47 research outputs found
Quantum Reflection of Antihydrogen in the GBAR Experiment
In the GBAR experiment, cold antihydrogen atoms will be left to fall on an
annihilation plate with the aim of measuring the gravitational acceleration of
antimatter. Here, we study the quantum reflection of these antiatoms due to the
Casimir-Polder potential above the plate. We give realistic estimates of the
potential and quantum reflection amplitudes, taking into account the
specificities of antihydrogen and the optical properties of the plate. We find
that quantum reflection is enhanced for weaker potentials, for example above
thin slabs, graphene and nanoporous media.Comment: Workshop on Antimatter and Gravity Bern 2013 Proceeding
Probing the braneworld hypothesis with a neutron-shining-through-a-wall experiment
The possibility for our visible world to be a 3-brane embedded in a
multidimensional bulk is at the heart of many theoretical edifices in
high-energy physics. Probing the braneworld hypothesis is thus a major
experimental challenge. Following recent theoretical works showing that matter
swapping between braneworlds can occur, we propose a
neutron-shining-through-a-wall experiment. We first show that an intense
neutron source such as a nuclear reactor core can induce a hidden neutron flux
in an adjacent hidden braneworld. We then describe how a low-background
detector can detect neutrons arising from the hidden world and quantify the
expected sensitivity to the swapping probability. As a proof of concept, a
constraint is derived from previous experiments.Comment: 12 pages, 4 figures, final version published in Physical Review
Search for passing-through-walls neutrons constrains hidden braneworlds
In many theoretical frameworks our visible world is a -brane, embedded in
a multidimensional bulk, possibly coexisting with hidden braneworlds. Some
works have also shown that matter swapping between braneworlds can occur. Here
we report the results of an experiment - at the Institut Laue-Langevin
(Grenoble, France) - designed to detect thermal neutron swapping to and from
another braneworld, thus constraining the probability of such an event.
The limit, at C.L., is orders of magnitude
better than the previous bound based on the disappearance of stored ultracold
neutrons. In the simplest braneworld scenario, for two parallel Planck-scale
branes separated by a distance , we conclude that in Planck length
units.Comment: 5 pages, 3 figures. Published in Physics Letters
Prospects for studies of the free fall and gravitational quantum states of antimatter
Different experiments are ongoing to measure the effect of gravity on cold
neutral antimatter atoms such as positronium, muonium and antihydrogen. Among
those, the project GBAR in CERN aims to measure precisely the gravitational
fall of ultracold antihydrogen atoms. In the ultracold regime, the interaction
of antihydrogen atoms with a surface is governed by the phenomenon of quantum
reflection which results in bouncing of antihydrogen atoms on matter surfaces.
This allows the application of a filtering scheme to increase the precision of
the free fall measurement. In the ultimate limit of smallest vertical
velocities, antihydrogen atoms are settled in gravitational quantum states in
close analogy to ultracold neutrons (UCNs). Positronium is another neutral
system involving antimatter for which free fall under gravity is currently
being investigated at UCL. Building on the experimental techniques under
development for the free fall measurement, gravitational quantum states could
also be observed in positronium. In this contribution, we review the status of
the ongoing experiments and discuss the prospects of observing gravitational
quantum states of antimatter and their implications.Comment: This work reviews contributions made at the GRANIT 2014 workshop on
prospects for the observation of the free fall and gravitational quantum
states of antimatte
Status of the GRANIT facility
The GRANIT facility is a follow-up project, which is motivated by the recent
discovery of gravitational quantum states of ultracold neutrons. The goal of
the project is to approach the ultimate accuracy in measuring parameters of
such quantum states and also to apply this phenomenon and related experimental
techniques to a broad range of applications in particle physics as well as in
surface and nanoscience studies. We overview the current status of this
facility, the recent test measurements and the nearest prospects.Comment: 11 pages, 20 figures, Proceedings of the GRANIT-2014 WORKSHOP
"Quantum gravitational spectroscopy with ultracold systems"(Les Houches
Gravitational and matter-wave spectroscopy of atomic hydrogen at ultra-low energies
We propose experiments with atomic hydrogen gas at ultra-low temperatures T <100K when the thermal energy of atoms is comparable with the changes of their potential energy in the Earth gravity field. At these conditions we suggest implementing a gravitational spectroscopy for studies of quantum properties of ultra-cold atomic hydrogen and its interactions with matter and gravity, similar to experiments with ultra-cold neutrons (Nesvizhevsky et al. Nature 415, 297 2002). A magnetic trap used for reaching the Bose-Einstein Condensation (Fried et al. Phys. Rev. Lett. 81, 3811 1998) can be used for cooling a large number of H atoms below 1 mK. Evaporative cooling over the trap barrier allows effective cooling of the vertical degree of freedom of the trapped atoms. Releasing these ultra-slow atoms from the trap onto the cold surface of superfluid helium will allow studies of quantum bounces and stationary gravitational states of H atoms in the potential well created by this surface and the field of Earth gravity. Experimental study of properties of gravitational quantum states of hydrogen and quantum reflection of ultracold hydrogen from surface would be of major importance for designing similar experiments with antihydrogen, which are currently prepared in CERN
Experimental limits on neutron disappearance into another braneworld
Recent theoretical works have shown that matter swapping between two parallel
braneworlds could occur under the influence of magnetic vector potentials. In
our visible world, galactic magnetism possibly produces a huge magnetic
potential. As a consequence, this paper discusses the possibility to observe
neutron disappearance into another braneworld in certain circumstances. The
setup under consideration involves stored ultracold neutrons - in a vessel -
which should exhibit a non-zero probability p to disappear into an invisible
brane at each wall collision. An upper limit of p is assessed based on
available experimental results. This value is then used to constrain the
parameters of the theoretical model. Possible improvements of the experiments
are discussed, including enhanced stimulated swapping by artificial means.Comment: 7 pages, 2 figures, 1 table. Published in Physics Letters
Casimir interaction between a dielectric nanosphere and a metallic plane
We study the Casimir interaction between a dielectric nanosphere and a
metallic plane, using the multiple scattering theory. Exact results are
obtained with the dielectric described by a Sellmeier model and the metal by a
Drude model. Asymptotic forms are discussed for small spheres, large or small
distances. The well-known Casimir-Polder formula is recovered at the limit of
vanishingly small spheres, while an expression better behaved at small
distances is found for any finite value of the radius. The exact results are of
particular interest for the study of quantum states of nanospheres in the
vicinity of surfaces.Comment: 6 pages, 5 figure