The CAST Micromegas detectors for the detection of rare events Esther Ferrer Ribas 9th February 2015 ©Firat Yilmaz Esther Ferrer Ribas Instrumentation days on gaseous detectors, 12-13 October 2016, Clermont Ferrand

CAST: CERN Axion Solar Telescope Baseline search: solar axions Why we are looking for axions? Predicted by SM extensions, neutral, very light, low interacting cross-section. Most elegant solution to explain the apparent symetry between matter and anti-matter in the strong interactions (CP violation). Dark matter candidates Axions couple to photons in the presence of a magnetic field in all models.

Search strategies Relic Axions Solar Axions Axions in the laboratory Axions that are part of galactic dark matter halo: Axion Haloscopes (ADMX) Solar Axions Emitted by the solar core. Axion Helioscopes (CAST  IAXO) Crystals Axions in the laboratory “Light shinning through wall” experiments Vacuum birefringence experiments (see Carlo Rizzo’s presentation)

 0.3 evts/hour with ga= 10-10 GeV-1 and A = 14 cm2 CAST Physics Detection in CAST Conversion of axions into photons via the inverse Primakoff effect in a strong magnetic field Production in the Sun Conversion of thermal photons into axions via Primakoff effect in the solar core Expected number of photons:  0.3 evts/hour with ga= 10-10 GeV-1 and A = 14 cm2

Helioscopes Brookhaven (a few hours of data): Lazarus et al. PRL 69 (92) Tokyo Helioscope (SUMICO): 2.3 m long 4 T magnet No Liq. He B=4T, L=2.3m 268A persistent current 16 PIN photodiodes Altazimuth:Horiz. 360°, vert.±28° Inoue et al. Phys.Lett.B668:93-97,2008. Presently running: CERN Axion Solar Telescope (CAST)

Rotating platform to follow the sun Search for solar axions with an LHC dipole LHC dipôle : L = 9 m, B = 9 T Rotating platform to follow the sun 2 sunset detectors 2 Sunrise detectors Signal: excess of X-rays when pointing towards the sun Need for X-ray detectors: Excellent background discrimination (natural radioactivity and cosmic rays) Radiopure components+shielding+offline discrimination

Originalities of CAST Use of X-ray telescope  increase S/B noise sensitivity improved by a factor 150 by focusing a ø43 mm x-ray beam to ø3mm Low background techniques shieldings, low radioactive materials, simulation and modeling of backgrounds….

CAST results 2003 – 2004 CAST phase I 2006 CAST phase II - 4He Run CAST Coll., JCAP 0704(2007) 010. CAST Coll., PRL (2005) 94, 121301. CAST Coll., JCAP 0902 (2009) 008. CAST Coll, PRL (2011) 107 261302. CAST Coll., Phys. Rev. D92 (2015) no2, 021101 2003 – 2004 CAST phase I vacuum in the magnet bores 2006 CAST phase II - 4He Run axion masses explored up to 0.39 eV (160 P-steps) 2007 3He Gas system implementation 2008 - 2011 CAST phase II - 3He Run axion masses explored up to 1.17 eV bridging the dark matter limit 2012 Revisit 4He Run with improved detectors 2013-2015 Revisit vacuum phase with improved detectors New data in the pipeline. Analysis ongoing… The axion has not been observed limit on the coupling constant Best world-wide limit for a wide range of masses

CAST Micromegas detectors Drift: transparent X-ray window coupled to a vacuum pipe Use of mesh and strip signal Kapton 2D readout signal

Background History of CAST micromegas detectors Classical Unshielded Shielded Microbulk Shielding Upgrade/muon veto

CAST Micromegas detectors: 2003-2006 •Active area: 6x6 cm2 with 2D readout 384 strips pitch 350 µm •Gas: Ar + 5%iC2H4 at atmospheric pressure. •Conversion region: 3 cm (100 V/cm). •Amplification gap: 50 μm (104 V/cm). •X-ray window: 4 μm aluminized mylar •GASSIPLEX electronics Unshielded detector P. Abbon et al., New J.Phys.9:170,2007, physics/0702190. Materials: plexiglass, copper mesh, kapton readout plane

Shielding test April 2004 Background reduction ~3 Polyethèlene Copper Lead Background reduction ~3

