E-831 (FOCUS): CHARM PHOTOPRODUCTION
E831 Experiment:
The goal of E831 from Fermilab is to study a production and decay of
particles with charm and research rare phenomenon using beam of photons of high
energy and an spectrometer with innovation technology which allow collect a
sample of data of more than a hundred charm reconstructed particles.
Spectrometer:
E831 is a fixed target experiment. The photons, with energy about of 150-200
GeV incident on a Berylium segmented target, producing photon-nucleon
collision.
To obtain a hundred charm reconstructed particles, was increment by factor of
5 the luminocity of the beam in relation to preview experiment (E687). The
beam had a incident flux of about 107 photon/sec.
To observe the charm particles (lifetime between 0.1 to 1 ps), E831 used a good
detector vertices system, the Silicom Microstrip Detector (SMD), which allowed
determine the interaction point that produce the charm particles (primary vertice)
and the decay point (secondary vertice) with a high resolution. These detector
allow measure decay modes of 0.04 ps.
The Cerenkov:
the identification of particles was done by 3 Cerenkov counters. Respect to
calorimetry and identifications of muons, the spectrometer is divide in two
parts to
detect low and high momentum particles in the inner and outer detectors. The
electromagnetic calorimeter has acceptance to long angles and the outer
electromagnetic calorimeter, OE, is used to detect muons of low energy;
Inner Electromagnetic Calorimeter, which has acceptance to small angles, is also
used to detect muons with high momentum. Both calorimeter are at final of
spectrometer.
Finally, there is a hadronic calorimeter, located inmediatly before the detection
system of energetic muons, which is used by trigger of transverse energy of
the experiment.
To obtain high statist and high signal/background relation was update all
acquisition data system, of tracking system, hadronic and
electromagnetic calorimeters and detection system muons. Significant change
were done in the calorimeters to improve the analysis of neutral particles.
Taking data:
the data taking was done during August 1996 to August 1997. The data was
recorded and simultaneouslly were reconstructed and analyzedupgread searched plentiful
charm particles (D mesons and Lambda_c baryon). This process allow a better
control the function of the spectrometer and the quality of data that has
being recorded. The charm particles found in this way become to be a sample of 5%
which allow estimate that the experiment will collect about 1 million 2
thousand charmed particles in the total sample. This sample let us an analysis
of high quality in many topics like described before.