A
bstract
A comprehensive set of azimuthal single-spin and double-spin asymmetries in semi-inclusive leptoproduction of pions, charged kaons, protons, and antiprotons from transversely polarized ...protons is presented. These asymmetries include the previously published HERMES results on Collins and Sivers asymmetries, the analysis of which has been extended to include protons and antiprotons and also to an extraction in a three-dimensional kinematic binning and enlarged phase space. They are complemented by corresponding results for the remaining four single-spin and four double-spin asymmetries allowed in the one-photon-exchange approximation of the semi-inclusive deep-inelastic scattering process for target-polarization orientation perpendicular to the direction of the incoming lepton beam. Among those results, significant non-vanishing cos (
ϕ−ϕ
S
) modulations provide evidence for a sizable worm-gear (II) distribution,
g
1
T
q
x
p
T
2
. Most of the other modulations are found to be consistent with zero with the notable exception of large sin (
ϕ
S
) modulations for charged pions and
K
+
.
Samples made from natural bismuth were exposed in 60 MeV end-point bremsstrahlung beam. In this paper, a simple model for determination the share of two ways of
203
Pb formation: by the decay of
203
...Bi, produced in
209
Bi(γ,6n)
203
Bi reaction and by
209
Bi(γ,p 5n)
203
Pb reaction is described. The method employs the ratio of
203
Pb and
203
Bi nuclei numbers and activities at the end of the exposure as the input value. This ratio was estimated from gamma spectra measured after irradiation of natural Bi sample. It was found that the rate of production of
203
Pb by
209
Bi(γ,p 5n)
203
Pb reaction is about 6% of the
203
Bi production rate in the
209
Bi(γ,6n)
203
Bi reaction. Obtained result is compared with TALYS based estimation.
In this work, we report on the measurement of the beam asymmetry $\Sigma$ for the reactions $\vec{\gamma}p\rightarrow p\eta$ and $\vec{\gamma}p \rightarrow p\eta^{\prime}$ from the GlueX experiment, ...using an 8.2–8.8-GeV linearly polarized tagged photon beam incident on a liquid hydrogen target in Hall D at Jefferson Lab. These measurements are made as a function of momentum transfer $-t$, with significantly higher statistical precision than our earlier $\eta$ measurements, and are the first measurements of $\eta^{\prime}$ in this energy range. We compare the results to theoretical predictions based on $t$--channel quasi-particle exchange. Furthermore, we compare the ratio of $\Sigma_{\eta}$ to $\Sigma_{\eta^{\prime}}$ to these models, as this ratio is predicted to be sensitive to the amount of $s\bar{s}$ exchange in the production. We find that photoproduction of both $\eta$ and $\eta^{\prime}$ is dominated by natural parity exchange with little dependence on $-t$.
.
The spin-exchange collision cross-section for hydrogen atoms has been measured for the first time in the low temperature range 40–100 K by using the polarized hydrogen gas target of the HERMES ...experiment at DESY (Hamburg, Germany). The results agree with a previous measurement in the overlapping temperature region 80–100 K, while seem to hint an increasing behaviour with temperature in the region 50–80 K.
We report on the measurement of spin density matrix elements of the Λ(1520) in the photoproduction reaction γp→Λ(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 Laboratory using a linearly polarized photon beam with Eγ=8.2GeV–8.8GeV. These are the first such measurements in this photon energy range. Results are presented in bins of momentum transfer squared, -(t-t0). We compare the results with a Reggeon exchange model and determine that natural exchange amplitudes are dominant in Λ(1520) photoproduction.
We report the first measurement of the average of the electron-proton and positron-proton elastic scattering cross sections. This lepton charge-averaged cross section is insensitive to the leading ...effects of hard two-photon exchange, giving more robust access to the proton's electromagnetic form factors. The cross section was extracted from data taken by the OLYMPUS experiment at DESY, in which alternating stored electron and positron beams were scattered from a windowless gaseous hydrogen target. Elastic scattering events were identified from the coincident detection of the scattered lepton and recoil proton in a large-acceptance toroidal spectrometer. The luminosity was determined from the rates of Møller, Bhabha, and elastic scattering in forward electromagnetic calorimeters. The data provide some selectivity between existing form factor global fits and will provide valuable constraints to future fits.
We report the latest results of azimuthal asymmetries in the DVCS process measured at the HERMES experiment on unpolarized hydrogen and deuterium targets. Exploiting the ability of HERA to provide ...lepton beams with both charges and spin orientations, it is possible to extract simultaneously asymmetry amplitudes attributed to the pure DVCS process and to the interference between the Bethe-Heitler and DVCS processes. The results are compared to the theoretical calculations.
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