Search for a Supersymmetry Signature with the Zgamma Plus Missing Transverse Energy Final State Using the D0 Detector

A search for a supersymmetry signature is conducted with events containing Zgamma and large missing transverse energy at Fermilab's Tevatron accelerator with pp¯ collisions at center of mass energy 1.96 GeV. The data used in the analysis was collected by the D0 experiment from June 2006 to July 2010 with a total integrated luminosity of 6.2 fb -1. This is the first search for the Zgamma plus large missing ET signature in a hadron collider experiment.;Supersymmetry, a symmetry which relates fermions and boson, is a highly motivated theory extending the standard model of particle physics. This work considers a specific experimental signature from the gauge mediated supersymmetry breaking (GMSB) model. Pairs of neutralinos would be produced and decay to a neutral boson and a gravitino. The production c&d5;01 c&d5;01 → ZG˜gammaG˜ (Z → ℓ +ℓ-) predicted by this model is investigated in detail. The experimental signature is two isolated leptons from the Z decay, an isolated photon, and large missing transverse energy due to the two gravitinos, G˜, escaping detection. Two Z decay channels are considered in the analysis, Z → e+e - and Z → mu+mu -;Where the photon has pT > 40 GeV and the missing ET is larger than 30 GeV for the electron channel and 40 GeV for the muon channel, the predicted number of events from the supersymmetric model with supersymmetry breaking scale Λ = 80 TeV is 5.2 +/- 0.18 and 4.23 +/- 0.16 for the electron and muon channels, respectively. No event is observed in the electron channel where the standard model background is expected to be 0.61 +/- 0.13 events. In the muon channel 3 events are observed where the standard model background is expected to be 1.55 +/- 0.38 events. We conclude that the observed data is consistent with the standard model prediction, no evidence for a supersymmetric signal is found. Employing a boosted decision tree selection process and combining the analysis results from both electron and muon channels we exclude the GMSB model at the 95% confidence level for 70 < Λ < 117.5 TeV, which corresponds to neutralino masses of 111 < c&d5;01 < 222 GeV.