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

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Abstract

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 \(\bar{\Lambda }\) to \(\bar{p}\) ratios at CERN SPS, attributed to a signature for the strangeness enhancement as well. As anti-particles are produced directly from the reaction, the \(\bar{\Lambda }\)/\(\bar{p}\) 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 \({\bar{\Lambda }}\) and \({\bar{p}}\), processes like baryon-anti-baryon (\(\textrm{B}{\bar{\textrm{B}}}\)) annihilation can have a significant impact. In this work, we use a hadronic transport model UrQMD, to investigate the role of baryon-anti-baryon (\(\textrm{B}{\bar{\textrm{B}}}\)) annihilation on \(\Lambda \), \(\bar{\Lambda }\) hyperon production and its effect on \(\bar{\Lambda }\)/\(\bar{p}\) ratios. The UrQMD calculations that include \(\textrm{B}{\bar{\textrm{B}}}\) annihilation can produce the trend of average transverse mass spectra for \(\Lambda \) and \(\bar{\Lambda }\), as well as, the characteristic enhancement in \(\bar{\Lambda }\)/\(\bar{p}\) ratios in data as a function of centrality and collision energy. Furthermore, \(\bar{\Lambda }\)/\(\bar{p}\) ratios extracted from the feed-down corrected SPS data are seen to be in good agreement with UrQMD model calculations with \(\textrm{B}{\bar{\textrm{B}}}\) annihilation. This suggests that \(\bar{\Lambda }\)/\(\bar{p}\) enhancement is not necessarily because of strangeness enhancement and \(\textrm{B}{\bar{\textrm{B}}}\) annihilation has a significant role to play.

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Data availability statement

This manuscript has no associated data or the data will not be deposited. [Authors’ comment: This paper uses UrQMD event generator with specific settings and experimental data points that are publicly available. In case the data are required, we can provide the same upon request to the corresponding author.]

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Acknowledgements

This research has used resources of grid computing facility at Variable Energy Cyclotron Centre (VECC), Kolkata. Authors would like to acknowledge discussions with Prof. Steffen A. Bass on baryon-anti-baryon annihilation in UrQMD.

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Authors and Affiliations

  1. Variable Energy Cyclotron Centre, 1/AF, Bidhan Nagar, Kolkata, 700064, India

    Ekata Nandy & Subhasis Chattopadhyay

  2. Homi Bhabha National Institute, Mumbai, 400094, India

    Ekata Nandy & Subhasis Chattopadhyay

Authors
  1. Ekata Nandy
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  2. Subhasis Chattopadhyay
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Correspondence to Ekata Nandy.

Additional information

Communicated by Che-Ming Ko.

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Nandy, E., Chattopadhyay, S. Impact of Baryon anti-Baryon annihilation on hyperon (\(\Lambda \), \(\bar{\Lambda }\)) production and apparent strangeness enhancement in \(\bar{\Lambda }/\bar{p}\) in heavy ion collisions at SPS energy. Eur. Phys. J. A 58, 199 (2022). https://doi.org/10.1140/epja/s10050-022-00856-x

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