Observation of proton-tagged, central (semi)exclusive production of high-mass lepton pairs in pp collisions at 13TeV with the CMS-TOTEM precision proton spectrometer

The process pp ! p`+`p( ), with `+` a muon or an electron pair produced at midrapidity with mass larger than 110 GeV, has been observed for the rst time at the LHC in pp collisions at ps = 13TeV. One of the two scattered protons is measured in the CMS-TOTEM precision proton spectrometer (CT-PPS), which operated for the rst time in 2016. The second proton either remains intact or is excited and then dissociates into a low-mass state p , which is undetected. The measurement is based on an integrated luminosity of 9.4 fb1 collected during standard, high-luminosity LHC operation. A total of 12 + and 8 e+e pairs with m(`+`) > 110 GeV, and matching forward proton kinematics, are observed, with expected backgrounds of 1:49 0:07 (stat) 0:53 (syst) and 2:36 0:09 (stat) 0:47 (syst), respectively. This corresponds to an excess of more than ve standard deviations over the expected background. The present result constitutes the rst observation of proton-tagged collisions at the electroweak scale. This measurement also demonstrates that CT-PPS performs according to the design specications