AN IMPROVED METHOD TO SEARCH FOR THE NEUTRON CHARGE

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Submitted on 1 Jan 1984

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AN IMPROVED METHOD TO SEARCH FOR THE NEUTRON CHARGE

J. Kalus, R. Gähler

To cite this version:

J. Kalus, R. Gähler. AN IMPROVED METHOD TO SEARCH FOR THE NEUTRON CHARGE.

Journal de Physique Colloques, 1984, 45 (C3), pp.C3-17-C3-20. �10.1051/jphyscol:1984304�. �jpa- 00224018�

JOURNAL DE PHYSIQUE

Colloque C 3 , supplement au n ° 3 , Tome 45, m a r s 1984 page C3-17

AN IMPROVED METHOD TO SEARCH FOR THE NEUTRON CHARGE

3. Kalus and R. Gahler*

Physik Institut, Universtitat Bayreuth, Postfach 3008, D-8580 Bayreuth, F.R.G.

Physik Department, Techn. Univer. Miinchen, D-8046 Garching, F.R.G.

Résumé.- Nous présentons les modifications d'un banc optique pour mesurer la charge électrique du neutron. Il est possible d'abaisser la limite actuelle par plus d'un ordre de grandeur.

Abstract.- We describe improvements on the optical bench to measure a neutron charge. These will lower the present limit by more than one order of magnitude.

There are two main theoretical aspects, which justify the search for a charge of the free neutron even beyond the present limit of

-20 1 (-1.5 ± 1.4) x 10 electron charges :

First, a finite neutron charge together with a still speculative neutron-antmeutron transition would be in contradiction to the 2 conservation of electric charge .

Second, if the electric charges of all baryons would be slightly dis- placed from their commonly accepted values, the conservation of baryons would follow from the conservation of electric charge, rather than being an independent principle . 3

The present experimental limit was obtained b> searching for a deflec- tion of a beam of slow neutrons passing through a strong electric field of 10 m length. The beam was focussed by a cylindrical lens which produced a sharp image of the 60 nm wide entrance slit. After passage through the electric fields the neutrons were counted be- hind a slit, which was positioned in the slope of the image. A change is count rate for opposite field directions would indicate a beam deflection and hence a charge of the neutron. The parameters to de- termine the sensitivity of a neutron-charge measurement using the de- flection of a beam in a homogeneous electric field can be combined in a figure of merit f, which is inversely proportional to the limit a neutron-charge can be determined.

E-l2 -Az/J

1 A

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1984304

C3-18 JOURNAL DE PHYSIQUE

A = width of the image, assuming Gaussian shape (90km) E = electric field strength (5.9 kV/mm)

1 = length of the flightpath in the E-field (10 m) A = wavelength (20 1 .5 A)

J = counts at the detector (J/sec = 30/sec)

The values in brackets correspond to the present measurement.

In an improved experiment we will use again the beam tube H18 at the HFR-Grenoble, which delivers a spectrum of about 10-30 A wavelength and which allows for an apparatus of 13 m length. The increase of the figure of merit will come through several improvements:

1. The chromatic lens will be replaced by a cylindrically shaped mirror (Lb, see fig. 1) of high precision, which allows a reduction of the width of the image from 90 Dm to 30 bm.

2. Due to the achromaticity of this mirror, the whole spectrum for neutrons with a wavelength > 10 A can be used for imaging. This gives, compared to our last measurement, roughly 10 times more intensity J. The reduction in the width A will be 3. Nevertheless the new figure of merit increases only for a factor of about 5.

The imaging properties of this curved mirror correct for the Coriolis deflection which is proportional to A (--2OPm for 30 neutrons for a flightpath of 10 m)

.

3. A multislit system (30 slits of 30 Dm width separated by 30 fim wide absorbers) instead of a single slit is used for imaging. To scan this multislit image we use a similar multislit and thus a possible shift of these 30 slits is observed simultaneously. This will in- crease the figure of merit by a factor J 3 0 giving an overall im- provement in f for an order of mdgnitude. This optical device

-

the multislit system and the spherical mirror - is similar to the apparatus used by Kashukeev and coworkers4, where neutrons with velocities around lOm/sec will be used for a charge measurement.

4. Efforts to improve the electric field from 5.9 kV/mm to 10kV/mrn did not yet give satisfactory results. At present the obtained field is 6.5 kV/mrn.

.

This beam collimation allows for the narrow electrode gap of

^/ 3 mm.

6. Upstream of the multislit MS1 the vertical spreading due to the divergence of the beam will be limited by plane mirrors. Further downstream this confinement seems not to be possible because of technical reasons.

7. For the electric field El antiparallel to E 2 we get half the de- flection we would expect without imaging. For both fields

parallel, the deflection for a finite neutron-charge is zero. This second configuration allows checking for systematic errors. Both statements hold in case of a magnification factor 1.

Combining all these improvements, we expect a sensitivity of less than electric charges for the new apparatus. The deflection of neutrons which carry a charge of 10

-*'

Scheme of the neutron optics

s1 . 0 4 2 0 ^I ' I

Sp .2 radius height E2 MS2

MS1 . 0 0 3 2 0

Fig. 1 The new design for the deflection apparatus

JOURNAL DE PHYSIQUE

REFERENCES

1. R. Gzhler, J. Kalus, W. Mampe, Phys. Rev. D 25, 2887 (1982)

2. Cern-ILL-Padua-Rutherford-Sussex Collaboration Conference o n the neutron and its applications Cambridge Sept. 82, paper 2.A.2

3. G. Feinberg and M. Goldhaber, Proc. Nat. Acad. Sci.

U.S.A. 45, 1301 (1959) 4. N.T. Kashukeev, N.F. Chikov

Dubna Reports P 3-1266 (1979) and P 3-81-3 (1981).