Measurement of Triple-Differential Dijet Cross Sections with the CMS Detector at 8 TeV and PDF Constraints

The first measurement of triple-differential dijet cross sections at the LHC is presented using 19. 71 fb−1 of data collected with the CMS detector in proton-proton collisions at 8TeV. The cross sections are measured as a function of the average transverse momentum, the rapidity separation, and the boost of the two leading jets. The unfolded cross sections agree with perturbative QCD calculations at NLO accuracy apart from phase space regions containing strongly boosted dijets events, in which the measurement is sensitive to the PDFs. Constraints on the PDFs are derived by including the data in a PDF fit together with DIS cross sections from the HERA experiments. Compared to a fit with HERA DIS data alone, the uncertainties of the PDFs, especially those of the gluon PDF, are significantly reduced and a harder gluon PDF is obtained.