First results of spherical neutral detector (SND) experiments at VEPP-2000

Analytic continuation of nucleon electromagnetic form factors in the time-like region

“…To have a direct comparison with the data, results are primarily given for the electric and magnetic Sachs FFs of a proton and neutron, G p E,M and G n E,M , even though the primary outcomes of this procedure (see equation (11)) are their isospin components G S E,M and G V E,M . These two sets of FFs are related by the linear combinations given in equation (5).…”

“…It is important to stress that TLFFs are purely relativistic quantities; they can be defined only in the framework of quantum electrodynamics and describe the vertex γNN, where a virtual photon produces a nucleon-antinucleon pair. In light of that, the only definition of an analytic continuation in TL q 2 represents by itself the first relativistic extension of the starting FF expressions given in equation (11). In spite of that, since such original FF expressions have been obtained for static nucleons, i.e., nucleons in their rest frame, a procedure has to be defined to extend FFs even at relativistic momenta.…”

“…In light of this, we should expect G N E,M (Q 2 ) |G N E,M (q 2 + 2q 2 CM )| (with the argument Q 2 we mean SLFF at |Q 2 | = |q 2 |) and using, for instance, q 2 CM = 1 GeV 2 , the SL-TL discrepancy can be reduced. Electric and magnetic FFs of a proton and neutron are obtained using the combinations, given in equation ( 5), of the isospin components, which are the Fourier transforms (see equation (11)) of the two profiles b(r) and t(r), defined in terms of the same chiral angle F(r) through the non-linear differential equation (12). It follows that FFs are all non-trivially interconnected.…”

Current results of the experiments at VEPP-2000

“…First results were obtained for many hadronic final states: e + e − → pp, nn, π + π − π 0 , π + π − π + π − , π + π − π 0 π 0 , π + π − π + π − π 0 , 3(π + π − ), 2(π + π − π 0 ), π + π − 4π 0 , ηπ + π − , K S K L , ωπ 0 → π 0 π 0 γ [14,15,16]. QED processes e + e − → e + e − and γγ were used to determine the integrated luminosity.…”

SND data acquisition system upgrade

“…The data acquisition (DAQ) system of the SND detector (figure 1) successfully operated [1,2] during four data-taking seasons (2010)(2011)(2012)(2013) at the e + e − collider VEPP-2000. Currently the collider is shut down for planned reconstruction, which is expected to increase the VEPP-2000 luminosity and data flow from the SND detector electronics by up to 10 times.…”