Search for Solar Axions with the CAST experiment

Search for Solar Axions with the CAST experiment

J. Galán on behalf of the CAST CollaborationUniversity of Zaragoza (Spain)

8/Oct/2009 J.Galán 11th ICATPP Como, Italy

The CAST CollaborationCanadaUniversiy of British Columbia, Department of Physics, VancouverM. Hasinoff

CroatiaRudjer Boskovic Institute, ZagrebRudjer Boskovic, M. Krcmar, B. Lakic, A. Ljubicic

FranceDAPNIA, CEA-Saclay, Gif-sur-YvetteS. Aune, E. Ferrer-Ribas, I. Giomataris, T. Papaevangelou

GermanyTU Darmstadt, Institut für KernphysikD. H. H. Hoffmann, M.Kuster, A. Nordt

GSI DarmstadtD. H. H. Hoffman

Universität Frankfurt, Institut für Angewandte Physik, FrankfurtJ. Jacoby

Universität FreiburgH. Fischer, J. Franz, F.H. Heinsus, D. Kang, K. Königsmann, J. Vogel

MPE GarchingH.Bräuninger, M. Kuster, A. Nordt

WHI MünchenR. Kotthaus, G. Lutz, G. Raffelt, P. Serpico

GreeceUniversity of PatrasA. Gardikiotis,Y. Semertzidis, M.Tsagri, K. Zioutas

National Center for Scientific Research “Demokritos”, AthensT. Karageorgoplou, G. Fanourakis, T. Geralis, K. Kousouris

Aristotle University of ThessalonikiC. Eleftheriadis, A. Liolios, I. Savvidis, T. Vafeiadis

Hellenic Open University, PatrasC. Bourlis, S. Tzamarias

RussiaRussian Academy of Science, Institute for Nuclear Research (INR),MoscowA.Belov, S. Gninenko

SpainUniversity of ZaragozaB. Beltrán, J. Carmona, S. Cebrián, T. Dafni, J. Galán, H. Gómez,I.G. Irastorza, G.Luzón, A. Morales, J. Morales, A. Ortiz, A. Rodríguez, J.Ruz, A. Tomás, J. Villar

TurkeyDogus University, IstambulE. Arik, S.Boydag, S.A. Cetin, O.B. Dogan, I. Hikmet, C. Yildiz

USALawrence Livermore National laboratory, Livermore, CAM. Pivovaroff, R. Soufli, K. van Bibber

University of Chicago, Enrico Fermi Institute and KICPJ. Collar, D. Miller

SwitzerlandEuropean Organization for Nuclear Research (CERN), GenèveD.Autiero, K. Barth, S. Borgui, M. Davenport, L. Di Lella, N. Elias,C. Lasseur, T. Ninikowski, A. Palacci, H.Riege, L. Stewart, L. Walkiers


Outline

• Introducing the Axion and Solar Axion Model.

• Review the Axion detection techniques.

• The CAST Helioscope Description.

• CAST Status (results from 4He Phase and progress in 3He Phase).

• The new He3 System and detector performances

• Future of Helioscope Axion Searches.


Why do we need Axions?

All you need is Axions!

Bad agreement between theoretical and experimental values for the

electric dipole moment of neutron

QCD predicts violation of CP in strong interactions

8/Oct/2009 J.Galán 11th ICATPP Como, Italy 4

Peccei-Quinn introduced the axion field to solve this problem

What are the Axion properties?

• Neutral pseudoscalar

• Practically stable

• Very low mass

• Very low cross-section

• Coupling to photons


The theory predicts one unique parameter (scale factor) to describe the axion.

If the axion mass is small enough could contribute to the content of Cold Dark Matter of the Universe.

5

Mass depends on this parameter and it needs to be determined experimentally.

