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Search for Solar Axions: the CAST experiment at CERN http://cast.web.cern.ch/CAST/. Berta Beltrán (University of Zaragoza, Spain) XXXXth Rencontres de Moriond La Thuile, March 2005. Outline. The physics behind CAST : Axions. Principle of detection The CAST experiment : Description :

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Search for solar axions the cast experiment at cern http cast web cern ch cast

Search for Solar Axions:the CAST experiment at CERNhttp://cast.web.cern.ch/CAST/

Berta Beltrán (University of Zaragoza, Spain)

XXXXth Rencontres de Moriond

La Thuile, March 2005


Outline

Outline

The physics behind CAST:

Axions.

Principle of detection

The CAST experiment:

Description:

Magnet, tracking, …

X-ray detectors.

Data Analysis and 2003 results.

Berta Beltrán


Search for solar axions the cast experiment at cern cast web cern ch cast

  • 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]

Axions : Motivation

Berta Beltrán


Search for solar axions the cast experiment at cern cast web cern ch cast

The Sun as an axion source

Thermal photons

Axions

Fluctuating electric fields of the

charged particles in the hot plasma

Solar physics

+

Primakoff effect

γ

a

Differential solar axion flux at Earth.

-e

[K. van Bibber et al. PRD 39,(1989)]

Ze

Berta Beltrán


Search for solar axions the cast experiment at cern cast web cern ch cast

CAST: Principle of detection

Transverse magnetic field (B)

Axion

X-ray (same energy and momentum)

X-ray detector

L

[Sikivie PRL 51 (1983)]

  • Expected number of photons in the x-ray detector:

Differential axion flux at the Earth

(cm-2 s -1 keV -1 )

Conversion probability of

an axion into photon ( (B×L)2)

For gaγγ =1×1O-10 GeV-1

t=100 h , S=15 cm2

N γ ≈ 30 events

S

Magnet bore area (cm2)

t

Measurement time (s)

Berta Beltrán


Search for solar axions the cast experiment at cern cast web cern ch cast

  • But this

is a coherent process only when the axion andphoton

fields remain in phase over L

Coherence condition states thatqL < 1

(axion-photon momentum transfer)

with

  • Vacuum inside the magnet: mγ =0 We are sensitive to axion masses ≤ 2.3×10 -2 eV (CAST phase I)

  • Buffer gas (He) inside the magnet:mγ,eff >0

Different gas pressures P will make us sensitive to different axion masses up to 1 eV(CAST phase II)

Berta Beltrán


Cast collaboration

CAST Collaboration

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.

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.

68 participants from 15 institutions

Berta Beltrán


Search for solar axions the cast experiment at cern cast web cern ch cast

Genève

CAST: Point 8

CERN

(Meyrin site)

CAST at CERN:

Berta Beltrán


Search for solar axions the cast experiment at cern cast web cern ch cast

CAST: Axion helioscope experimental setting

Magnet feed box

Sunsetdetector: TPC

10 m long LHC dipole prototype

14º

Sunrise detectors: CCD, Calorimeter, µMegas

80º

Berta Beltrán


Search for solar axions the cast experiment at cern cast web cern ch cast

Description of the experiment: LHC Magnet

  • Superconducting LHC test dipole.

  • Use of superfluid 4He 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 cm2 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

Berta Beltrán


Search for solar axions the cast experiment at cern cast web cern ch cast

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.

Berta Beltrán


Search for solar axions the cast experiment at cern cast web cern ch cast

N2 FLUX 200 l/h

5 mm COPPER

1.85×10 counts/KeV/sec/cm2

2 mm CADMIUM

Reduction by a factor ~4.5

25 mm LEAD

4.13×10-5 counts/KeV/sec/cm2

200 mm

POLYETHYLENE

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.

Berta Beltrán


Search for solar axions the cast experiment at cern cast web cern ch cast

2003

2004

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

Berta Beltrán


Search for solar axions the cast experiment at cern cast web cern ch cast

3 mm 

1.6 m

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 

Berta Beltrán


Search for solar axions the cast experiment at cern cast web cern ch cast

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.

Berta Beltrán


Search for solar axions the cast experiment at cern cast web cern ch cast

CAST experiment: status

  • 2003 data taking

    • Running for about six months.

    • Data already analyzed → First CAST results (K.Zioutas et. al. 2005 PRL, in press).

  • 2004 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.

  • 2005

    • Updating the experiment setup for the second phase of CAST

    • Analyzing 2004 data…

Berta Beltrán


Search for solar axions the cast experiment at cern cast web cern ch cast

TPC subtracted spectrum and “expected” axion-photons spectrum

c/keV/cm2/s

Solar-axion-photons spectrum for g ~ 6 x 10-10 GeV-1

(Tokyo Helioscope sensitivity)

Comparison of sensitivities of CAST and Tokyo Helioscope

CAST TPC Subtracted spectrum

Energy [keV]

Berta Beltrán


Search for solar axions the cast experiment at cern cast web cern ch cast

CAST 2003 result

Tracking (dots) and background (dashed line) spectra of the CCD.

Subtracted spectrum TPC , μMegas

  • No signal over background in any of the three detectors.

Berta Beltrán


Search for solar axions the cast experiment at cern cast web cern ch cast

CAST 2003 result

Axion exclusion plot

  • Combined upper limit obtained (95% C.L.):

    gaγγ<1.16×10-10 GeV-1

Berta Beltrán


Search for solar axions the cast experiment at cern cast web cern ch cast

Backup slides

Berta Beltrán


Search for solar axions the cast experiment at cern cast web cern ch cast

Axions: Motivation

  • Strong CP problem: QCD lagragian has a non-perturbative term:

field strength tensor and its dual

where

g

gauge coupling

and

Θ→ 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 ≤ 10-10 .Why so small?

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.

Berta Beltrán


Search for solar axions the cast experiment at cern cast web cern ch cast

Axions : Phenomenology

  • The AXION is:

    • pseudoscalar

    • neutral

    • practically stable

    • phenomenology driven by the breaking scale fa 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…

Berta Beltrán


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