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

The TOTEM & CMS collaborations
CMS-EXO-18-014, 2021.

Abstract (data 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 calculated from the momentum losses of the forward-moving protons equals the mass 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 $\left|\zeta_1\right|<2.88\times 10^{-13}$ GeV$^{-4}$ and $\left|\zeta_2\right|<6.02\times 10^{-13}$ GeV$^{-4}$.

  • Figure 2

    Data from Figure 2.


    Cut flow for the diphoton selection stages defined in the text (signal contribution is magnified by a factor 5000).

  • Figure 3

    Data from Figure 3.


    Invariant mass distribution of the diphoton pairs for the elastic selection region with events satisfying a < 0.005 (signal contribution...

  • Background yields

    Background yields described in the text.


    Predicted number of events having an elastic diphoton pair in association with a pair of protons observed within the range...

  • Upper limit on AQGC cross section

    Upper limits listed in the text.


    95% CL expected and observed frequentist upper limit for the LbL cross section within the $m_{\gamma\gamma} > 350$ GeV, $0.070...

  • 1-dimensional limits on AQGC

    One-dimensional limits quoted in the text.


    95% expected and observed one-dimensional limits on $\zeta_1$ and $\zeta_2$ anomalous LbyL production parameters, when the other parameter is set...

  • Figure 4

    Two-dimensional limits from Figure 4.


    95% expected and observed limits on $\zeta_1$ and $\zeta_2$ anomalous LbyL production parameters. The parametric elliptic form is assumed: $a_0\zeta_1^2+a_1\zeta_1\zeta_2+a_2\zeta_2^2=1$....

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