Search for contact interactions and large extra dimensions in dilepton events from $pp$ collisions at $\sqrt{s}\mathbf{=}7\mathrm{TeV}$ with the ATLAS detector

A search for nonresonant new phenomena, originating from either contact interactions or large extra spatial dimensions, has been carried out using events with two isolated electrons or muons. These events, produced at the LHC in proton-proton collisions at $\sqrt{s}=7\mathrm{TeV}$, were recorded by the ATLAS detector. The data sample, collected throughout 2011, corresponds to an integrated luminosity of 4.9 and $5.0{\mathrm{fb}}^{-1}$ in the $e^{+}{e}^{-}$ and ${\mu }^{+}{\mu }^{-}$ channels, respectively. No significant deviations from the Standard Model expectation are observed. Using a Bayesian approach, 95% confidence level lower limits ranging from 9.0 to 13.9 TeV are placed on the energy scale of $\ell \ell qq$ contact interactions in the left-left isoscalar model. Lower limits ranging from 2.4 to 3.9 TeV are also set on the string scale in large extra dimension models. After combining these limits with results from a similar search in the diphoton channel, slightly more stringent limits are obtained.

Figure 1

Lepton transverse momentum distributions in the dielectron (top panel) and dimuon (bottom panel) channels for data (points) and Monte Carlo simulation (histograms). The bin width is constant in $\log (p_{\mathrm{T}})$.

Figure 2

Dielectron (top panel) and dimuon (bottom panel) invariant mass distributions for data (points) and Monte Carlo simulation (filled histograms). The open histograms correspond to the distributions expected in the presence of contact interactions or large extra dimensions for several model parameters. The bin width is constant in $\log (m_{\ell \ell })$.

Figure 3

Distribution of the number of events with dilepton mass above $m_{\ell \ell }^{\min }$ for data (points) and SM prediction from Monte Carlo simulation (filled histograms, shaded gray) in the dielectron channel (top panel) and dimuon channel (bottom panel). The open solid and dashed histograms correspond to the expected distributions in the presence of contact interactions or large extra dimensions for several model parameters. The bin width is constant in $\log (m_{\ell \ell }^{\min })$.