  To experimentally search for signals of the Gardner transition, an active
quasi-thermal granular glass is constructed using a monolayer of air-fluidized
star-shaped granular particles. The pressure of the system is controlled by
adjusting the tension exerted on an enclosing boundary. Velocity distributions
of the internal particles and the scaling of the pressure, density,
effective-temperature, and relaxation time are examined, demonstrating that the
system has important features of a thermal system. Using a pressure-based
quenching protocol that brings the system into deeper glassy states, signals of
the Gardner transition are detected via cage size and separation order
parameters for both particle positions and orientations, offering experimental
evidence of the Gardner transition for a system with in low spatial dimensions
that is quasi-thermal.
