Precision analysis of electron energy spectrum and angular distribution of neutron beta decay with polarized neutron and electron [CL]

We give a precision analysis of the correlation coefficients of the electron-energy spectrum and angular distribution of the beta decay and radiative beta decay of the neutron with polarized neutron and electron to order 10^(-3). The calculation of correlation coefficients is carried out within the Standard model with contributions of order 10^(-3), caused by the weak magnetism and proton recoil, taken to next-to-leading order in the large proton mass expansion, and with radiative corrections of order “alpha/pi ~ 10^(-3”, calculated to leading order in the large proton mass expansion. The obtained results can be used for the planning of experiments on the search for contributions of order 10^(-4) of interactions beyond the Standard model.

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A. Ivanov, R. Hollwieser, N. Troitskaya, et. al.
Tue, 23 May 17

Comments: 11 pages, 2 figures, The results, obtained in this paper, were reported at the “Satellite workshop on symmetries in light and heavy flavour”, which was held on 7 – 8 November 2016 at Max Planck Institute for Astrophysics (MPA), M\”unchen, Germany

First Dark Matter Search Results from the XENON1T Experiment [CEA]

We report the first dark matter search results from XENON1T, a $\sim$2000-kg-target-mass dual-phase (liquid-gas) xenon time projection chamber in operation at the Laboratori Nazionali del Gran Sasso in Italy and the first ton-scale detector of this kind. The blinded search used 34.2 live days of data acquired between November 2016 and January 2017. Inside the (1042$\pm$12) kg fiducial mass and in the [5, 40] $\mathrm{keV}{\mathrm{nr}}$ energy range of interest for WIMP dark matter searches, the electronic recoil background was $(1.93 \pm 0.25) \times 10^{-4}$ events/(kg $\times$ day $\times \mathrm{keV}{\mathrm{ee}}$), the lowest ever achieved in a dark matter detector. A profile likelihood analysis shows that the data is consistent with the background-only hypothesis. We derive the most stringent exclusion limits on the spin-independent WIMP-nucleon interaction cross section for WIMP masses above 10 GeV/c${}^2$, with a minimum of 7.7 $\times 10^{-47}$ cm${}^2$ for 35-GeV/c${}^2$ WIMPs at 90% confidence level.

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E. Aprile, J. Aalbers, F. Agostini, et. al.
Fri, 19 May 17

Comments: 6 pages, 4 figures, submitting to PRL

Constraints on direction-dependent cosmic birefringence from Planck polarization data [CEA]

Cosmic birefringence is the process that rotates the plane of polarization by an amount, $\alpha$, as photons propagate through free space. Such an effect arises in parity-violating extensions to the electromagnetic sector, such as the Chern-Simons term common in axion models, quintessence models, or Lorentz-violating extensions to the standard model. Most studies consider the monopole of this rotation, but it is also possible for the effect to have spatial anisotropies. Paying particular attention to large scales, we implement a novel pixel-based method to extract the spherical harmonics for $L \le 30$ and a pseudo-$C_L$ method for $L > 30$. Our results are consistent with no detection and we set 95% upper limits on the amplitude of a scale-invariant power spectrum of $L(L+1)C_L/2\pi < [2.9\, (\mathrm{stat.})\, \pm 0.7\, (\mathrm{syst.})]\times10^{-5} = [0.09\, (\mathrm{stat.}) \pm 0.02\, (\mathrm{syst.})] \,\mathrm{deg}^2$, on par with previous constraints. This implies specific limits on the dipole and quadrupole amplitudes to be $\sqrt{C_1/4\pi} < 0.2^\circ$ and $\sqrt{C_2/4\pi} < 0.1^\circ$, at 95% CL, respectively, improving previous constraints by an order of magnitude. We further constrain a model independent $M=0$ quadrupole in an arbitrary direction to be $\alpha_{20} = 0.02^\circ \pm 0.21^\circ$, with an unconstrained direction. However, we find an excess of dipolar power with an amplitude $\sqrt{3C_1/4\pi} = 0.32^\circ \pm 0.10^\circ\, (\mathrm{stat.})\, \pm 0.08^\circ\, (\mathrm{syst.})$ in the direction $(l, b) = (295^\circ, 17^\circ) \pm (22^\circ, 17^\circ)\, (\mathrm{stat.})\, \pm (5^\circ, 16^\circ)\, (\mathrm{syst.})$ larger than 1.4% of simulations with no birefringence. We attribute part of this signal to the contamination of residual foregrounds not accounted for in our simulations, though it should be further investigated.

