Search results for " pion"
showing 10 items of 44 documents
Photoproduction of π 0 mesons off protons and neutrons in the second and third nucleon resonance regions
2018
Photoproduction of mesons off quasi-free nucleons bound in the deuteron allows to study the electromagnetic excitation spectrum of the neutron and the isospin structure of the excitation of nucleon resonances. The database for such reactions is much more sparse than for free proton targets. Single $\pi^0$ photoproduction off quasi-free nucleons from the deuteron was experimentally studied. Nuclear effects were investigated by a comparison of the results for free protons and quasi-free protons and used as a correction for the quasi-free neutron data. The experiment was performed at the tagged photon beam of the Mainz MAMI accelerator for photon energies between 0.45~GeV and 1.4~GeV, using an…
Beam-Helicity Asymmetries in Double-Pion Photoproduction off the Proton
2009
Beam-helicity asymmetries have been measured at the MAMI accelerator in Mainz in the three isospin channels $\vec{\gamma}p\to \pi^{+}\pi^0n$, $\vec{\gamma}p\to \pi^{0}\pi^0p$ and $\vec{\gamma}p\to \pi^{+}\pi^{-}p$ . The circularly polarized photons, produced from bremsstrahlung of longitudinally polarized electrons, were tagged with the Glasgow magnetic spectrometer. Charged pions and the decay photons of $\pi^0$ mesons were detected in a $~4\pi$ electromagnetic calorimeter which combined the Crystal Ball detector with the TAPS detector. The precisely measured asymmetries are very sensitive to details of the production processes and are thus key observables in the modeling of the reaction d…
Brodsky-Lepage-Mackenzie scale for the pion transition form factor
2002
The next-to-leading order (NLO) Brodsky-Lepage-Mackenzie (BLM) scale for the pion transition form factor is determined. To achieve that, a consistent calculation up to ${n}_{f}$-proportional next-to-next-to-leading order contributions to both the hard-scattering amplitude and the perturbatively calculable part of the pion distribution amplitude is performed. By combining and matching the results obtained for these two amplitudes, a proper cancellation of collinear singularities is established and the ${\ensuremath{\gamma}}_{5}$ ambiguity problem (related to the use of the dimensional regularization method) is resolved by using the naive-${\ensuremath{\gamma}}_{5}$ as well as the 't Hooft--V…
Multiplicities of charged pions and charged hadrons from deep-inelastic scattering of muons off an isoscalar target
2017
Multiplicities of charged pions and charged hadrons produced in deep-inelastic scattering were measured in three-dimensional bins of the Bjorken scaling variable x , the relative virtual-photon energy y and the relative hadron energy z . Data were obtained by the COMPASS Collaboration using a 160GeV muon beam and an isoscalar target ( 6 LiD). They cover the kinematic domain in the photon virtuality Q2>1(GeV/c)2 , 0.004 1(GeV/c$)^2$, $0.004 < x < 0.4$, $0.2 < z < 0.85$ and $0.1 < y < 0.7$. In addition, a leading-order pQCD analysis was performed using the pion multiplicity results to extract quark fragmentation functions.
Form factors of radiative pion decays in nonlocal chiral quark models
2012
We study the radiative pion decay π +→e +ν eγ within nonlocal chiral quark models that include wave function renormalization. In this framework we analyze the momentum dependence of the vector form factor F V(q2) and the slope of the axial-vector form factor F A(q2) at threshold. Our results are compared with available experimental information and with the predictions given by the Nambu-Jona-Lasinio model. In addition we calculate the low energy constants δ 5 and δ 6, comparing our results with the values obtained in chiral perturbation theory.
Master Clinico: I pionieri della terapia familiare a confronto, Accademia di Psicoterapia della Famiglia, Centro Congressi "Roma scout center", genna…
2011
El grupo Actum (1973-1983). Pioneros de la música experimental en Valencia
2011
NuSTEC White Paper: Status and challenges of neutrino–nucleus scattering
2018
International audience; The precise measurement of neutrino properties is among the highest priorities in fundamental particle physics, involving many experiments worldwide. Since the experiments rely on the interactions of neutrinos with bound nucleons inside atomic nuclei, the planned advances in the scope and precision of these experiments require a commensurate effort in the understanding and modeling of the hadronic and nuclear physics of these interactions, which is incorporated as a nuclear model in neutrino event generators. This model is essential to every phase of experimental analyses and its theoretical uncertainties play an important role in interpreting every result.In this Wh…
Jet-like correlations with neutral pion triggers in pp and central Pb–Pb collisions at 2.76 TeV
2016
Physics letters / B B763, 238 - 250 (2016). doi:10.1016/j.physletb.2016.10.048