Search for Signatures of Extra Dimensions in the Diphoton Mass Spectrum at the Large Hadron Collider

A search for signatures of extra spatial dimensions in the diphoton invariant-mass spectrum has been performed with the CMS detector at the LHC. No excess of events above the standard model expectation is observed using a data sample collected in proton-proton collisions at $\sqrt{s}=7\mathrm{TeV}$ corresponding to an integrated luminosity of $2.2{\mathrm{fb}}^{-1}$. In the context of the large-extra-dimensions model, lower limits are set on the effective Planck scale in the range of 2.3–3.8 TeV at the 95% confidence level. These limits are the most restrictive bounds on virtual-graviton exchange to date. The most restrictive lower limits to date are also set on the mass of the first graviton excitation in the Randall-Sundrum model in the range of 0.86–1.84 TeV, for values of the associated coupling parameter between 0.01 and 0.10.

Figure 1

Observed event yields (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 $E_T>70\mathrm{GeV}$ and $|\eta |<1.44$. The shaded band around the background estimation corresponds to the average systematic uncertainty over the spectrum. The precise per-bin uncertainty is not provided for the sake of clarity. The last bin includes the sum of all contributions for $M_{\gamma \gamma }>2.0\mathrm{TeV}$. The simulated distributions for two, nonexcluded signal hypotheses are shown for comparison as dotted (ADD) and dashed (RS) lines.

Figure 2

Signal cross section $S$ parametrization as a function of the strength of the ED effects ${\eta }_G$ (top) and as a function of $1/M_{\mathrm{S}}^4$ for the HLZ $n_{\mathrm{ED}}=2$ case (bottom).

Figure 3

The 95% C.L. exclusion region for the RS1 graviton model in the $M_1\mathrm{\text{−}}\tilde{k}$ plane. The expected limits coincide very closely with the measured limits and so are not shown in the figure. Also shown are bounds due to electroweak constraints and naturalness (${\Lambda }_{\pi }>10\mathrm{TeV}$). Perturbativity requirements bound $\tilde{k}\lesssim 0.10$.