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Measurement of the Pion Polarisability at COMPASS

The COMPASS experiment at CERN has investigated Primakoff reactions of 190 GeV/c pions with the Coulomb field of various target nuclei, predominatly lead, in a pilot run in the year 2004. The photoproduction process $\pi^{−}Z\rightarrow\pi^{-}Z\gamma$ is related to Compton scattering on the pion, a...

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Detalles Bibliográficos
Autor principal: Friedrich, Jan
Lenguaje:eng
Publicado: 2007
Materias:
Acceso en línea:http://cds.cern.ch/record/1498156
Descripción
Sumario:The COMPASS experiment at CERN has investigated Primakoff reactions of 190 GeV/c pions with the Coulomb field of various target nuclei, predominatly lead, in a pilot run in the year 2004. The photoproduction process $\pi^{−}Z\rightarrow\pi^{-}Z\gamma$ is related to Compton scattering on the pion, and gives access to the electric and magnetic polarisabilities, $\alpha_{\pi}$ and $\beta_{\pi}$. The unique feature of the COMPASS setup to measure the equivalent reaction with identified muons during the same beam time allows for a reliable treatment of systematic apparative effects. In a first analysis, the value $\alpha_{\pi} =$ 2.5 $\pm$ 1.7$_{stat}$ $\pm$ 0.6$_{sys}$ ·10$^{−4}$ fm$^{3}$ was obtained, assuming $\alpha_{\pi} = −\beta_{\pi}$ on theoretical reasons.