Francisco José Iguaz Gutiérrez On behalf of the CAST Collaboration IDM2010Montpellier 27th July 2010 Outline Theoretical motivation for axions The CAST experiment ID: 930524
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Slide1
The CAST experiment: status and perspectives
Francisco José Iguaz GutiérrezOn behalf of the CAST CollaborationIDM2010-Montpellier27th July 2010
Slide2Outline
Theoretical motivation for axionsThe CAST experiment
CAST resultsFuture
and outlook
Slide3Theoretical
motivation for axions: the strong CP problemCP-violation can explain in
the standard model the matter-antimatter-asymmetry
CP is violated in weak
interactions
but
not in strong ones: Neutron electric dipole moment not observed.A possible solution is the elimination of the CP-violating term in QCD Langrangian by the introduction of an additional symmetry U(1)
New
pseudo-scalar field: AXION First proposed by Peccei & Quinn (1977) Particle interpretation by Weinberg & Wilczek (1978)
Slide4Theoretical
motivation for axions:the axion propertiesNeutral
pseudoscalar Goldstone-Boson
Pratically stable for ma ≈ 1 eV
Very
low
mass
withVery low cross-sectionCoupling to photons withAxion is a solution to CP problem and a candidate to Dark Matter
Slide5Helioscope
principleAxions produced in the Sun’s
core could be
reconverted to x-rays
inside
an
intense
magnetic field. P. Sikivie Phys. Rev. Lett. 51 (1983) 1415The expected signal is an x-rays excess while
the magnet is
pointing to the Sun0.3 events/hour for ga ≈ 10-10 GeV-1 & A = 14 cm
2
Serpico
&
Raffelt
(
based
on
Solar
Model
)
JCAP04 (2007) 010
Slide6The CAST
experimentCAST uses a decommissioned prototype superconducting LHC dipole magnet to detect
solar axions
SUNSET
detectors
SUNRISE
detectors
LHC
dypole magnet: 9.3 m of length, 9 T of magnetic field Range of movement: 80º horizontally and ± 8º vertically Solar tracking possible during
sunrise and sunset
(2 x 1.5 h per day) X-ray detectors: Micromegas (MM) & Charge Coupled Device (CCD)
Slide7Present
detectorsSUNRISE side
Micromegas (2nd
generation) New technology
(
Microbulk
)
Low radioactivity materials Improved shieldingJ. Phys. Conf. Ser. 179 (2009) 012015JINST 5 (2010) P01009 & P02001X-ray telescope Prototype of ABRIXAS mission 27 gold-coated mirror shellsCCD
Excellent spatial &
energy resolution Simultaneous measurement of signal and backgroundNew J. Phys. 9 (2007) 169
Slide8Present
detectorsSUNSET side
Two
shielded
Micromegas
last generation Microbulk typeThe 5th line New line for visible photons connected to the sunrise MM line A 3.5 m aluminized Mylar foil (
transparent to x-
rays) deflects visible photons on an angle 90º towards the PMT/APDarXiv:0809.4581
Slide9CAST
sensitivity
Phase I
Phase II
0.02 eV
CAST Phase I: (vacuum operation)
completed
(2003 - 2004)
ma < 0.02 eV2) CAST Phase II: (buffer gas operation) 4He completed (2005 -2006)0.02 eV < ma < 0.39 eV3He run, commissioning in Nov 2007
3He run, data taking started in Mar 2008approved
until Dec 20100.39 eV < ma < 1.20 eV3) Low energy axions (2007 – 2010) in parallel with the main program~ few eV range and 5 eV – 1 keV range
Slide10Published
resultsFor ma < 0.02 eV:ga
γγ < 0
.88 × 10-10 GeV
-1
JCAP04(2007)010
PRL (2005) 94, 121301
For
ma < 0.39 eV:gaγγ < 2.2 × 10-10 GeV-1JCAP 0902:008,2009Other CAST results:High energy axions:Data taken with a -ray calorimeterJCAP 1003:032,201014.4 keV axions: TPC dataJCAP 0912:002,2009
Low Energy (visible) axionsData taken
with a PMT/APDarXiv:0809.4581CAST experimental limit dominates in most of the favoured parameter space
Slide11Extending
the sensitivity to higher axion masses…Axion to
photon conversion probability
Coherence
condition
: q L <
,
For CAST phase I (vacuum), coherence is lost for ma > 0.02 eVWith the presence of a buffer gas, the coherence can be restored
for a narrow
mass rangeNew discovery potencial for each density (pressure) setting!!!!
