Abstract
Results of a search for new phenomena in events with an energetic photon and large missing transverse momentum with the ATLAS experiment at the LHC are reported. Data were collected in proton--proton collisions at a center-of-mass energy of 8 TeV and correspond to an integrated luminosity of 20.3 fb$^{-1}$. The observed data are well described by the expected Standard Model backgrounds. The expected (observed) upper limit on the fiducial cross section for the production of such events is 6.1 (5.3) fb at 95% confidence level. Exclusion limits are presented on models of new phenomena with large extra spatial dimensions, supersymmetric quarks, and direct pair production of dark-matter candidates.
Highlights
Events that contain a high-momentum photon and large missing transverse momentum constitute a low-background sample that provides powerful sensitivity to some models of new phenomena [1,2,3,4,5,6,7]
Theories with large extra spatial dimensions (LED), presence of dark matter (DM), or supersymmetric partners of the quarks in a compressed mass spectrum scenario predict the production of γ þ EmT iss events in pp collisions beyond Standard Model (SM) expectations
The model of LED proposed by Arkani-Hamed, Dimopoulos, and Dvali [8] (ADD) aims to solve the hierarchy problem by hypothesizing the existence of n additional spatial dimensions of size R, leading to a new fundamental scale MD related to the Planck mass, MPlanck, through M2Planck ≈ M2DþnRn
Summary
Events that contain a high-momentum photon and large missing transverse momentum (referred to as γ þ EmT iss) constitute a low-background sample that provides powerful sensitivity to some models of new phenomena [1,2,3,4,5,6,7]. As observations so far do not provide strong constraints on the nature of the WIMPs and the theoretical framework to which they belong, it is interesting to study model-independent effective field theories (EFT) with various forms of interaction between the WIMPs and the Standard Model particles [10] In this case, the interaction is effectively described by four parameters: mχ, mV, the width of the mediator Γ, and the overall.
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