126 research outputs found
Seismic Coupling of Short-Period Wind Noise Through Marsâ Regolith for NASAâs InSight Lander
NASAâs InSight lander will deploy a tripod-mounted seismometer package onto the surface of Mars in late 2018. Mars is expected to have lower seismic activity than the Earth, so minimisation of environmental seismic noise will be critical for maximising observations of seismicity and scientific return from the mission. Therefore, the seismometers will be protected by a Wind and Thermal Shield (WTS), also mounted on a tripod. Nevertheless, wind impinging on the WTS will cause vibration noise, which will be transmitted to the seismometers through the regolith (soil). Here we use a 1:1-scale model of the seismometer and WTS, combined with field testing at two analogue sites in Iceland, to determine the transfer coefficient between the two tripods and quantify the proportion of WTS vibration noise transmitted through the regolith to the seismometers. The analogue sites had median grain sizes in the range 0.3â1.0 mm, surface densities of 1.3â1.8gcmâ3, and an effective regolith Youngâs modulus of 2.5â1.4+1.9MPa. At a seismic frequency of 5 Hz the measured transfer coefficients had values of 0.02â0.04 for the vertical component and 0.01â0.02 for the horizontal component. These values are 3â6 times lower than predicted by elastic theory and imply that at short periods the regolith displays significant anelastic behaviour. This will result in reduced short-period wind noise and increased signal-to-noise. We predict the noise induced by turbulent aerodynamic lift on the WTS at 5 Hz to be âŒ2Ă10â10msâ2Hzâ1/2 with a factor of 10 uncertainty. This is at least an order of magnitude lower than the InSight short-period seismometer noise floor of 10â8msâ2Hzâ1/2
Evolution of the Far-infrared Cloud at Titan's South Pole
A condensate cloud on Titan identified by its 220 cm (sup -1) far-infrared signature continues to undergo seasonal changes at both the north and south poles. In the north the cloud, which extends from 55 North to the pole, has been gradually decreasing in emission intensity since the beginning of the Cassini mission with a half-life of 3.8 years. The cloud in the south did not appear until 2012 but its intensity has increased rapidly, doubling every year. The shape of the cloud at the South Pole is very different from that in the north. Mapping in December 2013 showed that the condensate emission was confined to a ring with a maximum at 80 South. The ring was centered 4 degrees from Titan's pole. The pattern of emission from stratospheric trace gases like nitriles and complex hydrocarbons (mapped in January 2014) was also offset by 4 degrees, but had a central peak at the pole and a secondary maximum in a ring at about 70 South with a minimum at 80 South. The shape of the gas emissions distribution can be explained by abundances that are high at the atmospheric pole and diminish toward the equator, combined with correspondingly increasing temperatures. We discuss possible causes for the condensate ring. The present rapid build up of the condensate cloud at the South Pole is likely to transition to a gradual decline during 2015-16
Proposal for an Extended Run of T2K to POT
68 pages, 31 figures68 pages, 31 figures68 pages, 31 figuresRecent measurements by the T2K neutrino oscillation experiment indicate that CP violation in neutrino mixing may be observed in the future by long-baseline neutrino oscillation experiments. We propose an extension to the currently approved T2K running from 7.8\times 10^{21}~\mbox{POT} to 20\times 10^{21}~\mbox{POT}, aiming at initial observation of CP violation with 3 or higher significance for the case of maximum CP violation. The program also contains a measurement of mixing parameters, and , with a precision of 1.7 or better and 1%, respectively. With accelerator and beamline upgrades, as well as analysis improvements, this program would occur before the next generation of long-baseline neutrino oscillation experiments that are expected to start operation in 2026
Search for electron antineutrino appearance in a long-baseline muon antineutrino beam
Electron antineutrino appearance is measured by the T2K experiment in an accelerator-produced antineutrino beam, using additional neutrino beam operation to constrain parameters of the Pontecorvo-Maki-Nakagawa-Sakata (PMNS) mixing matrix. T2K observes 15 candidate electron antineutrino events with a background expectation of 9.3 events. Including information from the kinematic distribution of observed events, the hypothesis of no electron antineutrino appearance is disfavored with a significance of 2.40Ï and no discrepancy between data and PMNS predictions is found. A complementary analysis that introduces an additional free parameter which allows non-PMNS values of electron neutrino and antineutrino appearance also finds no discrepancy between data and PMNS predictions
Supernova neutrino burst detection with the Deep Underground Neutrino Experiment
The Deep Underground Neutrino Experiment (DUNE), a 40-kton underground liquid argon time projection chamber experiment, will be sensitive to the electron-neutrino flavor component of the burst of neutrinos expected from the next Galactic core-collapse supernova. Such an observation will bring unique insight into the astrophysics of core collapse as well as into the properties of neutrinos. The general capabilities of DUNE for neutrino detection in the relevant few- to few-tens-of-MeV neutrino energy range will be described. As an example, DUNE's ability to constrain the Îœe spectral parameters of the neutrino burst will be considered
Characterization of nuclear effects in muon-neutrino scattering on hydrocarbon with a measurement of final-state kinematics and correlations in charged-current pionless interactions at T2K
This paper reports measurements of final-state proton multiplicity, muon and proton kinematics, and
their correlations in charged-current pionless neutrino interactions, measured by the T2K ND280 near
detector in its plastic scintillator (C8H8) target. The data were taken between years 2010 and 2013,
corresponding to approximately 6 Ă 1020 protons on target. Thanks to their exploration of the proton
kinematics and of imbalances between the proton and muon kinematics, the results offer a novel probe of
the nuclear-medium effects most pertinent to the (sub-)GeV neutrino-nucleus interactions that are used in
accelerator-based long-baseline neutrino oscillation measurements. These results are compared to many
neutrino-nucleus interaction models which all fail to describe at least part of the observed phase space.
