We have searched for solar axions or other pseudoscalar particles that couple to two photons by using the CERN Axion Solar Telescope (CAST) setup. Whereas we previously have reported results from CAST with evacuated magnet bores (Phase I), setting limits on lower mass axions, here we report results from CAST where the magnet bores were filled with 4 He gas (Phase II) of variable pressure. The introduction of gas generates a refractive photon mass m γ , thereby achieving the maximum possible conversion rate for those axion masses m a that match m γ . With 160 different pressure settings we have scanned m a up to about 0.4 eV, taking approximately 2 h of data for each setting. From the absence of excess X-rays when the magnet was pointing to the Sun, we set a typical upper limit on the axion-photon coupling of g aγ 2.2 × 10 −10 GeV −1 at 95% CL for m a 0.4 eV, the exact result depending on the pressure setting. The excluded parameter range covers realistic axion models with a Peccei-Quinn scale in the neighborhood of f a ∼ 10 7 GeV. Currently in the second part of CAST Phase II, we are searching for axions with masses up to about 1.2 eV using 3 He as a buffer gas.

campus on the outskirts of Patras in western Greece. Currently 9 scintillators detectors and 3 Radio Frequency (RF) antennas have been installed and operated at the site. The detector units are arranged in three autonomous stations each consisting of three scintillator detectors and one RF antenna. We present the hardware components of the array, the online software for the remote control, monitor and Data Acquisition, as well as the offline simulation and reconstruction software. We report also briefly on the performance of the array demonstrating its potential to detect Extensive Air Showers. K: Hybrid detectors; Large detector systems for particle and astroparticle physics; Antennas; Scintillators, scintillation and light emission processes (solid, gas and liquid scintillators) 1Corresponding author.

The Astroneu array comprises 9 large charged particle detectors and 3 RF antennas arranged in three autonomous stations operating at the University Campus of the Hellenic Open University in the city of Patras. Each station of the array detects extensive air showers with primary energy threshold of about 10 TeV, while double station coincidence events select showers with energies higher than 10 3 TeV. In such an environment, the radio detection of air showers is challenging. The RF signals besides being extremely weak they also suffer from strong human made electromagnetic noise. In this work, we present the analysis of double station coincidence events and we study the correlation of the RF data with the particle detectors data. We use the experimental information from the particle detectors and the antennas to select very high energy showers and we compare the timing of the RF signals with the timing of the particle detector signals as well as the strength of the RF signals with the simulation predictions.

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The Hellenic Open University (HOU) Cosmic Ray Telescope (ASTRONEU) consists of 9 large scintillator detectors and 3 RF antennas arranged in three autonomous stations operating at the Hellenic Open University campus in the city of Patras. High energy showers that are detected simultaneously by two distant stations and in coincidence with the RF antennas are used to study the RF signature of cosmic events. In previous studies we have shown that the timing of the RF signals as well as the measured electric field at the antennas position are in very good agreement with the simulation predictions. In this work we concentrate on the transfer functions of the antennas which are strongly frequency and angular dependent. We show that the RF spectra (at frequencies 30-80 MHz) of the detected showers are exhibiting features of the antenna response as predicted by detailed Monte Carlo simulation suggesting that a single antenna RF spectrum gives access to the cosmic ray arrival direction.