The recent anomalies in $b\to s\ell^+\ell^-$ transitions could originate from some New Physics beyond the Standard Model. Either to confirm or to rule out this assumption, more tests of $b\to s\ell^+\ell^-$ transition are needed. Polarized $Λ_b$ decay to a $Λ$ and a dilepton pair offers a plethora of observables that are suitable to discriminate New Physics from the Standard Model. In this paper, we present a full angular analysis of a polarized $Λ_b$ decay to a $Λ(\to pπ)\ell^+\ell^-$ final state. The study is performed in a set of the operator where the Standard Model operator basis is supplemented with its chirality flipped counterparts, and new scalar and pseudo-scalar operators. The full angular distribution is calculated by retaining the mass of the final state leptons. At the low hadronic recoil, we use the Heavy Quark Effective Theory framework to relate the hadronic form factors which lead to simplified expression of the angular observables where short- and long-distance physics factorize. Using the factorized expressions of the observables, we construct a number of tests of short- and long-distance physics including null tests of the Standard Model and its chirality flipped counterparts that can be carried out using experimental data.
The chemical equilibration of a highly unsaturated quark-gluon plasma has been studied at finite baryon density. It is found that in the presence of small amount of baryon density, the chemical equilibration for gluon becomes slower and the temperature decreases less steeply as compared to the baryon free plasma. As a result, the space time integrated yield of dilepton is enhanced if the initial temperature of the plasma is held fixed. Even at a fixed initial energy density, the suppression of the dilepton yields at higher baryo-chemical potential is compensated, to a large extent, by the slow…
We discuss the transverse momentum Q_T distribution of Drell-Yan pair, produced in collisions of transversely polarized protons. We calculate the transversely polarized Drell-Yan cross section up to order α_s in the dimensional regularization scheme, which gives QCD prediction at large Q_T. For small Q_T region, we include all-orders resummation of large logarithms due to emission of soft gluons up to next-to-leading logarithmic accuracy. At intermediate Q_T region, the resummation formula is matched with the fixed-order α_s perturbative results in a systematic way, so that we derive the cross…
In this paper we present a comprehensive formalism for dilepton production from the collision of two polarized spin-$\tfrac{1}{2}$ hadrons by identifying the general angular distribution of the cross section in combination with a complete set of structure functions. The various structure functions are computed in the parton model approximation where we mainly consider the case when the transverse momentum of the dilepton pair is much smaller than its invariant mass. In this kinematical region dilepton production can be described in terms of transverse momentum dependent parton distributions.
It has been observed recently that while continuum dilepton production and open charm production in high-energy $pA$ collisions can be described in terms of the superposition of $pp$ collisions, dilepton yields in S+U collisions are in excess of similar extrapolations. This feature can be explained as arising from the interaction of gluons produced in different soft baryon-baryon collisions, leading to additional open-charm pairs in nucleus-nucleus collisions but not in $pA$ collisions.
We investigate the effects of a baryon-antibaryon asymmetry on the spectrum of dileptons radiating from a quark gluon plasma. We demonstrate the existence of a new set of processes in this regime. The dilepton production rate from the corresponding diagrams is shown to be as important as that obtained from the usual quark-antiquark annihilation.
It has recently been suggested that collisions of transversely polarized protons and antiprotons at the GSI could be used to determine the nucleon's transversity densities from measurements of the double-spin asymmetry for the Drell-Yan process. We analyze the role of higher-order perturbative QCD corrections in this kinematic regime, in terms of the available fixed-order contributions as well as of all-order soft-gluon resummations. We find that the combined perturbative corrections to the individual unpolarized and transversely polarized cross sections are large. We trace these large enhance…
We consider effects of $n-\bar n$ oscillations and resultant matter instability due to dinucleons decays. We point out that existing upper bounds on the rates for the dinucleon decays $nn \to 2π^0$, $nn \to π^+π^-$, and $np \to π^+π^0$ imply upper bounds on the rates for dinucleon decays to dileptons $nn \to e^+ e^-$, $nn \to μ^+μ^-$, $nn \to ν_\ell \barν_\ell$, and $np \to \ell^+ ν_\ell$, where $\ell=e, \ μ, \ τ$. We present estimates for these upper bounds. Our bounds are substantially stronger than corresponding limits from direct searches.
