Pseudorapidity distributions of charged hadrons in lead-lead collisions at <math altimg="si1.svg"><msqrt><mrow><msub><mrow><mi>s</mi></mrow><mrow><msub><mrow/><mrow><mi mathvariant="normal">NN</mi></mrow></msub></mrow></msub></mrow></msqrt><mo linebreak="goodbreak" linebreakstyle="after">=</mo><mn>5.36</mn><mspace width="0.25em"/><mtext>TeV</mtext></math>

Benecke, Anna;Bethani, Agni;Bruno, Giacomo;Caputo, Claudio;CMS;et.al.
(2025) Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics — Vol. 861 (2025)

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Abstract
The pseudorapidity (η) distributions of charged hadrons are measured using data collected at the highest ever nucleon-nucleon center-of-mass energy of <math altimg="si2.svg"><msqrt><mrow><msub><mrow><mi>s</mi></mrow><mrow><msub><mrow/><mrow><mi mathvariant="normal">NN</mi></mrow></msub></mrow></msub></mrow></msqrt><mo linebreak="goodbreak" linebreakstyle="after">=</mo><mn>5.36</mn><mspace width="0.25em"/><mtext>TeV</mtext></math> for collisions of lead-lead ions. The data were marc:recorded by the CMS experiment at the LHC in 2022 and correspond to an integrated luminosity of <math altimg="si3.svg"><mn>0.30</mn><mo>±</mo><mn>0.03</mn><mspace width="0.25em"/><msup><mrow><mi mathvariant="normal">μ</mi><mtext>b</mtext></mrow><mrow><mo linebreak="badbreak" linebreakstyle="after">−</mo><mn>1</mn></mrow></msup></math>. Using the CMS silicon pixel detector, the yields of primary charged hadrons produced in the range <math altimg="si4.svg"><mo stretchy="false">|</mo><mi>η</mi><mo stretchy="false">|</mo><mo linebreak="goodbreak" linebreakstyle="after">&lt;</mo><mn>2.6</mn></math> are reported. The evolution of the midrapidity particle density as a function of collision centrality is also reported. In the 5% most central collisions, the charged-hadron η density in the range <math altimg="si5.svg"><mo stretchy="false">|</mo><mi>η</mi><mo stretchy="false">|</mo><mo linebreak="goodbreak" linebreakstyle="after">&lt;</mo><mn>0.5</mn></math> is found to be <math altimg="si6.svg"><mn>2032</mn><mo>±</mo><mn>91</mn><mspace width="0.25em"/><mtext>(syst)</mtext></math>, with negligible statistical uncertainty. This result is consistent with an extrapolation from nucleus-nucleus collision data at lower center-of-mass energies. Comparisons are made to various Monte Carlo event generators and to previous measurements of lead-lead and xenon-xenon collisions at similar collision energies. These new data detail the dependence of particle production on the collision energy, initial collision geometry, and the size of the colliding nuclei.
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Benecke, A., Bethani, A., Bruno, G., Caputo, C., de Favereau de Jeneret, J., Delaere, C., Donertas, I. S., Giammanco, A., Guzel, A. O., Jain, S., Lemaitre, V., Lidrych, J., Mastrapasqua, P., Tran, T. T., Wertz, S., CMS, & et al. (2025). Pseudorapidity distributions of charged hadrons in lead-lead collisions at <math altimg=“si1.svg”><msqrt><mrow><msub><mrow><mi>s</mi></mrow><mrow><msub><mrow/><mrow><mi mathvariant=“normal”>NN</mi></mrow></msub></mrow></msub></mrow></msqrt><mo linebreak=“goodbreak” linebreakstyle=“after”>=</mo><mn>5.36</mn><mspace width=“0.25em”/><mtext>TeV</mtext></math>. Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics, 861. https://doi.org/10.1016/j.physletb.2025.139279 (Original work published 2025)