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Search for solar axions with the CAST experiment Biljana Lakić (Rudjer Bošković Institute, Zagreb) for the CAST Collaboration Time and Matter 2010, 04-08 October 2010, Budva, Montenegro CAST: CERN Axion Solar Telescope CAST Collaboration CEA Saclay -- CERN -- Dogus University -- Lawrence Livermore National Laboratory -- Max-Planck-Institut for Solar System Research/Katlenberg-Lindau -- Max-Planck-Institut für extraterrestrische Physik -- Max-Planck-Institut für Physik -National Center for Scientific Research Demokritos -- NTUA Athens -- Institut Ruđer Bošković Zagreb -- Institute for Nuclear Research (Moscow) -- TU Darmstadt -- University of British Columbia -- University of Chicago -- Universität Frankfurt -Universität Freiburg -- University of Patras -- University of Thessaloniki -- Universita di Trieste --Universidad de Zaragoza 21 institutions, 84 scientists Biljana Lakić TAM2010, 04-08 Oct 2010, Budva 2 CAST: CERN Axion Solar Telescope CAST Biljana Lakić TAM2010, 04-08 Oct 2010, Budva 3 Outline: Axions Theory Experimental searches Axion is named after a brand of washing powder (it cleaned up a long-standing problem in theoretical physics) The CAST experiment Physics Setup Results and prospects Biljana Lakić TAM2010, 04-08 Oct 2010, Budva 4 Axions Axions were introduced to solve the Strong CP Problem: It is well known that the weak nuclear force violates the CP symmetry (more matter than antimatter in the Universe) Strong CP problem: strong nuclear force theory violates the CP symmetry strongCP s μν ~ Ga Ga 8 Arg det M (QCD vacuum + EW quark mixing) It should be observable in the measurements of the electric dipole moment of the neutron (nEDM) Strong experimental bound on nEDM requires 10-9 Biljana Lakić TAM2010, 04-08 Oct 2010, Budva 5 Axions Peccei-Quinn solution: In 1977, Peccei and Quinn proposed an elegant solution: a new global chiral U(1)PQ symmetry spontaneously broken at scale fa Associated pseudo-Goldstone boson is axion Parameter is re-interpreted as dynamical variable (scalar field) and is absorbed in the definition of the axion field: a x f a s μν ~ s μν ~ strongCP Ga Ga a aGa Ga 8 8 f a No more CP violation in the theory! The only thing left is to find axions… Biljana Lakić TAM2010, 04-08 Oct 2010, Budva 6 Axions Axion mass and couplings axions generically couple to gluons and mix with pions f 106 GeV 6 eV mass: ma m fa fa couplings to photons, nucleons and electrons (optional) axion-photon coupling has two contributions: axion-photon coupling via triangle loop axion-pion mixing g a 2 f a Biljana Lakić E 24 z w E 1 . 92 0 . 08 N 31 z w 2 f N a TAM2010, 04-08 Oct 2010, Budva 7 Axions Axion models: standard axion model (fa fweak) excluded experimentally invisible axion models (fa >>fweak, g ~1/fa, ma ~1/fa) KSVZ (Kim, Shifman, Vainshtein, Zakharov) DFSZ (Dine, Fischler, Srednicki, Zhitnitskii) Axion properties: very low mass and coupling constant (fa >>fweak, g ~1/fa, ma ~1/fa) practically stable neutral pseudoscalar candidate for dark matter Biljana Lakić TAM2010, 04-08 Oct 2010, Budva 8 Axions Axions are candidates for the Dark Matter of the Universe (axions produced in the early Universe) CDM HDM Cold Dark Matter (CDM): responsible for small-scale structures (WIMPs, axions …) axion as CDM: coherent oscillations of the axion field Hot Dark Matter (HDM): neutrinos, axions … axions as HDM: thermal relics (in analogy to neutrinos) Cosmological limit: 10-5 eV ma 1 eV Biljana Lakić TAM2010, 04-08 Oct 2010, Budva 9 Axions Axions from astrophysical sources Low mass, weakly interacting particles (neutrinos, gravitons, axions etc.) are produced in hot stellar plasma and can transport energy out of stars. The couplings of these particles with