Diamonds are forever (like the Brout-Englert-Higgs mechanism)

... and the standard model Higgs boson is in good shape at LHC Run 2

The LHC’s jump in energy to 13 TeV in Run 2, together with the copious amount of collisions delivered over the last 12 months, has allowed the ATLAS experiment to collect a data sample that is more than equivalent to the one collected during Run 1.

The Higgs boson channels with decays into either two photons (H→γγ) or four leptons (H→ZZ→4l) offer the clearest signature. They both show a narrow resonant peak in the reconstructed invariant mass as illustrated in Figure [1]. For an assumed Higgs boson mass value of mH=125.09 GeV, which was measured from the data collected in Run 1, the statistical significance of the observed excess over the background prediction from the combination of the H→γγ and H→ZZ→4l channels is approximately 10σ and thus well beyond the 5σ threshold for a (re-)discovery. 

Figure [2] shows the measurement of the inclusive Higgs boson production cross section from both channels at center-of-mass-energies of 7 and 8 TeV (Run 1) as well as 13 TeV (Run 2). The measurements are compatible with Standard Model predictions at all three center-of-mass-energies. 

ATLAS also measured the cross sections for the two dominant Higgs boson production modes through the fusion of either gluons (ggF) or vector bosons (VBF). These measurements could reveal deviations from the Standard Model in the way the Higgs boson couples to fermions and weak intermediate vector bosons (W,Z). Figure [3] shows that the simultaneous measurements of both cross sections from the H→γγ and H→ZZ→4l channels are also compatible with Standard Model expectations.

Figure 1 : The distribution of the invariant mass of the two photons in the ATLAS measurement of H→γγ using the full 2015+2016 data set. An excess is observed for a mass of ~125 GeV. To improve the visibility of the excess, events are categorized and weighted according to the sensitivity of the various categories. (Image: ATLAS Experiment/CERN)

Figure 2 : The new measurements of the Higgs boson inclusive cross section at 13 TeV in the H→γγ and H→ZZ→4l channels and their combination are compared to previous results from ATLAS using the same analysis techniques. The measurements show good agreement with the best available theory predictions. (Image: ATLAS Experiment/CERN)

Figure 3 : The simultaneous measurement of the Higgs boson production cross section in the ggF and VBF production modes in the H→γγ (red) and H→ZZ→4l (blue) channels. Both measurements show good agreement with the SM prediction (black star). (Image: ATLAS Experiment/CERN)

ATLAS observes the Higgs boson with Run 2 data

By ATLAS Collaboration, 4th August 2016