Search for Contact Interactions and Large Extra Dimensions in Dimuon Events from $\mathrm{pp}$ Collisions at $\sqrt{s}$ = 8 TeV with the ATLAS Detector

A search is conducted for non-resonant new phenomena in the dimuon final states, originating from either contact interactions or large extra spatial dimensions. The proton-proton collision data recorded by the ATLAS detector at the LHC in 2012 at $\sqrt{s}$ = 8 TeV, corresponding to an integrated luminosity of 20.5 fb$^{-1}$, is used. The dimuon invariant mass spectrum is a discriminating variable in both searches, with the contact interaction search additionally utilizing the dimuon forward-backward asymmetry. No significant deviations from the Standard Model expectation are observed. Lower limits are set on the new physics parameters of interest at 95% credibility level. For $qq\mu\mu$ contact interactions, lower limits are set on the contact interaction scale $\Lambda$ between 11.8 and 20.5 TeV. Lower limits are also set on the string scale $M_{\mathrm{S}}$ for large extra spatial dimensions, from 2.8 TeV to 4.4 TeV. Results from the muon channel are combined with the electron channel to further extend the range of the lower limits on the contact interaction scale $\Lambda$ to 15.4-26.3 TeV and the range of the lower limits on the string scale $M_{\mathrm{S}}$ to 3.2-5.0 TeV. The lower limits both on $\Lambda$ and $M_{\mathrm{S}}$ are the most stringent limits to date.