Search results for "Polar"
showing 10 items of 3817 documents
Photo- and electroproduction of eta mesons
1995
Eta photo- and electroproduction off the nucleon is investigated in an effective lagrangian approach that contains Born terms and both vector meson and nucleon resonance contributions. In particular, we review and develop the formalism for coincidence experiments with polarization degrees of freedom. The different response functions appearing in single and double polarization experiments have been studied. We will present calculations for structure functions and kinematical conditions that are most sensitive to details of the lagrangian, in particular with regard to contributions of nucleon resonances beyond the dominant $S_{11}$(1535) resonance.
Nuclear effects on lepton polarization in charged-current quasielastic neutrino scattering
2006
We use a correlated local Fermi gas (LFG) model, which accounts also for long distance corrections of the RPA type and final-state interactions, to compute the polarization of the final lepton in charged-current quasielastic neutrino scattering. The present model has been successfully used in recent studies of inclusive neutrino nucleus processes and muon capture. We investigate the relevance of nuclear effects in the particular case of $\tau$ polarization in tau-neutrino induced reactions for several kinematics of relevance for neutrino oscillation experiments.
Polarization observables in elastic electron deuteron scattering including parity and time reversal violating contributions
2000
The general formalism for polarization observables in elastic electron deuteron scattering is extended to incorporate parity and time reversal violating contributions. Parity violating effects arise from the interference of $\gamma$ and $Z$ exchange as well as from the hadronic sector via a small parity violating component in the deuteron. In addition we have allowed for time reversal invariance violating contributions in the hadronic sector. Formal expressions for the additional structure functions are derived, and their decomposition into the various multipole contributions are given explicitly.
Nucleon polarizabilities: From Compton scattering to hydrogen atom
2016
We review the current state of knowledge of the nucleon polarizabilities and of their role in nucleon Compton scattering and in hydrogen spectrum. We discuss the basic concepts, the recent lattice QCD calculations and advances in chiral effective-field theory. On the experimental side, we review the ongoing programs aimed to measure the nucleon (scalar and spin) polarizabilities via the Compton scattering processes, with real and virtual photons. A great part of the review is devoted to the general constraints based on unitarity, causality, discrete and continuous symmetries, which result in model-independent relations involving nucleon polarizabilities. We (re-)derive a variety of such rel…
Relativistic direct Urca processes in cooling neutron stars
2001
We derive a relativistic expression for neutrino energy losses caused by the direct Urca processes in degenerate baryon matter of neutron stars. We use two different ways to calculate the emissivity caused by the reactions to our interest. First we perform a standard calculation by Fermi's ''golden'' rule. The second calculation, resulting in the same expression, is performed with the aid of polarization functions of the medium. Our result for neutrino energy losses strongly differs from previous non-relativistic results. We also discuss nonconservation of the baryon vector current in reactions through weak charged currents in the medium, when the asymmetry between protons and neutrons is c…
Constraints from lepton universality at the z-peak on unified theories
1995
We suggest the use of a universality-breaking observable based on lepton asymmetries as derived from the left-right asymmetry and the $\tau$ polarization at the $Z$ peak, which can efficiently constrain the parameter space of unified theories. The new observable is complementary to the leptonic partial width differences and it depends critically on the chirality of a possible non-universal $Z$-boson coupling to like-flavour leptons. The LEP/SLC potential of probing universality violation is discussed in representative low-energy extensions of the Standard Model (SM) that could be derived by supersymmetric grand unified theories, such as the SM with left-handed and/or right-handed neutral is…
Future physics with polarized protons at HERA
1999
Abstract The prospects of a physics program which can be addressed with polarized protons in HERA are summarized and compared to those of other existing or planned facilities. It is shown that polarised protons in HERA would provide unique access to several spin related observables of the nucleon and the photon in an unexplored kinematical range, if an appropriate level of polarization and luminosity can be achieved.
Incoherent pion photoproduction on the deuteron with polarization observables I: Formal expressions
2005
Formal expressions are developed for the general five-fold differential cross section of incoherent $\pi$-photoproduction on the deuteron including beam and target polarization. The polarization observables of the cross section are described by various beam, target and beam-target asymmetries for polarized photons and/or polarized deuterons. They are given as bilinear hermitean forms in the reaction matrix elements divided by the unpolarized cross section. In addition, the corresponding observables for the semi-exclusive reaction $\vec d(\vec \gamma,\pi)NN$ are also given.
Incoherent pion photoproduction on the deuteron with polarization observables II: Influence of final state rescattering
2005
Incoherent pion photoproduction on the deuteron is studied for photon energies from threshold up to 1 GeV with special emphasis on polarization observables. The elementary $\gamma N\to\pi N$ amplitude is taken from the MAID model. The influence of final state interactions on total and semi-exclusive cross sections $\vec d(\vec\gamma,\pi)NN$ is investigated by including complete rescattering in the final $NN$- and $\pi N$-subsystems. For charged pion-production the influence of $NN$-rescattering is moderate whereas $\pi N$-rescattering is almost negligible. Much stronger influences of $NN$-rescattering are seen in neutral pion production, which is due to the elimination of a significant spur…
Low-energy anti-neutrinos from the sun
1997
We consider the sensitivity of future neutrino experiments in the low energy region, such as BOREXINO or HELLAZ, to a solar electron antineutrino signal. We show that, if neutrino conversions within the Sun result in partial polarization of initial solar neutrino fluxes, then a new opportunity arises to observe the electron antineutrinos and thus to probe the Majorana nature of the neutrinos. This is achieved by comparing the slopes of the energy dependence of the differential neutrino electron scattering cross section for different neutrino conversion scenarios. We also show how the \nu_e -> \bar{\nu}_e conversions may take place for low energy solar neutrinos while being unobservable at t…