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Submitted on 1 Jan 1971
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NEUTRINO EXPERIMENTS IN GARGAMELLE
P. Musset
To cite this version:
P. Musset. NEUTRINO EXPERIMENTS IN GARGAMELLE. Journal de Physique Colloques, 1971, 32 (C3), pp.C3-105-C3-108. �10.1051/jphyscol:1971315�. �jpa-00214596�
JOURNAL DE PHYSIQUE Colloque C3, supp@ment au no 10, Tome 32, Octobre 1971, page C3-105
NEUTRINO EXPERIMENTS IN GARGAMELLE
P. MUSSET
Ecole Polytechnique Paris and GERN Geneva
R6sum6. - Les proprietb de la chambre B bulles Gargamelle pour la physique du neutrino sont passees en revue.
La premiere experience sera centree sul les proprietes d'invariance d'echelle, ie rapport a ( v ) / a ( i ) les recherches du boson intermkdiaire, des courants neutres, et d'un eventuel troisikme lepton.
Les possibilitk d'une experience au propane, su~tout destinee a l'etude des Cvenements sur hydro- gene, et le domaine des hautes energies sont evoques.
Abstract. - The properties of the bubble chamber Gargamelle in the neutrino physics are reviewed.
The first experiment is mainly centered on the study of the scaling, the ratio o(v)/g(V), the searches for the intermediate boson, the neutral currents, and a third possible lepton.
The possibilities of a propane experiment, the main interest of which is the hydrogen events study, and the high energy domain are also mentioned.
An experiment of lo6 pictures, v and 5 is planned for 1971-1972.
The heavy liquid chamber has been built by a colla- boration of CEA, DBpartement Saturne, Ecole Poly- technique, Paris, Laboratoire de 1'AccCltrateur Lineaire Orsay, with the participation of CERN.
The first pictures of cosmic rays have been taken in December 1970, and a first test run in a neutrino beam had taken place in January 1971 (Fig. 1).
FIG. 1. - One of the first neutrino events found in Gargamelle
tion of the muon, about a factor three better than in previous chambers.
FIG. 2. - The chamber body entering the magnet, which was
partially dismounted for that operation.
v + p + p - p n + . The characteristics of the beam are given in figure 3,
the pions contribute mostly to the low-energy part, The chamber has the following dimensions : and the kaons to the high-energy part of the spectrum.
Length : 4.8 m ; diameter : 1.9 m. The field is The flux will be carefully measured during the run by 20 kG (Fig. 2). We intend to use heavy freon CF,Br muons detectors placed inside the shielding of iron. We (d = 1.5 g/cm, 2 = 80 cm, Xo = 11 cm), in order to expect a precision of - 7 %, about a factor three obtain good statistics. We will have a good identifica- better than in previous runs.
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1971315
C3-106 P. MUSSET
FIG. 3. - Flux of v and of v at different energies.
Taking into account the volume of the chamber, the efficiencies of the beams and the nature of the liquid, we expect an increase of a factor 50 in statistics with respect t o the last 1967 run. We have tested that num- ber in the January run and found one v-event every twenty pictures.
Assuming some further improvements would have been done, a ratio 115 for the number of v/?, events (*) and 5 x lo5 pictures of each v and T, we obtain :
/ Elastic 7.5 K events
\, 1 strange p. 0.25 -
i Elastic 3 K events
Subjects of physical interest.
The emphasis of this experiment is on the scale- invariance properties.
1 . Study of the cross-section as a function of the energy. - Scale invariance predicts that o = KE, In that case, K will be determined to about 5 %. The pre- cision for the cross section at 10 GeV is for example of 6 %, Figure 4 gives the results of the previous expe- riments. I t is also possible to obtain a test of scaling independently from the knowledge of the flux : figure 5 gives the p a s a function of v for the previous experiments, and seems to indicate the same behaviour as the electro-production plots with the Bloom- Gilman variable x' = q2/(2 Mp v f M:) instead of x = q2/2 Mp v. (Fig. 5).
(*) A factor + to +, depending on the v-energy, is coming from the beam.
X FREON 1963164 (nwmalised) PROPANE 1967
/
9
/ '
NEUTRINO ENERGY E ( G ~ v )
FIG. 4. - Cross section as a function of energy.
FIG. 5. - Test of scaling : 2 as a function of v.
2. Ratio of the cross/section o,lo:. - There has been various predictions on the o,/o, ratio, depending on the partons models considered, ranging from 1 to 3.
Nachtman at this session predicts also bounds for this ratio. About 2 K events for v and 0.5 K events for 7 will be disponible on the (( scaling region D.
