DECAY OF MESOTRONS TabLe II. Co 吧心吧 p=(p2+ah2) for p2>3.0X108 ev/c have been ob 1+l2力2+a(h2-h /u h .(5) with range >186 g/cma of lead. Here h and ha are the atmospheric depths at the ERs BV/C-CAr \CaSR A ING elevations a1 and 2, P: is the momentum of A,3135 mesotron at s and a is the momentum loss per 94士0.9 323333133en g/cm2 of air. 1 The momentum p is intermediate 2594士 between the initial momentum pi=P2+a(h2-hi) and the final momentum pe. We shall refer to it 翡辈罐 he counters as the efective momentum Let us first consider the experimental result concerning mesotron which have residual mo- Rossi and ha +4-5.8/4.5340./counters the menta between 3. 1 and 4.5x108 ev/c at the lower elevation. The corresponding effective momenta are44×10sand5.8×108ev/ c and we may take 5.0X10 ev/ c as an average. For this probability that a mesotron present at th mesotron group the experimental value of the higher level s1 does not disintegrate before reaching the lower level 22. Then w1=n,/n, is 012=0.698+0.031, and therefore L=(4.5+0.6) 105 allows from (2): To/ 0.698 is the experimental value for the average =(9.07=1.3)X10-4 cm c/ev and accordingly, probability of survival between 1=3240 m and taking=8X107ev/c,, T0=(7. 2+0.9)x104cm/c, 32=1616 m of the mesotron which reach 32 with or so=(2.4+0.3)X10-6 sec. We shall next con momenta between Pa and Po, and Wi=Na/Ni sider the continuous mesotron spectrum which 0.883 is the corresponding value for the meso- reaches 1616 m with a residual momentum larger trons which reach ss with momenta larger than than 4.5x108 ev/c. The probability of survival Po. One sees that w1 is much smaller than Wi2, for this mesotron group is W12=0.883, and if hich shows that slow mesotron disintegrate at we take Eq. (4)as an experimental definition of a much faster rate than the more energetic ones. L we get L=(13.3_+0.9)X105 cm.Assuming his result is in agreement with the predictions To=2.4X10-6 sec., we then calculate formally based upon the disintegration hypothesis(see from Eq (2), p=1.5x10% ev/c. This momentum Eq.(2))and affords strong support to the should represent a sort of average effective hypothesis itself. For a mono-energetic group of momentum for the mesotron group considered mesotron, the probability of decay has a very The value p=1.5X10 ev/ c is quite compatible ple theoretical expression, provided the with our present knowledge of the momentum momentum loss in the air layer between 21 and 2? spectrum of mesotron 12 Thus, while a quanti can be neglected. In this case, Eg.(2)gives tative proof of Eg.(2)is still wanting, its ap (4) proximative validity may be considered as established It is convenient to use Eq (4)as a definition of L In evaluating the experimental results we have also when the momentum loss cannot be neg- only considered mesotron coming in the vertical lected. It can easily be proved that L is still direction. As a matter of fact, our experimental related to the lifetime To by an expression of the arrangement was strongly selective for vertical type of Eg.(2) l1 This follows immediatel L=p0/μ (2)r。 llowing (1937);D