Strange Components Research Articles

Improved Determination of Strange Distribution Function from the Global Analysis Using BHPS Model

We study the impact of intrinsic strange (IS) component of nucleon sea on the global analysis of parton distribution functions (PDFs) considering a wide range of experimental data. To this aim, we consider two scenarios on the basis of BHPS model results for the IS distribution. In the first scenario, we apply the results presented through the BHPS model and in the second scenario we use its evolved distributions. For each scenarios, we present the limit of the IS probability $$ \mathcal{P}_5^{s\bar{s}} $$ for the standard tolerance criteria $$ \Delta \chi ^2=1 $$ and 18.112 at $$ 1\sigma $$ and $$ 4\sigma $$ levels. Our results show that the experimental data can tolerate an IS component with a greater probability $$ \mathcal{P}_5^{s\bar{s}} $$ if one employs the second scenario. We obtain $$ \mathcal{P}_5^{s\bar{s}}\approx 0.01 $$ and $$ \mathcal{P}_5^{s\bar{s}}\approx 0.025 $$ for $$ \Delta \chi ^2=1 $$ and 18.112, respectively, at the $$ 4\sigma $$ level. We also calculate the ratio of strange-to-light sea-quark densities $$r_s$$ in the proton both including and excluding the IS component. Our results show that one can obtain a higher value for the ratio $$r_s$$ if the IS component is included.

Impact of LHC vector boson production in heavy ion collisions on strange PDFs

The extraction of the strange quark parton distribution function (PDF) poses a long-standing puzzle. Measurements from neutrino-nucleus deep inelastic scattering (DIS) experiments suggest the strange quark is suppressed compared to the light sea quarks, while recent studies of W^pm /Z boson production at the LHC imply a larger strange component at small x values. As the parton flavor determination in the proton depends on nuclear corrections, e.g. from heavy-target DIS, LHC heavy ion measurements can provide a distinct perspective to help clarify this situation. In this investigation we extend the nCTEQ15 nPDFs to study the impact of the LHC proton-lead W^pm /Z production data on both the flavor differentiation and nuclear corrections. This complementary data set provides new insights on both the LHC W^pm /Z proton analyses and the neutrino-nucleus DIS data. We identify these new nPDFs as nCTEQ15WZ. Our calculations are performed using a new implementation of the nCTEQ code (nCTEQ++) based on C++ which enables us to easily interface to external programs such as HOPPET, APPLgrid and MCFM. Our results indicate that, as suggested by the proton data, the small x nuclear strange sea appears larger than previously expected, even when the normalization of the W^{pm }/Z data is accommodated in the fit. Extending the nCTEQ15 analysis to include LHC W^pm /Z data represents an important step as we advance toward the next generation of nPDFs.

Formation of the Talysh Ethnos Worldview under Geoethnic Conservation Area Conditions

Formation and development of the Talysh ethnic consciousness under the conditions of the Talysh ‘geoethnic reserve’ have been analyzed. Certain ethnoforming elements of the Talysh culture, i.e. factors promoting preservation of the basic constants of the Talysh ethnic consciousness, have been revealed. On the one hand, it is a cult of rocks, stones, groves and trees, and on the other hand it is worship of air, water, land and fire, which with the appearance of Zoroastrianism at first, and later of Shia Muslim, were not absorbed and peripheralized, but filled with new religious and ethical contents presenting moral and esthetic ideals of the Talysh people. The role of a myth and religion as an obligatory early stage of formation of the Talysh ethnic culture has been determined; regularities of formation of the Talysh ethnic consciousness have been shown; steps of ethnogenesis and a world view of the Talysh ethnos have been enlightened. Introduction of strange cultural tradition components could not eliminate the existing valuable attitude of ‘the geoethnic reserve’, but right opposite, they created syncretic environment stimulating evolution of the Talysh ethnic consciousness towards world judgment in the system of moral and ethical images considerably enriching the Talysh ethnos outlook. Having been formed this syncretic environment effected significantly the Talysh ethnos social attitude, as well as, predetermined a prevalent character of religious values in Talyshes spiritual and socio-political life.

On the η and η′ photoproduction beam asymmetry at high energies

We show that, in the Regge limit, beam asymmetries in η and η′ photoproduction are sensitive to hidden strangeness components. Under reasonable assumptions about the couplings we estimate the contribution of the ϕ Regge pole, which is expected to be the dominant hidden strangeness contribution. The ratio of the asymmetries in η′ and η production is estimated to be close to unity in the forward region 0<−t/GeV2≤1 at the photon energy Elab=9 GeV, relevant for the upcoming measurements at Jefferson Lab.

