Abstract
Measurements of fiducial and differential cross sections are presented for Higgs boson production in proton-proton collisions at a centre-of-mass energy of $\sqrt{s}=8$ TeV. The analysis is performed in the $H \rightarrow \gamma\gamma$ decay channel using 20.3 fb$^{-1}$ of data recorded by the ATLAS experiment at the CERN Large Hadron Collider. The signal is extracted using a fit to the diphoton invariant mass spectrum assuming that the width of the resonance is much smaller than the experimental resolution. The signal yields are corrected for the effects of detector inefficiency and resolution. The $pp\rightarrow H \rightarrow \gamma\gamma$ fiducial cross section is measured to be $43.2 \pm 9.4 (stat) {}^{+3.2}_{-2.9} (syst) \pm 1.2 (lumi)$ fb for a Higgs boson of mass 125.4 GeV decaying to two isolated photons that have transverse momentum greater than 35% and 25% of the diphoton invariant mass and each with absolute pseudorapidity less than 2.37. Four additional fiducial cross sections and two cross-section limits are presented in phase space regions that test the theoretical modelling of different Higgs boson production mechanisms, or are sensitive to physics beyond the Standard Model. Differential cross sections are also presented, as a function of variables related to the diphoton kinematics and the jet activity produced in the Higgs boson events. The observed spectra are statistically limited but broadly in line with the theoretical expectations.
Highlights
ATLAS experiment at the CERN Large Hadron Collider
Higgs boson of mass decaying to two isolated photons that have transverse momentum greater than 35% and 25% of the diphoton invariant mass and each with absolute pseudorapidity less than 2.37
Differential cross sections are presented, as a function of variables related to the diphoton kinematics and the jet activity produced in the Higgs boson events
Summary
The ATLAS detector is described in detail elsewhere [22]. Charged-particle tracks and interaction vertices are reconstructed using information from the pixel detector, silicon microstrip detector and the transition radiation tracker, which are collectively referred to as. The inner detector has full azimuthal coverage over the pseudorapidity interval |η| < 2.5, and is immersed in a 2 T axial field to allow charged-particle transverse momentum reconstruction. The first layer, referred to as the strip layer, has a fine segmentation in the regions |η| < 1.4 and 1.5 < |η| < 2.4 to facilitate the separation of photons from neutral hadrons and to allow shower directions to be measured, while most of the energy is deposited in the second layer. The hadronic calorimeter is divided into three sub-regions; the barrel region (|η| < 1.7) consists of an active scintillator tiles and steel absorbers, whereas the end-cap (1.5 < |η| < 3.2) and forward (3.1 < |η| < 4.9) regions are based on liquid-argon technology. The Level-2 and Event Filter run software-based trigger algorithms that use the full granularity of the detector to refine the event selection, reducing the final rate of events to below 400 Hz
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