engleski

Probing eV-scale axions with CAST

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 4He gas (Phase II) of variable pressure. The introduction of gas generates a refractive photon mass m_gamma, thereby achieving the maximum possible conversion rate for those axion masses m_a that match m_gamma. 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_a<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 3He as a buffer gas.

dark matter ; axions ; solar axions ; coherent conversion ; magnetic-field ; search ; bounds ; telescope ; particles ; detector ; photons ; mass

CAST collaboration