V.V. Voronin

Direct measurement of the delay time for a neutron in a crystal in the case of the Laue diffraction

The dynamical Laue diffraction has been studied for a direct beam diffracted from a thin (∼3.5 cm) α-quartz crystal at the Bragg angles close to 90°. It is shown that diffraction occurs at Bragg angles up to 87°. The time-of-flight method is used to measure the time of the neutron presence in the crystal under the diffraction conditions. The time delay for a scattered neutron inside the crystal predicted earlier for the Bragg angles close to 90° confirmed experimentally. The effective velocity of the neutron propagation in a crystal measured at the incident-neutron velocity of 810 m/s and the diffraction angle of 87° equals (43±1) m/s. The result obtained confirms the possibility of increasing, by an order of magnitude, the sensitivity of the diffraction method of determining the dipole moment of a neutron at Bragg angles close to 90° predicted earlier theoretically.

Measurement of the neutron electric dipole moment via spin rotation in a non-centrosymmetric crystal

AbstractWe have measured the neutron electric dipole moment using spin rotation ina non-centrosymmetric crystal. Our result is d n = (2.5 ± 6.5 stat ± 5.5 syst ) ·10 −24 ecm. The dominating contribution to the systematic uncertainty is sta-tistical in nature and will reduce with improved statistics. The statistical sensi-tivity can be increased to 2·10 −26 ecm in 100 days data taking with an improvedsetup. We state technical requirements for a systematic uncertainty at the samelevel. Keywords: electric dipole moment, CP violation, perfect crystal, neutron,diffraction, three-dimensional polarisation analysis PACS: 14.20.Dh, 61.05.fm, 04.80.Cc1. IntroductionElectric dipole moments (EDMs) of elementary particles belong to the mostsensitive probes for CP violation beyond the Standard Model of Particle Physics[1]. Constraining or detecting EDMs of different systems allows to gather ex-perimental information about models for new physics that is complementary tohigh energy physics data.For the neutron EDM (nEDM), the most sensitive results [2, 3] were ob-tained using ultracold neutrons and Ramsey’s resonance method. See [4] fora recent review of measurements using free neutrons. Measurements using theinteractionof neutrons with the atomic electric field in absorbingmatter werepi-oneered by Shull and Nathans [5]. Abov and colleagues [6] first discussed a spin-dependent term in the scatteringamplitude for neutronsin non-centrosymmetricnon-absorptive crystals. This term is caused by the interference of nuclear and

Measurement of the neutron electric dipole moment by crystal diffraction

An experiment using a prototype setup to search for the neutron electric dipole moment by measuring spin rotation in a non-centrosymmetric crystal (quartz) was carried out to investigate statistical sensitivity and systematic effects of the method. It has been demonstrated that the concept of the method works. The preliminary result of the experiment is dn=(2.5±6.5)×10-24ecm. The experiment showed that an accuracy of ~2.5×10-26ecm can be obtained in 100 days data taking, using available quartz crystals and neutron beams.

Set-up for searching a neutron EDM by the crystal-diffraction method: first measurements

Abstract The first experimental study of the new effects predicted early was conducted, using the recently created set-up designed for searching a neutron EDM by the crystal-diffraction technique. The effect of a considerable delay of the diffracting neutron in the crystal for Bragg angles close to 90° and the effect of a depolarization of diffracting neutrons in the crystal without a centre of symmetry were first observed. The existence of the dynamical diffraction in a thick ( 14×14×3.5 cm 3 ) noncentrosymmetric α-quartz crystal for Bragg angles up to 87° was demonstrated. It is experimentally shown that the value Eτ, where E is an electric field and τ is the interaction time, determined the sensitivity of the method to neutron EDM in our case can be ∼0.2×10 6 V s / cm , what is comparable with the Ultracold neutrons (UCN) method.

