Measurement of the e+e−→π0γ cross section in the energy range 1.075–2 GeV at SND

Abstract

The process e + e − → π 0 γ is studied with the SND detector at the VEPP-2000 e + e − collider. Basing on data with an integrated luminosity of 41 pb −1 recorded in 2010-2012 we measure the e + e − → π 0 γ cross section in the center-of-mass energy range from 1.075 up to 2 GeV. In the range 1.4-2.0 GeV the process e + e − → π 0 γ is studied for the first time.

g−2 of charged leptons, α(MZ2) , and the hyperfine splitting of muonium

“…6. Notably, the π 0 γ channel now includes a new measurement from the SND experiment [41], which greatly extends the previous upper border of the channel from 1.35 to 1.935 GeV in this work. The changes to a π 0 γ μ are negligible, confirming that no higher-energy contributions were missed previously in this hadronic mode.…”

“…There have been a number of small data updates (see Refs. [41][42][43][44][45][46]) in other channels since Ref. [1].…”

The hadronic light-by-light contribution to the muon’s anomalous magnetic moment

“…Via dispersive sum rules, as given by Eqs. (43,44,45) the real parts for the forward light-by-light amplitude were then be compared with the integral over the absorptive parts. The latter were estimated in Refs.…”

Search for direct production of the f1(1285) resonance in e+e− collisions

“…In these experiments, the first upper limits were set on the probabilities of the inverse reactions, decays η , f 0 (975), f 2 (1270), f 0 (1300), a 0 (980), and a 2 (1320) to e + e − pairs. In recent experiments at the colliders VEPP-2M [2,3], VEPP-2000 [4,5] and BEPCII [6], this inverse-reaction technique was used to set the best upper limits on the electron widths of the resonances listed above, as well as η and X(3872). The existing upper limit on the decay f 2 (1270) → e + e − is close to theoretical predictions.…”