First Results from the CAST Experiment

Transcription

1 First Results from the CAST Experiment IKP/Technische Universität-Darmstadt CEA, Saclay

2 Outline The CAST experiment: Motivation Description The first results of CAST What follows

3 The CERN Axion Solar Telescope Collaboration

4 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) ]

5 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 ( E /kev) e a E /1.08keV a 1 cm s kev

6 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

7 CAST: Motivation The CAST agenda includes both configurations: N γ ( - GeV -1 /g aγ ) vacuum t=1y (33 days) Phase I: vacuum 1-1 Phase II: using 4 He and 3 He as buffer gases mbar m a [ev]

8 CAST is here: LEP Point 8 (former DELPHI point) Building SR8

9 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

10 CAST: The detectors TPC MICROMEGAS CCD with X-RayTelescope

11 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

12 kev -1-1 cm -2 counts s 2003 Analysis Background Level: ~1 x -4 cts cm -2 s -1 kev x -4 μm Set A Energy[keV] --Tracking (magnet aligned to the sun) --Background (any other time) /sec/kev 2 Counts/cm x CCD TPC x Energy (kev) 1

13 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.) < GeV -1 μm g aγγ (95% C.L.) < GeV -1 CCD g aγγ (95% C.L.) < GeV -1

14 2003 Result for CAST K.Z. et al., PRL 94 (2005) ) -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.) < GeV -1 Axion models m axion (ev)

15 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

16 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

17 The Future CAST Phase II Approved for Using a buffer gas to extend sensitivity to higher masses : with 4 He gas pressure increased from 0-6 mbar : m < 0.26 ev 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

18 ~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.

19 SCIENCE APRIL 2005 NATURE VOL APRIL

20 And yet For more on axions Axion CERN from 30 Nov to 2 Dec