Sea Quarks Research Articles

Temporal trends (1972-2017) and spatial differences of persistent halogenated aromatic hydrocarbons in osprey eggs in Finland.

Time trends and regional differences of polychlorinated dibenzo-p-dioxins and -furans (PCDD/Fs), polychlorinated biphenyls (PCBs), polychlorinated naphthalenes (PCNs), DDTs, polybrominated biphenyls (PBBs) and polybrominated diphenylethers (BDEs) were studied in unhatched osprey eggs collected by bird ringers in 1972-2017 from four areas in Finland. Two study areas were from Baltic Sea, Northern Quark and Finnish Archipelago Sea, while the two others were inland lake areas, eutrophicated Lake Vanajanselkä affected by industrial emissions, and Pristine SW Lake Area. The highest concentrations of most compound groups were in Lake Vanajanselkä consistent with high emissions, the predominance of bream as a prey, and higher concentrations in bream compared to other prey fish. Concentrations of all chlorinated compounds decreased significantly in all study areas. Average annual decreases were ∑PCDD/F 2.3-4.9%, ∑PCB 2.2-4.2%, ∑PCN 2.6-7.0% and ∑DDT 7.1-9.5%, primarily in line with decreased levels in prey fish. From 1972 PBBs and BDEs increased significantly until 1990s declining rapidly thereafter. PCDD/F congener profile was dominated by 2,3,4,7,8-PeCDF, except in Lake Vanajanselkä by 1,2,3,6,7,8-HxCDD. PCB congener profile was dominated by PCB 153 in all study areas, followed by PCB 180 and PCB 138. Among dioxin-like compounds PCBs contributed 82%, PCDDs 14% and PCDFs 4% to toxic equivalent quantity (∑TEQ). PCB 126 contributed most to ∑TEQ, followed by 1,2,3,7,8-PeCDD. BDE 47 being the dominant BDE congener, followed by BDE 100. ∑DDT concentrations were relatively similar across all study areas, with DDE contributing about 90%. Productivity of chicks per active nest was significantly decreased in Lake Vanajanselkä, and the likely explanation is embryotoxicity of dioxin-like compounds. It is plausible that dioxin-like compounds influenced embryonic survival among highly exposed ospreys prior to 2010, especially in Lake Vanajanselkä and Northern Quark. However, decreased survival due to DDE-induced eggshell thinning seems unlikely after 1985, and BDE levels were below those potentially causing adverse effects.

Chiral-odd generalized parton distributions of sea quarks at ξ=0 in the light-cone quark model

We study the chiral-odd generalized parton distributions (GPDs) of the u¯ and d¯ quarks inside the proton at zero skewness using the overlap representation within the light-cone formalism. Utilizing the light-cone wave functions of the proton obtained from the baryon-meson fluctuation model in terms of the |qq¯B⟩ Fock states, we provide expressions for the GPDs H˜Tq¯/P(x,0,t), HTq¯/P(x,0,t), and ETq¯/P(x,0,t) where q¯=u¯ and d¯. Numerical results for these GPDs in momentum space as well as in impact parameter space are presented. Additionally, we investigate specific combinations of the chiral-odd GPDs in impact parameter space, focusing on the spin-orbit correlation effect of the sea quarks. Published by the American Physical Society 2024

Flavor asymmetry of light sea quarks in proton: a light-front spectator model

We formulate a light-front spectator model for the proton that incorporates the presence of light sea quarks. In this particular model, the sea quarks are seen as active partons, whereas the remaining components of the proton are treated as spectators. The proposed model relies on the formulation of the light-front wave function constructed by the soft wall AdS/QCD. The model wave functions are parameterized by fitting the unpolarized parton distribution functions of light sea quarks from the CTEQ18 global analysis. We then employ the light-front wave functions to obtain the sea quarks generalized parton distribution functions, transverse momentum dependent parton distributions, and their asymmetries, which are accessible in the upcoming Electron-Ion-Colliders. We investigate sea quarks’ spin and orbital angular momentum contributions to the proton spin.