We present a recent study of the QCD corrections to dilepton production near partonic threshold in transversely polarized \bar{p}p scattering. We analyze the role of the higher-order perturbative QCD corrections in terms of the available fixed-order contributions as well as of all-order soft-gluon resummations for the kinematical regime of proposed experiments at GSI-FAIR. We find that perturbative corrections are large for both unpolarized and polarized cross sections, but that the spin asymmetries are stable. The role of the far infrared region of the momentum integral in the resummed expone…
We propose that local parity breaking induced by a large-scale fluctuation of topological charge at large temperatures and/or condensation of pseudoscalar mesons in the isotriplet channel for large baryon densities may be responsible for the substantial dilepton excess that is found for low invariant masses and moderate values of $p_T$ in central heavy ions collisions. This insofar unexplained enhancement could be understood by a combination of two effects leading both to an excess of $e^+e^-$ and $μ^+ μ^-$ pairs with respect to theoretical predictions based on conventional hadronic processes:…
Within an effective Lagrangian model, we present calculations for cross sections of the dilepton production in proton-proton and proton-neutron collisions at laboratory kinetic energies in 1-5 GeV range. Production amplitudes include contributions from the nucleon-nucleon bremsstrahlung as well as from the mechanism of excitation, propagation, and radiative decay of Delta(1232) and N*(1520) intermediate baryonic resonances. It is found that the delta isobar terms dominate the cross sections in the entire considered beam energy range. Our calculations are able to explain the data of the DLS col…
We investigate dilepton production in transport-based approaches and show that the baryon couplings of the $ρ$ meson represent the most important ingredient for understanding the measured dilepton spectra. At low energies (of a few GeV), the baryon resonances naturally play a larger role and affect already the vacuum spectra via Dalitz-like contributions, which can be captured well in an on-shell-transport scheme. At higher energies, the baryons mostly affect the in-medium self energy of the $ρ$, which is harder to tackle in transport models and requires advanced techniques.
We extend our recent analysis of the dilepton and photon emission rates to the case of finite temperature and baryon density, within the context of a density expansion. To leading order, the effects of the baryon density are assessed using data (photon emission) or constraints from broken chiral symmetry (dilepton emission). Next to leading order effects are worked out, and their contribution qualitatively assessed. The opening of the $πN$ cut causes the photon rate to saturate the empirical photon yield of WA80, but may not be enough to fully account for the excess low mass dileptons seen at …
The coefficients determining the dilepton decay angular distribution of vector particles obey certain positivity constraints and a rotation-invariant identity. These relations are a direct consequence of the covariance properties of angular momentum eigenstates and are independent of the production mechanism. The Lam-Tung relation can be derived as a particular case, simply recognizing that the Drell-Yan dilepton is always produced transversely polarized with respect to one or more quantization axes. The dilepton angular distribution continues to be characterized by a frame-independent identit…
We obtain the thermal photon and dilepton production rates in a strongly coupled quark-gluon plasma (QGP) at both zero and nonzero baryon chemical potential using a bottom-up Einstein-Maxwell-Dilaton (EMD) holographic model that is in good quantitative agreement with the thermodynamics of $(2+1)$-flavor lattice QCD around the crossover transition for baryon chemical potentials up to 400 MeV, which may be reached in the beam energy scan (BES) at RHIC. We find that increasing the temperature $T$ and the baryon chemical potential $μ_B$ enhances the peak present in both spectra. We also obtain the…
Hadronic polarization and the related anisotropy of the dilepton angular distribution are studied for the reaction $πN \rightarrow Ne^+ e^-$. We employ consistent effective interactions for baryon resonances up to spin-5/2, where non-physical degrees of freedom are eliminated, to compute the anisotropy coefficients for isolated intermediate baryon resonances. It is shown that the spin and parity of the intermediate baryon resonance is reflected in the angular dependence of the anisotropy coefficient. We then compute the anisotropy coefficient including the $N(1520)$ and $N(1440)$ resonances, w…
We study the $p$-wave polarization operator of the $ρ$-meson due to $ρN$ interactions via the $N^*$ (1720) and $Δ(1905)$ resonances and compute the corresponding production rate for $e^+e^-$-pairs at finite temperature and baryon density. At high baryon density we find a significant shift of the spectrum to lower invariant masses.
