Dijet Azimuthal Decorrelations in $pp$ Collisions at $\sqrt{s}=7\mathrm{TeV}$

Measurements of dijet azimuthal decorrelations in $pp$ collisions at $\sqrt{s}=7\mathrm{TeV}$ using the CMS detector at the CERN LHC are presented. The analysis is based on an inclusive dijet event sample corresponding to an integrated luminosity of $2.9{\mathrm{pb}}^{-1}$. The results are compared to predictions from perturbative QCD calculations and various Monte Carlo event generators. The dijet azimuthal distributions are found to be sensitive to initial-state gluon radiation.

Figure 1

Normalized $\Delta {\phi }_{\mathrm{dijet}}$ distributions in several $p_T{}^{\max }$ regions, scaled by the multiplicative factors given in the figure for easier presentation. The curves represent predictions from pythia6, pythia8, $\mathrm{HERWIG}++$, and madgraph. The error bars on the data points include statistical and systematic uncertainties.

Figure 2

Ratios of measured normalized $\Delta {\phi }_{\mathrm{dijet}}$ distributions to pythia6, pythia8, $\mathrm{HERWIG}++$, and madgraph predictions in several $p_T{}^{\max }$ regions. The shaded bands indicate the total systematic uncertainty.

Figure 3

Ratios of measured normalized $\Delta {\phi }_{\mathrm{dijet}}$ distributions to NLO pQCD predictions with nonperturbative corrections in several $p_T{}^{\max }$ regions. The error bars on the data points include statistical and systematic uncertainties. The effects on the NLO pQCD predictions due to ${\mu }_r$ and ${\mu }_f$ scale variations and PDF uncertainties, as well as the uncertainties from the nonperturbative corrections, are shown.

Figure 4

Ratios of measured normalized $\Delta {\phi }_{\mathrm{dijet}}$ distributions to pythia6 tune D6T with various values of $k_{\mathrm{ISR}}$ in several $p_T{}^{\max }$ regions. The shaded bands indicate the total systematic uncertainty.