Bose-Einstein Condensation in the Relativistic Pion Gas: Thermodynamic Limit and Finite Size Effects

Abstract

We consider the Bose-Einstein condensation (BEC) in a relativistic pion gas. The thermodynamic limit when the system volume $V$ goes to infinity as well as the role of finite size effects are studied. At $V\to \infty$ the scaled variance for particle number fluctuations, $ω=< ΔN^2>/< N>$, converges to finite values in the normal phase above the BEC temperature, $T>T_C$. It diverges as $ω\propto V^{1/3}$ at the BEC line $T=T_C$, and $ω\propto V$ at $T<T_C$ in a phase with the BE condensate. Possible experimental signals of the pion BEC in finite systems created in high energy proton-proton collisions are discussed.