Physicists spot rare nuclear effects in particle collisions, mapping gluon behavior
Researchers at CERN detected a subatomic particle being produced in a novel way inside lead nuclei, revealing that atomic nuclei behave differently than expected—with implications for understanding fundamental nuclear structure. The finding validates theoretical models of nuclear physics that could eventually inform particle detector design and nuclear energy applications.
Originaltitel: Observation of Coherent 𝜙(1020) Meson Photoproduction in Ultraperipheral PbPb Collisions at √𝑠<sub>NN</sub>=5.36 TeV
<p>The first observation of coherent 𝜙(1020) meson photoproduction off heavy nuclei is presented using ultraperipheral lead-lead collisions at a center-of-mass energy per nucleon pair of 5.36 TeV. The data were collected by the CMS experiment and correspond to an integrated luminosity of 1.62 μ𝑏<sup>−1</sup>. The 𝜙(1020) meson signals are reconstructed via the 𝐾<sup>+</sup>𝐾<sup>−</sup> decay channel. The production cross section is presented as a function of the 𝜙(1020) meson rapidity in the range 0.3<|𝑦|<1.0, probing gluons that carry a fraction of the nucleon momentum (𝑥) around 10<sup>−4</sup>. The observed cross section exhibits little dependence on rapidity and is significantly suppressed, by a factor of ∼5, compared to a baseline model that treats a nucleus as a collection of free nucleons. Theoretical models that incorporate the nuclear shadowing effect generally provide a better description of the 𝜙(1020) data than those incorporating gluon saturation. This study establishes a powerful new tool for exploring nuclear effects and nuclear gluonic structure in the small-𝑥 regime at a unique energy scale bridging the perturbative and nonperturbative quantum chromodynamics domains.</p>