Direct Axion Detection Techniques (I)Bragg Difraction

Microwave Cavity Searches

e.g. Asztalos et al., Phys. Rev. D 69, 011101(2004)

[astro-ph/0310042]

Geomagnetic Axion Conversion

Axions can convert to photons in Earth’s magnetic field

Davoudiasl & Huber, hep-ph/0509293

Idea is to observe the Sun through the Earth


Direct Axion Detection Techniques (II)Laser experiments

Light Shining Through Wall

Vacuum properties

e.g. Grin et al. 2006 astro-ph/0611502v1

Telescope Searches

Helioscope Searches

Inoue et al. 2002 astro-ph/0204388v1Lazarus et al. Phys. Rev. Lett. 69 2333 (1992)


Production: The Solar Axion SpectrumAxions should be produced in the

core of the Sun.

The well known Solar Model is used to calculate the expected axion flux in

Earth2

1101211

101067.3

GeV

gscmx a

a


Detection: The Probability Conversion

L = magnet lenght, Γ = absorption coefficient

atrackingCBaa

a dEtAPdE

dN

2N events/day

110100.1 GeVxgaAssuming :

Expected Number of counts


The Experimental Axion SignatureOn resonance

Off Resonance ∆m = 7 meV Off Resonance ∆m = 11 meV

Off Resonance ∆m = 2 meV


The Experimental Axion SignatureOn resonance

Off Resonance ∆m = 7 meV Off Resonance ∆m = 11 meV

Off Resonance ∆m = 2 meV

Signature to identify an axion signal.And a way to determine the axion mass

in a vacuum phase.


CAST Location


The CAST Helioscope

LHC dipole: L = 9.3m, B = 9TSolar Tracking : 3.5 h/day, background data rest of the day

4 x-ray detectors Signal : excess of x-rays while pointing the Sun


Tracking System PrecisionGRID Measurements

• Horizontal and Vertical encoders define the magnet orientation

• Correlation between H/V encoders has been established for a number of points (GRID points)

• Periodically checked with geometer measurements

CAST magnet is tracking the Sun with the required precision.

Sun Filming

• Twice a year (March – September)Direct optical check. Corrected for optical refraction• Verify that the dynamic Magnet Pointing precision (~ 1 arcmin) is with our aceptance


CAST Status and progress•ma<0.02eV•Completed(2003-2004)•PRL94(2005)121301•JCAP04(2007)020

•P< 13.4mbar, 160steps•0.02<ma<0.39eV•Completed(2005-2006)•JCAP02(2009)008

•P< 120 mbar•0.39<ma<1.16eV•Started in Nov 2007•Will continue to Dec2010

•2 weeks data in 2008 (2-4eV)•few eVup to 1keV range

CASTPhase I

(Vacuum)

CASTPhase II(4He)

CASTPhase II(3He)

Low Energy Solar Axions


CAST Status and progress•ma<0.02eV•Completed(2003-2004)•PRL94(2005)121301•JCAP04(2007)020

•P< 13.4mbar, 160steps•0.02<ma<0.39eV•Completed(2005-2006)•JCAP02(2009)008

•P< 120 mbar•0.39<ma<1.16eV•Started in Nov 2007•Will continue to Dec2010

•2 weeks data in 2008 (2-4eV)•few eVup to 1keV range

CASTPhase I

(Vacuum)

CASTPhase II(4He)

CASTPhase II(3He)

Low Energy Solar Axions

CAST continues taking data and measuring with sensitivity for axion masses above 0.75eV

Today -> Pstep : 564


The 3He System Upgrade: The metering volumes

• 4He gas saturates at ~16 mbar for T=1.8 K, for higher pressures only 3He remains gas•Controlled injection of He in the bores. Order of 1000 pressure steps required•Precise measurement of gas quantity•Precise monitoring of gas pressure and temperature•High reproducibility precision (back and forward)•Extra safety for 3He loss


The 3He System : Expansion volumeThe new 3He System is prepared to protect the thin

Cold windows in case of Magnet Quench.


