Quark and Gluon Momentum Fractions in the Pion and in the Kaon

Journal Article · 30 March 2025 · Physical Review Letters

DOI: https://doi.org/10.1103/PhysRevLett.134.131902 · OSTI ID:2543166

Alexandrou, Constantia; Bacchio, Simone; Constantinou, Martha; Delmar, Joseph; Finkenrath, Jacob; Kostrzewa, Bartosz; Petschlies, Marcus; Chacon, Luis Alberto Rodriguez; Spanoudes, Gregoris; Steffens, Fernanda; Urbach, Carsten; Wenger, Urs

We present the full decomposition of the momentum fraction carried by quarks and gluons in the pion and the kaon. We employ three gauge ensembles generated with $N_f=2+1+1$ Wilson twisted-mass clover-improved fermions at the physical quark masses. For both mesons we perform a continuum extrapolation directly at the physical pion mass, which allows us to determine for the first time the momentum decomposition at the physical point. We find that the total momentum fraction carried by quarks is 0.575(79) and 0.683(50) and by gluons 0.402(53) and 0.422(67) in the pion and in the kaon, respectively, in the $\overline{\mathrm{MS}}$ scheme and at the renormalization scale of 2 GeV. Having computed both the quark and gluon contributions in the continuum limit, we find that the momentum sum is 0.984(89) for the pion and 1.13(11) for the kaon, verifying the momentum sum rule. Published by the American Physical Society 2025

• Sponsoring Organization: USDOE Office of Science (SC), Nuclear Physics (NP)
• Grant/Contract Number: SC0020405; SC0025218
• OSTI ID: 2543166
• Journal Information: Physical Review Letters, Journal Name: Physical Review Letters Journal Issue: 13 Vol. 134; ISSN 0031-9007; ISSN PRLTAO
• Publisher: American Physical SocietyCopyright Statement
• Country of Publication: United States
• Language: English