Contact persons : Darin Acosta , Jacobo Konigsberg , Dmitri Tsybychev , Song Ming Wang
We report on a search for the pair production of first-generation leptoquarks using 191 pb**-1 of proton-antiproton collision data recorded by the CDF experiment during Run 2 of the Tevatron. The leptoquarks are sought via their decay into a neutrino and quark, which yields missing transverse energy and several high transverse momentum jets. In the leptoquark signal region, 124 events are observed with 118.3+-14.5 expected from background. Therefore, no evidence for leptoquark production is observed, and limits are set on the cross section times squared branching ratio. Using the next-to-leading order cross section for leptoquark production, we exclude the mass interval 78 to 117 GeV/c**2 at the 95% confidence level for 100% branching ratio into neutrino plus quark.
The missing transverse energy distribution in the leptoquark signal region for data (solid points) compared to Standard Model background (yellow histogram). Also shown is the distribution expected for leptoquark production and decay at a mass of 125 GeV/c**2 (red histogram). Links to this plot : EPS , GIF
Comparison of the number of events observed in data (solid points) with the number expected from Standard Model sources (histograms) for the control regions around the signal region. The electroweak contribution is shown separately from the contribution due to QCD multi-jet production and top pair production. The total uncertainty on the predicted background is shown by the hatched region.
In the signal region we required :
The upper limit on the cross section times squared branching ratio for scalar leptoquark production (beta=0). Also shown is the next leading order cross section for beta=0 for 3 choices of the factorization/renormalization scale: mu=m(LQ), mu=2*m(LQ), and mu=0.5*m(LQ).
