Search for New Particles in Two-Jet Final States in 7 TeV Proton-Proton Collisions with the ATLAS Detector at the LHC

A search for new heavy particles manifested as resonances in two-jet final states is presented. The data were produced in 7 TeV proton-proton collisions by the LHC and correspond to an integrated luminosity of $315{\mathrm{nb}}^{-1}$ collected by the ATLAS detector. No resonances were observed. Upper limits were set on the product of cross section and signal acceptance for excited-quark ($q^{*}$) production as a function of $q^{*}$ mass. These exclude at the 95% C.L. the $q^{*}$ mass interval $0.30<m_{q^{*}}<1.26\mathrm{TeV}$, extending the reach of previous experiments.

Figure 1

The data ($D$) dijet mass distribution (filled points) fitted by using a binned background ($B$) distribution described by Eq. (1) (histogram). The predicted $q^{*}$ signals [2, 3] for excited-quark masses of 500, 800, and 1200 GeV are overlaid, and the bin-by-bin significance of the data-background difference is shown.

Figure 2

The 95% C.L. upper limit on $\sigma ·\mathcal{A}$ as a function of dijet resonance mass (black filled circles). The black dotted curve shows the expected 95% C.L. upper limit, and the light and dark yellow shaded bands represent the 68% and 95% credibility intervals of the expected limit, respectively. The dashed curves represent excited-quark $\sigma ·\mathcal{A}$ predictions for different MC tunes, each using a different PDF set.