DAPHNE (Détecteur à Grande Acceptance pour
la Physique Photonucléaire Expérimentale)
was designed by the DAPNIA department of the
Commissariat à l'Energie Atomique, in collaboration
with the Istituto Nazionale di Fisica Nucleare.
The original purpose of the detector was to
explore the quantum chromodynamics (QCD) properties
of nucleons (i.e. protons and neutrons).
To explore these properties, excitation states
of the nuclei require to be measured (e.g.
Delta baryons, symbol Δ).
These excited states of nucleons decay via
the emission of light mesons such as pions
(π), eta mesons (η) or kaons (K).
Various models exist that describe the correlation
between the observed reactions, the excited
states and QCD.
DAPHNE was built to observe charged light
mesons from the decay of excited nucleon states.
The excitation of nuclei can be done with
either pion scattering, or real photon scattering
on the nucleon.
Real photon scattering has the advantage that
the first vertex can be cleanly described
by the well known quantum electrodynamics
(QED), while for the pion scattering at least
two strong interaction vertices exist that
require much more effort from models.
The detector was used by the Commissariat
à l'Énergie Atomique in– Saclay, France
(accelerator SATURNE, 19871990) and the Institut
für Kernphysik in Mainz, Germany (accelerator
MAMI, 1990–2003).
== Setup ==
DAPHNE is a cylinder symmetric detector that
was built to detect mainly charged particles
from excited
nucleons.
Its construction is made in such way that
a high coverage both in momentum and angular
space is provided.
The angular range of the detector is Ω = 0.94
× 4π steradians.
The detector consists of six layers of organic
scintillators divided into 16 segments and
is cylinder symmetric.
These scintillators were originally produced
by Nuclear Enterprises.
The following table shows the set-up of one
of the 16 identical sectors of DAPHNE, starting
from the most inner layer.
The 16 sectors represent the calorimeter.
To identify particles, the multilayered structure
represents
a range telescope that allows to determine
the energy deposit in each layer and the range
of a particle in the detector
at all.
By the energy losses in each layer and the
distribution of energy losses over the layers,
the type of particle
and its total energy can be determined.
This identification is done in a way that
measured values are compared to simulated
values of particle hypothesis.
The maximum likelihood method is used to evaluate
which particle hypothesis fits the best to
the measured data.
The algorithm used checks for proton and charged
pion signatures.
For a better identification of the observed
reaction, DAPHNE is provided with three concentric
and independent multiwire proportional chambers.
By analysis of data of the chambers it is
possible to safely identify up to five different
tracks of charged particles for each identified
event.
A reconstruction uncertainty of 0.2 degrees
(azimuthal) and 2 mm (along the beamline)
is provided.
The chambers are located around the target
place, which is in the very center of the
detector.
The tracks from the chambers are used to calculate
the kinematics of a photoproduction reaction.
The main information extracted is the path
of the proton and the path of charged pions.
This information can also be used to reconstruct
missing particles that failed getting identified
due to detector angular or momentum acceptance
or due to the efficiency of the calorimeter.