Unpolarized transverse momentum dependent parton distributions of the nucleon from lattice QCD

We present a first lattice QCD calculation of the unpolarized nucleon’s isovector transverse-momentum-dependent parton distribution functions (TMDPDFs), which are essential to predict observables of multiscale, semi-inclusive processes in the standard model. We use a Nf=2+1+1 MILC ensemble with valence clover fermions on a highly improved staggered quark (HISQ) sea to compute the quark momentum distributions in a large-momentum nucleon on the lattice. The state-of-the-art techniques in renormalization and extrapolation in the correlation distance on the lattice are adopted. The perturbative kernel up to next-to-next-to-leading order is taken into account, and the dependence on the pion mass and the hadron momentum is explored. Our results are qualitatively comparable with phenomenological TMDPDFs, which provide an opportunity to predict high energy scatterings from first principles. Published by the American Physical Society 2024

Wigner distributions of sea quarks in the light-cone quark model

We investigate the Wigner distributions of u¯ and d¯ quarks in a proton using the overlap representation within the light cone formalism. Using the light-cone wave functions which are obtained from the baryon-meson fluctuation model in terms of the |qq¯B⟩ Fock states, we calculate the Wigner distributions for the unpolarized/longitudinally polarized sea quarks in an unpolarized/longitudinally polarized proton. The Wigner distributions can be obtained through a Fourier transform on the generalized transverse-momentum dependent parton distributions (GTMDs). We also calculate the GTMDs of u¯ and d¯ quarks in the intermediate step. Numerical results for the Wigner distributions of u¯ and d¯ quarks in transverse momentum space, impact parameter space and the mixed plane are presented. We also study the orbital angular momentum and the spin-orbit correlations of the sea quarks. Published by the American Physical Society 2024

Trace anomaly form factors from lattice QCD

The hadron mass can be obtained through the calculation of the trace of the energy-momentum tensor in the hadron which includes the trace anomaly and sigma terms. The anomaly due to conformal symmetry breaking is believed to be an important ingredient for hadron mass generation and confinement. In this work, we will present the calculation of the glue part of the trace anomaly form factors of the pion up to Q2∼4.3 GeV2 and the nucleon up to Q2∼1 GeV2. The calculations are performed on a domain wall fermion ensemble with overlap valence quarks at seven valence pion masses varying from ∼250 to ∼540 MeV, including the unitary point ∼340 MeV. We calculate the radius of the glue trace anomaly for the pion and the nucleon from the z expansion. By performing a two-dimensional Fourier transform on the glue trace anomaly form factors in the infinite momentum frame with no energy transfer, we also obtain their spatial distributions for several valence quark masses. The results are qualitatively extrapolated to the physical valence pion mass with systematic errors from the unphysical sea quark mass, discretization effects in the renormalization sum rule, and finite-volume effects to be addressed in the future. We find the pion’s form factor changes sign, as does its spatial distribution, for light quark masses. This explains how the trace anomaly contribution to the pion mass approaches zero toward the chiral limit. Published by the American Physical Society 2024

Analysis of parton distributions in a pion with Bézier parametrizations

We explore the role of parametrizations for nonperturbative QCD functions in global analyses, with a specific application to extending a phenomenological analysis of the parton distribution functions (PDFs) in the charged pion realized in the xFitter fitting framework. The parametrization dependence of PDFs in our pion fits substantially enlarges the uncertainties from the experimental sources estimated in the previous analyses. We systematically explore the parametrization dependence by employing a novel technique to automate generation of polynomial parametrizations for PDFs that makes use of Bézier curves. This technique is implemented in a ++ module that is included in the xFitter program. Our analysis reveals that the sea and gluon distributions in the pion are not well disentangled, even when considering measurements in leading-neutron deep inelastic scattering. For example, the pion PDF solutions with a vanishing gluon and large quark sea are still experimentally allowed, which elevates the importance of ongoing lattice and nonperturbative QCD calculations, together with the planned pion scattering experiments, for conclusive studies of the pion structure. Published by the American Physical Society 2024

Transverse momentum weighted Sivers asymmetries in SIDIS and Drell-Yan processes at COMPASS

We investigate the transverse momentum weighted Sivers asymmetries in the processes with transversely polarized proton target, including the PhTzMpsin⁡(ϕh−ϕS) weighted asymmetry in charged hadron production in semi-inclusive deeply inelastic scattering (SIDIS) and the qTMpsin⁡(ϕS) weighted asymmetry in π−p Drell-Yan process. These asymmetries can be expressed as the product of the transverse-moments of the transverse momentum dependent (TMD) parton distribution functions (PDFs) and fragmentation functions (FFs). Using the parametrization for the Sivers function of the proton, the unpolarized PDFs of proton and pion, and the unpolarized FF of charged hadron, we present the numerical calculation for weighted Sivers asymmetries in SIDIS and Drell-Yan processes at the kinematics of COMPASS. We find that our prediction for the SIDIS process is in agreement with the recent COMPASS measurement. Recent new high-statistics data of Sivers asymmetry measured in SIDIS process and Drell-Yan process from COMPASS favored the sign change of Sivers function. High-precision experimental data of weighted asymmetries are still needed to test the sign change property of the Sivers function between SIDIS and Drell-Yan processes and to constrain the sea quark Sivers function.

