Isospin Breaking in Low-Energy Pion-Nucleon Scattering

Abstract

We have analyzed low-energy pion-nucleon data for isospin invariance by comparing chargeexchange amplitudes derived from charge-exchange data with those predicted from recent~p elastic data through the application of isospin invariance. A discrepancy of the order of 7% is observed beyond the contributions of the~p Coulomb interaction and the hadronic mass differences. PACS numbers: 13.75.Gx, 24.80.Dc, 25.80.Gn fcEx = Of the eight reactions of the form~N~' N' the only three directly accessible experimentally are those with charged pion beams and proton targets: 7Tp elasticscattering, with amplitudes f, and 7r p~~" n chargeexchange (CEX) scattering, with amplitude fcEx. Isospin conservation gives a relationship among these three amplitudes, the triangle identity

Charge symmetry violation in pn→dπ0 and chiral effective field theory

“…The quantity D is found [13] to be about 6%, leading to a very large negative value of δm N −δm N ≈ −17 MeV. If the 6% result is correct, there seems to be a serious problem with our current understanding of low-energy QCD.…”

Pion-nucleon scattering in chiral perturbation theory (I): Isospin-symmetric case

“…With the advent of high-precision data on pionic hydrogen and deuterium at PSI [1] and neutral pion photoproduction data from MAMI [2] and SAL [3], novel interest has been spurred in separating electromagnetic effects and trying to filter out isospin violating contributions. In addition, in the framework of some models it has been claimed that the presently available pion-nucleon data basis exhibits isospin violation of the order of a few percent [4] [5]. However, to really pin down isospin breaking due to the light quark mass difference, one needs a machinery that allows to simultaneously and consistently treat the electromagnetic and the strong contributions.…”

Differential cross section of the charge-exchange reactionπ−p→π0nin the momentum range from 148 to323MeVSadler1, Kulbardis2, Abaev3 et al. 2004Phys. Rev. C22070View full textAdd to dashboardCite

“…Fettes and Meissner [11,12] investigated isospin breaking in the framework of chiral perturbation theory up to 100 MeV/c and obtained only a 0.7% effect in the s-waves, where Ref. [9,10] observed the largest effect. In all three analyses the data for CEX were the most limited in quantity.…”

“…Mass differences between the neutron and proton and the charged and neutral pions are manifestations of these effects. Gibbs, Ai and Kaufman [9] incorporated these mass differences and Coulomb corrections in a coupled-channel potential model. They included data up to T π = 50 MeV (P π = 128 MeV/c), just below the range of data reported here.…”