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Register a new userUpdated analysis of recent results on electron and positron elastic scattering on proton
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We discuss recent experimental results concerning the cross section ratio of positron over electron elastic scattering on protons, and compare with the predictions of a pre-existent calculation. The deviation from unity of this ratio, $i.e.$, a charge asymmetry different from zero, is the signature of contributions beyond the Born approximation. After reviewing the published results, we compare the elastic data to a calculation which includes the diagram corresponding to two-photon exchange. It turns out that all the data on the cross section ratio, in the limit of their precision, do not show evidence of enhanced two-photon contribution beyond the expected percent level. Our results confirm that experimental evidence for a large contribution of two-photon exchange is not yet found.
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We review recent theoretical and experimental progress on the role of two-photon exchange (TPE) in electron-proton scattering at low to moderate momentum transfers. We make a detailed comparison and analysis of the results of competing experiments on the ratio of e+p to e-p elastic scattering cross sections, and of the theoretical calculations describing them. A summary of the current experimental situation is provided, along with an outlook for future experiments.
We apply a subtracted dispersion relation formalism with the aim to improve predictions for the two-photon exchange corrections to elastic electron-proton scattering observables at finite momentum transfers. We study the formalism on the elastic contribution, and make a detailed comparison with existing data for unpolarized cross sections as well as polarization transfer observables.
The differential cross section for elastic scattering of deuterons on electrons at rest is calculated taking into account the QED radiative corrections to the leptonic part of interaction. These model-independent radiative corrections arise due to emission of the virtual and real soft and hard photons as well as to vacuum polarization. We consider an experimental setup where both final particles are recorded in coincidence and their energies are determined within some uncertainties. The kinematics, the cross section, and the radiative corrections are calculated and numerical results are presented.
We report results on the total and elastic cross sections in proton-proton collisions at $sqrt{s}=200$ GeV obtained with the Roman Pot setup of the STAR experiment at the Relativistic Heavy Ion Collider (RHIC). The elastic differential cross section was measured in the squared four-momentum transfer range $0.045 leq -t leq 0.135$ GeV$^2$. The value of the exponential slope parameter $B$ of the elastic differential cross section $dsigma/dt sim e^{-Bt}$ in the measured $-t$ range was found to be $B = 14.32 pm 0.09 (stat.)^{scriptstyle +0.13}_{scriptstyle -0.28} (syst.)$ GeV$^{-2}$. The total cross section $sigma_{tot}$, obtained from extrapolation of the $dsigma/dt$ to the optical point at $-t = 0$, is $sigma_{tot} = 54.67 pm 0.21 (stat.) ^{scriptstyle +1.28}_{scriptstyle -1.38} (syst.)$ mb. We also present the values of the elastic cross section $sigma_{el} = 10.85 pm 0.03 (stat.) ^{scriptstyle +0.49}_{scriptstyle -0.41}(syst.)$ mb, the elastic cross section integrated within the STAR $t$-range $sigma^{det}_{el} = 4.05 pm 0.01 (stat.) ^{scriptstyle+0.18}_{scriptstyle -0.17}(syst.)$ mb, and the inelastic cross section $sigma_{inel} = 43.82 pm 0.21 (stat.) ^{scriptstyle +1.37}_{scriptstyle -1.44} (syst.)$ mb. The results are compared with the world data.
We estimate the target-normal single-spin asymmetry at nearly forward angles in elastic electron-nucleon scattering. In the leading-order approximation, this asymmetry is proportional to the imaginary part of the two-photon exchange (TPE) amplitude, which can be expressed as an integral over the doubly virtual Compton scattering (VVCS) tensor. We develop a model that parametrizes the VVCS tensor for the case of nearly forward scattering angles. Our parametrization ensures a proper normalization of the imaginary part of the TPE amplitude on the well-known forward limit expression, which is given in terms of nucleon structure functions measurable in inelastic electron-nucleon scattering experiments. We discuss applicability limits of our theory and provide target-normal single-spin asymmetry predictions for both elastic electron-proton and electron-neutron scattering.
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