Search forW̃1Z̃2Production

Abstract

We have searched for associated production of the lightest chargino, W 1 , and next-to-lightest neutralino, Z 2 , of the Minimal Supersymmetric Standard Model in pp collisions at √ s = 1.8 TeV using the DØ detector at the Fermilab Tevatron collider. Data corresponding to an integrated luminosity of 12.5±0.7 pb −1 were examined for events containing three isolated leptons. No evidence for W 1 Z 2 pair production was found. Limits on σ( W 1 Z 2 )Br( W 1 → lν Z 1 )Br( Z 2 → ll Z 1 ) are presented. Submitted to the Physical Review LettersTypeset using REVT E X At pp colliders charginos and neutralinos can be produced in pairs, with W 1 Z 2 pairs having the largest cross section over much of the parameter space [6]. Production cross sections O(100-10) pb are possible at the Tevatron for W 1 masses between 45 and 100GeV/c 2 [7,8]. The W 1 can decay into qq ′ or lν plus an LSP, while the Z 2 can decay into qq or ll plus an LSP. The presence of neutrinos or LSP's among the decay products will generally lead to missing transverse energy (E / T ). The final state consisting of three leptons and E / T (and little hadronic activity) has few SM backgrounds and is the subject of the present analysis. 6The spectra of the transverse momenta (p T ) of the final state leptons can be relatively soft due to the three-body decays of the W 1 and Z 2 involving massive non-interacting particles. Figure 1 shows the expected p T spectra of the final state leptons as well as the E / T distribution at the physics generator level for simulated W 1 Z 2 → 3l events, with M W 1 = 56 GeV/c 2 . These Monte Carlo events follow the mass relation common to many SUSY models:The data used in this analysis were obtained using the DØ detector at the Fermilab Tevatron pp collider operating at a center of mass energy of 1.8 TeV. The total integrated luminosity used in this analysis from the 1992-1993 Tevatron run was 12.5 ± 0.7 pb −1 .The DØ detector has three major subsystems: central tracking detectors (with no central magnetic field), uranium-liquid argon electromagnetic and hadronic calorimeters, and a muon spectrometer. The detector and data acquisition system are described in detail elsewhere [9]. The central tracking system is used to identify charged tracks in the pseudorapidity range |η| ≤ 3.5. The calorimeters provide full angular coverage for |η| ≤ 4.0, with transverse segmentation ∆η × ∆φ = 0.1 × 0.1, where φ is the azimuthal angle. The muon system consists of proportional drift chambers and magnetized iron toroids with coverage extending to |η| ≤ 3.3.Electrons were identified as calorimeter clusters having at least 90% of their energy deposition in the electromagnetic calorimeter, with one or more tracks pointing to the cluster.Jets were reconstructed from energy deposition in the calorimeters using a cone algorithm with cone size R = √ ∆η 2 + ∆φ 2 = 0.5. Muon tracks were reconstructed using hits in the muon drift chambers; their momenta were calculated from the bend of the tracks in the toroids.Combinations of single lepton and dile...

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