This is a schematic view of the KTeV detector, configured for the
E799 rare Kaon decay measurements.
The goal of E799 is to search for and study various rare Kaon decay
processes, with particular interest on studying direct CP violation.
Beams: The K-long beams are produced by scattering protons
from the TeVatron onto a target. Charged particles are swept away
using magnets near the target,
and only neutral particles are left. Of these, only K-long and certain
hyperons have the right life time to reach and decay in the Vacuum decay
region. Most hyperon decays are distinguishable from Kaon
decays, and are studied in their own right in KTeV.
Vacuum Decay Region: A large evacuuated region allows the Kaons
and their decay products to undergo minimal interactions with matter before
reaching the detectors.
Photon Vetoes: These are used to detect photons which would
miss the CsI calorimeter. Many backrounds involve extra photons, and missing
them could lead to the misidentification of an event.
Drift Chambers: Charged particles, such as pions, passing through
a drift chamber leave an electronic pulse. The positions of the pulses
among different chambers are used to reconstruct the path of the
particle.
Analysis magnet: The deflection of charged particle tracks in the
magnet gives the particle's momentum.
TRDs: The Transition Radiation Detectors help distinguish
between electrons and charged pions.
Trigger Hodoscopes: Segmented planes of scintillating plastic
give a pulse of light when a charged particle passes through. This
is used to provide a very fast "trigger" to alert the computers to
the possible occurence of an interesting decay.
CsI: The cesium-iodide calorimeter is used to measure the energy
deposited by various kinds of particles, and is the only means by which
photon energies are measured in KTeV.
Hadron Veto: Hadrons, such as charged pions, typically are
not stopped by the CsI. The hadron veto dowsnstream of the CsI
helps distinguish between charged pions and electrons.
Muon filter: Muons are the only charged particles which can
easily penetrate this thick wall of steel. If a particle makes it
to the muon veto, it is probably a muon, and not a charged pion.
