Abstract
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 7TeV during the initial running periods of the Large Hadron Collider. The measurement covers the transverse momentum interval 0.45<p_{t}<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 0.9TeV and R_{|y|<0.5}=0.991±0.005(stat)±0.014(syst) at 7TeV 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.
Highlights
In inelastic nondiffractive proton-proton collisions at very high energy, the incoming projectile breaks up into several hadrons that typically emerge, after the collision, at small angles close to the original beam direction
The deceleration of the incoming proton, or more precisely of the conserved baryon number associated with the beam particles, is often called ‘‘baryon-number transport’’ and has been debated theoretically for some time [1,2,3,4,5,6,7]
The diquark hadronizes after the reaction with some longitudinal momentum pz into a new particle, which carries the baryon number of the incoming proton
Summary
The background of secondary protons, which remains after the DCA cut under the peak of primaries, is subtracted by determining its shape from Monte Carlo simulations and adjusting the amount to the data at large values of the DCA This correction is calculated and applied differentially as a function of y and pt; it varies between 14% for the lowest and less than 0.3% for the highest transverse momentum bins. The contamination coming from feed-down [i.e., (anti-) protons originating from the weak decay of à and Ã" ] was subtracted in a similar way by parametrization and fitting to the data of the respective simulated DCA distributions This correction ranges from 20% to 12% for the lowest and highest pt bins, respectively. By changing the event selection, analysis cuts and track quality requirements within reasonable ranges, we find a maximum deviation of the results of 0.4%, which we
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