We present the result of an experiment to measure the electric dipole moment (EDM) of the neutron at the Paul Scherrer Institute using Ramsey's method of separated oscillating magnetic fields with ultracold neutrons. Our measurement stands in the long history of EDM experiments probing physics violating timereversal invariance. The salient features of this experiment were the use of a 199 Hg comagnetometer and an array of optically pumped cesium vapor magnetometers to cancel and correct for magnetic-field changes. The statistical analysis was performed on blinded datasets by two separate groups, while the estimation of systematic effects profited from an unprecedented knowledge of the magnetic field. The measured value of the neutron EDM is d n ¼ ð0.0 AE 1.1 stat AE 0.2 sys Þ × 10 −26 e:cm.

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DEAP-3600 is a single-phase liquid argon (LAr) direct-detection dark matter experiment, operating 2 km underground at SNOLAB (Sudbury, Canada). The detector consists of 3279 kg of LAr contained in a spherical acrylic vessel. This paper reports on the analysis of a 758 tonne · day exposure taken over a period of 231 live-days during the first year of operation. No candidate signal events are observed in the WIMP-search region of interest, which results in the leading limit on the WIMP-nucleon spin-independent cross section on a LAr target of 3.9 × 10 −45 cm 2 (1.5 × 10 −44 cm 2 ) for a 100 GeV=c 2 (1 TeV=c 2 ) WIMP mass at 90% C.L. In addition to a detailed background model, this analysis demonstrates the best pulseshape discrimination in LAr at threshold, employs a Bayesian photoelectron-counting technique to improve the energy resolution and discrimination efficiency, and utilizes two position reconstruction algorithms based on the charge and photon detection time distributions observed in each photomultiplier tube.

The Dark matter Experiment using Argon Pulse-shape discrimination (DEAP) has been designed for a direct detection search for particle dark matter using a single-phase liquid argon target. The projected cross section sensitivity for DEAP-3600 to the spin-independent scattering of Weakly Interacting Massive Particles (WIMPs) on nucleons is 10 −46 cm 2 for a 100 GeV/c 2 WIMP mass with a fiducial exposure of 3 tonne-years. This paper describes the physical properties and construction of the DEAP-3600 detector.

In case a mirror world with a copy of our ordinary particle spectrum would exist, the neutron n and its degenerate partner, the mirror neutron n ′ , could potentially mix and undergo nn ′ oscillations. The interaction of an ordinary magnetic field with the ordinary neutron would lift the degeneracy between the mirror partners, diminish the n ′ -amplitude in the n-wavefunction and, thus, suppress its observability. We report an experimental comparison of ultracold neutron storage in a trap with and without superimposed magnetic field. No influence of the magnetic field is found and, assuming negligible mirror magnetic fields, a limit on the oscillation time τ nn ′ > 103 s (95% C.L.) is derived.PACS numbers: 11.30. Er, 11.30.Fs, 14.20.Dh, The concept of a mirror world, as an attempt to restore global parity symmetry, has attracted interest since the 1950's, started by the famous paper of Lee and Yang [1] and significantly expanded in the work of Kobzarev, Okun, and Pomeranchuk [2]. The mirror matter idea was first applied to the Standard Model of particle physics in [3]. More recent overviews can be found in [4,5]. The mirror world could hold a copy of the particle spectrum of our ordinary world. Matter and mirror matter would interact via gravity and present a viable explanation to the dark matter problem [6,7,8,9,10]. Besides gravity, other (new) interactions could show up in minute mixings of neutral matter particles -such as neutrinos, pions, kaons, or positronium (see [11] for e + e − ) -and their degenerate mirror partners making oscillations between them possible. Recently it was pointed out [12] that no direct experimental limits exist on the oscillation time τ nn ′ [13] between ordinary matter neutrons (n) and the speculative mirror neutrons (n ′ ). An indirect limit of the order τ nn ′ ≥ 1 s has been derived in [12] based on the search for neutron -antineutron (nn) oscillations [14]. Fast nn ′ oscillations with τ nn ′ ∼ 1 s, or at least much shorter than the neutron β-decay lifetime, could explain [12,15] the origin of ultra-high energy cosmic rays above the Greisen-Zatsepin-Kuzmin (GZK) cutoff [16,17]. The viability of models and implications have been further discussed in [18].Possible approaches to nn ′ oscillation experiments with sensitivities of several hundred seconds have been discussed in [19]. One approach is to search for nn ′ oscillations by comparing the storage of ultracold neutrons (UCN) in vacuum in a trap in the presence and the absence, respectively, of a magnetic field. The essential idea is that the neutron and mirror neutron states would be degenerate in the absence of a magnetic field and nn ′ transitions could occur. (The absence of mirror magnetic fields at the location of the experiment is assumed throughout this paper [20].) The interaction of the neutron with a magnetic field would lift the degeneracy and suppress the transition into a mirror neutron which, of course, does not interact with the ordinary magnetic field, nor with the trap via the ordinary strong interaction. Thus...