Effect of Baryon Anti-baryon Annihilation on Strangeness Enhancement (baryon Sector) at SPS Energy

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