No abstract

Measurements of Higgs boson properties in thediphoton decay channel with 36 fb −1 of p p collision data at √ s = 13 TeV with the ATLAS detectorThe ATLAS CollaborationProperties of the Higgs boson are measured in the two-photon final state using 36.1 fb −1 of proton-proton collision data recorded at √ s = 13 TeV by the ATLAS experiment at the Large Hadron Collider. Cross-section measurements for the production of a Higgs boson through gluon-gluon fusion, vector-boson fusion, and in association with a vector boson or a top-quark pair are reported. The signal strength, defined as the ratio of the observed to the expected signal yield, is measured for each of these production processes as well as inclusively. The global signal strength measurement of 0.99 ± 0.14 improves on the precision of the ATLAS measurement at √ s = 7 and 8 TeV by a factor of two. Measurements of gluon-gluon fusion and vector-boson fusion productions yield signal strengths compatible with the Standard Model prediction. Measurements of simplified template cross sections, designed to quantify the different Higgs boson production processes in specific regions of phase space, are reported. The cross section for the production of the Higgs boson decaying to two isolated photons in a fiducial region closely matching the experimental selection of the photons is measured to be 55±10 fb, which is in good agreement with the Standard Model prediction of 64 ± 2 fb. Furthermore, cross sections in fiducial regions enriched in Higgs boson production in vector-boson fusion or in association with large missing transverse momentum, leptons or top-quark pairs are reported. Differential and double-differential measurements are performed for several variables related to the diphoton kinematics as well as the kinematics and multiplicity of the jets produced in association with a Higgs boson. These differential cross sections are sensitive to higher order QCD corrections and properties of the Higgs boson, such as its spin and CP quantum numbers. No significant deviations from a wide array of Standard Model predictions are observed. Finally, the strength and tensor structure of the Higgs boson interactions are investigated using an effective Lagrangian, which introduces additional CP-even and CP-odd interactions. No significant new physics contributions are observed. 9 Measurement of fiducial integrated and differential cross sections 53 9.1 Particle-level fiducial definition of the Higgs boson diphoton cross sections 53 9.2 Fiducial integrated and differential cross sections 54 9.3 Measurements of cross sections of fiducial integrated regions 56 9.4 Measurements of cross sections of inclusive and exclusive jet multiplicities 62 9.5 Measurements of differential and double-differential cross sections 63 9.5.1 Measurements of cross sections probing the Higgs boson production kinematics 63 9.5.2 Measurements of cross sections probing the jet kinematics 65 9.5.3 Measurements of cross sections probing spin and CP 66 9.5.4 Cross sections probing the VBF production mode 68 9....

The χ(b)(nP) quarkonium states are produced in proton-proton collisions at the Large Hadron Collider at sqrt[s] = 7  TeV and recorded by the ATLAS detector. Using a data sample corresponding to an integrated luminosity of 4.4  fb(-1), these states are reconstructed through their radiative decays to Υ(1S,2S) with Υ → μ+ μ-. In addition to the mass peaks corresponding to the decay modes χ(b)(1P,2P) → Υ(1S)γ, a new structure centered at a mass of 10.530 ± 0.005(stat) ± 0.009(syst)  GeV is also observed, in both the Υ(1S)γ and Υ(2S)γ decay modes. This structure is interpreted as the χ(b)(3P) system.

Measurement of the production cross section of prompt J/ψ mesons in association with a W ± boson in pp collisions at √ s = 7 TeV with the ATLAS detectorThe ATLAS collaboration E-mail: atlas.publications@cern.ch Abstract: The process pp → W ± J/ψ provides a powerful probe of the production mechanism of charmonium in hadronic collisions, and is also sensitive to multiple parton interactions in the colliding protons. Using the 2011 ATLAS dataset of 4.5 fb −1 of √ s = 7 TeV pp collisions at the LHC, the first observation is made of the production of W ± + prompt J/ψ events in hadronic collisions, using W ± → µν µ and J/ψ → µ + µ − . A yield of 27.4 +7.5 −6.5 W ± + prompt J/ψ events is observed, with a statistical significance of 5.1σ. The production rate as a ratio to the inclusive W ± boson production rate is measured, and the double parton scattering contribution to the cross section is estimated. The ATLAS collaboration 20 IntroductionStudy of the production of a W boson in association with a prompt J/ψ meson offers new tests of Quantum Chromodynamics (QCD) at the perturbative/non-perturbative boundary as well as developing the framework for future probes of the Higgs sector and beyond-thestandard-model searches in such final states. Perturbative calculations of heavy quarkonium production in hadronic collisions distinguish between terms that produce a heavy quark system (QQ) in a colour-singlet (CS) or a colour-octet (CO) state. The relative importance of these terms for inclusive J/ψ production is a subject of debate [1][2][3][4][5][6][7]. In the case of prompt J/ψ production in association with a W ± boson, the relative contributions of CS and CO processes differ from the inclusive process. Some theoretical studies [8,9] suggest W ± + prompt J/ψ production should be dominated by colour-octet processes, and thus be a distinctive test of the non-relativistic QCD (NRQCD) framework [10,11]. In contrast, recent work [12] suggests that in 7 TeV pp collisions, CO and CS (in particular, electromagnetic W ± γ * →W ± J/ψ) contributions to the W ± + prompt J/ψ cross section are comparable. Measurements of the production cross sections can help distinguish between these models. A search for the related processes W ± +Υ(1S) and Z + Υ(1S) performed by the CDF experiment saw no excess of events above the expected background and set upper limits on the production rate [13].Observation and measurement of W ± + prompt J/ψ production for the first time represents a step in our understanding toward measurements of the Higgs boson in rare quarkonia and associated vector boson decay modes, first proposed in ref. [14]. Recent -1 - JHEP04(2014)172phenomenological studies [15] have emphasised the value of these rare decay modes to provide a unique probe of the Higgs boson charm couplings. Such final states can also be sensitive probes of beyond-the-standard-model (BSM) frameworks. The presence of an anomalous rate of W ± /Z + prompt J/ψ/Υ associated production over standard model predictions can, for example, be an indication of a sig...

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.