First search for exclusive diphoton production at high mass with tagged protons in proton-proton collisions at $\sqrt{s} =$ 13 TeV

TL;DR

This paper reports the first search for exclusive high-mass diphoton production with tagged protons at 13 TeV, setting limits on anomalous four-photon couplings due to no observed candidate events.

Contribution

It introduces the first experimental search for exclusive diphoton production with proton tagging at the LHC and sets new limits on anomalous four-photon couplings.

Findings

No candidate events observed.

Set upper limits on anomalous four-photon couplings.

First constraints on these couplings at 95% CL.

Abstract

A search for exclusive two-photon production via photon exchange in proton-proton collisions, pp $\to$ p$\gamma\gamma$p with intact protons, is presented. The data correspond to an integrated luminosity of 9.4 fb$^{-1}$ collected in 2016 using the CMS and TOTEM detectors at a center-of-mass energy of 13 TeV at the LHC. Events are selected with a diphoton invariant mass above 350 GeV and with both protons intact in the final state, to reduce backgrounds from strong interactions. The events of interest are those where the invariant mass and rapidity calculated from the momentum losses of the forward-moving protons matches the mass and rapidity of the central, two-photon system. No events are found that satisfy this condition. Interpreting this result in an effective dimension-8 extension of the standard model, the first limits are set on the two anomalous four-photon coupling parameters. If the other parameter is constrained to its standard model value, the limits at 95% CL are $\lvert\zeta_1\rvert$ $\lt$ 2.9 $\times$ 10$^{-13}$ GeV$^{-4}$ and $\lvert\zeta_2\rvert$ $\lt$ 6.0 $\times$ 10$^{-13}$ GeV$^{-4}$.