Abstract
We studied simultaneously the He4(e,e′p), He4(e,e′pp), and He4(e,e′pn) reactions at Q2=2(GeV/c)2 and xB>1, for an (e,e′p) missing-momentum range of 400 to 830MeV/c. The knocked-out proton was detected in coincidence with a proton or neutron recoiling almost back to back to the missing momentum, leaving the residual A=2 system at low excitation energy. These data were used to identify two-nucleon short-range correlated pairs and to deduce their isospin structure as a function of missing momentum, in a region where the nucleon-nucleon (NN) force is expected to change from predominantly tensor to repulsive. The abundance of neutron-proton pairs is reduced as the nucleon momentum increases beyond ∼500MeV/c. The extracted fraction of proton-proton pairs is small and almost independent of the missing momentum. Our data are compared with calculations of two-nucleon momentum distributions in He4 and discussed in the context of probing the elusive repulsive component of the NN force.
Original language | English |
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Article number | 022501 |
Journal | Physical Review Letters |
Volume | 113 |
Issue number | 2 |
DOIs | |
State | Published - 9 Jul 2014 |