Search for new particles decaying into dijets in proton-antiproton collisions at sqrt(s) = 1.96 TeV

TL;DR

This paper reports a search for new particles decaying to dijets in $p\bar{p}$ collisions at $\sqrt{s}=1.96$ TeV using 1.13 fb$^{-1}$ with the CDF II detector. The authors measure the dijet mass spectrum, correct for detector effects, and compare to NLO pQCD predictions, finding agreement and no evidence of narrow resonances. They perform a resonance search by fitting a smooth background to the spectrum and set 95% C.L. upper limits on $\sigma^{sig}=\sigma\cdot\mathcal{B}\cdot\mathcal{A}$ for various models, including $q^*$, axigluon/coloron, $E_6$ diquark, $\rho_{T8}$, RS graviton, $W'$, and $Z'$. From these limits, they derive the most stringent mass exclusions to date for several models, extending or surpassing prior dijet-resonance results and providing important constraints on new strong-interaction scenarios.

Abstract

We present a search for new particles whose decays produce two jets (dijets) using proton-antiproton collision data corresponding to an integrated luminosity of 1.13 fb-1 collected with the CDF II detector. The measured dijet mass spectrum is found to be consistent with next-to-leading-order perturbative QCD predictions, and no significant evidence of new particles is found. We set upper limits at the 95% confidence level on cross sections times the branching fraction for the production of new particles decaying into dijets with both jets having a rapidity magnitude |y| < 1. These limits are used to determine the mass exclusions for the excited quark, axigluon, flavor-universal coloron, E6 diquark, color-octet technirho, W', and Z'.

Figures (4)

• Figure 1: (a) The measured dijet mass spectrum for both jets to have $|y|<1$ compared to the NLO pQCD prediction obtained using the CTEQ6.1 PDFs. (b) The ratio of the data to the NLO pQCD prediction. The experimental systematic uncertainties, theoretical uncertainties from PDF, the ratio of MRST2004/CTEQ6.1, and the dependence on the choice of renormalization and factorization scales are also shown. An additional 6% uncertainty in the determination of the luminosity is not shown.
• Figure 2: (a) The measured dijet mass spectrum (points) fitted to Eq. (\ref{['eqn:ab']}) (dashed curve). The bin-by-bin unfolding corrections is not applied. Also shown are the predictions from the excited quark, $q^*$, simulations for masses of 300, 500, 700, 900, and 1100 $\hbox{GeV}/c^2$, respectively (solid curves). (b) The fractional difference between the measured dijet mass distribution and the fit (points) compared to the predictions for $q^*$ signals divided by the fit to the measured dijet mass spectrum (curves). The inset shows the expanded view in which the vertical scale is restricted to $\pm 0.04$.
• Figure 3: Dijet mass distributions for simulated signals of the $q^*$, RS graviton, $W'$, and $Z'$ with the mass of 800 GeV/$c^2$.
• Figure 4: Observed 95% C.L. upper limits on new particle production cross sections times the branching fraction to dijets obtained with the signal shapes from (a) $W'$, (b) $Z'$, (c) RS graviton, and (d) $q^*$ production. Also shown are the cross section predictions for the production of $W'$, $Z'$, RS graviton, $\rho_{T8}$, $q^*$, axigluon, flavor-universal coloron, and $E_6$ diquark for the set of parameters described in the text. The limits and theoretical predictions are for events in which both of the leading two jets have $|y|<1$.