Flavor Decomposition for the Proton Helicity Parton Distribution Functions

Area of Science:

• High Energy Physics
• Quantum Chromodynamics
• Lattice Quantum Chromodynamics

Background:

• Proton structure is fundamental to understanding the strong force.
• Quark helicity parton distribution functions (PDFs) describe quark spin contributions within the proton.
• Previous calculations lacked precision for individual quark contributions.

Purpose of the Study:

• To perform the first ab initio calculation of up, down, and strange quark helicity PDFs.
• To provide precise, lattice-based results for these fundamental proton properties.
• To improve upon existing phenomenological estimates.

Main Methods:

• Utilizing the twisted mass clover-improved fermion formulation of lattice QCD.
• Employing an ensemble of dynamical up, down, strange, and charm quarks.
• Nonperturbative renormalization of lattice matrix elements and MS[over ¯] renormalization scheme at 2 GeV.

Main Results:

• Presented the first ab initio calculations of individual up, down, and strange quark helicity PDFs.
• Included disconnected quark loop contributions for Δu⁺(x), Δd⁺(x), Δu⁻(x), and Δd⁻(x).
• Achieved unprecedented precision for strange quark helicity PDFs (Δs⁺(x), Δs⁻(x)) compared to phenomenological data.

Conclusions:

• The study establishes a new benchmark for precision in calculating quark helicity PDFs.
• These results provide crucial data for refining models of proton structure.
• The methodology paves the way for future, more comprehensive lattice QCD studies of PDFs.