Observation of Higgs boson production in association with a top quark pair at the LHC with the ATLAS detector

Abstract

The ATLAS CollaborationThe observation of Higgs boson production in association with a top quark pair (ttH), based on the analysis of proton-proton collision data at a centre-of-mass energy of 13 TeV recorded with the ATLAS detector at the Large Hadron Collider, is presented. Using data corresponding to integrated luminosities of up to 79.8 fb −1 , and considering Higgs boson decays into bb, WW * , τ + τ − , γγ, and Z Z * , the observed significance is 5.8 standard deviations, compared to an expectation of 4.9 standard deviations. Combined with the ttH searches using a dataset corresponding to integrated luminosities of 4.5 fb −1 at 7 TeV and 20.3 fb −1 at 8 TeV, the observed (expected) significance is 6.3 (5.1) standard deviations. Assuming Standard Model branching fractions, the total ttH production cross section at 13 TeV is measured to be 670 ± 90 (stat.) +110 −100 (syst.) fb, in agreement with the Standard Model prediction.

Higgs boson decay into a lepton pair and a photon revisited

“…A possible imprint of an extended Higgs sector are deviations of the measured couplings from their SM predictions [3]. To date CMS and ATLAS have studied the couplings of the dicovered Higgs boson to W [4][5][6][7] and Z [7][8][9][10] bosons, τ leptons [11][12][13], b [14,15] and t [16,17] quarks, as well as photons [18,19]. The latter coupling is loop-suppressed and has been probed though the rare decay H → γγ.…”

Anomaly detection with density estimation

“…using events with inverted selection criteria to define the background data sample for optimization [79,80].…”

Topic model for four-top at the LHC

“…We have used Gaussian for S and B distributions, randomly sampling their means and deviations, and keeping only cases with mutual irreducibility, under a certain tolerance. For the noise functions ξ S,B (x) we sampled randomly for each bin a value between [−0.1, 0.1], then renormalizing the functions in order to satisfy relation (7) (and the analogous for the p B (x) distribution). Then the two mixture samples having fractions f 1 = 0.45, f 2 = 0.22 were generated by summing the underlying distributions.…”