We investigate dilepton production in transport-based approaches and show that the baryon couplings of the $ρ$ meson represent the most important ingredient for understanding the measured dilepton spectra. At SIS energies, the baryon resonances naturally play a major role and affect already the vacuum spectra via Dalitz-like contributions, which can be captured well in transport simulations. Recent pion-beam measurements at GSI will help to constrain the properties of the involved resonances further.
In this paper we systematically consider the baryon ($B$) and lepton ($L$) number violating dinucleon to dilepton decays ($pp\to \ell^+\ell^{\prime+}, pn\to \ell^+\barν^\prime, nn\to \barν\barν^\prime$) with $ΔB=ΔL=-2$ in the framework of effective field theory. We start by constructing a basis of dimension-12 (dim-12) operators mediating such processes in the low energy effective field theory (LEFT) below the electroweak scale. Then we consider their standard model effective field theory (SMEFT) completions upwards and their chiral realizations in baryon chiral perturbation theory (B$χ$PT) do…
We calculate the double transverse-spin asymmetries, $\aqt$, in transversely polarized Drell-Yan process at the transverse-momentum $Q_T$ of the produced lepton pair. We perform all-order resummation of the logarithmically enhanced contributions in the relevant Drell-Yan cross sections at small $Q_T$, which are due to multiple soft gluon emission in QCD, up to the next-to-leading logarithmic accuracy. The asymmetries $\aqt$ to be observed in polarized experiments at RHIC and J-PARC are studied numerically as a function of $Q_T$. We show that the effects of the soft gluon resummation to the pol…
We present studies of QCD corrections to dilepton production in transversely polarized pp and \bar{p}p scattering. In particular we briefly discuss the effects of NNLL threshold resummation on the rapidity distribution of the lepton pair.
We study hadronic polarization and the related anisotropy of the dilepton angular distribution for the reaction $πN \to Ne^+e^-$. We employ consistent effective interactions for baryon resonances up to spin-5/2 to compute their contribution to the anisotropy coefficient. We show that the spin and parity of the intermediate baryon resonance is reflected in the angular dependence of the anisotropy coefficient. We present results for the anisotropy coefficient including the $N(1520)$ and $N(1440)$ resonances, which are essential at the collision energy of the recent data obtained by the HADES col…
We complement the results for the radiative corrections to the s2.l angular correlation of baryon semileptonic decays of Ref. [1] with the final results in the rest frame of the decaying baryon.
We study the inclusive production of doubly heavy baryon $Ξ_{cc}$ at polarized photon collider. Our results show that proper choice of the initial beam polarizations may increase the production rate of $Ξ_{cc}$ approximately 10%.
We study the bremsstrahlung of virtual omega mesons due to the collective deceleration of nuclei at the initial stage of an ultrarelativistic heavy-ion collision. It is shown that electromagnetic decays of these mesons may give an important contribution to the observed yields of dileptons. Mass spectra of positron-electron and muon pairs produced in central Au+Au collisions are calculated under some simplifying assumptions on the space-time variation of the baryonic current in a nuclear collision process. Comparison with the CERES data for 160 AGev Pb+Au collisions shows that the proposed mech…
We present a decomposition of the hadronic tensor for a general polarized Drell-Yan process AB --> l^+ l^- X in terms of helicity structure functions using the helicity axes of the dilepton rest frame as a basis. Next, we consider a QCD parton model and in the framework of a generalized QCD factorization scheme, which applies when the dilepton invariant mass M is much larger than the transverse component of the photon momentum, q_T, in the hadronic center of mass frame. In this approximation we compute the angular distribution of the unpolarized Drell Yan cross section and of the Sivers effect…
We calculate the transverse-momentum $Q_T$ spectrum of the dilepton in the transversely polarized Drell-Yan process on the basis of the factorization theorem in QCD. We take into account universal logarithmically enhanced corrections in edge region of phase space by resumming multiple soft-gluon emissions to all orders in the small $Q_T$ region.
