Probing Forward-Backward Multiplicity Correlations and Fluctuations Using the Strongly Intensive Observable Σ in Pb-Pb Collisions at SPS Energies with UrQMD

@misc{nandy2026probing,
  title = {{Probing Forward-Backward Multiplicity Correlations and Fluctuations Using the Strongly Intensive Observable $Σ$ in Pb-Pb Collisions at SPS Energies with UrQMD}},
  author = {Ekata Nandy and Subhasis Chattopadhyay},
  howpublished = {arXiv},
  year = {2026},
  month = sep,
  doi = {10.48550/arxiv.2609.20246},
  eprint = {2609.20246},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2609.20246},
}

TY  - UNPB
TI  - Probing Forward-Backward Multiplicity Correlations and Fluctuations Using the Strongly Intensive Observable Σ in Pb-Pb Collisions at SPS Energies with UrQMD
AU  - Ekata Nandy
AU  - Subhasis Chattopadhyay
PY  - 2026
DA  - 2026/09/01
PB  - arXiv
DO  - 10.48550/arxiv.2609.20246
UR  - https://arxiv.org/abs/2609.20246
AB  - The strongly intensive observable Σ, constructed from charged-pion multiplicities in separated forward (F) and backward (B) pseudorapidity intervals Δη, is studied within the UrQMD transport model for Pb--Pb collisions at SPS energies. The dependence of Σ on Δη is investigated as a function of collision energy, centrality, and acceptance to probe the longitudinal structure of multiplicity fluctuations and correlations. For √(s_NN)>6 GeV, Σ exhibits a non-monotonic dependence on Δη, increasing from values near unity at small separation, reaching a maximum at intermediate Δη, and decreasing towards unity at larger separation. Decomposition into scaled variance and covariance terms shows that this behavior arises from their different Δη dependences. Calculations with resonance decays switched off show that resonances dominate short-range correlations, while Σ>1 at larger Δη indicates fluctuations and correlations extending over broader pseudorapidity intervals. The magnitude of Σ, together with its fluctuation and covariance components, increases from central to peripheral collisions, with fluctuations dominating over covariance at large Δη. As the collision energy increases, the pseudorapidity interval over which Σ>1 persists becomes significantly larger, whereas at lower energies, where resonance dynamics dominate particle production, Σ is nearly independent of Δη. An acceptance-scaling study reveals deviations from simple binomial scaling in regions of strong correlations. These results demonstrate the sensitivity of Σ to the interplay between multiplicity fluctuations and forward--backward correlations in heavy-ion collisions.
ER  -