Neutron diffraction test on spin-dependent short range interaction

The direct constraint on the parameters of short range pseudomagnetic interaction of free neutron with matter is obtained from the recent test experiment on a search for neutron EDM by crystal-diffraction method [1]. It is shown that this constraint on a product of scalar to pseudo-scalar coupling constants gSgP is better than that of any other method for the range λ < 10−5 cm.

Depolarization of a neutron beam in Laue diffraction by a noncentrosymmetric crystal

The depolarization of a neutron beam executing Laue diffraction in a thick (∼3.5 cm) noncentrosymmetric α-quartz crystal is observed. This effect was predicted by us earlier and suggested for measuring the electric dipole moment (EDM) of a neutron. The effect is due to an interaction of the magnetic moment of a moving neutron with a strong crystal electric field, as a result of which the neutron spin rotates in opposite directions for waves of two types excited in the crystal. The effect is studied for neutron diffraction by a system of crystallographic (110) planes at Bragg angles close to π/2, up to 87°. It is shown that, for a crystal of thickness L=3.5 cm, a direct beam initially polarized along the reciprocal lattice vector becomes depolarized upon diffraction, irrespective of the value of Bragg angle, whereas the beam polarized perpendicular to the diffraction plane retains its polarization. The Eτ value determining the sensitivity of the method to EDM is experimentally estimated.

Rotation of neutron spin in passing through a noncentrosymmetric single crystal

Rotation of the spin of cold neutrons passing through a noncentrosymmetric single crystal is observed. This effect is caused by the Schwinger interaction of the magnetic moment of a moving neutron with the crystalline electric field in a noncentrosymmetric single crystal and depends both on the direction of neutron trajectory in the crystal and on its energy. It is shown that the characteristic magnitude of the effect for α-quartz is ≃(1–2)×10−4 rad/cm over a wide wavelength range (from 2.8 to 5.5 Å) and is determined by the degree of beam monochromaticity [Δλ/λ=(2–5)×10−2 in our experiment]. This magnitude corresponds to an electric field of ≃(0.5–1)×105 V/cm acting on a neutron. The measured value agrees well with the theoretical calculation.

Neutron laue diffraction in a weakly deformed crystal at the Bragg angles close to π/2

An essential magnification of an external force acting on a diffracting neutron for the Bragg angles θB close to the right one is observed. Any external action (caused by either crystal deformation or external force affected the neutron) results in a bend of the so called “Kato trajectories” inside the crystal and, for the case of a finite crystal, gives considerable variation of the intensities of both diffracted neutron beams (direct and reflected). It is shown that the magnification factor is proportional to tan2 (θb) and can reach (102−103) for Bragg angles surfficiently close to 90°.

Diffraction enhancement effect and new possibilities of measuring the electric charge of the neutron and its inertial-to-gravitational mass ratio

Diffraction enhancement of small effects affecting a neutron undergoing Laue diffraction at Bragg angles θB close to 90° is predicted and experimentally observed. The enhancement is due to the delay of the neutron inside the crystal during diffraction and is proportional to tan2θB. As a result, the diffraction enhancement factor may be as large as ∼108–109. On this basis, a new method is proposed for searching for the electric charge of the neutron and for measuring the ratio of its inertial mass mi to the gravitational mass mG. It is shown that the accuracy of the neutron charge measurement can be improved by more than two orders of magnitude in relation to the present-day accuracy and that the ratio mi/mG can be measured to an precision of σ(mi/mG) ∼ 10−6.

FIRST OBSERVATION OF THE NEUTRON SPIN ROTATION FOR LAUE DIFFRACTION IN A DEFORMED NONCENTROSYMMETRIC CRYSTAL

Detailed study of a neutron Laue diffraction in a noncentrosymmetric crystal was carried out using a prototype of the experimental setup to measure the neutron electric dipole moment (nEDM) by Laue diffraction method (LDM). A new kind of spin rotation effect was observed for the first time. We attribute this effect to a difference of the two Bloch waves amplitudes in the crystal, which is caused by the presence of the definite small crystal deformation. In a revised scheme of the experiment, this effect could be exploited for a purposeful manipulation of the Bloch waves.