Constraints on the &lt;em&gt;χ&lt;sub&gt;c&lt;/sub&gt;&lt;/em&gt;&lt;sub&gt;1&lt;/sub&gt; versus &lt;em&gt;χ&lt;sub&gt;c2&lt;/sub&gt;&lt;/em&gt; polarizations in proton-proton collisions at √&lt;em&gt;s&lt;/em&gt; = 8  TeV

Sirunyan, A.M.; Tumasyan, A.; Adam, W.; Ambrogi, F.; Bergauer, T.; Dragicevic, M.; Erö, J.; Escalante Del Valle, A.; Flechl, M.; Frühwirth, R.; Caminada, L.; Deiters, K.; Erdmann, W.; Horisberger, R.; Ingram, Q.; Kaestli, H.C.; Kotlinski, D.; Langenegger, U.; Rohe, T.; Trembath-Reichert, S.

doi:10.1103/PhysRevLett.124.162002

Constraints on the χ_c₁ versus χ_c2 polarizations in proton-proton collisions at √s = 8 TeV

Sirunyan AM, Tumasyan A, Adam W, Ambrogi F, Bergauer T, Dragicevic M, Erö J, Escalante Del Valle A, Flechl M, Frühwirth R, Caminada L, Deiters K, Erdmann W, Horisberger R, Ingram Q, Kaestli HC, Kotlinski D, Langenegger U, Rohe T, Trembath-Reichert S, et al.

Citation

Sirunyan, A. M., Tumasyan, A., Adam, W., Ambrogi, F., Bergauer, T., Dragicevic, M., … Trembath-Reichert, S. (2020). Constraints on the χ_c₁ versus χ_c2 polarizations in proton-proton collisions at √s = 8 TeV. Physical Review Letters, 124(16), 162002 (18 pp.). https://doi.org/10.1103/PhysRevLett.124.162002

Persistent URL https://www.dora.lib4ri.ch/psi/islandora/object/psi:33189

The polarizations of promptly produced χ_c₁ and χ_c₂ mesons are studied using data collected by the CMS experiment at the LHC, in proton-proton collisions at √s = 8 TeV. The χ_c states are reconstructed via their radiative decays χ_c→ J/ψγ, with the photons being measured through conversions to e⁺e^-, which allows the two states to be well resolved. The polarizations are measured in the helicity frame, through the analysis of the χ_c₂ to χ_c₁ yield ratio as a function of the polar or azimuthal angle of the positive muon emitted in the J/ψ → μ⁺μ^- decay, in three bins of J/ψ transverse momentum. While no differences are seen between the two states in terms of azimuthal decay angle distributions, they are observed to have significantly different polar anisotropies. The measurement favors a scenario where at least one of the two states is strongly polarized along the helicity quantization axis, in agreement with nonrelativistic quantum chromodynamics predictions. This is the first measurement of significantly polarized quarkonia produced at high transverse momentum.