QCD tests in pp collisions at sqrt(s) = 7 TeV using the ATLAS detector at the LHC
by
Javier Merino
→
Asia/Shanghai
Description
Several aspects of the strong interaction are tested in this work using the ATLAS detector at the LHC. The parton shower and hadronisation models are probed by means of a measurement of jet shapes in tbar events. The main observation is that the momentum density inside $b$-quark jets is higher at large values of the jet internal radius r, while light-quark jets present larger densities at low values of r. This effect is explained by the so-called angular screening effects, due to the heavier mass of the b-quark. This difference allows us to determine the mass of the bottom quark to be mb = 4.86^{+0.49}_{-0.42} GeV. The value of the strong coupling constant αs at the Z-pole scale has also been measured in this work. To do this, a sample of multijet events at high-momentum scales is selected by demanding the scalar sum of transverse momenta of the two leading jets to be greater than 500 GeV. A measurement of the transverse energy-energy correlation function and its asymmetry is performed and a comparison between the data and NLO pQCD calculations is presented. This allows us to determine $\alpha_s(m_\Zboson) = 0.1173 \pm 0.0010 \mbox{ (exp.)}^{+0.0065}_{-0.0026} \mbox{ (theo.)}$