Yu. Sobolev

New measurement of the electric dipole moment of the neutron

Abstract A new experiment on the search for the electric dipole moment of the neutron was carried out using a magnetic resonance set-up with electric field and stored ultracold neutrons. The EDM of the neutron was measured to be +(2.6±4.2±1.6)×10−26 e cm, the first error being RMS or statistical and the second one systematical. An upper limit at the 95% CL is |dn|

New Limit on Lorentz-Invariance- and CPT-Violating Neutron Spin Interactions Using a Free-Spin-Precession

We report on the search for a CPT- and Lorentz-invariance-violating coupling of the He3 and Xe129 nuclear spins (each largely determined by a valence neutron) to posited background tensor fields that permeate the Universe. Our experimental approach is to measure the free precession of nuclear spin polarized He3 and Xe129 atoms in a homogeneous magnetic guiding field of about 400 nT using LTC SQUIDs as low-noise magnetic flux detectors. As the laboratory reference frame rotates with respect to distant stars, we look for a sidereal modulation of the Larmor frequencies of the colocated spin samples. As a result we obtain an upper limit on the equatorial component of the background field interacting with the spin of the bound neutron b(⊥)(n)<8.4 × 10(-34)  GeV (68% C.L.). Our result improves our previous limit (data measured in 2009) by a factor of 30 and the worlds best limit by a factor of 4.

^3

We discuss the design and performance of a very sensitive low-field magnetometer based on the detection of free spin precession of gaseous, nuclear polarized 3He or 129Xe samples with a SQUID as magnetic flux detector. The device will be employed to control fluctuating magnetic fields and gradients in a new experiment searching for a permanent electric dipole moment of the neutron as well as in a new type of 3He/129Xe clock comparison experiment which should be sensitive to a sidereal variation of the relative spin precession frequency. Characteristic spin precession times T_2 of up to 60h could be measured. In combination with a signal-to-noise ratio of>5000:1, this leads to a sensitivity level of deltaB= 1fT after an integration time of 220s and to deltaB= 10^(-4)fT after one day. Even in that sensitivity range, the magnetometer performance is statistically limited, and noise sources inherent to the magnetometer are not limiting. The reason is that free precessing 3He (129Xe) nuclear spins are almost completely decoupled from the environment. That makes this type of magnetometer in particular attractive for precision field measurements where a long-term stability is required.

He -

Abstract An installation using a light-water neutron trap in the reactor core as a proton target is described. Results of the main and control measurements are presented which permit one to conclude that the parity-violating circular polarization of the γ-rays from the np → d γ reaction is P γ = (1.8 ± 1.8) × 10 −7 .

^{129}

The neutron drip line in a neon–magnesium region has been explored by the projectile fragmentation of a 59.8 A MeV 48Ca beam using the new fragment separator LISE 2000 at GANIL. New neutron-rich isotopes, 34Ne and 37Na, have been observed together with some evidence for the particle instability of 33Ne and 36Na.

Xe Comagnetometer

The result of measuring the electric dipole moment (EDM) of the neutron by using ultracold neutrons is presented. The results of the measurements give the value of the EDM: d/sub n/4=(plus-or-minus7.5) x 10/sup -25/ excm. Hence, it can be concluded that vertical-bardvertical-bar<1.6 x 10/sup -24/ excm at the 90% confidence level.

Ultra-sensitive magnetometry based on free precession of nuclear spins

A clock comparison experiment, analyzing the ratio of spin precession frequencies of stored ultracold neutrons and 199Hg atoms, is reported. No daily variation of this ratio could be found, from which is set an upper limit on the Lorentz invariance violating cosmic anisotropy field b perpendicular < 2 x 10(-20) eV (95% C.L.). This is the first limit for the free neutron. This result is also interpreted as a direct limit on the gravitational dipole moment of the neutron |gn| < 0.3 eV/c2 m from a spin-dependent interaction with the Sun. Analyzing the gravitational interaction with the Earth, based on previous data, yields a more stringent limit |gn| < 3 x 10(-4) eV/c2 m.

A new experimental study of the circular polarization of np capture γ-rays

The effort towards a new measurement of the neutron electric dipole moment (nEDM) at the Paul Scherrer Instituts (PSI) new high intensity source of ultracold neutrons (UCN) is described. The experimental technique relies on Ramseys method of separated oscillatory fields, using UCN in vacuum with the apparatus at ambient temperature. In the first phase, R&D towards the upgrade of the RAL/Sussex/ILL apparatus is being performed at the Institut Laue-Langevin (ILL). In the second phase the apparatus, moved from ILL to PSI, will allow an improvement in experimental sensitivity by a factor of 5. In the third phase, a new spectrometer should gain another order of magnitude in sensitivity. The improvements will be mainly due to (1) much higher UCN intensity, (2) improved magnetometry and magnetic field control, and (3) a double chamber configuration with opposite electric field directions.

Experimental evidence for the particle stability of 34Ne and 37Na

We report on the search for Lorentz-violating sidereal variations of the frequency difference of colocated spin species while the Earth and hence the laboratory reference frame rotates with respect to a relic background field. The comagnetometer used is based on the detection of freely precessing nuclear spins from polarized 3 He and 129 Xe gas samples using SQUIDs as low-noise magnetic flux detectors. As result we can determine the limit for the equatorial component of the background field interacting with the spin of the bound neutron to be b n ⊥ < 3.7 · 10- 32 GeV (95% C.L.).

Search for an Electric Dipole Moment of the Neutron

Abstract The precise knowledge of the neutron polarisation is needed in tests of the electroweak Standard Model using angular correlations in polarised neutron beta decay. We performed an experimental comparison study of two different methods of polarisation analysis of a cold neutron beam which are based on spin-dependent reflection, respectively, transmission. The compared devices are a supermirror analyser used in prior neutron decay studies and an opaque transmission spin filter of either polarised 3 He or polarised protons. The results of the neutron polarisation measured with the supermirror analyser and with the spin filter coincided in three different experiments within 0.1–0.2%.