Peter Friedrich

An improved limit on the axion–photon coupling from the CAST experiment

We have searched for solar axions or similar particles that couple to two photons by using the CERN Axion Solar Telescope (CAST) setup with improved conditions in all detectors. From the absence of excess X-rays when the magnet was pointing to the Sun, we set an upper limit on the axion-photon coupling of 8.8 x 10^{-11} GeV^{-1} at 95% CL for m_a<~ 0.02 eV. This result is the best experimental limit over a broad range of axion masses and for m_a<~ 0.02 eV also supersedes the previous limit derived from energy-loss arguments on globular-cluster stars.We have searched for solar axions or similar particles that couple to two photons by using the CERN Axion Solar Telescope (CAST) set-up with improved conditions in all detectors. From the absence of excess x-rays when the magnet was pointing to the Sun, we set an upper limit on the axion–photon coupling of gaγ<8.8 × 10−11xa0GeV−1 at 95% CL for . This result is the best experimental limit over a broad range of axion masses and for also supersedes the previous limit derived from energy-loss arguments on globular cluster stars.

First results from the CERN Axion Solar Telescope

Hypothetical axion-like particles with a two-photon interaction would be produced in the Sun by the Primakoff process. In a laboratory magnetic field (``axion helioscope) they would be transformed into X-rays with energies of a few keV. Using a decommissioned LHC test magnet, CAST has been running for about 6 months during 2003. The first results from the analysis of these data are presented here. No signal above background was observed, implying an upper limit to the axion-photon coupling<1.16 10^{-10} GeV^-1 at 95% CL for m_a<~0.02 eV. This limit is comparable to the limit from stellar energy-loss arguments and considerably more restrictive than any previous experiment in this axion mass range.

Search for Sub-eV Mass Solar Axions by the CERN Axion Solar Telescope with 3He Buffer Gas

S. Aune, K. Barth, A. Belov, S. Borghi, ∗ H. Bräuninger, G. Cantatore, J. M. Carmona, S. A. Cetin, J. I. Collar, T. Dafni, M. Davenport, C. Eleftheriadis, N. Elias, C. Ezer, G. Fanourakis, E. Ferrer-Ribas, P. Friedrich, J. Galán, J. A. Garćıa, A. Gardikiotis, E. N. Gazis, T. Geralis, I. Giomataris, S. Gninenko, H. Gómez, E. Gruber, T. Guthörl, R. Hartmann, † F. Haug, M. D. Hasinoff, D. H. H. Hoffmann, F. J. Iguaz, ‡ I. G. Irastorza, J. Jacoby, K. Jakovčić, M. Karuza, K. Königsmann, R. Kotthaus, M. Krčmar, M. Kuster, 16, § B. Lakić, ¶ J. M. Laurent, A. Liolios, A. Ljubičić, V. Lozza, G. Lutz, † G. Luzón, J. Morales, ∗∗ T. Niinikoski, †† A. Nordt, 16, ‡‡ T. Papaevangelou, M. J. Pivovaroff, G. Raffelt, T. Rashba, H. Riege, A. Rodŕıguez, M. Rosu, J. Ruz, 2 I. Savvidis, P. S. Silva, S. K. Solanki, L. Stewart, A. Tomás, M. Tsagri, ‡‡ K. van Bibber, §§ T. Vafeiadis, 9, 12 J. Villar, J. K. Vogel, 20, ¶¶ S. C. Yildiz, and K. Zioutas 12

Search for solar axions by the CERN axion solar telescope with 3He buffer gas: closing the hot dark matter gap.

Introduction.—The most promising method to searchfor axions and axion-likeparticles (ALPs) [1–4], low-massbosons with a two-photon interaction vertex, is their con-version to photons in macroscopic magnetic fields [5–7].This approach includes the search for solar axions by thehelioscope technique [8–15], photon regeneration exper-iments (“shining light through a wall”) [16–18], axion-photon conversion in astrophysical B fields [19–22], andthe search for galactic axion dark matter [23–27].One limiting factor in any of these efforts is the mo-mentum difference between freely propagating photonsand axions caused by the axion mass m

The x-ray telescope of CAST

The CERN Axion Solar Telescope (CAST) has been in operation and taking data since 2003. The main objective of the CAST experiment is to search for a hypothetical pseudoscalar boson, the axion, which might be produced in the core of the sun. The basic physics process CAST is based on is the time inverted Primakoff effect, by which an axion can be converted into a detectable photon in an external electromagnetic field. The resulting x-ray photons are expected to be thermally distributed between 1 and 7u2009keV. The most sensitive detector system of CAST is a pn-CCD detector combined with a Wolter I type x-ray mirror system. With the x-ray telescope of CAST a background reduction of more than 2 orders of magnitude is achieved, such that for the first time the axion photon coupling constant gaγγ can be probed beyond the best astrophysical constraints gaγγ < 1 × 10−10u2009GeV−1.

