E. Chesi

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.

The CAST time projection chamber

One of the three x-ray detectors of the CERN Axion Solar Telescope (CAST) experiment searching for solar axions is a time projection chamber (TPC) with a multi-wire proportional counter (MWPC) as a readout structure. Its design has been optimized to provide high sensitivity to the detection of the low intensity x-ray signal expected in the CAST experiment. A low hardware threshold of 0.8?keV is set to a safe level during normal data taking periods, and the overall efficiency for the detection of photons coming from conversion of solar axions is 62%. Shielding has been installed around the detector, lowering the background level to 4.10 ? 10?5?counts?cm?2?s?1?keV?1 between 1 and 10?keV. During phase I of the CAST experiment the TPC has provided robust and stable operation, thus contributing with a competitive result to the overall CAST limit on axion?photon coupling and mass.

Axion searches at CERN with the CAST telescope

The CERN Axion Solar Telescope (CAST) searches for axions coming from photon to axion conversion in the suns core, as stated by the Primakoff effect. Axions arise in particle physics as a consequence of the breaking of Peccei-Quinn symmetry which has been introduced as a solution to the strong CP problem. As cosmological axions they are candidates for at least some part of cold Dark Matter.They are also expected to be produced copiously in stellar interiors with energies as high as the thermal photons undergoing photon to axion conversion. In our sun the axion energy spectrum peaks at about 4.4 keV, extending up to 10 keV. CAST collected preliminary data in 2002 and data taking with its full capability will start in the beginning of 2003.The CERN Axion Solar Telescope (CAST) searches for axions coming from photon to axion conversion in the suns core, as stated by the Primakoff effect. Axions arise in particle physics as a consequence of the breaking of Peccei-Quinn symmetry which has been introduced as a solution to the strong CP problem. As cosmological axions they are candidates for at least some part of cold Dark Matter.They are also expected to be produced copiously in stellar interiors with energies as high as the thermal photons undergoing photon to axion conversion. In our sun the axion energy spectrum peaks at about 4.4 keV, extending up to 10 keV. CAST collected preliminary data in 2002 and data taking with its full capability will start in the beginning of 2003.

First results from the CAST experiment

The CAST Experiment commenced its first phase of solar axion-searching in 2003, and ran successfully for two years. In the transverse field of a decommissioned Large Hadron Collider (LHC) test magnet (9.26m, 9T), the CERN Axion Solar Telescope intends to transform axions -that would be produced in the sun- into X-rays with energies of a few keV. The first results from the analysis of the data taken in 2003 show no signature of axions, implying an upper limit to the axion-photon coupling gaγ ≤ 1.16 × 10−10 GeV−1 at 95% C.L. for ma < 0.02 eV, already a factor 100 better than previous searches. In Phase I the twin bores of the magnet were kept in vacuum. In Phase II (due to start in November 2005) the bores of the magnet will be filled with a buffer gas, which will allow CAST to explore the region of higher axion masses.

Search for Solar Axions: CAST

Biljana Lakić∗1, S. Andriamonje3, V. Arsov14, S. Aune3, D. Autiero2,a, F. Avignone4, K. Barth2, A. Belov12, B. Beltrán7, H. Bräuninger6, J.M. Carmona7, S. Cebrián7, E. Chesi2, J.I. Collar8, R. Creswick4, T. Dafni5,b, M. Davenport2, L. Di Lella2,c, C. Eleftheriadis6, J. Englhauser6, G. Fanourakis10, H. Farach4, E. Ferrer3, H. Fischer11, J. Franz11, P. Friedrich6, T. Geralis10, I. Giomataris3, S. Gninenko12, N. Goloubev12, R. Hartmann6, M.D. Hasinoff13, F.H. Heinsius11, D.H.H. Hoffmann5, I.G. Irastorza3, J. Jacoby14, D. Kang11, K. Königsmann11, R. Kotthaus15, M. Krčmar1, K. Kousouris10, M. Kuster5,6, C. Lasseur2, A. Liolios9, A. Ljubičić1, G. Lutz15, G. Luzón7, D.W. Miller8, A. Morales7,d, J. Morales7, M. Mutterer5, A. Nikolaidis9, A. Ortiz7, T. Papaevangelou2, A. Placci2, G. Raffelt15, J. Ruz7, H. Riege5, M.L. Sarsa7, I. Savvidis9, W. Serber15, P. Serpico15, Y. Semertzidis5,e, L. Stewart2, J.D. Vieira8, J. Villar7, L. Walckiers2, K. Zachariadou10 and K. Zioutas9, f 1Rudjer Bošković Institute, Zagreb, Croatia Email: Biljana.Lakic@cern.ch 2European Organization for Nuclear Research (CERN), Geneve, Switzerland 3DAPNIA, Centre d’Études Nucléaires de Saclay (CEA-Saclay), Gif-sur-Yvette, France 4Department of Physics and Astronomy, University of South Carolina, Columbia, SC, USA 5GSI-Darmstadt and Institut für Kernphysik, TU Darmstadt, Darmstadt, Germany 6Max-Planck-Institut für Extraterrestrische Physik, Garching, Germany 7Instituto de Física Nuclear y Altas Energías, Universidad de Zaragoza, Zaragoza, Spain 8Enrico Fermi Institute and KICP, University of Chicago, Chicago, IL, USA 9Aristotle University of Thessaloniki, Thessaloniki, Greece 10National Center for Scientific Research ‘Demokritos”, Athens, Greece 11Albert-Ludwigs-Universität Freiburg, Freiburg, Germany 12Institute for Nuclear Research (INR), Russian Academy of Sciences, Moscow, Russia 13Department of Physics and Astronomy, University of British Columbia, Vancouver, Canada 14Johann Wolfgang Goethe-Univ., Inst. für Angewandte Physik, Frankfurt am Main, Germany 15Max-Planck-Institut für Physik (Werner-Heisenberg-Institut), Munich, Germany