Here, the process e + e – →π + 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 center-of-mass energy of √s=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 (gπ + π – 2π 0 μ –2)/2=(17.9 ± 0.1 stat ± 0.6 syst )×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 Δαπ + π – 2π 0 (M 2 Z )=(4.44 ± 0.02 stat ± 0.14 syst ) × 10 –4 . Furthermore, intermediate resonances are studied and especially the cross section of the process e + e – →ωπ 0 →π + π – 2π 0 is measured.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2017

Measurement of the D * ( 2010 ) + - D + Mass Difference

Here, we measure the mass difference, Δm + , between the D* (2010) + and the D + using the decay chain D* (2010) + → D + π 0 with D + → K - π + π + . The data were recorded with the BABAR detector at center-of-mass energies at and near the Υ(4S) resonance, and correspond to an integrated luminosity of approximately 468 fb -1 . We measure Δm + = (140 601.0 ± 6.8 [stat] ± 12.9 [syst] ) keV . We combine this result with a previous BABAR measurement of Δm 0 ≡ m(D* (2010) + ) - m (D 0 ) to obtain Δm D = m (D + ) - m (D 0 ) = ( 4824.9 ± 6.8 [stat] ± 12.9 [syst]) keV . These results are compatible with and approximately five times more precise than the Particle Data Group averages.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2017

Search for Invisible Decays of a Dark Photon Produced in e + e − Collisions at BaBar

Not Available

Lees, J. P.↗