Projected sensitivity to the ADD large extra dimensions model in the monojet plus missing transverse momentum final state at HL-LHC, HE-LHC, and FCC-hh

Abstract

We present a unified projection of the sensitivity to the Arkani-Hamed-Dimopoulos-Dvali (ADD) model of large extra dimensions in the monojet plus missing transverse momentum final state at the HL-LHC ($\sqrt{s}=14$ TeV, 3 ab$^{-1}$), the HE-LHC (27 TeV, 15 ab$^{-1}$) and the FCC-hh (100 TeV, 30 ab$^{-1}$), for $n=2,3,4,6$ extra dimensions, with one selection, significance estimator and calibration throughout. Signal samples are generated with Pythia 8 and combined with the post-fit Standard-Model background yields released by ATLAS and CMS on HEPData; the expected significance combines the thirteen exclusive $E_{\mathrm{T}}^{\mathrm{miss}}$ bins of the ATLAS signal region, matching the binning of the published likelihood fit. Two elements are new. First, the energy scaling of the background to higher $\sqrt{s}$, including the $13\to14$ TeV step, is measured as a function of $E_{\mathrm{T}}^{\mathrm{miss}}$ from dedicated $Z(ν\barν)$+jets and $W(\ellν)$+jets samples rather than assumed constant; this reduces the projected FCC-hh reach by 39% relative to a constant-factor treatment. Second, the framework is anchored to the published ATLAS Run-2 expected 95% CL limits through a transparent $n$-dependent calibration, determined directly for all five values of $n$ and found consistent with unity ($1.001\pm1.4\%$), so that it acts as a consistency check rather than a sizeable correction; the selection response is validated against the published ATLAS cutflow. The projected 95% CL exclusion reach in $M_D$ for $n=2$ is 12.5, 15.2 and 22.0 TeV at the three colliders, with $5σ$ discovery reach of 9.8, 12.0 and 17.0 TeV, extending the ATLAS Run-2 bound of $M_D>11.2$ TeV by factors of 1.1-2.0. The calibration scheme provides a template for analogous future-collider studies; the projections hold within the stated Run-2-anchored detector and uncertainty assumptions.