101 st Meeting of the CERN / SPSC CAST Physics Proposal to SPSC K. Zioutas on behalf of CAST and in collaboration with D. Anastassopoulos, O. Baker, M. Betz, P. Brax, F. Caspers, J. Jaeckel, A.Lindner, Y. Semertzidis, N. Spiliopoulos, S. Troitsky, A. Vradis. CERN 5 th April

CAST results dominate the parameter phase space CAST data taking since 2003: Phase I Vacuum in the magnet bores: m a < 2.3  eV ( 2003 – 2004) Phase II 4 He gas: m a < 0.39 eV (2005 – 2006) 3 He gas: m a < 1.16 eV (2008 – 2011) ? WMAP: m a <1.05eV  m a <0.9eV  next run ? 2

Physics cases after 3 He completed - 4 He Axions (Paraphotons) - Vacuum Axions Chameleons Paraphotons - Relic axions? Detector requirements - Low threshold - Low background 3

Future: repeat 4 He runs with current CAST 4 months 8 months 12 months 16 months 6 months 12 months 18 months existing MM  significant improvement in background wrt  crossing axion model  could start in autumn 2011 (with present detectors)  no competition in sight ULB MM (10 -7 cts/keV/cm 2 /s ) existing MM  mbar: 6, 12 & 18 calendar months (1.5, 3 and 4.5 trackings/step) ULB MM (10 -7 cts/keV/cm 2 /s) 4

12 calendar months data taking with existing MM 12calendars months data taking ULB MM (~10 -7 cts /keV/cm 2 /s) Future: repeat vacuum runs  parallel with paraphoton & chameleon runs Axions or WISPs with g aγγ  – GeV -1 are interesting in the context of explanation of some astrophysical phenomena (e.g. propagation of HE gamma rays from distant sources, WD cooling, …). 5

Solar paraphotons Hidden Sector particles  Theoretically motivated - kinetic mixing: γ ↔ γ’ oscillations  NO magnetic field!  NO cold bores needed  Vacuum path length relevant for oscillations -> upstream in front of the detector  a good sensitivity requires: 3 ULB MMs & FS pnCCD  also for chameleons! 6

Solar paraphotons – CAST already provided strong limit 7

constraints on the parameters: 2: TeV strings 1: WMAP 3: dark matter, hidden Higgs 1: LSW, solar eV 2: solar keV only 3: accelerators Solar paraphotons 8

Interpretation of CAST TPC(2004) null result. J. Redondo calculation “CAST-keV” CAST estimate of 2004 (idealized XRT/CCD) Solar paraphotons: present limits Crosscheck! 9

no resonance: central part brighter resonance: thin slice brighter Converted from thermal photons inside the Sun due to kinetic mixing Region of interest for CAST < m < 10 eV Resonant production in a shell inside sun for m > eV Clear signature …….. ring images r/R o > 0.7 CAST XRT/CCD - our solar imaging system– investigated the potential Solar paraphotons 10

Idealized XRT/CCD (not corrected for cold bore obscurations and low ε for large off axis angles in XRT) 1.0 – 7 keV – 7 keV keV 1.0 – 7 keV – 7 keV keV Lowering energy threshold – increases the sensitivity  more flux New Vacuum Run (2x10 6 sec) New FS-CCD (nominal threshold 100 eV) Paraphoton detection sensitivity with XRT/CCD Low energy threshold: MM + CCD! 11

FOV Problem: XRT r/R o > 0.6 suppressed due to limited LE? Off-pointing solar tracking FOV Normal solar tracking Vignetting due to cold bore and large off-axis angles in XRT (1.5 keV)  CCD size  (1cm x 3cm) 12  Under investigation

More realistic estimate of XRT/CCD ( assume only 60% of sun visible via XRT) 1.0 – 7 keV 2years – 7 keV keV 1.0 – 7 keV 2years – 7 keV keV Paraphoton detection sensitivity with XRT/CCD New Vacuum Run (2x10 6 sec): normal tracking, XRT FOV strongly limits sensitivity.  Off-pointing Could be used to look for structure with good ε over reduced region Ideal XRT Real XRT? 1.5keV response 13

Assumptions: Hz ( 3x10 -7 cts/s/keV/cm 2 ) ULB ! Energy range: eV LET ! Exposure = sec = 0.15 Vacuum length: 14m (black) Obscuration by cold bore not corrected Full simulation required 1m (purple) Obscuration not corrected but small  Higher masses independent of large oscillation path length – can use local vacuum lines  CAST keV sensitivity improved by times  TeV String region entered for m> 1 eV (region inaccessible to future eV experiments) MM detectors – no solar imaging but larger FOV Paraphoton detection sensitivity with 3 MMs (ULB & LET) 14

Paraphotons - Conclusions Region of interest for CAST’ contribution: < m < 10 eV Potential 3-10x increase in existing CAST keV limit  MMs Localization of a source of paraphotons could be possible from XRT/CCD with off- pointing TeV String region entered for m> 1 eV (region inaccessible to future eV exp’s) Parallel run with axion vacuum run (even also with 4 He run) Detector requirements:  simulation for all detectors’ FOV  XRT performance! – MM LET ULB Operational energy range 200eV – 7 keV (paraphotons/axions/chameleons) – XRT/CCD FS-CCD with ~ 100 eV threshold  feasible !!  Theoretical estimates in progress 15

