Central Pseudorapidity Gaps in Events with a Leading Antiproton at the Fermilab Tevatron $\overline{p}p$ Collider

We report a measurement of the fraction of events with a large pseudorapidity gap $\Delta \eta$ within the pseudorapidity region available to the proton dissociation products $X$ in $\overline{p}+p\to \overline{p}+X$. For a final state $\overline{p}$ of fractional momentum loss ${\xi }_{\overline{p}}$ and 4-momentum transfer squared $t_{\overline{p}}$ within $0.06<{\xi }_{\overline{p}}<0.09$ and $|t_{\overline{p}}|<1.0$ [0.2] ${\mathrm{G}\mathrm{e}\mathrm{V}}^2$ at $\sqrt{s}=1800$ [630] GeV, the fraction of events with $\Delta \eta >3$ is found to be $0.246\pm 0.001\mathrm{(}\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{t}\mathrm{)}\pm 0.042\mathrm{(}\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{t}\mathrm{)}$ [$0.184\pm 0.001\mathrm{(}\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{t}\mathrm{)}\pm 0.043\mathrm{(}\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{t}\mathrm{)}$]. Our results are compared with gap fractions measured in minimum bias $\overline{p}p$ collisions and with theoretical expectations.

Figure 1

Schematic diagram and event topology in pseudorapidity space of a SDD (single diffraction plus gap) interaction, $\overline{p}+p\to \overline{p}+{\mathrm{G}\mathrm{A}\mathrm{P}}_{\overline{p}}+M_1+\mathrm{G}\mathrm{A}\mathrm{P}+M_2$, with a leading outgoing antiproton of fractional momentum loss ${\xi }_{\overline{p}}$, associated with a pseudorapidity gap $\Delta {\eta }_{\overline{p}}=\ln \frac{1}{{\xi }_{\overline{p}}}$, and a gap within the region of $\eta$ spanned by $\ln s^{\prime }=\ln s-\ln \frac{1}{{\xi }_{\overline{p}}}$.

Figure 2

The number of events as a function of ${\eta }_{\mathrm{m}\mathrm{a}\mathrm{x}}$ and $-{\eta }_{\mathrm{m}\mathrm{i}\mathrm{n}}$, the $\eta$ of the track or hit tower closest to $\eta =0$ in the proton and antiproton direction, respectively, at $\sqrt{s}=1800$ GeV: (a) data; (b) Monte Carlo simulation; (c),(d) the individual contributions of Monte Carlo generated SD and SDD ($\mathrm{S}\mathrm{D}+\mathrm{\text{gap}}$) events. The MC distributions are normalized by a two-component fit to the data using distributions (c) and (d).

Figure 3

The number of events as a function of $\Delta {\eta }_{\mathrm{e}\mathrm{x}\mathrm{p}}^0={\eta }_{\mathrm{m}\mathrm{a}\mathrm{x}}-{\eta }_{\mathrm{m}\mathrm{i}\mathrm{n}}$ for data at $\sqrt{s}=1800$ GeV (points), for SD plus SDD ($\mathrm{S}\mathrm{D}+\mathrm{\text{gap}}$) MC generated events (solid line), and for only SD MC events (dashed line).

Figure 4

Ratios of SDD (single-diffraction plus gap) to single-diffractive rates (solid circles) and double-diffractive to total cross sections (open circles) as a function of the collision energy of the subprocess, Pomeron-proton, and $\overline{p}p$, respectively. The uncertainties are mainly due to systematic effects, which are highly correlated among all four data points. The dashed lines are predictions from Regge theory and the solid lines from the renormalized gap probability model [10].