DPI studies

A Double Parton Interaction (DPI) is the occurrence of two hard parton scatterings within the same hadron-hadron collisions. A better understanding of DPI gives insight into the (double) Parton Distribution Functions (PDFs). At Sheffield we study DPI through the process Z+Z->4 leptons, which is also a background to the Higgs -> 4 lepton measurements. Previous DPI studies have involved jets and the 4 lepton final state is much cleaner.

In addition to the PhD thesis of D.Kyriazopoulos, DPI upper limits to the 4 lepton final state was an important background consideration in the H->ZZ->4l analysis:
  • Measurements of Higgs boson production and couplings in diboson final states with the ATLAS detector at the LHC, 10.1016/j.physletb.2013.08.010 Phys.Lett. B726 (2013) 88-119.

  • Minimum bias

    Studies of minimum bias (MB) and underlying events (UE) were first initiated on ATLAS by the Sheffield group, with Dr. I. Dawson taking a leading role. Measurements of MB and UE characteristics allow a better understanding of the structure of the proton, which in turn lead to better predictions of backgrounds to SM and BSM physics processes.

    MB data taken in December 2009 provided ATLAS with its first physics publication using collision data, followed collisions at 7 TeV in 2010:

  • Charged-particle multiplicities in pp Interactions at 900 GeV measured with the ATLAS detector at the LHC, Phys Lett B 688, Issue 1, 21-42 (2010)
  • Charged-particle multiplicities in pp interactions measured with the ATLAS detector at the LHC, New J Phys 13 (2011) 053033
  • Measurement of underlying event characteristics using charged particles in pp collisions at 900 GeV and 7 TeV with the ATLAS detector, Phys. Rev. D 83, 112001 (2011)
  • Old papers:
  • Prediction for Minimum Bias and the Underlying Event at LHC Energies, A.Moraes, C.Buttar, I.Dawson: Eur.Phys.J.C50:435-466,2007
  • Minimum bias and the underlying event: towards the LHC, I.Dawson, C.Buttar, A.Moraes: Czech. J. Phys.: 54 (2004) pp.A221-A228
  • Simulations of minimum bias events and the underlying event, MC tuning and predictions for the LHC, C.Buttar, D.Clements, I.Dawson, A.Moraes: Acta Phys. Polon. B35, (2004) pp.433-441
  • Comparison of predictions for minimum bias event generators, A.Moraes, I.Dawson, C.Buttar: ATL-PHYS-2003-020, July 2003.
  • Charge multiplicity measurement at √s =13 TeV pp interactions

    Charged-particle measurements in proton proton (pp) collisions provide insight into the strong interaction in the low-energy, non-perturbative region of quantum chromodynamics (QCD). Particle interactions at these energy scales are typically described by QCD-inspired models implemented in Monte Carlo (MC) event generators with free parameters that can be constrained by such measurements. An accurate description of low-energy strong interaction processes is essential for simulating single pp interactions as well as the effects of multiple pp interactions at high instantaneous luminosity in hadron colliders.

    The Sheffield group played an important role in this one of the first paper at 13 TeV.

  • Charged-particle distributions in √s =13 TeV pp interactions measured with the ATLAS detector at the LHC, Physics Letters B (2016), Vol. 758, pp. 67-88


  • Department of Physics and Astronomy, University of Sheffield, Hounsfield Road, Sheffield S3 7RH, UK

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