Universit`a degli studi Roma Tre Measurement of the KL meson ...

20 CHAPTER 2. THE DAΦNE COLLIDER
in the Linac, where positrons are created in a thin target, then follow the same
processing as electrons and are injected with another transfer line. Since the main
rings beam intensity decays rapidly in time, the transfer cycle is repeated in average
three times per hour to maintain high luminosity. The luminosity is defined by the
beam parameters:
L = n νN+ N −
(2.1)
4πσxσy
where n is the number of the bunches, each collecting N particles, ν is the revolution
frequency in the storage ring, σx and σy are the standard deviations of the horizontal
and vertical transverse beam profile at the interaction point. The main parameters
of DAΦNE are summarized in Table 2.1.
Energy 0.51 GeV
Trajectory length 97.69 m
RF frequency 368.26 MHz
Harmonic number 120
Damping time, τE/τx
17.8/36.0 ms
Bunch length at full current e − /e + 2.8/2.2 cm
Beam currents e − /e + 2/1.4 Amps
Number of colliding bunches, n 108
σx
700 µm
σy
7 µm
25 mm
σz
Table 2.1: Parameters of DAΦNE during the 2004-2005 run period.
DAΦNE runs mostly at center-of-mass energy of Mφ ≈ 1019.45 MeV. The φ
production cross section is σ(e + e − → φ) ≃ 3.1 µb.
The dominant φ meson decays [18] are shown in Tab. 2.2.
Decay mode Branching ratio
K + K− ( 48.9 ± 0.5 )%
K0 LK0 S ( 34.2 ± 0.4 )%
ρπ + π + π−π0 ( 15.32 ± 0.32 )%
ηγ ( 1.309 ± 0.024 )%
π0γ ( 1.27 ± 0.06 )×10−3 e + e− ( 2.954 ± 0.030 )×10−4 µ + µ − ( 2.87 ± 0.19 )×10−4 η e + e− ( 1.15 ± 0.10 )×10−4 Table 2.2: Main branching ratios of φ meson decays.
A φ factory is thus a copious source of monochromatic kaons, both neutral and
charged. The production of a kaon with known energy and direction is guaranteed
by the detection of the anti-kaon. This procedure will be called the kaon tagging