The status of the solar axion search with the CERN Axion Solar Telescope
(CAST) will be discussed. Results from the first part of CAST phase II where
the magnet bores were filled with \hefour gas at variable pressure in order to
scan \ma up to 0.4 eV will be presented. From the absence of excess X-rays when
the magnet was pointing to the Sun, we set a typical upper limit on the
axion-photon coupling of $\gag \lesssim 2.17 \times10^{-10}$GeV$^{-1}$ at 95%
CL for \ma$<0.4$ eV, the exact result depending on the pressure setting. Our
search for axions with masses up to about 1.2 eV using \hethree as a buffer gas
is, since last year, in progress in the second part of CAST phase II.
Expectations for sensibilities will be given. Near future perspectives as well
as more long term options for a new helioscope experiment will be evoked.Comment: 4 pages, 1 figure to be publish in the proceedings of the 5th Patras
  Workshop on Axions, WIMPs and WISP

Ribas, Esther Ferrer

English

arXiv

The status of the solar axion search with the CERN Axion Solar Telescope (CAST) will be discussed. Results from the first part of CAST phase II where the magnet bores were filled with \hefour gas at variable pressure in order to scan \ma up to 0.4 eV will be presented. From the absence of excess X-rays when the magnet was pointing to the Sun, we set a typical upper limit on the axion-photon coupling of $\gag \lesssim 2.17 \times10^{-10}$GeV$^{-1}$ at 95% CL for \ma$<0.4$ eV, the exact result depending on the pressure setting. Our search for axions with masses up to about 1.2 eV using \hethree as a buffer gas is, since last year, in progress in the second part of CAST phase II. Expectations for sensibilities will be given. Near future perspectives as well as more long term options for a new helioscope experiment will be evoked.The status of the solar axion search with the CERN Axion Solar Telescope (CAST) will be discussed. Results from the first part of CAST phase II where the magnet bores were filled with \hefour gas at variable pressure in order to scan \ma up to 0.4 eV will be presented. From the absence of excess X-rays when the magnet was pointing to the Sun, we set a typical upper limit on the axion-photon coupling of $\gag \lesssim 2.17 \times10^{-10}$GeV$^{-1}$ at 95% CL for \ma$<0.4$ eV, the exact result depending on the pressure setting. Our search for axions with masses up to about 1.2 eV using \hethree as a buffer gas is, since last year, in progress in the second part of CAST phase II. Expectations for sensibilities will be given. Near future perspectives as well as more long term options for a new helioscope experiment will be evoked