CAST constraints on the axion-electron coupling

In non-hadronic axion models, which have a tree-level axion-electron interaction, the Sun produces a strong axion flux by bremsstrahlung, Compton scattering, and axio-recombination, the ``BCA processes. Based on a new calculation of this flux, including for the first time axio-recombination, we derive limits on the axion-electron Yukawa coupling gae and axion-photon interaction strength ga? using the CAST phase-I data (vacuum phase). For ma10?meV/c2 we find ga??gae?<?8.1???10?23?GeV?1 at 95% CL. We stress that a next-generation axion helioscope such as the proposed IAXO could push this sensitivity into a range beyond stellar energy-loss limits and test the hypothesis that white-dwarf cooling is dominated by axion emission.

eROSITA on SRG

eROSITA (extended ROentgen Survey with an Imaging Telescope Array) is the core instrument on the Russian Spektrum-Roentgen-Gamma (SRG) mission which is scheduled for launch in late 2012. eROSITA is fully approved and funded by the German Space Agency DLR and the Max-Planck-Society. The instrument development is in phase C/D since fall 2009. The design driving science is the detection 100.000 Clusters of Galaxies up to redshift z ~1.3 in order to study the large scale structure in the Universe and test cosmological models, especially Dark Energy. This will be accomplished by an all-sky survey lasting for four years plus a phase of pointed observations. eROSITA consists of seven Wolter-I telescope modules, each equipped with 54 Wolter-I shells having an outer diameter of 360 mm. This would provide an effective area of ~1500 cm2 at 1.5 keV and an on axis PSF HEW of 15 arcsec resulting in an effective angular resolution of 28 - 30 arcsec, averaged over the field of view. In the focus of each mirror module, a fast frame-store pn-CCD provides a field of view of 1° in diameter.

Search for 14.4 keV solar axions emitted in the M1-transition of 57Fe nuclei with CAST

We have searched for 14.4 keV solar axions or more general axion-like particles (ALPs), that may be emitted in the M1 nuclear transition of 57Fe, by using the axion-to-photon conversion in the CERN Axion Solar Telescope (CAST) with evacuated magnet bores (Phase I). From the absence of excess of the monoenergetic X-rays when the magnet was pointing to the Sun, we set model-independent constraints on the coupling constants of pseudoscalar particles that couple to two photons and to a nucleon g{sub ay}|-1.19g{sub aN}{sup 0}+g{sub aN}{sup 3}| < 1.36 x 10{sup -16} GeV{sup -1} for ma < 0.03 eV at the 95% confidence level.

Manufacturing of Wolter-I mirror segments with slumped glass

In our ongoing studies of high precision glass slumping we have successfully formed the first Wolter-I X-ray mirror segments with parabola and hyperbola in one piece. It could be demonstrated that the excellent surface roughness of the 0.55 mm thick display glass chosen is conserved during the slumping process. The influence of several parameters of the process, such as maximum temperature, heating and cooling rates etc. have to be measured and controlled with adequate metrology. Currently, we are optimizing the process to reduce the figure errors down to 1 micrometer what will be the starting point for further, final figure error corrections. We point out that metrology plays an important role in achieving a high precision optics, i.e. an angular resolution of a few arcsec. In this paper we report on the results of our studies and discuss them in the context of the requirements for future X-ray telescopes with large apertures.

The manufacturing of the XEUS x-ray glass segmented mirrors: status of the investigation and last results

The XEUS mission (X-ray Evolving-Universe Spectroscopy Mission) is a future ESA project currently under study. With a mirror collecting area of up to 30 m2 @ 1 keV and 3 m2 @ 8 keV it will outperform the x-ray space observatories like XMM-Newton. In fact it will have a source flux sensitivity and angular resolution respectively 250 times and 7.5 times better if compared to that mission. This huge collecting area is obtained with a 10 m diameter telescope of 50 m focal length. It is foreseen that the whole telescope will be formed by two free flying satellites, one for the mirror assembly and the other for the detectors. The two satellites will be kept aligned by an active tracking/orbit control system. The angular resolution of the optics is set to 5 arcsec with a goal of 2 arcsec. Of course the requirement of high resolution and large diameter of the optics create new technological problems which have to be overcome. First of all the impossibility to create closed Wolter I shells (due to the large diameter) means that the optics will be assembled using rectangular segments of ~1 m x ~0.5 m size. A set of these segments will form a petal. The petals will be assembled to form the whole mirror assembly. Another difficulty arises from the fact that the current design foresees a mass/geometric-area ratio of 0.08 kg/cm2, which is very small and much lower compared with XMM-Newton. Hence the use of materials that can offer both low weight and high stiffness is mandatory. The impossibility to have a thermal control for the huge area of the optics means also that the mirrors have to operate at temperatures between -30 and -40°C. This requirement excludes the epoxy-replication method as option for their manufacturing (CTE mismatch between resin and substrate). Considering all these constrains a possible solution for the realization of the XEUS mirrors has been found that foresees the use of glass or ceramics materials. In this paper we will describe an investigation currently on-going aimed at the development of a procedure to produce large mirror segments from thin Borofloat glass and the preliminary results obtained, that corroborate the viability of the proposed approach. A previous article has introduced the basic ideas and concepts behind this investigation.