Measurement of the $\Upsilon(1S)$ Production Cross Section in Proton-Proton Collisions at Center of Mass Energy 7 TeV

A measurement of the cross section for $\Upsilon(1S)$ production in proton-proton collisions at center of mass energy 7 TeV is presented. The measurement uses the $\Upsilon(1S) \to \mu^{+}\mu^{-}$ decay mode and covers up to a transverse momentum of $26$ GeV in two bins of rapidity; $|y^{\Upsilon(1S)}|<1.2$ and $1.2<|y^{\Upsilon(1S)}|<2.4$. The results are based on an integrated luminosity of 1.13~pb$^{-1}$, collected with the ATLAS detector at the Large Hadron Collider. Templates derived from data are used to model the continuum background. In order to eliminate theoretical uncertainties due to the unknown polarization, the measurement is restricted to the case where both muons have a transverse momentum of $p_T^{\mu}>4$~GeV and a pseudorapidity $|\eta^{\mu}|<2.5$. The results are compared to two theoretical predictions: they agree to within a factor of two with the {\sc PYTHIA} implementation of NRQCD while disagreeing by up to a factor of ten with the color singlet model at next-to-leading order.