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In-medium modifications of the $ππ$ interaction in photon-induced reactions

J. G. Messchendorp·S. Janssen·M. Kotulla·J. Ahrens·J. R. H. Annand·R. Beck·F. Bloch·G. Caselotti·L. Fog·D. Hornidge·B. Krusche·W. Langgärtner·J. C. McGeorge·I. J. D. MacGregor·K. Mengel·V. Metag·R. Novotny·R. O. Owens·M. Pfeiffer·S. Sack·R. Sanderson·S. Schadmand
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Abstract

Differential cross sections of the reactions $(γ,π^\circπ^\circ)$ and $(γ,π^\circπ^++π^\circπ^-)$ have been measured for several nuclei ($^1$H,$^{12}$C, and $^{\rm nat}$Pb) at an incident-photon energy of $E_γ$=400-460 MeV at the tagged-photon facility at MAMI-B using the TAPS spectrometer. A significant nuclear-mass dependence of the $ππ$ invariant-mass distribution is found in the $π^\circπ^\circ$ channel. This dependence is not observed in the $π^\circπ^{+/-}$ channel and is consistent with an in-medium modification of the $ππ$ interaction in the $I$=$J$=0 channel. The data are compared to $π$-induced measurements and to calculations within a chiral-unitary approach.

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J. G. Messchendorp, S. Janssen, M. Kotulla, J. Ahrens, J. R. H. Annand, R. Beck, F. Bloch, G. Caselotti, L. Fog, D. Hornidge, B. Krusche, W. Langgärtner, J. C. McGeorge, I. J. D. MacGregor, K. Mengel, V. Metag, R. Novotny, R. O. Owens, M. Pfeiffer, S. Sack, R. Sanderson, S. Schadmand. 2002-10-14. In-medium modifications of the $ππ$ interaction in photon-induced reactions. https://doi.org/10.1103/physrevlett.89.222302

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