Feigling
53881
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Feigling
do
with the X-ray telescopes during 2004. The analysis of the
2004 data is still in progress and we expect to further improve
the upper limit in the CAST axion sensitive mass
range ma < 0:02 eV, although the present preliminary result
is already comparable to the best astrophysical constraints
(see Fig. 2). Due to coherence effects, the CAST
helioscope in its configuration during 2004 was sensitive
for axions with masses ma < 0:02 eV, only. To extend
the sensitivity of CAST to ma < 0:8 eV, the refractive index
of the conversion volume has to be changed using a
buffer gas, either 4He or 3He. Then, the photon acquires
an effective mass (m= ma) and the momentum exchange
during the Primakoff process becomes negligible (phase II
of CAST). During 2005 the CAST magnet has been transformed
into its phase II configuration, allowing to be operated
with a buffer gas (4He) inside the conversion volume.
First data has successfully been taken with the new experimental
setup at the end of 2005 and data taking will be
continued at the beginning of this year.
2004 data is still in progress and we expect to further improve
the upper limit in the CAST axion sensitive mass
range ma < 0:02 eV, although the present preliminary result
is already comparable to the best astrophysical constraints
(see Fig. 2). Due to coherence effects, the CAST
helioscope in its configuration during 2004 was sensitive
for axions with masses ma < 0:02 eV, only. To extend
the sensitivity of CAST to ma < 0:8 eV, the refractive index
of the conversion volume has to be changed using a
buffer gas, either 4He or 3He. Then, the photon acquires
an effective mass (m= ma) and the momentum exchange
during the Primakoff process becomes negligible (phase II
of CAST). During 2005 the CAST magnet has been transformed
into its phase II configuration, allowing to be operated
with a buffer gas (4He) inside the conversion volume.
First data has successfully been taken with the new experimental
setup at the end of 2005 and data taking will be
continued at the beginning of this year.
During the last two years CAST was taking data for
about twelve months, six months during 2003 and during
2004. The analysis of the data reveals no significant excess
signal over background and allows us to set a new upper
limit on the axion to photon coupling. Fig. 2 shows
the preliminary corresponding upper limit for the axion to
photon coupling constant ga
derived from the data aquired
about twelve months, six months during 2003 and during
2004. The analysis of the data reveals no significant excess
signal over background and allows us to set a new upper
limit on the axion to photon coupling. Fig. 2 shows
the preliminary corresponding upper limit for the axion to
photon coupling constant ga
derived from the data aquired
The heart of CAST is a prototype LHC superconducting
magnet providing a dipole magnetic field of 9 T in
the interior of two parallel pipes over a distance of 9:26m.
On both ends of the magnet X-ray detectors are looking
for a potential axion signal as an excess signal over detector
background. A TPC detector covers two magnet bores
on one end looking for axions during sunset. On the opposite
side of the magnet, a micro mesh gas detector and
an X-ray telescope with a pn-CCD detector are looking for
axions at sunrise. The magnet can be pointed towards the
sun for about 1:5 h during sunrise and sunset, resulting in
3 h observation time per day. The remaining time is used
for systematic background studies. The most sensitive detector
system of CAST is theWolter I type X-ray telescope
which enhances the signal-to-background ratio by a factor
of 100 by concentrating the potential signal flux on a
small spot on the pn-CCD detector.
magnet providing a dipole magnetic field of 9 T in
the interior of two parallel pipes over a distance of 9:26m.
On both ends of the magnet X-ray detectors are looking
for a potential axion signal as an excess signal over detector
background. A TPC detector covers two magnet bores
on one end looking for axions during sunset. On the opposite
side of the magnet, a micro mesh gas detector and
an X-ray telescope with a pn-CCD detector are looking for
axions at sunrise. The magnet can be pointed towards the
sun for about 1:5 h during sunrise and sunset, resulting in
3 h observation time per day. The remaining time is used
for systematic background studies. The most sensitive detector
system of CAST is theWolter I type X-ray telescope
which enhances the signal-to-background ratio by a factor
of 100 by concentrating the potential signal flux on a
small spot on the pn-CCD detector.
With the CAST experiment at CERN, we aim to detect
such solar axions on earth by “converting” them back to Xray
photons inside a strong transversal magnetic field (inverse
Primakoff effect, see Fig. 1). The conversion probability
of axions to photons is proportional to the square of
the strength of the magnetic field and its length. Thus, a
strong magnetic field is essential to achieve a high sensitivity
of the experiment.
such solar axions on earth by “converting” them back to Xray
photons inside a strong transversal magnetic field (inverse
Primakoff effect, see Fig. 1). The conversion probability
of axions to photons is proportional to the square of
the strength of the magnetic field and its length. Thus, a
strong magnetic field is essential to achieve a high sensitivity
of the experiment.
The sun provides a deep insight into the physics of fusion,
the physics of hot plasmas and is an excellent laboratory
for astroparticle physics. As such the sun can be
used to probe the existence of novel particles and dark matter
candidates like the axion. The axion is a direct consequence
(2; 3) of the theoretical solution of the CP problem
in strong interactions proposed by (1). Inside the core of
the sun axions could be produced by coherent conversion of
thermal photons interacting with the electromagnetic field
of charged particles of the solar plasma (Primakoff effect).
the physics of hot plasmas and is an excellent laboratory
for astroparticle physics. As such the sun can be
used to probe the existence of novel particles and dark matter
candidates like the axion. The axion is a direct consequence
(2; 3) of the theoretical solution of the CP problem
in strong interactions proposed by (1). Inside the core of
the sun axions could be produced by coherent conversion of
thermal photons interacting with the electromagnetic field
of charged particles of the solar plasma (Primakoff effect).