Jet Signals for Low Mass Strings at the Large Hadron Collider

The mass scale $M_s$ of superstring theory is an arbitrary parameter that can be as low as few TeVs if the Universe contains large extra dimensions. We propose a search for the effects of Regge excitations of fundamental strings at the CERN Large Hadron Collider (LHC), in the process $pp\to \gamma +\mathrm{\text{jet}}$. The underlying parton process is dominantly the single photon production in gluon fusion, $gg\to \gamma g$, with open string states propagating in intermediate channels. If the photon mixes with the gauge boson of the baryon number, which is a common feature of $D$-brane quivers, the amplitude appears already at the string disk level. It is completely determined by the mixing parameter—and it is otherwise model (compactification) independent. Even for relatively small mixing, $100{\mathrm{fb}}^{-1}$ of LHC data could probe deviations from standard model physics, at a $5\sigma$ significance, for $M_s$ as large as 3.3 TeV.

Figure 1

In the left panel we display the behavior of the QCD cross section (dot-dashed line) and $\mathrm{\text{string}}+\mathrm{QCD}$ cross section (solid line) for $pp\to \gamma +\mathrm{\text{jet}}$ for two values of the string scale. In the right panel we show the cross section and the number of events for fixed $k_{\perp \min }=300\mathrm{GeV}$ and varying string scale. The horizontal dashed line represents the SM background.

Figure 2

Signal-to-noise ratio for an integrated luminosity of $100{\mathrm{fb}}^{-1}$. The solid line indicates the optimistic case with 100% detector efficiency and ${\kappa }^2=0.02$. The dashed (${\kappa }^2=0.01$) and dot-dashed (${\kappa }^2=0.02$) lines indicate more conservative scenarios in which considerations of detector efficiency and selection cuts reduce the total number of events by a factor of 2. The dotted line corresponds to a very optimistic nonminimal case with ${\kappa }^2=0.1$ and 100% detector efficiency.