Ferrer Ribas, Esther

CERN Document Server

arXiv:0912.4222v1  [hep-ex]  21 Dec 2009T he C A ST experim ent: status and perspectivesEstherFerrerRibason behalfofthe CAST CollaborationIRFU,CEA/Saclay,91190 G ifsurYvette,FranceD O I:willbe assignedThe status ofthe solar axion search with the CERN Axion Solar Telescope (CAST) willbe discussed. Resultsfrom the rstpartofCAST phase IIwhere the m agnetboreswerelled with4Hegasatvariablepressurein orderto scan m a up to 0.4 eV willbepresented.From the absence ofexcess X-rays when the m agnet was pointing to the Sun,we set atypicalupperlim iton the axion-photon coupling ofga . 2:17 10  10G eV  1at95% CLform a< 0:4 eV,theexactresultdepending on thepressure setting.O ursearch foraxionswith m asses up to about1.2 eV using3He as a buergas is,since last year,in progressin the second part ofCAST phase II.Expectations for sensibilities willbe given. Nearfutureperspectivesaswellasm orelong term optionsfora new helioscope experim entwillbe evoked.1 IntroductionThe CAST (Cern Axion Solar Telescope) experim ent is using a decom m issioned LHC dipolem agnet to convert solar axions into detectable x-ray photons. Axions are light pseudoscalarparticlesthatarisein thecontextofthePeccei-Q uinn[1]solution to thestrongCP problem andcan be Dark M attercandidates[2].Starscould produce axionsvia the Prim ako conversion ofthe plasm a photons.The CAST experim entispointing atourcloseststar,the Sun,aim ing todetectsolaraxions.Thedetection principleisbased on thecoupling ofan incom ing axion to avirtualphoton provided by thetransverse eld ofan intensedipolem agnet,being transform edinto a real,detectablephoton thatcarriestheenergy and them om entum oftheoriginalaxion.The axion to photon conversion probability is proportionalto the square ofthe transverse eld ofthe m agnetand to the active length ofthe m agnet. Using an LHC m agnet(9 T and9:26 m long)im provesthe sensitivity by a factor100 com pared to previousexperim ents. TheCAST experim enthasbeen taking data since2003 providing them ostrestrictivelim itson theaxion-photon coupling [3,4]form assesm a . 0:02eV.Atthism assthe sensitivity isdegradeddueto coherenceloss.In orderto restorecoherence,them agnetcan be lled with a bu ergasprovidingan e ectivem asstothephoton[5].By changingthepressureofthebu ergasin steps,one can scan an entire range ofaxion m assvalues. Atthe end of2005 the CAST experim entstarted such a program ,entering its phase II by  lling the m agnet bore with He gas. From2005 to 2007,the m agnetbore was lled with4He gasextending oursensitivity to m assesupto 0:4 eV, nalresultswillbe presented here.From M arch 2008 onwardsthe m agnetbore hasbeen  lled with3He and the sensitivity should be increased to sensivitiesup to m a . 1:2 eVby the end ofthe 3Herun in 2010.Patras2009 12 T he C A ST experim entalset-up: recent upgradesTheCAST setup hasbeen described elsewhere[3,9].From 2002to 2006threeX-ray detectorswere m ounted on the two sidesofthe m agnet: a conventionalTPC[10]covering both m agnetboreslookingforsunsetaxions;in thesunrisesideoneoftheboreswascoveredby aM icrom egasdetector[11]andin theotherboreaCCD detectorcoupledtoatelescope[12]im provingthesignalto background ratio by a factor150.In 2006 theTPC started to show a degraded perform ancedue to aging. It was then decided to replace the sunset TPC and the existing M icrom egasdetectorin the sunrise side by a new generation ofM icrom egasdetectors[13,14]thatcoupledwith suitable shielding would im prove greatly their perform ance. The new detectors werecom m issioning end of 2007 and by m id 2008 they have already shown an im provem ent inperform ancethathasbeen translated in a background reduction ofa factor15 com pared to theTPC perform ancesand a factor3 com pared to thestandard M icrom egasdetectorused withoutshielding till2006.TheCCD detectorwillalso beupgraded by thefall2009 by a new detectorwith im proved perform ance: better low energy response,lowerintrinsic background by usingm oreradio-purem aterialsand lessoutoftim e events.In 2005,theexperim entwentthrough am ajorupgradetoallow operation with Hebu ergasin thecold bore.Thisupgradewasdonein twosteps: rstthesystem wasdesigned foroperationusing 4Heand in 2007thesystem wasupgraded foroperation athigherbu ergasdensitiesusing3He. The system has been designed to controlthe injection ofHe in the m agnetbores withprecision and to m onitoraccurately thegaspressureand tem perature[15,16].Specialcarehasbeen taken toachievehigh precision in thereproducibility ofsteps(< 0:01m bar)and toprotectthe system for3Heloss.The 3He system hasbeen operating succesfully sincedecem ber2007.3 R esultsAsduring phaseI,thetracking data (m agnetpointing thesun)represented about2 1.5 hoursper day while the rest ofthe day was used to m easure background. The procedure was todaily increase the 4He density so that sunrise and sunset detectors m easure every pressure.Every speci c pressure ofthe gasallowsto testa speci c axion m asshaving a new discoverypotential.The 4Hedata recorded end of2005and 2006representsaround 300hoursoftrackingdata and 10 tim es m ore hours ofbackground data for each detector,covering 160 pressuresettingsallowing to scan a new axion m assrangebetween 0.02 and 0.39 eV.An independentanalysiswasperform ed foreach data setofthethreedi erentdetectors.Acom bined prelim inary resultwasderived wherefrom theabsenceofa signalabovebackgroundCAST excludes a new range in the ga{m a plane shown in  gure1 from axion m asses of0.02eV (PhaseI)up to m assesof0.39eV.Thisparam eterspacewasnotpreviously explored inlaboratory experim ents.CAST hasthereforeentered theQ CD axion band forthe rsttim einthisrangeofaxion m asses,excluding an im portantportion oftheaxion param eterspace.The nalresultshavebeen published in [17].The collaboration has perform ed by-productanalysis ofthe data taken,to look for otheraxion scenario to which CAST would also be sensitive. The TPC phase I data has beenreanalysed in orderlook for14 keV axionscom ing from M 1 transitions.In addition,data takenwith a calorim eterduring the phase I,were used to search for high energy (M eV) lines fromhigh energy axion conversion [6,7].M orerecently a few daysofdata weretaken with a visibledetectorcoupled to one end ofthe CAST m agnet[8],in search foraxionswith energy in the2 Patras2009"visible" range. It is foressen that a perm anent setup willbe installed in the experim ent inorderto takedata withoutinterfering with the standard program ofCAST.Atpresent,we arerunning with 3He since 2008 and by the end ofthisyearweshoud havereached sensitivitiesofaround m a < 0.8eV.