Search for Solar Axions: the CAST experiment at CERN 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

La Thuile, March 2005 Berta Beltrán 2

Outline The physics behind CAST: Axions. Principle of detection

The CAST experiment:Description:

• Magnet, tracking, …• X-ray detectors.

Data Analysis and 2003 results.


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]


The Sun as an axion source

γ a

-eZe

[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. 2

GeV10

g110

aγγ

Solar physics+

Primakoff effect


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)]

aγaa

aγ dEtSP

dE

dΦN a

a

dE

dΦ

γaP

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 (cm2)

Measurement time (s)

For gaγγ =1×1O-10 GeV-

1

t=100 h , S=15 cm2

N γ ≈ 30 events


But this γaP is a coherent process only when the axion and photonfields remain in phase over L

witha

2a

2γ

E2

mmq

Coherence condition states that qL < 1 (axion-

photon momentum transfer)

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

T(K)

P(mbar) 0.02(eV)mγ

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)


University of British Columbia, Department of Physics, Vancouver, CanadaMichael HASINOFF

Ruder Boskovic Institute, Zagreb, CroatiaMilica KRCMAR, Biljana LAKIC, Ante LJUBICIC

Centre d''Etudes de Saclay (CEA-Saclay), DAPNIA, Gif-Sur-Yvette, FranceSamuel ANDRIAMONJE, Stephan AUNE, Esther FERRER, Ioanis GIOMATARIS, Igor G. IRASTORZA

Technische Universitat Darmstadt, Institut für Kernphysik, Darmstadt, GermanyTheopisti DAFNI, Dieter HOFFMANN, Manfred MUTTERER, Yannis SEMERTZIDI, Hans RIEGE

Johann-Wolfgang-Goethe Universität Frankfurt, Institut für Kernphysik, Frankfurt Am Main, GermanyVladimir 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, GermanyHeinrich BRAEUNINGER, Jakob ENGLHAEUSER, Peter FRIEDRICH, Markus KUSTER

Max-Planck-Institut fur Physik Muenchen, GermanyRainer KOTTHAUS, Gerhard LUTZ, Georg RAFFELT, William SERBER,Pasquale SERPICO.

Aristotle University of Thessaloníki, Thessaloniki, GreeceChristos ELEFTHERIADIS, Anastasios LIOLIOS, Argyrios NIKOLAIDIS, Konstantin ZIOUTAS, Ilias SAVVIDIS.

Scuola Normale Superiore (SNS), Pisa, ItalyLuigi DI LELLA

Russian Academy of Sciences, Institute for Nuclear Research (INR), Moskva, RussiaAlexandre BELOV, Sergei GNINENKO, Nikolai GOLUBEV

Instituto de Física Nuclear y Altas Energías, Universidad de Zaragoza, Zaragoza, SpainBerta 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, SwitzerlandKlaus 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 AmericaDavid MIlLER, Juan COLLAR, Joaquin VIEIRA

University of South Carolina, Department of Physics and Astronomy, Columbia, Sc, United States of AmericaFrank 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


CAST: Point 8

CERN(Meyrin site)

Genève

CAST at CERN:


Sunset detector:

TPC

Magnet feed box

Sunrise detectors: CCD, Calorimeter,

µMegas80º

14º

10 m long LHC dipole prototype

CAST: Axion helioscope experimental setting


Description of the experiment: LHC MagnetSuperconducting LHC test dipole.

Use of superfluid 4He to cool the system down to 1.8 KL= 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


Tracking systemSnapshot of the tracking

programSoftware 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.


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/cm2

1.85×10

counts/KeV/sec/cm2 Reduction by a factor ~4.5

200 mm POLYETHYLENE

25 mm LEAD

5 mm COPPER

2 mm CADMIUM

N2 FLUX 200 l/h


X-ray detectors: μMegas (Saclay/Athens/CERN)

20032003

20042004

Very good spatial resolution (350 μm X-Y strip pitch)

Low threshold (0.8 keV)

CAST prototype: two dimensional strip read out


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 43 mm mm

1.6 m1.6 m

3 3 mm mm


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.


CAST experiment: status2003 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…


c/k

eV

/cm

2/ s

Solar-axion-photons spectrum for g ~ 6 x

10-10 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


CAST 2003 result

Subtracted spectrum TPC , μMegasTracking (dots) and background (dashed line) spectra of the CCD.

No signal over background in any of the three detectors.


CAST 2003 resultAxion exclusion plot

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

gaγγ<1.16×10-10

GeV-1


Backup slides


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

aa GG

~, field strength

tensor and its dual

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?


Axions : Phenomenology

The AXION is: pseudoscalar neutralpractically stablephenomenology

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…

Documents

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