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Submitted on 1 Jan 1971
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THE MUD EXPERIMENT
J.-M. Gaillard
To cite this version:
J.-M. Gaillard. THE MUD EXPERIMENT. Journal de Physique Colloques, 1971, 32 (C3), pp.C3- 123-C3-124. �10.1051/jphyscol:1971319�. �jpa-00214600�
JOURNAL DE PHYSIQUE Colloque C3, supplbment au no 10, Tome 32, Octobre 1971, page C3-123
THE MUD EXPERIMENT
J.-M. GAILLARD CERN, Geneva, Switzerland
R6sum6. - Une experience est en cours au Laboratoire de 1'Acctlerateur lintaire de Stanford pour explorer Ia possibilite qu'une particule nouvelle traverse un blindage tr6s tpais lorsqu'un faisceau intense d'electrons de grande energie le frappe. Les rtsultats prtliminaires sont suffisam- ment int6ressants pour que I'experience soit poursuivie.
Abstract. - An experiment is under way at Stanford Linear Accelerator to find out whether some unknown particle is making its way through a very thick shielding when an intense high energy electron beam is sent into it. Preliminary results are interesting enough to warrant a more extensive search.
High energy experimental physics is more and more confined into the role of checking theoretical ideas. The
(( mud experiment )) is a jump out of the beaten track, a gamble which has very little chance to succeed. The experiment is performed by a group led by M. Schwartz.
1. Experimental set-up (Fig. 1). - The SLAC elec- tron beam impinges on the water dump of the accelera- tor. The intensity is around l O I 4 electrons per second and the energy is varied between 13 and 19.5 GeV. For parts of the run a water target equivalent to 2 radiation lengths is set up 50 feet upstream from the water dump.
A natural hill constitutes a 60 metre shielding and the
60 meters
Water Dump
Spark Chambers /
Water Target
~l Beam Direction
Scintillation
v
CountersFIG. la. - Experimental layout.
lb. - Experimental apparatus.
experimental apparatus is set into a hole 12 metres deep.
Figure l b shows that apparatus. It is composed of four optical spark chamber modules ; each has nine 8 feet x 8 feet aluminium plates, 1 inch thick. The gaps between plates are 318 inch. Thirteen very large scintillation counters are arranged into two banks covering the area of the chambers to provide a trigger.
The trigger logic requires a coincidence between a counter of the first bank and one or both counters facing it in the second bank. During the second part of the run the second bank of counters was moved forward into the position 2' to increase the efficiency.
2. Running conditions and results. - Neutrinos make it through the shielding without difficulty. Other known particles are completely eliminated by strong interactions or by energy loss.
The data were taken at a rate of about 100 pictures/
hour. Roughly 90
%
of the pictures are due to acci- dental coincidences between very slow particles which do not produce tracks in the chambers. That accidental rate is caused by the skyshine of slow neutrons. The remaining 10%
contains essentially cosmic rays and neutrino events. At a level of about 1 O/,, come the two prong and multiprong (N < 2) events born in the chamber and where there is always room for one particle being a muon. Tn addition there are a few purely hadronic events, which are hard to interpret and could be compatible in rate with events which are also seen during cosmic ray test in the same apparatus.The crucial question is whether the multiprong and the two-prong events must be attributed to neutrino events or to something else. In order to test the neutrino hypothesis a run was done with a water target upstream from the water dump, letting pions and kaons decay in the free space between the target and the water dump.
The neutrino flux is then enhanced by a factor of 6-8 with respect to the water dump runs. Table I summa- rizes the results obtained for the multiprong and the
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1971319
C3-124 J.-M. GAILLARD
Observed multiprong and two-prong events
Beam energy
-
< 15 GeV/c 15 GeV/c 17 GeV/c 18 GeV/c 19 GeV/c 19.5 GeV/c 18 GeV/c
Charge Target (coulombs)
- -
Water dump 3.8
- 2.8
- 1 .o
- 3.9 - 4 2 - 0.8 Water target 3.3
Events observed Multi- Two- prongs prongs
- -
0 0
2 0
0 0
2 1
3 2
0 0
2 8
two-prong events. The intensity used for each operation is measured in terms of the corresponding charge accumulated (about 2 coulombs per day of run). For a
total charge of 13 coulombs the water dump runs give 7 multiprong events and 3 two prong events. If all those events had to be attributed to neutrino interactions, one would expect for the water target run 11 $. 4 multi- prong events and 5 two prong events. These predictions are obtained by taking the lowest limit of 6 for the enhancement factor. The numbers observed are 2 multi- prong events and 8 two-prong events. For the two- prong events with the water target the expected and observed number of events are in agreement ; for the multiprong events, the disagreement between the expectation and the observation suggests that there could be something more than the conventional neu- trino events, for instance some type of new boson.
However it is clear that more statistics are needed to reach a definite conclusion.
