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Register a new userExceptional Sensitivity to Neutrino Parameters with a Two Baseline Beta-Beam Set-up
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We examine the reach of a Beta-beam experiment with two detectors at carefully chosen baselines for exploring neutrino mass parameters. Locating the source at CERN, the two detectors and baselines are: (a) a 50 kton iron calorimeter (ICAL) at a baseline of around 7150 km which is roughly the magic baseline, e.g., ICAL@INO, and (b) a 50 kton Totally Active Scintillator Detector at a distance of 730 km, e.g., at Gran Sasso. We choose 8B/8Li source ions with a boost factor gamma of 650 for the magic baseline while for the closer detector we consider 18Ne/6He ions with a range of Lorentz boosts. We find that the locations of the two detectors complement each other leading to an exceptional high sensitivity. With gamma=650 for 8B/8Li and gamma=575 for 18Ne/6He and total luminosity corresponding to 5times (1.1 times 10^{18}) and 5times (2.9times 10^{18}) useful ion decays in neutrino and antineutrino modes respectively, we find that our two detector set-up can probe maximal CP violation and establish the neutrino mass ordering if sin^22theta_{13} is 1.4times 10^{-4} and 2.7times 10^{-4}, respectively, or more. The sensitivity reach for sin^22theta_{13} itself is 5.5 times 10^{-4}. With a factor of 10 higher luminosity, the corresponding sin^22theta_{13} reach of this set-up would be 1.8times 10^{-5}, 4.6times 10^{-5} and 5.3times 10^{-5} respectively for the above three performance indicators. CP violation can be discovered for 64% of the possible delta_{CP} values for sin^22theta_{13} geq 10^{-3} (geq 8times 10^{-5}), for the standard luminosity (10 times enhanced luminosity). Comparable physics performance can be achieved in a set-up where data from CERN to INO@ICAL is combined with that from CERN to the Boulby mine in United Kingdom, a baseline of 1050 km.
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In order to address some fundamental questions in neutrino physics a wide, future programme of neutrino oscillation experiments is currently under discussion. Among those, long baseline experiments will play a crucial role in providing information on the value of theta13, the type of neutrino mass ordering and on the value of the CP-violating phase delta, which enters in 3-neutrino oscillations. Here, we consider a beta-beam setup with an intermediate Lorentz factor gamma=450 and a baseline of 1050 km. This could be achieved in Europe with a beta-beam sourced at CERN to a detector located at the Boulby mine in the United Kingdom. We analyse the physics potential of this setup in detail and study two different exposures (1 x 10^{21} and 5 x 10^{21} ions-kton-years). In both cases, we find that the type of neutrino mass hierarchy could be determined at 99% CL, for all values of delta, for sin^2(2 theta13) > 0.03. In the high-exposure scenario, we find that the value of the CP-violating phase delta could be measured with a 99% CL error of ~20 deg if sin^2 (2 theta13) > 10^{-3}, with some sensitivity down to values of sin^2(2 theta13) ~ 10^{-4}. The ability to determine the octant of theta23 is also studied, and good prospects are found for the high-statistics scenario.
Neutrino beam with about 300 MeV in energy, high-flux and medium baseline is considered a rational choice for measuring CP violation before the more powerful Neutrino Factory will be built. Following this concept, a unique neutrino beam facility based on muon-decayed neutrinos is proposed. The facility adopts a continuous-wave proton linac of 1.5 GeV and 10 mA as the proton driver, which can deliver an extremely high beam power of 15 MW. Instead of pion-decayed neutrinos, unprecedentedly intense muon-decayed neutrinos are used for better background discrimination. The schematic design for the facility is presented here, including the proton driver, the assembly of a mercury-jet target and capture superconducting solenoids, a pion/muon beam transport line, a long muon decay channel of about 600 m and the detector concept. The physics prospects and the technical challenges are also discussed.
A Beta-beam would be a high intensity source of pure $ u_e$ and/or $bar u_e$ flux with known spectrum, ideal for precision measurements. Myriad of possible set-ups with suitable choices of baselines, detectors and the beta-beam neutrino source with desired energies have been put forth in the literature. In this talk we present a comparitive discussion of the physics reach of a few such experimental set-ups.
One of the unknown parameters in neutrino oscillations is the octant of the mixing angle theta_{23}. In this paper, we discuss the possibility of determining the octant of theta_{23} in the long baseline experiments T2K and NOvA in conjunction with future atmospheric neutrino detectors, in light of non-zero value of theta_{13} measured by reactor experiments. We consider two detector technologies for atmospheric neutrinos - magnetized iron calorimeter and non-magnetized Liquid Argon Time Projection Chamber. We present the octant sensitivity for T2K/NOvA and atmospheric neutrino experiments separately as well as combined. For the long baseline experiments, a precise measurement of theta_{13}, which can exclude degenerate solutions in the wrong octant, increases the sensitivity drastically. For theta_{23} = 39^o and sin^2 2 theta_{13} = 0.1, at least ~2 sigma sensitivity can be achieved by T2K+NOvA for all values of delta_{CP} for both normal and inverted hierarchy. For atmospheric neutrinos, the moderately large value of theta_{13} measured in the reactor experiments is conducive to octant sensitivity because of enhanced matter effects. A magnetized iron detector can give a 2 sigma octant sensitivity for 500 kT yr exposure for theta_{23} = 39^o, delta_{CP} = 0 and normal hierarchy. This increases to 3 sigma for both hierarchies by combining with T2K+NOvA. This is due to a preference of different theta_{23} values at the minimum chi^2 by T2K/NOvA and atmospheric neutrino experiments. A Liquid Argon detector for atmospheric neutrinos with the same exposure can give higher octant sensitivity, due to the interplay of muon and electron contributions and superior resolutions. We obtain a ~3 sigma sensitivity for theta_{23} = 39^o for normal hierarchy. This increases to > ~4 sigma for all values of delta_{CP} if combined with T2K+NOvA. For inverted hierarchy the combined sensitivity is ~3 sigma.
Recent global fits to short-baseline neutrino oscillation data have been performed finding preference for a sterile neutrino solution (3+1) over null. In the most recent iteration, it was pointed out that an unstable sterile neutrino (3+1+decay) may be a better description of the data. This is due to the fact that this model significantly reduces the tension between appearance and disappearance datasets. In this work, we add a one-year IceCube dataset to the global fit obtaining new results for the standard 3+1 and 3+1+decay sterile neutrino scenarios. We find that the 3+1+decay model provides a better fit than the 3+1, even in the presence of IceCube, with reduced appearance to disappearance tension. The 3+1+decay model is a 5.4$sigma$ improvement over the null hypothesis and a 2.8$sigma$ improvement over the standard 3+1 model.
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