Detecting dark matter waves with precision measurement tools [CL]

Virialized Ultra-Light Fields (VULFs) are viable cold dark matter candidates and include scalar and pseudo-scalar bosonic fields, such as axions and dilatons. Direct searches for VULFs rely on low-energy precision measurement tools. While the previous proposals have focused on detecting coherent oscillations of the VULF signals at the VULF Compton frequencies at individual devices, here I consider a network of such devices. VULFs are essentially dark matter {\em waves} and as such they carry both temporal and spatial phase information. Thereby, the discovery reach can be improved by using networks of precision measurement tools. To formalize this idea, I derive a spatio-temporal two-point correlation function for the ultralight dark matter fields in the framework of the standard halo model. Due to VULFs being Gaussian random fields, the derived two-point correlation function fully determines $N$-point correlation functions. For a network of $N_{d}$ devices within the coherence length of the field, the sensitivity compared to a single device can be improved by a factor of $\sqrt{N_{d}}$. Further, I derive a VULF dark matter signal profile for an individual device. The resulting line shape is strongly asymmetric due to the parabolic dispersion relation for massive non-relativistic bosons. I discuss the aliasing effect that extends the discovery reach to VULF frequencies higher than the experimental sampling rate. I present sensitivity estimates and develop a stochastic field SNR statistic. Finally, I consider an application of the developed formalism to atomic clocks and their networks.

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A. Derevianko
Thu, 22 Feb 18

Comments: 16 pages, 5 figs. Revised and expanded version

A Binary Offset Effect in CCD Readout and Its Impact on Astronomical Data [IMA]

We have discovered an anomalous behavior of CCD readout electronics that affects their use in many astronomical applications. An offset in the digitization of the CCD output voltage that depends on the binary encoding of one pixel is added to pixels that are read out one, two and/or three pixels later. One result of this effect is the introduction of a differential offset in the background when comparing regions with and without flux from science targets. Conventional data reduction methods do not correct for this offset. We find this effect in 16 of 22 instruments investigated, covering a variety of telescopes and many different front-end electronics systems. The affected instruments include LRIS and DEIMOS on the Keck telescopes, WFC3-UVIS and STIS on HST, MegaCam on CFHT, SNIFS on the UH88 telescope, GMOS on the Gemini telescopes, HSC on Subaru, and FORS on VLT. The amplitude of the introduced offset is up to 4.5 ADU per pixel, and it is not directly proportional to the measured ADU level. We have developed a model that can be used to detect this “binary offset effect” in data and correct for it. Understanding how data are affected and applying a correction for the effect is essential for precise astronomical measurements.

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K. Boone, G. Aldering, Y. Copin, et. al.
Wed, 21 Feb 18

Comments: 22 pages, 9 figures, 2 tables. Accepted for publication in PASP

Projected WIMP sensitivity of the LUX-ZEPLIN (LZ) dark matter experiment [IMA]

LUX-ZEPLIN (LZ) is a next generation dark matter direct detection experiment that will operate 4850 feet underground at the Sanford Underground Research Facility (SURF) in Lead, South Dakota, USA. Using a two-phase xenon detector with an active mass of 7 tonnes, LZ will search primarily for low-energy interactions with Weakly Interacting Massive Particles (WIMPs), which are hypothesized to make up the dark matter in our galactic halo. In this paper, the projected WIMP sensitivity of LZ is presented based on the latest background estimates and simulations of the detector. For a 1000 live day run using a 5.6 tonne fiducial mass, LZ is projected to exclude at 90% confidence level spin-independent WIMP-nucleon cross sections above $1.6 \times 10^{-48}$ cm$^{2}$ for a 40 $\mathrm{GeV}/c^{2}$ mass WIMP. Additionally, a $5\sigma$ discovery potential is projected reaching cross sections below the existing and projected exclusion limits of similar experiments that are currently operating. For spin-dependent WIMP-neutron(-proton) scattering, a sensitivity of $2.7 \times 10^{-43}$ cm$^{2}$ ($8.1 \times 10^{-42}$ cm$^{2}$) for a 40 $\mathrm{GeV}/c^{2}$ mass WIMP is expected. With construction well underway, LZ is on track for underground installation at SURF in 2019 and will start collecting data in 2020.