We consider the inclusive production of longitudinally polarized baryons in ${\vec p}p$ collisions at RHIC-BNL, with one longitudinally polarized proton. We study the spin transfer between the initial proton and the produced baryon as a function of its rapidity and we elucidate its sensitivity to the quark helicity distributions of the proton and to the polarized fragmentation functions of the quark into the baryon. We make predictions using an SU(6) quark spectator model and a perturbative QCD (pQCD) based model. We discuss these different predictions, and what can be learned from them, in vi…
Two-photon decays of vector mesons and dilepton decays of scalar mesons which are forbidden in vacuum and can occur in dense baryonic matter due to the explicit violation of Lorentz symmetry are described within a quark model of the Nambu--Jona-Lasinio type. The temperature and chemical potential dependence of these processes is investigated. It is found that their contribution to the production of photons and leptons in heavy-ion collisions is enhanced near the conditions corresponding to the restoration of chiral symmetry. Moreover, in the case of the a_0 meson and especially the ρ-meson, a …
We have calculated the radiative corrections to the Dalitz plot of baryon semileptonic decays with angular correlation between polarized emitted baryons and charged leptons. This work covers both charged and neutral decaying baryons and is restricted to the so-called three-body region of the Dalitz plot. Also it is specialized at the center-of-mass frame of the emitted baryon. We have considered terms up to order (alpha/pi)(q/M_1)^0, where q is the momentum-transfer and M_1 is the mass of the decaying baryon, and neglected terms of order (alpha/pi)(q/M_1)^n$ for n >= 1. The expressions display…
We investigate the decay of $Λ_b\toΛν\barν$ with the polarized baryons of $Λ_b$ and $Λ$. With the most general hadronic form factors, we first study the decay branching ratio and then derive the longitudinal, normal and transverse polarizations of $Λ$ in terms of the spin unit vectors of $Λ_b$ and $Λ$ and the momentum of $Λ$. A polarization of $Λ_b$ is also discussed.
We study the production of longitudinally polarized Lambda-baryons in single-spin pp collisions at RHIC and HERA-N as a means of determining the spin-dependent Lambda fragmentation functions. It is shown that a measurement of the rapidity distribution of the Lambda's would provide an excellent way of clearly discriminating between various recently suggested sets of polarized Lambda fragmentation functions that are all compatible with present e^+e^- data. We also address the main theoretical uncertainties, which appear to be well under control.
We employ OPE techniques within HQET to calculate the inclusive semileptonic decays of polarized $Λ_b$ baryons. Lepton mass effects are included which enables us to also discuss rates into polarized $τ$-leptons. We present explicit results for the longitudinal polarization of the $τ$ in the $Λ_b$ rest frame as well as in the $(τ^-, \bar ν_τ)$ c.m. frame. In both cases we make use of novel calculational techniques which considerably simplify the calculations. The transverse polarization components of the $τ$ are calculated in the $(τ^-,\barν_τ)$ c.m. frame. We delineate how to measure the full …
Analytical radiative corrections of order (α/π)(q/M_1) are calculated for the four-body region of the Dalitz plot of baryon semileptonic decays when the s_1 \cdot p_2 correlation is present. Once the final result is available, it is possible to exhibit it in terms of the corresponding final result of the three-body region following a set of simple changes in the latter. We cover two cases, a charged and a neutral polarized decaying baryon.
Analytical radiative corrections of order (alpha/pi)(q/M) are calculated for the four-body region of the Dalitz plot of baryon semileptonic decays when the s1.l correlation is present. Once the final result is available, it is possible to exhibit it in terms of the corresponding final result of the three-body region following a set of simple changes in the latter, except for a few exceptions. We cover two cases, a charged and a neutral polarized decaying baryon.
Parton distributions are constructed in a statistical physical picture of the nucleon. The chiral properties of QCD lead to strong relations between quarks and antiquarks distributions and the importance of the Pauli exclusion principle is also emphasized. A global next-to-leading order QCD analysis of unpolarized and polarized deep-inelastic scattering data is performed to determine a small number of free parameters. Some predictions are compared to recent experimental results. We also present an extension of the statistical approach to the description of baryon fragmentation functions.
Angular distribution of the final particles in the decay $Λ_c^+\to K^- \, Δ(1232)^{++} \to K^- \, p \, π^+$ of the polarized charmed baryon is discussed. Asymmetries are proposed which allow for determination of the components of the $Λ_c^+$ polarization vector. The precession angle of the polarization in the process of baryon channeling in a bent crystal is directly related to these asymmetries. The decay rate and asymmetry parameter for the $Λ_c^+\to K^- \, Δ(1232)^{++}$ decay are calculated in the pole model and compared with experiment.
