Search for Randall-Sundrum gravitons in the diphoton channel at CDF

We report on a search for new particles in the diphoton channel using a data sample of $p\overline{p}$ collisions at $\sqrt{s}=1.96\mathrm{TeV}$ collected by the CDF II detector at the Fermilab Tevatron, with an integrated luminosity of $5.4{\mathrm{fb}}^{-1}$. The diphoton invariant mass spectrum of the data agrees well with the standard model expectation. We set upper limits on the production cross section times branching ratio for the Randall-Sundrum graviton, as a function of diphoton mass. We subsequently derive lower limits on the graviton mass of $459\mathrm{GeV}/c^2$ and $963\mathrm{GeV}/c^2$, at the 95% confidence level, for coupling parameters ($k/{\overline{M}}_{\mathrm{Pl}}$) of 0.01 and 0.1, respectively.

Figure 1

The diphoton invariant mass distribution of events, histogrammed in bins of approximately one unit of calorimeter mass resolution. The width of the horizontal bar represents the bin size. The bin size is $2.4(10.4)\mathrm{GeV}/c^2$ at $m(\gamma \gamma )=100(500)\mathrm{GeV}/c^2$.

Figure 2

The diphoton invariant mass spectrum with the fitted total background overlaid. The points are the data. The width of the horizontal bar represents the bin size which is fixed at $5\mathrm{GeV}/c^2$. The dotted line shows the contribution from events where at least one selected photon is from a misidentified jet, and the solid line shows this background plus the diphox SM diphoton distribution. For clarity, the SM background is not shown in the figure since it is almost indistinguishable from the total background. The gray band shows the uncertainty on the total background.

Figure 3

The 95% C.L. upper limit on the production cross section times branching fraction of an RS model graviton decaying to diphotons [$\sigma \times \mathrm{Br}(G\to \gamma \gamma )$] as a function of graviton mass. Also shown are the predicted ($\sigma \times \mathrm{Br}$) curves for $k/{\overline{M}}_{\mathrm{Pl}}=0.01$, 0.07, 0.05, and 0.1 [20].

Figure 4

The 95% C.L. excluded region in the plane of $k/{\overline{M}}_{\mathrm{Pl}}$ and graviton mass from $5.4{\mathrm{fb}}^{-1}$ of integrated luminosity compared with the expected limit and the previously published exclusion contour [4].