19 research outputs found
The physics impact of proton track identification in future megaton-scale water Cherenkov detectors
In this paper, we investigate the impact in future megaton-scale water
Cherenkov detectors of identifying proton Cherenkov rings. We estimate the
expected event rates for detected neutral current and charged current
quasi-elastic neutrino interactions from atmospheric neutrinos in a
megaton-scale Super-Kamiokande-like detector with both 40% and 20%
photo-cathode coverage. With this sample we examine the prospects for measuring
the neutrino oscillation pattern, and searching for sterile neutrinos. We also
determine the size of selected charged current quasi-elastic samples in a
300-kton fiducial volume Super-Kamiokande-like detector from examples of both
conventional super-beams and beta-beams proposed in the literature. With these
samples, it is shown that full kinematic neutrino reconstruction using the
outgoing proton can improve the reconstructed energy resolution, and give good
neutrino versus anti-neutrino tagging capabilities, adding important
capabilities to water Cherenkov detectors in future projects. We determine the
beam parameters necessary to make use of this technique and present
distributions of neutrino and anti-neutrino selection efficiencies.Comment: 21 pages, 8 figures. Revised version with improved figures, text and
structure, published in JHE
General bounds on non-standard neutrino interactions
We derive model-independent bounds on production and detection non-standard
neutrino interactions (NSI). We find that the constraints for NSI parameters
are around O(10^{-2}) to O(10^{-1}). Furthermore, we review and update the
constraints on matter NSI. We conclude that the bounds on production and
detection NSI are generally one order of magnitude stronger than their matter
counterparts.Comment: 18 pages, revtex4, 1 axodraw figure. Minor changes, matches published
versio
Neutrino Probes of the Nature of Light Dark Matter
Dark matter particles gravitationally trapped inside the Sun may annihilate
into Standard Model particles, producing a flux of neutrinos. The prospects of
detecting these neutrinos in future multi-\kton{} neutrino detectors designed
for other physics searches are explored here. We study the capabilities of a
34/100 \kton{} liquid argon detector and a 100 \kton{} magnetized iron
calorimeter detector. These detectors are expected to determine the energy and
the direction of the incoming neutrino with unprecedented precision allowing
for tests of the dark matter nature at very low dark matter masses, in the
range of 5-50 GeV. By suppressing the atmospheric background with angular cuts,
these techniques would be sensitive to dark matter - nucleon spin dependent
cross sections at the fb level, reaching down to a few ab for the most
favorable annihilation channels and detector technology.Comment: Minor changes and clarifications, matches JCAP versio
Optimized Two-Baseline Beta-Beam Experiment
We propose a realistic Beta-Beam experiment with four source ions and two
baselines for the best possible sensitivity to theta_{13}, CP violation and
mass hierarchy. Neutrinos from 18Ne and 6He with Lorentz boost gamma=350 are
detected in a 500 kton water Cerenkov detector at a distance L=650 km (first
oscillation peak) from the source. Neutrinos from 8B and 8Li are detected in a
50 kton magnetized iron detector at a distance L=7000 km (magic baseline) from
the source. Since the decay ring requires a tilt angle of 34.5 degrees to send
the beam to the magic baseline, the far end of the ring has a maximum depth of
d=2132 m for magnetic field strength of 8.3 T, if one demands that the fraction
of ions that decay along the straight sections of the racetrack geometry decay
ring (called livetime) is 0.3. We alleviate this problem by proposing to trade
reduction of the livetime of the decay ring with the increase in the boost
factor of the ions, such that the number of events at the detector remains
almost the same. This allows to substantially reduce the maximum depth of the
decay ring at the far end, without significantly compromising the sensitivity
of the experiment to the oscillation parameters. We take 8B and 8Li with
gamma=390 and 656 respectively, as these are the largest possible boost factors
possible with the envisaged upgrades of the SPS at CERN. This allows us to
reduce d of the decay ring by a factor of 1.7 for 8.3 T magnetic field.
Increase of magnetic field to 15 T would further reduce d to 738 m only. We
study the sensitivity reach of this two baseline two storage ring Beta-Beam
experiment, and compare it with the corresponding reach of the other proposed
facilities.Comment: 17 pages, 3 eps figures. Minor changes, matches version accepted in
JHE
On the impact of systematical uncertainties for the CP violation measurement in superbeam experiments
Superbeam experiments can, in principle, achieve impressive sensitivities for
CP violation in neutrino oscillations for large . We study how
those sensitivities depend on assumptions about systematical uncertainties. We
focus on the second phase of T2K, the so-called T2HK experiment, and we
explicitly include a near detector in the analysis. Our main result is that
even an idealised near detector cannot remove the dependence on systematical
uncertainties completely. Thus additional information is required. We identify
certain combinations of uncertainties, which are the key to improve the
sensitivity to CP violation, for example the ratio of electron to muon neutrino
cross sections and efficiencies. For uncertainties on this ratio larger than
2%, T2HK is systematics dominated. We briefly discuss how our results apply to
a possible two far detector configuration, called T2KK. We do not find a
significant advantage with respect to the reduction of systematical errors for
the measurement of CP violation for this setup.Comment: 30 pages, 10 figures, version accepted for publication in JHE
Loop bounds on non-standard neutrino interactions
We reconsider the bounds on non-standard neutrino interactions with matter
which can be derived by constraining the four-charged-lepton operators induced
at the loop level. We find that these bounds are model dependent. Naturalness
arguments can lead to much stronger constraints than those presented in
previous studies, while no completely model-independent bounds can be derived.
