ISSN - 0217751X, International Journal of Modern Physics A, 2005, vol. 20, p. 1747-1752
Two-pion production, γγ line and aspects of σ meson, Bose-Einstein correlations and isospin breaking
The pp → ppx(x = γγ, π0π0, π+π-) reactions have been measured at CELSIUS in the energy range Tp = 775 - 1360 MeV using the WASA 4π detector with hydrogen pellet target. Close to threshold the ppπ+π - data are in accordance with the Roper resonance concept and/or a dynamic formation of the σ meson. At higher energies the formation of the ΔΔ system becomes increasingly dominant. The ppπ0π 0 channel basically shows similar features, however, develops a peculiar enhancement at small invariant masses Mπ0π0 - in resemblance of Bose-Einstein correlations. Alternatively, the enhancement could be also indicative of a (dynamic) isospin breaking due to ππ rescattering in the σ channel. The latter is favored by the results on pd →3He x (x = π0π0, π+π-), where the observed π0π 0 enhancements are still much larger. In the γγ channel a line at Mγγ = 2mπ is observed. The possible nature of this line is discussed. © World Scientific Publishing Company.