Study of the reactions e+e−→π+π−

Abstract

We study the processes e þ e − → π þ π − π 0 π 0 π 0 γ and π þ π − π 0 π 0 ηγ in which an energetic photon is radiated from the initial state. The data are collected with the BABAR detector at SLAC. About 14 000 and 4700 events, respectively, are selected from a data sample corresponding to an integrated luminosity of 469 fb −1. The invariant mass of the hadronic final state defines the effective e þ e − center-of-mass energy. From the mass spectra, the first precise measurement of the e þ e − → π þ π − π 0 π 0 π 0 cross section and the first measurement ever of the e þ e − → π þ π − π 0 π 0 η cross section are performed. The center-of-mass energies range from threshold to 4.35 GeV. The systematic uncertainty is typically between 10% and 13%. The contributions from ωπ 0 π 0 , ηπ þ π − , and other intermediate states are presented. We observe the J=ψ and ψð2SÞ in most of these final states and measure the corresponding branching fractions, many of them for the first time.

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

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

“…Once again, it is encouraging to verify that no large contributions were missed from these channels in the KNT18 data compilation. Last, it is important to mention that the three modes π þ π − 3π 0 , π þ π − 2π 0 η and ωπ 0 π 0 that were previously unmeasured have now been measured by BABAR [42]. These allow, for the first time, for their corresponding hadronic contributions to be estimated using experimental data instead of previously used isospin relations.…”

Strong coupling from an improved τ vector isovector spectral function

“…First, BaBar has measured the spectrum of τ → K − K 0 ν τ [14]. Second, thanks to a wealth of new experimental measurements of many exclusive-channel cross sections in e + e − → hadrons [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29] by the CMD-3, BaBar, and SND collaborations, conserved vector current (CVC) relations allow essentially all remaining vector isovector mode contributions to be obtained using exclusive mode electroproduction cross-section data (with negligible isospin-breaking corrections, as we discuss below). In Ref.…”

Probing the dark axion portal with muon anomalous magnetic moment

“…The first two are the QED and electroweak (EW) predictions, respectively, while a HVP μ is the hadronic vacuum polarization (HVP) and a HLbL μ the hadronic light-by-light (HLbL) contribution. Although the biggest source of uncertainty comes from the hadronic part [9][10][11][12], the most recent calculations [13][14][15] have included the updated measurement of the hadronic contributions [16][17][18]. The latest theoretical calculation [21] gives a SM μ = 116591810 (43) × 10 −11 , (…”