We present a measurement of the production of Xi(-) and Lambda Lambda in the C-12(K-, K+) reaction at an incident beam momentum of 1.8 GeV /c , based on high-statistics data from J-PARC E42. The cross section for the C-12(K-, K+ Xi(-)) reaction, compared to the inclusive C-12(K-, K+) reaction cross section, indicates that the Xi(- )emission probability peaks at 70% in the energy region of E-Xi = 100-150 MeV above the Xi(- )emission threshold. A classical approach using eikonal approximation shows that the total cross section for Xi(- )inelastic scattering ranges between 42 mb and 23 mb in the Xi(- )momentum range from 0.4 to 0.6 GeV/c . Furthermore, based on the relative cross section for the C-12(K-, K+Lambda Lambda) reaction, the total cross section for Xi(-)p -> Lambda Lambda is estimated in the same approach to vary between 2.2 mb and 1.0 mb in the momentum range of 0.40-0.65 GeV/c . Specifically, a cross section of 1.0 mb in the momentum range of 0.5-0.6 GeV /c imposes a constraint on the upper bound of the decay width of the Xi(- )particle in infinite nuclear matter, revealing Gamma(Xi )< similar to 0.6 MeV.

For the first time, differential cross sections and photon beam asymmetries were measured for the reaction gamma p -> f0(980) p -> pi 0 pi 0p by using a linearly polarized photon beam up to 2.4 GeV and a liquid hydrogen target. The f0(980) photoproduction signal was clearly observed owing to the absence of contributions from vector-meson photoproduction. The results indicate the t-channel exchange of vector mesons as a mechanism of the f0(980) photoproduction at E gamma approximate to 2.1 GeV, putting constraints on the nature of f0(980).

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

For the first time, differential cross sections and photon beam asymmetries were measured for the reaction $\ensuremath{\gamma}p\ensuremath{\rightarrow}{f}_{0}(980)p\ensuremath{\rightarrow}{\ensuremath{\pi}}^{0}{\ensuremath{\pi}}^{0}p$ by using a linearly polarized photon beam up to $2.4\phantom{\rule{4pt}{0ex}}\mathrm{GeV}$ and a liquid hydrogen target. The ${f}_{0}$(980) photoproduction signal was clearly observed owing to the absence of contributions from vector-meson photoproduction. The results indicate the $t$-channel exchange of vector mesons as a mechanism of the ${f}_{0}(980)$ photoproduction at ${E}_{\ensuremath{\gamma}}\ensuremath{\approx}2.1\phantom{\rule{4pt}{0ex}}\mathrm{GeV}$, putting constraints on the nature of ${f}_{0}(980)$.

