B. Beltrán

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.

Recent developments on scintillating bolometers for WIMP searches: ROSEBUD status

The particle discrimination capability of various scintillating bolometers has been tested, proving their suitability for dark matter searches. In particular, BGO and undoped sapphire have shown low particle discrimination energy threshold (down to around 20 and 10 keV, respectively). We report on the present status of the ROSEBUD (Rare Objects SEarch with Bolometers UnDerground) Experiment and its prospects.

Cosmogenic activation in germanium double beta decay experiments

A new estimate of the production rates of several long-lived isotopes cosmogenically induced in germanium is presented, paying attention to those products relevant in Double Beta Decay searches. Special care has been taken in the selection of reliable excitation functions.

Background understanding and improvement in NaI scintillators

Sodium Iodide scintillators are very interesting particle and radiation detectors. Low background requirements could limit their application in a variety of fields. We report the e.orts to understand and reduce the background in a set of 14 NaI detectors, stored underground since 1988, undertaken in the frame of the ANAIS experiment [1] in several directions, including PSD techniques, Monte Carlo simulations and detector upgrading.

Neutrons from rock radioactivity in the new Canfranc underground laboratory

Measurements of radioactivity and composition of rock from the main hall of the new Canfranc underground laboratory are reported. Estimates of neutron production by spontaneous fission and (α, n) reactions are given.

Cosmogenic activation of materials

The production of radioactive isotopes in materials due to exposure to cosmic rays can become an hazard for experiments demanding ultra-low background conditions. Generation of long-lived products by cosmic nucleons at sea level has been studied for detector materials like germanium and tellurium and for other materials commonly used like copper; the main results will be summarized, considering both measurements and calculations. The isotope production cross sections and the cosmic ray spectrum are the two main ingredients when calculating this cosmogenic activation; the different alternatives for implementing them will be discussed. But cosmogenic activation can take place also deep underground due to cosmic muons, being relevant in this case the short-lived products. Studies carried out to evaluate the underground activation mainly for liquid scintillator materials will be commented too.

Search for solar axions: the CAST experiment

Hypothetical axion‐like particles with a two‐photon interaction would be produced in the sun by the Primakoff process. In a laboratory magnetic field they would be transformed into X‐rays with energies of a few keV. The CAST experiment at CERN is using a decommissioned LHC magnet as an axion helioscope in order to search for these axion‐like particles. The analysis of the 2003 data showed no signal above the background, thus implying an upper limit to the axion‐photon coupling of gaγ < 1.16 × 10−10 GeV−1 at 95% CL for ma ≲ 0.02 eV. The stable operation of the experiment during 2004 data taking allowed us to lower down this parameter to a preliminary value of gaγ < 0.9 × 10−10 GeV−1.

UZ Dark Matter Searches at Canfranc

A lasting Dark Matter Search Program is being carried out in the facilities of the Canfranc Underground Laboratory since 1990 with the participation of the University of Zaragoza (UZ) Nuclear and Astroparticle Physics group. A brief summary of the most relevant experiments will be followed by the report on the status of the present experimental efforts at Canfranc: ANAIS and ROSEBUD. ANAIS (Annual modulation with NAI) will look for the annual modulation effect in the WIMP signal with about 100 kg sodium iodide as target. In the framework of the ROSEBUD (Rare Objects SEarch with Bolometers UnDerground) collaboration, the particle discrimination capability of different scintillating bolometers has been tested. These detectors are showing excellent performances for their application in dark matter searches and enable a multi‐target strategy in the search for WIMPs, which is planned to be used in the near future at the Canfranc Underground Laboratory.

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.

Dark matter searches with NaI scintillators in the Canfranc underground laboratory: ANAIS experiment

A large mass dark matter search experiment with NaI scintillators at the Canfranc Underground Laboratory is underway. A 10.7 kg prototype with improved light collection efficiency and special low-background improvements has been tested and started taking data underground in summer 2005. Preliminary results and prospects for the experiment are presented.