We study the polarized $Λ_b$ baryon semileptonic decay $Λ_b \to Λ_cl{\barν}$ using perturbative QCD factorization theorem. In this approach heavy baryon transition form factors are expressed as the convolutions of hard $b$ quark decay amplitudes with universal $Λ_b$ and $Λ_c$ baryon wave functions. With the heavy baryon wave functions determined in our previous work, we predict the asymmetry parameter $α({\hat e})\equiv (N_+-N_-)/(N_++N_-)=-0.31 {\bf P}\cdot{\hat e}$, where ${\bf P}$ is the $Λ_b$ baryon polarization, ${\hat e}$ a unit vector perpendicular to the $Λ_b$ baryon momentum, $N_+$ ($…
We calculate the parton distributions for both polarized and unpolarized octet and decuplet baryons, using the MIT bag, dressed by mesons. We show that the hyperfine interaction responsible for the $Δ- N$ and $Σ^0 - Λ$ splittings leads to large deviations from SU(3) and SU(6) predictions. For the $Λ$ we find significant polarized, non-strange parton distributions which lead to a sizable $Λ$ polarization in polarized, semi-inclusive $ep$ scattering. We also discuss the flavour symmetry violation arising from the meson-cloud associated with the chiral structure of baryons.
We consider spin-momentum correlations between the spin of the bottom baryon $Λ_{\mathrm{b}}$ and the momenta of its decay products in its inclusive semileptonic decay. We define several polar and azimuthal spin-momentum correlation measures in different event coordinate systems. The values of the spin-momentum correlation measures are calculated up to ${\cal O}(1/m_b^2)$ using the standard OPE und HQET methods. Some of the measures turn out to be sufficiently large to make them good candidates for a determination of the polarization of the $Λ_{\mathrm{b}}$ in e.g. $\mathrm{Z}$ decays.
We investigate the Lambda_b polarization problem in the inclusive semileptonic decays of a polarized Lambda_b baryon, using the modified perturbative QCD formalism which includes Sudakov suppression. According to HQEFT, we show that, at the leading order in the 1/M_b expansion, the polarized and unpolarized distribution functions become one single universal distribution function. To explore the mechanisms which determine the spin properties of a polarized Lambda_b baryon, we construct four formalisms which are the naive quark model (QM), the modified quark model (MQM), the naive parton model (…
We study the dilepton forward-backward and the longitudinal, normal and transverse lepton polarization asymmetries in the heavy baryon decays of $Λ_b\toΛl^+l^-$. We show that the asymmetries have a less dependence on the non-perturbative QCD effects. In the standard model, we find that the integrated forward-backward asymmetries (FBAs) and three components of the polarizations in the QCD sum rule approach (pole model) are $-0.13\ (-0.12)$ and $(58.3,-9.4,-0.07)%$ ($(58.3,-12.6,-0.07)%$) for $Λ_b\toΛμ^+μ^-$ and $-0.04 (-0.03)$ and $(10.9,-10.0,-0.39)%$ ($(10.9,-0.2,-0.34)%$) for $Λ_b\toΛτ^+τ^-$…
The fractured Boer-Mulders functions describe an inriguing class of polarization effects for the production of baryons in the target fragmentation region of deep-inelastic processes. These functions characterize transverse momentum asymmetries related to the spin orientation for different flavors of axial vector diquarks in an unpolarized ensemble of protons just as the familiar Boer-Mulders functions characterize transverse momentum asymmetries connected to the spin orientation of quarks in unpolarized targets. The asymmetries of the fractured Boer-Mulders effect originating in the proton dis…
We analyze experimental data for the production of Lambda baryons in e^+e^- annihilation in terms of scale dependent, QCD evolved, Lambda fragmentation functions. Apart from the vast majority of the data for which the polarization of an observed Lambda was not determined, we also consider the recent LEP measurements of the longitudinal polarization of Lambda's produced on the Z-resonance. Such data correspond to spin-dependent fragmentation functions for the Lambda. We point out that the present data are insufficient to satisfactorily fix these. We therefore suggest several different sets of f…
We study the T violating effects in the baryonic decays of $Λ_b\toΛl^+l^- (l=e ,μ)$ with polarized $Λ$. We show that the transverse $Λ$ polarizations in these baryonic decays could be as large as 50% in CP violating theories beyond the standard model such as the SUSY models, which can be tested in various future hadron colliders.
