Search for Solar Axions: the CAST experiment at CERN Berta Beltrán (University of Zaragoza, Spain) XXXXth Rencontres de Moriond La Thuile, March 2005

Berta Beltrán2 Outline The physics behind CAST : Axions. Principle of detection The CAST experiment : Description : Magnet, tracking, … X-ray detectors. Data Analysis and 2003 results.

La Thuile, March 2005Berta Beltrán3 Axions : Motivation The Axion is a light pseudoscalar resulting from the Peccei-Quinn mechanism to enforce strong-CP conservation [Peccei-Quinn(1977),Wilczek (1978), Weinberg(1978)] Axions may exist as primordial cosmic relics copiously produced in the very early universe, and these axions are one of the most interesting non-baryonic cold dark matter candidates. [See the PDG for an interesting review on axions]

La Thuile, March 2005Berta Beltrán4 The Sun as an axion source γ a -e Ze [K. van Bibber et al. PRD 39,(1989)] Thermal photons Fluctuating electric fields of the charged particles in the hot plasma Axions Differential solar axion flux at Earth. Solar physics + Primakoff effect

La Thuile, March 2005Berta Beltrán5 CAST: Principle of detection Expected number of photons in the x-ray detector: L Transverse magnetic field (B) X-ray detector X-ray (same energy and momentum) Axion [Sikivie PRL 51 (1983)] S t Differential axion flux at the Earth (cm -2 s -1 keV -1 ) Conversion probability of an axion into photon ( (B×L) 2 ) Magnet bore area ( cm 2 ) Measurement time ( s) For g aγγ =1×1O -10 GeV -1 t=100 h, S=15 cm 2 N γ ≈ 30 events

La Thuile, March 2005Berta Beltrán6 But this is a coherent process only when the axion and photon fields remain in phase over L with Coherence condition states that qL < 1 (axion-photon momentum transfer) Vacuum inside the magnet: m γ =0 We are sensitive to axion masses ≤ 2.3×10 -2 eV (CAST phase I) Buffer gas (He) inside the magnet: m γ, eff > 0 Different gas pressures P will make us sensitive to different axion masses up to 1 eV (CAST phase II)

La Thuile, March 2005Berta Beltrán7 University of British Columbia, Department of Physics, Vancouver, Canada Michael HASINOFF Ruder Boskovic Institute, Zagreb, Croatia Milica KRCMAR, Biljana LAKIC, Ante LJUBICIC Centre d''Etudes de Saclay (CEA-Saclay), DAPNIA, Gif-Sur-Yvette, France Samuel ANDRIAMONJE, Stephan AUNE, Esther FERRER, Ioanis GIOMATARIS, Igor G. IRASTORZA Technische Universitat Darmstadt, Institut für Kernphysik, Darmstadt, Germany Theopisti DAFNI, Dieter HOFFMANN, Manfred MUTTERER, Yannis SEMERTZIDI, Hans RIEGE Johann-Wolfgang-Goethe Universität Frankfurt, Institut für Kernphysik, Frankfurt Am Main, Germany Vladimir ARSOV, Joachim JACOBY Albert-Ludwigs-Universität Freiburg, Freiburg, Germany Horst FISCHER, Jurgen FRANZ, Donghwa KANG, Kay KONIGSMANN, Fritz-Herber HEINSIUS Max-Planck-Gesellschaft (MPG) Max-Planck-Institut für Extraterrestrische Physik, Garching, Germany Heinrich BRAEUNINGER, Jakob ENGLHAEUSER, Peter FRIEDRICH, Markus KUSTER Max-Planck-Institut fur Physik Muenchen, Germany Rainer KOTTHAUS, Gerhard LUTZ, Georg RAFFELT, William SERBER, Pasquale SERPICO. Aristotle University of Thessaloníki, Thessaloniki, Greece Christos ELEFTHERIADIS, Anastasios LIOLIOS, Argyrios NIKOLAIDIS, Konstantin ZIOUTAS, Ilias SAVVIDIS. Scuola Normale Superiore (SNS), Pisa, Italy Luigi DI LELLA Russian Academy of Sciences, Institute for Nuclear Research (INR), Moskva, Russia Alexandre BELOV, Sergei GNINENKO, Nikolai GOLUBEV Instituto de Física Nuclear y Altas Energías, Universidad de Zaragoza, Zaragoza, Spain Berta BELTRAN, Jose Manuel CARMONA, Susana CEBRIAN, Gloria LUZON, Angel MORALES, Julio MORALES, Alfonso ORTIZ DE SOLORZANO, Jaime RUZ, Jose VILLAR, Maria Luisa SARSA. European Organization for Nuclear Research (CERN), Geneve, Switzerland Klaus BARTH, Enrico CHESI, Martyn DAVENPORT, Christian LASSEUR, Thomas PAPAEVANGELOU, Alfredo PLACCI, Louis WALCKIERS, Laura STEWART, Dario AUTIERO. Enrico Fermi Institute, University of Chicago, Chicago, Il, United States of America David MIlLER, Juan COLLAR, Joaquin VIEIRA University of South Carolina, Department of Physics and Astronomy, Columbia, Sc, United States of America Frank AVIGNONE, Richard CRESWICK, Horacio FARACH National Center for Scientific Research "Demokritos" (NRCPS), Athens, Greece George FANOURAKIS, Theodoros GERALIS, Konstantin KOUSOURIS, Katerina ZACHARIADOU. CAST Collaboration 68 participants from 15 institutions