Slide12First
preliminary results of 3He phase
PRELIMINARY
J. Galan
,
PhD
Thesis
2010CCD detector not yet included1st term: Expected number of axions.2nd term: Contribution of each detected eventDuring the tracking, the gas pressure is changed. A new definition of the Likelihood function is necessary
Slide13Future
and outlook of CASTSee
T. Papaevangelou’s talk at New opportunities
in the Physics Landscape at
CERN Workshop (May 2009)
where
different
scenarios were presented
Slide14Future
of helioscopesMagnet possible upgrades
Strong dependence on B & L but small improvement margins for next decade
Effort on m
agnet bore’s aperture
Work with magnet expert’s to design a dedicated magnet for a
helioscope
The constraints are different from accelerator magnets, i.e homogeneity is not as important as in acceleratorsAn “ATLAS – like” configuration proposed by L.Walckiers is the most promisingBig aperture (~1 m) / multiple bores seem possibleBig magnetic field possible (new superconductive material)Lighter construction than a dipole
Slide15Future
of detectorsFirst design of the new MMdetector for CAST (J.P.
Mols)
Ultra-Low-Background periods
(> 1
week
each
) have been observed with 4 different detectors.Not yet fully understood but Simulations by Zaragoza’s group Background measurements in the Undeground
Laboratory of Canfranc
New optimized detector designNew x-rays optics feasible Cover big aperture High efficiency (50%)
Sunrise
MM line in Geant4
simulations
by
Zaragoza
Slide16Conclusions
During10 years, CAST exclusion limits are up to nowcompatible with best astrophysical limits
entering realistic
QCD axion model band over a wide mass range
The
hunt
for the
axion
continues. Everyday place for discovery! Thinking of the next generation of Helioscopes which could be complementary with dark matter axion seraches (ADMX) a big part of model region could
be explored
in the next decadeDedicated magnet developmentR&D on detectors and X-ray optics
Slide17Back-up
Slide18The CAST
collaboration
Slide19The CAST
experiment
Slide20Past CAST
detectorsSUNSET sideSUNRISE side
Unshielded
Micromegas
X-
ray
telescope
+ CCDShielded TPC looking at both magnet bores
Slide21Ultralow
background periods in Micromegas detectors
Typical
background of MM in CAST is 10-5
c keV
-1
cm
-2
s-1 Periods of 10-7 c keV-1 cm-2 s-1 have been observed. Related with the presence of Radon near the detector???
Slide22Analysis
of 3He data High precision filling and reproducibility is mandatory for each
pressure setting.
Gas homogeneity is guaranted
by
the
surrounding superfluid 4He along the magnet region. During the 3He Phase, the temperature of the window cannot be kept as much stable. It can vary during tracking and may
depend on
the buffer gas density. Installation of temperature sensors along the magnet & simulation efforts
Temperature
and
density
at
different
angles
Agreement
between
simulated
and
measured
pressure
Slide23Experimental
searches• Galactic axions Haloscopes (ADMX, Carrack) Telescopes
(Haystack)•
Laboratory axionsShining
-Light-
through
-
Walls
(OSQAR, LIPSS, ALPS)Polarization (PVLAS)• Solar axionsCrystals (SOLAX, COSME)Helioscopes (Tokyo, CAST)