Nonperturbative running of the tensor operator for Nf=3 QCD from the chirally rotated Schrödinger functional

We study the renormalization group (RG) running of the nonsinglet tensor operator, for Nf=3 QCD with Wilson fermions in a mixed action setup, with standard Schrödinger functional (SF) boundary conditions for sea quarks and chirally rotated Schrödinger functional (χSF) boundary conditions for valence quarks. Based on a recursive finite-size scaling technique we compute nonperturbatively the tensor step-scaling function for an energy range between a hadronic scale and an electroweak scale, above which perturbation theory may be safely applied. Our result is expressed as the RG-running factor TRGI/[T(μhad)]R, where the numerator is the scale independent (renormalization group invariant—RGI) tensor operator and the denominator is its renormalized counterpart at a hadronic scale μhad=233(8) MeV in a given scheme. We determine the step-scaling function in four distinct renormalization schemes. We also compute the renormalization parameters of these schemes at μhad which, combined with the RG-running factor, gives the scheme-independent quantity ZTRGI(g02) in four schemes and for a range of bare gauge couplings in which large volume hadronic matrix element simulations are performed by the CLS consortium in Nf=2+1 QCD. All four results are compatible and also agree with a recent determination based on a unitary setup for Wilson quarks with Schrödinger functional boundary conditions [arXiv:2309.04314]. This provides a strong universality test. Published by the American Physical Society 2024

Role of sea quarks in the nucleon transverse spin

We present a phenomenological extraction of transversity distribution functions and Collins fragmentation functions by simultaneously fitting to semi-inclusive deep inelastic scattering and electron-positron annihilation data. The analysis is performed within the transverse-momentum-dependent factorization formalism, and sea quark transversity distributions are taken into account for the first time. We find the u¯ quark favors a negative transversity distribution, while that of the d¯ quark is consistent with zero according to the current accuracy. In addition, based on a combined analysis of world data and simulated data, we quantitatively demonstrate the impact of the proposed Electron-Ion Collider in China on precise determinations of the transversity distributions, especially for sea quarks, and the Collins fragmentation functions. Published by the American Physical Society 2024

Quantum Chromodynamics of the Nucleon in Terms of Complex Probabilistic Processes

Despite the obvious progress made by the Feynman, Ravndal, and Kislinger relativistic model in describing the internal motion of a system with confinement of quarks in a nucleon, it turned out to be insufficiently realistic for a number of reasons. In particular, the model does not take into account some cornerstone properties of QCD, namely, gluon exchange between quarks, the influence of the resulting quark sea on valence quarks, and the self-interaction of colored gluons. It is these phenomena that spontaneously break the chiral symmetry of the quark system and form the bulk of the nucleon. To eliminate the above shortcomings of the model, the problem of self-organization of a three-quark dynamical system immersed in a colored quark–antiquark sea is considered within the framework of complex probabilistic processes that satisfy the stochastic differential equation of the Langevin–Kline–Gordon–Fock type. Taking into account the hidden symmetry of the internal motion of a dynamical system, a mathematically closed nonperturbative approach was developed, which makes it possible to construct the mathematical expectation of the wave function and other parameters of the nucleon in the form of multiple integral representations. It is shown that additional subspaces arising in a representation characterized by a noncommutative geometry with topological features participate in the formation of an effective interaction between valence quarks against the background of harmonic interaction between them.

Exploring the spin structure of the nucleon at STAR

Understanding the internal spin structure of the nucleon remains a challenge in strong interaction physics. The unique capability of RHIC opened new avenues in studying the internal structure of the proton with unprecedented depth and precision. Significant progress has been made in the last few years through various measurements at STAR. The longitudinal spin measurements have contributed significantly to our understanding of the quark and gluon helicity distributions inside the proton. The longitudinal double-spin asymmetry, ALL, from STAR inclusive jet and dijet measurements provides the first evidence of a positive gluon polarization with partonic momentum fraction x > 0.05. The reconstruction of W±/Z in longitudinally polarized proton-proton collisions indicates that there is a flavor separation of the light sea quark helicity distributions. In transversely polarized proton collisions, W±/Z-bosons provide the first constraint on the sea-quark Sivers function and contributes to the tests of the predicted sign change. The tilt of the dijet opening angle provides a direct access to the first Mellin momentum of the Sivers function and avoids the spin-correlated fragmentation contributions. The novel measurements of the azimuthal distributions of identified hadrons in jets and spin-dependent dihadron correlations directly probe the collinear quark transversity in the proton, with the former coupled to the transverse momentum dependent (TMD) Collins fragmentation function and the latter to the dihadron interference fragmentation function. These measurements shed lights on Sivers function, quark transversity and spin-dependent fragmentation functions in both collinear and TMD formalism. In this proceeding, recent jet results on both the longitudinal and transverse spin structure of the proton from STAR are presented.