La Thuile, March 2005Berta Beltrán8 CAST: Point 8 CERN (Meyrin site) Genève CAST at CERN:

La Thuile, March 2005Berta Beltrán9 Sunset detector: TPC Magnet feed box Sunrise detectors: CCD, Calorimeter, µMegas 80º 14º 10 m long LHC dipole prototype CAST: Axion helioscope experimental setting

La Thuile, March 2005Berta Beltrán10 Description of the experiment: LHC Magnet Superconducting LHC test dipole. Use of superfluid 4 He to cool the system down to 1.8 K L= 9.26 m long and magnetic field up to 9 Tesla. The magnetic filed is confined in twin pipes of ~14.5 cm 2 area each. The aperture of each of the bores fully covers the potentially axion-emitting solar core (~1/10th of the solar radius) Mount on a moving platform allowing ± 8º V; ± 40º H

La Thuile, March 2005Berta Beltrán11 Tracking system Snapshot of the tracking program Software with astronomical calculations. Communicates with the motors→ interface to move the magnet. The overall CAST pointing precision in better than 0.01º Both the hardware and the software of the tracking system have been precisely calibrated by means of geometric survey measurements.

La Thuile, March 2005Berta Beltrán12 X-ray detectors: TPC (CERN) Position sensitive Conventional technology: robustness and stability guaranteed Use of a passive shielding to reduce the level of the background. 4.13×10 -5 counts/KeV/sec/cm ×10 counts/KeV/sec/cm 2 Reduction by a factor ~ mm POLYETHYLENE 25 mm LEAD 5 mm COPPER 2 mm CADMIUM N 2 FLUX 200 l/h

La Thuile, March 2005Berta Beltrán13 X-ray detectors: μMegas (Saclay/Athens/CERN) Very good spatial resolution (350 μm X-Y strip pitch) Low threshold (0.8 keV) CAST prototype: two dimensional strip read out

La Thuile, March 2005Berta Beltrán14 X-ray focusing device + CCD (MPI/HLL) Focusing device; Space technology (prototype for the ABRIXAS satellite) From 48 mm Ø (LHC magnet aperture) →~3 mm Ø Big signal to noise ratio improvement About 35% efficiency due to reflections The CCD camera: Very good energy resolution (<0.5 keV) Low threshold Windowless operation in vacuum: efficiency close to 100% in the full energy range. 43 mm  1.6 m 3 mm 

La Thuile, March 2005Berta Beltrán15 X-ray detectors: Calorimeter (Chicago) In the experiment only during the 2004 data taking. The goal is to extend sensitivity to axion induced γ ’s from few keV to ~150 Mev First time that this kind of search is performed.

La Thuile, March 2005Berta Beltrán16 CAST experiment: status 2003 data taking Running for about six months. Data already analyzed → First CAST results (K.Zioutas et. al PRL, in press) data taking Improved conditions in the three detectors (shiledings,….). Add of a fourth detector (calorimeter) for High Energy axions. Improvements in the tracking system and in the magnet: more reliability and longer periods of data tacking. Running from May to November without problems Updating the experiment setup for the second phase of CAST Analyzing 2004 data…

La Thuile, March 2005Berta Beltrán17 c/keV/cm 2 /s Solar-axion-photons spectrum for g ~ 6 x GeV -1 (Tokyo Helioscope sensitivity) CAST TPC Subtracted spectrum Comparison of sensitivities of CAST and Tokyo Helioscope Energy [keV] TPC subtracted spectrum and “expected” axion-photons spectrum

La Thuile, March 2005Berta Beltrán18 CAST 2003 result Subtracted spectrum TPC, μMegas Tracking (dots) and background (dashed line) spectra of the CCD. No signal over background in any of the three detectors.

La Thuile, March 2005Berta Beltrán19 CAST 2003 result Axion exclusion plot Combined upper limit obtained (95% C.L.): g aγγ <1.16× GeV -1

La Thuile, March 2005Berta Beltrán20 Backup slides

La Thuile, March 2005Berta Beltrán21 Peccei-Quinn solution: is a dynamical variable with classical potential that is minimized by =0. The prize for this is the introduction of an additional spontaneously broken global symmetry and its associated pseudo-Goldstone boson, the axion. Axions: Motivation Strong CP problem: QCD lagragian has a non-perturbative term: where field strength tensor and its dual g gauge coupling andΘ→ QCD vacuum; M = quark mass matrix This is an arbitrary parameter that violates CP if ≠ 0 ; but it is constrained by t he neutron dipole moment to be ≤ Why so small?

La Thuile, March 2005Berta Beltrán22 Axions : Phenomenology The AXION is: pseudoscalar neutral practically stable phenomenology driven by the breaking scale f a and the specific axion model Axion mass: Axion-photon coupling present in almost every axion model This gives rise to the Primakoff effect: axion- photon conversion (and vice versa) in the presence of electromagnetic fields. That is the only axion phenomenology on which CAST relies…