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arXiv · 2610.33365

Measurement of pseudorapidity distributions from Au+Au collisions with the STAR Event Plane Detector

The STAR Collaboration
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Abstract

The measurement of charged-particle pseudorapidity distributions using the STAR Event Plane Detector (EPD) in gold-gold collisions at center-of-mass energies per nucleon pair of $\sqrt{s_{\mathrm{NN}}} =$ 200, 54.4, 27, 19.6, 14.6, 11.5, 9.2, and 7.7 GeV is presented. Charged particles are detected by the EPD within the $2.14 < |η| < 5.09$ pseudorapidity interval. The number of charged particles passing through each EPD ring is extracted using convoluted Landau fits to the deposited energy spectra. To account for the detector's response to the primary particles, these measured EPD hit numbers are unfolded using response matrices determined via Monte Carlo simulations. The response matrix is calculated separately for each energy and centrality class using the UrQMD event generator embedded into the GEANT3 simulation for the STAR detector. The new STAR measurements are consistent with the previous PHOBOS results in the corresponding rapidity intervals at 19.6 and 200 GeV, while providing improved precision. In addition, the new data extend the energy coverage to 7.7--200 GeV across multiple centrality classes. This expanded dataset enables a more comprehensive test of the limiting fragmentation hypothesis from central to peripheral collisions. The measurements are also compared with theoretical model calculations, including UrQMD, HIJING, and AMPT, in order to investigate the underlying physics implications.

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The STAR Collaboration. 2026-10-23. Measurement of pseudorapidity distributions from Au+Au collisions with the STAR Event Plane Detector. https://arxiv.org/abs/2610.33365

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