Professor Amanda Cooper-Sarkar

Abstract:

Many extensions of the Standard Model predict new resonances decaying to a Z, W, or Higgs boson and a photon. This paper presents a search for such resonances produced in pp collisions at s=13 TeV using a data set with an integrated luminosity of 36.1 fb-1 collected by the ATLAS detector at the LHC. The Z/W/H bosons are identified through their decays to hadrons. The data are found to be consistent with the Standard Model expectation in the entire investigated mass range. Upper limits are set on the production cross section times branching fraction for resonance decays to Z/W+γ in the mass range from 1.0 to 6.8 TeV and for the first time into H+γ in the mass range from 1.0 to 3.0 TeV.

Abstract:

Searches for dijet resonances with sub-TeV masses using the ATLAS detector at the Large Hadron Collider can be statistically limited by the bandwidth available to inclusive single-jet triggers, whose data-collection rates at low transverse momentum are much lower than the rate from standard model multijet production. This Letter describes a new search for dijet resonances where this limitation is overcome by recording only the event information calculated by the jet trigger algorithms, thereby allowing much higher event rates with reduced storage needs. The search targets low-mass dijet resonances in the range 450–1800 GeV. The analyzed data set has an integrated luminosity of up to 29.3 fb−1 and was recorded at a center-of-mass energy of 13 TeV. No excesses are found; limits are set on Gaussian-shaped contributions to the dijet mass distribution from new particles and on a model of dark-matter particles with axial-vector couplings to quarks.

Abstract:

Fits to the final combined HERA deep-inelastic scattering cross-section data within the conventional DGLAP framework of QCD have shown some tension at low x and low Q2 . A resolution of this tension incorporating ln(1/x) -resummation terms into the HERAPDF fits is investigated using the xFitter program. The kinematic region where this resummation is important is delineated. Such high-energy resummation not only gives a better description of the data, particularly of the longitudinal structure function FL , it also results in a gluon PDF which is steeply rising at low x for low scales, Q2≃2.5GeV2 , contrary to the fixed-order NLO and NNLO gluon PDF

Abstract:

The mass of the Higgs boson is measured in the H→ZZ⁎→4ℓ and in the H→γγ decay channels with 36.1 fb−1 of proton–proton collision data from the Large Hadron Collider at a centre-of-mass energy of 13 TeV recorded by the ATLAS detector in 2015 and 2016. The measured value in the H→ZZ⁎→4ℓ channel is mHZZ⁎=124.79±0.37GeV, while the measured value in the H→γγ channel is mHγγ=124.93±0.40GeV. Combining these results with the ATLAS measurement based on 7 and 8 TeV proton–proton collision data yields a Higgs boson mass of mH=124.97±0.24GeV.