Measurement of dijet production with a leading proton in proton-proton collisions at $\sqrt{s}=8\,\mathrm{TeV}$

A study of dijet production associated with a leading proton is presented. The analysis is based on a common data set collected simultaneously with the CMS and TOTEM detectors at the LHC with proton-proton collisions at $\sqrt{s}=8\,\mathrm{TeV}$ during a dedicated run with $\beta^{\ast}=90\,\mathrm{m}$, at low instantaneous luminosity. The data correspond to an integrated luminosity of $37.5\,\mathrm{nb}^{-1}$. The analysis presents the measurement of the dijet production cross section, as a function of $\xi$, the proton fractional momentum loss, and as a function of $t$, the 4-momentum transfer squared at the proton vertex. The dijet cross section in the kinematic region defined by $\xi < 0.1$, $0.03 < \lvert t \rvert < 1\,\mathrm{GeV}^2$, with at least two jets with transverse momentum $p_{\mathrm{T}} > 40\,\mathrm{GeV}$, and pseudorapidity $\lvert \eta \rvert < 4.4$, is measured as $21.7 \pm 0.9 \,\text{(stat)} \,^{+3.0}_{-3.3} \,\text{(syst)} \pm 0.9 \,\text{(lumi)} \,\mathrm{nb}$. Both the processes $\mathrm{pp} \to \mathrm{pX}$ and $\mathrm{pp} \to \mathrm{Xp}$, i.e. with the proton scattering to either side of the interaction, are measured, with X including a system of two jets. The results correspond to the average of their cross sections. The ratio of the single-diffractive to inclusive dijet yields, normalised per unit of $\xi$, is presented as a function of $x$, the longitudinal momentum fraction of the proton carried by the struck parton. The ratio in the kinematic region defined above, for $x$ values in the range $-2.9 \leq \log_{10} x \leq -1.6$, was measured as $R = \left(\sigma^{\mathrm{pX}}_{\mathrm{jj}}/\Delta\xi\right)/\sigma_{\mathrm{jj}} = 0.025 \pm 0.001 \,\text{(stat)} \pm 0.003 \,\text{(syst)}$. The results are compared to the predictions from models of diffractive and non-diffractive interactions.