ordinary matter and radiation are bounded by the constraint that stellar lifetimes do not conflict with the observations. For axion-photon coupling, the most restrictive astrophysical limit derives from globular cluster (GC) stars, by comparing the number of horizontal branch (HB) stars with the number of red giants. Biljana Lakić TAM2010, 04-08 Oct 2010, Budva 10 Axions Astrophysical and cosmological limits: Globular clusters (a - coupling) Laboratory Tel. Hot dark matter limits (a - coupling) Biljana Lakić Axion dark matter possible (Late inflation scenario) DM ok Too much DM (String scenario) TAM2010, 04-08 Oct 2010, Budva 11 Axions Experimental searches (a- coupling): Laser experiments: Photon regeneration (“invisible light shining through wall”) Polarization experiments (PVLAS) Search for dark matter axions: Microwave cavity experiments (ADMX) Search for solar axions: Bragg + crystal (SOLAX, COSME, DAMA) Helioscope (SUMIKO, CAST) Biljana Lakić TAM2010, 04-08 Oct 2010, Budva 12 CAST: Physics Principle of the Axion helioscope Sikivie, Phys. Rev. Lett 51 (1983) Sun: a thermal photon converts into an axion in the Coulomb fields of nuclei and electrons in the solar plasma (Primakoff process) Earth: an axion converts into a photon in a strong transverse magnetic field -expected number of photons dΦa Nγ Paγ A t dEa dEa Biljana Lakić A = detector effective area t = measurement time TAM2010, 04-08 Oct 2010, Budva 13 CAST: Physics - differential axion flux at the Earth: g aγ Ea / keV 2.481 dΦa 10 6.02 10 10 Ea / 1.205 keV 1 dEa 10 GeV e 2 cm 2s 1keV 1 Ea = 4.2 keV g aγ 10 1 10 GeV Biljana Lakić 2 TAM2010, 04-08 Oct 2010, Budva 14 CAST: Physics ga=10-10 GeV-1 conversion probability in gas (in vacuum: = 0, m=0): 2 Pa γ Bg aγ 1 Γ L Γ L/ 2 2 1 e 2 e cosqL 2 2 q Γ /4 L=magnet length, =absorption coeff. q mγ2 ma2 2 Ea mγ (eV) 0.02 axion-photon momentum transfer P(mbar) T (K) effective photon mass (T=1.8 K) coherence condition for a → conversion qL π mγ2 2πEa 2πEa ma mγ2 L L In case of vacuum, coherence is lost for ma > 0.02 eV. It can be restored with the presence of a buffer gas, but only for a narrow mass range. Biljana Lakić TAM2010, 04-08 Oct 2010, Budva 15 CAST: Physics Novel technique (developed by CAST) for observing axion solar signature: Off-resonance spectra S=0 S = FWHM/2 S = Shift from the resonance S = FWHM Biljana Lakić TAM2010, 04-08 Oct 2010, Budva S = 3FWHM 16 CAST: Physics CAST exclusion plot CAST operation: Phase I Vacuum in the magnet bores: ma < 2.310-2 eV (during 2003 and 2004) Phase II 4He gas pressure increased from 0 - 14 mbar: ma < 0.39 eV (during 2005 and 2006) 3He gas pressure increased from 14 - 120 mbar: ma < 1.16 eV (2008 – 2010) Biljana Lakić TAM2010, 04-08 Oct 2010, Budva 17 CAST: Physics CAST and ADMX enter the theoretically favoured QCD axion region (“Axion models”) World exclusion plot The rest of the parameter space belongs to axion-like particles (ALPs): particles with two-photon coupling PVLAS result in 2006: a “signal” with possible particle interpretation in the region excluded by stellar loss arguments and CAST limit numerous theoretical papers and experimental projects! after upgrades, the signal was lost Biljana Lakić TAM2010, 04-08 Oct 2010, Budva 18 CAST: Physics Astrophysical and cosmological limits: Globular clusters (a - coupling) Laboratory Axion dark matter possible (Late inflation scenario) Tel. Hot dark matter limits (a - coupling) CAST Biljana Lakić DM ok Too much DM (String scenario) ADMX TAM2010, 04-08 Oct 2010, Budva 19 CAST: Setup LHC test magnet (B=9 T, L=9.26 m) Rotating platform (hor. ±40, ver. ±8) X-ray detectors Exposure time: 2×1.5h per day X-ray Focusing Device LHC test magnet Sunset Detectors Biljana Lakić Sunrise Detectors TAM2010, 04-08 Oct 