Dynamics of ${}^1{S}_0$ diproton formation in the $\mathit{pd}\to \{\mathit{pp}\}{}_{s}n$ and $\mathit{pN}\to \{\mathit{pp}\}{}_s\pi$ reactions in the GeV region

Mechanisms for the production of ${}^1{S}_0$ diproton pairs, $\{\mathit{pp}\}{}_s$, in the $\mathit{pd}\to \{\mathit{pp}\}{}_{s}n$ reaction are studied at proton beam energies 0.5–2 GeV in kinematics similar to those of backward elastic $\mathit{pd}$ scattering. This reaction provides valuable information on the short-range $\mathit{NN}$ and $\mathit{pd}$ interactions that is complementary to that investigated in the well-known $\mathit{pd}\to \mathit{dp}$ and $\mathit{dp}\to p(0^{°})X$ processes. The $\mathit{pd}\to \{\mathit{pp}\}{}_{s}n$ reaction is related to the subprocesses ${\pi }^{0}d\to \mathit{pn}$ and $\mathit{pN}\to \{\mathit{pp}\}{}_s\pi$ using two different one-pion-exchange (OPE) diagrams. Within both these models a reasonable agreement could be obtained with the data below 1 GeV. The similar energy dependence of the $\mathit{pd}\to \{\mathit{pp}\}{}_{s}n$ and $\mathit{pd}\to \mathit{dp}$ cross sections and the small ratio of about 1.5% in the production of $\{\mathit{pp}\}{}_s$ to deuteron final states follow naturally within the OPE models.

Figure 1

The one nucleon exchange (ONE) mechanisms of the reactions (a) $\mathit{pd}\to \mathit{dp}$, (b) $\mathit{dA}\to p(0^{°})X$, and (c) $\mathit{pd}\to \{\mathit{pp}\}{}_{s}n$.

Figure 2

The one-pion-exchange (OPE) mechanisms considered for the reactions $\mathit{pd}\to \mathit{dp}$ (a,c) and $\mathit{pd}\to \{\mathit{pp}\}{}_{s}n$ (b,d,e): OPE-I–a,b; OPE-II – c,d,e.

Figure 3

Possible mechanisms for the $\mathit{pp}\to \{\mathit{pp}\}{}_s{\pi }^0$ reaction: (a) Δ-isobar excitation in $\pi N$-rescattering, (b) $\pi N$-rescattering in the $T=\frac{1}{2}$ state (nucleon or $N^{*}$ in the $s$-channel), (c) $T=\frac{1}{2}$ baryon ($N,N^{*}$) or Reggeon exchange (BRE) in the $t$-channel.

Figure 4

The exchange of baryons with isospin $T=\frac{1}{2}$ ($N,N^{*}$, and Reggeon) in the $t$-channel of the $\mathit{pp}\to \{\mathit{pp}\}{}_s{\pi }^0,\mathit{pn}\to d{\pi }^0,\mathit{pd}\to \{\mathit{pp}\}{}_{s}n$ and $\mathit{pd}\to \mathit{dp}$ reactions.

Figure 5

Differential cross sections for $\mathit{pd}\to \mathit{dp}$ at ${\theta }_{\text{c.m.}}={180}^{°}$ and $\mathit{pd}\to \{\mathit{pp}\}{}_{s}n$ averaged over ${\theta }_{\text{c.m.}}={166}^{°}\text{−}{180}^{°}$ versus the proton beam energy compared with the predictions of the OPE-II model for different values of the cut-off parameter: $\Lambda =1$ GeV/$c$ (full line), 0.8 (dashed-dotted), 0.65 GeV/$c$ (dashed). The cross section of the $\mathit{pn}\to d{\pi }^0$ reaction is taken from the SAID SP96 solution [31]. Data for $\mathit{pd}\to \{\mathit{pp}\}{}_{s}n$ and $\mathit{pd}\to \mathit{dp}$ are those of Refs. [20] and [32, 33, 34], respectively.

Figure 6

Differential cross section for the $\mathit{pd}\to \{\mathit{pp}\}{}_{s}n$ reaction [20]. The full thick curve shows the OPE-II results for $\Lambda =1$ GeV/$c$. The predictions [21] of the ONE (DWBA) mechanism with the CD Bonn potential are shown by the dashed (Born approximation) and dotted (with distortions) curves. The coherent sum of the OPE-II and the ONE(DWBA) is shown by the thin full line.

Figure 7

Differential cross sections for the $\mathit{pd}\to \mathit{dp}$ and $\mathit{pd}\to \{\mathit{pp}\}{}_{s}n$ reactions as shown in Fig. 5. The dashed-dotted lines give the results of fitting the data within the CCR approach of Eq. (39), where the invariant cross section behaves as $\mathrm{d}\sigma /\mathrm{d}t=\text{const}\times s^{-12.9}.$