The Sivers asymmetry in charged Kaon and Λ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Lambda $$\\end{document} hyperon produced SIDIS process at electron ion colliders

We investigate the single transverse-spin asymmetry with a sin(ϕh-ϕS)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sin (\\phi _h-\\phi _S)$$\\end{document} modulation in the charged Kaon produced and in Λ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Lambda $$\\end{document} hyperon produced SIDIS process within the theoretical framework of transverse momentum dependent (TMD) factorization at the next-to-leading-logarithmic order. The asymmetry is contributed by the convolution of Sivers function and the unpolarized fragmentation function D1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$D_1$$\\end{document} for the produced hadron. The parametrization for the proton Qiu–Sterman function, which is closely related to the Sivers function, is adopted to numerically estimate the Sivers asymmetry at the kinematical region of Electron Ion Collider (EIC) and Electron Ion Collider in China (EicC). The TMD evolution of the TMD parton distribution functions are considered by employing the non-perturbative Sudakov form factor. It is found that the predicted Sivers asymmetries AUTsin(ϕh-ϕS)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$A_{UT}^{\\sin (\\phi _h-\\phi _S)}$$\\end{document} as functions of x, z and PhT\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$P_{hT}$$\\end{document} are sizable at the kinematical configurations of both EIC and EicC. The strange constituent of the produced charged Kaon and Λ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Lambda $$\\end{document} hyperon in the final state can be a promising probe of the sea quark Sivers function as well as the flavor dependence in the proton target. Therefore, it is important to utilize the future EIC facilities to constrain the sea quark distribution functions as well as the validity of the generalized universality of the Sivers function.

Hide and seek: how PDFs can conceal new physics

The interpretation of LHC data, and the assessment of possible hints of new physics, require the precise knowledge of the proton structure in terms of parton distribution functions (PDFs). We present a systematic methodology designed to determine whether and how global PDF fits might inadvertently ‘fit away’ signs of new physics in the high-energy tails of the distributions. We showcase a scenario for the High-Luminosity LHC, in which the PDFs may completely absorb such signs of new physics, thus biasing theoretical predictions and interpretations. We discuss strategies to single out the effects in this scenario, and disentangle the inconsistencies that stem from them. Our study brings to light the synergy between the high luminosity programme at the LHC and future low-energy non-LHC measurements of large-x sea quark distributions. The analysis code used in this work is made public so that any users can test the robustness of the signal associated to a given BSM model against absorption by the PDFs.

Proton structure functions at low x: The fractal distributions

This paper presents a method for extracting the parton distribution functions (PDFs) at small momentum fractions [Formula: see text] and at the next-to-leading order (NLO) accuracy in perturbative quantum chromodynamics. It turns out that the PDFs can be described by the “Fractal” or self-similar distributions at low [Formula: see text] below [Formula: see text]. To this end, a simple parametrization for the unintegrated PDFs based on the “Fractal” approach is considered. These functions have self-similar behavior at low [Formula: see text] and [Formula: see text] for sea quarks and have self-similar behavior at low [Formula: see text] for gluon distribution. By integration from these transverse momentum distributions (TMDs), the initial input densities are obtained and the model’s free parameters are then calculated using the experimental data released by the HERA experiment. The small-[Formula: see text] experimental datasets on electron–proton ([Formula: see text]) and positron–proton ([Formula: see text]) for natural current (NC) interactions in deep inelastic scattering (DIS) processes at HERA for the range of [Formula: see text] (GeV2) and [Formula: see text] are included in this analysis. The uncertainty estimations in this analysis are carried out using the standard “Hessian” method. Considering the overall value of [Formula: see text] and theory-to-data comparisons, the results indicate good agreements between the experimental datasets and the theoretical predictions. A detailed comparison is also presented between the model’s predictions for the relevant small-[Formula: see text] observable and recent parametrizations for the PDFs.

