Measurement of the properties of the new particle observed within the search for the Higgs boson in the $H \rightarrow ZZ^{(*)} \rightarrow 4\ell$ channel at ATLAS.

The discovery of a new particle within the search for the Standard Model Higgs boson in the $H \rightarrow ZZ^{(∗)} \rightarrow 4\ell$ channel at ATLAS, with about 25 fb$^{−1}$ of data collected in pp collisions at the LHC, is discussed. Different hypotheses on the quantum numbers of the new boson are tested, by means of spin–parity studies based on a matrix element description of the $H \rightarrow ZZ$ decay amplitude. Prospects for the measurement of the tensor structure of the $HZZ$ vertex in the spin zero hypothesis at a high–luminosity LHC are also presented.