This analysis presents an observation of the photon-fusion production of W boson pairs using the CMS detector at the LHC. The total cross section of the W$^+$W$^-$ production in photon fusion is measured using proton-proton collision data with an integrated luminosity of 138 fb$^{-1}$ collected with the CMS detector in 2016$-$2018 at a center-of-mass energy of $\sqrt{s}$ = 13 TeV. Events are selected in the final state with one isolated electron and one isolated muon, and no additional tracks associated with the electron-muon production vertex. The total and fiducial production cross sections are 643$^{+82}_{-78}$ fb and 3.96$^{+0.53}_{-0.51}$ fb, respectively, in agreement with the standard model predictions of 631 $\pm$ 126 fb and 3.87 $\pm$ 0.77 fb. This agreement enables stringent constraints to be imposed on anomalous quartic gauge couplings within a dimension-8 effective field theory framework.
Normalized simulated $N_{tracks}$ distributions for signal and background processes.
Normalized simulated acoplanarity distributions for signal and background processes. The acoplanarity distribution is shown for events with $N_{tracks}=0$.
Observed and predicted $p_{T}^{e\mu}$ distributions for events with $N_{tracks}=0$, using 2016--2018 data. The distributions are shown after the maximum likelihood fit to the data ('postfit distributions'). The observed data and their associated Poissonian statistical uncertainty are shown with black markers with vertical error bars. The uncertainty band accouts for all sources of background and signal uncertainty, systematic as well as statistical, after the fit. The last bin includes the overflow. The lower panels show the ratio of data to sum of signal and background contributions, before (prefit, open red circles) and after (black full markers) the maximum likelihood fit.
The target asymmetry T, recoil asymmetry P, and beam-target double polarization observable H were determined in exclusive $\pi ^0$ and $\eta $ photoproduction off quasi-free protons and, for the first time, off quasi-free neutrons. The experiment was performed at the electron stretcher accelerator ELSA in Bonn, Germany, with the Crystal Barrel/TAPS detector setup, using a linearly polarized photon beam and a transversely polarized deuterated butanol target. Effects from the Fermi motion of the nucleons within deuterium were removed by a full kinematic reconstruction of the final state invariant mass. A comparison of the data obtained on the proton and on the neutron provides new insight into the isospin structure of the electromagnetic excitation of the nucleon. Earlier measurements of polarization observables in the $\gamma p \rightarrow \pi ^0 p$ and $\gamma p \rightarrow \eta p$ reactions are confirmed. The data obtained on the neutron are of particular relevance for clarifying the origin of the narrow structure in the $\eta n$ system at $W = 1.68\ \textrm{GeV}$. A comparison with recent partial wave analyses favors the interpretation of this structure as arising from interference of the $S_{11}(1535)$ and $S_{11}(1650)$ resonances within the $S_{11}$-partial wave.
Target asymmetry T, recoil asymmetry P, and polarization observable H for $\gamma p \to \pi^0 p$ as a function of the polar center-of-mass angle for bins at the given centroid c.m. energies.
Target asymmetry T, recoil asymmetry P, and polarization observable H for $\gamma n \to \pi^0 n$ as a function of the polar center-of-mass angle for bins at the given centroid c.m. energies.
Target asymmetry T, recoil asymmetry P, and polarization observable H for $\gamma p \to \eta p$ as a function of the polar center-of-mass angle for bins at the given centroid c.m. energies.
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