Detectors after 2006: shielding + new Micromegas technology Sunrise Side: shielded Micromegas Sunset Side: 2 shielded Micromegas New Micromegas technology: Microbulk Shielding: copper+ lead+polyethylene

Microbulk technology Intrinsically radiopure (kapton and copper only) Read-out plane and mesh ALL IN ONE Micromesh 5µm copper Kapton 50 µm Read-out plane S. Andriamonje et al., JINST 5 (2010) P02001 Intrinsically radiopure (kapton and copper only) S. Cebrian et al., Astr . Part. 34 (2011) 354 Microbulk used in CAST but also in NTOF, PANDAX J. Galan et al., JINST 11 (2016) no.04, P04024

Detectors after 2006 : shielding + Microbulk technology Detector description Active area: 6x6 cm2 with 2D readout 240 strips pitch 550 µm Gas: Ar + 5%iC2H4 at 1.4 bar. Conversion region: 3 cm (100 V/cm). Amplification gap: 50 μm (104 V/cm). X-ray window: 4 μm aluminized mylar GASSIPLEX electronics Shielding 0.5 cm of Copper 2.5 cm archeological Lead Polyethylene bricks (variable thickness up to 10 cm) Enclosed in plexiglass box flushed with nitrogen S. Aune et al., JINST 9 (2014) 9 P01001.

Detectors after 2006 : results Background rejection Rejection of at least two orders of magnitude

Detectors after 2006 : results Stability sunrise Detector 3 years !!!!

Detectors after 2006 : measurements in the underground laboratory of Canfranc Different shielding configurations

Detectors after 2006 : measurements in the underground laboratory of Canfranc Testing different materials

Detectors after 2006 : modelling the background Simulated CAST area gamma flux Production of background counts by different interactions

Detectors after 2006 : adding an active shielding

Sunrise detector 2014-2015: new design, new electronics, X-ray optics Use the 10 years of experience to design an optimised detector Couple to an optimised X-ray optics for solar axion search Based on the X-ray optics for NUSTAR satellite F. Aznar et al., JCAP 12 (2015) 9 008.

Sunrise detector 2014-2015

Sunrise detector 2014-2015 X-ray telescope calibrated in Summer 2016 Data analysis on going

AFTER CAST: IAXO (International Axion Observatory) JCAP 06 (2011) 013 CAST is established as a reference result in experimental axion physics CAST PRL 2004 most cited experimental paper in axion physics No other technique can realistically improve CAST in such wide mass range. Future helioscope generation: improve the sensibility by 1 order of magnitude LOW BACKGROUND DETECTORS X RAYS OPTICS MAGNET

IAXO International Axion Observatory No technology challenge (built on CAST experience) New dedicated superconducting magnet Use of X-ray focalisation over ~m2 area Low background detectors (improve bck by 1-2 orders of magnitude) Goal: in terms of signal to background ratio 4-5 orders of magnitude more sensitive in than CAST, which means sensitivity to axion-photon couplings down to a few ×10−12 GeV−1 IAXO baseline detectors: Microbulk technology Key elements: Radiopure components + shielding + Offline discrimination E. Armengaud et al., "Conceptual Design of the International Axion Observatory", JINST 9 (2014) T05002.

IAXO Sensibility Exploration of very extended QCD axion region IAXO complements ADMX Exploration of very extended QCD axion region

IAXO Detectors Micromegas detectors are the base-line for IAXO but additional tecnologies, Ingrid Micromegas, TES, MMC, CCD will also show their potential in the coming years Improvements foreseen for Micromegas to achieve background levels of 10-7 – 10-8 c keV-1 cm-2 s-1 Optimised gas to reduce the fluorescences peaks Improved shielding Autotrigger electronics

CONCLUSIONS Succes of Micromegas detectors in CAST: Development of a new Micromegas technology « Microbulk » Intrinsically radiopure Stable High topological discrimination Low background techniques (shielding, underground laboratories, background simulations…) Collaborations: CERN MPGD/ U. Zaragoza/LLNL/IRFU Solar axion search goes on: IAXO IAXO can become a generic axion facility with discovery protential in the next decade Exciting work in front us: join us!

