560
K. Kleinknecht and U. Uwer
In the high-energy domain, this method has also been used by the NA31
collaboration [184]. In a 3.6 mrad neutral beam derived from 450 GeV protons,
kaons of mean momentum around 100 GeV were allowed to decay. Two different
target positions were chosen, at distances of 48 m and 33.6 m from the defining
collimator of the neutral beam, which marked the upstream end of the decay
volume. Kaons that decayed along 50 m in an evacuated tank were detected
further downstream at about 120 m from the final collimator by the NA31 detector
(Sect. 9.5.4.4, Fig. 9.7). The measured time distribution of π + π − decays is similar
to the one in Fig. 9.12. There are 2.24 × 10 6 and 0.57 × 10 6 π + π − events in the data
for the target in the near and far positions, respectively; the corresponding numbers
of π 0 π 0 events are 1.81 × 10 6 and 0.31 × 10 6 . The phases were extracted from a
fit to the time distribution of the ratio of the data in the near and far positions of the
target.
The results are
Φ +− = (46.9
◦
± 1.4
◦ ) + 310
◦ ((m − 0.5351 × 10 10 s −1 )
+ 270
◦ (τ S − 0.8922 × 10 −10 s)
τ S
(9.138)
and
Φ 00 = (47.1
◦
± 2.1
◦ ) + 310
◦ ((m − 0.5351 × 10 10 s −1 )
+ 225
◦ (τ S − 0.8922 × 10 −10 s)
τ S
.
(9.139)
The difference between the two phases comes out to be
Φ 00 − Φ +− = 0.2
◦
± 2.6
◦
± 1.2
◦ .
(9.140)
9.5.5.4 Measurements of the Phase Difference 00 − +−
For small |ε /ε|, this phase difference is related to ε /ε by the equation
Φ 00 − Φ +− = −3
ε
ε
.
(9.141)
In this way, the component of ε orthogonal to the direction of ε can be measured.
In the absence of CPT violation and for small |ε /ε|, both of the phases Φ 00 and
Φ +− are close to the superweak phase Φ SW (9.102).
The measurement of this phase difference by the NA31 experiment (Sect. 9.5.5.3)
was improved by the simultaneous measurement of the time distributions of π + π −