An optical spark-chamber counter experiment at Adone, the Italian colliding electron-positron ring, has succeeded in measuring the cross-section for the process e+e−→p\(\bar p\) near threshold (Ec.m.=2.1 GeV). The result isσ(e+e−→p\(\bar p\))=(0.91±0.22) nb.
ISOTROPIC ANGULAR DISTRIBUTION ASSUMED.
The e + e − → p p cross section has been measured between 1925 and 2180 MeV. About 50 p p events were detected. The total cross section decreases from 1.31 ± 0.4 nb near 1937 MeV to 0.55 ± 0.2 nb near 2135 MeV. The proton form factors | G E | 2 and | G M | 2 , assumed identical, decrease from 0.15 ± 0.05 to 0.043 ± 0.015. They are an order of magnitude higher than predicted by the well-known dipole fit. The energy range has been scanned in steps of about 2 MeV. No significant structure was found in this p p sample.
TOTAL CROSS SECTION ASSUMING ISOTROPIC PRODUCTION. RADIATIVE CORRECTIONS CALCULATED USING PEAKING APPROXIMATION (ABOUT 20 PCT). AUTHORS ALSO QUOTE RESULTS FOR LIMITED (COSMIC RAY FREE) ACCEPTANCE AS A CHECK. FORM FACTOR DERIVED ASSUMING ELECTRIC AND MAGNETIC FORM FACTORS EQUAL IN MAGNITUDE.