Measurement and Analysis of the Reaction $\gamma \gamma \to \pi^+ \pi^- \pi^+ \pi^-$
- Berger, Christoph
- Genzel, H.
- Deuter, A.
- Ferrarotto, F.
- Franke, G.
- Gaspero, Mario
- Gerke, C.
- Knies, G.
- Lewendel, B.
- Meyer, J.
- Michelsen, U.
- Pape, K. H.
- Lackas, W.
- Stella, B.
- Timm, U.
- Winter, G. G.
- Zachara, M.
- Zimmermann, W.
- Bussey, P. J.
- Cartwright, S. L.
- Dainton, J. B.
- Hendry, D.
- King, B. T.
- Pielorz, J.
- Raine, C.
- Scarr, J. M.
- Skillicorn, I. O.
- Smith, K. M.
- Thomson, J. C.
- Achterberg, O.
- Blobel, V.
- Burkart, D.
- Diehlmann, K.
- Feindt, M.
- Raupach, F.
- Kapitza, H.
- Koppitz, B.
- Kruger, M.
- Poppe, M.
- Spitzer, H.
- Van Staa, R.
- Chang, C. Y.
- Glasser, R. G.
- Kellogg, R. G.
- Maxfield, S. J.
- Wagner, W.
- Polvado, R. O.
- Sechi-Zorn, B.
- Skard, J. A.
- Skuja, A.
- Tylka, A. J.
- Welch, G. E.
- Zorn, G. T.
- Almeida, F.
- Backer, A.
- Barreiro, F.
- Klovning, A.
- Brandt, S.
- Derikum, K.
- Grupen, C.
- Meyer, H. J.
- Muller, H.
- Neumann, B.
- Rost, M.
- Stupperich, K.
- Zech, Gunter
- Alexander, G.
- Lillestol, E.
- Bella, G.
- Gnat, Y.
- Grunhaus, J.
- Junge, H.
- Kraski, K.
- Maxeiner, C.
- Maxeiner, H.
- Meyer, H.
- Schmidt, D.
- PLUTO Collaboration
- Burger, J.
- Criegee, L.
DOIAbstract
We have measured the cross section of four charged pion production in photon-photon interactions in the invariant mass range 1.0≦Wγγ≦3.2 GeV and up toQ2=16 GeV2. For 1.2 GeV≦Wγγ≦1.7 GeV the process is dominated by ρ0ρ0 production with a rapid rise in cross section around 1.2 GeV, well below the nominal ρ0ρ0 threshold. The observed distributions in the two particle masses and in the production and decay angles are well described by an incoherent sum of the phase-space subprocesses γγ →ρ0ρ0, →ρ0π+π−, and →π+π−π+π−. A spin-parity analysis of the ρ0ρ0 system showsJP=2+ to dominate, although 0+ is also possible forWγγ≦1.4 GeV. Negative partity states are excluded
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