Coherent production of the long-lived pionium nP states in relativistic nucleus-nucleus collisions
The coherent production of the nP states of the $π^+π^-$ atoms ($A_{2π}$) in relativistic nucleus-nucleus collisions is considered as a possible source of the $A_{2π}(nP)$ beam for the pionium Lamb-shift measurement. A general expression for estimation of the $A_{2π}(nP)$ yield is derived in the framework of the equivalent photon approximation.
hep-ph↗