η(c) production at the LHC challenges nonrelativistic QCD factorization.

Area of Science:

• High Energy Physics
• Quantum Chromodynamics
• Particle Physics

Background:

• The production of heavy quarkonium states like eta_c (η_{c}) is crucial for testing Quantum Chromodynamics (QCD).
• Previous analyses often relied on theoretical frameworks with varying degrees of accuracy.

Purpose of the Study:

• To analyze the first measurement of eta_c (η_{c}) production by the LHCb Collaboration.
• To compare predictions from the nonrelativistic QCD (NRQCD) factorization framework and the color-singlet model with experimental data.

Main Methods:

• Utilized the NRQCD factorization framework at next-to-leading order (NLO) in the strong-coupling constant (α_{s}) and relative quark velocity (v).
• Incorporated feeddown contributions from h_{c} mesons.
• Applied heavy-quark spin symmetry to convert long-distance matrix elements from J/ψ data to the η_{c} case.

Main Results:

• NLO NRQCD predictions for η_{c} production significantly overshot the LHCb experimental data.
• The color-singlet model provided an excellent description of the observed η_{c} production.

Conclusions:

• The standard NLO NRQCD framework, as applied, fails to accurately describe η_{c} production data.
• The color-singlet model emerges as a more successful approach for describing η_{c} production at this level of accuracy.