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

Abstract

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 √s=7 TeV corresponding to an integrated luminosity of 2.2 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.

Graviton phenomenology of linear dilaton geometries

“…We can set bounds on this scenario from current LHC Randall-Sundrum resonance searches, which depend on the coupling strength and mass of each KK mode, as shown in Figure 2 [16][17][18]. These searches are sensitive to KK gravitons decaying to pairs of photons or leptons that can be seen as invariant mass peaks above the background.…”

“…The dominant contribution is from on-shell s-channel KK gravitons; the width of each resonance is much smaller than the mass difference between consecutive modes, and there is minimal interference with Standard Model particles. We model the production and decay of KK modes up to the cutoff M 5 for a range of |α| and M 5 in Madgraph 5.0 [19] and compare the signal cross-section as a function of center of mass energy with published limits [16][17][18]20]. The dependence on the cutoff is insignificant due to the extremely low production rates at multi-TeV energies.…”

“…Unlike the ADD and RS theories, in the linear dilaton geometry the coupling of each mode is a function of mode number (18). To compute total cross-sections we calculate the continuum integral of the sum n σ n .…”

“…Based of the fact that in n ≥ 2 extra dimensions the signal cross-section does not fall with center of mass energy, the experimental signal regions have been selected to be at very high invariant masses [16][17][18]20]. For the linear dilaton geometry, the cross-section is inversely proportional to s and so the searches optimized for δ ≥ 2 are less effective.…”

“…Then limits are set by comparing the observed and expected event counts in the signal region. Current searches have signal regions start at an invariant masses near 1 TeV, depending on the channel [16][17][18]20].…”