Forward Differential Cross Sections for the Reactionp+p→d+π+in the Range3.4−12.3 GeVc
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Abstract
A missing-mass spectrometer, employing optical spark chambers with automatic vidicon readout, was used to measure the forward differential cross section ($cos{\ensuremath{\theta}}_{\mathrm{c}.\mathrm{m}.}\ensuremath{\approx}0.995$) for the reaction $p+p\ensuremath{\rightarrow}d+{\ensuremath{\pi}}^{+}$ at closely spaced settings of the incident proton momentum in the range ${p}_{0}=3.4\ensuremath{-}12.3 \frac{\mathrm{GeV}}{c}$. 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 $p+p\ensuremath{\rightarrow}d+{\ensuremath{\pi}}^{+}$ 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 ${E}_{\mathrm{c}.\mathrm{m}.}=3.0$ GeV and show a hitherto unreported shoulder at ${E}_{\mathrm{c}.\mathrm{m}.}=3.7$ GeV. This structure, along with the well-known sharp maximum at ${E}_{\mathrm{c}.\mathrm{m}.}=2.2$ GeV, may be understood on the basis of a one-pion-exchange model as reflecting the behavior of the $T=\frac{3}{2}$ isobars in pion-nucleon scattering. Above ${E}_{\mathrm{c}.\mathrm{m}.}=3.9$ 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 $\ensuremath{\pi}p$ scattering cross section. The structureless upper-energy region can also be accommodated within the framework of Regge theory. The cross section $\frac{d\ensuremath{\sigma}}{\mathrm{du}}$ extrapolated to $u=0$ varies as the -3.2 power of $s$, midway between that expected for the ${N}_{\ensuremath{\alpha}}$ and ${N}_{\ensuremath{\gamma}}$ trajectories.