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Search for solar axions with the CAST experiment

Search for solar axions with the CAST experiment. Biljana Laki ć (Rudjer Bo š kovi ć Institute, Zagreb ) for the CAST Collaboration. Time and Matter 20 10 , 04 - 08 October 20 10 , Budva , Montenegro. CAST : CERN Axion Solar Telescope. CAST Collaboration

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Search for solar axions with the CAST experiment

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  1. Search for solar axions with theCAST experiment Biljana Lakić (Rudjer Bošković Institute, Zagreb) for the CAST Collaboration Time and Matter 2010, 04-08October 2010, Budva, Montenegro

  2. 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

  3. CAST CAST: CERN Axion Solar Telescope Biljana Lakić

  4. Outline: • Axions • Theory • Experimental searches • The CAST experiment • Physics • Setup • Results and prospects Axionis named after a brand of washing powder (it cleaned up a long-standing problem in theoretical physics) Biljana Lakić

  5. 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 • It should be observable in the measurements of the electric dipole moment of the neutron (nEDM) • Strong experimental bound on nEDM requires   10-9 (QCD vacuum + EW quark mixing) Biljana Lakić

  6. 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: • No more CP violation in the theory! The only thing left is to find axions… Biljana Lakić

  7. Axions Axion mass and couplings • axions generically couple to gluons and mix with pions • mass: • couplings to photons, nucleons and electrons (optional) • axion-photon coupling has two contributions: • axion-photon coupling via triangle loop • axion-pion mixing Biljana Lakić

  8. 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) • very low mass and coupling constant (fa>>fweak, g ~1/fa, ma~1/fa) • practically stable • neutral pseudoscalar • candidate for dark matter Axion properties: Biljana Lakić

  9. Axions Axions are candidates for the Dark Matter of the Universe(axions produced in the early Universe) 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) CDM HDM Cosmological limit: 10-5 eV ma 1 eV Biljana Lakić

  10. Axions • Axionsfrom 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

  11. Axions Astrophysical and cosmological limits: Globular clusters (a -  coupling) Axion dark matter possible (Late inflation scenario) Laboratory DM ok Too much DM (String scenario) Tel. Hot dark matter limits(a -  coupling) Biljana Lakić

  12. 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

  13. Principle of the Axion helioscope Sikivie, Phys. Rev. Lett 51 (1983) CAST: Physics Sun: a thermal photon converts into an axion in the Coulomb fieldsof 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 A = detector effective area t = measurement time Biljana Lakić

  14. CAST: Physics - differential axion flux at the Earth: Ea = 4.2 keV Biljana Lakić

  15. CAST: Physics ga=10-10 GeV-1 • conversion probability in gas (in vacuum:  = 0, m=0): L=magnet length,  =absorption coeff. axion-photon momentum transfer effective photon mass (T=1.8 K) • coherencecondition for a→  conversion 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

  16. 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 S = 3FWHM Biljana Lakić

  17. CAST: Physics CAST exclusion plot CAST operation: Phase I • Vacuum in the magnet bores: ma < 2.310-2 eV(during 2003 and 2004) Phase II • 4He gas pressure increased from 0 - 14 mbar: ma < 0.39eV(during 2005 and 2006) • 3He gas pressure increased from 14 - 120 mbar: ma < 1.16 eV(2008 – 2010) Biljana Lakić

  18. CAST: Physics Worldexclusion plot • CAST and ADMX enter the theoretically favoured QCD axion region (“Axion models”) • 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

  19. CAST: Physics Astrophysical and cosmological limits: Globular clusters (a -  coupling) Axion dark matter possible (Late inflation scenario) Laboratory DM ok Too much DM (String scenario) Tel. Hot dark matter limits(a -  coupling) ADMX CAST Biljana Lakić

  20. Sunset Detectors Sunrise Detectors CAST: Setup • LHC test magnet (B=9 T, L=9.26 m) • Rotating platform (hor. ±40, ver. ±8) • X-ray detectors • X-ray Focusing Device Exposure time: 2×1.5h per day LHC test magnet Biljana Lakić

  21. CAST: Setup … one solar tracking (1.5 h) … Biljana Lakić

  22. 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

  23. 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

  24. CAST: Tracking precision … Sun, airplane, sunspot … Biljana Lakić

  25. CAST: Detectors before 2007 4He phase X-ray telescope + CCD (sunrise side) pn-CCD chip • 20064 pixels (13 cm2) • Pixel size: 150150 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

  26. CAST: Detectors before 2007 4He phase unshielded Micromegas (sunrise side) 25 counts/h (2-10 keV) shielded TPC (sunset side) 85 counts/h (2-12 keV) • Covering both magnet bores • Geometry: 30cm15cm 10cm • Gas: Ar 95%, CH4 5% Biljana Lakić

  27. Micromesh 5µm copper Kapton 50 µm Readout pads CAST: Detectors after 2007 3He phase • Sunrise side: CCD+Telescope & shielded MicrobulkMM • Sunset side: 2 shielded MicrobulkMM Microbulk: new technique, high radio-purity materials, very low background 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

  28. CAST: Gas system for the 3He phase 3He phase 3He 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 tosudden rise of pressure Biljana Lakić

  29. CAST:Magnet quench Magnet quench: superconducting magnet resistive transition Biljana Lakić

  30. 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 CAST:Simulations for the3He phase Biljana Lakić

  31. 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” Biljana Lakić 31

  32. 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 32

  33. CAST: Phase II data taking Sunset Micromegas 2010 counts in different pressure settings: background (red), tracking (blue) Biljana Lakić 33

  34. CAST: Phase II analysis CCD one single tracking integrated trackings background Biljana Lakić

  35. Preliminary CAST: First 3He phase results • no signal over background observed yet Biljana Lakić

  36. 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

  37. CAST: Additional Physics Search for monoenergetic high-energy axions 7Li* →7Li + a (478 keV) 7Be + e-→7Li* + νe p + d →3He + a (5.5 MeV) Calorimeter : Results : Biljana Lakić

  38. 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

  39. CAST published physics results • For ma<0.02 eV: gaγ0.88 10-10 GeV-1 JCAP04(2007)010 PRL (2005) 94, 121301 • For ma<0.39 eV typical upper limit: gaγ2.2 10-10 GeV-1 JCAP 0902:008,2009 CAST byproducts: • High Energy Axions: Data taking with a HE calorimeterJCAP 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

  40. 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 4thPatras Workshop on Axions, WIMPs and WISPs 2008, DESY 5thPatras Workshop on Axions, WIMPs and WISPs 2009, Durham 6thPatras Workshop on Axions, WIMPs and WISPs 2010, Zurich Biljana Lakić 40

  41. 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 AxionHelioscope(detectors, optics, magnet) • coupling constant dependence: Biljana Lakić

  42. 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 42

  43. 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 axionhelioscope 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 43

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