Heavy baryons with strangeness in a soliton model

We present results from a chiral soliton model calculation for the spectrum of baryons with a single heavy quark (charm or bottom) and non-zero strangeness. We treat the strange components within a three flavor collective coordinate quantization of the soliton that fully accounts for light flavor symmetry breaking. Heavy baryons emerge by binding a heavy meson to the soliton. The dynamics of this heavy meson is described by the heavy quark effective theory with finite mass effects included.

Study of hyperon-pion resonances from kaonic absorption with KLOE

Through the study of the absorptions of low momentum kaons in light target ( 4 He and 12 C), aspects of the hyperon-nucleon interaction in medium are investigated with the KLOE drift chamber with almost full acceptance.The in-medium modification of hadron properties is the main field of study for the strangeness sector in the non-perturbative regime of the low energy region of QCD. The behaviour of strange hadrons at extreme densities are of capital importance for the description of the nuclear equation of state and the evaluation of the strangeness component in the core of the neutron stars.The study of the antiK-hadron interactions inside the drift chamber of KLOE was initiated in order to search for signals from the formation of deeply bound kaonic nuclear states and the study of resonances like the Λ(1405) and the Σ(1385), and constitute a first step towards the preparation of the AMADEUS experiment at DAFNE, the e + e − collider of the Frascati National Laboratories (Italy) of INFN.

Next-to-next-to-leading-order nucleon parton distributions from a light-cone quark model dressed with its virtual meson cloud

A detailed study of nucleon parton distribution functions is performed within a radiative Next-to-Next-to Leading Order (NNLO) parton model whose low-scale input is rigidly described by wave functions which include quarks and dressing meson-cloud. The light-front Hamiltonian dynamics fixes the three-quark wave functions and the meson cloud is introduced by means of high-order Fock component in time-ordered perturbation theory in the infinite momentum frame. Non-strange as well as strange mesons-baryon fluctuations are considered ($\pi$, $\rho$, $\omega$, $K$ and $K^*$, together with $N$, $\Delta$, $\Lambda$ and $\Sigma$) and the effects on strange and non-strange parton distributions investigated showing the large effects due to (non-strange) sea asymmetries and the delicate balance of the strange asymmetry. The non-strange and the strange components, the valence as well as the gluon distributions are compared with available experimental data confirming the need of both non-perturbative degrees of freedom and perturbative (NNLO) radiative effects.

Strangeness magnetic form factor of the proton in the extended chiral quark model

Background: Unravelling the role played by nonvalence flavors in baryons is crucial in deepening our comprehension of QCD. Strange quark, a component of the higher Fock states in baryons, is an appropriate tool to investigate nonperturbative mechanisms generated by the pure sea quark. Purpose: Study the magnitude and the sign of the strangeness magnetic moment $\mu_s$ and the magnetic form factor ($G_M^s$) of the proton. Methods: Within an extended chiral constituent quark model, we investigate contributions from all possible five-quark components to $\mu_s$ and $G_M^s (Q^2)$ in the four-vector momentum range $Q^2 \leq 1$ (GeV/c)$^2$. Probability of the strangeness component in the proton wave function is calculated employing the $^3 P_0$ model. Results: Predictions are obtained without any adjustable parameters. Observables $\mu_s$ and $G_M^s (Q^2)$ are found to be small and negative, consistent with the lattice-QCD findings as well as with the latest data released by the PVA4 and HAPPEX Collaborations. Conclusions: Due to sizeable cancelations among different configurations contributing to the strangeness magnetic moment of the proton, it is indispensable to (i) take into account all relevant five-quark components and include both diagonal and non-diagonal terms, (ii) handle with care the oscillator harmonic parameter $\omega_5$ and the ${s \bar s}$ component probability.

Lystrup Østergård – En værkstedsplads fra yngre stenalder

Lystrup Østergård – En værkstedsplads fra yngre stenalder

A minimal dark matter interpretation for the CRESST-II signal

AbstractWe report on the possible interpretation of the two proposed dark matter mass values mχ=11.6 GeV and mχ=25.3 GeV from CRESST-II within the framework of the Higgs portal minimal dark matter model. We find that the higher mass value yields a suitable fit with a dark matter-Higgs coupling η/2=0.157 and a recoil cross section which is compatible with contemporary estimates of the effective Higgs–nucleon coupling. On the other hand, the lower mass solution would require a large strangeness component in the nucleon to explain the corresponding nucleon recoil cross section reported by CRESST-II.

