Cross Section Measurements of Deuteron Electro-Disintegration at Very High Recoil Momenta and Large 4-Momentum Transfers (Q2)

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The 2H(e,e′p)n cross sections have been measured at negative 4-momentum transfers of Q2 = 4.5±0.5 (GeV/c)2 and Q2 = 3.5±0.5 (GeV/c)2 reaching neutron recoil (missing) momenta up to pr ∼1.0 GeV/c. The data have been obtained at fixed neutron recoil angles 5o ≤ θnq ≤ 95o with respect to the 3-momentum transfer q. The new data agree well with the previous data which reached pr ∼ 500 MeV/c. At θnq = 35o and 45o, final state interactions (FSI), meson exchange currents (MEC) and isobar configurations (IC) are suppressed and the plane wave impulse approximation (PWIA) provides the dominant cross section contribution. The new data are compared to recent theoretical calculations, and a significant disagreement for recoil momenta pr > 700 MeV/c is observed. The experiment was carried out in experimental Hall C at the Thomas Jefferson National Accelerator Facility (TJNAF) and formed part of a group of four experiments that were used to commission the new Super High Momentum Spectrometer (SHMS). The experiment consisted of a 10.6 GeV electron beam incident on a liquid deuterium target which resulted in the break-up of the deuteron into a proton and neutron. The scattered electrons were detected by the SHMS in coincidence with the knocked-out protons detected in the previously existing High Momentum Spectrometer (HMS) and the recoiling neutrons were reconstructed from energy-momentum conservation laws. To ensure that the 2H(e,e′p)n reaction channel was selected, we required the missing energy of the system to be the binding energy of the deuteron (∼2.22 MeV). The spectrometers’ central angles and momenta were set to measure three central missing momentum settings of the neutron corresponding to pr = 80, 580 and 750 MeV/c which required the SHMS central angle and momentum to be fixed and the HMS to be rotated from smaller to larger angles corresponding to the lower and higher missing momentum settings, respectively. The experiment was carried out in a time period of six days with typical electron beam currents of 45-60 μA at about 50% beam efficiency.