Measurement of angular correlations of jets at sqrt(s)=1.96 TeV and determination of the strong coupling at high momentum transfers

TL;DR

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Abstract

We present a measurement of the average value of a new observable at hadron colliders that is sensitive to QCD dynamics and to the strong coupling constant, while being only weakly sensitive to parton distribution functions. The observable measures the angular correlations of jets and is defined as the number of neighboring jets above a given transverse momentum threshold which accompany a given jet within a given distance Delta-R in the plane of rapidity and azimuthal angle. The ensemble average over all jets in an inclusive jet sample is measured and the results are presented as a function of transverse momentum of the inclusive jets, in different regions of Delta-R and for different transverse momentum requirements for the neighboring jets. The measurement is based on a data set corresponding to an integrated luminosity of 0.7 fb-1 collected with the D0 detector at the Fermilab Tevatron Collider in pp-bar collisions at sqrt(s)=1.96 The results are well described by a perturbative QCD calculation in next-to-leading order in the strong coupling constant, corrected for non-perturbative effects. From these results, we extract the strong coupling and test the QCD predictions for its running over a range of momentum transfers of 50-400 GeV.

Figures (3)

• Figure 1: (Color online.) The measurement of $R_{\Delta R}$ as a function of inclusive jet $p_T$ for three different intervals in $\Delta R$ and for four different requirements of $p_{T \rm min}^{\rm nbr}$. The inner uncertainty bars indicate the statistical uncertainties, and the total uncertainty bars display the quadratic sum of the statistical and systematic uncertainties. The theory predictions are shown with their uncertainties.
• Figure 2: (Color online.) The ratios of the $R_{\Delta R}$ measurements and the theory predictions obtained for MSTW2008NLO PDFs and $\alpha_s(M_Z)=0.118$. The ratios are shown as a function of inclusive jet $p_T$ in different regions of $\Delta R$ (rows) and for different $p_{T \rm min}^{\rm nbr}$ requirements (columns). The inner uncertainty bars indicate the statistical uncertainties, and the total uncertainty bars display the quadratic sum of the statistical and systematic uncertainties. The theory uncertainty is the quadratic sum of PDF and scale uncertainties.
• Figure 3: (Color online.) The strong coupling $\alpha_s$ at large momentum transfers, $Q$, presented as $\alpha_s(Q)$ (a) and evolved to $M_Z$ using the RGE (b). The uncertainty bars indicate the total uncertainty, including the experimental and theoretical contributions. The new $\alpha_s$ results from $R_{\Delta R}$ are compared to previous results obtained from inclusive jet cross section data Abazov:2009nc and from event shape data Dissertori:2009ik. The $\alpha_s(M_Z)$ result from the combined fit to all selected data points (b) and the corresponding RGE prediction (a) are also shown.