This study reports new exclusive cross sections for ep→e'π+π–p' using the CLAS detector at Jefferson Laboratory. These results are presented for the first time at photon virtualities 2.0 GeV2 < Q2 < ...5.0 GeV2 in the center-of-mass energy range 1.4 GeV < W < 2.0 GeV, which covers a large part of the nucleon resonance region. Using a model developed for the phenomenological analysis of electroproduction data, we see strong indications that the relative contributions from the resonant cross sections at W < 1.74 GeV increase with Q2. These data considerably extend the kinematic reach of previous measurements. Exclusive ep→e'π+π–p' cross section measurements are of particular importance for the extraction of resonance electrocouplings in the mass range above 1.6 GeV.
We present final results on the photon electroproduction ($\vec{e}p\rightarrow ep\gamma$) cross section in the deeply virtual Compton scattering (DVCS) regime and the valence quark region from ...Jefferson Lab experiment E00-110. Results from an analysis of a subset of these data were published before, but the analysis has been improved which is described here at length, together with details on the experimental setup. Furthermore, additional data have been analyzed resulting in photon electroproduction cross sections at new kinematic settings, for a total of 588 experimental bins. Results of the $Q^2$- and $x_B$-dependences of both the helicity-dependent and helicity-independent cross sections are discussed. The $Q^2$-dependence illustrates the dominance of the twist-2 handbag amplitude in the kinematics of the experiment, as previously noted. Thanks to the excellent accuracy of this high luminosity experiment, it becomes clear that the unpolarized cross section shows a significant deviation from the Bethe-Heitler process in our kinematics, compatible with a large contribution from the leading twist-2 DVCS$^2$ term to the photon electroproduction cross section. The necessity to include higher-twist corrections in order to fully reproduce the shape of the data is also discussed. The DVCS cross sections in this study represent the final set of experimental results from E00-110, superseding the previous publication.
Differential cross sections of the reaction γd→K+Σ−(p) have been measured with the CLAS detector at Jefferson Lab using incident photons with energies between 1.1 and 3.6 GeV. This is the first ...complete set of strangeness photoproduction data on the neutron covering a broad angular range. At energies close to threshold and up to Eγ∼1.8 GeV, the shape of the angular distribution is suggestive of the presence of s-channel production mechanisms. For Eγ>1.8 GeV, a clear forward peak appears and becomes more prominent as the photon energy increases, suggesting contributions from t-channel production mechanisms. These data can be used to constrain future analysis of this reaction.
We report the first measurement of the transverse momentum dependence of double-spin asymmetries in semi-inclusive production of pions in deep-inelastic scattering off the longitudinally polarized ...proton. Data have been obtained using a polarized electron beam of 5.7 GeV with the CLAS detector at the Jefferson Lab (JLab). Modulations of single spin asymmetries over the azimuthal angle between lepton scattering and hadron production planes {phi} have been measured over a wide kinematic range in Bjorken x and virtual photon squared four-momentum Q{sup 2}. A significant nonzero sin2{phi} single spin asymmetry was observed for the first time indicating strong spin-orbit correlations for transversely polarized quarks in the longitudinally polarized proton.
Differential cross sections of the reaction gamma d-->K super(+)sigma super(-)(p) have been measured with the CLAS detector at Jefferson Lab using incident photons with energies between 1.1 and 3.6 ...GeV. This is the first complete set of strangeness photoproduction data on the neutron covering a broad angular range. At energies close to threshold and up to E sub() gamma not, vert, similar1.8 GeV, the shape of the angular distribution is suggestive of the presence of s-channel production mechanisms. For E sub() gamma 1.8 GeV, a clear forward peak appears and becomes more prominent as the photon energy increases, suggesting contributions from t-channel production mechanisms. These data can be used to constrain future analysis of this reaction.
This paper describes the Jas4pp framework for exploring physics cases and for detector-performance studies of future particle collision experiments. Jas4pp is a multi-platform Java program for ...numeric calculations, scientific visualization in 2D and 3D, storing data in various file formats and displaying collision events and detector geometries. It also includes complex data-analysis algorithms for function minimisation, regression analysis, event reconstruction (such as jet reconstruction), limit settings and other libraries widely used in particle physics. The framework can be used with several scripting languages, such as Python/Jython, Groovy and JShell. Several benchmark tests discussed in the paper illustrate significant improvements in the performance of the Groovy and JShell scripting languages compared to the standard Python implementation in C. The improvements for numeric computations in Java are attributed to recent enhancements in the Java Virtual Machine.
Measuring Deeply Virtual Compton Scattering on the neutron is one of the necessary steps to understand the structure of the nucleon in terms of Generalized Parton Distributions (GPDs). Neutron ...targets play a complementary role to transversely polarized proton targets in the determination of the GPD \(E\). This poorly known and poorly constrained GPD is essential to obtain the contribution of the quarks' angular momentum to the spin of the nucleon. DVCS on the neutron was measured for the first time selecting the exclusive final state by detecting the neutron, using the Jefferson Lab longitudinally polarized electron beam, with energies up to 10.6 GeV, and the CLAS12 detector. The extracted beam-spin asymmetries, combined with DVCS observables measured on the proton, allow a clean quark-flavor separation of the imaginary parts of the GPDs \(H\) and \(E\).
High-quality cross sections for the reaction γ
d
→ π
0
d
have been measured using the CLAS at Jefferson Lab over a wide energy range near and above the
η
-meson photoproduction threshold. At backward ...c.m. angles for the outgoing pions, we observe a resonance-like structure near
E
γ
= 700 MeV. Our model analysis shows that it can be explained by
η
excitation in the intermediate state. The effect is the result of the contribution of the
N
(1535)
S
11
-resonance to the amplitudes of the subprocesses occurring between the two nucleons and of a two-step process in which the excitation of an intermediate
η
-meson dominates.