Coherent forward neutron propagation in gas is discussed as a new approach to search for neutron-antineutron oscillations (<math><mi>n</mi><mo>−</mo><mover><mrow><mi>n</mi></mrow><mrow><mo>¯</mo></mrow></mover></math>), which violate both B and <math><mi>B</mi><mo>−</mo><mi>L</mi></math> conservation. We show that one can increase the probability of neutron - antineutron transitions in the presence of a nonzero external magnetic field to essentially free neutron oscillation probability by tuning the density of an appropriate mixture of gases so that the neutron optical potential of the gas cancels that from the magnetic field.

United States

V. Gudkov

France

V.V. Nesvizhevsky

K.V. Protasov

W.M. Snow

Russia

A.Yu. Voronin

A new approach to search for free neutron-antineutron oscillations using coherent neutron propagation in gas

We measured the spatial splitting of a non-polarized neutron beam passed through a crystal under diffraction conditions in heterogeneous magnetic field (analog to the Stern-Gerlach effect) into two polarized components with opposite polarization. The measurements were carried out using Laue diffraction scheme, small gradients of the magnetic field and Bragg angles close to orthogonality <math><msub><mrow><mi>θ</mi></mrow><mrow><mi>B</mi></mrow></msub><mo>=</mo><msup><mrow><mo>(</mo><mn>78</mn><mo>−</mo><mn>82</mn><mo>)</mo></mrow><mrow><mo>∘</mo></mrow></msup></math>. After a flight path in crystal of 21.6 cm a splitting of <math><mn>4.1</mn><mo>±</mo><mn>0.1</mn></math> cm was achieved (using a field gradient of ∼3 G/cm and a diffraction angle of <math><msup><mrow><mn>82</mn></mrow><mrow><mo>∘</mo></mrow></msup></math>). In the absence of a diffraction (crystal) but otherwise the same flight path and field gradient the spatial splitting would be <math><mo>∼</mo><mn>4</mn><mo>⋅</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>7</mn></mrow></msup></math> cm. From those we deduce an experimental amplification factor in the order of about <math><mo>∼</mo><mn>2</mn><mo>⋅</mo><msup><mrow><mn>10</mn></mrow><mrow><mn>5</mn></mrow></msup><msup><mrow><mi>tan</mi></mrow><mrow><mn>2</mn></mrow></msup><mo>⁡</mo><msub><mrow><mi>θ</mi></mrow><mrow><mi>B</mi></mrow></msub></math> due to the use of diffraction in crystals, which agrees with theory.

V.V. Voronin

S.Yu. Semenikhin

D.D. Shapiro

Yu.P. Braginets

V.V. Fedorov

M. Jentschel

Germany

A. Ioffe

Ya.A. Berdnikov

7-order enhancement of the Stern-Gerlach effect of neutrons diffracting in a crystal

Comment on B.O. Kerbikov, “The effect of collisions with the wall on neutron-antineutron transitions”, Phys. Lett. B 795 (2019) 362

We present measurements of P-odd asymmetry of emission of α -particles in the B10(n,α)Li7 nuclear reaction, which are carried out using beams of polarized cold neutrons at Petersburg Nuclear Physics Institute (PNPI, Gatchina, Russia) and Institut Max von Laue – Paul Langevin (ILL, Grenoble, France) nuclear reactors. The α -particle detector is an ionization chamber with insensitive gaseous layer.

JINR

Yu.M. Gledenov

P.V. Sedyshev

E.V. Shul'gina

Poland

P. Szalanski

V.A. Vesna

First observation of P-odd asymmetry of α -particle emission in the B10(n,α)Li7 nuclear reaction

We present estimations of systematic corrections and results of their experimental studies for our neutron lifetime experiment carried out in 2008–2010 at ILL. Taking into account these systematic corrections, we reduce the data of three independent sets of measurements (obtained during period 2008–2010) performed with different energy spectra of ultracold neutrons (UCNs) at different trap temperatures to the mean neutron lifetime value equal to 880.2(1.2) s.

