Search for solar axions with the Search for solar axions with the CAST CAST experiment experiment Biljana Laki Biljana Laki ć ć (Rudjer Bo (Rudjer Bo š š kovi kovi ć ć Institute, Institute, Zagreb Zagreb ) ) for the for the CAST Collaboration CAST Collaboration Time and Time and Matter 20 Matter 20 10 10 , , 04 04 - - 08 08 October October 20 20 10 10 , , Budva Budva , , Montenegro Montenegro
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 - PowerPoint PPT Presentation
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Search for solar axions with theSearch for solar axions with theCASTCAST experiment experiment
Search for solar axions with theSearch for solar axions with theCASTCAST experiment experiment
Biljana LakiBiljana Lakićć(Rudjer Bo(Rudjer Bošškovikovićć Institute, Institute, Zagreb Zagreb))
for the for the
CAST CollaborationCAST Collaboration
Time andTime and Matter 20 Matter 201010, , 0404--0808 OctoberOctober 20 201010, , BudvaBudva,, Montenegro Montenegro
CASTCAST:: CERN Axion Solar Telescope 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
AxionAxion is is named after a brand of named after a brand of washing washing powderpowder (it cleaned up a long-standing (it cleaned up a long-standing problem in theoretical physics)problem in theoretical physics)
AxionsAxions were introduced to solve the were introduced to solve the Strong CP ProblemStrong CP Problem::
It is well known that the weak nuclear force violates the CP It is well known that the weak nuclear force violates the CP symmetry (more matter than antimatter in the Universe) symmetry (more matter than antimatter in the Universe)
Strong CP problem: strong nuclear force theory violates the CP Strong CP problem: strong nuclear force theory violates the CP symmetry symmetry
It should be observable in the measurements of the electric dipole It should be observable in the measurements of the electric dipole moment of the neutron (nEDM)moment of the neutron (nEDM)
Strong experimental bound on nEDM requires Strong experimental bound on nEDM requires 10 10-9 -9
55Biljana LakiBiljana Lakićć
AxionsAxions
a
μνa GG
~
8s
CP strong MdetArg
(QCD vacuum + EW quark mixing)(QCD vacuum + EW quark mixing)
In 1977, Peccei and Quinn proposed an elegant solution: a In 1977, Peccei and Quinn proposed an elegant solution: a new global new global chiral U(1)chiral U(1)PQPQ symmetry spontaneously broken at scale symmetry spontaneously broken at scale ffaa
Associated pseudo-Goldstone boson is Associated pseudo-Goldstone boson is axionaxion
ParameterParameter is re-interpreted as dynamical variable (scalar field) and is is re-interpreted as dynamical variable (scalar field) and is
absorbed in the definition of the axion field: absorbed in the definition of the axion field:
No more CP violation in the theory! The only thing left is to find axions…No more CP violation in the theory! The only thing left is to find axions…
very low mass and coupling constant (very low mass and coupling constant (ffaa >>>>ffweakweak, , gg ~ ~1/1/ffaa, , mmaa ~1/~1/ffaa)) practically stable practically stable neutral pseudoscalar neutral pseudoscalar candidate for dark mattercandidate for dark matter
AxionsAxions are candidates for the are candidates for the Dark Matter of the UniverseDark Matter of the Universe (axions produced in the (axions produced in the early Universe)early Universe)
99Biljana LakiBiljana Lakićć
AxionsAxions
Cold Dark Matter (CDM)Cold Dark Matter (CDM):: responsible for small-scale responsible for small-scale
structuresstructures (WIMPs, axions …) (WIMPs, axions …) axion as CDM: coherent axion as CDM: coherent
oscillations of the axion fieldoscillations of the axion fieldHot Dark Matter (HDM)Hot Dark Matter (HDM):: neutrinos, axions …neutrinos, axions … axions as HDM: thermal relics axions as HDM: thermal relics
(in analogy to neutrinos)(in analogy to neutrinos)
CDMCDM
HDMHDM
Cosmological limit: Cosmological limit: 1010-5 -5 eVeV mma a 1 eV1 eV
AxionsAxions from astrophysical sourcesfrom astrophysical sources
Low mass, weakly interacting particles Low mass, weakly interacting particles (neutrinos, gravitons, axions etc.) are (neutrinos, gravitons, axions etc.) are produced in hot stellar plasma and can produced in hot stellar plasma and can transport energy out of stars.transport energy out of stars.
