Study of 3D nucleon structure at the J-PARC π20 beamline

One of the keys to understand 3D nucleon structure is precise measurements of Generalized Parton Distribution Functions (GPDs). Measurements in different reactions help to verify universality of GPDs and derive GPDs in wide kinematic region. Hadron induced exclusive reactions are complementary to lepton induced reactions such as deeply virtual Compton scattering (DVCS) and deeply virtual meson production (DVMP).

In the J-PARC hadron experimental hall, measurements of GPDs using hadron beam are planned. At the high momentum beam line, 30 GeV/c primary proton beam from the J-PARC Main Ring is derived. In addition, positive and negative π/K/p secondary beam up to 20 GeV/c will be delivered by installing a new production target. The secondary beam line is called π20 beam line.

At the π20 beam line, measurements of the exclusive Drell-Yan reaction (π^-p→γ^*n→μ⁺μ^-n) and 2→3 reactions (such as pp→pπ⁺n) are planned to access GPDs. The medium beam momentum of the π20 beam line is suited for the measurements of those reactions since cross sections of these reactions decrease with beam momentum. A new high-resolution, high-rate capable spectrometer is under construction. The new spectrometer enables the first measurements of above exclusive reactions thanks to a good momentum resolution under high rate. We will report details and prospects of these experiments.