Kristian Hahn

Assistant Professor

PhD, University of Pennsylvania, 2006

Kristian Hahn and his research group collect and analyze data from high-energy proton-proton collisions at the CERN Large Hadron Collider (LHC) in Geneva, Switzerland. Their research is performed with the Compact Muon Solenoid (CMS) detector and seeks to establish the mechanism by which elementary particles acquire mass. The standard model of particle physics, the enormously successful theory of electromagnetic, weak and strong interactions, provides a possible explanation; particles gain mass through interactions with a Higgs field. The model also makes an important prediction; a corresponding particle (the Higgs boson) should be experimentally accessible through its decay into well known final-states. And with CMS data collected through 2012, we may have observed exactly that! The experiment has published significant excesses in the most important standard model Higgs decay channels, including the "golden" ZZ → 4 lepton channel with which Hahn's group is deeply involved.

The recent CMS observations are a discovery of something, but is this something really the standard model Higgs? A conclusive answer to this question requires data from the upgraded LHC, which is scheduled to operate in 2015 at sqrt(s) 13-14 TeV -- roughly twice the current LHC center of mass collision energy, which is already the highest ever achieved. Hahn's group is developing data analysis techniques that will be crucial for Higgs studies in the challenging 14 TeV environment. His group is also participating in the upgrade of the CMS "Level-1" trigger for 14 TeV operations. The hardware-based Level-1 trigger is the first stage of data refinement in the experiment and is permitted just 25 ns to determine whether data from a given collision should be saved for additional processing or discarded.

Selected Publications

  • CMS Collaboration
    Observation of a new boson at a mass of 125 GeV with the CMS experiment at the LHC
    Phys. Lett. B, 716, 1 (2012).
  • CMS Collaboration
    Search for the standard model Higgs boson in the decay channel H → ZZ → 4ℓ in pp collisions at sqrt(s) 7 TeV
    Phys. Rev. Lett., 108, 111804 (2012).
  • CMS Collaboration
    Measurements of Inclusive W and Z Cross Sections in pp Collisions at sqrt(s) = 7 TeV
    JHEP, 80, 1 (2011).
  • M Chan et al.
    Studies of the CMS tracker at high trigger rate
    JINST, 5 P07007 (2010).
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August 26, 2013