Asymmetry in ${\mathrm{\Lambda }}_b$ and ${\overline{\mathrm{\Lambda }}}_b$ production

In CMS data at the CERN Large Hadron Collider, the ratio $\sigma (pp\to {\overline{\mathrm{\Lambda }}}_{b}X)/\sigma (pp\to {\mathrm{\Lambda }}_{b}X)$ appears to fall as the baryons become more forward. Mechanisms which could give rise to this effect are discussed. It is urged that the same physics be explored in data from the ATLAS and LHCb detectors at CERN and the Fermilab Tevatron proton-antiproton collider. In the latter, if such leading-baryon effects are present, one expects ${\mathrm{\Lambda }}_b$ to be preferentially produced in the direction of the proton and ${\overline{\mathrm{\Lambda }}}_b$ to be preferentially produced in the direction of the antiproton.

Figure 1

Ratio of ${\overline{\mathrm{\Lambda }}}_b$ and ${\mathrm{\Lambda }}_b$ cross sections reported by the CMS Collaboration [11] as a function of rapidity. Only statistical errors are shown; systematic errors for the points are $\pm 0.09,\pm 0.09,\pm 0.13,\pm 0.12,\pm 0.15,\pm 0.16$, respectively. The dashed line denotes a ratio of 1.

Figure 2

Quasidiffractive production of ${\mathrm{\Lambda }}_b$ along the direction of a proton beam. The circles denote vertices for exchange of a pomeron, denoted by the dashed line.

Figure 3

Interaction of final-state heavy quark with spectator system, as proposed in Ref. [12]. The pairs of dashed lines denote QCD strings connecting the final-state heavy quarks to the spectator systems.

Figure 4

Distribution (“Tsallis function” [29]) fitting $p_T$ dependence of ${\mathrm{\Lambda }}_b$ production reported by the CMS Collaboration [11] at $\sqrt{s}=7\mathrm{TeV}$.