Search for first Generation Leptoquarks in the Dielectron Channel

The D0 Collaboration

Contact Persons: Shaohua Fu, Vishnu Zutshi

Leptoquarks are hypothesized particles which appear in many extensions of the Standard Model (theories of extended gauge sectors, composite models etc.). At the Tevatron they are assumed to be pair-produced, through gluon splitting, and decay to a lepton and a quark with a branching ratio of beta. Here we report on a direct search for first generation leptoquarks in the dielectron plus dijet final state with the D0 detector. This search is based on 135 pb-1 of integrated luminosity collected in Run 2. The major backgrounds to the 2e+2j signal are Z/Drell-Yan process, top pair production, and QCD fake background. The data are consistent with Standard Model background and no evidence of leptoquark production is observed. We set a lower mass limit of 231 GeV for scalar leptoquark at 95% Confidence Level, in the case of beta=1. We then combine this result with Run 1 results, under assumption of completely uncorrelated errors. The combined mass limit for scalar leptoquark is 253 GeV from D0 Run 2 and Run 1 results, which is the most stringent limit to date.

A detailed description is available as Dě note 4227 (restricted access; non-D0-speakers, please contact the D0 NP Convenors).

Upper cross-section limits at 95% C.L. from D0 Run II only (open circles), D0 Run II combined with D0 Run I (triangles), and D0 Run II combined with CDF+D0 Run I (inverted triangles) leptoquark analyses. The NLO theoretical cross sections are plotted for Q=1, 0.5, 2 x Mlq. Arrows correspond to the respective 95% C.L. lower mass limits.

St distribution of eejj events in data (triangles) compared to background (histogram) after applying Z-veto cut. The dashed histogram is the St distribution for a 220 GeV LQ signal.

95% C.L. lower limits on the mass of first generation leptoquarks as a function of beta=BR(LQ->eq) from a combination with the search in the electron-neutrino channel.

Volker Buescher
Last modified: Wed Sep 10 10:39:27 CDT 2003