Search

We report the results of radioactivity assays and heat leak calculations for a range of common cryogenic materials, considered for use in the QUEST-DMC superfluid 3 He dark matter detector. The bolometer, instrumented with nanomechanical resonators, will be sensitive to energy deposits from dark matter interactions. Events from radioactive decays and cosmic rays constitute a significant background and must be precisely modelled, using a combination of material screening and Monte Carlo simulations. However, the results presented here are of wider interest for experiments and quantum devices sensitive to minute heat leaks and spurious events, thus we present heat leak per unit mass or surface area for every material studied. This can inform material choices for other experiments, especially if underground operation is considered – where the radiogenic backgrounds will dominate even at shallow depths. [ABSTRACT FROM AUTHOR]

The focus of dark matter searches to date has been on Weakly Interacting Massive Particles (WIMPs) in the GeV/ c 2 -TeV/ c 2 mass range. The direct, indirect and collider searches in this mass range have been extensive but ultimately unsuccessful, providing a strong motivation for widening the search outside this range. Here we describe a new concept for a dark matter experiment, employing superfluid 3 He as a detector for dark matter that is close to the mass of the proton, of order 1 GeV/ c 2 . The QUEST-DMC detector concept is based on quasiparticle detection in a bolometer cell by a nanomechanical resonator. In this paper we develop the energy measurement methodology and detector response model, simulate candidate dark matter signals and expected background interactions, and calculate the sensitivity of such a detector. We project that such a detector can reach sub-eV nuclear recoil energy threshold, opening up new windows on the parameter space of both spin-dependent and spin-independent interactions of light dark matter candidates. [ABSTRACT FROM AUTHOR]

In relativistic quantum field theories, compact objects of interacting bosons can become stable owing to conservation of an additive quantum number Q. Discovering such Q balls propagating in the universe would confirm supersymmetric extensions of the standard model and may shed light on the mysteries of dark matter, but no unambiguous experimental evidence exists. We have created long-lived Q-ball solitons in superfluid -3He, where the role of the Q ball is played by a Bose-Einstein condensate of magnon quasiparticles. The principal qualitative attribute of a Q ball is observed experimentally: its propagation in space together with the self-created potential trap. Additionally, we show that this system allows for a quantitatively accurate representation of the Q-ball Hamiltonian. Our Q ball belongs to the class of the Friedberg-Lee-Sirlin Q balls with an additional neutral field ζ , which is provided by the orbital part of the Nambu-Goldstone mode. Multiple Q balls can be created in the experiment, and we have observed collisions between them. This set of features makes the magnon condensates in superfluid -3He a versatile platform for studies of Q-ball dynamics and interactions in three spatial dimensions. [ABSTRACT FROM AUTHOR]

In a rotating two-phase sample of ³He-B and magnetic-field stabilized ³He-A the large difference in mutual friction dissipation at 0.20Tc gives rise to unusual vortex flow responses. We use noninvasive NMR techniques to monitor spin down and spin up of the B-phase superfluid component to a sudden change in the rotation velocity. Compared to measurements at low field with no A phase, where these responses are laminar in cylindrically symmetric flow, spin down with vortices extending across the AB interface is found to be faster, indicating enhanced dissipation from turbulence. Spin up in turn is slower, owing to rapid annihilation of remanent vortices before the rotation increase. As confirmed by both our NMR signal analysis and vortex filament calculations, these observations are explained by the additional force acting on the B phase vortex ends at the A B interface. [ABSTRACT FROM AUTHOR]

In superfluid He-B the damping of vortex motion varies many orders of magnitude in the currently accessible temperature range from T to below 0.2 T. The large variation in the dynamics switches on sequentially different processes of vortex formation as a function of temperature. These can be examined in a smooth-walled rotating cylinder in the absence of surface pinning. We provide an overview of vortex formation in spin-up and of annihilation in spin-down measurements at temperatures below the hydrodynamic transition at 0.6 T where turbulence in the bulk volume becomes possible. Of central current interest are the very lowest temperatures at 0.2 T where the dynamic processes reflect on the properties of the T→0 limit. [ABSTRACT FROM AUTHOR]

Long-lived coherent spin precession of 3He-B at low temperatures around 0.2Tc is a manifestation of Bose-Einstein condensation of spin-wave excitations or magnons in a magnetic trap which is formed by the order-parameter texture and can be manipulated experimentally. When the number of magnons increases, the orbital texture reorients under the influence of the spin-orbit interaction and the profile of the trap gradually changes from harmonic to a square well, with walls almost impenetrable to magnons. This is the first experimental example of Bose condensation in a box. By selective rf pumping the trap can be populated with a ground-state condensate or one at any of the excited energy levels. In the latter case the ground state is simultaneously populated by relaxation from the exited level, forming a system of two coexisting condensates. [ABSTRACT FROM AUTHOR]

Steady-state turbulent motion is created in superfluid ³He-B at low temperatures in the form of a turbulent vortex front, which moves axially along a rotating cylindrical container of ³He-B and replaces vortex-free flow with vortex lines at constant density. We present the first measurements on the thermal signal from dissipation as a function of time, recorded at O.2Tc during the front motion, which is monitored using NMR techniques. Both the measurements and the numerical calculations of the vortex dynamics show that at low temperatures the density of the propagating vortices falls well below the equilibrium value, i.e., the superfluid rotates at a smaller angular velocity than the container. This is the first evidence for the decoupling of the superfluid from the container reference frame in the zero-temperature limit. [ABSTRACT FROM AUTHOR]