Precise Measurement of thee+e−→π+π−(γ)Cross Section with the Initial State Radiation Method atBABAR

Precise measurement of the e + e − → π + π − (γ) cross section with the initial state radiation method at BABAR

“…The folding probability P ij of an event produced in a true ( ffiffiffi ffi s 0 p ) bin j to be reconstructed in a (m xx ) bin i is computed directly in simulation from the transfer matrix A ij (the number of events produced in a true bin j that are reconstructed in bin i). 5 Conversely, the matrix of unfolding probabilities P 0 ij indicates the probability for an event reconstructed in a bin i to originate from the true bin j, and is also computed from the transfer matrix. A ij and P 0 ij depend on the assumed true spectrum while P ij , which describes detector and FSR effects, does not.…”

“…The spectra obtained under the central region conditions (loose 2 criterion) and under the tails conditions (tight 2 criterion) are unfolded separately over the full mass signal and multihadron background components, with their shapes both taken from simulation. 5 The matrix of folding probabilities is related to the transfer matrix A ij by P ij ¼ A ij = P N k¼1 A kj while the matrix of unfolding probabilities is P range. The unfolded spectra are combined afterwards, each being used in its respective mass region.…”

“…The accuracy of the theoretical prediction for a is linked to the advances in e þ e À measurements. A discrepancy of roughly 3 standard deviations () including systematic uncertainties between the measured [1] and predicted [2][3][4] values of a persisted for years before the results of this analysis became available [5], possibly hinting at new physics. An independent approach using decay data leads to a smaller difference of 1:8 [6] in the same direction, with enlarged systematic uncertainties due to isospin-breaking corrections.…”

“…þ À ðÞ cross section on the same data and compare it to the QED prediction. The reported results and their application to the contribution to the muon magnetic anomaly have been already published in shorter form [5].…”

Cross sections for the reactions e+e−→KS0Lees1, Poireau2, Tisserand3 et al. 2017Phys. Rev. DSelf Cite18090View full textAdd to dashboardCite

“…Studies of the ISR processes e þ e − → μ þ μ − γ [6,7] and e þ e − → X h γ, where X h represents any of several exclusive multihadron final states, using data of the BABAR experiment at SLAC, have been reported previously. The X h studied so far include charged hadron pairs π þ π − [7], [8], and pp [9]; four or six charged mesons [10][11][12]; charged mesons plus one or two π 0 mesons [11][12][13][14]; a K 0 S plus charged and neutral mesons [15]; and the first ISR measurement from BABAR that includes K 0 L mesons [16].…”