2 research outputs found

    First observation of the Λ(1405) line shape in electroproduction

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    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

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    International audienceWe report the first measurement of xBx_B-scaling in (e,ep)(e,e'p) cross-section ratios off nuclei relative to deuterium at large missing-momentum of 350pmiss600350 \leq p_{miss} \leq 600 MeV/c. The observed scaling extends over a kinematic range of 0.7xB1.80.7 \leq x_B \leq 1.8, which is significantly wider than 1.4xB1.81.4 \leq x_B \leq 1.8 previously observed for inclusive (e,e)(e,e') cross-section ratios. The xBx_B-integrated cross-section ratios become constant (i.e., scale) beginning at pmisskFp_{miss}\approx k_F, the nuclear Fermi momentum. Comparing with theoretical calculations we find good agreement with Generalized Contact Formalism calculations for high missing-momentum (>375> 375 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 pmisskFp_{miss}\le k_F, and suggest that contributions to the measured cross-section ratios from scattering off single, un-correlated, nucleons are non-negligible up to pmiss350p_{miss}\approx 350 MeV/c. Therefore, SRCs become dominant in nuclei at pmiss350p_{miss}\approx 350 MeV/c, well above the nuclear Fermi Surface of kF250k_F \approx 250 MeV/c
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