ϕmeson production inpp¯annihilation at rest

Apparent channel-dependent violations of the Okubo-Zwieg-Iizuka (OZI) rule in nucleon-antinucleon annihilation reactions in the presence of an intrinsic strangeness component in the nucleon are discussed. Admixture of $s\overline{s}$ quark pairs in the nucleon wave function enables the direct coupling to the $\ensuremath{\phi}$-meson in the annihilation channel without violating the OZI rule. Three forms are considered in this work for the strangeness content of the proton wave function, namely, the $uud$ cluster with a $s\overline{s}$ sea-quark component, kaon-hyperon clusters based on a simple chiral quark model, and the pentaquark picture $uuds\overline{s}$. Nonrelativistic quark model calculations reveal that the strangeness magnetic moment ${\ensuremath{\mu}}_{s}$ and the strangeness contribution to the proton spin ${\ensuremath{\sigma}}_{s}$ from the first two models are consistent with recent experimental data, where ${\ensuremath{\mu}}_{s}$ and ${\ensuremath{\sigma}}_{s}$ are negative. For the third model, the $uuds$ subsystem with the configurations $[31{]}_{FS}[211{]}_{F}[22{]}_{S}$ and $[31{]}_{FS}[31{]}_{F}[22{]}_{S}$ leads to negative values of ${\ensuremath{\mu}}_{s}$ and ${\ensuremath{\sigma}}_{s}$. With effective quark line diagrams incorporating the $^{3}P_{0}$ model, we give estimates for the branching ratios of the annihilation reactions at rest $p\overline{p}\ensuremath{\rightarrow}\ensuremath{\phi}X$ ($X={\ensuremath{\pi}}^{0}$, $\ensuremath{\eta}$, ${\ensuremath{\rho}}^{0}$, $\ensuremath{\omega}$). Results for the branching ratios of $\ensuremath{\phi}X$ production from atomic $p\overline{p}$ $s$-wave states are for the first and third model found to be strongly channel dependent, in good agreement with measured rates.

Strong decay of low-lyingS11andD13nucleon resonances to pseudoscalar mesons and octet baryons

Partial decay widths of the nucleon resonances $S_{11}(1535)$, $S_{11}(1650)$, $D_{13}(1520)$ and $D_{13}(1700)$ to the pseudoscalar mesons and octet baryons are studied within a chiral constituent quark model. The effects of the configurations mixing between the states $|N^{2}_{8}P_{M}>$ and $|N^{4}_{8}P_{M}>$ are considered, taking into account the breakdown of the $SU(6)\otimes O(3)$ symmetry. In addition, possible contributions of the strangeness components in the $S_{11}$ resonances are investigated. Experimental data for the partial decay widths of the $S_{11}$ and $D_{13}$ resonances are well reproduced. Predictions for coupling constants of the four nucleon resonances to pseudoscalar mesons and octet baryons, crucial issues in the photo- and hadron-induced meson production reactions, are reported.

STRANGENESS AND CHIRAL SYMMETRY BREAKING

The implications of chiral symmetry breaking and SU(3) symmetry breaking have been studied in the chiral constituent quark model (χCQM). The role of hidden strangeness component has been investigated for the scalar matrix elements of the nucleon with an emphasis on the meson–nucleon sigma terms. The χCQM is able to give a qualitative and quantitative description of the "quark sea" generation through chiral symmetry breaking. The significant contribution of the strangeness is consistent with the recent available experimental observations.

Recent results on nucleon sigma terms in lattice QCD

It has proven a significant challenge to experiment and phenomenology to extract a precise values of the nucleon sigma terms. This difficulty opens the window for lattice QCD simulations to lead the field in resolving this aspect of nucleon structure. Here we report on recent advances in the extraction of nucleon sigma terms in lattice QCD. In particular, the strangeness component is now being resolved to a precision that far surpasses best phenomenological estimates.

