Midrapidity Antiproton-to-Proton Ratio in pp Collisons at s=0.9 and 7 TeV Measured by the ALICE Experiment

The ratio of the yields of antiprotons to protons in $pp$ collisions has been measured by the ALICE experiment at √s=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 $|y|<0.5$. The ratio is measured to be R|y|<0.5=0.957±0.006(stat)±0.014(syst) at 0.9 TeV and R|y|<0.5=0.991±0.005(stat)±0.014(syst) 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.