Abstract
Two striking features of the e + e − → p p ¯ and e + e − → n n ¯ cross sections near threshold are discussed: the e + e − → p p ¯ data show a nearly flat cross section in the 200 MeV region above threshold. The e + e − → n n ¯ results, published in 1998 by the FENICE collaboration at ADONE collider, show a neutron cross section larger or equal to the proton one. This surprising behavior has been confirmed recently by SND experiment at VEPP-2000. The FENICE and SND results have been obtained with energy scan measurements, while for the BaBar data the initial state radiation technique has been used. This technique has a high efficiency even at the production threshold and appears to be the best solution to a better understanding of these behaviors. To this purpose the zero degree photon detector, now in the installation stage with BESIII experiment at BEPCII collider, has been constructed. A preliminary analysis on the improvements achievable with this detector is presented.
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