at absolute zero, how much kinetic energy do the particles have?
It depends on the system. The average kinetic energy of electrons in a metal is almost the same at absolute zero as at room temperature.
http://www.economicexpert.com/a/Absolute:zero.htm
At absolute zero, particles have no kinetic energy. Absolute zero, which is defined as 0 Kelvin (-273.15 degrees Celsius or -459.67 degrees Fahrenheit), is the lowest possible temperature at which all molecular motion ceases. At this temperature, all particles are in their lowest energy state, and their motion and vibrations come to a complete stop.
The concept of kinetic energy can be understood using the formula: Kinetic Energy = 0.5 * mass * velocity^2. Since the particles have no velocity at absolute zero, their kinetic energy is zero. This means that the particles are completely still and do not possess any energy associated with motion.