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Coherence with applications to CAST

Axion Academic Training Patras, 19 May 2006. Coherence with applications to CAST. Yannis K. Semertzidis Brookhaven National Lab. Axion photon coherence/oscillations Wide or narrow axion mass scan, S/N. Axion/photon oscillations in a magnetic field B with length L.

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Coherence with applications to CAST

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  1. Axion Academic Training Patras, 19 May 2006 Coherence with applications to CAST Yannis K. Semertzidis Brookhaven National Lab • Axion photon coherence/oscillations • Wide or narrow axion mass scan, S/N

  2. Axion/photon oscillations in a magnetic field B with length L Yannis Semertzidis, BNL

  3. Axion to photon conversion probability With q=ma2/2, is the momentum transfer and ma,  the axion mass and energy respectively. The coherence length is defined by Yannis Semertzidis, BNL

  4. Axion-photon conversion in gas • For wave-numbers k and ka, we have coherence when Yannis Semertzidis, BNL

  5. Hence, (after some algebra) for coherence requirements we get Yannis Semertzidis, BNL

  6. Example with 4He gas Generalized for any ma Yannis Semertzidis, BNL

  7. How about spatial coherence? axions  x-rays r n’ x-ray refraction: • The x-rays/axions do not overlap • The x-rays travel longer paths than axions n i The coherence is lost… The important parameter here is pressure uniformity in cross section… Yannis Semertzidis, BNL

  8. A numerical example For a 10m long magnet the axion/photon missing each other by 1/2 wavelength when Yannis Semertzidis, BNL

  9. Checking the temperature uniformity • Can use a laser light to probe the uniformity, e.g. 5mK temperature gradient in the cross section, along the whole length of the magnet can produce up to 4mmshift on a red laser light…(effect goes as (1/2)2= 20002=4106). Yannis Semertzidis, BNL

  10. Actually photons and axions mix… G. Raffelt and L. Stodolsky PRD 37 (1988) 1237. • A transverse magnetic field is necessary • The mixing angle is • The oscillation lengthL is Yannis Semertzidis, BNL

  11. For axion and photon plane-waves Yannis Semertzidis, BNL

  12. For solar axions Yannis Semertzidis, BNL

  13. For axion Production in a magnetic field with a laser light (e.g. PVLAS or E840 @BNL) Yannis Semertzidis, BNL

  14. CAST: narrow or wide mass scans? Wide mass scan, i.e. a small part of the magnet length is sensitive to a specific axion mass. The number of axion to photon conversions is: The advantage is that n axion mass ranges are covered in ONE setting… Yannis Semertzidis, BNL

  15. CAST: narrow or wide mass scans? Narrow mass scan, i.e. the total magnet length is sensitive to one specific axion mass: The advantage is that the axionconversion is higher by n2 However, longer time (nt) is needed to cover the same axion mass range. Yannis Semertzidis, BNL

  16. CAST: narrow or wide mass scans? Not really: For shorter coherent lengths the covered mass range is larger!!! That balances out the two rates. The SIGNAL counts ~same. Yannis Semertzidis, BNL

  17. CAST: narrow or wide mass scans? However, the total noise counts for a specific axion mass are larger by a factor of n… Yannis Semertzidis, BNL

  18. A numerical example: • Total axionphoton counts: S=150 • Total noise/specific axion mass (in narrow mass scan): Ns=900. • Total noise (in wide mass scan): Nw=9000 (using n=10). • Then in one case S/N=5 sigma, and in the other 1.5 sigma. Yannis Semertzidis, BNL

  19. Karl van Bibber et al., PRD 39, 2089 (1989) Yannis Semertzidis, BNL

  20. Summary • The difference in the axion coupling limit is not very large. • However, if one is interested in a discovery, the difference can be significant! Yannis Semertzidis, BNL

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