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

The CMS Collaboration, TOTEM Collaboration, A. M. Sirunyan, P. Eerola, H. Kirschenmann, J. Pekkanen, M. Voutilainen, J. Havukainen, J. K. Heikkilä, T. Järvinen, V. Karimäki, R. Kinnunen, T. Lampén, K. Lassila-Perini, S. Laurila, S. Lehti, T. Lindén, P. Luukka, T. Mäenpää, H. SiikonenE. Tuominen, J. Tuominiemi, T. Tuuva, M. Berretti, F. Garcia, J. Heino, R. Lauhakangas, T. Naaranoja, F. Oljemark, K. Österberg, H. Saarikko, J. Welti

Research output: Contribution to journalArticleScientificpeer-review


The process pp -> pl(+)l(-)p(()*()), with l(+)l(-) 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 root s = 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(l(+)l(-)) > 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 five standard deviations over the expected background. The present result constitutes the first observation of proton-tagged gamma gamma collisions at the electroweak scale. This measurement also demonstrates that CT-PPS performs according to the design specifications.
Original languageEnglish
Article number153
JournalJournal of High Energy Physics
Issue number7
Number of pages45
Publication statusPublished - 24 Jul 2018
MoE publication typeA1 Journal article-refereed

Fields of Science

  • 114 Physical sciences
  • Forward physics
  • Hadron-Hadron scattering (experiments)
  • Photon production
  • proton-proton scattering
  • LHC

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