Solar Chameleons Chameleons are DE candidates to explain the acceleration of the Universe Chameleon particles can be created by the Primakoff effect in a strong magnetic field. This can happen in the Sun. The chameleons created inside the sun eventually reach earth where they are energetic enough to penetrate the CAST experiment. Like axions, they can then be back-converted to X-ray photons. In vacuum, CAST observations lead to stronger constraints on the chameleon coupling to photons than previous exp’s. When gas is present in the CAST pipe, the analogue spectrum of regenerated photons shows characteristic oscillations: ID  axion helioscope = chameleon helioscope, LE!! 16

Solar Chameleons - CAST The analogue spectrum [/hour/keV] of regenerated photons as predicted to be seen by CAST: matter coupling = 10 6, B=30T in a shell of width 0.1R solar around the tachocline (~0.7R solar ). The mass of the chameleon in eV in the CAST pipe with vacuum is: m ch = 40 μeV [keV] vacuum 0.1 mbar [keV] 1 mbar [keV]  Low energy threshold: MM + CCD! + + vacuum ~ Vacuum: ~ Axions  ~ In CAST: CH  γ 17

Solar chameleons: simulated exclusion plots Assumption: B=30T in a shell of 0.1R solar around ~0.7R solar. The analog spectrum has been cut below a mass of ~55eV due to Pb in front of the CAST pipes.  log m CH [eV] 1mbar 10mbar 0.1mbar 1mbar10mbar ? ! Note: mass = derived quantity! 18

Semitransparent mirror set-up on CAST Vacuum manipulator for alignment light-source The BaRBE detector is coupled to the CAST magnet bore through a 40 m long, 200 µm core, multimode optic al fiber (not shown in the images). The fiber looks at the cold bore through a coupling telescope and a semitransparent mirror reflecting only optical photons The fiber output is split in two ports by means of an optical switch actuated by a TTL signal. Each port can be instrumented with a photon counter In the present configuration one port is coupled to a cooled Photo Multiplier Tube and the other is blocked, allowing on-line monitoring of the instantaneous background In future set-ups the second port will also be coupled to a detector, presumably a TES-based sensor, thus doubling the “ live ” tracking time (Future) search in the visible: a, γ ’, CH  BaRBE 19

Towards a new relic axion antenna? Dielectric waveguide inside the CAST magnet may perform as a new kind of “macroscopic fiber”, being a sensitive detector for relic axions:  ~ meV rest mass range (experimentally inaccessible) 20

The 2 parts of the detector: Axion antenna – Axion  Microwave photon conversion by the Primakoff effect in one bore of the CAST magnet – Dielectric waveguide collects and concentrates converted microwave photons  mono mode operation Radiometer – The antenna outputs mostly thermal background noise (T=2K) + a faint additional signal from converted Axions. – Radiometer = device to accurately measure small differences in noise power – Do we see a difference in noise power with the magnetic field switched on and off? 21

The dielectric waveguide structure Large „active volume“ Low loss transmission at 30 GHz Essentially an optical monomode fiber for microwaves Operation in travelling wave or standing wave (resonant) mode possibleStatic magn. field Metallic waveguide (to Radiometer) 3.6 mm x 7.1 mm Core Teflon ε R = mm x 10 mm Cladding Styrofoam ε R = mm x 30 mm To the radiometer 22

Field distribution in the dielectric waveguide structure f = 30 GHz E/M wave Shown is the field component in X – direction, parallel to the static magnetic field of CAST magnet  coupling to axions Electric field distribution inside this waveguide is similar to a gaussian beam in free space Velocity of propagation ~80% speed of light This structure can be operated at choice in standing wave or travelling wave modeStatic magn. field 23

The radiometer Measures the output signal of the “relic axion antenna” (thermal noise like) Wide detection bandwidth = significant amount of thermal noise. Incoming axion flux reveals itself in a slight enhancement of the noise floor. Very sensitive radiometers in this frequency range already exist in various satellites, which are used to observe the CMB radiation Pictures show a Radiometer from the PLANCK satellite. Center frequency = 30 GHz, Bandwidth = 8 GHz, Detector temperature = 20 K, Detector sensitivity = ± 20 μK 24

Conclusion A dielectric waveguide inside the CAST magnet provides a large interaction volume for axion-to-photon conversion, with low transmission loss > 30 GHz dielectric waveguides are, in general, better suited for this kind of experiment (up to the optical range) compared to metallic wave-guiding structures due to much lower losses & large cross section Start implementation of this novel detection scheme for relic axion detection: we propose to use a radiometer that operates at ~30 GHz. This range can be extended in future updates by additional higher frequency instrumentation Very sensitive radiometers can be used in this frequency range, which already operate in space missions, mapping the CMB radiation The wide bandwidth accepts a significant contribution from the thermal noise even if the structure is at 2 K. The converted relic axion flux would reveal itself as a slight enhancement of this noise level Noise of possible interference with environmental devices can be excluded or confirmed using suitable test signals Directionality characteristic: depending on the direction of incidence of the axions and their velocity, this “antenna” will have a specific directional diagram: ON-axis axions cancellation might occur, but OFF-axis axions will show constructive interference Feasibility study of the proposed concept is in progress 25