(eV)axionm-710 -610 -510 -410 -310 -210 -110 1 10)-1(GeVγag-1610-1510-1410-1310-1210-1110-1010-910-810-710-610-510-410Axion modelsKSVZ [E/N = 0]Tokyo helioscopeLaser exps.OverclosureCASTMicrowave cav.crystalsHB starsHDMHe3Figure 1:Exclusion plotin the axion-photon coupling versusthe axion m assplane fora widerange ofparam eters. The lim it achieved by the CAST experim ent (com bined result oftheCAST phaseIand 4HepartofphaseII)iscom pared with constraintsobtained from theSum icoexperim ent(the Tokyo helioscope)and HB stars.The red dashed line showsourprospectsforthe 3He run started in M arch 2008. The verticalline (HDM ) is the hot dark m atter lim itfor hadronic axions m a < 1:0 eV inferred from observations ofthe cosm ologicallarge-scalestructure. The yellow band represents typicaltheoreticalm odels with jE =N   1:95jin therange 0.07{7 where the green solid line corresponds to the case when E =N = 0 is assum ed.Lim its from laser, m icrowave and underground detectors [18]for axion searches have beenincluded.4 A fter C A ST ?CAST originalphysics program will nish at the end of2011. The CAST collaboration islooking into possibilitiesin orderto achieve greatersensitivities. The sensitivity ofhelioscopeaxion searchesdepends strongly on the m agnet’s characteristics. O ngoing R & D on dipoleswilllead to strongerand biggerm agnetsin thecom ing years(2013-2015).Such m agnetscouldeither be adopted to the existing infrastructure of CAST,thus elim inating the cost to them agnet itself,or be used with a new tracking and cryogenics system ,im proving thus m anycharacteristics(like daily tracking tim e,safety etc)butincreasing the cost. In parallel,e ortPatras2009 3willbe devoted on the developm entofhigh e ciency focusing devicesand new electronicsforthe detectors,aim ing to achieve very low background levels.Allthiswould allow pushing thesensitivity oftheexperim entto thelevelof10  11G eV   1,probing theQ CD axion m odelregionform asseshigherthan 10  2 eV.In orderto exceed thelim itof10  11G eV   1 with a helioscope,specially developed m agnets are necessary. Taking advantage ofthe fact that the im portantparam eter is the strength and not the hom ogeneity ofthe m agnetic  eld,a stronger m agnetwith bigger aperture,could be designed and constructed especially for such an experim ent.This is a m ore expensive and long term option,which would allow reaching the lim its ofthehelioscopeaxion searcheswith an increased discovery potential.Thesedi erentoptionsaswellasexpected sensitivitieswerepresented in detailin [19].5 C onclusionsTheCAST experim enthasestablished them oststringentexperim entallim iton axion couplingconstantovera wide rangeofm asses,exceeding astrophysicalconstraints.The 4He phase hasallowed toenterin an unexplored region favoured by thetheoryaxion m odels.From theabsenceofexcessX-rayswhen them agnetwaspointing to theSun,weseta prelim inary upperlim itontheaxion-photon coupling ofga . 2:22 10  10 G eV  1at95% CL form a . 0:4 eV,theexactresultdepending on thepressuresetting.Atpresent,with the 3Herun weareexploring deeperthisregion to reach sensitivitiesofm a < 1.2eV.The Collaboration islooking into developpingthe new generation ofhelioscopes in order to reach sensitivities ofthe order of10  11G eV   1leading to explore a large part of the Q CD favoured m odelregion including the otherwisenon-accessiblesub-keV range.R eferences[1] R .D .Pecceiand H .R .Q uinn,Phys.R ev.Lett.38,1440 (1977).[2] P.Sikivie,Int.J.M od.Phys.D 3 S,1 (1994) and Phys.R ev.Lett.51,1415 (1983).[3] K .Zioutasetal.(CA ST collaboration),Phys.R ev.Lett.94 ,121301 (2005),arX iv:hep-ex/0411033.[4] S.A ndriam onjeetal.(CA ST collaboration),JCA P 04 10 (2007),arX iv:hep-ex/0702006.[5] K .van Bibber,P.M M cIntyre,D .E.M orrisand G .G R aelt,Phys.R ev.D 39,2089 (1989).[6] S.A ndriam onje etal.(CA ST collaboration),accepted forpublication atJCA P,arX iv:hep-ex/09064488[7] K .Jakovcic etal.(CA ST collaboration),these proceedings.[8] M .K aruza etal.(CA ST collaboration),these proceedings.[9] K .Zioutas etal,N ucl.Instrum .M ethods Phys.R es.,A 425 480 (1999),arX iv:astro-ph/9801176.[10] D .A utiero etal.,N ew J.Phys 9,171 (2007) arX iv:hep-ex/0702189.[11] P.A bbon etal.,N ew J.Phys 9,170 (2007),arX iv:hep-ex/0702190.[12] M .K uster etal.,N ew J.Phys 9,169 (2007),arX iv:hep-ex/0702188.[13] J.G alan etal.,N ucl.Instr.and M eth.A 604 15-19 (2009).[14] S.A une etal.,J.Phys.Conf.Ser.179 012015 (2009).[15] T.O .N iinikoskietal.,Subm itted to Proc.ICEC 22,Seoul(2008).[16] CA ST Collaboration,SPSC-TD R -001,CER N -SPSC-2006-029.[17] E.A rik etal.(CA ST collaboration),JCA P 0902,008 (2009).[18] Z.A hm ed etal.(CD M S Collaboration),Phys.R ev.Lett.103 141802 (2009),arX iv:hep-ex/0902.4693.[19] T.Papaevangelou (CA ST collaboration),Presentation at\N ew opportunities in the PhysicsLandscape atCER N ".4 Patras2009

The CAST experiment: status and perspectives

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