Search for nonpointing and delayed photons in the diphoton and missing transverse momentum final state in 8 TeVppcollisions at the LHC using the ATLAS detector

Abstract

A search has been performed, using the full 20.3 fb −1 data sample of 8 TeV proton-proton collisions collected in 2012 with the ATLAS detector at the LHC, for photons originating from a displaced vertex due to the decay of a neutral long-lived particle into a photon and an invisible particle. The analysis investigates the diphoton plus missing transverse momentum final state, and is therefore most sensitive to pair production of long-lived particles. The analysis technique exploits the capabilities of the ATLAS electromagnetic calorimeter to make precise measurements of the flight direction, as well as the time of flight, of photons. No excess is observed over the Standard Model predictions for background. Exclusion limits are set within the context of gauge mediated supersymmetry breaking models, with the lightest neutralino being the next-to-lightest supersymmetric particle and decaying into a photon and gravitino with a lifetime in the range from 250 ps to about 100 ns.

Search for photonic signatures of gauge-mediated supersymmetry in 8 TeVppcollisions with the ATLAS detector

“…detector is consistent with that of a prompt photon (a separate analysis [27] searches for GGM models with a longer-lived binolike NLSP, leading to signatures with nonprompt photons). In addition, the ratio tan β of the two SUSY Higgs-doublet vacuum-expectation values is set to a value of 1.5; for all five models, the phenomenology relevant to this search is only weakly dependent on the value of tan β.…”

The dark penguin shines light at colliders

“…For the search of the displaced photon signal plus missing energy, we follow the nonpointing photon analysis in [80], performed by the ATLAS collaboration on about 20 fb −1 of 8 TeV data. The full search also uses the delayed photon measurement, however, due to the complication of modeling the time of flight of the photon from the displaced vertex to the electromagnetic calorimeter (ECAL), we only focus on the measurement of ∆z γ of nonpointing photons (see figure 9).…”

“…In figure 9 the generated ∆z γ signal distribution is shown, on top of the expected background. The latter is taken from figure 4 of the ATLAS paper [80]. Because we are focusing on the non-pointing photon signals, to set constraints on the DM couplings we remove events with |∆z γ | < 30 mm.…”

“…The bounds obtained using the ATLAS non-pointing photon search [80] are shown in figure 20, for some representative choices of the parameters. The bounds are computed by means of a simple counting experiment, by comparing the signal and background yields in two different regions, corresponding to |∆z γ | > 30 mm (exclusion shaded in blue) and |∆z γ | > 220 mm (shaded in red).…”

Search for Supersymmetry in pp Collisions at √s = 8 TeV with a Photon, Lepton, and Missing Transverse Energy

“…Prompt sleptons are covered by the general slepton search already described. There are also dedicated analyses looking for displaced leptons and photons [53,54,55], exploiting the spectacular angular resolution of the calorimeters.…”