Charged Kaons at the Main Injector - CKM Page: 2 of 5
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' ,(K ,CD FDO
Tr,~ ~ ~ Ci am
Figure 1. Experiments proposed sensitivity in the
measurement of the CP violating parameters of
the Standard Model .
nitude larger than the expected signal.
2.1. The K+ 7+7o background
This decay, with branching ratio ~ 21%, can
mimic the signal if the two y from the decay of
the ir0 are undetected. It will be controlled by
a combination of kinematic rejection and a pho-
ton veto system. The CKM detector must veto
photons with a very high efficiency.
2.2. The K+ - pv background
In this decay , with a branching ratio ~63.5%,
the p can be misidentified as a i .This is con-
trolled by a muon veto and RICH systems.
2.3. Background from Interactions
The interactions of the undecayed beam or
daughter ors contribute to the background. In
order to minimize this contribution, as little ma-
terial as possible should be encountered by the
particles. This dictates the choice of the various
3. The Apparatus
In Figure 2 are shown the detector elements
which will be detailed below. To detect K+
hadronic interactions before the decay volume
entrance, a hadron calorimeter surrounding the
Figure 2. The Detector
beam (not described)is used .
3.1. The RICH and the Spectrometers
The charged particles in the reaction, namely
the K and the ' are both measured by Ring Imag-
ing CHerenkov counters (RICH) as velocity vec-
tors and as momentum vectors in upstream and
downstream spectrometers. The gas in the pion
RICH is chosen in order to meet the low disper-
sion required for good resolution. In order to
allow as little material in the beam as possible
rather thin mirrors and windows are mandatory.
This require the RICHs to operate at or near at-
mospheric pressure. These considerations have
contributed to the choice of the K beam to be
22GeV energy and the radiator gas of the decay
pion RICH to be neon. The ' momentum resolu-
tion achieved by the RICH is better than 1% for
this configuration. The K and ' magnetic spec-
trometers use conventional trackers, silicon strips
and straw tubes respectively. Straws have been
chosen to minimize the material in the beam.
They are 5mm in diameter with a 20 pm sense
wire, 5 to 8 straw layers per station (x,y,u,v).
4 . 10-4 Xo, with 150pm hit resolution per layer.
The straws are located in the vacuum decay vol-
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al., Milstene Caroline et. Charged Kaons at the Main Injector - CKM, article, November 14, 2000; Batavia, Illinois. (digital.library.unt.edu/ark:/67531/metadc723261/m1/2/: accessed January 20, 2019), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.