Midrapidity antiproton-to-proton ratio in pp collisions measured at √s=900 GeV and √s=7 TeV by the ALICE experiment

The ratio of the yields of antiprotons to protons in pp collisions has been measured by the ALICE experiment at 0.9 and 7 TeV during the initial running periods of the Large Hadron Collider. The measurement covers the transverse momentum interval 0.45<pt < 1.05 GeV/c and rapidity eta < 0.5. The ratio is measured to be R= 0.957 at 0.9 TeV and 0.991 at 7 TeV and it is independent of both rapidity and transverse momentum. The results are consistent with the conventional model of baryon-number transport and set stringent limits on any additional contributions to baryon-number transfer over very large rapidity intervals in pp collisions.