The ratio of the yields of antiprotons to protons in $pp$ collisions has been measured by the ALICE experiment at $\sqrt{s}=0.9$ and 7 TeV during the initial running periods of the Large Hadron Collider. The measurement covers the transverse momentum interval $0.45<p_t<1.05\mathrm{GeV}/c$ and rapidity $|y|<0.5$. The ratio is measured to be $R_{|y|<0.5}=0.957\pm 0.006(\mathrm{stat})\pm 0.014(\mathrm{syst})$ at 0.9 TeV and $R_{|y|<0.5}=0.991\pm 0.005(\mathrm{stat})\pm 0.014(\mathrm{syst})$ 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.

• Received 29 June 2010

DOI:https://doi.org/10.1103/PhysRevLett.105.072002

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© 2010 CERN, for the ALICE Collaboration