The 3He System : Expansion volumeThe new 3He System is prepared to protect the thin

Cold windows in case of Magnet Quench.

Refilling must be done as fast as posible to dont loss data taking efficiency.


3He Control, Monitoring and Recovery System


Daily Data Taking Protocol


• Detectors data is analysed daily and sent by mail to the CAST collaboration.

• A protocol takes into account the background level of the detectors.• All the information from the 4 detectors taking data in CAST is taken into account

The protocol allows us to decide if we should continue measuring in the same pressure step.

In such way, we avoid to skip a signal that is close to the sensitivity limit of the experiment.

21

Detectors Systems (4He Phase)


2) X-ray Telescope coupled to pnCCDpn CCD chip

Pixels 150μm x 150μmExcellent Energy resol.X-ray finger automated calibration

ABRIXAS space X-ray telescope27 nested mirror cells.

Magnet bore size (42.5 mm) pnCCD Focus from d=43mm to d=3mm

Improved signal/noise by a factor of up ~200

Background in Signal Region:0.18cts/h (1-7keV)

22

Detectors Systems (4He Phase)


2) Micromegas X-ray detector (sunrise)

3) TPC detector (sunset both bores)

23

Detectors Data (4He Phase)


TPC Mean background versus Tracking SpectrumCCD Hitmap Integrated background and Tracking + 1 day tracking

Micromegas Mean Background Rate + Trackings

24

Detector Systems (2008)New Sunrise Micromegas Detection Line

• New vacuum detection line holding space for focussing device installed in 2007.

• Implemented frontal calibration system.

• Implemented new shielding (Cupper, Lead, Cadmium, Plexiglass and Polyethylene.

• Improved control and monitoring of detector gas system and improved vacuum.

• Clean Nitrogen flux surrounding the detector inside the inner shielding.


Detector Systems (2008)


New Sunset Micromegas Detectors• 2 new Micromegas detectors installed in Sunset side replacing the previous TPC.

• Background level reduced by more than a factor 20 due to discrimination capabilities from micromegas detectors versus TPC detector.

• System redesigned and vacuum improvements achieved.

• Calibration is taken daily from the detectors back. Some work already schedulled for implementing frontal calibrators.

26

CAST Frame Store CCD (fall 2009)• Better low energy response:

•0.2 keV < E < 1 keV

• Lower background (built of radio pure materials)

• Better energy resolution (<160eV(FWHM) @ 6keV)

• Mechanical design, cooling system (CERN: engineers, Cryolab)

Imaging area256 x 256 Pixels75 x 75 μm21.92 x 1.92 cm2


Prospects for the post-CAST era


Experience gathered during last years running with the improved detectors systems and the latests and expected new technology in the coming years could push the limits in axion searches even lower.

8/18/14/12/12/1 )( tbALBga

Sensitivity Estimator

29

• CAST has published (JCAP02(2009)008, arXiv:0810.4482v2 [hep-ex])the best laboratory limit for the mass range 0.02eV-0.39eV, with 4He as buffer gas inside the magnet bores.

• Since 2008 CAST has been collecting data with 3He in the magnet bores.

• 2010: CAST should be able to fulfil its program• In parallel, we are developing the low energy (visible)

axion program• High sensitivity detectors may lead to great

improvements in mass region up to 0.02 eV (Vaccuum)

Conclusions


Backup Slides

MICROMEGAS Ultralow Background Periods


Observed periods of very low background in micromegas detectors.

Several improvements:• New designed shielding.• New micromegas detectors made of low radiactivity materials.• More sofisticated statistical analysis. Still not well understood nature background could

be dominated by:• Radon• Compton scattering (not signal like in 85-90% of the cases)• Ectons ( explosive electron emission )

Work in progress for understanding the low background nature.• Full simulation process chain.• Underground Laboratory controlled measurements.

28

Documents

Search for Solar Axions with the CAST experiment