Erratum: Coupled-channel analysis forϕphotoproduction withΛ(1520)[Phys. Rev. C80, 035201 (2009)

We investigate photoproduction of $\phi$-mesons off protons within a coupled-channel effective-Lagrangian method which is based on the K-matrix approach. Since the threshold energy of the $K\Lambda(1520)$ channel is close to that of $\phi N$, the contribution of this channel to $\phi$-photoproduction near the threshold energy region may give rise to some unexpected structures. In the transition amplitude $K\Lambda(1520) \to \phi N$, the kinematics allows an intermediate kaon to be on-shell. This happens in the energy region where a peak structure has been observed in $\phi$-photoproduction. In our calculations the on-shell kaon effect indeed reproduces a peak structure, however, with a magnitude that is far too small to explain the observed effect. As a following step we introduce a nucleon resonance in our model. The coupling of the resonance to the $K\Lambda(1520)$ and $\phi N$ channels is not suppressed by the OZI rule if the resonance contains a dominant hidden strangeness component. We find that the resonance can reproduce a peak structure of the correct magnitude at the right energy. We also investigate the effects of coupled channels and the resonance on the angular distribution and the spin density matrices for $\phi$ photoproduction.

Five-quark components in N*(1535)

Here we employ the extended chiral constituent quark model to investigate the five-quark components in the N*(1535) resonance. The axial charge of N*(1535) and the electromagnetic transition γ*N → N*(1535) are also analyzed. The results show that there may be sizable strangeness component in N*(1535).

Coupled-channel analysis for ϕ photoproduction with Λ(1520)

We investigate photoproduction of phi mesons off protons within a coupled-channel effective-Lagrangian method which is based on the K-matrix approach. Since the threshold energy of the K Lambda(1520) channel is close to that of phi N, the contribution of this channel to f photoproduction near the threshold energy region may give rise to some unexpected structures. In the transition amplitude K Lambda(1520) -> phi N, the kinematics allows an intermediate kaon to be on-shell. This happens in the energy region where a peak structure has been observed in f photoproduction. In our calculations, the on-shell kaon effect indeed reproduces a peak structure, though with a magnitude that is far too small to explain the observed effect. As a following step, we introduce a nucleon resonance in our model. The coupling of the resonance to the K Lambda (1520) and phi N channels is not suppressed by the Okubo-Zweig-Iizuka (OZI) rule if the resonance contains a dominant hidden strangeness component. We find that the resonance can reproduce a peak structure of the correct magnitude at the right energy. We also investigate the effects of coupled channels and the resonance on the angular distribution and the spin-density matrices for phi photoproduction.

Parity-violating effects in elastic electron deuteron scattering

The general expressions for parity violation observables in elastic scattering of polarized and/or unpolarized electrons from unpolarized deuterons are given and are numerically evaluated for the kinematics of SAMPLE, PVA4 and G0 experiments. The dominant contribution from the interference of \( \gamma\) and Z exchange as well as the smaller contributions from strangeness (s \( \bar{{s}}\) components of the nucleon, parity odd admixtures in the deuteron wave function, anapole moments and radiative corrections are included and discussed in the context of parity-violating electron scattering experiments of present interest.

Baryon Magnetic Moment and Beta Decay Ratio in Colored Quark Cluster Model

Baryon magnetic moments of p, n, Σ+, Σ−, Ξ0, Ξ− and the beta decay ratios (GA/GV) of n → p, Σ− → n and Ξ0 → Σ+ are calculated in a colored quark cluster model. With SU(3) breaking, the model gives a good fit to the experimental values of those baryon magnetic moments and the beta decay ratios. Our results show that the orbital motion has a significant contribution to the spin and magnetic moments of those baryons and the strange component in nucleon is small.

Isospin Mixing in the Nucleon andHe4and the Nucleon Strange Electric Form Factor

In order to isolate the contribution of the nucleon strange electric form factor to the parity-violating asymmetry measured in 4He(e-->],e')4He experiments, it is crucial to have a reliable estimate of the magnitude of isospin-symmetry-breaking (ISB) corrections in both the nucleon and 4He. We examine this issue in the present Letter. Isospin admixtures in the nucleon are determined in chiral perturbation theory, while those in 4He are derived from nuclear interactions, including explicit ISB terms. A careful analysis of the model dependence in the resulting predictions for the nucleon and nuclear ISB contributions to the asymmetry is carried out. We conclude that, at the low momentum transfers of interest in recent measurements reported by the HAPPEX Collaboration at Jefferson Lab, these contributions are of comparable magnitude to those associated with strangeness components in the nucleon electric form factor.