The CAST experiment: status and perspectives - PowerPoint Presentation

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The CAST experiment: status and perspectives

Francisco José Iguaz GutiérrezOn behalf of the CAST CollaborationIDM2010-Montpellier27th July 2010

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Outline

Theoretical motivation for axionsThe CAST experiment

CAST resultsFuture

and outlook

Slide3

Theoretical

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)

Slide4

Theoretical

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

Slide5

Helioscope

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

Slide6

The 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)

Slide7

Present

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

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Present

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

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CAST

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

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Published

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

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Extending

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!!!!

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First

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

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Future

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

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Future

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

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Future

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

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Conclusions

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

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Back-up

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The CAST

collaboration

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The CAST

experiment

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Past CAST

detectorsSUNSET sideSUNRISE side

Unshielded

Micromegas

X-

ray

telescope

+ CCDShielded TPC looking at both magnet bores

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Ultralow

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???

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Analysis

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

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Experimental

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)