Nucleon sea in the effective chiral quark model

Abstract

The asymmetries of both light-flavor antiquark $\bar{d}(x)-\bar{u}(x)$ and strange-antistrange $s(x)-\bar{s}(x)$ distributions of the nucleon sea are considered with more details in the effective chiral quark model. We find that the asymmetric distribution of light-flavor antiquarks $\bar{d}(x)-\bar{u}(x)$ matches the experiment data well and that the asymmetry of strange and antistrange distributions can bring about 60-100% correction to the NuTeV anomaly of $\sin^{2}\theta_{w}$, which are three standard deviations from the world average value measured in other electroweak processes. The results on the correction to the NuTeV anomaly are insensitive to the inputs of the constituent quark distributions and the cut-off parameters. The ratios of $\bar{d}(x)/\bar{u}(x)$ and $s(x)/\bar{s}(x)$ are also discussed, and it is found that the ratio $s(x)/\bar{s}(x)$ is compatible with the available experiments with an additional symmetric sea contribution being considered effectively.Comment: 24 Latex pages, 8 figure

The CDF dijet excess from intrinsic quarks

“…Thus the d quark contribution to W +t single top quark production should be also included as a background in the Tevatron W +dijet analysis. For the intrinsic strange quarks, the strange-antistrange asymmetry is a remarkable feature which is predicted from theory [21] and is further found to provide a viable explanation [30,31,32] of the NuTeV anomaly. Here we find that the strange quark has an important contribution to the W +t single top production at the Tevatron collider of proton and antiproton collision.…”

“…There is an additional valence d quark inside the proton besides the intrinsic s quarks at larger x. As the intrinsic s quark is of 1/3 of the sea d quark distribution as in previous data analysis [32], we can thus use a larger probability of 5 times of finding a d quark than an s quark at larger x. The d quark contribution to W +t production is highly suppressed due to the quark mixing…”

“…As s(x)/s(x) ranges between 1.5 → 5 for x ≥ 0.1 (See fig.5 of Ref. [32]), we can therefore suspect that the s quark contribution is dominant thans quark for the W +t single top production for the colliding proton. This may also enhance the intrinsic strange quark contribution to the W +t production by a factor of 2 → 3, corresponding to 2 → 3 pb.…”

“…A number of models concerning the sea content of the nucleon, such as the baryon-meson fluctuation model [21] and the chiral quark model [22,23], not only play significant roles to understand the proton spin structure [20,21,24], but also show their remarkable significance to explain the flavor asymmetry of the nucleon sea [21,25,26,27] reported by the NMC collaboration [28,29]. More interestingly, the baryon-meson fluctuation model and the chiral quark model have been also found to produce a strange-antistrange asymmetry of the nucleon, and such strangeness asymmetry with natural model estimations [30,31,32] can explain the NuTeV anomaly [33,34] of the deviation of the NuTeV measured value of weak mixing angle compared with other measurements. From the above discussion, we see that the intriguing features of the nucleon sea have played significant roles in the understanding of several anomalies beyond theoretical predictions.…”

Asymmetries of quark sea in nucleon

“…Recently, there has been substantial theoretical progress to take into account the effects of quark sea in determining the flavor structure of the baryons and the question of sea asymmetry has been investigated by several authors using various phenomenological models [13][14][15][16][17][18][19]. However, the inclusion of x-dependence has not yet been successfully included in the quark distribution functions.…”