First Results from the CAST Experiment IKP/Technische Universität-Darmstadt CEA, Saclay
Outline The CAST experiment: Motivation Description The first results of CAST 2003 2004 What follows
The CERN Axion Solar Telescope Collaboration
CAST: Motivation Axion: a light pseudoscalar resulting from the Peccei-Quinn mechanism to enforce strong CP conservation [Peccei-Quinn(1977),Wilczek (1978), Weinberg(1978)] Most interesting property: coupling to photons: PRIMAKOFF effect CAST principle of detection [ Sikivie PRL 51 (83) ]
CAST: Motivation van Bibber et al., PRD 39 (89) Expected number of γ in detector: <E a >= 4.2 kev For g aγγ 1 GeV 2 P a γ the conversion probability S the magnet bore area t the exposure time Differential axion flux at the Earth: dφa = de a 4.02 g aγγ GeV 1 2 3 ( E /kev) 2 1 1 e a E /1.08keV a 1 cm s kev
CAST: Motivation In vacuum Conversion probability In a buffer gas Conversion probability where momentum transfer a γ (detected) where m γ the refractive photon mass P a γ is max for P a γ is max for For a m long field, max sensitivity for m a < 0.02 ev Different gas pressures allow max sensitivity for higher masses
CAST: Motivation The CAST agenda includes both configurations: N γ ( - GeV -1 /g aγ ) 4 3 2 vacuum t=1y (33 days) Phase I: vacuum 1-1 Phase II: using 4 He and 3 He as buffer gases -2-3 -4 6.08 mbar -5-4 -3-2 -1 1 m a [ev]
CAST is here: LEP Point 8 (former DELPHI point) Building SR8
CAST: Description Decommissioned LHC Prototype magnet Operated at T=1.8 K L= 9.26 m B= 9 T Much higher sensitivity than any previous experiment 4 bores (14.5 cm 2 )to look for X rays 3 detectors assigned to the job X ray Focusing System to increase signal/noise ratio. Vertical :±8 Horizontal :±40 Exposure time: 2 x 1.5 h per day ~50 days per year
CAST: The detectors TPC MICROMEGAS CCD with X-RayTelescope
2003 Data Taking Approximately 6 months of data taking Continuous upgrading of the detectors and the system Encountered several problems: 2003 Analysis Tracking Data: Data taken when magnet pointing at Sun Background Data: Data taken any other time Signal: Excess of X-rays in Tracking - Background Quenches mechanical structure
kev -1-1 cm -2 counts s 2003 Analysis Background Level: ~1 x -4 cts cm -2 s -1 kev -1 2 1.8 1.6 1.4 1.2 1 0.8 0.6 0.4 0.2 0 x -4 μm 0 1 2 3 4 5 6 7 8 9 Set A Energy[keV] --Tracking (magnet aligned to the sun) --Background (any other time) /sec/kev 2 Counts/cm 0.8 0.6 0.4 0.2 0-3 x CCD TPC x 0.2 0.4 0.6 0.8 1 Energy (kev) 1
2003 Analysis All spectra compatible with Zero No sign of axions But we can give a limit for the coupling aγγ TPC g aγγ (95% C.L.) < 1.55 - GeV -1 μm g aγγ (95% C.L.) < 1.50 - GeV -1 CCD g aγγ (95% C.L.) < 1.23 - GeV -1
2003 Result for CAST K.Z. et al., PRL 94 (2005) 121301 ) -1-7 g aγ (GeV -8 Lazarus et al. SOLAX, COSME DAMA -9 Tokyo helioscope For m a <0.02 ev - CAST 2003 globular cluster s -11 g aγγ (95% C.L.) < 1.16 - GeV -1 Axion models -12-5 -4-3 -2-1 1 m axion (ev)
2004 Data Taking MICROMEGAS Improved version of the detector with better strip quality less cross-talk. Automatic calibration. CCD with X-RayTelescope Additional shielding inside the vessel. Installed x-ray source for continuous checking of the telescope alignment. Differential pumping system to protect the windows. Addition of a passive shielding: PE, Cd, Pb and Cu. Continuous flux of N 2 to reduce radon. Conclusions: At least 2 times more data compared to 2003 (in 6 months) All detectors operated smoothly Data quality significantly improved compared to 2003 TPC
2004: The HE Calorimeter Installed in 2004 Search for energetic axions: the goal is to extend the sensitivity to axion-induced γ s from few kev to ~150 Mev
The Future CAST Phase II Approved for 2005-2007 Using a buffer gas to extend sensitivity to higher masses 2005-2006: with 4 He gas pressure increased from 0-6 mbar : m < 0.26 ev 2006-2007 with 3 He gas pressure increased from 6-60 mbar : m < 0.83 ev Implementing a second X-ray focusing device for mm will enhance detection capability New collaborators LLNL I II II
~14min later... CAST: An experiment looking for axions (coming from the Sun) using an LHC prototype magnet, with the help of X-ray detectors. FIRST RESULTS: CAST has given an upper limit on axion coupling to photons (at 95%C.L.) to g aγ <1.16x - GeV -1 for m a <0.02 ev CAST Future: Waiting for 2004 result and results from the HEC Phase II coming up to look in higher axion masses.
SCIENCE 308 15 APRIL 2005 NATURE VOL 434 14 APRIL 2005 www.nature.com www.nature.com/nature 839
And yet For more on axions Axion training @ CERN from 30 Nov to 2 Dec 2005.. http://cast.mppmu.mpg.de/cast/axion-training-2005/axion-training.php