Review and prospects of the Review and prospects of the CAST experiment CAST experiment Konstantinos Kousouris
Outline Outline � Axion physics � Strong CP problem � Peccei-Quinn solution � Axion properties � The CAST experiment � Solar axions � Concept & Design � Detectors � Results from Phase I � Prospects of Phase II HEP2006, Ioannina 2 Konstantinos Kousouris
The Strong CP problem The Strong CP problem Extra term in the QCD Lagrangian: CP violating, total derivative, not affecting the perturbative behaviour of the theory. � � � � θ 1 2 θ = θ + g Arg(det(M )) � = ε αβ � G G = μν ⋅ q L s G G μν μναβ 2 μν θ π 2 32 � � � Non trivial QCD vacuum Electroweak sector μν μ ⋅ = ∂ G G K μν μ � � � � ⎧ ⎫ g ( ) α β γ β γ = ε ⋅ ∂ + × Neutron electric dipole moment: K 2 A A s A A ⎨ ⎬ μ μναβ ⎩ 3 ⎭ − ⎫ theory ≈ θ× 15 ⋅ d 10 e cm − ⇒ θ n 10 ∼ 10 ⎬ − exp < × 25 ⋅ d 0.63 10 e cm ⎭ n θ Why do the contributions to cancel so perfectly?? HEP2006, Ioannina 3 Konstantinos Kousouris
The Peccei-Quinn mechanism PQ symmetry: global, axial, beyond the standard model. PQ symmetry: global, axial, beyond the standard model. Axion Axion Spontaneously broken at Spontaneously broken at Goldsone boson, pseudoscalar, neutral, Goldsone boson, pseudoscalar, neutral, some scale f a some scale f a with gluon interaction through the with gluon interaction through the triangle anomaly triangle anomaly The axionic field develops a non zero vacuum The axionic field develops a non zero vacuum �� �� 2 expectation value which eliminates the CP g expectation value which eliminates the CP μν ( ) � = ⋅ L C s a x G G μν violating term. violating term. a π 2 32 f a Model dependent constant HEP2006, Ioannina 4 Konstantinos Kousouris
Axion properties Axion mass Axion lifetime Electromagnetic interaction 7 23 1 10 GeV 10 ( ) � = μν ≈ → L g aF F m 0.6eV τ α γγ ∼ sec αγγ μν a a ( ) 5 4 f ⎡ ⎤ m eV ⎣ ⎦ a a Original axion: f a = f ew (ruled out) Invisible axion: f a >> f ew , Λ QCD Invisible = ∑ DFSZ model ( the PQ charge is carried by 2 e 2 C Q Q αγγ = g C 2 em PQ ordinary quarks and leptons ) π 2 f fermions a KSVZ model ( Hadronic axion: the PQ charge is carried by an exotic quark ) HEP2006, Ioannina 5 Konstantinos Kousouris
Solar axions Primakoff effect � � 2 × σ 2 2 2 p p d g Z e α γ α→γ αγγ = � � Ω π 4 2 d 32 − p p α γ = • Hadronic axions (KSVZ) E 4.2 keV α Photon – axion conversion in 2 ⎛ ⎞ g • Primakoff effect αγγ − − Φ = × 11 2 1 3.67 10 cm s ⎜ ⎟ the Coulomb field of a nucleus. α − − 10 1 10 GeV ⎝ ⎠ • Charge screening effects • Standard Solar Model HEP2006, Ioannina 6 Konstantinos Kousouris
Axion parametric space Sources Sources • Helioscopes . • Laser (rotation of elipticity). • Dark Matter search . • Astrophysics (evolution of the Sun and HB stars). • Cosmology (axionic relic density should not overclose the universe). HEP2006, Ioannina 7 Konstantinos Kousouris
The CAST principle Inverse Primakoff effect Axion - Photon conversion in a transverse magnetic field 2 2 B g ( ) αγγ ⎡ −Γ −Γ ⎤ = + − L L/ 2 P 1 e 2e cos qL ⎣ ⎦ α→γ + Γ 2 2 4q Momentum transfer 2 − 2 m m α γ = q Ε 2 HEP2006, Ioannina 8 Konstantinos Kousouris
The CAST experiment • Decommissioned LHC, test dipole magnet. Superconducting, I = 13kA, T = 1.8K. B = 9T, L=9.26m. • ±8 o vertical, 80 o horizontal movement. • 1.5h Sun tracking during both sunrise and sunset. HEP2006, Ioannina 9 Konstantinos Kousouris
