Midrapidity dip and limiting fragmentation of charged hadrons from RHIC to LHC energies
Abstract
The charged-hadron pseudorapidity density dndeta in central heavy-ion collisions has a midrapidity depression that deepens with collision energy. Whether it reflects structure in the rapidity density dndy or only the kinematics of the y→η transformation has mostly been argued with effective or model-based Jacobians. We test this without an event generator, with a y→η kernel built from measured identified-hadron spectra. In central Au+Au and Pb+Pb collisions from snn=19.6~GeV to 5.36~TeV the data do not require a dip in dndy: the decisive null-hypothesis family gives p≥pMinAll in all variants. For dips up to one rapidity unit wide, the depth giving p<0.05 in half the pseudo-experiments is \rng{\dminLHClo}{\dminLHChi}\% at the LHC and \rng{\dminRHIClo}{\dminRHIChi}\% at 62.4--200~GeV. Generator closure tests show a false dip at top RHIC energy caused by the forward region. As the LHC data barely constrain the fragmentation region, an energy sum rule calibrated on RHIC data, with the RHIC shape of that region, gives best-fit LHC/RHIC ratios of \rng{\sLoE}{\sHiE}, \rng{\sLoF}{\sHiF} and \rng{\sLoG}{\sHiG} at 2.76, 5.02 and 5.36~TeV for three shape families, with 95\% intervals over the families of \rng{\sNFLoE}{\sNFHiE}, \rng{\sNFLoF}{\sNFHiF} and \sNFG{} that include unity, although at 2.76 and 5.02~TeV the fits prefer \rng{\pullLoEF}{\pullHiEF}σ more energy than calibrated. Over plausible RHIC covariances and kernels the best-fit ratios span \rng{\sSystAllLo}{\sSystAllHi}, and single variants exclude unity at \systUnionAbs: limiting fragmentation is neither established nor excluded.
Related
- Final-state effects on the transverse-momentum spectra of charged hadrons in p+Pb and Pb+Pb collisions at √(sNN) = 5.02~TeV using the modified Tsallis distribution
- Revisiting Unidentified Charged-Hadron Fragmentation Functions with Modern COMPASS SIDIS Multiplicities
- Dynamical Coulomb effects on charged-pion HBT-radius splitting in central Au+Au collisions at few-GeV energies
- Dynamical Coulomb effects on charged-pion HBT-radius splitting in central Au+Au collisions at few-GeV energies
- Monte Carlo study of extending the BM@N tracking acceptance toward midrapidity with the Vertex Silicon Plane
BibTeX
@misc{neeraj2026midrapidity,
title = {{Midrapidity dip and limiting fragmentation of charged hadrons from RHIC to LHC energies}},
author = {Neeraj and Md. Kaosar Ali Mondal and Amal Sarkar},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.35456},
eprint = {2610.35456},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.35456},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Midrapidity dip and limiting fragmentation of charged hadrons from RHIC to LHC energies
AU - Neeraj
AU - Md. Kaosar Ali Mondal
AU - Amal Sarkar
PY - 2026
DA - 2026/10/26
PB - arXiv
DO - 10.48550/arxiv.2610.35456
UR - https://arxiv.org/abs/2610.35456
AB - The charged-hadron pseudorapidity density dndeta in central heavy-ion collisions has a midrapidity depression that deepens with collision energy. Whether it reflects structure in the rapidity density dndy or only the kinematics of the y→η transformation has mostly been argued with effective or model-based Jacobians. We test this without an event generator, with a y→η kernel built from measured identified-hadron spectra. In central Au+Au and Pb+Pb collisions from snn=19.6~GeV to 5.36~TeV the data do not require a dip in dndy: the decisive null-hypothesis family gives p≥pMinAll in all variants. For dips up to one rapidity unit wide, the depth giving p<0.05 in half the pseudo-experiments is \rng{\dminLHClo}{\dminLHChi}\% at the LHC and \rng{\dminRHIClo}{\dminRHIChi}\% at 62.4--200~GeV. Generator closure tests show a false dip at top RHIC energy caused by the forward region. As the LHC data barely constrain the fragmentation region, an energy sum rule calibrated on RHIC data, with the RHIC shape of that region, gives best-fit LHC/RHIC ratios of \rng{\sLoE}{\sHiE}, \rng{\sLoF}{\sHiF} and \rng{\sLoG}{\sHiG} at 2.76, 5.02 and 5.36~TeV for three shape families, with 95\% intervals over the families of \rng{\sNFLoE}{\sNFHiE}, \rng{\sNFLoF}{\sNFHiF} and \sNFG{} that include unity, although at 2.76 and 5.02~TeV the fits prefer \rng{\pullLoEF}{\pullHiEF}σ more energy than calibrated. Over plausible RHIC covariances and kernels the best-fit ratios span \rng{\sSystAllLo}{\sSystAllHi}, and single variants exclude unity at \systUnionAbs: limiting fragmentation is neither established nor excluded.
ER -