Abstract
In the ‘fat-brane’ realization of Universal Extra Dimension (UED) models, the gravity mediated decays of Kaluza–Klein (KK) excitations of the Standard Model (SM) particles offer interesting collider signals. Colored level-1 KK-particles (quarks q1 and/or gluons g1) are pair-produced at the colliders due to conserved KK-parity. These particles, then, cascade decay into lighter level-1 KK-particle in association with one or more SM particles until producing lightest KK particle (LKP). The gravity mediation allows LKP to decay into photon or Z-boson plus gravity excitation, hence resulting in di-photon/ZZ/Zγ plus missing transverse energy signatures at collider experiments. Alternatively, pair-produced level-1 KK quarks/gluons may directly decay into the corresponding SM quark/gluon and a gravity excitation resulting in di-jet plus missing transverse energy signal. The ATLAS Collaboration has recently communicated the results for di-photon and multi-jet plus missing transverse energy searches with 36.1 inverse-femtobarn of integrated luminosity at 13TeV center-of-mass energy. No significant excess of events above the SM expectation was observed in both searches. We constrain the ‘fat-brane’ UED model parameters, namely the fundamental Planck mass MD and the size of small extra dimensions R, in the light of above-mentioned ATLAS searches.
Highlights
In the ’fat-brane’ realization of Universal Extra Dimension (UED) models, the gravity mediated decays of Kaluza-Klein (KK) excitations of the Standard Model (SM) particles offer interesting collider signals
If the Gravity Mediated Decays (GMD) dominate over the KKnumber conserving decays (KKCD), the pair-produced strongly interacting level-1 KK particles directly decay to their SM partners in association with a gravity excitation resulting in di-jet plus large E/ T 2 signature
We have studied the collider phenomenology of ’fat brane’ realization of minimal version of UED (mUED) in the context of recent ATLAS searches for di-photon/multi-jets plus E/ T signatures with 36.1 inverse-femtobarn of integrated luminosity data collected at 13 TeV center-of-mass energy of proton-proton collisions
Summary
We will discuss the phenomenology of level-1 excitations of the SM fields in the context of the LHC experiment. The partial gravity mediated decay width of level-1 matter fields into a level-n gravity excitation Gn can be computed using the Feynman rules for the gravity-matter interactions and the total decay width is obtained by summing over all possible gravity excitations with mass smaller than the decaying particle as given in Eq. The GMD widths are quite sensitive to the number of large extra dimensions and increases for decreasing value of N This feature can be attributed to the fact that smaller N (for example, N = 2) corresponds to small mass splittings between KK-gravity excitations and larger density of KK-gravity states and larger GMD widths. This has interesting consequences at the collider experiments which will be discussed in the following
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