SIMPLIFIED MUON LIFETIME EXPERIMENT 1199 it was approximately 1X10-3. It is low for the following reasons. First of all, the muon flux peaks in intensity somewhat above 1 GeV. This means that a large number of muons can easily pass through the scintillator which can only slow a muon down by approximately 2 Mev/emX 38 cm=76 Mev. In order to trigger the discrim inator with a-0.8 V setting, approximately Mev of energy must be deposited in the scintil lator. Consequently, almost all muons passing hrough the counter contribute to the trigger rate without contributing to the analyzing rate Also, those muons which stop in the scintillator FIG. 6. Momentum distribution of electrons or positrons may decay without providing a stop pulse to the produced by muon decay. Taken from Ref. 2 TAC if less than 10 Mev of energy is deposited in the scintillator in the decay process. The mo- plastic, which means that electrons of more than mentum of electrons or positrons produced by 10 Mev of energy can fail to trigger the discrimi- muon decay has a continuous distribution and nator if they are formed within 5 em of the side is described by Fig. 6. Since the neutrinos do not of the scintillator. Another very small contribu- interact with the scintilator, we need only be tion to the trigger rate and not the analysis rate concerned with the electrons. A small number of arises from those muons which enter the scintilla- the decay electrons produced in the scintillator tor with less than 10 Mev of energy. Only a decay will not have sufficient energy to trigger the dis- pulse can then be observed, and these particles criminator. Also, some of those with more than therefore contribute to the random rate 10 Mev of energy may escape the scintillator This information would indicate that the aver- before they deposit 10 MeV of energy. The depo- age muon encountering the scintillator will pro- sition of 10 Mev requires approximately 5 cm of duce one discriminator pulse and not two. In general, one would expect that the ratio of ana- lyzing rate to discriminator trigger rate would be increased if the scintillator were made larger. It would be interesting to examine the cor- respondence between the rate at which muons encounter the scintillator and the discriminator agger rate. The muon flux will be taken as 2X10- muons/cm sr see. Because the scintillator is oriented with its longest axis vertical and the muon flux is most intense near the vertical, the usable solid angle will be taken as 2 sr. The avail- able detector area is 23 X24 cm=552 cm2. TI discriminator trigger rate should be of the orde 2×10-2(552cm2)(28r) To obtain discrim FiG. 5. Data from a 24-h run. The time width of each of this value, the discriminator level must be channel is 0.0329: +0.0009 usec. A computer fit of a straight line to the data points has been drawn in. Its lowered to about -0 4 v. It is also at discrimina- tor levels below -0.4 to -05v that the time