Bose–Einstein statistics : The Bose–Einstein probability distribution function is used to find the probability that a boson occupies a specific quantum state in a system at thermal equilibrium. Bosons are particles which do not obey the Pauli exclusion principle (e.g. phonons and photons). The distribution function can be written as f B E ( E ) = 1 exp ⁡ ⁡ ( E − − μ μ k B T ) − − 1 .