Search for Quark Compositeness with the Dijet Centrality Ratio in pp Collisions at sqrt(s)=7 TeV

TL;DR

This paper searches for signs of quark compositeness by analyzing dijet angular distributions in proton-proton collisions at 7 TeV, setting new lower limits on the energy scale of possible contact interactions.

Contribution

It introduces a measurement of the dijet centrality ratio to probe quark compositeness and sets the most stringent limits to date using early LHC data.

Findings

Observed limit on contact interaction scale is 4.0 TeV.

Measured dijet centrality ratio agrees with Standard Model predictions.

Expected limit on quark compositeness is 2.9 TeV.

Abstract

A search for quark compositeness in the form of quark contact interactions, based on hadronic jet pairs (dijets) produced in proton-proton collisions at sqrt(s)=7 TeV, is described. The data sample of the study corresponds to an integrated luminosity of 2.9 inverse picobarns collected with the CMS detector at the LHC. The dijet centrality ratio, which quantifies the angular distribution of the dijets, is measured as a function of the invariant mass of the dijet system and is found to agree with the predictions of the Standard Model. A statistical analysis of the data provides a lower limit on the energy scale of quark contact interactions. The sensitivity of the analysis is such that the expected limit is 2.9 TeV; because the observed value of the centrality ratio at high invariant mass is below the expectation, the observed limit is 4.0 TeV at the 95% confidence level.