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Register a new userExcited electron contribution to the e+e- -> gammagamma cross-section
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Authors
Brigitte Vachon
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The differential cross-section for the process e+e- -> gammagamma is calculated assuming the presence of excited electrons with a chiral magnetic coupling. This calculation permits constraining the excited electron coupling using the same theoretical framework as the one generally used for direct production searches.
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First correction to the high-energy asymptotics of the total $e^+e^-$ photoproduction cross section in the electric field of a heavy atom is derived with the exact account of this field. The consideration is based on the use of the quasiclassical electron Green function in an external electric field. The next-to-leading correction to the cross section is discussed. The influence of screening on the Coulomb corrections is examined in the leading approximation. It turns out that the high-energy asymptotics of the corresponding correction is independent of the photon energy. In the region where both produced particles are relativistic, the corrections to the high-energy asymptotics of the electron (positron) spectrum are derived. Our results for the total cross section are in good agreement with experimental data for photon energies down to a few $MeV$. In addition, the corrections to the bremsstrahlung spectrum are obtained from the corresponding results for pair production.
In the experiment with the SND detector at the VEPP-2M $e^+e^-$ collider measuring the $e^+e^-to etagamma$ cross section in the energy range $0.6<sqrt{s}<1.38 mathrm{GeV}$ the reanalysis of data is performed. The goal is to improve the accuracy of the previous results by analysing ambiguities in the approximation of energy dependence of the $e^+e^-to etagamma$ cross section, which were not taken into account in our previous study. We report new results on the approximation of the $e^+e^-to etagamma$ cross section based on Vector Dominance Model under new model parameter assumptions.
Using a total of 11.0 fb$^{-1}$ of $e^{+}e^{-}$ collision data with center-of-mass energies between 4.009 GeV and 4.6 GeV and collected with the BESIII detector at BEPCII, we measure fifteen exclusive cross sections and effective form factors for the process $e^{+}e^{-}rightarrowXi^{-}barXi^{+}$ by means of a single baryon-tag method. After performing a fit to the dressed cross section of $e^{+}e^{-}rightarrowXi^{-}barXi^{+}$, no significant $psi(4230)$ or $psi(4260)$ resonance is observed in the $Xi^{-}barXi^{+}$ final states, and upper limits at the 90% confidence level on $Gamma_{ee}mathcal{B}$ for the processes $psi(4230)$/$psi(4260)rightarrowXi^{-}barXi^{+}$ are determined. In addition, an excited $Xi$ baryon at 1820 MeV/$c^{2}$ is observed with a statistical significance of 6.2 $sim$ 6.5$sigma$ by including the systematic uncertainty, and the mass and width are measured to be $M = (1825.5 pm 4.7 pm 4.7)$~MeV/$c^{2}$ and $Gamma = (17.0 pm 15.0 pm 7.9)$~MeV, which confirms the existence of the $J^{P}=frac{3}{2}^{-}$ state $Xi(1820)$.
We suggest returning to a different presentation of the e+e- to bar{f} f data off the Z peak, with the hope of using zeroes of specific amplitudes to enhance the sensitivity to new physics.
The cross section for the process $e^+e^- to omegaeta$ is measured in the center-of-mass energy range 1.34--2.00 GeV. The analysis is based on data collected with the SND detector at the VEPP-2000 $e^+e^-$ collider. The measured $e^+e^- to omegaeta$ cross section is the most accurate to date. A significant discrepancy is observed between our data and previous BABAR measurement.
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