Measurement of single-diffractive dijet production in proton-proton collisions at s = 8 Te with the CMS and TOTEM experiments

Abstract

Measurements are presented of the single-diffractive dijet cross section and the diffractive cross section as a function of the proton fractional momentum loss $\xi$ and the four-momentum transfer squared t. Both processes $\text{p}\text{p}\to \text{p}\text{X}$ and $\text{p}\text{p}\to \text{X}\text{p}$ , i.e. with the proton scattering to either side of the interaction point, are measured, where $\text{X}$ includes at least two jets; the results of the two processes are averaged. The analyses are based on data collected simultaneously with the CMS and TOTEM detectors at the LHC in proton-proton collisions at $\sqrt{s}=8\text{Te}$ during a dedicated run with ${\beta }^{\ast }=90\text{m}$ at low instantaneous luminosity and correspond to an integrated luminosity of $37.5{\text{nb}}^{-1}$ . The single-diffractive dijet cross section ${\sigma }_{\mathrm{jj}}^{\text{p}\text{X}}$ , in the kinematic region $\xi <0.1$ , $0.03<\left|t\right|<1{\text{Ge}}^2$ , with at least two jets with transverse momentum $p_T>40\text{Ge}$ , and pseudorapidity $\left|\eta \right|<4.4$ , is $21.7\pm 0.9\text{(stat)}{}_{-3.3}^{+3.0}\text{(syst)}\pm 0.9\text{(lumi)}\text{nb}$ . 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 $-2.9\le {log}_{10}x\le -1.6$ , is $R=({\sigma }_{\mathrm{jj}}^{\text{p}\text{X}}/\Delta \xi )/{\sigma }_{\mathrm{jj}}=0.025\pm 0.001\text{(stat)}\pm 0.003\text{(syst)}$ , where ${\sigma }_{\mathrm{jj}}^{\text{p}\text{X}}$ and ${\sigma }_{\mathrm{jj}}$ are the single-diffractive and inclusive dijet cross sections, respectively. The results are compared with predictions from models of diffractive and nondiffractive interactions. Monte Carlo predictions based on the HERA diffractive parton distribution functions agree well with the data when corrected for the effect of soft rescattering between the spectator partons.

Fig. 1

Schematic diagram of single-diffractive dijet production. The exchange of a virtual object with the vacuum quantum numbers (i.e. a Pomeron) is indicated by the symbol $\text{I}\text{P}$. The diagram shows an example of the $\text{g}\text{g}\to \text{dijet}$ hard scattering process; the $\text{q}\text{q}$ and $\text{g}\text{q}$ initial states also contribute

Fig. 2

Distribution of ${\xi }_{\mathrm{CMS}}-{\xi }_{\mathrm{TOTEM}}$ for events with a reconstructed proton in sector 45 (left) and sector 56 (right). The data are indicated by solid circles. The blue histogram is the mixture of pomwig or pythia6 and zero bias (ZB) data events described in the text. An event with a proton measured in the RPs contributes to the open histogram (signal) if the proton originates from the MC sample, or to the filled histogram (background) if it originates from the ZB sample

Fig. 3

Distribution of ${\xi }_{\mathrm{TOTEM}}$ before (upper) and after (middle) the ${\xi }_{\mathrm{CMS}}-{\xi }_{\mathrm{TOTEM}}$ requirement and distribution of t after the ${\xi }_{\mathrm{CMS}}-{\xi }_{\mathrm{TOTEM}}$ requirement (lower) for events in which the proton is detected in sector 45 (left) and sector 56 (right). The data are indicated by solid circles. The blue histogram is the mixture of pomwig or pythia6 and zero bias (ZB) data events described in the text. An event with the proton measured in the RPs contributes to the open histogram (signal) if the proton originates from the MC sample, or to the filled histogram (background) if it originates from the ZB sample

Fig. 4

Differential cross section as a function of t (left) and as a function of $\xi$ (right) for single-diffractive dijet production, compared to the predictions from pomwig, pythia8 4C, pythia8 CUETP8M1, and pythia8 DG. The pomwig prediction is shown with no correction for the rapidity gap survival probability ($⟨S^2⟩=1$) and with a correction of $⟨S^2⟩=7.4\%$. The vertical bars indicate the statistical uncertainties and the yellow band indicates the total systematic uncertainty. The average of the results for events in which the proton is detected on either side of the interaction point is shown. The ratio between the data and the pomwig prediction, when no correction for the rapidity gap survival probability is applied, is shown in the bottom

Fig. 5

Ratio per unit of $\xi$ of the single-diffractive and inclusive dijet cross sections in the region given by $\xi <0.1$ and $0.03<|t|<1{\text{Ge}}^2$, compared to the predictions from the different models for the ratio between the single-diffractive and nondiffractive cross sections. The pomwig prediction is shown with no correction for the rapidity gap survival probability ($⟨S^2⟩=1$) (left) and with a correction of $⟨S^2⟩=7.4\%$ (right). The vertical bars indicate the statistical uncertainties and the yellow band indicates the total systematic uncertainty. The average of the results for events in which the proton is detected on either side of the interaction point is shown. The ratio between the data and the pomwig prediction using pythia6 or herwig6 as the nondiffractive contribution, when no correction for the rapidity gap survival probability is applied, is shown in the bottom of the left panel

Fig. 6

Ratio per unit of $\xi$ of the single-diffractive and inclusive dijet cross sections in the kinematic region given by $\xi <0.1$ and $0.03<|t|<1{\text{Ge}}^2$. The vertical bars indicate the statistical uncertainties and the yellow band indicates the total systematic uncertainty. The red squares represent the results obtained by CDF at $\sqrt{s}=1.96\text{Te}$ for jets with $Q^2\approx 100{\text{Ge}}^2$ and $|\eta |<2.5$, with $0.03<\xi <0.09$