I.A. Kuznetsov

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.

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.

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.

VERIFICATION OF THE WEAK EQUIVALENCE PRINCIPLE WITH LAUE DIFFRACTING NEUTRONS: TEST EXPERIMENT

We propose a novel experiment to test the weak equivalence principle (WEP) for the Laue diffracting neutron. Our experiment is based on an essential magnification of an external affect on neutron diffracting by Laue for the Bragg angles close to the right one in couple with additional enhancement factor which exists due to the delay of the Laue diffracting neutron at such Bragg angles. This enhancement phenomena is proposed to be utilized for measuring the force which deviates from zero if WEP is violated. The accuracy of measuring inertial to gravitational neutron masses ratio for the introduced setup can reach ∼10−5, which is more than one order superior to the best present-day result.

Birefringent magnetic field system for experimental checking of neutron electroneutrality by the spin interferometry technique

We describe the structure design and present the results of experimental testing of a birefringent magnetic neutron prisms for spin-echo small-angle neutron scattering (SESANS). The SESANS setup, equipped with perfect single crystals for measuring diffraction-enhanced spin interference effects, must possess unprecedented sensitivity with respect to small external actions on a neutron and is intended for use in experiments for checking the neutron electroneutrality.

The crystal acceleration effect for cold neutrons

A new mechanism of neutron acceleration is discussed and studied experimentally in detail for cold neutrons passing through the accelerated perfect crystal with the energies close to the Bragg one. The effect arises due to the following reason. The crystal refraction index (neutron-crystal interaction potential) for neutron in the vicinity of the Bragg resonance sharply depends on the parameter of deviation from the exact Bragg condition, i.e. on the crystal-neutron relative velocity. Therefore the neutrons enter into accelerated crystal with one neutron-crystal interaction potential and exit with the other. Neutron kinetic energy cannot vary inside the crystal due to its homogeneity. So after passage through such a crystal neutrons will be accelerated or decelerated because of the different energy change at the entrance and exit crystal boundaries.

Bragg resonance behavior of the neutron refractive index and crystal acceleration effect

The energy dependence of neutron refraction index in a perfect crystal for neutron energy, close to the Bragg ones, was studied. The resonance shape of this dependence with approximately the Darwin width was found. As a result, the value of deviation from the exact Bragg condition can change during the neutron time of flight through the accelerated crystal and so the refraction index and the velocity of outgoing neutron can change as well. Such new mechanism of neutron acceleration in the accelerating perfect crystal was proposed and found experimentally. This mechanism is march more effective then known one concerning with the neutron acceleration in the accelerating usual media.

Anomalous behavior of neutron refraction index in a perfect crystal near the Bragg reflex

Anomalous behavior of neutron refraction index in a perfect crystal near Bragg resonance was studied. This phenomenon is connected with the resonance behavior of potential of neutron interaction with crystal near the Bragg reflex. The amplitude of this resonance is equal to magnitude of g-harmonic of neutron interaction potential Vg and width is about the Bragg width of reflex. Recently, it was shown that for the case of noncentrosymmetric crystal this effect result in a large electric field acting on a neutron (value of the field can reach about 108V/cm) . This effect is planed using to search for the electric dipole moment of a neutron. If the degree of crystal imperfect is less than the Bragg reflection width (case of perfect crystal) the width of the reflex is determined by the own width of crystal reflex that is about 10−5 of the neutron energy. The value of g-harmonics of interaction of neutron with crystal Vg and optical potential of the interaction of neutron with crystal V0 are usually about the same. Therefore the variation of neutron energy on a 10−5 of its value will change significantly a potential of neutron interaction with crystal.