Tests: e.g., with ALPS DESY 26

Detectors: ULB and LE: - CCD - MM - TES Note: this is a quite rich / wide proposal for the physics potential of CAST for the next years: solar/relic axions (DM) solar paraphotons (HS) solar chameleons (DE) To give a flavour of the ongoing work, we also present the detectors needed! 27

 X-rays focusing opticsCAST’s X-ray telescope (XRT)  unique in axion helioscopes  signal-to-noise + ID 1.7 meters Nested paraboloids Nested Hyperboloids Focal plane 28

Frame store pnCCD Prototype  E=100 eV [eV] 200 Events [a.u] N. Meidinger, private communication (2011) 29

Detectors: ULB and LE: - CCD - MM - TES 30

Background levels of Micromegas detectors in CAST over the last years. Nominal values during data taking periods Unshielded Micromegas (classic technology) Shielded Micromegas (bulk and microbulk technology) Special shielding conditions in Canfranc Underground Lab 31

Canfranc Tests: Summary (M10 microbulk detector) 1 week with 109 Cd source Hz trigger rate First approach to final background limited only by intrinsic radioactivity (from microbulk, chamber materials, inner shielding): < 2·10 -7 counts keV -1 cm -2 s -1 [2-7 keV] (~1 count/day) This result proves that background levels >20 times lower that current CAST MM nominal background are possible via shielding improvement. 0.2 Hz trigger rate 32

Cover the stainless steel  tube in front of MM with Cu Partial front shielding Fuller front shielding Preliminary bkg: (2.75  0.5)x10 -7 cts/sec/cm keV ULB MM s: ongoing measurements 33

Design for a new detector Main features Improved shielding Radiopurity of materials Upgraded electronics: include time information for each strip  detector becomes TPC Present design Design being finalised with input from simulation, Canfranc tests and measurements at CAST. Radon is avoided with a leak- tight vessel of lead, which also works as shielding. Stainless steel and plexiglass have been replaced by copper and peek. A new drift cage guarantees an uniform drift field. 34

Operating in the sub-keV range Low threshold Argon is used in CAST Micromegas because of good absorption efficiency in the energy range 1-7 keV Neon gives higher gain (> factor 10)  Single electron detection!!! Good absorption up to 3 keV Mixture of Ar-Ne can be used to cover all range keV Transparent Windows Spectrum taken with a UV lamp 5eV Ne absorption efficiency Nanotube Porous aluminum membrane  fraction of incident photons can be transmitted either directly or “channeled” through the pores Small gas diffusion Porosity 12-50%, hole  nm, thickness ~50 μm 1) CCD: windowless 2) MM: transparent windows 35

Detectors: ULB and LE: - CCD - MM - TES 36

Transition Edge Sensor (TES) working principle Incident energy heats an absorber (the choice of absorber material sets the spectral range of the sensor) Thermometer: A thin film (e.g., Ir or Ti) at the transition temperature between normally and super-conducting measures the temperature change of the absorber The thin film (the actual TES) is biased by a voltage: a change in its resistance is sensed as a change in current with amplitude proportional to the energy deposited in the absorber At the end of an event the absorber slowly thermalizes towards an heat-sink The background noise is virtually zero since at the operating temperature, mK, there are no “internal” heat sources TES working principle schematic View of two sample sensors: the small (50 µm)x(50 µm) square is the actual TES, and the larger two rectangles are Al contact pads. Output pulse sample from D. Bagliani et al,  J Low Temp Phys. 151 (2008)

TES-based photon counters Transition Edge Sensor (TES)-based photon counters hold the promise of becoming the detectors of choice for WISP searches Main advantages -VERY LOW background (at least < 1 mHz measured over short acquisition times, potentially “zero” over long exposure times) -single-photon counting capability even at low energies (1 eV or less) -spectroscopic capability Main drawbacks -relatively small active area (typically 100x100 µm 2 or less for a single sensors) -T ~ 100 mK However -Work in progress on TES arrays with active surfaces up to 1 cm 2 1 eV to 1 keV, depending on absorber material 38

In the coming months, after feedback from SPSC: More detailed running proposal can be submitted with - R&D milestones for ULB & LET detectors - Theoretical calculations ( γ ’, CH, relics) - Simulation (XRT/MM - FOV, sensitivity optimization,…) - Approximate time schedule towards fully commissioned detectors on CAST ready to take data for axions, paraphotons and chameleons, while remaining competitive! This proposal is also: - suggestive for CAST data re-evaluation with a new code, like XRT spot size, energy bin, etc.: search for novel signals! - motivating also new collaborators from CERN, DESY, Saclay, INP-Moscow, UoPatras, Yale: promising fruitful collaboration work! Conclusion - Summary 39