Muon reconstruction performance and constraints on off-shell Higgs Boson production and the Higgs Boson total width with the ATLAS detector and charm production at low transverse momentum with the CDF detector

The latest constraints on the signal strength of the off-shell Higgs boson production and the Higgs boson total width in the ZZ → 𝓁𝓁νν final state are presented. The Higgs boson is studied in decays to a pair of on-shell Z bosons where one of the two Z bosons decays to a pair of leptons - 𝓁 stands for either an electron or a muon - and the other to a pair of neutrinos. The analysis is based on proton-proton collision data collected by the ATLAS detector in 2015 and 2016 at a centre-of-mass energy of 13 TeV at the Large Hadron Collider (LHC), corresponding to a total integrated luminosity of 36.1 fb−1. An observed (expected) upper limit on the off-shell Higgs signal strength, defined as the event yield normalised to the Standard Model prediction, of 5.3 (4.4) is obtained at 95% confidence level (CL) in the ZZ → 𝓁𝓁νν channel. After the combination with similar results from the ZZ → 4𝓁 channel the reported observed (expected) limit is 3.8 (3.4) at 95% CL. Assuming the ratio of the Higgs boson couplings to the Standard Model predictions is independent of the momentum transfer of the Higgs production mechanism considered in the analysis, a combination with the on-shell signal-strength measurements yields an observed (expected) 95% CL upper limit on the Higgs boson total width of 14.4 (15.2) MeV.
The ATLAS simulation includes the best knowledge of the detector geometry, material distribution, and physics modeling of the muon interaction with the material of the ATLAS sub-detectors. However, this is not enough to reproduce the muon momentum scale(resolution) of data at the needed level of permille(percent) precision for important measurements, such as the Higgs boson mass. Additional corrections are applied to achieve such data/MC agreement. They are based on J/ψ → µµ and Z → µµ decays. A new independent validation of these corrections is possible using the Υ → µµ resonance. At ATLAS this is challenging as the momentum resolution is not sufficient to fully resolve the Υ(1S), Υ(2S) and Υ(3S) resonances. Results are based on proton-proton collision data collected by the ATLAS detector in 2015 and 2016 at a centre-of-mass-energy of 13 TeV at the LHC, corresponding to a total integrated luminosity of 36.5 fb−1. They demonstrate that the Υ resonance is a reliable validation channel. The corrected MC is in very good agreement with data, with the momentum scale within the scale systematic uncertainty of 0.05% in the barrel region and up to 0.25% in the forward region, ∣η∣ ∼ 2.5. The muon momentum resolution is measured to be of 1.7% and 2.9% in the centre of the detector and in the endcaps, respectively. The observed level of agreement demonstrates that the ATLAS simulation provides a very accurate description of the muon momentum scale and resolution in all η regions, over a wide pT range.
A measurement of the D+-meson production cross section as a function of the transverse momentum is reported. Results are based on the full dataset of protonantiproton collisions collected by the CDF detector at 1.96 TeV centre-of-mass energy at the Tevatron Run II and corresponding to 10 fb−1 of integrated luminosity. Fully reconstructed D+ → K−π+π+ decays in the central rapidity region ∣y∣ < 1 with transverse momentum down to 1.5 GeV are used. This is a range previously unexplored in pp¯ collisions, close to a kinematic range where it is challenging to make predictions in perturbative QCD. Inelastic pp¯-scattering events are selected online using minimally biasing requirements followed by an optimized offline selection. The K−π+π+ mass distribution is used to identify the D+ signal, and the D+ transverse impact-parameter distribution is used to separate prompt production, occurring directly in the hard-scattering process, from secondary production from b-hadron decays. The final number of prompt D+ candidates is 2950 corresponding to a total cross section σ(D+,1.5 < pT < 14.5 GeV, ∣y∣ < 1) = 71.9 ± 6.8(stat) ± 9.3(syst) µb. While the measured cross sections are consistent with theoretical estimates in each pT bin, the shape of the observed pT spectrum is softer than the expectation from QCD. This is the first time the D+-meson production cross section in pp¯ collisions has been measured at such low transverse momenta. It provides important input to improve future QCD predictions. In addition, in searches for astrophysical neutrinos, knowledge of charm production cross-sections may improve estimations of background rates from neutrinos produced in decays of charm hadrons from cosmicray interactions with atmospheric nuclei.

Keywords: CDF
Muon
Higgs Boson Width
ATLAS
Particle Physics
Tevatron
Charm
LHC
Advisor: Shipsey, IP