Search results for "Pion"
showing 10 items of 1304 documents
Parity violating pion electroproduction off the nucleon
1995
Parity violating (PV) contributions due to interference between $\gamma$ and $Z^0$ exchange are calculated for pion electroproduction off the nucleon. A phenomenological model with effective Lagrangians is used to determine the resulting asymmetry for the energy region between threshold and $\Delta(1232)$ resonance. The $\Delta$ resonance is treated as a Rarita-Schwinger field with phenomenological $N \Delta$ transition currents. The background contributions are given by the usual Born terms using the pseudovector $\pi N$ Lagrangian. Numerical results for the asymmetry are presented.
Dispersion relation analysis of neutral pion photoproduction and electroproduction at threshold
2002
Neutral pion photoproduction and electroproduction at threshold is analyzed in the framework of dispersion relations. For this purpose, we evaluate the real threshold amplitudes in terms of Born contributions and dispersion integrals determined by the imaginary parts of the multipoles of the unitary isobar model (MAID) and the phenomenological partial-wave analysis (SAID). The results show considerable cancellations between Born terms and resonance contributions. Good agreement with the data is found for photoproduction. While our dispersion analysis suggests considerable discrepancies for electroproduction, the present state of the experimental multipole analysis at finite ${Q}^{2}$ does n…
Search for the charge-conjugation-forbidden decayω→ηπ0
2009
A new upper limit of 2.3x10{sup -4} on the branching ratio of the decay {omega}{yields}{eta}{pi}{sup 0} has been obtained using the Crystal Ball multiphoton spectrometer at the Mainz Microtron MAMI. This decay is forbidden by charge-conjugation invariance of the strong and electromagnetic interactions. We have also obtained the upper limit of 2.3x10{sup -4} for the forbidden decay {omega}{yields}3{pi}{sup 0} and the upper limit of 2.4x10{sup -4} for {omega}{yields}2{pi}{sup 0}.
Pion-Photon TDAs in the NJL Model
2008
The pion-photon Transition Distribution Amplitudes (TDAs) are studied, treating the pion as a bound state in the sense of Bethe-Salpeter, in the formalism of the NJL model. The results obtained explicitly verify support, sum rules and polynomiality conditions. The role of PCAC is highlighted.
Constraining nPDFs with inclusive pions and direct photons at forward rapidities in p+Pb collisions at the LHC
2014
Abstract In this talk, we present NLO pQCD predictions for inclusive pion and direct photon nuclear modifications in p + Pb collisions at mid- and forward rapidities at the LHC. In addition to the minimum bias predictions, we also address the centrality dependence with spatially dependent nuclear PDFs. To understand which regions of the nuclear momentum fraction x 2 these observables predominantly probe, we present also the underlying x 2 distributions at different rapidities. We are led to conclude that the isolated photons at forward rapidities are more sensitive to the small- x 2 dynamics than the inclusive pions.
Exclusive πo- and η-meson production in 40Ar + natCa at 800A MeV
1997
Abstract The impact-parameter dependence of π o - and η-meson production is reported for the system 40 Ar+ nat Ca at a beam energy of 800 A MeV. Scaling of the meson abundances with the transverse mass is observed. The experimental results are compared to calculations within the BUU model.
Photodisintegration of the deuteron in the Δ-resonance region
1993
Abstract Photodisintegration of the deuteron in the Δ-resonance region is calculated treating the final state interaction within a N N−NΔ coupled channel approach including explicit pion degrees of freedom. For the electromagnetic interaction the nucleonic one-body current, meson exchange currents and the direct Δ-excitation are taken into account. The γN Δ-coupling is fixed in accordance with the M 1+ ( 3 2 ) multipole amplitude for pion photoproduction on the nucleon. The resulting total cross section underestimates the experimental data for photon energies below 340 MeV, whereas a good agreement is achieved by uaing a modified γN Δ-coupling effectively including the nonresonant Born term…
Coherent pion production in neutrino nucleus collision in the 1 GeV region
1996
We calculate cross sections for coherent pion production in nuclei induced by neutrinos and antineutrinos of the electron and muon type. The analogies and differences between this process and the related ones of coherent pion production induced by photons, or the (p,n) and $(^3 He, t)$ reactions are discussed. The process is one of the several ones occurring for intermediate energy neutrinos, to be considered when detecting atmospheric neutrinos. For this purpose the results shown here can be easily extrapolated to other energies and other nuclei.
Single-spin asymmetries of $d(\gamma,\pi)NN$ in the first resonance region
2003
Incoherent photoproduction of pions on the deuteron in the first resonance region is investigated with special emphasis on single-spin asymmetries. For the elementary pion production operator an effective Lagrangian model which includes the standard pseudovector Born terms and a resonance contribution from the $\Delta$(1232)-excitation is used. Single-spin asymmetries, both for charged and neutral pion photoproduction on the deuteron, are analyzed and calculated for the first time in the first resonance region. The linear photon asymmetry $\Sigma$, vector target asymmetry $T_{11}$ and tensor target asymmetries $T_{20}$, $T_{21}$, and $T_{22}$ for the reaction $d(\gamma,\pi)NN$ are predicted…
A unitary isobar model for pion photo- and electroproduction on the proton up to 1 GeV
1998
A new operator for pion photo- and electroproduction has been developed for nuclear applications at photon equivalent energies up to 1 GeV. The model contains Born terms, vector mesons and nucleon resonances ($P_{33}(1232)$, $P_{11}(1440)$, $D_{13}(1520)$, $S_{11}(1535)$, $F_{15}(1680)$, and $D_{33}(1700)$). The resonance contributions are included taking into account unitarity to provide the correct phases of the pion photoproduction multipoles. The $Q^2$ dependence of electromagnetic resonance vertices is described with appropriate form factors in the electromagnetic helicity amplitudes. Within this model we have obtained good agreement with the experimental data for pion photo- and elect…