‘Fat-brane’ universal extra dimension model confronted with the ATLAS multi-jet and photonic searches at 13 TeV LHC
Esra Akyumuk (Department of Physics, Middle East Technical University, Ankara, TR06800, Turkey)
; Durmus Karabacak (Department of Energy System’s Engineering, Mugla Sitki Kocman University, Mugla, TR48000, Turkey)
The current status of ‘fat-brane’ minimal Universal Extra Dimension (fat-mUED) is studied in light of recent results reported by the ATLAS experiment. At the Large Hadron Collider (LHC), color charged first-level Kaluza–Klein (KK) particles (first-level excited quarks and gluons) can be abundantly pair-produced due to conserved quantity, viz., KK-parity, and the strong interaction. The cascade decay of these particles to one or more Standard Model (SM) particle(s) and lighter first-level KK particle(s) stops after producing the lightest excited massive state, named as the lightest KK particle (LKP). In the presence of gravity induced decays, the stability of the LKP is lost, allowing it to decay to photon or Z-boson by radiating KK-excited gravitons, leading to final states with photon(s) at the LHC. A variant signal topology emerges when pair-produced first-level colored KK particles undergo direct decay to their associated SM partners together with KK-excitations of gravitons resulting in a signature characterized by two hard jets and substantial missing energy. The ATLAS experiment lately reported two relevant searches at the 13 TeV LHC with 139 inverse-femtobarn of data: (i) multi-jet, and (ii) photon and jets accompanied by missing energy. Neither search observed substantial deviations from SM background expectations. Provided the absence of any number of excess events in both searches, we constrained parameters of the fat-mUED model, viz., the higher-dimensional Planck mass and the compactification scale.