S. Morán,1, 3 R. Dupre,2 H. Hakobyan,1, 52 M. Arratia,3 W.K. Brooks,1 A. Bórquez,1 A. El Alaoui,1 L. El Fassi,4, 5 K. Hafidi,5 R. Mendez,1 T. Mineeva,1 S.J. Paul,3 M.J. Amaryan,36 Giovanni Angelini,19 Whitney R. Armstrong,5 H. Atac,43 N.A. Baltzell,44 L. Barion,20 M. Bashkanov,49 M. Battaglieri,44, 22 I. Bedlinskiy,31 Fatiha Benmokhtar,14 A. Bianconi,46, 26 L. Biondo,22, 25, 47 A.S. Biselli,15, 8 F. Bossù,10 S. Boiarinov,44 W.J. Briscoe,19 D. Bulumulla,36 V.D. Burkert,44 D.S. Carman,44 P. Chatagnon,2 V. Chesnokov,41 T. Chetry,4 G. Ciullo,20, 16 P.L. Cole,30, 9, 44 M. Contalbrigo,20 G. Costantini,46, 26 A. D’Angelo,23, 40 N. Dashyan,52 R. De Vita,22 M. Defurne,10 A. Deur,44 S. Diehl,37, 12 C. Djalali,35, 42 H. Egiyan,44 L. Elouadrhiri,44 P. Eugenio,18 R. Fersch,11, 51 A. Filippi,24 G. Gavalian,44, 32 Y. Ghandilyan,52 G.P. Gilfoyle,39 A.A. Golubenko,41 R.W. Gothe,42 K.A. Griffioen,51 M. Guidal,2 M. Hattawy,36 F. Hauenstein,36 T.B. Hayward,12 D. Heddle,11, 44 K. Hicks,35 A. Hobart,2 M. Holtrop,32 Y. Ilieva,42 D.G. Ireland,48 E.L. Isupov,41 H.S. Jo,29 D. Keller,50 A. Khanal,17 M. Khandaker,34, ∗ W. Kim,29 F.J. Klein,9 A. Kripko,37 V. Kubarovsky,44, 38 S.E. Kuhn,36 L. Lanza,23 M. Leali,46, 26 P. Lenisa,20, 16 K. Livingston,48 I .J .D. MacGregor,48 D. Marchand,2 L. Marsicano,22 V. Mascagna,45, 26 B. McKinnon,48 C. McLauchlin,42 Z.E. Meziani,5 S. Migliorati,46, 26 M. Mirazita,21 V. Mokeev,44, 41 C. Munoz Camacho,2 P. Nadel-Turonski,44 K. Neupane,42 S. Niccolai,2 G. Niculescu,28 T. R. O’Connell,12 M. Osipenko,22 A.I. Ostrovidov,18 M. Ouillon,2 P. Pandey,36 M. Paolone,33 L.L. Pappalardo,20, 16 E. Pasyuk,44 W. Phelps,11, 19 O. Pogorelko,31 J. Poudel,36 J.W. Price,6 Y. Prok,36, 50 B.A. Raue,17 Trevor Reed,17 M. Ripani,22 J. Ritman,27 A. Rizzo,23, 40 G. Rosner,48 J. Rowley,35 F. Sabatié,10 C. Salgado,34 A. Schmidt,19 R.A. Schumacher,8 Y.G. Sharabian,44 E.V. Shirokov,41 U. Shrestha,12 D. Sokhan,10, 48 O. Soto,21 N. Sparveris,43 S. Stepanyan,44 I.I. Strakovsky,19 S. Strauch,42, 19 R. Tyson,48 M. Ungaro,44, 38 L. Venturelli,46, 26 H. Voskanyan,52 A. Vossen,13, 44 E. Voutier,2 D.P. Watts,49 Kevin Wei,12 X. Wei,44 L.B. Weinstein,36 R. Wishart,48 M.H. Wood,7, 42 B. Yale,51 N. Zachariou,49 J. Zhang,50 and Z.W. Zhao13

We report a new measurement of the beam-spin asymmetry, Sigma, for the (gamma) over right arrown -> K+Sigma(-) reaction using quasi-free neutrons in a liquid-deuterium target. The new dataset includes data at previously unmeasured photon energy and angular ranges, thereby providing new constraints on partial wave analyses used to extract properties of the excited nucleon states. The experimental data were obtained using the CEBAF Large Acceptance Spectrometer (CLAS), housed in Hall B of the Thomas Jefferson National Accelerator Facility (JLab). The CLAS detector measured reaction products from a liquid-deuterium target produced by an energy-tagged, linearly polarised photon beam with energies in the range 1.1 to 2.3 GeV. Predictions from an isobar model indicate strong sensitivity to N(1720)3/2(+), Delta(1900)1/2(-), and N(1895)1/2(-), which corroborates results from a recent combined analysis of all K Sigma channels. When our data are incorporated in the fits of partial-wave analyses, one observes significant changes in gamma-n couplings of resonances which have small branching ratios to the pi N channel. (c) 2022 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). Funded by SCOAP(3).

We report exclusive measurements for the eta photoproduction on a proton target. The differential cross sections and photon beam asymmetries of the gamma p -> eta p reaction are measured in a center-of-mass energy (W) range of 1.82-2.32 GeV and a polar angle range of -1.0 < cos theta eta c.m. < 0.6 by using a large acceptance calorimeter (BGOegg) and forward-angle charged-particle detectors at the SPring-8 LEPS2 beamline. The reaction is identified with a kinematic fitting method to select a recoil proton and two photons produced in an eta meson decay. A bump structure at W = 2.0-2.3 GeV in the differential cross section is confirmed at extremely backward eta polar angles, where the existing data are inconsistent with each other. This bump structure is likely associated with high-spin resonances that couple with ss over bar quarks. The photon beam asymmetries in a wide eta polar angle range for the photon beam energies above 2.1 GeV are reported for the first time, providing an additional constraint to nucleon resonance studies at high energies.