2010, Budva 20 CAST: Setup … one solar tracking (1.5 h) … Biljana Lakić TAM2010, 04-08 Oct 2010, Budva 21 CAST: Tracking precision GRID measurements Horizontal and vertical encoders determine the magnet orientation Correlation between encoder value-magnet orientation has been established for a number of points (GRID) Periodical measurements show that CAST points to the Sun within the required precision Comparison of March 2010 and September 2002 GRID. The required precision of 1 arcmin is indicated by the green circle, while the red one represents the 10% of the Sun projected at 10 m. Biljana Lakić TAM2010, 04-08 Oct 2010, Budva 22 CAST: Tracking precision Solar filming Twice per year (March and September) we can film the Sun through the window A camera is placed on top of the magnet and is aligned with the bore axis Corrections for visible light refractions are taken into account Since March 2008, 2 independent systems are in use Biljana Lakić TAM2010, 04-08 Oct 2010, Budva 23 CAST: Tracking precision … Sun, airplane, sunspot … Biljana Lakić TAM2010, 04-08 Oct 2010, Budva 24 CAST: Detectors before 2007 4He phase X-ray telescope + CCD (sunrise side) pn-CCD chip 20064 pixels (13 cm2) Pixel size: 150150 m2 0.18 counts/h (1-7 keV) from 43 mm ∅ (LHC magnet aperture) to ~3 mm ∅ signal-to-noise improvement (up to 200!) Biljana Lakić TAM2010, 04-08 Oct 2010, Budva 25 CAST: Detectors before 2007 unshielded Micromegas (sunrise side) shielded TPC (sunset side) 4He phase 25 counts/h (2-10 keV) 85 counts/h (2-12 keV) Covering both magnet bores Geometry: 30cm 15cm 10cm Gas: Ar 95%, CH4 5% Biljana Lakić TAM2010, 04-08 Oct 2010, Budva 26 CAST: Detectors after 2007 3He phase Sunrise side: CCD+Telescope & shielded Microbulk MM MM Sunset side: 2 shielded Microbulk MM CCD 0.18 count/h (1-7 keV) 2 counts/h (2-10 keV) Microbulk: new technique, high radio-purity materials, very low background Micromesh 5µm copper Kapton 50 µm Readout pads sunrise sunset Low energy axions In 2010, a “5th line” was added: a 3.5 μm aluminized Mylar foil (transparent to X-rays) is placed on the sunrise Micromegas line to deflect visible photons on an angle of 90o, towards the PMT Biljana Lakić TAM2010, 04-08 Oct 2010, Budva 27 CAST: Gas system for the 3He phase 3He 3He phase gas system Accuracy in measuring the quantity of gas introduced in the cold bore (100ppm) Flexible operation modes (stepping and ramping) Hermetic system to avoid loss of 3He Absence of thermo-acoustic oscillations Protection of cold thin X-ray windows during a quench X-ray windows High X-ray transmission (polypropylene 15 m) Robust (strongback mesh) Minimum He leakage Mechanical endurance to sudden rise of pressure Biljana Lakić TAM2010, 04-08 Oct 2010, Budva 28 CAST: Magnet quench Magnet quench: superconducting magnet resistive transition Biljana Lakić TAM2010, 04-08 Oct 2010, Budva 29 CAST: Simulations for the 3He phase Simulations & new instrumentation have been essential in understanding 3He system in CAST temperature and density conditions, 3He is not an ideal gas (Van der Waals forces) convergence between simulation results & experimental data Knowledge of gas density / setting reproducibility possible Gas density stable along magnet bore Coherence length slowly decreases with increasing density Biljana Lakić TAM2010, 04-08 Oct 2010, Budva 30 CAST: Phase II data taking Phase II data taking is demanding and exciting Every day a new pressure setting every day a new experiment ! Daily quick-look analysis shows if we have a “candidate” COUNTS SEEN IN ALL STEPS OF SAME DENSITY counts/s tep CCD MM MMs MMs OUTCOME Repetition m_i Det 1 Det 2 Det 3 Det 4 0 1 4 0 0 1 0 0 0 0 NO CANDIDATE 2 0 0 0 0 NO CANDIDATE 3 0 0 0 0 NO CANDIDATE Biljana Lakić CANDIDATE TAM2010, 04-08 Oct 