Search for New Gauge Bosons Decaying into Dileptons in p̄p Collisions at s} = 1.8 TeV

We have searched for heavy neutral gauge bosons (2’) in jjp collisions at Js = 1.8 TeV. The data were obtained using the CDF detector during 19921993 run corresponding to an integrated luminosity of 19.7f0.7 pb-‘. We present a 95% confidence level upper limit on the production cross section times branching ratio of 2’ decaying into dielectrons as a function of 2’ mass. Assuming Standard Model coupling strengths, we exclude a 2’ with mass less than 505 GeV/c 2. We also present lower mass limits for 2’ bosons from & models and the Alternative Left-Right Model. PACS numbers: 13.85.Rm, 12.15.Cc, 14.80.Er Neutral gauge bosons in addition to the 2’ are expected in many extensions of the Standard Model [l]. These models typically specify the strengths of the couplings of such bosons to quarks and leptons but make no mass predictions [2]. In up collisions, 2’ bosons may be observed directly via their decay to lepton pairs. Observation of a 2’ boson would provide dramatic evidence for physics beyond the Standard Model. To date there is no experimental evidence for the existence of any 2’ [3]. The current experimental 2’ mass limit Mzt > 412 GeV/c2 (95% C.L.) was established by the CDF collaboration [4] with the assumption that the coupling strengths of the 2’ to quarks and leptons were the same as those for the Standard Model (SM) 2’. This result was based upon data collected during the 1988-89 run with an integrated luminosity of 4 pb-’ and used both the dielectron [5] and dimuon decay modes. We report an extension of this search using 19.7 pb* of integrated luminosity from the 1992-93 run. Results reported here are obtained using only the dielectron decay mode. We present a 95% confidence level upper limit on the production cross section times branching ratio of 2’ decaying into dielectrons (g(Z) . B(Z’ + ee)). Mass limits are 5 again derived assuming SM coupling strengths. In addition, we present 2’ mass limits using several different theoretical models based on the Es symmetry group [6][‘7] and one limit based upon an Alternative Left-Right Model [8]. The CDF detector has been described in detail elsewhere [9]. We give a brief description of the components relevant to this analysis. Momenta of charged particles are measured in the Central Tracking Chamber (CTC), which is immersed in a 1.4 T axial magnetic field. Outside the CTC, electromagnetic and hadronic calorimeters are arranged in a projective tower geometry. There are three separate pseudorapidity (7) regions of calorimeters, central, end-plug, and forward, where 7 = ln(tan $) and 0 is the polar angle with respect to the direction of the proton beam. Each region has an electromagnetic calorimeter and behind it a hadronic calorimeter. For this analysis we use electrons detected in the central (CEM) or end-plug (PEM) regions. The CEM covers ]q] 9 GeV or an energy cluster in the PEM with ET > 20 GeV. If the cluster was in the CEM the trigger also required a coincidence with a track of transverse momentum PT > 9.2 GeV/c. In addition, the trigger required that the ratio of hadronic to electromagnetic energy (HAD/EM) in the trigger cluster be less than 12.5%. For electrons with 25 150 GeV), the energy deposited