Eta photoproduction off the neutron at GRAAL: Evidence for a resonant structure at W=1.67 GeV

New (preliminary) data on eta photoproduction off the neutron are presented. These data reveal a resonant structure at W=1.67 GeV.Comment: 8 pages, 4 figures. Published in Proceedings of Workshop on the Physics of Excited Nucleons NSTAR2004, Grenoble, France, March 24 - 27, pg.19

Lowering the Light Speed Isotropy Limit: European Synchrotron Radiation Facility Measurements

The measurement of the Compton edge of the scattered electrons in GRAAL facility in European Synchrotron Radiation Facility (ESRF) in Grenoble with respect to the Cosmic Microwave Background dipole reveals up to 10 sigma variations larger than the statistical errors. We now show that the variations are not due to the frequency variations of the accelerator. The nature of Compton edge variations remains unclear, thus outlining the imperative of dedicated studies of light speed anisotropy

A new limit on the light speed isotropy from the GRAAL experiment at the ESRF

When the electrons stored in the ring of the European Synchrotron Radiation Facility (ESRF, Grenoble) scatter on a laser beam (Compton scattering in flight) the lower energy of the scattered electron spectra, the Compton Edge (CE), is given by the two body photon-electron relativistic kinematics and depends on the velocity of light. A precision measurement of the position of this CE as a function of the daily variations of the direction of the electron beam in an absolute reference frame provides a one-way test of Relativistic Kinematics and the isotropy of the velocity of light. The results of GRAAL-ESRF measurements improve the previously existing one-way limits, thus showing the efficiency of this method and the interest of further studies in this direction.Comment: Proceed. MG12 meeting, Paris, July, 200

Search for light-speed anisotropies using Compton scattering of high-energy electrons

Based on the high sensitivity of Compton scattering off ultra relativistic electrons, the possibility of anisotropies in the speed of light is investigated. The result discussed in this contribution is based on the gamma-ray beam of the ESRF's GRAAL facility (Grenoble, France) and the search for sidereal variations in the energy of the Compton-edge photons. The absence of oscillations yields the two-sided limit of 1.6 x 10^{-14} at 95 % confidence level on a combination of photon and electron coefficients of the minimal Standard Model Extension (mSME). This new constraint provides an improvement over previous bounds by one order of magnitude.Comment: Talk presented at the Fifth Meeting on CPT and Lorentz Symmetry, University of Indiana, June 28-July 2, 201

Limits on light-speed anisotropies from Compton scattering of high-energy electrons

The possibility of anisotropies in the speed of light relative to the limiting speed of electrons is considered. The absence of sidereal variations in the energy of Compton-edge photons at the ESRF's GRAAL facility constrains such anisotropies representing the first non-threshold collision-kinematics study of Lorentz violation. When interpreted within the minimal Standard-Model Extension, this result yields the two-sided limit of 1.6 x 10^{-14} at 95% confidence level on a combination of the parity-violating photon and electron coefficients kappa_{o+} and c. This new constraint provides an improvement over previous bounds by one order of magnitude.Comment: 4 pages, 4 figure

Computing the pressure of agricultural tractors on soil and mapping its compaction

Manufacturers of agricultural machines, when designing, pay a little attention to its impact on soil, thus producing models with high compression loads on the soil or with a small contact area between the tyres/tracks and the soil surface. Therefore, the aim of this study is to evaluate the negative impact of both wheeled and tracked agricultural tractors on the soil, in terms of soil compaction, and its causes (i. e. design features of tractor tyres/tracks), during the last six decades (i. e. from 1961 to 2021). Soil compaction is caused by the pressure applied by agricultural machines on the soil through the contact area of their tyres/tracks with the soil surface. So, the main indicator of the negative impact on the soil by the tractors manufactured during the last 60 years, i. e. the average pressure applied by the tyres or tracks of tractors manufactured in EU and in the post-Soviet cuntries from 1961 to 2021 to the soil, was computed. A general decrease of the average pressure of the tyres/tracks on the soil can be observed in 1980s and 1990s, followed by its general increase since 2000, above all for the tractors having power higher than 140 kW. Thus, there is an urgent need to assess spatial and temporal changes in soil vulnerability to compaction, that depends on weather conditions and soil properties, as well as agricultural management practices, and can only be fully assessed by means of a combination of traditional techniques (i. e. use of soil cone penetrometer followed by 2D mapping using GIS or 3D mapping through geostatistics) and mechanical approaches (i. e. computation of agricultural machine parameters – soil contact area). The results show that tractor manufacturers did not take care of reducing soil compaction during the considered period

Eta photoproduction off the neutron at GRAAL

The gamma n -> eta n quasi-free cross section reveals a resonant structure at W ~ 1.675 GeV. This structure may be a manifestation of a baryon resonance. A priori its properties, the possibly narrow width and the strong photocoupling to the neutron, look surprising. This structure may also signal the existence of a narrow state.Comment: To appear in Proceedings of Workshop on the Physics of Excited Nucleons NSTAR2005, 12 - 15 October 2005, Tallahassee, Florida, US

Eta photoproduction on the neutron at GRAAL: Measurement of the differential cross section

In this contribution, we will present our first preliminary measurement of the differential cross section for the reaction gamma+n->eta+n. Comparison of the reactions gamma+p->eta+p for free and bound proton (D2 target) will also be discussed.Comment: 6 pages, 4 figures, Proceedings of the 10th International Symposium on Meson-Nucleon Physics and the Structure of the Nucleon, August 29-September 4 2004, Beijing, Chin

Measurement of eta photoproduction on the proton from threshold to 1500 MeV

Beam asymmetry and differential cross section for the reaction gamma+p->eta+p were measured from production threshold to 1500 MeV photon laboratory energy. The two dominant neutral decay modes of the eta meson, eta->2g and eta->3pi0, were analyzed. The full set of measurements is in good agreement with previously published results. Our data were compared with three models. They all fit satisfactorily the results but their respective resonance contributions are quite different. The possible photoexcitation of a narrow state N(1670) was investigated and no evidence was found.Comment: 18 pages, 14 figures, 4 tables Submitted to EPJ