Large Extra Dimension effects through Light-by-Light Scattering at the CERN LHC

TL;DR

The study investigates LED-induced light-by-light scattering at the LHC through the exclusive process ${\rm pp\to p\gamma\gamma p}$, incorporating forward proton tagging and EPA photon fluxes to compute cross sections. It compares graviton-exchange signals against SM ${\gamma\gamma}$ loops and DPE backgrounds, including both qq and gg initial states, and applies realistic detector acceptances and survival probabilities. The analysis yields LED sensitivity up to ${M_S} \approx 5$ TeV for ${\delta=4}$ with ${\mathcal{L}}=200\ {\rm fb}^{-1}$, highlighting the role of high-${p_T}^{\gamma}$ regions and forward detectors as a complementary probe to dijet and diphoton channels. Overall, photon-induced processes offer a clean, though challenging, avenue to explore LED scenarios at the TeV scale, reinforcing the need for multiple observables to robustly uncover new physics.

Abstract

Observing light-by-light scattering at the Large Hadron Collider (LHC) has received quite some attention and it is believed to be a clean and sensitive channel to possible new physics. In this paper, we study the diphoton production at the LHC via the process $\rm pp\rightarrow pγγp\rightarrow pγγp$ through graviton exchange in the Large Extra Dimension (LED) model. Typically, when we do the background analysis, we also study the Double Pomeron Exchange (DPE) of $γγ$ production. We compare its production in the quark-quark collision mode to the gluon-gluon collision mode and find that contributions from the gluon-gluon collision mode are comparable to the quark-quark one. Our result shows, for extra dimension $δ=4$, with an integrated luminosity $\rm {\cal L} = 200 fb^{-1}$ at the 14 TeV LHC, that diphoton production through graviton exchange can probe the LED effects up to the scale $\rm M_S=5.06 (4.51, 5.11) TeV$ for the forward detector acceptance $ξ_1 (ξ_2, ξ_3)$, respectively, where $0.0015<ξ_1<0.5$, $0.1<ξ_2<0.5$ and $0.0015<ξ_3<0.15$.

Figures (7)

• Figure 1: A generic diagram for the two photon exclusive production, $\rm pp \rightarrow p\gamma\gamma p \rightarrow pXp$ at the CERN LHC. Two incoming protons are scattered quasi elastically at very small angles. The produced system X can be detected in the central detectors.
• Figure 2: Feynman diagrams for light-light scattering of the diphoton production through graviton exchange in the LED model.
• Figure 3: Feynman diagrams for DPE contributions in $\rm u\bar{u}$, $\rm d\bar{d}$ and gg collision modes.
• Figure 4: The transverse momentum ($\rm p_T$) and Rapidity (y) distribution of a leading photon for the background production of $\rm pp\rightarrow p\gamma\gamma p\rightarrow p\gamma\gamma p$, on the basis of their transverse momentum $\rm p_T^{\gamma_1}\geq p_T^{\gamma_2}$. The kinematic cuts are considered and no survival probability factor is taken into account. Solid curve present the SM $\gamma\gamma$ loop contribution. Dashed, short-dashed, dotted and dashed-dotted lines refer to the DPE $\rm u\bar{u}$-collision mode, $\rm d\bar{d}$-collision mode, gg-collision mode and their sum, respectively. Here $0.0015<\xi_1<0.5$.
• Figure 5: The signal and total background transverse momentum ($\rm p_T^{\gamma}$) distribution of leading photon for the process $\rm pp\rightarrow p\gamma\gamma p\rightarrow p\gamma\gamma p$, on the basis of their transverse momentum $\rm p_T^{\gamma_1}\geq p_T^{\gamma_2}$ with $\rm M_S = 3.5, 4.5, 5.5 TeV$, $\rm \sqrt{s}=14 TeV$ and $\delta=4$. The high transverse momentum range includes up to 1 TeV. The kinematic cuts and survival probability factor $\rm S_{DPE}=0.03$ and $\rm S_{\gamma\gamma}=0.9$ are taken into account.