Experimental data on analyzing power for inclusive meson and baryon production in hadron-proton(polarized) collisions have been analyzed. It is found that the existing data can be described by a simple function of collision energy, transverse momentum (Pt) and a new scaling variable Xa = E/Ebeam. At beam energies above 40 GeV and Pt above 1 GeV/c the analyzing power is described by a function of Xa and Pt only (AN = F(Pt)G(Xa)) for both polarized proton fragmentation and central regions of proton-hadron collision. Comparison of data from Fermilab and new IHEP data measured using 40 GeV/c polar…
We give a general parameterization of the Lambda_b --> Lambda(1520) gamma decay amplitude, applicable to any strange isosinglet spin-3/2 baryon, and calculate the branching fraction and helicity amplitudes. Large-energy form factor relations are worked out, and it is shown that the helicity-3/2 amplitudes vanish at lowest order in soft-collinear effective theory (SCET). The suppression can be tested experimentally at the LHC and elsewhere, thus providing a benchmark for SCET. We apply the results to assess the experimental reach for a possible wrong-helicity b --> s gamma dipole coupling in La…
The production of heavy flavor quark pairs, including top-anti-top, at the LHC proceeds primarily through gluon fusion. The correlation between the gluon spins affects various spin correlations between the produced quark and anti-quark. Both single spin asymmetries and double correlations of the quark pair spins will be manifest in the subsequent hadronization and decay distributions. For top pairs this is most pronounced. Dilepton, single lepton, and purely hadronic top pair decay channels allow for the extraction of gluon spin information as well as providing a window into possible interacti…
We study $pK^-$ scattering in the energy range from threshold through the $Λ(1520)$ peak in UBChPT, taking into account $\mathcal{O}(q)$ vertices from meson-baryon contact interactions and $s$- and $u$-channel ground-state baryon exchange, $s$- and $u$-channel decuplet- and nonet-baryon exchange and $t$-channel vector-meson exchange, as well as $\mathcal{O}(q^2)$ flavor-breaking vertices. Detailed fits to data are presented, including a substantial body of differential cross-section data with meson momentum $q_\mathrm{lab} > 300$ MeV not considered in previous treatments.
It is known that limits on baryon-violating nucleon decays do not, in general, imply corresponding suppression of $n - \bar n$ transitions. In the context of a model with fermions propagating in higher dimensions, we investigate a related question, namely the implications of limits on $ΔL=-1$ proton and bound neutron decays mediated by four-fermion operators for rates of nucleon decays mediated by $k$-fermion operators with $k =6$ and $k=8$. These include a variety of nucleon and dinucleon decays to dilepton and trilepton final states with $ΔL=-3, \ -2, \ 1$, and $2$. We carry out a low-energy…
B-meson decays are very useful probes for testing the Standard Model and its various extensions. Leptonic decays of B have very clean signatures in this respect and hence can be very useful testing grounds. In this work we study the effects of MSSM (Minimal Supersymmetric Extension of Standard Model) on various kinematical distributions in the radiative dileptonic decay (\bsllg). We study the Forward Backward asymmetry (of the lepton pair), and the various polarization asymmetries of both final state leptons ($\ell^-$ and $\ell^+$). In radiative dileptonic decay of B-meson (\bsllg) the final s…
To extract information about polarized gluons in the proton, production of charmed hadrons, in particular, Λ_c^+ baryon in pp collisions was studied. We calculated the transverse momentum distribution and the pseudo-rapidity distribution of the spin correlation asymmetry A_{LL} between the initial proton and the produced Λ_c^+. Those statistical sensitivities were also calculated under the condition of RHIC experiment. We found that the pseudo-rapidity distribution of A_{LL} is promising for testing the model of polarized gluons in the proton and also the spin-dependent fragmentation model of …
We study the response of diquark wave function in Λ-type baryons to strong magnetic fields. It is found that quantum state of J=0 diquark (ud) in the magnetic field changes due to magnetic polarizability, and constituent quarks in (ud) diquark become polarized. The phenomenon influences polarized quark distribution functions Δu(x) and Δd(x), which therefore may be sensitive to the internal electromagnetic fields in hypernuclei. We also speculate, that strange quark polarization in nucleon may originate from the interaction of virtual (ss') quark pairs with the intrinsic magnetic field of nucle…
