Study of the Dijet Mass Spectrum in $pp\to W\mathbf{+}\mathrm{\text{jets}}$ Events at $\sqrt{s}\mathbf{=}7\mathrm{TeV}$

We report an investigation of the invariant mass spectrum of the two jets with highest transverse momentum in $pp\to W+2$-jet and $W+3$-jet events to look for resonant enhancement. The data sample corresponds to an integrated luminosity of $5.0{\mathrm{fb}}^{-1}$ collected with the CMS detector at $\sqrt{s}=7\mathrm{TeV}$. We find no evidence for the anomalous structure reported by the CDF Collaboration, and establish an upper limit of 5.0 pb at 95% confidence level on the production cross section for a generic Gaussian signal with mass near 150 GeV. Additionally, we exclude two theoretical models that predict a CDF-like dijet resonance near 150 GeV.

Figure 1

(a) Distribution of the invariant mass spectrum of the leading two jets observed in data. Overlaid are the fit projections of the various components. The region between the vertical dashed lines is excluded from the fit. (b) The same distribution after subtraction of all SM components except the electroweak processes $WW/WZ$. Error bars correspond to the statistical uncertainties. The hatched band represents the uncertainty on the sum of the SM components including correlations from the fit. The dark blue histogram is a resonance consistent with detector resolution and normalized to the CDF cross section scaled as described in the text. (c) The bin-by-bin pull, (data fit)/(fit uncertainty). The bins in the figures are representative of the expected resolution for a given mass and the number of entries in each bin is scaled by its width.

Figure 2

(a) The observed and expected values of the ${\mathrm{CL}}_{\mathrm{S}}$ statistic for a generic Gaussian signal hypothesis with $M=150\mathrm{GeV}$ and ${\sigma }_{jj}=15\mathrm{GeV}$, as a function of the dijet signal cross section. (b) Observed and expected 95% C.L. upper limits, with one- and two-sigma error bands, on the cross section divided by the expected values for various signal models. The limits are calculated using the ${\mathrm{CL}}_{\mathrm{S}}$ method. A value of the excluded cross section over the predicted cross section of less than one indicates that the model is excluded at 95% C.L. Table 3 lists the cross sections for these models.