Search for contact interactions using the inclusive jet $p_{\mathrm{T}}$ spectrum in $pp$ collisions at $\sqrt{s}\mathbf{=}7\mathrm{TeV}$

Results are reported of a search for a deviation in the jet production cross section from the prediction of perturbative quantum chromodynamics at next-to-leading order. The search is conducted using a 7 TeV proton-proton data sample corresponding to an integrated luminosity of $5.0{\mathrm{fb}}^{-1}$, collected with the Compact Muon Solenoid detector at the Large Hadron Collider. A deviation could arise from interactions characterized by a mass scale $\Lambda$ too high to be probed directly at the LHC. Such phenomena can be modeled as contact interactions. No evidence of a deviation is found. Using the ${\mathrm{CL}}_{\mathrm{s}}$ criterion, lower limits are set on $\Lambda$ of 9.9 TeV and 14.3 TeV at 95% confidence level for models with destructive and constructive interference, respectively. Limits obtained with a Bayesian method are also reported.

Figure 1

The cross section ratios, $f=[{\mathrm{QCD}}_{\mathrm{NLO}}+\mathrm{CI}(\Lambda )]/{\mathrm{QCD}}_{\mathrm{NLO}}$, with $\Lambda =3$, 5, 8, and 12 TeV. The points with error bars are the theoretical values of the cross section ratios. The curves are the results of a fit of Eq. (4) simultaneously to the four cross section ratios. The NLO QCD jet $p_{\mathrm{T}}$ spectrum is calculated using the nominal values of the JES, JER, PDF, renormalization and factorization scales for models with destructive interference. The values of the parameters of the fit are given in Table 1.

Figure 2

The cross section ratios, $f=[{\mathrm{QCD}}_{\mathrm{NLO}}+\mathrm{CI}(\Lambda )]/{\mathrm{QCD}}_{\mathrm{NLO}}$, with $\Lambda =8$, 10, 12, and 14 TeV, for models with destructive (top) and constructive (bottom) interference.

Figure 3

The CI signal spectra, defined as $d{\sigma }_{\mathrm{QCD}+\mathrm{CI}}/d{p}_{\mathrm{T}}-d{\sigma }_{\mathrm{QCD}}/d{p}_{\mathrm{T}}(\mathrm{pb}/\mathrm{GeV})$ with $\Lambda =8$, 10, 12, and 14 TeV, for models with destructive (top) and constructive (bottom) interference.

Figure 4

The observed jet $p_{\mathrm{T}}$ spectrum compared with the NLO QCD jet $p_{\mathrm{T}}$ spectrum (top). The bands represent the total uncertainty in the prediction and incorporate the uncertainties in the PDFs, jet energy scale, jet energy resolution, the renormalization and factorization scales, and the modeling of the jet $p_{\mathrm{T}}$ dependence of the parameters in Eq. (4). The ratio of the observed to the predicted spectrum (bottom). The error bars represent the statistical uncertainties in the expected bin count.

Figure 5

The data compared with model spectra for different values of $\Lambda$ for models with destructive interference (top). The ratio of these spectra to the NLO QCD jet $p_{\mathrm{T}}$ spectrum (bottom).

Figure 6

The data compared with model spectra for different values of $\Lambda$ for models with constructive interference (top). The ratio of these spectra to the NLO QCD jet $p_{\mathrm{T}}$ spectrum (bottom).

Figure 7

The likelihood functions assuming a model with either destructive (top) or constructive (bottom) interference. The dashed curve is the likelihood function including statistical uncertainties only and the central values of all nuisance parameters. The solid curve is the likelihood marginalized over all systematic uncertainties.