.
We report on a high-statistics measurement of the most basic double-pionic fusion reaction
over the energy region of the
d
*
(2380) resonance by use of a polarized deuteron beam and observing the ...double fusion reaction in the quasifree scattering mode. The measurements were performed with the WASA detector setup at COSY. The data reveal substantial analyzing powers and confirm conclusions about the d
*
resonance obtained from unpolarized measurements. We also confirm the previous unpolarized data obtained under complementary kinematic conditions.
We report on a high-statistics measurement of the most basic double-pionic fusion reaction over the energy region of the d (*)(2380) resonance by use of a polarized deuteron beam and observing the ...double fusion reaction in the quasifree scattering mode. The measurements were performed with the WASA detector setup at COSY. The data reveal substantial analyzing powers and confirm conclusions about the d(*) resonance obtained from unpolarized measurements. We also confirm the previous unpolarized data obtained under complementary kinematic conditions.
The spin-exotic hybrid meson $\pi_{1}(1600)$ is predicted to have a large
decay rate to the $\omega\pi\pi$ final state. Using 76.6~pb$^{-1}$ of data
collected with the GlueX detector, we measure the ...cross sections for the
reactions $\gamma p \to \omega \pi^+ \pi^- p$, $\gamma p \to \omega \pi^0 \pi^0
p$, and $\gamma p\to\omega\pi^-\pi^0\Delta^{++}$ in the range $E_\gamma =$ 8-10
GeV. Using isospin conservation, we set the first upper limits on the
photoproduction cross sections of the $\pi^{0}_{1}(1600)$ and
$\pi^{-}_{1}(1600)$. We combine these limits with lattice calculations of decay
widths and find that photoproduction of $\eta'\pi$ is the most sensitive
two-body system to search for the $\pi_1(1600)$.
We report the measurement of spin-density matrix elements of the
$\Delta^{++}(1232)$ in the photoproduction reaction $\gamma p \to
\pi^-\Delta^{++}(1232)$ with the GlueX experiment in Hall D at ...Jefferson Lab.
The measurement used a linearly polarized photon beam with
$E_\gamma=8.2-8.8$~GeV and the statistical precision exceeds the previous
measurement from SLAC by three orders of magnitude for the momentum transfer
squared region $-t < 1.4$ GeV$^2$. The data are sensitive to the previously
undetermined relative sign between couplings in existing Regge exchange models.
Linear combinations of the extracted SDMEs allow for a decomposition into
natural and unnatural exchange amplitudes, which shows that the unnatural
exchange plays an important role in the low $-t$ region.
Phys. Rev. C 108, 055204 (2023) The GlueX experiment at Jefferson Lab studies photoproduction of mesons using
linearly polarized $8.5\,\text{GeV}$ photons impinging on a hydrogen target
which is ...contained within a detector with near-complete coverage for charged
and neutral particles. We present measurements of spin-density matrix elements
for the photoproduction of the vector meson $\rho$(770). The statistical
precision achieved exceeds that of previous experiments for polarized
photoproduction in this energy range by orders of magnitude. We confirm a high
degree of $s$-channel helicity conservation at small squared four-momentum
transfer $t$ and are able to extract the $t$-dependence of natural and
unnatural-parity exchange contributions to the production process in detail. We
confirm the dominance of natural-parity exchange over the full $t$ range. We
also find that helicity amplitudes in which the helicity of the incident photon
and the photoproduced $\rho(770)$ differ by two units are negligible for
$-t<0.5\,\text{GeV}^{2}/c^{2}$.
We report the total and differential cross sections for $J/\psi$
photoproduction with the large acceptance GlueX spectrometer for photon beam
energies from the threshold at 8.2~GeV up to 11.44~GeV ...and over the full
kinematic range of momentum transfer squared, $t$. Such coverage facilitates
the extrapolation of the differential cross sections to the forward ($t = 0$)
point beyond the physical region. The forward cross section is used by many
theoretical models and plays an important role in understanding $J/\psi$
photoproduction and its relation to the $J/\psi-$proton interaction. These
measurements of $J/\psi$ photoproduction near threshold are also crucial inputs
to theoretical models that are used to study important aspects of the gluon
structure of the proton, such as the gluon Generalized Parton Distribution
(GPD) of the proton, the mass radius of the proton, and the trace anomaly
contribution to the proton mass. We observe possible structures in the total
cross section energy dependence and find evidence for contributions beyond
gluon exchange in the differential cross section close to threshold, both of
which are consistent with contributions from open-charm intermediate states.
The proposed measurement is a dedicated study of the exclusive electroproduction process,1H(e,e'p)pi0, in the backward-angle regime (u-channel process) above the resonance region. The produced pi0 is ...emitted 180 degrees opposite to the virtual-photon momentum. This study also aims to apply the well-known Rosenbluth separation technique that provides the model-independent differential cross-sections at the never explored u-channel kinematics region. Currently, the "soft-hard transition" in u-channel meson production remains an interesting and unexplored subject. The available theoretical frameworks offer competing interpretations for the observed backward-angle cross section peaks. In a "soft" hadronic Regge exchange description, the backward meson production comes from the interference between nucleon exchange and the meson produced via re-scattering within the nucleon. Whereas in the "hard" GPD-like backward collinear factorization regime, the scattering amplitude factorizes into a hard subprocess amplitude and baryon to meson transition distribution amplitudes (TDAs), otherwise known as super skewed parton distributions (SuperSPDs). Both TDAs and SPDs are universal non-perturbative objects of nucleon structure accessible only through backward-angle kinematics. The separated cross sections:sigma_T,sigma_L and T/L ratio at Q2=2-6 GeV2, provide a direct test of two predictions from the TDA model. The magnitude and u-dependence of the separated cross sections also provide a direct connection to the re-scattering Regge picture. The extracted interaction radius (from u-dependence) at different Q2 can be used to study the soft-hard transition in the u-channel kinematics. The acquisition of these data will be an important step forward in validating the existence of a backward factorization scheme of the nucleon structure function and establishing its applicable kinematic range.
Phys. Rev. C 105, 035201 (2022) We report on the measurement of spin density matrix elements of the
$\Lambda(1520)$ in the photoproduction reaction $\gamma p\rightarrow
\Lambda(1520)K^+$, via its ...subsequent decay to $K^{-}p$. The measurement was
performed as part of the GlueX experimental program in Hall D at Jefferson Lab
using a linearly polarized photon beam with $E_\gamma =$ 8.2-8.8 GeV. These are
the first such measurements in this photon energy range. Results are presented
in bins of momentum transfer squared, $-(t-t_\text{0})$. We compare the results
with a Reggeon exchange model and determine that natural exchange amplitudes
are dominant in $\Lambda(1520)$ photoproduction.
The spin-exotic hybrid meson \(\pi_{1}(1600)\) is predicted to have a large decay rate to the \(\omega\pi\pi\) final state. Using 76.6~pb\(^{-1}\) of data collected with the GlueX detector, we ...measure the cross sections for the reactions \(\gamma p \to \omega \pi^+ \pi^- p\), \(\gamma p \to \omega \pi^0 \pi^0 p\), and \(\gamma p\to\omega\pi^-\pi^0\Delta^{++}\) in the range \(E_\gamma =\) 8-10 GeV. Using isospin conservation, we set the first upper limits on the photoproduction cross sections of the \(\pi^{0}_{1}(1600)\) and \(\pi^{-}_{1}(1600)\). We combine these limits with lattice calculations of decay widths and find that photoproduction of \(\eta'\pi\) is the most sensitive two-body system to search for the \(\pi_1(1600)\).
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