Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userReinterpretation of classic proton charge form factor measurements
390
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
In 1963, a proton radius of $0.805(11)~mathrm{fm}$ was extracted from electron scattering data and this classic value has been used in the standard dipole parameterization of the form factor. In trying to reproduce this classic result, we discovered that there was a sign error in the original analysis and that the authors should have found a value of $0.851(19)~mathrm{fm}$. We additionally made use of modern computing power to find a robust function for extracting the radius using this 1963 datas spacing and uncertainty. This optimal function, the Pad{e} $(0,1)$ approximant, also gives a result which is consistent with the modern high precision proton radius extractions.
rate research
Read More
We present an updated extraction of the proton electromagnetic form factor ratio, mu_p G_E/G_M, at low Q^2. The form factors are sensitive to the spatial distribution of the proton, and precise measurements can be used to constrain models of the proton. An improved selection of the elastic events and reduced background contributions yielded a small systematic reduction in the ratio mu_p G_E/G_M compared to the original analysis.
The electromagnetic form factors of the nucleon characterize the effect of its internal structure on its response to an electromagnetic probe as studied in elastic electron-nucleon scattering. These form factors are functions of the squared four-momentum transfer $Q^2$ between the electron and the proton. The two main classes of observables of this reaction are the scattering cross section and polarization asymmetries, both of which are sensitive to the form factors in different ways. When considering large momentum transfers, double-polarization observables offer superior sensitivity to the electric form factor. This thesis reports the results of a new measurement of the ratio of the electric and magnetic form factors of the proton at high momentum transfer using the recoil polarization technique. A polarized electron beam was scattered from a liquid hydrogen target, transferring polarization to the recoiling protons. These protons were detected in a magnetic spectrometer which was used to reconstruct their kinematics, including their scattering angles and momenta, and the position of the interaction vertex. A proton polarimeter measured the polarization of the recoiling protons by measuring the azimuthal asymmetry in the angular distribution of protons scattered in CH$_2$ analyzers. The scattered electron was detected in a large-acceptance electromagnetic calorimeter in order to suppress inelastic backgrounds. The measured ratio of the transverse and longitudinal polarization components of the scattered proton is directly proportional to the ratio of form factors $G_E^p/G_M^p$. The measurements reported in this thesis took place at $Q^2=$5.2, 6.7, and 8.5 GeV$^2$, and represent the most accurate measurements of $G_E^p$ in this $Q^2$ region to date.
Measurements of the electric and the magnetic neutron form factors have been performed at the Mainz Microtron for more than 20 years. These MAMI experiments are reviewed in the context of measurements from other groups, and future measurements at MAMI are outlined.
The possibility of measuring the proton electromagnetic form factors in the time-like region at FAIR with the PANDA detector is discussed. Detailed simulations on signal efficiency for the annihilation of $bar p +p $ into a lepton pair as well as for the most important background channels have been performed. It is shown that precision measurements of the differential cross section of the reaction $bar p +p to e^++ e^-$ can be obtained in a wide angular and kinematical range. The individual determination of the moduli of the electric and magnetic proton form factors will be possible up to a value of momentum transfer squared of $q^2simeq 14$ (GeV/c)$^2$. The total $bar p +pto e^++e^-$ cross section will be measured up to $q^2simeq 28$ (GeV/c)$^2$. The results obtained from simulated events are compared to the existing data. Sensitivity to the two photons exchange mechanism is also investigated.
The distribution of the parton content of nuclei, as encoded via the generalized parton distributions (GPDs), can be accessed via the deeply virtual Compton scattering (DVCS) process contributing to the cross section for leptoproduction of real photons. Similarly to the scattering of light by a material, DVCS provides information about the dynamics and the spatial structure of hadrons. The sensitivity of this process to the lepton beam polarization allows to single-out the DVCS amplitude in terms of Compton form factors that contain GPDs information. The beam spin asymmetry of the $^4$He($vec {mathrm e}$,e$ gamma ^4$He) process was measured in the experimental Hall B of the Jefferson Laboratory to extract the real and imaginary parts of the twist-2 Compton form factor of the $^4$He nucleus. The experimental results reported here demonstrate the relevance of this method for such a goal, and suggest the dominance of the Bethe-Heitler amplitude to the unpolarized process in the kinematic range explored by the experiment.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
