DEPARTMENT OF PHYSICS / HIP JOINT COLLOQUIA / SEMINARS 2025

• Tuesday 4 February 2025 at 10:15 in A315 and using Zoom: Laurids Jeppe (DESY)
  Searching for new scalars, pseudoscalars and top quark pair bound states at CMS
  Abstract: I will present a search for heavy pseudoscalar or scalar bosons decaying to a top quark pair ($t\bar{t}$) in final states with one or two charged leptons, using 138 fb$^{-1}$  of proton-proton collisions at $\sqrt{s} = 13$ TeV recorded by the CMS experiment. The invariant mass of the reconstructed $t\bar{t}$ system and variables sensitive to its spin state are used to discriminate against the standard model $t\bar{t}$ background and to infer spin quantum numbers. An excess of the data above the background prediction, as modeled using perturbative quantum chromodynamics (QCD) only, is observed with a significance of above five standard deviations. I will discuss three possible hypotheses to interpret the excess, which is located close to the $t\bar{t}$ production threshold: by production of an additional scalar or pseudoscalar boson, or by the existence of a color singlet pseudoscalar $t\bar{t}$ bound state, as predicted in a simplified model of nonrelativistic QCD. For the first two hypotheses, I will outline upper limits on the coupling of pseudoscalar or scalar bosons to top quarks in a mass range of 365-1000 GeV and relative widths of 0.5-25%. For the third scenario, I will present and discuss an extracted cross section of 7.1 pb with an uncertainty of 11%.
  
• Tuesday 25 February 2025 at 10:15 in A315 and using Zoom: Samuli Autti (Lancaster)
  TBA
  Abstract: TBA
• Tuesday 6 May 2025 at 10:15 in A315 and using Zoom: Andreas Schmitt (Southampton)
  TBA
  Abstract: TBA

Hopefully the up to 50 min + 10 min discussion long seminar/colloquium will be understandable to a wide audience.
Contacts: Keijo Kajantie (keijo kajantie at helsinki fi) [ HIP seminar],
Jaakko Annala (jaakko annala at helsinki fi) [cosmo seminar]

New Nordic series of seminars over the web, link: https://sites.google.com/view/nordictheory/home
For more information, and to subscribe to email announcements, contact Oscar Henriksson (oscar henriksson at helsinki fi)

Other related seminars

Friday 10-12 seminar series in D114:Astrophysics seminar
Mathematical Physics Seminar and Workshop series Wed 14-16 in Exactum C123.
InstituteQ Events and Seminars