Light Sea Quarks Research Articles

Properties of hadrons in lattice quantum chromodynamics with dynamical Wilson fermions.

New results of a large-scale simulation of lattice quantum chromodynamics with three (u,d,s) dynamical Wilson fermions on a 10 x 10 x 10 x 30 space-time lattice are presented. The computations presented here confirm earlier results that indicated the presence of substantial effects due to fermion vacuum-polarization loops. As a check on the results two values for the gauge coupling constant are considered and some degree of scaling is observed. The quark mass dependence of the physical pseudoscalar-meson mass is explicitly determined both in the case of equal-mass and unequal- (heavy-light) mass systems, as well as in the case of light sea quarks versus heavy valence quarks, with the latter situation being relevant for heavy-quark bound states. Further results include estimates for other lowest-lying hadron masses, for the (current-algebra) quark masses (m/sub u/, m/sub d/, m/sub s/, and m/sub c/), and for the pseudoscalar-meson decay constants (f/sub ..pi../, f/sub K/, f/sub D/, f/sub eta//sub >//sub c//sub =/, and f/sub B/). An estimate of the strangeness content of the proton is given. Relatively small mass values are found for the light quarks (u,d,s). In the case of the decay constants the full lattice QCD estimates could give new predictions, since somemore » of the experimental values are not known yet.« less

Hadron masses in lattice QCD with internal fermion loops

Results are presented for light hadron and quark masses in lattice quantum chromodynamics with fermion vacuum polarization effects. A lattice of size 10×10×10×30 is used with a gauge coupling g 2=1.111 and n f=3. Previous qualitative results obtained with Wilson fermions on a smaller lattice at the same value of the coupling constant are confirmed and extended. The values for the hadron masses in units of the lattice spacing are significantly affected by the inclusion of three light fermion flavors, but the change can be reabsorbed to a large degree in a rescaling of the cutoff. For small quark mass the physical hadron mass estimates are comparable to the results with no loops and in reasonable agreement with phenomenology. Fermion loop effects on the other hand tend to change the dependence of the physical hadron masses on the quark mass, which in turn affects the estimates for the quark masses. These are found to be smaller than had previously been estimated. By considering heavy valence and light sea quarks, light quark masses are directly compared to the heavier quark masses.

Inclusive ϕ meson production, the parton fusion model and strange quark structure functions

The parton fusion model is used to describe the longitudinal differential cross section (dσ/dxF) of hadronic ϕ production. Thedσ/dxF for ϕ production in π±p,\(\mathop p\limits^{( - )} p\) andK±p interactions is evaluated in the model by using structure functions for the constituents of the interacting particles. A comparison between the model and high statistics data in the Feynmanx range 0.0<xF(ϕ)<0.4 allows the determination of the strange valence quark distribution inK mesons and the strange sea quark distribution in π mesons, which appears to be harder than the light sea quark distribution. The comparison also shows that a significant part of inclusive ϕ production is due to the OZI allowed fusion of strange quarks, while the OZI inhibited fusion diagrams are strongly suppressed.

Deep inelastic quantum chromodynamic charm leptoproduction

The consequences of calculating inclusive charm (or any heavy quark flavor) electroproduction are investigated using a virtual Bethe-Heitler photon-gluon pair creation process. Implications for the light quark sea of the nucleon are studied by comparison with recent μp data in the small x region. Predictions for heavy quarkonium ( J Ψ , ϒ) electroproduction are also given. For example, at Q 2 = 10 GeV 2 and x = 0.01 we find F charm 2 ≈ 0.08 and F J Ψ 2 ≈ 0.003 .