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Small angle electron scattering with intense electron beams opens up the possibility of performing almost real photon induced reactions with thin, polarized hydrogen and few body targets, allowing for the detection of low energy charged particles.This promises to be much more effective than conventional photon tagging techniques. For photo-pion reactions some fundamental new possibilities include: tests of charge symmetry in the N-N system by measurement of the neutron-neutron scattering length $a_{nn}$ in the $gamma D rightarrow pi^{+} nn$ reaction; tests of isospin breaking due to the mass difference of the up and down quarks; measurements with polarized targets are sensitive to $pi$N phase shifts and will test the validity of the Fermi-Watson (final state interaction) theorem. All of these experiments will test the accuracy and energy region of validity of chiral effective theories.
In the past two decades, pions created in the high density regions of heavy ion collisions have been predicted to be sensitive at high densities to the symmetry energy term in the nuclear equation of state, a property that is key to our understanding
We summarize the pertinent experimental and theoretical developments in the field of pion photo- and electroproduction in the threshold region. We discuss which experiments and which calculations should be done/performed in the future.
New data on the production of single neutral pions in the $pdrightarrow{}^3textrm{He},pi^0$ reaction are presented. For fifteen proton beam momenta between $p_p=1.60;textrm{GeV}/c$ and $p_p=1.74;textrm{GeV}/c$, differential cross sections are determi
The $NDeltato NN$ cross sections, which take into account the $Delta$-mass dependence of M-matrix and momentum $p_{NDelta}$, are applied on the calculation of pion production within the framework of the UrQMD model. Our study shows that UrQMD calcula
Exclusive $pi^+pi^-p$ photo- and electroproduction data from CLAS have considerably extended the information on the spectrum and structure of nucleon resonances. The data from the $pi^+pi^-p$ and $Npi$ channels have provided results on the electrocou