Impact of charge symmetry breaking on gluon and sea quark distributions in the pion and kaon

In this exploratory study, I present, for the first time, the implications of the charge symmetry breaking (CSB) that arise from the [Formula: see text] and [Formula: see text] quark-mass differences on gluon and sea quark distribution functions of the pion and kaon in the framework of the Nambu–Jona-Lasino (NJL) model, which is a quark-level chiral effective theory of QCD, with the help of the proper-time regularization scheme to simulate color confinement of QCD. From the analysis, one finds that the charge symmetry (CS) gluon distribution for the pion has a good agreement with the prediction results obtained from the recent lattice QCD simulation and JAM global fit QCD analysis at a higher scale of [Formula: see text][Formula: see text]GeV2. The size of the CSB effects on gluon and sea quark distributions for the pion with the realistic ratios of [Formula: see text] at [Formula: see text][Formula: see text]GeV2 are, respectively, estimated by 1.3% and 2.0% at [Formula: see text] in comparison with those for [Formula: see text], while those for the kaon are approximately about 0.3% and 0.5% at [Formula: see text], respectively. A remarkable result is found that the CSB effects on gluon distribution for the kaon are smaller than that for the pion, which has a similar prediction result as that for the CS case.

Impact of SeaQuest data on PDF fits at large x

We evaluate the impact of recent SeaQuest (FNAL-E906 experiment) data on dimuon production in proton-deuteron and proton-proton collisions on parton distribution functions (PDFs). We find these data in a good agreement with the QCD predictions based on PDFs fitted to the Tevatron and LHC data on forward production of W and Z bosons. As a basis for this study we use the ABMP16 PDF fits and show that they turn out to be compatible with the SeaQuest data, and that these data have constraining power, allowing to reduce the uncertainties on the isospin asymmetry of the light-sea-quark distribution at large longitudinal momentum fraction x. We discuss the nuclear corrections needed to describe the deuteron and show that they affect the theoretical description of the proton-deuteron Drell–Yan cross section at the level of mathcal {O}(0.5{-}1)%. We also comment on the compatibility of the SeaQuest results with other state-of-the-art PDF fits and show that these data are in clear disagreement with models proposing an SU(3)-flavor symmetric quark sea. Finally, we perform a comparison between the second Mellin moments of the light-quark PDFs and recent results from various lattice QCD computations, which demonstrates good compatibility, albeit limited by the uncertainties inherent in current lattice QCD simulations.

Shadowing corrections to the evolution of singlet structure function

In this paper, a semi-analytical approach is introduced to address the solution of the nonlinear Gribov-Levin-Ryskin-Mueller-Qiu (GLR-MQ) evolution equation for sea quark distribution. Here the effect of gluon shadowing on the behaviour of singlet structure function, , has been investigated, particularly in the regime of small-x and moderate-Q 2. The predicted values of singlet structure functions with shadowing corrections align well with different experimental data and existing parametrizations. It is very fascinating to observe signatures of gluon recombination within these predictions. Notably, as x decreases, the rapid growth of singlet structure function is eventually tamed by the shadowing or nonlinear term appeared in the QCD evolution due to gluon recombination. This taming behaviour of shadowing singlet structure function towards small-x become significant at the hot spots, at R = 2 GeV−1. Further the computed ratios of with shadowing, in comparison to those without shadowing, clearly indicate that towards smaller values of x and Q 2 the nonlinear effects gradually become prominent.

Effect of symmetry breaking of polarized light sea quarks on the nucleon and nuclear structure functions, and sum rules

Effect of symmetry breaking of polarized light sea quarks on the nucleon and nuclear structure functions, and sum rules

Constraining the Sea Quark Distributions Through W Cross-Section Ratios Measured in pp Collisions at STAR

Although the precision to which we know the unpolarized parton distribution functions (PDFs) of the nucleon has improved over the years, there remain kinematic regions where more data are needed to constrain PDFs, such as the ratio of the sea quark distributions near the valence region. Furthermore, different measurements appear to suggest different high-x behaviors of this ratio. The W cross-section ratio (W+/W −) in pp collisions is sensitive to the unpolarized sea quark distributions at large Q 2, set by the W mass, and can be used to help constrain the ratio. The STAR experiment at RHIC is well equipped to measure the leptonic decays of W bosons produced in pp collisions at center of mass energies of 500 and 510 GeV. These proceedings present recent W cross-section ratio results measured by STAR, including preliminary results from data collected in 2017, which double the statistics when combined with the published results based on data samples recorded in 2011-2013.