Exclusive Particle Production in pp and pPb Collisions at CMS

摘要

Exclusive processes provide a useful method to study a broad range of high energy physics fields from gluon density evolutions to searches for new physics. Three measurements from the Compact Muon Solenoid experiment are reviewed. Exclusive π π production is studied in proton–proton collisions. Low-mass meson resonances are observed in the invariant mass distribution of pion pairs. The total exclusive π + π ? cross-section is also measured in the p T ( π ) 0 . 2 GeV, | y | 2 region, yielding 26.5 ± 0.3 ( stat ) ± 5.0 ( syst ) ± 1.1 ( lumi ) μ b. The photoproduction of Y ( n S ) mesons is observed in ultraperipheral pPb collisions. The differential cross-sections are measured as a function of | t | and y . The comparison with previous measurements and theoretical models provides a better understanding of the gluon density evolution at low x values. Evidence for the γ γ → W + W ? process is shown with a 3.7 σ observed significance. According to the results, limits on anomalous quartic gauge couplings can be provided.