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D. Akerib, C. Akerlof, S. Alsum, et. al.
Mon, 19 Feb 18

Comments: 14 pages, 11 figures

Remote sensing of geomagnetic fields and atomic collisions in the mesosphere [CL]

Magnetic-field sensing has contributed to the formulation of the plate-tectonics theory, the discovery and mapping of underground structures on Earth, and the study of magnetism in other planets. Filling the gap between space-based and near-Earth observation, we demonstrate a novel method for remote measurement of the geomagnetic field at an altitude of 85-100 km. The method consists of optical pumping of atomic sodium in the upper mesosphere with an intensity-modulated laser beam, and simultaneous ground-based observation of the resultant magneto-optical resonance when driving the atomic-sodium spins at the Larmor precession frequency. The experiment was carried out at the Roque de Los Muchachos Observatory in La Palma (Canary Islands) where we validated this technique and remotely measured the Larmor precession frequency of sodium as 260.4(1) kHz, corresponding to a mesospheric magnetic field of 0.3720(1) G. We demonstrate a magnetometry accuracy level of 0.28 mG/$\sqrt{\text{Hz}}$ in good atmospheric conditions. In addition, these observations allow us to characterize various atomic-collision processes in the mesosphere. Remote detection of mesospheric magnetic fields has potential applications such as mapping of large-scale magnetic structures in the lithosphere and the study of electric-current fluctuations in the ionosphere.

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F. Bustos, D. Calia, D. Budker, et. al.
Wed, 14 Feb 18

Comments: 10 pages, 7 figures

Modal Noise Mitigation through Fiber Agitation for Fiber-fed Radial Velocity Spectrographs [IMA]

Optical fiber modal noise is a limiting factor for high precision spectroscopy signal-to-noise in the near-infrared and visible. Unabated, especially when using highly coherent light sources for wavelength calibration, modal noise can induce radial velocity (RV) errors that hinder the discovery of low-mass (and potentially Earth-like) planets. Previous research in this field has found sufficient modal noise mitigation through the use of an integrating sphere, but this requires extremely bright light sources, a luxury not necessarily afforded by the next generation of high-resolution optical spectrographs. Otherwise, mechanical agitation, which “mixes” the fiber’s modal patterns and allows the noise to be averaged over minutes-long exposures, provides some noise reduction but the exact mechanism behind improvement in signal-to-noise and RV drift has not been fully explored or optimized by the community. Therefore, we have filled out the parameter space of modal noise agitation techniques in order to better understand agitation’s contribution to mitigating modal noise and to discover a better method for agitating fibers. We find that modal noise is best suppressed by the quasi-chaotic motion of two high-amplitude agitators oscillating with varying phase for fibers with large core diameters and low azimuthal symmetry. This work has subsequently influenced the design of a fiber agitator, to be installed with the EXtreme PREcision Spectrograph, that we estimate will reduce modal-noise-induced RV error to less than 3.2 cm/s.

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R. Petersburg, T. McCracken, D. Eggerman, et. al.
Wed, 7 Feb 18

Comments: Accepted by The Astrophysical Journal

Accuracy of Flight Altitude Measured with Low-Cost GNSS, Radar and Barometer Sensors: Implications for Airborne Radiometric Surveys [CL]

Flight height is a fundamental parameter for correcting the gamma signal produced by terrestrial radionuclides measured during airborne surveys. The frontiers of radiometric measurements with UAV require light and accurate altimeters flying at some 10 m from the ground. We equipped an aircraft with seven altimetric sensors (three low-cost GNSS receivers, one inertial measurement unit, one radar altimeter and two barometers) and analyzed $\sim$ 3 h of data collected over the sea in the (35-2194) m altitude range. At low altitudes (H $<$ 70 m) radar and barometric altimeters provide the best performances, while GNSS data are used only for barometer calibration as they are affected by a large noise due to the multipath from the sea. The $\sim$ 1 m median standard deviation at 50 m altitude affects the estimation of the ground radioisotope abundances with an uncertainty less than 1.3%. The GNSS double-difference post-processing enhanced significantly the data quality for H $>$ 80 m in terms of both altitude median standard deviation and agreement between the reconstructed and measured GPS antennas distances. Flying at 100 m the estimated uncertainty on the ground total activity due to the uncertainty on the flight height is of the order of 2%.

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M. Alberi, M. Baldoncini, C. Bottardi, et. al.
Fri, 2 Feb 18

Comments: N/A

First Limit on the direct detection of Lightly Ionizing Particles for Electric Charge as Low as $e$/1000 with the \textsc{Majorana Demonstrator} [CL]

The Majorana Demonstrator is an ultra low-background experiment searching for neutrinoless double-beta decay in $^{76}$Ge. The heavily shielded array of germanium detectors, placed nearly a mile underground at the Sanford Underground Research Facility in Lead, South Dakota, also allows searches for new exotic physics. Free, relativistic, lightly-ionizing particles with electrical charges less than $e$ are forbidden by the standard model but predicted by some of its extensions. If such particles exist, they might be detected in the Majorana Demonstrator by searching for multiple- detector events with individual-detector energy depositions down to 1 keV. This search is background free and no candidate events have been found in 285 days of data taking. New direct-detection limits are set for the flux of lightly ionizing particles for charges as low as $e$/1000.

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S. Alvis, I. Arnquist, F. Avignone, et. al.
Wed, 31 Jan 18

Comments: N/A