Beam dump experiments at the AGS

Searches for the prompt production of weak or semi-strongly interacting particles in a neutrino beam dump and their subsequent interaction or decay have been performed at the AGS. The experiment using the totally active liquid scintillator detector is described and the results of the spark chamber detector are mentioned. An exposure of a copper beam dump to two orders of magnitude more protons than in previous searches at 28 GeV has yielded 104 neutrino-like events in the detector. The events from the beam dump are compared directly with those from π and K decay neutrinos produced concurrently in the normal long neutrino decay path following a 15 cm brass target. The characteristics of the events are similar. However, when compared to the rate of events predicted by scaling the 15 cm target yields, the beam dump data show an excess of 45 +- 16 events. The excess events from the beam dump appear to deposit energies greater than or equal to 1 GeV. Their source remains puzzling. Future experiments at the AGS could verify the existence of the effect, decrease the uncertainty in the predicted number of events from 30% to 10% by directly measuring the pion absorption length with a variable density target, search for threshold effects, and measure the sign of the charge of the exiting muons