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Succes of Micromegas detectors in CAST 2002 2013 Succes of Micromegas detectors in CAST Development of a new Micromegas technology « Microbulk » (kapton and copper) very radiopure Collaborations: CERN MPGD U. Zaragoza Low background techniques (shielding, underground laboratories, background simulations…) Student network between Zaragoza-Irfu First experience with Micromegas for rare event detection: Now Micromegas detectors used in a wide variety of applications (dark-matter, double beta…)

Microbulk used in CAST but also in NTOF, PANDAX Microbulk Micromegas Read-out plane and mesh ALL IN ONE Micromesh 5µm copper Kapton 50 µm Read-out plane Intrinsically radiopure (kapton and copper only) S. Cebrian et al., Astr . Part. 34 (2011) 354 S. Andriamonje et al., JINST 5 (2010) P02001 Small gaps (< 50 µm) Optimised for high pressure D. Attié et al., JINST 9 (2014)C04013. 2D detectors ultra-thin: segmented mesh Rare event detection, Neutron profiles T. Geralis et al., PoS TIPP2014 (2014) 055 Microbulk used in CAST but also in NTOF, PANDAX J. Galan et al., JINST 11 (2016) no.04, P04024

Micromegas family Mesh Readout plane TWO mechanical entities STANDARD 1996 BULK 2003 INGRID 2005 MICROBULK 2006 Mesh Readout plane TWO mechanical entities INTEGRATED: ONE single entity Type of mesh Any type 30 µm Stainless steel 1 µm Aluminium 5 µm Copper Advantages Demontability Large Surface Robust Industrial manufacturing process (PCB) Excellent energy resolution Single electron efficiency Intrinsically Flexible Low mass Radiopure

Historical context MWPC TPC Micro Pattern Gaseous Detectors: MPGD Multi-Wire Proportional Chamber G. Charpak et al., 1968 TPC Time Projection Chamber D. R. Nygren et al., 1974 ANODE CATHODE 200 µm MSGC Micro-Strip Gas Chamber A. Oed, 1988 Micro Pattern Gaseous Detectors: MPGD GEM Gas Electron Multiplier F. Sauli, 1997 MICROMEGAS MICRO-MEsh GAseous Structure I. Giomataris et al., 1996 CLASSICAL 1996 BULK 2003 INGRID 2005 MICROBULK 2006 RESISTIVE ANODE 2005-2013

IAXO Collaboration ~80 authors

IAXO costs

IAXO timeline Construction ~ 2.5 years Integration + commissioning TDR: ~ 18 months

Mini Charged Particles The WISPs zoo Weakly Interacting Sub-eV Particles (WISPs) Hidden Photons (HPs) Mini Charged Particles Chameleons Axion Like particles (ALPs) Axions Stringy axion Arion Majoron gag and ma are two independent “phenomenological” parameters

Extending sensitivity to higher masses Axion to photon conversion probability: Vacuum: Γ=0, mγ=0 with Coherence condition: qL < π For CAST phase I conditions (vacuum), coherence is lost for ma > 0.02 eV With the presence of a buffer gas it can be restored for a narrow mass range: 1.0 dP e.g. for 50 mbar Δma ~ 10-3 eV 39

IAXO proto-collaboration Big effort to strengthen collaboration  large consortium involved in a number of funding applications, covering all TDR needs Zaragoza (Spain) CEA-Saclay (France) Mainz (Germany) Bonn (Germany) Heidelberg (Germany) INR-Moscow (Russia) LLNL Columbia MIT INAF-Milano (Italy) DTU (Denmark) RBI (Croatia) DESY (Germany) U. Hamburg (Germany) U.Valencia (Spain) U. Cartagena (Spapin) INFN-Frascati, (Italy) U. Barry S. Carolina + … CERN CEA/Saclay (France) New partners welcome… (*) Only shown groups for which formal activity is ongoing or under discussion/preparation. Potentiaal interest in more groups than shown IDM2016, Sheffield Igor G. Irastorza / Universidad de Zaragoza

2003: CCD+Xray telescope, TPC (2), MM 2006: CCD+Xray telecope, 3 MM, 2013: 3MM, Ingrid+Xray telescope 2014-2015: 2MM, MM+Xray telescope (designed for axion search) , Ingrid+Xray telescope