NEUTRINO EXPERIMENTS I N GARGAMELLE 3. Intermediate vector boson. - It has been pro-
posed that the intermediate vector boson may manifest itself by producing a curvature of the cross-section curve (Fig. 6j. In that case we will be able to detect these effects for a boson mass of 4-5 GeV.
Expected accuracy on total 3 cross -section for 5x10' pictures and effect of finite Boson mass
FIG. 6. - Expected effect of a W-boson on the cross section.
A study of the differential cross-sections do/dq2 may be a better check, looking directly at the specified q2 dependence of the W-propagator.
4. Structure functions and sum rules. - The struc- ture functions defined elsewhere in the Meribel report will be studied with the scale variable x = q2/2 M, v and various predicted forms can be tested from this study. In particular the Callan-relation 2 Fl/xF2 = 1 which tells us that, in partons models, the spin of the partons is 4, and the ratio xF3/F2, which is a mesure of the cc mean baryonic number D of the partons will be examined.
The fact that the number of protons and neutrons in nuclei are approximately equal, enable us to have a good precision for the even structure functions W: + WXn = wi+ that is true also for the sum rules of
f (x) dx(W: + W:). The V-A interference term, i. e. w:, is simply obtained by substracting v from 7 differential cross-sections. Separate W: and W:
are possible but more difficult to obtain. The present status of the ratio
could pose a problem, since in the absence of isoscalar contribution to the electromagnetic current, and assuming an equivalent contribution of v and A weak currents, it is predicted to be 0.25 and may even rise to 0.5 with further assumptions. This also will be measu- red with better precision.
5. Strange particle production. - The problem is complicated by the associated production background, at the lower vertex or in the reinteraction of pions inside the nucleus. The chamber has good efficiency to detect strange particles by their decays ( A , KO, K + ...) so that we can hope to evaluate and substract this background from the one-strange particle events.
The ratio of the A S = 1 to the A S = 0 cross sections have been predicted in different models, and is always of the o (tg2 0,). We will obtain o (250 events) in the v run, half of them being identified.
We can also look for specific channels for kaons production, for example,
and compare their rates to the corresponding rates for the pion production.
We expect also to obtain 150 events in the 7 run, which may serve to test the inverse hyperon leptonic decays. Here also the background has to be substracted.
5. Direct search for the intermediate vector boson. -
The search for the decay of the intermediate boson W + pv, W -+ ev will enable us to move the previous limit of 1.8 GeV to 3 GeV on its mass. We can also look for the mass spectrum of 2 and 3 pions in inelastic collisions.
6. Diagonal coupling. - The search for the pro- cesses ve + e- -+ ve + e- will permit to put a limit on the diagonal coupling. A diagonal constant equal to the ordinary Fermi constant corresponds to 0.3 event in the v run.
7. Neutral currents. - We can look for process like
The background here is due to neutron interactions.
One can evaluate the background by measuring the exponential decrease of the background over the length of the chamber (5 1) and the limit for the ratio
ovp'vp can be lowered to -- 0.03.
ovn-tpp
8. Third neutrino. - We intend to search for weak neutrals particles produced practically at the proton
C3-108 P. MUSSET interactions by eliminating the decay path, the protons being sent in an uranium target placed in the shielding.
Assuming a cross-section for these hypothetical objects equal to that of neutrinos, one can have a sensitivity of cm2 for the production cross-sections in a few- days run.
9. Propane runs. - It will be useful to complete our sample of neutrino events by making a propane run after the freon run. The free proton events (18 %) can be separated with a small (5-10 %) background, so that the separation neutron-proton can be achieved in particular for the deep inelastic reactions. The details of the hadronic shower (distributions in p,, q2, etc.. .) can also be studied.
Gargamelle is a unique instrument for such studies : it is necessary to have at the same time free-proton events and the precise measure of the energies of the
secondaries, including neutrals, since the v-energy has to be measured by the secondaries.
The production of strange particles, hyperon and kaon will be subject to less background Finally the quasi-elastic reactions Tp -+ y' n, y + nno can be better studied than in a hydrogen chamber, since they include neutral secondaries.
We finally note that in the long future, the neutrino interactions at a 150 GeV machine seem to be promi- sing, for example for the search or the study of an inter- mediate vector boson, for the extension of the scaling region by a large factor, for reactions on heavy nuclei giving rise to coherent production of lepton pairs :
that tests the purely leptonic interactions, and finally because of the increase of statistics due to the assumed energy behaviour of the cross-sections.
