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J. -P. Didelez

Publications and source records attributed to J. -P. Didelez.

11 recordsLinked to original sources
arXiv2011

Distillation of hydrogen isotopes for polarized HD target

We have developed a cryogenic distillation system to purify Hydrogen-Deuteride (HD) gas for a polarized HD target in LEPS experiments at SPring-8. A small amount of ortho-H$_2$ ($\sim$0.01%) in the HD gas plays an important role in efficiently polarizing the HD target. Since there are 1$\sim$5% impurities of H$_2$ and D$_2$ in commercially available HD gases, it is inevitable that the HD gas is purified up to $\sim$99.99%. The distillation system has a cryogenic pot (17$\sim$21 K) containing many small stainless steel cells called Heli-pack. Commercial HD gas with an amount of 5.2 mol is fed into the pot. We carried out three distillation runs by changing temperatures (17.5 K and 20.5 K) and gas extraction speeds (1.3 ml/min and 5.2 ml/min). The extracted gas was analyzed by using a gas analyzer system combining a quadrupole mass spectrometer with a gas chromatograph. The HD gas of 1 mol with a purity better than 99.99% has been successfully obtained. The effective NTS (Number of Theoretical Stages), which is an indicator of the distillator performances, is obtained as 37.2$\pm$0.6. This value is in reasonable agreement with a designed value of 37.9. The HD target is expected to be efficiently polarized under a well-controlled condition by doping an optimal amount of ortho-H$_2$ to the purified HD gas.

physics.ins-det↗
arXiv2011

HD gas analysis with Gas Chromatography and Quadrupole Mass Spectrometer

A gas analyzer system has been developed to analyze Hydrogen-Deuteride (HD) gas for producing frozen-spin polarized HD targets, which are used for hadron photoproduction experiments at SPring-8. Small amounts of ortho-H$_{2}$ and para-D$_{2}$ gas mixtures ($\sim$0.01%) in the purified HD gas are a key to realize a frozen-spin polarized target. In order to obtain reliable concentrations of these gas mixtures in the HD gas, we produced a new gas analyzer system combining two independent measurements with the gas chromatography and the QMS. The para-H$_{2}$, ortho-H$_{2}$, HD, and D$_{2}$ are separated using the retention time of the gas chromatography and the mass/charge. It is found that the new gas analyzer system can measure small concentrations of $\sim$0.01% for the otho-H$_2$ and D$_2$ with good S/N ratios.

nucl-ex↗
arXiv2008

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.

astro-ph↗
arXiv2005

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.

hep-ex↗
arXiv2005

Probing the Light Speed Anisotropy with respect to the Cosmic Microwave Background Radiation Dipole

We have studied the angular fluctuations in the speed of light with respect to the apex of the dipole of Cosmic Microwave Background (CMB) radiation using the experimental data obtained with GRAAL facility, located at the European Synchrotron Radiation Facility (ESRF) in Grenoble. The measurements were based on the stability of the Compton edge of laser photons scattered on the 6 GeV monochromatic electron beam. The results enable to obtain a conservative constraint on the anisotropy in the light speed variations Δc(θ)/c < 3 10^{-12}, i.e. with higher precision than from previous experiments.

astro-ph↗
arXiv2003

Generalized Parton Distributions and Nucleon Resonances

We discuss the relations between Generalized Parton Distributions (GPDs) and nucleon resonances. We first briefly introduce the concept of "transition" GPDs. Then we discuss a straightforward application to the modelization of the N-$Δ$ magnetic transition form factor. Finally, we discuss the experimental aspects of the subject and present first preliminary experimental investigations in this field.

hep-ph↗
arXiv2002

Precise Measurement of Sigma Beam Asymmetry for Positive Pion Photoproduction on the Proton from 800 to 1500 Mev

The Sigma beam asymmetry for positive pion photoproduction on the proton has been measured over an angular range of 40-170 deg at photon energies from 0.8 to 1.5 GeV. The resulting data set includes 237 accurate points, 136 of these belonging to an almost unexplored domain above 1.05 GeV. Data of such high precision provide severe constraints for partial wave analyses. The influence of this experiment on the GW multipole analysis is demonstrated. Significant changes are found in multipoles connected to the S31(1620) and P13(1720) resonances. Comparisons using the MAID analysis are also presented.

nucl-ex↗
arXiv2001

Differential cross section measurement of eta photoproduction on the proton from threshold to 1100 MeV

The differential cross section for the reaction p(gamma, eta p) has been measured from threshold to 1100 MeV photon laboratory energy. For the first time, the region of the S11(1535) resonance is fully covered in a photoproduction experiment and allows a precise extraction of its parameters at the photon point. Above 1000 MeV, S-wave dominance vanishes while a P-wave contribution is observed whose nature will have to be clarified. These high precision data together with the already measured beam asymmetry data will provide stringent constraints on the extraction of new couplings of baryon resonances to the eta meson.

hep-ex↗
arXiv1999

Role of nucleon resonance excitation in $ϕ$ meson photoproduction

The resonance effects are investigated in the $ϕ$ meson photoproduction near threshold through a quark model approach with an effective Lagrangian. The diffractive contribution is consistently estimated by the {\it t}-channel Pomeron exchange. Another non-diffractive process, {\it t}-channel $π^0$ exchange is also included. The numerical result shows that the Pomeron exchange plays dominant role in the $ϕ$ meson photoproduction, while the cross sections of the non-diffractive processes, i.e. {\it s}- and {\it u}-channel excitations, and {\it t}-channel $π^0$ exchange, are quite small. In the polarization observables, we find that large asymmetries are produced in the backward direction by the interferences from the {\it s}- and {\it u}-channel resonances, while in the forward direction, only very small asymmetries are generated. Meanwhile, we find that the effects from the $π^0$ exchange are generally negligible.

nucl-th↗
arXiv1999

Nucleonic resonance effects in the $ϕ$ meson photoproduction

The process $γp \to ϕp$ close to threshold is investigated focusing on the role played by the {\it s}- and {\it u}-channel nucleonic resonances. For this purpose, a recent quark model approach, based on the $SU(6)\otimes O(3)$ symmetry with an effective Lagrangian, is extended to the $ϕ$ meson photoproduction. Another non-diffractive process, the {\it t}-channel $π^0$ exchange, is also included. The diffractive contribution is produced by the {\it t}-channel Pomeron exchange. Contributions from non-diffractive {\it s}- and {\it u}-channel process are found small in the case of cross sections and polarization observables at forward angles. However, backward angle polarization asymmetries show high sensitivity to this non-diffractive process. Different prescriptions to keep gauge invariance for the Pomeron exchange amplitudes are investigated. Possible deviations from the exact $SU(6)\otimes O(3)$ symmetry, due to the configuration mixing, are also discussed.

nucl-th↗