arXiv subjects

J. Long

Publications and source records attributed to J. Long.

44 records · Page 3Linked to original sources

arXiv2020

LBECA: A Low Background Electron Counting Apparatus for Sub-GeV Dark Matter Detection

Two-phase noble liquid detectors, with large target masses and effective background reduction, are currently leading the dark matter direct detection for WIMP masses above a few GeV. Due to their sensitivity to single ionized electron signals, these detectors were shown to also have strong constraints for sub-GeV dark matter via their scattering on electrons. In fact, the most stringent direct detection constraints for sub-GeV dark matter down to as low as ~5 MeV come from noble liquid detectors, namely XENON10, DarkSide-50, XENON100 and XENON1T, although these experiments still suffer from high background at single or a few electron level. LBECA is a planned 100-kg scale liquid xenon detector with significant reduction of the single and a few electron background. The experiment will improve the sensitivity to sub-GeV dark matter by three orders of magnitude compared to the current best constraints.

physics.ins-det↗

arXiv2019

A New Cryogenic Apparatus to Search for the Neutron Electric Dipole Moment

A cryogenic apparatus is described that enables a new experiment, nEDM@SNS, with a major improvement in sensitivity compared to the existing limit in the search for a neutron Electric Dipole Moment (EDM). It uses superfluid $^4$He to produce a high density of Ultra-Cold Neutrons (UCN) which are contained in a suitably coated pair of measurement cells. The experiment, to be operated at the Spallation Neutron Source at Oak Ridge National Laboratory, uses polarized $^3$He from an Atomic Beam Source injected into the superfluid $^4$He and transported to the measurement cells as a co-magnetometer. The superfluid $^4$He is also used as an insulating medium allowing significantly higher electric fields, compared to previous experiments, to be maintained across the measurement cells. These features provide an ultimate statistical uncertainty for the EDM of $2-3\times 10^{-28}$ e-cm, with anticipated systematic uncertainties below this level.

physics.ins-det↗

arXiv2019

First characterization of Swift J1845.7-0037 with NuSTAR

The hard X-ray transient source Swift J1845.7-0037 was discovered in 2012 by Swift/BAT. However, at that time no dedicated observations of the source were performed. On Oct 2019 the source became active again, and X-ray pulsations with a period of ~199s were detected with Swift/XRT. This triggered follow-up observations with NuSTAR. Here we report on the timing and spectral analysis of the source properties using NuSTAR and Swift/XRT. The main goal was to confirm pulsations and search for possible cyclotron lines in the broadband spectrum of the source to probe its magnetic field. Despite highly significant pulsations with period of 207.379(2) were detected, no evidence for a cyclotron line was found in the spectrum of the source. We therefore discuss the strength of the magnetic field based on the source flux and the detection of the transition to the "cold-disc" accretion regime during the 2012 outburst. Our conclusion is that, most likely, the source is a highly magnetized neutron star with B 1e13G at a large distance of d~10 kpc. The latter one consistent with the non-detection of a cyclotron line in the NuSTAR energy band.

astro-ph.HE↗

arXiv2019

The neutron electric dipole moment experiment at the Spallation Neutron Source

Novel experimental techniques are required to make the next big leap in neutron electric dipole moment experimental sensitivity, both in terms of statistics and systematic error control. The nEDM experiment at the Spallation Neutron Source (nEDM@SNS) will implement the scheme of Golub & Lamoreaux [Phys. Rep., 237, 1 (1994)]. The unique properties of combining polarized ultracold neutrons, polarized $^3$He, and superfluid $^4$He will be exploited to provide a sensitivity to $\sim 10^{-28}\,e{\rm \,\cdot\, cm}$. Our cryogenic apparatus will deploy two small ($3\,{\rm L}$) measurement cells with a high density of ultracold neutrons produced and spin analyzed in situ. The electric field strength, precession time, magnetic shielding, and detected UCN number will all be enhanced compared to previous room temperature Ramsey measurements. Our $^3$He co-magnetometer offers unique control of systematic effects, in particular the Bloch-Siegert induced false EDM. Furthermore, there will be two distinct measurement modes: free precession and dressed spin. This will provide an important self-check of our results. Following five years of "critical component demonstration," our collaboration transitioned to a "large scale integration" phase in 2018. An overview of our measurement techniques, experimental design, and brief updates are described in these proceedings.

nucl-ex↗

arXiv2016

The length of an s-increasing sequence of r-tuples

We prove a number of results related to a problem of Po-Shen Loh, which is equivalent to a problem in Ramsey theory. Let $a=(a_1,a_2,a_3)$ and $b=(b_1,b_2,b_3)$ be two triples of integers. Define $a$ to be 2-less than $b$ if $a_i<b_i$ for at least two values of $i$, and define a sequence $a^1,\dots,a^m$ of triples to be 2-increasing if $a^r$ is 2-less than $a^s$ whenever $r<s$. Loh asks how long a 2-increasing sequence can be if all the triples take values in $\{1,2,\dots,n\}$, and gives a $\log_*$ improvement over the trivial upper bound of $n^2$ by using the triangle removal lemma. In the other direction, a simple construction gives a lower bound of $n^{3/2}$. We look at this problem and a collection of generalizations, improving some of the known bounds, pointing out connections to other well known problems in extremal combinatorics, and asking a number of further questions.

math.CO↗

arXiv2016

Identifying close binary central stars of PN with Kepler

Six planetary nebulae (PN) are known in the Kepler space telescope field of view, three newly identified. Of the 5 central stars of PN with useful Kepler data, one, J193110888+4324577, is a short-period, post common envelope binary exhibiting relativistic beaming effects. A second, the central star of the newly identified PN Pa5, has a rare O(He) spectral type and a periodic variability consistent with an evolved companion, where the orbital axis is almost aligned with the line of sight. The third PN, NGC~6826 has a fast rotating central star, something that can only be achieved in a merger. Fourth, the central star of the newly identified PN Kn61, has a PG1159 spectral type and a mysterious semi-periodic light variability which we conjecture to be related to the interplay of binarity with a stellar wind. Finally, the central star of the circular PN A61 does not appear to have a photometric variability above 2 mmag. With the possible exception of the variability of Kn61, all other variability behaviour, whether due to binarity or not, would not easily have been detected from the ground. We conclude, based on very low numbers, that there may be many more close binary or close binary products to be discovered with ultra-high precision photometry. With a larger number of high precision photometric observations we will be able to determine how much higher than the currently known 15 per cent, the short period binary fraction for central stars of PN is likely to be.

astro-ph.SR↗

arXiv2016

Search for Lorentz Violation using Short-Range Tests of Gravity

Experimental tests of the newtonian inverse square law at short range, one at Indiana University and the other at the Huazhong University of Science and Technology, have been used to set limits on Lorentz violation in the pure gravity sector of the nonminimal Standard-Model Extension. In the nonrelativistic limit, the constraints derived for the 14 independent SME coefficients for Lorentz violation acting simultaneously are of order $10^{-9}$ m$^{2}$.

hep-ph↗

arXiv2010

Search for Lorentz Violation in a Short-Range Gravity Experiment

An experimental test of the Newtonian inverse square law at short range has been used to set limits on Lorentz violation in the pure gravity sector of the Standard-Model Extension. On account of the planar test mass geometry, nominally null with respect to inverse square forces, the limits derived for the SME coefficients of Lorentz violation are on the order s ~ 10000.

gr-qc↗