Forward Differential Cross Sections for the Reaction p+pd+π+ in the Range 3.412.3 GeVc

Abstract
A missing-mass spectrometer, employing optical spark chambers with automatic vidicon readout, was used to measure the forward differential cross section (cosθc.m.0.995) for the reaction p+pd+π+ at closely spaced settings of the incident proton momentum in the range p0=3.412.3 GeVc. The deuterons from the reaction were identified by time of flight, and their momentum and angle of emission measured by a reconstruction of the spark-chamber tracks. Since the incoming proton momentum was accurately known, the missing mass associated with deuteron production could be deduced. The reaction p+pd+π+ was identified by the appearance of a distinct peak corresponding to the pion mass in a missing-mass plot. The data confirm the existence of a prominent peak in the forward cross section at Ec.m.=3.0 GeV and show a hitherto unreported shoulder at Ec.m.=3.7 GeV. This structure, along with the well-known sharp maximum at Ec.m.=2.2 GeV, may be understood on the basis of a one-pion-exchange model as reflecting the behavior of the T=32 isobars in pion-nucleon scattering. Above Ec.m.=3.9 GeV, the forward differential cross section decreases monotonically as the -2.5 power of s, the square of the total c.m. energy. This feature also reflects the behavior of the πp scattering cross section. The structureless upper-energy region can also be accommodated within the framework of Regge theory. The cross section dσdu extrapolated to u=0 varies as the -3.2 power of s, midway between that expected for the Nα and Nγ trajectories.