Search for Pair Production of Second-Generation Scalar Leptoquarks in $pp$ Collisions at $\sqrt{s}=7\mathrm{TeV}$

A search for pair production of second-generation scalar leptoquarks in the final state with two muons and two jets is performed using proton-proton collision data at $\sqrt{s}=7\mathrm{TeV}$ collected by the CMS detector at the LHC. The data sample used corresponds to an integrated luminosity of $34{\mathrm{pb}}^{-1}$. The number of observed events is in good agreement with the predictions from the standard model processes. An upper limit is set on the second-generation leptoquark cross section times ${\beta }^2$ as a function of the leptoquark mass, and leptoquarks with masses below 394 GeV are excluded at a 95% confidence level for $\beta =1$, where $\beta$ is the leptoquark branching fraction into a muon and a quark. These limits are the most stringent to date.

Figure 1

The distribution of $M_{\mu \mu }$ (top) after requiring at least two muons and at least two jets with $p_T>30\mathrm{GeV}$ and $S_T>250\mathrm{GeV}$, and the distribution of $S_T$ (bottom) after requiring at least two muons and at least two jets with $p_T>30\mathrm{GeV}$ and $M_{\mu \mu }>115\mathrm{GeV}$. The $Z/{\gamma }^{*}\to \mu \mu +\mathrm{\text{jets}}$ and $t\overline{t}$ contributions are rescaled by the normalization factors determined from data. Other backgrounds correspond to $VV$, $W+\mathrm{\text{jets}}$, and multijet processes. Uncertainties are statistical.

Figure 2

(Top) The expected and observed 95% C.L. upper limit on the scalar leptoquark pair production cross section multiplied by ${\beta }^2$ as a function of the LQ mass, together with the NLO theoretical cross section curve. The shaded band on the theoretical values includes PDF uncertainties and the error on the leptoquark production cross section due to renormalization and factorization scale variation by a factor of 2. The shaded region is excluded by the current D0 limits [10]. (Bottom) The minimum $\beta$ for 95% C.L. exclusion of the leptoquark hypothesis as a function of leptoquark mass. The observed limit and corresponding uncertainty band is obtained by considering the observed upper limit and theoretical branching ratio and its uncertainty in the top figure. Note: The shaded area excluded by the D0 experiment was determined with combined information from the decay channel with two muons and two jets and the decay channel with one muon, missing transverse energy, and two jets.