The Crystal Barrel experiment at the Low Energy Antiproton Ring (LEAR)
at CERN studied the annihilation of antiprotons with protons in liquid
hydrogen. The emphasis was on the detection of electrically neutral mesons.
Several new light mesons were discovered.
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Crystal Barrel apparatus annihilation into charged and neutral mesons: magnet yoke (1,2),
coil (3), CsI-crystals (4), drift chamber (5), wire chamber (6), hydrogen target (7)
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Experimental Dalitz plot of the proton antiproton annihilation into three neutral pseudoscalar mesons
decaying into 6 photons (a) - (c). Red and blue regions correspond to high and low event densities,
respectively. (a):1 neutral pion + 2 eta, 198 000 events; (b) 2 neutral pions + 1 eta, 280 000 events;
(c) 3 neutral pions, 712 000 events. Each event is entered six times for symmetry reasons;
(d) 1 neutral pion and to long-lived neutral kaons, 37 358 events.
C. Amsler et al. (Crystal Barrel Collaboration), Phys. Lett. B 355 (1995) 425
A.
Abele et al. (Crystal Barrel Collaboration), Phys. Lett. B 385 (1996) 425
Review: C. Amsler, Rev. Mod. Phys. 70 (1998) 1293