The detectors TPC TPC • Time Projection Chamber: conventional gas chamber with 48 anode wires and 96 cathode wires, 3mm apart. • Shielded. Constructed by Zaragoza Univ. • Covers both magnet bores and tracks the sunset axions. Telescope and CCD CCD • Wolter I optics, prototype for the ABRIXAS space MICROMEGAS MICROMEGAS mission. 27 nested gold coated nickel shells. • Novel micropattern parallel plate gas Axionic image of the Sun. detector with spatial sensitivity. • Charged Coupled Device (solid state photon • Constructed by Saclay and Demokritos. detector from Si). Pixel size: 150x150 μ m 2 . • Covers one magnet bore and tracks the • Spot: 3mm diameter, improving significantly the sunrise axions. CAST sensitivity. • Covers one magnet bore and tracks sunrise axions. HEP2006, Ioannina 10 Konstantinos Kousouris
PHASE I (2003 run) Magnet bores in vacuum vacuum : axion-photon oscillation coherent for axion masses m m a <0.02 eV a <0.02 eV Analysis completed ( Phys. Rev. Lett. 94 (2005) 121301 Phys. Rev. Lett. 94 (2005) 121301 ) NO axion signal NO axion signal Combined re sult 95% C.L. (Bayes) upper limit − − αγγ < × 10 1 g 1.16 10 Ge V HEP2006, Ioannina 11 Konstantinos Kousouris
PHASE I (2004 run) All detectors significantly improved CCD Combined result 95% C.L. (Bayes) upper limit αγγ < × − − 10 1 g 0.9 10 GeV preliminary HEP2006, Ioannina 12 Konstantinos Kousouris
PHASE II (2005-2007) Magnet bores filled with buffer buffer gas : effective photon mass gas ( ) πα P mbar 4 N = = m em e 0.02 eV ( ) γ m T K e • 4 He: 74 pressure steps, 0 < P < 6mbar, m a < 0.26eV . • 3 He: 590 pressure steps, 6 < P < 60mbar, m a < 0.8eV . HEP2006, Ioannina 13 Konstantinos Kousouris
PHASE II (challenges) Cold windows Cold windows • High transmisivity in the 1-7 keV region. • Minimizing He leak rate. • Withstand pressure differences during a “Quench”. • Robust under normal operating conditions at 1.8K. Gas system Gas system Additional optics device Additional optics device • Control of pressure steps. Extra X-ray focusing device installed • Restore of previous pressure settings. in a new Micromegas line. Increase • Recovery of gas in case of a “Quench”. of the overall CAST sesnitivity. • Safe storage of the gas. • Control of gas dynamics (thermoacoustic oscillations). HEP2006, Ioannina 14 Konstantinos Kousouris
Conclusions • The strong CP problem remains unsolved for 30 years and the PQ solution is still the most elegant and economic. Axions searches are worthwile!!! • The CAST experiment completed PHASE I with sensitivity to axion masses m a <0.02 eV and no signal was discovered. However, it improved the axion - photon coupling limit significantly and reached the Astrophysical limit. • The 2003 run analysis results are already published while the 2004 results will be published soon. • The CAST Phase II was approved by CERN and will last until fall of 2007 (Already started). • During Phase II the CAST magnet bores are filled with gas (He) to make the experiment sensitive to higher axion masses, enetering the theoretically most favoured region of the axion parametric space. • The technical challenges and demands of Phase II are being met succesfully and the experience gained from Phase I allow the collaboration to be optimistic about the outcome of the experiment. HEP2006, Ioannina 15 Konstantinos Kousouris
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