S. Arzumanov

L. Bondarenko

S. Chernyavsky

P. Geltenbort

V. Morozov

Yu. Panin

A. Strepetov

A measurement of the neutron lifetime using the method of storage of ultracold neutrons and detection of inelastically up-scattered neutrons

We propose a new method for production of ultracold neutrons (UCNs) in superfluid helium. The principal idea consists in installing a helium UCN source into an external beam of thermal or cold neutrons and in surrounding this source with a solid methane moderator/reflector cooled down to ~4 K. The moderator plays the role of an external source of cold neutrons needed to produce UCNs. The flux of accumulated neutrons could exceed the flux of incident neutrons due to their numerous reflections from methane; also the source size could be significantly larger than the incident beam diameter. We provide preliminary calculations of cooling of neutrons. These calculations show that such a source being installed at an intense source of thermal or cold neutrons like the ILL or PIK reactor or the ESS spallation source could provide the UCN density 105 cm−3, the production rate 107 UCN/s−1. Main advantages of such an UCN source include its low radiative and thermal load, relatively low cost, and convenient accessibility for any maintenance. We have carried out an experiment on cooling of thermal neutrons in a methane cavity. The data confirm the results of our calculations of the spectrum and flux of neutrons in the methane cavity.

A. Yu. Muzychka

E.V. Lychagin

G.V. Nekhaev

E.I. Sharapov

A.V. Strelkov

UCN Source at an External Beam of Thermal Neutrons

Results of recent SANS experiments with impurity-helium gel (IHG) samples in He-II are presented. We estimate the mean size of the impurity nanoparticles that form the frame of the IHG samples and discuss the possibility to use IHG samples for the production of ultracold neutrons (UCNs) in He-II cooled to the temperature of a few mK, as well as the reflection of UCNs at any temperature. Our results indicate that the most promising materials for these purposes might be the heavy water gel samples with the mean sizes of D2O clusters of <math id="M1"><mi>d</mi><mo>~</mo><mn>8</mn></math> nm and the heavy alcohol gel samples with the mean sizes of clusters of <math id="M2"><mi>d</mi><mo>~</mo><mn>15</mn></math> nm.

United Kingdom

V.B. Efimov

L.P. Mezhov-Deglin

C.D. Dewhurst

A.V. Lokhov

Neutron Scattering on Impurity Nanoclusters in Gel Samples

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 at 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 report on the status of the ongoing experiments and discuss the prospects of observing gravitational quantum states of antimatter and their implications.

G. Dufour

D.B. Cassidy

Switzerland

P. Crivelli

P. Debu

A. Lambrecht

S. Reynaud

A. Yu. Voronin

T.E. Wall

Prospects for Studies of the Free Fall and Gravitational Quantum States of Antimatter

We consider the feasibility of observing the gravitational quantum states of positronium. The proposed scheme employs the flow-throw technique used for the first observation of this effect with neutrons. Collimation and Stark deceleration of Rydberg positronium atoms allow selecting the required velocity class. If this experiment could be realized with positronium, it would lead to a determination of <math id="M1"><mrow><mi>g</mi></mrow></math> for this matter-antimatter system at the few % level. As discussed in this contribution, most of the required techniques are currently available but important milestones have to be demonstrated experimentally before such an experiment could become reality. Those are the efficient focusing of a bunched positron beam, Stark deceleration of Rydberg positronium, and its subsequent excitation into states with large angular momentum. We provide an estimate of the efficiencies we expect for these steps and assuming those could be confirmed we calculate the signal rate.

Can We Observe the Gravitational Quantum States of Positronium?

Gravitational resonance spectroscopy consists in measuring the energy spectrum of bouncing ultracold neutrons above a mirror by inducing resonant transitions between different discrete quantum levels. We discuss how to induce the resonances with a flow through arrangement in the GRANIT spectrometer, excited by an oscillating magnetic field gradient. The spectroscopy could be realized in two distinct modes (so called DC and AC) using the same device to produce the magnetic excitation. We present calculations demonstrating the feasibility of the newly proposed AC mode.

G. Pignol

S. Baeßler

K. Protasov

D. Rebreyend

A. Voronin

Gravitational Resonance Spectroscopy with an Oscillating Magnetic Field Gradient in the GRANIT Flow through Arrangement