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Abstract:

Measurements of the total and differential Higgs boson production cross-sections, via WH and ZH associated production using H → WW* → ℓνℓν and H → WW* → ℓνjj decays, are presented. The analysis uses proton-proton events delivered by the Large Hadron Collider at a centre-of-mass energy of 13 TeV and recorded by the ATLAS detector between 2015 and 2018. The data correspond to an integrated luminosity of 140 fb−1. The sum of the WH and ZH cross-sections times the H → WW* branching fraction is measured to be 0.44−0.09+0.10stat.−0.05+0.06syst. pb, in agreement with the Standard Model prediction. Higgs boson production is further characterised through measurements of the differential cross-section as a function of the transverse momentum of the vector boson and in the framework of Simplified Template Cross-Sections.

Abstract:

A measurement is presented of elliptic ( $v_2$ ) and triangular ( $v_3$ ) azimuthal anisotropy coefficients for charged particles produced in $\mathrm{Pb}+\mathrm{Pb}$ collisions at $\sqrt{s_{{}_{\text{NN}}}}=5.02��\text{TeV}$ using a dataset corresponding to an integrated luminosity of $0.44{\text{nb}}^{-1}$ collected with the ATLAS detector at the LHC in 2018. The values of $v_2$ and $v_3$ are measured for charged particles over a wide range of transverse momentum ( $p_{\text{T}}$ ), 1–400 $\text{GeV}$ , and $\mathrm{Pb}+\mathrm{Pb}$ collision centrality, 0–60%, using the scalar-product and multiparticle cumulant methods. These methods are sensitive to event-by-event fluctuations and nonflow effects in the measurements of azimuthal anisotropies. Positive values of $v_2$ are observed up to a $p_{\text{T}}$ of approximately 100 $\text{GeV}$ from both methods across all centrality intervals. Positive values of $v_3$ are observed up to approximately 25 $\text{GeV}$ using both methods, though the application of the three-subevent technique to the multiparticle cumulant method leads to significant changes at the highest $p_{\text{T}}$ . At high $p_{\text{T}}$ ( $p_{\text{T}}⪆10��\text{GeV}$ ), charged particles are dominantly from jet fragmentation. These jets, and hence the measurements presented here, are sensitive to the path-length dependence of parton energy loss in the quark-gluon plasma produced in $\mathrm{Pb}+\mathrm{Pb}$ collisions.

Abstract:

With increasing demand for active sensor surface and compact modularization, monolithic active pixel sensors are gaining track in high-energy physics experiments. The analog circuits in these mixed-signal ASICs are often black boxes where the components’ function and the circuitry’s behavior can only be evaluated through simulation or educated guesses. Further, parameters acting on these components are often present, allowing the tuning of the behavior towards optimal performance of the circuitry while in operation. These parameters span a multidimensional feature space that is highly intertwined, making precise predictions of their influence on the sensor performance challenging. An approach to evaluate the interplay and importance of these parameters based on Shapley values is presented, which can provide information about the implemented circuit on the ASIC. We show how input–output information can be used, to assess the importance and influence of the components in the analog circuit on the performance of an exemplary pixel sensor. The resulting increase in information can help to evaluate the best tuning parameters of the circuit respective to the present requirements of the users as well as generate valuable feedback for designers guaranteeing the optimal performance of the sensor.

Abstract:

Jets with different radius parameters R are an important tool for probing quantum chromodynamics processes at different angular scales. Jets with small R=0.2$$R=0.2$$ are instrumental in measurements of the substructure of large-R jets resulting from collimated hadronic decays of energetic W,�� Z,�� and Higgs bosons, top quarks, and of potential new resonances. This paper presents measurements of the energy scale, resolution, and associated uncertainties of jets with radius parameters R=0.2$$R=0.2$$ and 0.6,�� obtained using the ATLAS detector. The results are based on 37fb-1$$37~\text {fb}^{-1}$$ of proton–proton collision data from the Large Hadron Collider at a centre-of-mass energy of s=13$$\sqrt{s}=13$$��TeV. A new in situ method for measuring jet energy scale differences between data and Monte Carlo simulations is presented. The systematic uncertainties in the jet energy scale for central jets (|η|<1.2)$$(|\eta | < 1.2)$$ typically vary from 1% to about 5% as a function of |η|$$|\eta |$$ at very low transverse momentum, pT,$$p_{\text {T}},$$ of around 20��GeV for both R=0.2$$R=0.2$$ and 0.6 jets. The relative energy resolution ranges from (35±6)%$$(35 \pm 6)\%$$ at pT=20$$p_{\text {T}} = 20$$��GeV to (6±0.5)%$$(6 \pm 0.5)\%$$ at pT=300$$p_{\text {T}} = 300$$��GeV for central R=0.2$$R=0.2$$ jets, and is found to be slightly worse for R=0.6$$R=0.6$$ jets. Finally, the effect of close-by hadronic activity on the jet energy scale is investigated and is found to be well modelled by the ATLAS Monte Carlo simulations.

Abstract:

We determine the value of the strong coupling αs and study its running over a wide range of scales as probed by the dijet production process at hadron colliders, based on an NNLO QCD analysis of LHC dijet data. From a large subset of these data a value of αs(mZ) =0.1178 ± 0.0022 is obtained for the strong coupling at the scale of the Z-boson mass mZ, using the invariant mass of the dijet system to select the scale where is probed. The combination of different data sets enhances the reach and precision of the analysis in the multi-TeV range and allows for the first determination of up to scales of 7. Complementing the LHC data with dijet cross sections measured at the HERA electron–proton collider, the kinematic range is extended to test the running of the strong coupling towards smaller scales. Our results exhibit excellent agreement with predictions based on the renormalization group equation of QCD, and represent a comprehensive test of the asymptotic behavior of QCD, spanning more than three orders of magnitude in energy scale.