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D. Contreras, P. Boubel and D. Scott
Fri, 19 May 17

Comments: 18 pages, 6 figures, 3 tables

Advanced Reconstruction Strategies for the Auger Engineering Radio Array [IMA]

The Auger Engineering Radio Array (AERA) aims to detect extensive air showers caused by the interactions of ultra-high energy cosmic rays with the Earth’s atmosphere, providing complementary information to the Auger surface, fluorescence and muon detectors. AERA, currently consisting of 124 radio stations, comprises an area of about 6 km$^{2}$. The main objective for exploiting a radio detector is to measure the fundamental air-shower parameters, such as the direction, energy and composition. We have developed reconstruction strategies and algorithms to precisely measure the air-shower parameters with high efficiency. In addition, we will present the results obtained by applying the reconstruction strategies on the experimental data taken by AERA.

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Qader Dorosti Hasankiadeh
Thu, 18 May 17

Comments: N/A

Gamma-ray Showers Observed at Ground Level in Coincidence With Downward Lightning Leaders [CL]

Bursts of energetic particle showers have been observed in coincidence with downward propagating negative leaders in lightning flashes by the Telescope Array Surface Detector (TASD). The TASD is a 700 square kilometer cosmic ray observatory located in western Utah. Lightning position, time, and electric field information was collected by a lightning mapping array and slow antenna colocated with the TASD. The observed showers arrived in bursts lasting several hundred microseconds, and were associated with the initial stages of leaders at an altitude of a few kilometers above ground level prior to cloud-to-ground lightning strikes. Simulation studies indicate that the observed showers are consistent with originating in forward-beamed primary gamma rays, from a source altitude greater than one kilometer above the ground and distributed according to a relativistic runaway electron avalanche spectrum with energies greater than 100 keV. We conclude that the showers observed are compatible with downward terrestrial gamma ray flashes (TGFs), and provide new insights into the TGF phenomenon.

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R. Abbasi, T. Abu-Zayyad, M. Allen, et. al.
Thu, 18 May 17

Comments: N/A

Measurement of the directional sensitivity of DMTPC detectors [IMA]

The Dark Matter Time Projection Chamber (DMTPC) is a direction-sensitive detector designed to measure the direction of recoiling $^{19}$F and $^{12}$C nuclei in low-pressure CF$_4$ gas using optical and charge readout systems. In this paper, we employ measurements from two DMTPC detectors, with operating pressures of 30-60 torr, to develop and validate a model of the directional response and performance of such detectors as a function of recoil energy. Using our model as a benchmark, we formulate the necessary specifications for a scalable directional detector with sensitivity comparable to that of current-generation counting (non-directional) experiments, which measure only recoil energy. Assuming the performance of existing DMTPC detectors, as well as current limits on the spin-dependent WIMP-nucleus cross section, we find that a 10-20 kg scale direction-sensitive detector is capable of correlating the measured direction of nuclear recoils with the predicted direction of incident dark matter particles and providing decisive (3$\sigma$) confirmation that a candidate signal from a non-directional experiment was indeed induced by elastic scattering of dark matter particles off of target nuclei.

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C. Deaconu, M. Leyton, R. Corliss, et. al.
Thu, 18 May 17

Comments: 27 pages, 10 figures. Accepted for publication in Phys. Rev. D

Backward Monte-Carlo applied to muon transport [CL]

We discuss a backward Monte-Carlo technique for muon transport problem, with emphasis on its application in muography. Backward Monte-Carlo allows exclusive sampling of a final state by reversing the simulation flow. In practice it can be made analogous to an adjoint Monte-Carlo, though it is more versatile for muon transport. A backward Monte-Carlo was implemented as a dedicated muon transport library: PUMAS. It is shown for case studies relevant for muography imaging that the implementations of forward and backward Monte-Carlo schemes agree to better than 1%.

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V. Niess, A. Barnoud, C. Cristina, et. al.
Wed, 17 May 17

Comments: 43 pages, 7 figures