Studies of the spin and parity quantum numbers of the Higgs boson are presented, based on proton–proton collision data collected by the ATLAS experiment at the LHC. The Standard Model spin–parity JP=0+JP=0+ hypothesis is compared with alternative hypotheses using the Higgs boson decays H→γγH→γγ, H→ZZ⁎→4ℓH→ZZ⁎→4ℓ and H→WW⁎→ℓνℓνH→WW⁎→ℓνℓν, as well as the combination of these channels. The analysed dataset corresponds to an integrated luminosity of 20.7 fb−1 collected at a centre-of-mass energy of √s=8TeV. For the H→ZZ⁎→4ℓH→ZZ⁎→4ℓ decay mode the dataset corresponding to an integrated luminosity of 4.6 fb−1 collected at √s=7TeV is included. The data are compatible with the Standard Model JP=0+JP=0+ quantum numbers for the Higgs boson, whereas all alternative hypotheses studied in this Letter, namely some specific JP=0−,1+,1−,2+JP=0−,1+,1−,2+ models, are excluded at confidence levels above 97.8%. This exclusion holds independently of the assumptions on the coupling strengths to the Standard Model particles and in the case of the JP=2+JP=2+ model, of the relative fractions of gluon-fusion and quark–antiquark production of the spin-2 particle. The data thus provide evidence for the spin-0 nature of the Higgs boson, with positive parity being strongly preferre

The luminosity calibration for the ATLAS detector at the LHC during pp collisions at in 2010 and 2011 is presented. Evaluation of the luminosity scale is performed using several luminosity-sensitive detectors, and comparisons are made of the long-term stability and accuracy of this calibration applied to the pp collisions at . A luminosity uncertainty of is obtained for the 47 pb−1 of data delivered to ATLAS in 2010, and an uncertainty of is obtained for the 5.5 fb−1 delivered in 2011.

High energy photon colliders (γγ,γe) are based on e-e-linear colliders where high energy photons are produced using Compton scattering of laser light on high energy electrons just before the interaction point. This paper is a part of the Technical Design Report of the linear collider TESLA.1Physics program, possible parameters and some technical aspects of the photon collider at TESLA are discussed.

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Abstract:The ATLAS experiment at the LHC has measured the production cross section of events with two isolated photons in the final state, in proton-proton collisions at √ s = 7 TeV. The full data set collected in 2011, corresponding to an integrated luminosity of 4.9 fb −1 , is used. The amount of background, from hadronic jets and isolated electrons, is estimated with data-driven techniques and subtracted. The total cross section, for two isolated photons with transverse energies above 25 GeV and 22 GeV respectively, in the acceptance of the electromagnetic calorimeter (|η| < 1.37 and 1.52 < |η| < 2.37) and with an angular separation ∆R > 0.4, is 44.0The differential cross sections as a function of the di-photon invariant mass, transverse momentum, azimuthal separation, and cosine of the polar angle of the largest transverse energy photon in the Collins-Soper di-photon rest frame are also measured. The results are compared to the prediction of leading-order parton-shower and next-to-leading-order and next-to-next-to-leading-order parton-level generators. The ATLAS collaboration 26 IntroductionThe measurement at the LHC of the production cross section, in pp collisions, of two isolated photons not originating from hadronic decays, pp → γγ + X, provides a tool to probe perturbative Quantum Chromodynamics (QCD) predictions and to understand the irreducible background to new physics processes involving photons in the final state. These processes include Higgs boson decays to photon pairs (H → γγ) or graviton decays predicted in some Universal Extra-Dimension models [1, 2]. Recent cross section measurements for di-photon production at hadron colliders were performed by the DØ In this paper, the production cross section of two isolated photons with transverse energies (E T ) above 25 GeV and 22 GeV respectively, in the acceptance of the ATLAS electromagnetic calorimeter (|η| < 1.37 and 1.52 < |η| < 2.37) and with an angular separation -1 - JHEP01(2013)086∆R > 0.4, is measured. The results are obtained using the data collected by the ATLAS experiment in 2011, which corresponds to an integrated luminosity 1 of (4.9 ± 0.2) fb −1 , thus increasing the sample size by more than a factor of 100 compared to the previous measurement. The transverse energy thresholds for the two photons are higher than in the previous measurement (16 GeV).The integrated di-photon production cross section is measured, as well as the differential cross sections as a function of four kinematic variables: the di-photon invariant mass (m γγ ), the di-photon transverse momentum (p T,γγ ), the azimuthal 2 separation between the photons in the laboratory frame (∆φ γγ ), and the cosine of the polar angle of the highest E T photon in the Collins-Soper di-photon rest frame (cos θ * γγ ) [9]. The first distribution is of obvious interest for resonance searches; the second and the third provide important information in the study of higher-order QCD perturbative effects and fragmentation, especially in some specific regions such as the small ∆φ γγ limit; t...