Related papers: Pion (Kaon) and Sigma polarizabilities
Can one expect gamma rays rates from the QGP to be higher than from the hot hadronic gas phase? Xiong, Shuryak, Brown (XSB) calculate photon production from a hot hadronic gas via the reaction $\pi^- + \rho^0 \rightarrow \pi^- + \gamma$.…
A recent analysis of pion photo-production multipoles using p(g,pi0) data from Mainz is repeated, successively adding constraints from other observables and varying the number of fitted partial waves. The original analysis is shown to have…
Recent attempts to detect the pion polarizability via analysis of $\gamma\gamma\rightarrow\pi\pi$ measurements are examined. The connection between calculations based on dispersion relations and on chiral perturbation theory is established…
Differential cross sections for the gamma p -> pi^0 p reaction have been measured with the A2 tagged-photon facilities at the Mainz Microtron, MAMI C, up to the center-of-mass energy W=1.9 GeV. The new results, obtained with a fine energy…
Pion photoproduction is analyzed with the chiral Lagrangian. Partial-wave amplitudes are obtained by an analytic extrapolation of subthreshold reaction amplitudes computed in chiral perturbation theory, where the constraints set by…
The polarizabilities of light pseudoscalar mesons can be extracted from differential cross sections for Compton scattering near threshold. While this has been accomplished for charged pions employing Primakoff reactions, a corresponding…
We develop polarization observables for the processes $\gamma N\to\pi\pi N$ and $\pi N\to\pi\pi N$, using both a helicity and hybrid helicity-transversity basis. Such observables are crucial if processes that produce final states consisting…
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…
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…
A new transversely polarised frozen spin target has been developed at MAMI which will be used in conjunction with the photon tagger and the Crystal Ball detector. The new target permits a major new programme of accurate measurement of…
New data for the differential cross sections, polarization observables $T$, $F$, and $E$ in the reaction of $\eta$ photoproduction on proton from the threshold up to a center-of-mass energy of W=1.9 GeV are presented. The data were obtained…
The electric ($\alpha_\pi$) and magnetic ($\beta_\pi$) Compton polarizabilities of both the charged and the neutral pion are of fundamental interest in the low-energy sector of quantum chromodynamics (QCD). Pion polarizabilities affect the…
The electric (${\alpha}_{\pi}$) and the magnetic (${\beta}_{\pi}$) polarisabilities are fundamental properties of the pion characterising the rigidity of its internal structure. They have been precisely measured at the COMPASS experiment at…
Beam-helicity asymmetries have been measured at the MAMI accelerator in Mainz for the photoproduction of neutral pion pairs in the reactions $\vec{\gamma}p\rightarrow p\pi^0\pi^0$ and $\vec{\gamma}d\rightarrow (n)p\pi^0\pi^0$,…
At the Frascati phi-factory DAPHNE the pion formfactor is measured by means of the 'radiative return', i.e. by using events in which one of the collider electrons (positrons) has radiated an initial state radiation photon, lowering in such…
Precise total cross-sections and invariant-mass distributions have been measured for photoproduction of pion pairs off the proton producing $p\pi^0\pi^0$ and $n\pi^+\pi^0$ final states from the threshold region up to 800 MeV incident photon…
The quasifree $\overrightarrow{\gamma} d\to\pi^0n(p)$ photon beam asymmetry, $\Sigma$, has been measured at photon energies, $E_\gamma$, from 390 to 610 MeV, corresponding to center of mass energy from 1.271 to 1.424 GeV, for the first…
First results from the longitudinally polarized frozen-spin target (FROST) program are reported. The double-polarization observable E, for the reaction $\vec \gamma \vec p \to \pi^+n$, has been measured using a circularly polarized…
The beam-helicity asymmetry has been measured simultaneously for the reactions (e p \to e p \gamma) and (e p \to e p \pi^0) in the $\Delta (1232)$ resonance region at $Q^2=$ 0.35 (GeV/c)$^2$. The experiment was performed at MAMI with a…
We discuss main experimental works, where dipole polarizabilities of charged pions have been determined. Possible reasons for the differences between the experimental data are discussed. In particular, it is shown that the account of the…