The MICROMEGAS detector in CAST Theopisti Dafni IKP/Technische Universität-Darmstadt, Large TPC Workshop December 2004, Paris

Introduction :Axions-CAST MICROMEGAS in CAST Outline: Introduction :Axions-CAST MICROMEGAS in CAST Description Results from 2003 data Improvements in 2004 Further steps Paris, 2004

The strong CP problem: Peccei-Quinn solution: Axions PRIMAKOFF effect The strong CP problem: Theory redicts violation of CP in the strong interactions, that the experiment contradicts Peccei-Quinn solution: New symmetry; spontaneously broken (t scale fα) introduces axion K. van Bibber et al.,1989 Axion: pseudoscalar, neutral, practically stable -conversion probability: Paris, 2004

Cern Axion Solar Telescope X-ray detector Transverse magnetic field (B) L TPC mM ±8° CCD+Telescope B = 9T L = 9,26m ±40° Paris, 2004

X-Ray Telescope (Focusing Device) + CCD X-Ray Detectors: Detectors X-Ray Telescope (Focusing Device) + CCD TPC MICROMEGAS Signal: X-rays while tracking (magnet pointing to the Sun) over background Paris, 2004

Micromegas In situ… …and on the table Paris, 2004

Micromegas The CAST Prototype Magnet 4µm polypropylene Pumping group (required leak rate < 10-5 mbar l sec-1) 4µm aluminized polypropylene + strongback Read-out: 1st: Mesh 2nd: Strips Paris, 2004

CAST Prototype: FIRST time the x-y read-out used Micromegas CAST Prototype: FIRST time the x-y read-out used ~70 mm ~310 mm Via of ~75 mm 192 charge collection strips for x 192 charge collection strips for y Paris, 2004

Micromegas : diff.pumping Zone C Tube P = 10-6 mbar Zone A Detector P= 1 bar (Ar) Zone B In-between chamber P = 10-2 mbar P1 P2 A B C Gate valve Micromegas : diff.pumping 4µm poly 4µm aluminized poly+ strongback micromesh Clean materials (low natural radioactivity) : mechanical pieces out of plexiglas Paris, 2004

Mean value of 5.9keV peak vs time Analysis 2003 data: Gas: 95%Ar+5%Isobutane Calibration 55Fe Mean value of 5.9keV peak vs time 5.9 keV ~ 16% (FWHM) Detector Stable 95Ar escape peak Paris, 2004

Conditions based on pulse shape and strips’ information: Analysis 2003 data: Conditions based on pulse shape and strips’ information: X-Y strips Multiplicity Correlation between strip charge and Pulse charge Pulse rise time information Fiducial Dead time :~ 4% Software efficiency: SetA 3keV: 94.5% 6keV: 92% SetB 3keV: 96% 6keV: 97% SetC 3keV: 86% 6keV: 85.5% Paris, 2004

GOOD (Calibration) pulse Analysis 2003 data: Bkg pulses Pulse info GOOD (Calibration) pulse Paris, 2004

Analysis 2003 data: In one look Efficiency * Time (h) Bkg Level ** (cts/s/cm2/keV) Tracking Level** Set A 53% 431.4 6.03x10-5 43.8 6.26x10-5 Set B 54% 121 8.22x10-5 11.5 8.14x10-5 Set C 48.5% 251 7.96x10-5 21.8 7.67x10-5 *: This is the efficiency over the axion spectrum (hardware, software), including the change in the hardware efficiency mentioned. **: Between 1-7 keV Paris, 2004

Analysis 2003 data: Superimposing… --Tracking (magnet aligned to the sun) --Background (any other time) Paris, 2004

Analysis 2003 data: Combined for the 3 sets gαγγ(95% CL):1.51x10-10 GeV Paris, 2004

ga (95% C.L.) < 1.1610-10 GeV-1 CAST RESULTS 2003 Combined upper limit for 2003 data for all 3 detectors Submitted to PRL hep-ex/0411033 Phase I: 1 year with vacuum in the magnet bores: m < 2.310-2 eV (during 2003 and 2004) Phase II 1 year with 4He gas pressure increased from 0 - 6 mbar :m < 0.26 eV 1 year with 3He gas pressure increased from 6 - 60 mbar : m < 0.83 eV Paris, 2004

2004 run: Improvements 2003 -- Very few dead strips (< 3 ) -- No cross talk between x-y strips -- New electronic cards, new decoding -- Completely new cabling Preliminary Efficiency @ 6 keV ~88 % @ 3 keV ~68 % 392 h 538.8 h Efficiency @ 6 keV ~93 % @ 3 keV ~89 % 2.2× 10-5 counts keV-1cm-2 s-1 5 × 10-5 counts keV-1cm-2 s-1 Paris, 2004

Use of X-ray focusing optics MICROMEGAS PHASE II : Poly? mM Shielding (factor ~ 4 in background) (in collaboration with Zaragoza) Improved detector efficiency. --By using heavier gas: Xenon (to be studied in Saclay) --Optimization of the gas (to be studied in Athens) --Not geometrical factor in the window transmission due to strongback Improved intrinsic background (“golden strips”) --Shield the copper surfaces directly in contact with the detector (strips) with a thin layer of gold. Use of X-ray focusing optics Paris, 2004

MICROMEGAS PHASE II : Optics Goal: Xrays focused on a diameter < 1 mm In collaboration with Livermore, NASA and Uni Chicago pump mM Tube VT3 gate Cold window Focusing Device Paris, 2004

MICROMEGAS on a telescope At the PANTER facility in Munich in 2002 Paris, 2004

MICROMEGAS on a telescope Tests in Munich 6.5 keV γ + Panter telescope Beam of photons of different energies available 0.6-8 keV X-ray detection threshold : 0.6 keV Energy resolution 18% @ 6 keV Background (after off-line analysis): 3 × 10-6 counts keV-1cm-2 s-1 for 47% efficiency Paris, 2004

CAST end of phase I last November Conclusions CAST end of phase I last November MICROMEGAS has successfully operated during 2003 and 2004 looking for axions 2003 result presented. 2004 data under analysis Work on progress to face CAST phase II. Improvements on detector: telescope, shielding… Paris, 2004

And yet… Paris, 2004

This is the end, my friend Paris, 2004

A focusing device for MICROMEGAS? pump mM Tube VT3 gate Cold window Optics Paris, 2004

X-ray conversion efficiency Dead time :~ 4% Software efficiency: SetA 3keV: 94.5% 6keV 92% SetB 3keV: 96% 6keV 97% SetC 3keV: 86% 6keV 85.5% Hardware efficiency: strongback transparency 95% Paris, 2004

Micromegas : Background Most of the present background comes from cosmics and X-ray fluorescence (mainly Cu) Paris, 2004