Separated structure functions for exclusiveK+ΛandK+Σ0electroproduction at 5.5 GeV measured with CLAS

Abstract

We report measurements of the exclusive electroproduction of K + Λ and K + Σ 0 final states from an unpolarized proton target using the CLAS detector at the Thomas Jefferson National Accelerator Facility. The separated structure functions σ U , σ LT , σ T T , and σ LT ′ were extracted from the Φ-dependent differential cross sections acquired with a longitudinally polarized 5.499 GeV electron beam. The data span a broad range of momentum transfers Q 2 from 1.4 to 3.9 GeV 2 , invariant energy W from threshold to 2.6 GeV, and nearly the full center-of-mass angular range of the kaon. The separated structure functions provide an unprecedented data sample, which in conjunction with other meson photo-and electroproduction data, will help to constrain the higher-level analyses being performed to search for missing baryon resonances.

K+Λelectroproduction above the resonance region

“…III) to 2.5 GeV. There are 25 published data points that meet these kinematic restrictions: nine data points measured at Cornell in the 1970s [18][19][20] and 16 recent data points from CLAS [21]. Most of the p(γ * ,K + )Λ data are available at W < 2.5 GeV, recent examples of which can be found in Refs.…”

Nucleon Resonance Structure Studies via Exclusive KY Electroproduction

“…The CLAS program has yielded by far the most extensive and precise measurements of KY electroproduction data ever measured across the nucleon resonance region. These measurements have included the separated structure functions σ T , σ L , σ U = σ T + ǫσ L , σ LT , σ T T , and σ LT ′ for K + Λ and K + Σ 0 [13,14,15,16], recoil polarization for K + Λ [17], and beam-recoil transferred polarization for K + Λ and K + Σ 0 [18,19]. For the hyperon polarization measurements, we have taken advantage of the self-analyzing nature of the weak decay of the Λ.…”

“…Shown in Figs. 4 and 5 is a small sample of the available data in the form of the K + Λ and K + Σ 0 structure functions σ U , σ LT , σ T T , and σ LT ′ [16,20], illustrating its broad kinematic coverage and statistical precision.…”

“…While there has been progress toward a better understanding of the low-lying N * states in the region below 1.6 GeV, the vast majority of the predicted missing N * and ∆ * states lie in the region from 1.6 < W < 3 GeV. To date the PDG lists only four N * states, N (1650) 1 W (GeV) cos K *=-0.775 cos K *=-0.525 cos K *=-0.300 cos K *=-0.100 cos K *=0.100 cos K *=0.300 cos K *=0.500 cos K *=0.675 cos K *=0.825 cos K *=0.950 [16,20]. The error bars represent the statistical uncertainties only.…”

“…The red curves are from the hadrodynamic KY model of Maxwell [21] and the blue curves are from the hybrid RPR-2011 KY model from Ghent [22]. Figure 5: Structure functions σ U = σ T + ǫσ L , σ LT , σ T T , and σ LT ′ (nb/sr) for K + Σ 0 production vs. W (GeV) for E beam =5.5 GeV for Q 2 =1.80 GeV 2 and cos θ * K values as shown from CLAS data [16,20]. The error bars represent the statistical uncertainties only.…”