Coulomb deexcitation of pionic hydrogen within close-coupling method

The Coulomb deexcitation of $(\pi p)$ atom in collisions with the hydrogen atom has been studied in the fully quantum mechanical close-coupling approach for the first time. The total Coulomb deexcitation cross-sections of $nl\to n’l’$transitionsand$l$-averagedcross-sectionsarecalculatedfor$n=3 - 8$andattherelativeenergies$E=0.01 - 100$ eV. The strong interaction and vacuum polarization shifts of $ns$-states are taken into account. It is shown that the $\mathrm{\Delta }n>1$ transitions are very important and make up a substantial fraction of the Coulomb deexcitation cross-section (up to $\sim 47%$).