  Even before its role in electroweak symmetry breaking, the Anderson-Higgs
mechanism was introduced to explain the Meissner effect in superconductors.
Spontaneous symmetry-breaking yields massless phase modes representing the
low-energy excitations of the Mexican-Hat potential. Only in superconductors
does the gauge field move the phase mode towards higher energies, as a
consequence of the charged condensate. This results in a low-energy excitation
spectrum governed by the amplitude mode - the Higgs mode. Consequently, the
Meissner effect signifies a macroscopic quantum condensate in which a photon
acquires mass, representing a one-to-one analogy to high-energy physics. We
report on the direct observation of the Higgs particle in the high-temperature
superconductor Bi-2212 by developing an innovative technique to study its
distinct symmetries and energies after a soft quench of the Mexican-Hat
potential. By comparing transient Stokes and anti-Stokes data, we identify the
Higgs particle as an additional anti-Stokes Raman cross section after
quenching. With our technique we discriminate quasi-particle excitations from
excitations in the Cooper channel and argue that alternatives to the Higgs
excitation can be ruled out. This opens the avenue for Higgs Spectroscopy in
quantum condensates and provides a unique pathway to control and explore Higgs
physics.
