A permanent electric dipole moment of fundamental spin-1/2 particles violates both parity (P) and time re- versal (T) symmetry, and hence, also charge-parity (CP) symmetry since there is no sign of ...CPT-violation. The search for a neutron electric dipole moment (nEDM) probes CP violation within and beyond the Stan- dard Model. The experiment, set up at the Paul Scherrer Institute (PSI), an improved, upgraded version of the apparatus which provided the current best experimental limit, dn < 2.9E-26 ecm (90% C.L.), by the RAL/Sussex/ILL collaboration: Baker et al., Phys. Rev. Lett. 97, 131801 (2006). In the next two years we aim to improve the sensitivity of the apparatus to sigma(dn) = 2.6E-27 ecm corresponding to an upper limit of dn < 5E-27 ecm (95% C.L.), in case for a null result. In parallel the collaboration works on the design of a new apparatus to further increase the sensitivity to sigma(dn) = 2.6E-28 ecm.
Phys.Rev.C78:018201,2008 We report on new H$(e,e^\prime p)\gamma$ measurements in the $\Delta(1232)$
resonance at $Q^2=0.06$ (GeV/c) carried out simultaneously with H$(e,e^\prime
p)\pi^0$. It is the ...lowest $Q^2$ for which the virtual Compton scattering (VCS)
reaction has been studied in the first resonance region. The VCS measured cross
sections are well described by dispersion-relation calculations in which the
multipole amplitudes derived from H$(e,e^\prime p)\pi^0$ data are used as
input, thus confirming the compatibility of the results. The derived resonant
magnetic dipole amplitude $M^{3/2}_{1+} = (40.60 \pm
0.70_{stat+sys})(10^{-3}/m_{\pi^+})$ at $W=$ 1232 MeV is in excellent agreement
with the value extracted from H$(e,e^\prime p)\pi^0$ measurements.
Phys.Lett.B651:102-107,2007 We report new precise p$(\vec{e},e^\prime p)\pi^0$ measurements at the peak
of the $\Delta^{+}(1232)$ resonance at $Q^2=\unit0.20(GeV/c)^2$ performed at
the Mainz ...Microtron (MAMI). The new data are sensitive to both the electric
quadrupole ($E2$) and the coulomb quadrupole ($C2$) amplitudes of the $\gamma^*
N\to\Delta$ transition. They yield precise quadrupole to dipole amplitude
ratios CMR $= (-5.09 \pm 0.28_{stat+sys}\pm 0.30_{model})%$ and EMR $= (-1.96
\pm 0.68_{stat+sys} \pm 0.41_{model})%$ for $M^{3/2}_{1+} = (39.57 \pm
0.75_{stat+sys}\pm 0.40_{model})(10^{-3}/m_{\pi^+})$. The new results are in
disagreement with Constituent Quark Model predictions and in qualitative
agreement with models that account for mesonic contributions, including recent
Lattice calculations. They thus give further credence to the conjecture of
deformation in hadronic systems favoring the attribution of the origin of
deformation to the dominance of mesonic effects.
We report on new H\((e,e^\prime p)\gamma\) measurements in the \(\Delta(1232)\) resonance at \(Q^2=0.06\) (GeV/c) carried out simultaneously with H\((e,e^\prime p)\pi^0\). It is the lowest \(Q^2\) ...for which the virtual Compton scattering (VCS) reaction has been studied in the first resonance region. The VCS measured cross sections are well described by dispersion-relation calculations in which the multipole amplitudes derived from H\((e,e^\prime p)\pi^0\) data are used as input, thus confirming the compatibility of the results. The derived resonant magnetic dipole amplitude \(M^{3/2}_{1+} = (40.60 \pm 0.70_{stat+sys})(10^{-3}/m_{\pi^+})\) at \(W=\) 1232 MeV is in excellent agreement with the value extracted from H\((e,e^\prime p)\pi^0\) measurements.
We report new precise p\((\vec{e},e^\prime p)\pi^0\) measurements at the peak of the \(\Delta^{+}(1232)\) resonance at \(Q^2=\unit0.20(GeV/c)^2\) performed at the Mainz Microtron (MAMI). The new data ...are sensitive to both the electric quadrupole (\(E2\)) and the coulomb quadrupole (\(C2\)) amplitudes of the \(\gamma^* N\to\Delta\) transition. They yield precise quadrupole to dipole amplitude ratios CMR \(= (-5.09 \pm 0.28_{stat+sys}\pm 0.30_{model})%\) and EMR \(= (-1.96 \pm 0.68_{stat+sys} \pm 0.41_{model})%\) for \(M^{3/2}_{1+} = (39.57 \pm 0.75_{stat+sys}\pm 0.40_{model})(10^{-3}/m_{\pi^+})\). The new results are in disagreement with Constituent Quark Model predictions and in qualitative agreement with models that account for mesonic contributions, including recent Lattice calculations. They thus give further credence to the conjecture of deformation in hadronic systems favoring the attribution of the origin of deformation to the dominance of mesonic effects.
