The discovery of a new boson with a mass of approximately 125 GeV in 2012 at the LHC has heralded a new era in understanding the nature of electroweak symmetry breaking and possibly completing the standard model of particle physics. Since the first observation in decays to gamma-gamma, WW, and ZZ boson pairs, an extensive set of measurements of the mass and couplings to W and Z bosons, as well as multiple tests of the spin-parity quantum numbers, have revealed that the properties of the new boson are consistent with those of the long-sought agent responsible for electroweak symmetry breaking. An important open question is whether the new particle also couples to fermions, and in particular to down-type fermions, since the current measurements mainly constrain the couplings to the up-type top quark. Determination of the couplings to down-type fermions requires direct measurement of the corresponding Higgs boson decays, as recently reported by the CMS experiment in the study of Higgs decays to bottom quarks and tau-leptons. In this paper we report the combination of these two channels which results, for the first time, in strong evidence for the direct coupling of the 125-GeV Higgs boson to down-type fermions, with an observed significance of 3.8 standard deviations, when 4.4 are expected.
Evidence for the direct decay of the 125 GeV Higgs boson to fermions
CAVALLO, Nicola;FABOZZI, FRANCESCO;
2014-01-01
Abstract
The discovery of a new boson with a mass of approximately 125 GeV in 2012 at the LHC has heralded a new era in understanding the nature of electroweak symmetry breaking and possibly completing the standard model of particle physics. Since the first observation in decays to gamma-gamma, WW, and ZZ boson pairs, an extensive set of measurements of the mass and couplings to W and Z bosons, as well as multiple tests of the spin-parity quantum numbers, have revealed that the properties of the new boson are consistent with those of the long-sought agent responsible for electroweak symmetry breaking. An important open question is whether the new particle also couples to fermions, and in particular to down-type fermions, since the current measurements mainly constrain the couplings to the up-type top quark. Determination of the couplings to down-type fermions requires direct measurement of the corresponding Higgs boson decays, as recently reported by the CMS experiment in the study of Higgs decays to bottom quarks and tau-leptons. In this paper we report the combination of these two channels which results, for the first time, in strong evidence for the direct coupling of the 125-GeV Higgs boson to down-type fermions, with an observed significance of 3.8 standard deviations, when 4.4 are expected.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
