters by performing a global and unified χ 2 analysis of the solar neutrino data in the framework of two neutrino mixing. We consider both ν e – ν active and ν e – ν sterile solutions and perform (i) analysis of the total rates data of Cl, Ga, SK and SNO experiments and (ii) global analysis including the total rates data, the recoil electron spectrum data of SK and the CC spectrum observed at SNO. For the ν e – ν active case the inclusion of the SNO results in the analysis of the total rates reduces (enhances) the goodness-of-fit (GOF) of the SMA (LMA) solution. The flat spectrum observed at SK further favours the LMA solution over the SMA solution and no allowed area is obtained in the SMA region at 3 σ level from the global analysis. For the ν e – ν sterile case, with the inclusion of the SNO results, all the solutions are disfavoured with a probability of more than 99% from the total rates analysis while for the global analysis the GOF of these become much worse.

Constraints on neutrino oscillation parameters from the SNO salt phase data

Abstract The physics implications of the just published salt phase data from the SNO experiment are examined. The effect of these data on the allowed ranges of the solar neutrino oscillation parameters, Δ m 21 2 and sin2θ12, are studied in the cases of two- and three-neutrino mixing. In the latter case we derive an upper limit on the angle θ13. Constraints on the solar νe transitions into a mixture of active and sterile neutrinos are also presented. Finally, we give predictions for the day–night asymmetry in the SNO experiment, for the event rate in the BOREXINO and LowNu experiments, and discuss briefly the constraints on the solar neutrino oscillation parameters which can be obtained with prospective KamLAND data.

Testing non-unitarity of neutrino mixing matrices at neutrino factories

In this paper we explore the effect of non-unitary neutrino mixing on neutrino oscillation probabilities both in vacuum and matter. In particular, we consider the νµ ! ν� channel and using a Neutrino Factory as the source for νµ’s discuss the constraints that can be obtained on the moduli and phases of the parameters characterizing the violation of unitarity. We point out how the new CP violation phases present in the case where the non-unitary mixings give rise to spurious “degenerate” solutions in the parameter space and discuss how the true solutions can be extricated by combining measurements at several baselines.

Constraining Neutrino Mass from Neutrinoless Double Beta Decay

We re-analyze the compatibility of the claimed observation of neutrinoless double beta decay (0 ) in 76 Ge with the new limits on the half-life of 136 Xe from EXO-200 and KamLAND-Zen. Including recent calculations of the nuclear matrix elements (NMEs), we show that while the claim in 76 Ge is still compatible with the individual limits from 136 Xe for a few NME calculations, it is inconsistent with the KamLAND-Zen+EXO-200 combined limit for all but one NME. After imposing the most stringent upper limit on the sum of light neutrino masses from Planck, we nd that the canonical light neutrino contribution cannot satisfy the claimed 0 signature or saturate the current limit, irrespective of the NME uncertainties. However, inclusion of the heavy neutrino contributions, arising naturally in TeV-scale Left-Right symmetric models, can saturate the current limit of 0 . In a type-II seesaw framework, this imposes a lower limit on the lightest neutrino mass. Depending on the mass hierarchy, we obtain this limit to be in the range of 0.07 - 4 meV for a typical choice of the right-handed (RH) gauge boson and RH neutrino masses relevant for their collider searches. Using the 0 bounds, we also derive correlated constraints in the RH sector, complimentary to those from the LHC.

Exploring the sensitivity of current and future experiments to

The first results from the KamLAND experiment in conjunction with the global solar neutrino data has demonstrated striking ability to constrain them 2 (�m 2 ) very pre- cisely. However the allowed range of �� (�12) did not change much with the inclusion of the KamLAND results. In this paper we probe if future data from KamLAND can increase the accuracy of the allowed range in �� and conclude that even after 3 kton-year of statistics and most optimistic error estimates, KamLAND may find it hard to significantly improve the bounds on the mixing angle obtained from the solar neutrino data. We discuss the �12 sensitivity of the survival probabilities in matter (vacuum) as is relevant for the solar (Kam- LAND) experiments. We find that the presence of matter effects in the survival probabilities for 8 B neutrinos give the solar neutrino experiments SK and SNO an edge over KamLAND, as far as �12 sensitivity is concerned, particularly near maximal mixing. Among solar neu- trino experiments we identify SNO as the most promising candidate for constraining �12 and make a projected sensitivity test for the mixing angle by reducing the error in the neutral current measurement at SNO. Finally we argue that the most accurate bounds on �12 can be achieved in a reactor experiment, if the corresponding baseline and energy can be tuned to a minimum in the survival probability. We propose a new reactor experiment which can give the value of tan 2 �12 to within 14%. We also discuss the future Borexino and LowNu experiments.