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The proton is composed of quarks and gluons, bound by the most elusive mechanism of strong interaction called confinement. In this work, the dynamics of quarks and gluons are investigated using deeply virtual Compton scattering (DVCS): produced by a multi-GeV electron, a highly virtual photon scatters off the proton which subsequently radiates a high energy photon. Similarly to holography, measuring not only the magnitude but also the phase of the DVCS amplitude allows to perform 3D images of the internal structure of the proton. The phase is made accessible through the quantum-mechanical interference of DVCS with the Bethe-Heitler (BH) process, in which the final photon is emitted by the electron rather than the proton. We report herein the first full determination of the BH-DVCS interference by exploiting the distinct energy dependences of the DVCS and BH amplitudes. In the high energy regime where the scattering process is expected to occur off a single quark in the proton, these accurate measurements show an intriguing sensitivity to gluons, the carriers of the strong interaction.
Beam helicity independent cross sections. The first systematic uncertainty is the combined correlated systematic uncertainty, the second is the point-to-point systematic uncertainty to add quadratically to the statistical uncertainty.
Beam helicity dependent cross sections. The first systematic uncertainty is the combined correlated systematic uncertainty, the second is the point-to-point systematic uncertainty to add quadratically to the statistical uncertainty.
Beam helicity independent cross sections. The first systematic uncertainty is the combined correlated systematic uncertainty, the second is the point-to-point systematic uncertainty to add quadratically to the statistical uncertainty.
The process $e^+e^-\to\omega\eta\pi^0$ is studied in the energy range $1.45-2.00$ GeV using data with an integrated luminosity of 33 pb$^{-1}$ accumulated by the SND detector at the $e^+e^-$ collider VEPP-2000. The $e^+e^-\to\omega\eta\pi^0$ cross section is measured for the first time. The cross section has a threshold near 1.75 GeV. Its value is about 2 nb in the energy range $1.8-2.0$ GeV. The dominant intermediate state for the process $e^+e^- \to \omega\eta\pi^0$ is found to be $\omega a_0(980)$.
The energy interval, integrated luminosity ($L$), number of selected events ($N$), estimated number of background events ($N_{bkg}$), detection efficiency for $e^+e^-\to\omega\eta\pi^0\to 7\gamma$ events ($\epsilon$), radiative correction ($\delta+1$), and $e^+e^-\to\omega\eta\pi^0$ Born cross section ($\sigma$). The shown cross-section errors are statistical. The systematic error is 4.2%. The 90% confidence level upper limits are listed for the first two energy intervals.
We have studied ω photoproduction using 7.5- to 10.5-GeV tagged photons. Cross sections from hydrogen lie 22% below the bubble chamber results of Ballam et al., but have a similar slope. Density matrices indicate approximate s-channel helicity conservation. The proton-neutron cross-section difference is midway between zero and the value suggested by the γp−γn total-cross-section difference. Fits to the cross sections for D, Be, and Cu and those for Be, C, Al, Cu, and Pb from a previous experiment yield σωN=25.4±2.7 mb and γω24π=7.6±1.2.
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FORWARD CROSS SECTION IS 366 +- 49 MUB/GEV**2 AND SLOPE IS 47.1 +- 8.0 GEV**-2.
An experimental study of $\omega$ photoproduction on the proton was conducted by using the Crystal Ball and TAPS multiphoton spectrometers together with the photon tagging facility at the Mainz Microtron MAMI. The $\gamma p\to\omega p$ differential cross sections are measured from threshold to the incident-photon energy $E_\gamma=1.40$ GeV ($W=1.87$ GeV for the center-of-mass energy) with 15-MeV binning in $E_\gamma$ and full production-angle coverage. The quality of the present data near threshold gives access to a variety of interesting physics aspects. As an example, an estimation of the $\omega N$ scattering length $\alpha_{\omega p}$ is provided.
Total cross section as a function of c.m. energy W.
Differential cross section at W= 1.7245 GeV
Differential cross section at W= 1.7319 GeV
The analysis of 1466 events of the type e + e − → μ ± μ ± , in the time-lifke range from 1.44 to 9.00 GeV 2 , sh that the absolute value of the cross-section and its energy dependence follow QED expectations within (± 3.2%) and (± 1.2%), respectively.
The cross section of the reaction $e^+ e^- \to \mu^\pm \mu^\mp$ integrated over the experimental apparatus at 14 values of the colliding beam energy $E$ corresponding to total centre-of-mass energy $\sqrt{s}=2E$ from 1.2 to 3.0 GeV.
The forward $\eta$ mesons production has been observed by the Large Hadron Collider forward (LHCf) experiment in proton-proton collision at $\sqrt{s}$=13 TeV. This paper presents the measurement of the inclusive production rate of $\eta$ in $p_T<$ 1.1 GeV/c, expressed as a function of the Feynman-x variable. These results are compared with the predictions of several hadronic interaction models commonly used for the modelling of the air showers produced by ultra-high energy cosmic rays. This is both the first measurement of $\eta$ mesons from LHCf and the first time a particle containing strange quarks has been observed in the forward region for high-energy collisions. These results will provide a powerful constraint on hadronic interaction models for the purpose of improving the understanding of the processes underlying the air showers produced in the Earth's atmosphere by ultra-energetic cosmic rays.
Inclusive eta production rate in $p_{T}<1.10\,GeV/c$
We have observed the production of the Ds± by a high-energy neutron beam on nuclear targets. The Ds± was observed in the decay mode Ds±→φπ±, φ→K+K−. The average of the inclusive cross sections for Ds+ and Ds− hadroproduction is measured to be BdσdxF=2.85±0.80±0.86 μb/nucleon at xF=0.175 on the assumption of a linear A dependence, where B≡Γ(Ds±→φπ±)Γ(Ds±→all).
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