Search for resonant $WZ$ production in the $WZ\to l\nu l^{\prime }{l}^{\prime }$ channel in $\sqrt{(}s)\mathbf{=}7\mathrm{TeV}$ $pp$ collisions with the ATLAS detector

A generic search is presented for a heavy particle decaying to $WZ\to \ell \nu {\ell }^{\prime }{\ell }^{\prime }$ ($\ell$, ${\ell }^{\prime }=e$, $\mu$) final states. The data were recorded by the ATLAS detector in $\sqrt{s}=7\mathrm{TeV}$ $pp$ collisions at the Large Hadron Collider and correspond to an integrated luminosity of $1.02{\mathrm{fb}}^{-1}$. The transverse mass distribution of the selected $WZ$ candidates is found to be consistent with the standard model expectation. Upper limits on the production cross section times branching ratio are derived using two benchmark models predicting a heavy particle decaying to a $WZ$ pair.

Figure 1

Observed and predicted $W$ boson transverse mass ($m_{\mathrm{T}}^W$) distribution in the SM $WZ$ control region (a), and dilepton invariant mass ($m_Z$) distribution in the $\ell {\ell }^{\prime }+\mathrm{\text{jets}}$ control region (b).

Figure 2

Observed and predicted $m_{\mathrm{T}}^{WZ}$ distribution for events with all selection cuts applied. Predictions from three $W^{\prime }$ samples with masses of 350 GeV, 500 GeV, and 750 GeV and a ${\rho }_{\mathrm{T}}$ sample with a mass of 500 GeV using pythia are also shown.

Figure 3

The observed and expected limits on $\sigma \times \mathrm{BR}(W^{\prime }\to WZ)$ for $W^{\prime }\to WZ$ (a) and $pp\to {\rho }_T$,$a_T\to WZ$ (b). The theoretical prediction is shown with a systematic uncertainty of 5% due to the choice of PDF and is estimated by comparing the differences between the predictions of the nominal PDF set MRST2007 ${\mathrm{LO}}^{*}$ and the ones given by MSTW2008 LO PDF using the LHAPDF framework. The green and yellow bands represent, respectively, the $1\sigma$ and $2\sigma$ uncertainties on the expected limit.

Figure 4

The 95% CL expected and observed excluded mass regions in the $(m_{{\rho }_{\mathrm{T}}},m_{{\pi }_{\mathrm{T}}})$ plane for $m_{a_{\mathrm{T}}}=1.1m_{{\rho }_{\mathrm{T}}}$ (a) and $m_{a_{\mathrm{T}}}\gg m_{{\rho }_{\mathrm{T}}}$ (b), above the curves. Two different assumptions about the ${\rho }_{\mathrm{T}}$ signal $A\times ϵ$ are used: assuming a ${\rho }_{\mathrm{T}}$ signal where $A\times ϵ$ is equal to that of the $W^{\prime }$ signal, and assuming a ${\rho }_{\mathrm{T}}$ signal where $A\times ϵ$ is obtained through its implementation in pythia.