High precision measurements of the polarized electron beam-spin asymmetry in semi-inclusive deep inelastic scattering (SIDIS) from the proton have been performed using a 10.6 GeV incident electron beam and the CLAS12 spectrometer at Jefferson Lab. We report here a high precision multidimensional study of single π^{+} SIDIS data over a large kinematic range in Bjorken x, fractional energy, and transverse momentum of the hadron as well as photon virtualities Q^{2} ranging from 1-7  GeV^{2}. In particular, the structure function ratio F_{LU}^{sinϕ}/F_{UU} has been determined, where F_{LU}^{sinϕ} is a twist-3 quantity that can reveal novel aspects of emergent hadron mass and quark-gluon correlations within the nucleon. The data's impact on the evolving understanding of the underlying reaction mechanisms and their kinematic variation is explored using theoretical models for the different contributing transverse momentum dependent parton distribution functions.

The first results on the ${\ensuremath{\sigma}}_{L{T}^{\ensuremath{'}}}$ structure function in exclusive ${\ensuremath{\pi}}^{0}p$ electroproduction at invariant masses of the final state of $1.5\phantom{\rule{4.pt}{0ex}}\text{GeV}<W<1.8\phantom{\rule{4.pt}{0ex}}\text{GeV}$ and in the range of photon virtualities $0.4\phantom{\rule{4pt}{0ex}}{\mathrm{GeV}}^{2}<{Q}^{2}<1.0\phantom{\rule{4pt}{0ex}}{\mathrm{GeV}}^{2}$ were obtained from data on beam spin asymmetries and differential cross sections measured with the CLAS detector at Jefferson Lab. The Legendre moments determined from the ${\ensuremath{\sigma}}_{L{T}^{\ensuremath{'}}}$ structure function have demonstrated sensitivity to the contributions from the nucleon resonances in the second and third resonance regions. These new data on the beam spin asymmetries in ${\ensuremath{\pi}}^{0}p$ electroproduction extend the opportunities for the extraction of the nucleon resonance electro-excitation amplitudes in the mass range above 1.6 GeV.

We report on the measurement of the beam spin asymmetry in the deeply virtual Compton scattering off ^4He using the CEBAF Large Acceptance Spectrometer (CLAS) at Jefferson Lab using a 6 GeV longitudinally polarized electron beam incident on a pressurized ^4He gaseous target. We detail the method used to ensure the exclusivity of the measured reactions, in particular the upgrade of CLAS with a radial time projection chamber to detect the low-energy recoiling ^4He nuclei and an inner calorimeter to extend the photon detection acceptance at forward angles. Our results confirm the theoretically predicted enhancement of the coherent (e^4He→ e'^4He'γ') beam spin asymmetries compared to those observed on the free proton, while the incoherent (e^4He→ e'p'γ'X') asymmetries exhibit a 30% suppression. From the coherent data, we were able to extract, in a model-independent way, the real and imaginary parts of the only ^4He Compton form factor, H_A, leading the way toward 3D imaging of the partonic structure of nuclei.

M. Yoshimoto, J. K. Ahn, B. Bassalleck, H. Ekawa, Y. Endo, M. Fujita, Y. Han, T. Hashimoto, S. H. Hayakawa, K. Hicks, K. Hoshino, S. Hoshino, S. H. Hwang, Y. Ichikawa, M. Ichikawa, K. Imai, Y. Ishikawa, H. Kanauchi, A. Kasagi, S. H. Kim, S. Kinbara, P. M. Lin, T. L. Ma, K. Miwa, A. T. Moe, Y. Nagase, K. Nakazawa, T. Nanamura, M. Naruki, A. N. L. Nyaw, J. Pochodzalla, H. Sako, S. Sato, M. M. Soe, M. K. Soe, J. Y. Sohn, H. Takahashi, T. Takahashi, H. Tamura, K. Tanida, A. M. M. Theint, K. T. Tint, M. Ukai, T. O. Yamamoto, S. B. Yang, C. S. Yoon, J. Yoshida, D. H. Zhang, and Z. Zhang

We report on the measurement of the beam spin asymmetry in the deeply virtual Compton scattering off He-4 using the CEBAF Large Acceptance Spectrometer (CLAS) at Jefferson Lab using a 6 GeV longitudinally polarized electron beam incident on a pressurized He-4 gaseous target. We detail the method used to ensure the exclusivity of the measured reactions, in particular the upgrade of CLAS with a radial time projection chamber to detect the low-energy recoiling He-4 nuclei and an inner calorimeter to extend the photon detection acceptance at forward angles. Our results confirm the theoretically predicted enhancement of the coherent (e(4)He -> e'4He'gamma') beam spin asymmetries compared to those observed on the free proton, while the incoherent (e(4)He -> e'p'gamma'X') asymmetries exhibit a 30% suppression. From the coherent data, we were able to extract, in a model-independent way, the real and imaginary parts of the only He-4 Compton form factor, H-A, leading the way toward 3D imaging of the partonic structure of nuclei.

