Search for Large Extra Dimensions in the Diphoton Final State at the Large Hadron Collider

TL;DR

This work tests large extra dimensions in the ADD framework by searching for virtual-graviton contributions to diphoton production in CMS data at $\sqrt{s}=7$ TeV with $36~\mathrm{pb}^{-1}$. ED effects are encoded via $\eta_G=\mathcal{F}/M_S^4$ and interpreted under GRW, HLZ, and Hewett conventions, including interference with the SM and potential UV truncation. No excess is found, yielding 95% CL lower bounds on the cutoff scale $M_S$ in the approximate range $1.6$–$2.3$ TeV (varying with $n_{\rm ED}$ and convention), plus a model-independent cross-section limit. The results tighten prior bounds from the Tevatron and demonstrate the sensitivity of high-mass diphoton channels to virtual-graviton effects in ADD scenarios, while acknowledging theoretical uncertainties from LO calculations and UV completion.

Abstract

A search for large extra spatial dimensions via virtual-graviton exchange in the diphoton channel has been carried out with the CMS detector at the LHC. No excess of events above the standard model expectations is found using a data sample collected in proton-proton collisions at sqrt(s) = 7 TeV and corresponding to an integrated luminosity of 36 inverse picobarns. New lower limits on the effective Planck scale in the range of 1.6-2.3 TeV at the 95% confidence level are set, providing the most restrictive bounds to date on models with more than two large extra dimensions.

Figures (3)

• Figure 1: Distributions in $\eta$ and $E_T$ for the leading and sub-leading photons. Points with error bars represent observed data; the solid histogram corresponds to the expected background from control regions. Shading corresponds to the systematic uncertainty on the background expectation.
• Figure 2: Observed data (points with error bars) and background expectations (filled solid histograms) as a function of the diphoton invariant mass. Photons are required to be isolated, with $E_{\mathrm{T}}\xspace>30$ GeV and $|\eta|<1.44$. Also shown with dashed lines are the signal distributions for two sets of model parameters. Shaded bands around the background estimation correspond to systematic uncertainties. The last bin is an overflow, including the sum of all contributions for $M_{\gamma\gamma}>1.0$ TeV.
• Figure 3: Parameterization of $S$ as a function of the strength of the ED effect, $\eta_G$ for all cases except HLZ $n_{\rm ED}=2$ (left) and as a function of $1/M_{\rm S}^4$ for the $n_{\rm ED}=2$ case (right). The parameterization shown is a fit according to Eq. (\ref{['eq:CS']}). The solid line is the 95% CL exclusion limits on $S$, and is matched to the corresponding limits on $\eta_G$ and $1/M_{\rm S}^4$.