376 research outputs found
Observation of Correlations Between Spin and Transverse Momenta in Back-to-Back Dihadron Production at CLAS12
We report the first measurements of deep inelastic scattering spin-dependent azimuthal asymmetries in back-to-back dihadron electroproduction in the deep inelastic scattering process. In this reaction, two hadrons are produced in opposite hemispheres along the z axis in the virtual photon-target nucleon center-of-mass frame, with the first hadron produced in the current-fragmentation region and the second in the target-fragmentation region. The data were taken with longitudinally polarized electron beams of 10.2 and 10.6 GeV incident on an unpolarized liquid-hydrogen target using the CLAS12 spectrometer at Jefferson Lab. Observed nonzero sinΔϕ modulations in ep→e\u27pπ+ X events, where Δϕ is the difference of the azimuthal angles of the proton and pion in the virtual photon and target nucleon center-of-mass frame, indicate that correlations between the spin and transverse momenta of hadrons produced in the target- and current-fragmentation regions may be significant. The measured beam-spin asymmetries provide a first access in dihadron production to a previously unexplored leading-twist spin- and transverse-momentum-dependent fracture function. The fracture functions describe the hadronization of the target remnant after the hard scattering of a virtual photon off a quark in the target particle and provide a new avenue for studying nucleonic structure and hadronization
Beam-Recoil Transferred Polarization in K+Y Electroproduction in the Nucleon Resonance Region with CLAS12
Beam-recoil transferred polarizations for the exclusive electroproduction of K + Λ and K + Σ0 final states from an unpolarized proton target have been measured using the CLAS12 spectrometer at Jefferson Laboratory. The measurements at beam energies of 6.535 and 7.546 GeV span the range of four-momentum transfer Q2 from 0.3 to 4.5 GeV2 and invariant energy W from 1.6 to 2.4 GeV, while covering the full center-of-mass angular range of the K+. These new data extend the existing hyperon polarization data from CLAS in a similar kinematic range but from a significantly larger dataset. They represent an important addition to the world data, allowing for better exploration of the reaction mechanism in strangeness production processes, for further understanding of the spectrum and structure of excited nucleon states, and for improved insight into the strong interaction in the regime of nonperturbative dynamics
Comment on the narrow structure reported by Amaryan et al
The CLAS Collaboration provides a comment on the physics interpretation of
the results presented in a paper published by M. Amaryan et al. regarding the
possible observation of a narrow structure in the mass spectrum of a
photoproduction experiment.Comment: to be published in Physical Review
Exclusive ⁻ Electroproduction Off The Neutron In Deuterium In The Resonance Region
New results for the exclusive and quasifree cross sections off neutrons bound in deuterium vn(p) → pπ− (p) are presented over a wide final state hadron angle range with a kinematic coverage of the invariant mass (W) up to 1.825 GeV and the four-momentum transfer squared (Q2) from 0.4 to 1.0 GeV2. The exclusive structure functions were extracted and their Legendre moments were obtained. Final-state-interaction contributions have been kinematically separated from the extracted quasifree cross sections off bound neutrons solely based on the analysis of the experimental data. These new results will serve as long-awaited input for phenomenological analyses to extract the Q2 evolution of previously unavailable n → N∗ electroexcitation amplitudes and to improve state-of-the-art models of neutrino scattering off nuclei by augmenting the already available results from free protons
Photoproduction of K+K− meson pairs on the proton
The exclusive reaction γp→pK+K− was studied in the photon energy range 3.0–3.8 GeV and momentum transfer range 0.6<−t<1.3 GeV2. Data were collected with the CLAS detector at the Thomas Jefferson National Accelerator Facility. In this kinematic range the integrated luminosity was approximately 20 pb−1. The reaction was isolated by detecting the K+ and the proton in CLAS, and reconstructing the K− via the missing-mass technique. Moments of the dikaon decay angular distributions were extracted from the experimental data. Besides the dominant contribution of the ϕ meson in the P wave, evidence for S−P interference was found. The differential production cross sections dσ/dt for individual waves in the mass range of the ϕ resonance were extracted and compared to predictions of a Regge-inspired model. This is the first time the t-dependent cross section of the S-wave contribution to the elastic K+K− photoproduction has been measured
Induced polarization of {\Lambda}(1116) in kaon electroproduction
We have measured the induced polarization of the in the
reaction , detecting the scattered and
in the final state along with the proton from the decay .The present study used the CEBAF Large Acceptance Spectrometer (CLAS),