2010, Budva 31 CAST: Phase II data taking Sunrise Micromegas Tracking (red) and background (blue) spectra in 2010 2010 counts in different pressure settings: tracking (red), background (blue) Biljana Lakić TAM2010, 04-08 Oct 2010, Budva 32 CAST: Phase II data taking Sunset Micromegas 2010 counts in different pressure settings: background (red), tracking (blue) Biljana Lakić TAM2010, 04-08 Oct 2010, Budva 33 CAST: Phase II analysis one single tracking Biljana Lakić CCD integrated trackings TAM2010, 04-08 Oct 2010, Budva background 34 CAST: First 3He phase results no signal over background observed yet Biljana Lakić TAM2010, 04-08 Oct 2010, Budva 35 CAST: Additional Physics Search for monoenergetic 14.4 keV axions strong emission of 14.4 keV axions is expected from de-excitation of thermally excited 57Fe nuclei in the Sun TPC data from phase I were used Biljana Lakić TAM2010, 04-08 Oct 2010, Budva 36 CAST: Additional Physics Search for monoenergetic high-energy axions 1) 7Li* 7Be → 7Li + a (478 keV) + e- → 7Li* + νe Calorimeter : Biljana Lakić 2) p + d → 3He + a (5.5 MeV) Results : TAM2010, 04-08 Oct 2010, Budva 37 CAST: Additional Physics Low energy solar axions Sun could be a strong source of low energy axions (in the visible – UV) created below sunspots. CAST is complementary (and competitive) with laboratory–based experiments Kaluza – Klein axions Due to the coherence condition, CAST could be sensitive to the existence of large extra dimensions particular Kaluza-Klein states Biljana Lakić TAM2010, 04-08 Oct 2010, Budva 38 CAST published physics results For ma<0.02 eV: gaγ0.88 10-10 GeV-1 JCAP04(2007)010 PRL (2005) 94, 121301 For ma<0.39 eV typical upper limit: gaγ2.2 10-10 GeV-1 JCAP 0902:008,2009 CAST byproducts: High Energy Axions: Data taking with a HE calorimeter JCAP 1003:032,2010 14.4 keV Axions: TPC data JCAP 0912:002,2009 Low Energy (visible) Axions: Data taking with a PMT arXiv:0809.4581 Biljana Lakić TAM2010, 04-08 Oct 2010, Budva 39 CAST outreach 13th April 2010: CAST 10th anniversary Organization of Axion workshops 1st Joint ILIAS-CAST-CERN Axion Training Workshop 2005, CERN 2nd Joint ILIAS-CAST-CERN Axion Training Workshop 2006, Patras 3rd Joint ILIAS-CERN-DESY Axion-WIMPs training-workshop 2007, Patras 4th Patras Workshop on Axions, WIMPs and WISPs 2008, DESY 5th Patras Workshop on Axions, WIMPs and WISPs 2009, Durham 6th Patras Workshop on Axions, WIMPs and WISPs 2010, Zurich Biljana Lakić TAM2010, 04-08 Oct 2010, Budva 40 CAST prospects CAST will finish the planned program by July 2011 Proposal in preparation for the period 2011 – 2013 Improve vacuum limit low noise Micromegas detectors low treshold Search for chameleons, paraphotons, low energy axions ... R&D towards New Generation Axion Helioscope (detectors, optics, magnet) coupling constant dependence: g a BL 1/ 8 1/ 8 A1/ 4 b t detector tracking 1/ 2 magnet Biljana Lakić TAM2010, 04-08 Oct 2010, Budva system 41 Axion helioscopes prospects Midterm scenario Ongoing R&D on magnets at CERN Possible after 2013: B=13 T, L=4 m, =10 cm Development of x-ray optics (high efficiency) Longer term scenario Ongoing R&D on magnets at CERN Possible after 2016 + “some funds”: B=14 T, L=8 m, =14 cm Development of x-ray optics (high efficiency) And more … Biljana Lakić TAM2010, 04-08 Oct 2010, Budva 42 Conclusions CAST provides the best experimental limit on axion-photon coupling constant over a broad range of axion masses. CAST Collaboration has gained a lot of experience in axion helioscope searches. R&D on superconducting magnets can lead to much more sensitive helioscopes. Future helioscope experiments and Microwave cavity searches (ADMX) could cover a big part of QCD axion model region until 2020. Biljana Lakić TAM2010, 04-08 Oct 2010, Budva 43