2 research outputs found
First observation of the Λ(1405) line shape in electroproduction
We report the first observation of the line shape of the Λ(1405) from electroproduction, and show that it is not a simple Breit-Wigner resonance. Electroproduction of K+Λ(1405) off the proton was studied by using data from CLAS at Jefferson Lab in the range 1.0<Q2<3.0 (GeV/c)2. The analysis utilized the decay channels Σ+π− of the Λ(1405) and pπ0 of the Σ+. Neither the standard Particle Data Group resonance parameters, nor free parameters fitting to a single Breit-Wigner resonance represent the line shape. In our fits, the line shape corresponds approximately to predictions of a two-pole meson-baryon picture of the Λ(1405), with a lower mass pole near 1368 MeV/c2 and a higher mass pole near 1423 MeV/c2. Furthermore, with increasing photon virtuality the mass distribution shifts toward the higher mass pole
First Observation of Large Missing-Momentum (e,e'p) Cross-Section Scaling and the onset of Correlated-Pair Dominance in Nuclei
International audienceWe report the first measurement of -scaling in cross-section ratios off nuclei relative to deuterium at large missing-momentum of MeV/c. The observed scaling extends over a kinematic range of , which is significantly wider than previously observed for inclusive cross-section ratios. The -integrated cross-section ratios become constant (i.e., scale) beginning at , the nuclear Fermi momentum. Comparing with theoretical calculations we find good agreement with Generalized Contact Formalism calculations for high missing-momentum ( MeV/c), suggesting the observed scaling results from interacting with nucleons in short-range correlated (SRC) pairs. For low missing-momenta, mean-field calculations show good agreement with the data for , and suggest that contributions to the measured cross-section ratios from scattering off single, un-correlated, nucleons are non-negligible up to MeV/c. Therefore, SRCs become dominant in nuclei at MeV/c, well above the nuclear Fermi Surface of MeV/c