Measurement of prompt ψ(2S) production cross sections in proton–lead and proton–proton collisions at s _NN =5.02TeV

Measurements of prompt ψ(2S) meson production cross sections in proton–lead (pPb) and proton–proton (pp) collisions at a nucleon–nucleon center-of-mass energy of s _NN =5.02TeV are reported. The results are based on pPb and pp data collected by the CMS experiment at the LHC, corresponding to integrated luminosities of 34.6 nb ⁻¹ and 28.0 pb ⁻¹ , respectively. The nuclear modification factor R _pPb is measured for prompt ψ(2S) in the transverse momentum range 4<p _T <30GeV/c and the center-of-mass rapidity range −2.4<y _CM <1.93. The results on ψ(2S) R _pPb are compared to the corresponding modification factor for prompt J/ψ mesons. The results point to different nuclear effects at play in the production of the excited charmonium state compared to the ground state, in the region of backward rapidity and for p _T <10GeV/c.