Download Search for solar axions with the CAST experiment

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
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CAST: CERN Axion Solar Telescope
CAST
Biljana Lakić
TAM2010, 04-08 Oct 2010, Budva
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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
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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
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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
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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 24  z  w
 E




1
.
92

0
.
08
 N 31  z  w  2 f  N



a 
TAM2010, 04-08 Oct 2010, Budva
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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
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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
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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
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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
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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
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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  
Paγ A t dEa
dEa
Biljana Lakić
A = detector effective area
t = measurement time
TAM2010, 04-08 Oct 2010, Budva
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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
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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
cosqL 
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
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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 = 3FWHM
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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 < 0.39 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
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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
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CAST: Setup
… one solar tracking (1.5 h) …
Biljana Lakić
TAM2010, 04-08 Oct 2010, Budva
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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
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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
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CAST: Tracking precision
… Sun, airplane, sunspot …
Biljana Lakić
TAM2010, 04-08 Oct 2010, Budva
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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
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
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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: 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 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