Search for New Physics with the Dijet Angular Ratio

A search for dijet resonances is performed using 2.2 fb$^{-1}$ of proton-proton collision data at $\sqrt{s}=7$ TeV recorded by the CMS detector at CERN. The study is based on the dijet angular ratio, the ratio of the number of events with the two leading jets having pseudorapidity difference $\vert \Delta\eta\vert<1.3$ to the number of events with $1.3<\vert \Delta\eta\vert<3.0$. Models of new resonances which decay into two jets typically predict dijet angular distributions and hence, values of the dijet angular ratio which differ from standard model processes. We thus use the measurement of the angular ratio as a function of mass to set limits on the cross sections of new spin-$\frac{1}{2}$ quark-gluon resonances. We exclude excited quarks of mass less than 3.2 TeV at 95\% confidence level, where a limit of 2.8~TeV is expected.