Abstract
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.
Highlights
In high-energy physics, exclusive processes are a special type of collision where both colliding particles remain intact and we observe all of the produced particles
The results are compared with the Minimum Bias Rockefeller (MBR) model of Pythia 8, Dime MC and STARlight Monte Carlo (MC) event generators
They are useful in a wide range of topics such as studying low mass meson resonances, evolution of gluon PDF at low x values, and testing
Summary
In high-energy physics, exclusive processes are a special type of collision where both colliding particles remain intact and we observe all of the produced particles. Studying exclusive and semi-exclusive dipion production provides a good opportunity to study certain low mass resonances, since the quantum numbers of the final state are restricted by the exchanged objects. In these processes, two pions are produced centrally, while the two colliding protons remain intact (exclusive) or dissociate into the |η | > 4.9 region (semi-exclusive), producing particles that cannot be detected by the forward calorimeter of the CMS detector. A slightly larger cross-section is measured in the mass region of ρ(770), since the forward proton dissociation of semi-exclusive processes is not modelled by the MC event generators. The results are compared with the Minimum Bias Rockefeller (MBR) model of Pythia 8, Dime MC and STARlight Monte Carlo (MC) event generators
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
