Search for short-lived axions in an electron-beam-dump experiment

We report results of an electron-beam-dump search for neutral particles with masses in the range 1 to 15 MeV and lifetimes τ between 10^-14 and 10^-10 s. No evidence was found for such an object. We fule out the existence of any 1.8-MeV pseudoscalar boson with τ>8.2×10^-15 s and an absorption cross section in matter less than 1 mb per nucleon, and exclude τ>1×10^-14 s were its cross section to equal 50 mb per nucleon. In conjunction with measurements of the electron’s anomalous magnetic moment, this experiment shows that the narrow positron peaks observed in heavy-ion collisions at the Gessellschaft für Schwerionenforschung are not due to an elementary pseudoscalar

Measurement of the Electric and Magnetic Form Factors of the Proton from Q2 1.75 to 8.83 (GeV/c)2

The proton elastic electric and magnetic form factors, GEM and G’bfP(Q2), have been separately measured in the range Q” =1.75 to 8.83 (GeV/c)2, more than doubling the Q3 range of previous data. Scaled by the dipole fit, Go(Q2), the results for Gnlp(Q2)//+G~(Q2) d ecrease smoothly from 1.05 to 0.91, while G~p(Q~)lcdQ~) is consistent with unity. Comparisons are made to QCD Sum L-eRule, diquark, constituent quark, and VMD models, none of whic,h agree with all of the new data. The ratio Q2F2/Fl approaches a constant value for Q2 \u3e 3 ( GeV/c)2. --p;. .- --

Transverse Electrodisintegration of the Deuteron in the Threshold Region at High Q2,

Cross sections for 180° deuteron electrodisintegration have been measured near threshold for the Q2 range 1.21 to 2.77 (GeV/c)2. The data are compared to several nonrelativistic meson-nucleon and hybrid quark-hadron models. The data are in strong disagreement with the impulse approximation, indicating the importance of non-nucleonic degrees of freedom. None of the models are in good agreement with the data at all values of Q2. The ratio W1/W2 of inelastic structure functions has been extracted using previous forward angle data and is found to decrease strongly near threshold, also indicating the importance of interaction effects

Measurements of transverse electron scattering from the deuteron in the threshold region at high momentum transfers

Deuteron electrodisintegration cross sections near 180\u27 have been measured near breakup threshold for the four-momentum transfer squared Q\u27 range 1.21—2.76 (GeV/c) . Evidence for a change of slope in the cross section near Q =1 (GeV/c ) has been obtained. The data are compared to nonrelativistic calculations, which predict a strong influence of meson-exchange currents. The data are also compared to a hybrid quark-hadron model ~ None of these calculations agrees with the data over the entire measured range of Q\u27. The ratio of inelastic structure functions W, (Q\u27, E„~)/Wz(Q\u27, E„~)is extracted from the present results and previous forward angle data. No prediction is in good agreement with the deduced ratios at small relative energy E„~