In case of events without a proton above a detection threshold in the final state, a fully consistent
implementation of the local Fermi gas model with multinucleon interactions gives the best description of
the data. In the case of at least one proton in the final state, the spectral function model agrees well with the
data, most notably when measuring the kinematic imbalance between the muon and the proton in the plane
transverse to the incoming neutrino. Within the models considered, only the existence of multinucleon
interactions are able to describe the extracted cross section within regions of high transverse kinematic
imbalance. The effect of final-state interactions is also discussed
Search for CP Violation in Neutrino and Antineutrino Oscillations by the T2K Experiment with 2.2 x 10(21) Protons on Target
The T2K experiment measures muon neutrino disappearance and electron neutrino
appearance in accelerator-produced neutrino and antineutrino beams. With an
exposure of protons on target in neutrino
(antineutrino) mode, 89 candidates and 7 anti- candidates were
observed while 67.5 and 9.0 are expected for and normal mass
ordering. The obtained confidence interval for the violating
phase, , does not include the -conserving cases
(). The best-fit values of other parameters are
and .Comment: 9 pages, 6 figure
Search for light sterile neutrinos with the T2K far detector Super-Kamiokande at a baseline of 295 km
We perform a search for light sterile neutrinos using the data from the T2K far detector at a baseline of 295 km, with an exposure of 14.7Ă°7.6Ă Ă 1020 protons on target in neutrino (antineutrino) mode. A selection of neutral-current interaction samples is also used to enhance the sensitivity to sterile mixing.
No evidence of sterile neutrino mixing in the 3 ĂŸ 1 model was found from a simultaneous fit to the charged-current muon, electron and neutral-current neutrino samples. We set the most stringent limit on the sterile oscillation amplitude sin2 Ξ24 for the sterile neutrino mass splitting Îm241 < 3 Ă 10â3 eV2=c4
Constraint on the matter-antimatter symmetry-violating phase in neutrino oscillations
The charge-conjugation and parity-reversal (CP) symmetry of fundamental particles is a symmetry between matter and antimatter. Violation of this CP symmetry was first observed in 19641, and CP violation in the weak interactions of quarks was soon established2. Sakharov proposed3 that CP violation is necessary to explain the observed imbalance of matter and antimatter abundance in the Universe. However, CP violation in quarks is too small to support this explanation. So far, CP violation has not been observed in non-quark elementary particle systems. It has been shown that CP violation in leptons could generate the matterâantimatter disparity through a process called leptogenesis4. Leptonic mixing, which appears in the standard modelâs charged current interactions5,6, provides a potential source of CP violation through a complex phase ÎŽCP, which is required by some theoretical models of leptogenesis7,8,9. This CP violation can be measured in muon neutrino to electron neutrino oscillations and the corresponding antineutrino oscillations, which are experimentally accessible using accelerator-produced beams as established by the Tokai-to-Kamioka (T2K) and NOvA experiments10,11. Until now, the value of ÎŽCP has not been substantially constrained by neutrino oscillation experiments. Here we report a measurement using long-baseline neutrino and antineutrino oscillations observed by the T2K experiment that shows a large increase in the neutrino oscillation probability, excluding values of ÎŽCP that result in a large increase in the observed antineutrino oscillation probability at three standard deviations (3Ï). The 3Ï confidence interval for ÎŽCP, which is cyclic and repeats every 2Ï, is [â3.41, â0.03] for the so-called normal mass ordering and [â2.54, â0.32] for the inverted mass ordering. Our results indicate CP violation in leptons and our method enables sensitive searches for matterâantimatter asymmetry in neutrino oscillations using accelerator-produced neutrino beams. Future measurements with larger datasets will test whether leptonic CP violation is larger than the CP violation in quarks
Search for neutral-current induced single photon production at the ND280 near detector in T2K
Neutrino neutral-current (NC) induced single photon production is a sub-leading order process for accelerator-based neutrino beam experiments including T2K. It is, however, an important process to understand because it is a background for electron (anti)neutrino appearance oscillation experiments. Here, we performed the first search of this process below 1 GeV using the fine-grained detector at the T2K ND280 off-axis near detector. By reconstructing single photon kinematics from electron-positron pairs, we achieved 95% pure gamma ray sample from 5.738 x 10(20) protons-on-targets neutrino mode data. We do not find positive evidence of NC induced single photon production in this sample. We set the model-dependent upper limit on the cross-section for this process, at 0.114 x 10(-38) cm(2) (90% C.L.) per nucleon, using the J-PARC off-axis neutrino beam with an average energy of similar to 0.6 GeV. This is the first limit on this process below 1 GeV which is important for current and future oscillation experiments looking for electron neutrino appearance oscillation signals
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