We will illustrate how large loop-contributions to four-charged-lepton
operators are induced within a particular model that realizes gauge invariant
non-standard interactions and discuss conditions to avoid these bounds. These
considerations mainly affect the constraint on the
non-standard coupling strength \eps_{e\mu}, which is lost. The only
model-independent constraints that can be derived are .
However, significant cancellations are required in order to saturate this
bound.Comment: Minor changes, version to be published in JHEP. 17 pages, 3 Axodraw
figures, REVTeX
Robust Neutrino Constraints by Combining Low Redshift Observations with the CMB
We illustrate how recently improved low-redshift cosmological measurements
can tighten constraints on neutrino properties. In particular we examine the
impact of the assumed cosmological model on the constraints. We first consider
the new HST H0 = 74.2 +/- 3.6 measurement by Riess et al. (2009) and the
sigma8*(Omegam/0.25)^0.41 = 0.832 +/- 0.033 constraint from Rozo et al. (2009)
derived from the SDSS maxBCG Cluster Catalog. In a Lambda CDM model and when
combined with WMAP5 constraints, these low-redshift measurements constrain sum
mnu<0.4 eV at the 95% confidence level. This bound does not relax when allowing
for the running of the spectral index or for primordial tensor perturbations.
When adding also Supernovae and BAO constraints, we obtain a 95% upper limit of
sum mnu<0.3 eV. We test the sensitivity of the neutrino mass constraint to the
assumed expansion history by both allowing a dark energy equation of state
parameter w to vary, and by studying a model with coupling between dark energy
and dark matter, which allows for variation in w, Omegak, and dark coupling
strength xi. When combining CMB, H0, and the SDSS LRG halo power spectrum from
Reid et al. 2009, we find that in this very general model, sum mnu < 0.51 eV
with 95% confidence. If we allow the number of relativistic species Nrel to
vary in a Lambda CDM model with sum mnu = 0, we find Nrel =
3.76^{+0.63}_{-0.68} (^{+1.38}_{-1.21}) for the 68% and 95% confidence
intervals. We also report prior-independent constraints, which are in excellent
agreement with the Bayesian constraints.Comment: 19 pages, 6 figures, submitted to JCAP; v2: accepted version. Added
section on profile likelihood for Nrel, improved plot
Perturbation Theory of Neutrino Oscillation with Nonstandard Neutrino Interactions
We discuss various physics aspects of neutrino oscillation with non-standard
interactions (NSI). We formulate a perturbative framework by taking \Delta
m^2_{21} / \Delta m^2_{31}, s_{13}, and the NSI elements \epsilon_{\alpha
\beta} (\alpha, \beta = e, \mu, \tau) as small expansion parameters of the same
order \epsilon. Within the \epsilon perturbation theory we obtain the S matrix
elements and the neutrino oscillation probability formula to second order
(third order in \nu_e related channels) in \epsilon. The formula allows us to
estimate size of the contribution of any particular NSI element
\epsilon_{\alpha beta} to the oscillation probability in arbitrary channels,
and gives a global bird-eye view of the neutrino oscillation phenomena with
NSI. Based on the second-order formula we discuss how all the conventional
lepton mixing as well as NSI parameters can be determined. Our results shows
that while \theta_{13}, \delta, and the NSI elements in \nu_e sector can in
principle be determined, complete measurement of the NSI parameters in the
\nu_\mu - \nu_\tau sector is not possible by the rate only analysis. The
discussion for parameter determination and the analysis based on the matter
perturbation theory indicate that the parameter degeneracy prevails with the
NSI parameters. In addition, a new solar-atmospheric variable exchange
degeneracy is found. Some general properties of neutrino oscillation with and
without NSI are also illuminated.Comment: manuscript restructured, discussion of new type of parameter
degeneracy added. 47 page
The reconstruction software for the MICE scintillating fibre trackers
The Muon Ionization Cooling Experiment (MICE) will demonstrate the principle of muon beam phase-space reduction via ionization cooling. Muon beam cooling will be required for the proposed Neutrino Factory or Muon Collider. The phase-space before and after the cooling cell must be measured precisely. This is achieved using two scintillating-fibre trackers, each placed in a solenoidal magnetic field. This paper describes the software reconstruction for the fibre trackers: the GEANT4 based simulation; the implementation of the geometry; digitisation; space-point reconstruction; pattern recognition; and the final track fit based on a Kalman filter. The performance of the software is evaluated by means of Monte Carlo studies and the precision of the final track reconstruction is evaluated
, and the neutrino mass hierarchy at a double baseline Li/B -Beam
We consider a -Beam facility where Li and B ions are
accelerated at , accumulated in a 10 Km storage ring and let
decay, so as to produce intense and beams. These beams
illuminate two iron detectors located at Km and
Km, respectively. The physics potential of this setup is analysed in full
detail as a function of the flux. We find that, for the highest flux ( ion decays per year per baseline), the sensitivity to
reaches ; the sign of
the atmospheric mass difference can be identified, regardless of the true
hierarchy, for ; and, CP-violation
can be discovered in 70% of the -parameter space for , having some sensitivity to CP-violation down to
for .Comment: 35 pages, 20 figures. Minor changes, matches the published versio