Impact of Baryon anti-Baryon annihilation on hyperon (Λ, (Λ)over-bar) production and apparent strangeness enhancement in (Λ)over-bar/(p)over-bar in heavy ion collisions at SPS energy

A deconfined medium of quarks and gluon, called the Quark-Gluon Plasma (QGP) is produced when heavy-nuclei are collided at relativistic energies. The QGP formation is often characterized by a phenomenon called strangeness enhancement where, the relative production of strange-to-non-strange particles are enhanced in central collisions compared to peripheral or proton-proton interactions. Besides the enhancement in K/pi ratios, a non-monotonic energy dependence was also reported for (Lambda) over bar to (p) over bar ratios at CERN SPS, attributed to a signature for the strangeness enhancement as well. As anti-particles are produced directly from the reaction, the (Lambda) over bar/(p) over bar ratios are considered as a cleaner probe for the strangeness enhancement. However, at this energy range hadronic interactions have a dominant role to play and, importantly for (Lambda) over bar and (p) over bar, processes like baryonanti-baryon (B (B) over bar) annihilation can have a significant impact. In this work, we use a hadronic transport model UrQMD, to investigate the role of baryon-anti-baryon (B (B) over bar) annihilation on Lambda, (Lambda) over bar hyperon production and its effect on (Lambda) over bar/(p) over bar ratios. The UrQMD calculations that include B (B) over bar annihilation can produce the trend of average transverse mass spectra for Lambda and (Lambda) over bar, as well as, the characteristic enhancement in (Lambda) over bar/(p) over bar ratios in data as a function of centrality and collision energy. Furthermore, (Lambda) over bar/(p) over bar ratios extracted from the feed-down corrected SPS data are seen to be in good agreement with UrQMD model calculations with B (B) over bar annihilation. This suggests that (Lambda) over bar/(p) over bar enhancement is not necessarily because of strangeness enhancement and B (B) over bar annihilation has a significant role to play.

Automated summary

A deconfined medium of quarks and gluons, known as the Quark-Gluon Plasma (QGP), is generated during heavy-nuclei collisions at relativistic energies. The formation of QGP is characterized by strangeness enhancement, where the production of strange-to-non-strange particles is relatively increased in central collisions compared to peripheral or proton-proton interactions.