The research programs in the hadron physics section are done by several
collaborations, which are all working with external beams:
Collaborations, currently taking data:
Crystal Barrel at
ELSA and TAPS (started in fall 1999)
The Crystal Barrel detector was initially used
at LEAR (CERN) and has been modified for the
conditions at ELSA.
For the first two data acquisition periods, the detector was built up at the former SAPHIR area.
Since 2001 the detector is supplemented by the TAPS detector, which is used for the detection of
particles under forward angles.
The collaboration investigates the
photoproduction of meson resonances (search for missing resonances, exploring the decay modes of known resonances
and looking for less established resonances).
Its results will help to understand QCD at low energies.
After the end of the second data acquisition period (end of 2003) the detector was moved to
the former ELAN/GDH area. At this occasion extensive improvements and modification of the detector
and the data acquisition system were made. At the new area, measurements with polarized target and
polarized electron beam (production of circularly polarized photons) are feasible. The modfications are
now finished and the data acquisition has been started, the first double polarized mearsurements were
carried out in summer 2007.
This collaboration investigates the photoproduction of mesons off nucleons. The detector system
consists mainly of the BGO-ball detector (consisting of 480 modules, 11.3 sr acceptance), a
dipole magnet with large angular acceptance (horizontal 12°, vertical 8°) in forward direction
for momentum separation, followed by eight drift chambers and four time-of-flight detectors
for track reconstruction.
Collaborations, data acquisition finished:
GDH at ELSA (summer 1998 till spring 2002)
This collaboration makes use of
polarized photons (generated by bremsstrahlung of
and a polarized target. It will provide
an experimental test of the Gerasimov-Drell-Hearn sum rule, which links the
anomalous magnetic moment of the proton to the difference of the integrated
cross sections for the absorption of photons with spins parallel and
antiparallel to that of the proton. The energy range of up to 800 MeV has been
covered at MAMI in
Mainz, and higher energies of up to 3.0 GeV were investigated at ELSA in
ELAN (until 1997),
scattering facility on hydrogen, deuterium or similar targets (that could be
polarized) with a magnetic spectrometer for detection of the scattered
electrons and a TOF detector for the hadronic fragment(s).
was working with external beam currents of up to 50 nA at energies between 0.8
and 2.6 GeV. The duty factor, describing the quality (mainly time independence
of intensity) of the extracted beam was about 65% for this experiment (up to
99% during the extraction time).
SAPHIR (until 1998)
This collaboration used a magnetic wide
angle (4*π) detector with multiwire central drift chamber (CDC) enclosed in a
large magnet, forward and sideward drift chambers, electromagnetic calorimeter
and scintillating TOF detectors worked with tagged photons, which were
generated by bremsstrahlung of extracted electrons on a thin foil.
The detector worked with low intensities (in the region of 100
pA electron current in front of the tagging target), but at energies of up to
2.8 GeV. The overall duty cycle with respect to both the microstructure of the
extracted beam and the ratio of extraction to total cycle time was in the
region of 90%. The data acquisition ran until 1998 and the detector has now been
In fall 1996 a group from Frascati performed some measurements
concerning total photoabsorption cross sections on different nuclear targets at
the SAPHIR experimental place.
Tuesday, 22. December 2015, 17:18
- F. Frommberger