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Submitted on 1 Jan 1984
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SEARCH FOR NEUTRINO OSCILLATION AT BUGEY
J. Cavaignac, Y. Declais, A. Hoummada, H. de Kerret, D. Koang, H. Pessard, J. Thenard, B. Vignon
To cite this version:
J. Cavaignac, Y. Declais, A. Hoummada, H. de Kerret, D. Koang, et al.. SEARCH FOR NEUTRINO
OSCILLATION AT BUGEY. Workshop on Reactor Based Fundamental Physics, 1983, Grenoble,
France. pp.C3-133-C3-134, �10.1051/jphyscol:1984324�. �jpa-00224038�
JOURNAL DE PHYSIQUE
Colloque C3, supplgment au n03, Tome 45, mars 1984 page C3-133
SEARCH FOR NEUTRINO OSCILLATION AT BUGEY
J.F. H. Pessard, J.M. ~henard*and Cavai nac, Y. ~eclais*;
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A. B. Hoummada, Vignon H. de ~ e r r e c D.H. Koang,I n s t i t u t des Sciences Nuclgaires, IN2P3, 38026 Grenoble Cedex, France
*LAPP, IN2P3, B.P. 909, 74019 Annecy l e vieux Cedex, France
R6sm6
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Le flux des ve produits par l e coeur d'un r6acteurPWR
de-Bugey a 6t6 u t i l i s 6 pour rechercher l e s o s c i l l a t i o n s neutrino 2 l ' a i d e de l a reaction ve + p + e+ + n.Les mesures ont 6t6 e f f e c t d e s B 2 distances : 13,s m e t 18,5 m. Environ 50 000 6vbne- ments neutrino ont 6t6 d6tect6s 2 l a premiSre position e t 25 000 6vSnements 2 l a se- conde position. L'analyse des r e s u l t a t s e s t en cours d'achsvement.
Abstract - The high f l u x of low energy
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produced by the core of a PWR reactor of Bugey power plant has been used t o sear& f o r evidence of neutrino o s c i l l a t i o n s through the inverse beta decay reaction Te + p -+ e+ + n.Measurements have been performed a t two distances (13.5 and 18.5m). About 50 000 events have been collected a t the f i r s t position and 25
Om
ve events a t the secons one. Data analysis is allnost completed.Introduction
The high flux of lo3u energy
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produced by the core of a PWR reactor (2785 Wth) of Bugey power plant i s use8 t o search f o r evidence of neutrino o s c i l l a - tions through t h e inverse beta decay reaction Fe + p -+ e+ + n. The previous experi- ment a t ILL-Grenoble, [ r e f . 1 1, has shown t h a t o s c i l l a t i o n s i f they e x i s t i n t h e eV range would happen only with a small mixing angle. To reduce both the s t a t l s t l c a l and systematical uncertainties, we have undertaken a two distance measurement taking avan- tage of the high ve flux available a t tne Bugey basement (2.10-13 ve/cm2 sec.a t 13.5 m and 1013 ve/cm2 sec a t 18.5 m ; a s compared t o the 1012 Ge/cm2 sec a t ILL.).
Experimental set-up
The detector, similar t o the one previously used a t the ILL reactor r e f . l , consists o f f i v e planes of s i x t a r g e t c e l l s f i l l e d with liquid s c i n t i l l a t o r (321 li- t e r s of IVL: 23:L), a l t e r n a t e d with four 3 ~ e wire-chambers. The l i q u i d s c i n t i l l a t o r ser- ves as PI-oton t a r g e t , prompt positron detector and neutron moderator. The thermalized neutrons a r e detected by the neighbouring 3~e-counters. A neutrino event is signed by the delayed coincidence between t a r g e t c e l l and 3 ~ e chamber.
The detector i s completyly surrounded by 7 cm of low a c t i v i t y lead, 10 cnl of veto counters f i l l e d with l i q u i d s c i n t i l l a t o r , 25 cm of bored water and 10 cm of lead. For both positions, the same designs of shielding a r e used arid t h e aiiount of material overhead i s more than 25 cm of water equivalent, reducing the mon f l u x by nlm-e than a factor of 5. In addition, t h e remining f a s t neutrons a r e rejected by the pulse shape discrimination technique. Background was melisured f o r both positions du- r i n g the annual shut-down of the reactor i n March-April 1983 and no s i p i f i c a n t reactor associated accidental background was found. S t a b i l i t i e s of apparatus, were controlled on l i n e and have been frequently checked using g m a and neutron sources.
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1984324
C3-134 JOURNAL DE PHYSIQUE
The detector efficiency mapping using calibrated Sb(Be1 neutron source have been achived in July 1983. About 50 OUO neutrino-events have been detected at 13.5 m and 25 000 at 18.5 m.
The data analysis is almost completed. The final results on the oscillation of neutrinos from the present experiment could be soon presented.
The aim of our present experimeilt is to measured with high statistics the neutrino spectrum at two distances and thus to reduce drastically both the systenati-
cal (S 3 %) and statistical errors. Assuming a simple two state oscillation model, (ve -t v ) our experiment is most sensitive in the range of Am2 from few ev2 down to 0.03
&f?
and a limit of mixing angle sin2 20 4 0.07 could be attained.Ref. 1 : Caltech, ILL-ISN Grenoble, hnich collaboration, H. Kwon et a1
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Phys. Rev.
