Mid-rapidity anti-baryon to baryon ratios in pp collisions at sqrt(s) = 0.9, 2.76 and 7 TeV measured by ALICE

The ratios of yields of anti-baryons to baryons probes the mechanisms of baryon-number transport. Results for anti-p over p, anti-Lambda over Lambda, anti-Xi+ over Xi− and anti-Omega+ over Omega- in pp collisions at √s = 0.9, 2.76 and 7 TeV, measured with the ALICE detector at the LHC, are reported. Within the experimental uncertainties and ranges covered by our measurement, these ratios are independent of rapidity, transverse momentum and multiplicity for all measured energies. The results are compared to expectations from event generators, such as PYTHIA and HIJING/B, that are used to model the particle production in pp collisions. The energy dependence of anti-p/p, anti-Lambda/Lambda, antiXi+/Xi- and anti-Omega+/Omega- , reaching values compatible with unity for √s = 7 TeV, complement the earlier anti-p/p measurement of ALICE. These dependencies can be described by exchanges with the Regge-trajectory intercept of alpha_J ≈ 0.5, which are suppressed with increasing rapidity interval Delta_y. Any significant contribution of an exchange not suppressed at large Delat_y (reached at LHC energies) is disfavoured