Anatolii P. Serebrov

Measurement of the Neutron Lifetime Using a Gravitational Trap and a Low-Temperature Fomblin Coating

We present a new value for the neutron lifetime of 878.5 ± 0.7stat. ± 0.3syst. This result differs from the world average value by 6.5 standard deviations and by 5.6 standard deviations from the previous most precise result. However, this new value for the neutron lifetime together with a β-asymmetry in neutron decay, A 0, of -0.1189(7) is in a good agreement with the Standard Model.

Experimental search for neutron–mirror neutron oscillations using storage of ultracold neutrons

Abstract The idea of a hidden sector of mirror partners of elementary particles has attracted considerable interest as a possible candidate for dark matter. Recently it was pointed out by Berezhiani and Bento that the present experimental data cannot exclude the possibility of a rapid oscillation of the neutron n to a mirror neutron n′ with oscillation time much smaller than the neutron lifetime. A dedicated search for vacuum transitions n → n ′ has to be performed at weak magnetic field, where both states are degenerate. We report the result of our experiment, which compares rates of ultracold neutrons after storage at a weak magnetic field well below 20 nT and at a magnetic field strong enough to suppress the seeked transitions. We obtain a new limit for the oscillation time of n–n′ transitions, τ osc ( 90 % C.L. ) > 414 s . The corresponding limit for the mixing energy of the normal and mirror neutron states is δ m ( 90 % C.L. ) 1.5 × 10 −18 eV .

Low-energy heating of ultracold neutrons during their storage in material bottles

Abstract We have studied the low-energy heating of ultracold neutrons during their storage. On fomblin, it is greatly suppressed for the low temperature liquid and at solidification. For non-magnetic solid materials, upper limits of 5×10 −9 (Be) and 3.6×10 −8 (Cu) per collision were found. Therefore, low-energy heating is not the reason for “anomalous losses” of (2–3)×10 −5 per collision on beryllium surfaces.

Measurement of the parity violating asymmetry Aγ in n→+p→d+γ

The weak pion-nucleon coupling constant H{sub {pi}}{sup 1} remains poorly determined, despite many years of effort. The recent measurement of the {sup 133}Cs anapole moment has been interpreted to give a value of H{sub {pi}}{sup 1} almost an order of magnitude larger than the limit established in the {sup 18}F parity doublet experiments. A measurement of the gamma ray directional asymmetry A{sub {gamma}} for the capture of polarized neutrons by hydrogen has been proposed at Los Alamos National Laboratory. This experiment will determine H{sub {pi}}{sup 1} independent of nuclear structure effects. However, since the predicted asymmetry is small, A{sub {gamma}} {approximately} 5 x 10{sup {minus}8}, systematic effects must be reduced to < 5 x 10{sup {minus}9}. The design of the experiment will is presented, with an emphasis on the techniques used for controlling systematic errors.

Performance of the prototype LANL solid deuterium ultra-cold neutron source

A prototype of a solid deuterium (SD 2 ) source of Ultra-Cold Neutrons (UCN) is currently being tested at LANSCE. The source is contained within an assembly consisting of a 4 K polyethylene moderator surrounded by a 77 K beryllium #ux trap in which is embedded a spallation target. Time-of-#ight measurements have been made of the cold neutron spectrum emerging directly from the #ux trap assembly. A comparison is presented of these measurements with results of Monte Carlo (LAHET/MCNP) calculations of the cold neutron #uxes produced in the prototype assembly by a beam of 800 MeV protons incident on the tungsten target. A UCN detector was coupled to the assembly through a guide system with a critical velocity of 8 m/s (58Ni). The rates and time-of-#ight data from this detector are compared with calculated values. Measurements of UCN production as a function of SD 2 volume (thickness) are compared with predicted values. The dependence of UCN production on SD 2 temperature and proton beam intensity are also presented. ( 2000 Elsevier Science B.V. All rights reserved.

Experimental value of GA/GV from a measurement of both P-odd correlations in free-neutron decay

A new experimental value of the fundamental weak-interaction parameter λ=GA/GV (−1.2686±0.0046) is obtained for the first time by an original method that consists in measuring both P-odd correlations in free-neutron decay.

UCN anomalous losses and the UCN capture cross-section on material defects

Abstract Experimental data shows anomalously large ultra cold neutrons (UCN) reflection losses and that the process of UCN reflection is not completely coherent. UCN anomalous losses under reflection cannot be explained in the context of neutron optics calculations. UCN losses by means of incoherent scattering on material defects are considered and cross-section values calculated. The UCN capture cross section on material defects is enhanced by a factor of 10 4 due to localization of UCN around defects. This phenomenon can explain anomalous losses of UCN.

Depolarization of ultracold neutrons during their storage in material bottles

The depolarization of ultracold neutrons (UCN) during their storage in traps has been investigated. The neutron spin-flip probability for the materials studied amounts to ∼ (1–2) × 10 −5 per collision and does not depend on the temperature. The possible connection between the phenomenon of UCN depolarization and that of anomalous losses is discussed.  2003 Published by Elsevier Science B.V.

Low energy upscattering of UCN in interaction with the surface of solid state

Abstract In connection with the problem of anomalous losses of ultracold neutrons (UCN) in the storage in the material traps the measurements of quasi-elastic scattering of UCN in collisions with trap surface coated with beryllium have been carried out. It was observed that the probability of quasi-elastic scattering of UCN from energy interval 0–77 neV to 90–200 neV is ( 2.2 ± 0.2 ) × 10 −8 per collision therefore the process of quasi-elastic scattering cannot explain the effect of anomalous losses which is on the level 3 × 10 −5 .

A proposed measurement of the ß asymmetry in neutron decay with the Los Alamos Ultra-Cold Neutron Source

This article reviews the status of an experiment to study the neutron spin-electron angular correlation with the Los Alamos Ultra-Cold Neutron (UCN) source. The experiment will generate UCNs from a novel solid deuterium, spallation source, and polarize them in a solenoid magnetic field. The experiment spectrometer will consist of a neutron decay region in a solenoid magnetic field combined with several different detector possibilities. An electron beam and a magnetic spectrometer will provide a precise, absolute calibration for these detectors. An A-correlation measurement with a relative precision of 0.2% is expected by the end of 2002.