Characterizing the initial state and dynamical evolution in XeXe and PbPb collisions using multiparticle cumulants
(2026) Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics — Vol. 876 (2026)
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- For the first time, correlations among mixed-order moments of two or three flow harmonics —(<math altimg="si15.svg"><mrow><msubsup><mi>v</mi><mrow><mi>n</mi></mrow><mi>k</mi></msubsup><mo>,</mo><msubsup><mi>v</mi><mrow><mi>m</mi></mrow><mi>l</mi></msubsup></mrow></math>) and (<math altimg="si16.svg"><mrow><msubsup><mi>v</mi><mrow><mi>n</mi></mrow><mi>k</mi></msubsup><mo>,</mo><msubsup><mi>v</mi><mrow><mi>m</mi></mrow><mi>l</mi></msubsup><mo>,</mo><msubsup><mi>v</mi><mrow><mi>p</mi></mrow><mi>q</mi></msubsup></mrow></math>), with k, l, and q denoting the respective orders—are measured in xenon–xenon (XeXe) collisions and compared with lead–lead (PbPb) results, providing a novel probe of collective behavior in heavy ion collisions. These measurements compare a nearly spherical, doubly-magic <sup loc="post">208</sup>Pb nucleus to a triaxially deformed <sup loc="post">129</sup>Xe nucleus, emphasizing the sensitivity to initial-state geometry fluctuations arising from nuclear deformation. The dependence of these results (vn, <math altimg="si17.svg"><mrow><mi>n</mi><mo linebreak="goodbreak">=</mo><mn>2</mn><mo>,</mo><mn>3</mn><mo>,</mo><mn>4</mn></mrow></math>) on the shape and size of the nuclear overlap region is studied. Comparisons between v2, v3, and v4 demonstrate the importance of v3 and v4 in exploring the nonlinear hydrodynamic response of the quark-gluon plasma (QGP) to the initial spatial anisotropy. The results constrain initial-state model parameters that influence the evolution of the QGP. The CMS detector was used to collect XeXe and PbPb data at nucleon-nucleon center-of-mass energies of <math altimg="si18.svg"><mrow><msqrt><msub><mi>S</mi><mrow><mi>N</mi><mi>N</mi></mrow></msub></msqrt><mo linebreak="goodbreak">=</mo><mn>5.44</mn></mrow></math> and 5.36 TeV, respectively. Correlations are extracted using multiparticle mixed-harmonic cumulants (up to eight-particle cumulants) with charged particles in the pseudorapidity range |η| < 2.4 and transverse momentum range 0.5 < pT < 3 GeV/c.
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Bein, S., Benecke, A., Bethani, A., Bruno, G., Cappati, A., de Favereau de Jeneret, J., Delaere, C., Giammanco, A., Guzel, A. O., Lemaitre, V., Lidrych, J., Malek, P., Mastrapasqua, P., Turkcapar, S., CMS, & et al. (2026). Characterizing the initial state and dynamical evolution in XeXe and PbPb collisions using multiparticle cumulants. Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics, 876. https://doi.org/10.1016/j.physletb.2026.140359 (Original work published 2026)