The reaction γp→K+Λ(1520) using photoproduction data from the CLAS g12 experiment at Jefferson Lab is studied. The decay of Λ(1520) into two exclusive channels, Σ+π− and Σ−π+, is studied from the detected K+, π+, and π− particles. A good agreement is established for the Λ(1520) differential cross sections with the previous CLAS measurements. The differential cross sections as a function of center-of-mass angle are extended to higher photon energies. Newly added are the differential cross sections as a function of invariant four-momentum transfer t, which is the natural variable to use for a theoretical model based on a Regge-exchange reaction mechanism. No new N* resonances decaying into the K+Λ(1520) final state are found.

The observation of beam spin asymmetries in two-pion production in semi-inclusive deep inelastic scattering off an unpolarized proton target is reported. The data presented here were taken in the fall of 2018 with the CLAS12 spectrometer using a 10.6 GeV longitudinally spin-polarized electron beam delivered by CEBAF at JLab. The measured asymmetries provide the first opportunity to extract the parton distribution function e(x), which provides information about the interaction between gluons and quarks, in a collinear framework that offers cleaner access than previous measurements. The asymmetries also constitute the first ever signal sensitive to the helicity-dependent two-pion fragmentation function G_{1}^{⊥}. A clear sign change is observed around the ρ mass that appears in model calculations and is indicative of the dependence of the produced pions on the helicity of the fragmenting quark.

We report measurements of π+ and π0 meson photoproduction from longitudinally spin-polarised protons by an energy tagged (0.73-2.3 GeV) and linearly polarised photon beam. A close to complete solid angle coverage for the reaction products was provided by the CEBAF Large Acceptance Spectrometer at Jefferson Laboratory. The double-polarisation observable G is extracted from Maximum Likelihood fits to the data, enabling the first accurate determination for the reaction γ→p→→π+n, while also significantly extending the kinematic coverage for γ→p→→π0p. This large data set provides an important constraint on the properties and spectrum of excited nucleon states decaying to Nπ in the mass range from 1.4 to 2.2 GeV, as well as for background (non-resonant) photoproduction processes. The considerable improvement achieved in the description of the observable G within the SAID and Bonn-Gatchina approaches after implementation of our data, illustrates that the partial-wave analyses now significantly extend the knowledge on Nπ photoproduction amplitudes at W>1.8 GeV. A partial-wave analysis using the new high-precision data set has a large impact on the extracted properties of high-spin nucleon excited states.

Strange matter is believed to exist in the cores of neutron stars based on simple kinematics. If this is true, then hyperon-nucleon interactions will play a significant part in the neutron star equation of state (EOS). Yet, compared to other elastic scattering processes, there is very little data on Λ-N scattering. This experiment utilized the CLAS detector to study the Λ p →Λ p elastic scattering cross section in the incident Λ momentum range 0.9-2.0 GeV/c. This is the first data on this reaction in several decades. The new cross sections have significantly better accuracy and precision than the existing world data, and the techniques developed here can also be used in future experiments.

The first results on the σ_LT' structure function in exclusive π^0p electroproduction at invariant masses of the final state of 1.5 GeV < W < 1.8 GeV and in the range of photon virtualities 0.4 GeV^2 < Q^2 < 1.0 GeV^2 were obtained from data on beam spin asymmetries and differential cross sections measured with the CLAS detector at Jefferson Lab. The Legendre moments determined from the σ_LT' structure function have demonstrated sensitivity to the contributions from the nucleon resonances in the second and third resonance regions. These new data on the beam spin asymmetries in π^0p electroproduction extend the opportunities for the extraction of the nucleon resonance electroexcitation amplitudes in the mass range above 1.6 GeV.

The first results on the $\sigma_{LT'}$ structure function in exclusive $\pi^0p$ electroproduction at invariant masses of the final state of 1.5 GeV $<$ $W$ $<$ 1.8 GeV and in the range of photon virtualities 0.4 GeV$^2 < Q^2 < 1.0$ GeV$^2$ were obtained from data on beam spin asymmetries and differential cross sections measured with the CLAS detector at Jefferson Lab. The Legendre moments determined from the $\sigma_{LT'}$ structure function have demonstrated sensitivity to the contributions from the nucleon resonances in the second and third resonance regions. These new data on the beam spin asymmetries in $\pi^0p$ electroproduction extend the opportunities for the extraction of the nucleon resonance electroexcitation amplitudes in the mass range above 1.6 GeV.