The process pp$ oell^+ell^-$p$^(*)$, with $ell^+ell^-$ a muon or an electron pair produced at midrapidity with mass larger than 110 GeV, has been observed for the first time at the LHC in pp collisions at $sqrts =$ 13 TeV. One of the two scattered protons is measured in the CMS-TOTEM precision proton spectrometer (CT-PPS), which operated for the first 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 fb$^-1$ collected during standard, high-luminosity LHC operation. A total of 12 $mu^+mu^-$ and 8 e$^+$e$^-$ pairs with $m(ell^+ell^-) >$ 110 GeV, and matching forward proton kinematics, are observed, with expected backgrounds of 1.49 $pm$ 0.07 (stat) $pm$ 0.53 (syst) and 2.36 $pm$ 0.09 (stat) $pm$ 0.47 (syst), respectively. This corresponds to an excess of more than five standard deviations over the expected background. The present result constitutes the first observation of proton-tagged $gammagamma$ collisions at the electroweak scale. This measurement also demonstrates that CT-PPS performs according to the design specifications.

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

Calabria, Cesare;Cristella, Leonardo;De Palma, Mauro;Di Florio, Adriano;Errico, Filippo;Gelmi, Andrea;Lezki, Samet;Miniello, Giorgia;My, Salvatore;Nuzzo, Salvatore;Pompili, Alexis;Radogna, Raffaella;Selvaggi, Giovanna;Venditti, Rosamaria;Galati, Giuliana;
2018-01-01

Abstract

The process pp$ oell^+ell^-$p$^(*)$, with $ell^+ell^-$ a muon or an electron pair produced at midrapidity with mass larger than 110 GeV, has been observed for the first time at the LHC in pp collisions at $sqrts =$ 13 TeV. One of the two scattered protons is measured in the CMS-TOTEM precision proton spectrometer (CT-PPS), which operated for the first 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 fb$^-1$ collected during standard, high-luminosity LHC operation. A total of 12 $mu^+mu^-$ and 8 e$^+$e$^-$ pairs with $m(ell^+ell^-) >$ 110 GeV, and matching forward proton kinematics, are observed, with expected backgrounds of 1.49 $pm$ 0.07 (stat) $pm$ 0.53 (syst) and 2.36 $pm$ 0.09 (stat) $pm$ 0.47 (syst), respectively. This corresponds to an excess of more than five standard deviations over the expected background. The present result constitutes the first observation of proton-tagged $gammagamma$ collisions at the electroweak scale. This measurement also demonstrates that CT-PPS performs according to the design specifications.