The couplings of these particles with The couplings of these particles with ordinary matter and radiation are ordinary matter and radiation are bounded by the constraint that stellar bounded by the constraint that stellar lifetimes do not conflict with the lifetimes do not conflict with the observations.observations.
For axion-photon coupling, the most For axion-photon coupling, the most restrictive astrophysical limit derives restrictive astrophysical limit derives from globular cluster (GC) stars, by from globular cluster (GC) stars, by comparing the number of horizontal comparing the number of horizontal branch (HB) stars with the number of branch (HB) stars with the number of red giants. red giants.
CASTCAST:: Physics PhysicsPrinciple of the Axion helioscope Principle of the Axion helioscope Sikivie, Phys. Rev. Lett 51 (1983)Sikivie, Phys. Rev. Lett 51 (1983)
a thermal photon converts into an a thermal photon converts into an axion in the Coulomb fieldsaxion in the Coulomb fields of of nuclei and electrons in the solar nuclei and electrons in the solar plasma (plasma (Primakoff processPrimakoff process))
Sun:Sun: an axion converts into a an axion converts into a photon in a strong photon in a strong transverse magnetic fieldtransverse magnetic field
Earth:Earth:
aγaa
aγ dEtAP
dE
dΦN
-expected number of photons-expected number of photons
A = detector effective areaA = detector effective area
axion-photon momentum transfer axion-photon momentum transfer
effective photon mass (T=1.8 K)effective photon mass (T=1.8 K)
coherencecoherence condition condition for for aa → → conversion conversion
ga=10-10 GeV-1
In case of vacuum, coherence is lost for In case of vacuum, coherence is lost for mma a > 0.02 > 0.02
eV. It can be restored with the presence of a buffer eV. It can be restored with the presence of a buffer gas, but only for a narrow mass range.gas, but only for a narrow mass range.
Novel techniqueNovel technique (developed by CAST) for (developed by CAST) for observing axion solar signature: Off-resonance observing axion solar signature: Off-resonance spectraspectra
CAST and ADMX enter the CAST and ADMX enter the theoretically favoured QCD axion theoretically favoured QCD axion region (“Axion models”)region (“Axion models”)
The rest of the parameter space The rest of the parameter space belongs to axion-like particles belongs to axion-like particles (ALPs): particles with two-photon (ALPs): particles with two-photon couplingcoupling
PVLAS result in 2006: PVLAS result in 2006: a “signal” with possible particle a “signal” with possible particle
interpretation in the region excluded interpretation in the region excluded by stellar loss arguments and CAST by stellar loss arguments and CAST limit limit numerous theoretical numerous theoretical papers and experimental projects!papers and experimental projects!
after upgrades, the signal was lostafter upgrades, the signal was lost
Horizontal and vertical encoders determine the magnet orientationHorizontal and vertical encoders determine the magnet orientation
Correlation between encoder value-magnet orientation has been established for a Correlation between encoder value-magnet orientation has been established for a number of points (GRID)number of points (GRID)
Periodical measurements show that CAST points to the Sun within the required Periodical measurements show that CAST points to the Sun within the required precisionprecision
Comparison of March 2010 and Comparison of March 2010 and September 2002 GRID. The September 2002 GRID. The required precision of 1 arcmin is required precision of 1 arcmin is indicated by the green circle, indicated by the green circle, while the red one represents the while the red one represents the 10% of the Sun projected at 10 m. 10% of the Sun projected at 10 m.