which allowed for a large kinematic acceptance in invariant energy
( GeV) and covered the full range of the kaon production
angle at an average momentum transfer GeV.In this experiment a
5.50 GeV electron beam was incident upon an unpolarized liquid-hydrogen target.
We have mapped out the and kaon production angle dependencies of the
induced polarization and found striking differences from photoproduction data
over most of the kinematic range studied. However, we also found that the
induced polarization is essentially independent in our kinematic domain,
suggesting that somewhere below the covered here there must be a strong
dependence. Along with previously published photo- and electroproduction
cross sections and polarization observables, these data are needed for the
development of models, such as effective field theories, and as input to
coupled-channel analyses that can provide evidence of previously unobserved
-channel resonances.Comment: 13 figure
Demonstration of a novel technique to measure two-photon exchange effects in elastic scattering
The discrepancy between proton electromagnetic form factors extracted using
unpolarized and polarized scattering data is believed to be a consequence of
two-photon exchange (TPE) effects. However, the calculations of TPE corrections
have significant model dependence, and there is limited direct experimental
evidence for such corrections. We present the results of a new experimental
technique for making direct comparisons, which has the potential to
make precise measurements over a broad range in and scattering angles. We
use the Jefferson Lab electron beam and the Hall B photon tagger to generate a
clean but untagged photon beam. The photon beam impinges on a converter foil to
generate a mixed beam of electrons, positrons, and photons. A chicane is used
to separate and recombine the electron and positron beams while the photon beam
is stopped by a photon blocker. This provides a combined electron and positron
beam, with energies from 0.5 to 3.2 GeV, which impinges on a liquid hydrogen
target. The large acceptance CLAS detector is used to identify and reconstruct
elastic scattering events, determining both the initial lepton energy and the
sign of the scattered lepton. The data were collected in two days with a
primary electron beam energy of only 3.3 GeV, limiting the data from this run
to smaller values of and scattering angle. Nonetheless, this measurement
yields a data sample for with statistics comparable to those of the
best previous measurements. We have shown that we can cleanly identify elastic
scattering events and correct for the difference in acceptance for electron and
positron scattering. The final ratio of positron to electron scattering:
for GeV and
Towards a resolution of the proton form factor problem: new electron and positron scattering data
There is a significant discrepancy between the values of the proton electric
form factor, , extracted using unpolarized and polarized electron
scattering. Calculations predict that small two-photon exchange (TPE)
contributions can significantly affect the extraction of from the
unpolarized electron-proton cross sections. We determined the TPE contribution
by measuring the ratio of positron-proton to electron-proton elastic scattering
cross sections using a simultaneous, tertiary electron-positron beam incident
on a liquid hydrogen target and detecting the scattered particles in the
Jefferson Lab CLAS detector. This novel technique allowed us to cover a wide
range in virtual photon polarization () and momentum transfer
() simultaneously, as well as to cancel luminosity-related systematic
errors. The cross section ratio increases with decreasing at . This measurement is consistent with the size of the form
factor discrepancy at GeV and with hadronic calculations
including nucleon and intermediate states, which have been shown to
resolve the discrepancy up to GeV.Comment: 6 pages, 4 figures, submitted to PR
Cross sections for the γp→K*+Λ and γp→K*+Σ0 reactions measured at CLAS
The first high-statistics cross sections for the reactions γp→K*+Λ and γp→K*+Σ0 were measured using the CLAS detector at photon energies between threshold and 3.9 GeV at the Thomas Jefferson National Accelerator Facility. Differential cross sections are presented over the full range of the center-of-mass angles, and then fitted to Legendre polynomials to extract the total cross section. Results for the K*+Λ final state are compared with two different calculations in an isobar and a Regge model, respectively. Theoretical calculations significantly underestimate the K*+Λ total cross sections between 2.1 and 2.6 GeV, but are in better agreement with present data at higher photon energies
Transverse Polarization of in Photoproduction on a Hydrogen Target in CLAS
Experimental results on the hyperon transverse polarization
in photoproduction on a hydrogen target using the CLAS detector at Jefferson
laboratory are presented. The was reconstructed in the
exclusive reaction via the
decay mode. The was reconstructed in the
invariant mass of two oppositely charged pions with the identified in
the missing mass of the detected final state. Experimental data
were collected in the photon energy range = 1.0-3.5 GeV
( range 1.66-2.73 GeV). We observe a large negative polarization of
up to 95%. As the mechanism of transverse polarization of hyperons produced in
unpolarized photoproduction experiments is still not well understood, these
results will help to distinguish between different theoretical models on
hyperon production and provide valuable information for the searches of missing
baryon resonances.Comment: pages 1
- …