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Submitted on 1 Jan 1984
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AN EXPERIMENTAL SEARCH FOR THE NEUTRON ELECTRIC DIPOLE MOMENT : RESULTS AND PROSPECTS OF REFINEMENT
V. Lobashev, A. Serebrov
To cite this version:
V. Lobashev, A. Serebrov. AN EXPERIMENTAL SEARCH FOR THE NEUTRON ELECTRIC DIPOLE MOMENT : RESULTS AND PROSPECTS OF REFINEMENT. Journal de Physique Col- loques, 1984, 45 (C3), pp.C3-11-C3-12. �10.1051/jphyscol:1984302�. �jpa-00224016�
JOURNAL DE PHYSIQUE
Colloque C 3 , supplement au n ° 3 , Tome ^ 5 , mars 198<f page C3-11
AN EXPERIMENTAL SEARCH FOR THE NEUTRON ELECTRIC DIPOLE MOMENT : RESULTS AND PROSPECTS OF REFINEMENT
V.M. Lobashev and A.P. Serebrov
Leningrad Nuclear Physics Institute, Gatchina, Leningrad District 188350, U.S.S.R.
Résumé.- Les résultats de l'expérience concernant la recherche du moment de dipôle électrique du neutron sont présentés. Les perspectives d'amélioration de la précision des mesures sont discutées.
Abstract.- The results of an experimental search for the neutron electric dipole moment are presented and prospects of further refinements discussed.
Experiments searching for the neutron electric dipole moment (EDM) as a measure of CP violation are of crucial importance for the physics of elementary particles. The interest to this problem stem from the need of incorporating CP violation into the gauge invariant theories and from the connection of CP violation with the baryon asymmetry in the Universe.
The most precise way to measure the neutron EDM is to use the magne- tic resonance method involving ultracold neutrons (UCN). Two experi- mental installations of this type are available at present, namely, in the Leningrad Nuclear Physics Institute, Academy of Sciences of the U.S.S.R. (LNPI, Gatchina), and the Institute Laue-Langevin (ILL, Grenoble).
This communication reports on the results of an experimental search for the neutron EDM carried out in LNPI in 1981-82. The installation is at present under reconstruction undertaken with the purpose of improving the measurement precision. The second part of the communication deals with possible ways of refining the experiment and with results obtained in this direction.
The installation used is a flow-through type with a neutron contain- ment time of 5 - 7 s, the UCN gas density at spectrometer entrance of
2 n/cm3, and electric field strength of 15 kV/cm. A detailed description of the installation is given elsewhere /1,2,3/. The measurements performed, on the whole, for about 60 days yielded for
the neutron EDM a value dn = -(2.0 ± 1. 0 ) • 1C^-* e.cm which is equivalent to establishing an upper level of |dn| 4. 4.10~2-> e«cm at a 90% confidence level. For a more comprehensive discussion of this result see /4,5/.
Further refinement of the measurement precision assumes an increase of UCN flux density and of neutron containment time by turning over from a flow-through to storage type specrtometer. The latter requires a substantial improvement of magnetic field stability. To achieve these goals, the following work is being carried out:
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1984302
C3-12 J O U R N A L D E PHYSIQUE
1. Development of a new UCN source and guide;
2. Development of a system for neutron containment in the storage mode ;
3. Development of a superconducting screen for magnetic field stabi- lization in the spectrometer,
The enhancement of UCN flux density at the exit of the new channel estimated as a factor 4 - 5 is achieved by placing the cold source in the maximum reactor thermal neutron flux (at core center1,increasing the size and optimising the shape of liquid hydrogen moderator, and improving the transmission of the neutron guide by increasing its cross sectional area, The expected characteristics of UCN flux at the new channel exit are: total UCN flux 4.105 n/s, UCN flux den- sity 5.103 n/cm2s, UCN gas density 10 n/cm3, Apart from this
,
the cold source will simultaneously be used to produce a polarised cold neutron beam of total flux 2.1010 n/s, maximum. density 7.108 n/cds, with the maximum of the spectrum at 4 A. The new all-purpose channel of ultracold and polarised cold neutron is at present under construction.
Work on the assembly of the storage-type spectrometer with super- conducting screen and a special refrigarator for its cooling has just been completed, The superconducting screen has been tested.
The storage chambers of the spectrometer are, as before, of diffe- rential design (i,e, two chambers with oppositely directed electric fields), thus providing a possibility of monitoring the various systematic effects in the cource of measurements. In contrast to the previous design, high voltage is applied to the central electrode (which is common for the two chambers), the upper and lower electrodes being grounded, This permits one localise leakage currents in the storage chambers and facilitates control of the possible spurious effects due to the leakage currents. IfIeasurements are planned to begin at the end of this year with the previous liquid hydrogen UCN source. It would be difficult to estimate the actual gain in precision due to the spectrometer operating in the storage mode. Combining a certain audacity with cautions optimism, one may expect a gain in precision by a factor 2 - 3
,
and afterputting in service the new UCN source, by a factor 5 - 6 , whict will then yield for the precision of measurements a value -2-10-2 e~cm, References
1. ALTAREV I.S. et al., Nucl.Phys, (1980) 269.
2. ALTAREV 1.S. et al,, ?hys,Lett, (1980) 413, 3. ALTAREV 1,s. et al., Phys,Lett.
a
(1981) 13.4. ALTAREV I.S, et al,, 4th International Sysmposim on (n,f)-spec- troscopy and related topics, 7-11 September 1981, Grenoble.
5. LOBASHEV V.hl., Proceedings of International Conference Neutrino-82. 14-1 9 July 1982, Balaton, Hungary, v. 2, p. 107.