CASTCAST:: Detectors after 2007 Detectors after 2007 33He phaseHe phase
Micromesh5µm copper
Kapton 50 µm
Readout pads
Sunrise sideSunrise side: CCD+Telescope & shielded : CCD+Telescope & shielded Microbulk Microbulk MM MM
Sunset sideSunset side: 2 shielded : 2 shielded Microbulk Microbulk MM MM
MicrobulkMicrobulk: : new technique, high radio-purity materials, very low backgroundnew technique, high radio-purity materials, very low background
MM 2 counts/h (2-10 keV)
CCD 0.18 count/h (1-7 keV)
sunrisesunrise
sunsetsunset
In 2010, a In 2010, a “5“5thth line” line” was added: was added: a 3.5 a 3.5 μμm aluminized Mylar foil m aluminized Mylar foil (transparent to X-rays) is placed (transparent to X-rays) is placed on the sunrise Micromegas line on the sunrise Micromegas line to deflect to deflect visible photonsvisible photons on an on an angle of 90angle of 90oo, towards the , towards the PMTPMT
CASTCAST:: Gas system for the Gas system for the 33He phase He phase
33He gas systemHe gas system Accuracy in measuring the quantity of gas Accuracy in measuring the quantity of gas
introduced in the cold boreintroduced in the cold bore (100ppm) (100ppm) Flexible operation modes (stepping and Flexible operation modes (stepping and
ramping)ramping) Hermetic system to avoid loss of Hermetic system to avoid loss of 33HeHe Absence of thermo-acoustic oscillationsAbsence of thermo-acoustic oscillations Protection of cold thin X-ray windows Protection of cold thin X-ray windows
during a quenchduring a quench
33He phaseHe phase
X-ray windowsX-ray windows High X-ray transmission (polypropylene 15 High X-ray transmission (polypropylene 15 m)m) Robust (strongback mesh)Robust (strongback mesh) Minimum He leakageMinimum He leakage Mechanical endurance toMechanical endurance to sudden rise of pressuresudden rise of pressure
CASTCAST:: Simulations for theSimulations for the 33He phase He phase
Simulations & new instrumentation Simulations & new instrumentation have been essential in understanding have been essential in understanding 33He systemHe system
in CAST temperature and density in CAST temperature and density conditions, conditions, 33He He is not an ideal gasis not an ideal gas (Van (Van der Waals forces)der Waals forces)
convergence between simulation convergence between simulation results & experimental data results & experimental data
Knowledge of gas density / setting Knowledge of gas density / setting reproducibility possiblereproducibility possible
Gas density stable along magnet boreGas density stable along magnet bore
Coherence length slowly Coherence length slowly decreases with increasing densitydecreases with increasing density
CASTCAST:: Phase II data taking Phase II data taking
Sunrise MicromegasSunrise Micromegas
Tracking (red) and Tracking (red) and background (blue) background (blue) spectra in 2010spectra in 2010
2010 counts in 2010 counts in different pressure different pressure settings: tracking (red), settings: tracking (red), background (blue)background (blue)
CASTCAST:: Phase II data taking Phase II data taking
2010 counts in different 2010 counts in different pressure settings: pressure settings: background (red), background (red), tracking (blue)tracking (blue)
Search for Search for monoenergetic 14.4 keV axionsmonoenergetic 14.4 keV axions
strong emission of 14.4 keV axions is expected from de-excitation of strong emission of 14.4 keV axions is expected from de-excitation of thermally excited thermally excited 5757Fe nuclei in the SunFe nuclei in the Sun
TPC data from phase I were used TPC data from phase I were used
Due to the coherence condition, CAST could be sensitive to the existence of Due to the coherence condition, CAST could be sensitive to the existence of large extra dimensions large extra dimensions particular Kaluza-Klein states particular Kaluza-Klein states
Low energy solar axions Low energy solar axions
Sun could be a Sun could be a strong strong source of low energy axions (in the visible – UV) source of low energy axions (in the visible – UV) created below sunspots. created below sunspots.
CAST CAST isis complementary (and competitive complementary (and competitive)) with laboratory–based with laboratory–based experimentsexperiments
ConclusionsConclusions CAST provides the best experimental CAST provides the best experimental
limit on axion-photon coupling limit on axion-photon coupling constant over a broad range of axion constant over a broad range of axion masses.masses.
CAST Collaboration has gained a lot CAST Collaboration has gained a lot of experience in axion helioscope of experience in axion helioscope searches. searches. R&D on superconducting magnets R&D on superconducting magnets can lead to much more sensitive can lead to much more sensitive helioscopes.helioscopes.
Future helioscope experiments and Future helioscope experiments and Microwave cavity searches (ADMX) Microwave cavity searches (ADMX) could cover a big part of QCD axion could cover a big part of QCD axion model region until 2020. model region until 2020.