Measurement of the e+e−→π+π−π0π0 cross section using initial

Abstract

The process e þ e − → π þ π − 2π 0 γ is investigated by means of the initial-state radiation technique, where a photon is emitted from the incoming electron or positron. Using 454.3 fb −1 of data collected around a centerof-mass energy of ffiffi ffi s p ¼ 10.58 GeV by the BABAR experiment at SLAC, approximately 150000 signal events are obtained. The corresponding nonradiative cross section is measured with a relative uncertainty of 3.6% in the energy region around 1.5 GeV, surpassing all existing measurements in precision. Using this new result, the channel's contribution to the leading order hadronic vacuum polarization contribution to the anomalous magnetic moment of the muon is calculated as ðg π þ π − 2π 0 μ − 2Þ=2 ¼ ð17.9 AE 0.1 stat AE 0.6 syst Þ × 10 −10 in the energy range 0.85 GeV < E CM < 1.8 GeV. In the same energy range, the impact on the running of the fine-structure constant at the Z 0 -pole is determined as Δα π þ π − 2π 0 ðM 2 Z Þ ¼ ð4.44 AE 0.02 stat AE 0.14 syst Þ × 10 −4 . Furthermore, intermediate resonances are studied and especially the cross section of the process e þ e − → ωπ 0 → π þ π − 2π 0 is measured.

Common explanation of the behavior of some e+e− annihilation processes around s=1.9 GeV

“…The cross section for this process is very small because the ρ 0 φπ 0 vertex is suppressed by the Okubo-Zweig-Iizuka (OZI) rule [40]. In comparison with the cross section for a similar twobody OZI allowed process e + e − → ωπ 0 [41] it is smaller by almost two orders of magnitude. For us, this process is extremely interesting because it is one of the known processes where the ρ(1900) manifests itself as a narrow peak in the excitation curve, see Fig.…”

Dispersion relation for hadronic light-by-light scattering: pion pole

“…inelasticities become important. For instance, in the isovector channel, the two-pion states (and the virtual photon) couple to four-pion states [59,113,114,[137][138][139]. Although the threshold for four pions lies significantly below 1 GeV, both the smallness of four-pion phase space near threshold and the derivative couplings of the pions demanded by chiral symmetry effectively delay the onset of the importance of the four-pion states to the πω threshold.…”

Long distance effects in inclusive rare B decays and phenomenology of $$ \overline{B} $$→ Xdℓ+ℓ−

“…The BESII data [79] dominates the statistics in the charm threshold region. The broad oscillation at √ s ∼ 1.6 GeV due to the phase space enhancements of isobar processes including e + e − → ρ + ρ − → π + π − π 0 π 0 has been resolved by precise measurements of multi-body final states at BABAR [80][81][82][83][84][85][86][87][88][89]. The total nonstrange vector spectral function from τ decays is taken from ALEPH [90].…”