Quark Content Research Articles

Pseudoscalar mixing in J/ψ and ψ(2S) decay

Based on the branching fractions of J/ψ (ψ (2S)) → VP from different collaborations, pseudoscalar mixing is extensively discussed with a well established phenomenological model. The mixing angle is determined to be −14° by fitting to the new world average if only quark content is considered. After taking into account the gluonic content in η and η′ simultaneously, the investigation shows that η favors only consisting of light quarks, while the gluonic content of η′ is Z2η′ = 0.30±0.24.

Vacuum properties of mesons in a linear sigma model with vector mesons and global chiral invariance

We present a two-flavor linear sigma model with global chiral symmetry and vector and axial-vector mesons. We calculate $\ensuremath{\pi}\ensuremath{\pi}$ scattering lengths and the decay widths of scalar, vector, and axial-vector mesons. It is demonstrated that vector and axial-vector meson degrees of freedom play an important role in these low-energy processes and that a reasonable theoretical description requires globally chirally invariant terms other than the vector-meson mass term. An important question for meson vacuum phenomenology is the quark content of the physical scalar ${f}_{0}(600)$ and ${a}_{0}(980)$ mesons. We investigate this question by assigning the quark-antiquark $\ensuremath{\sigma}$ and ${a}_{0}$ states of our model with these physical mesons. We show via a detailed comparison with experimental data that this scenario can describe all vacuum properties studied here except for the decay width of the $\ensuremath{\sigma}$, which turns out to be too small. We also study the alternative assignment ${f}_{0}(1370)$ and ${a}_{0}(1450)$ for the scalar mesons. In this case the decay width agrees with the experimental value, but the $\ensuremath{\pi}\ensuremath{\pi}$ scattering length ${a}_{0}^{0}$ is too small. This indicates the necessity to extend our model by additional scalar degrees of freedom.

Sea quark contents of octet baryons

The flavor asymmetry of the nucleon sea, i.e., the excess of dd¯ quark–antiquark pairs over uu¯ ones in the proton, can be explained by several different models; therefore, it is a challenge to discriminate these models from each other. We examine in this Letter three models: the balance model, the meson cloud model, and the chiral quark model, and we show that these models give quite different predictions on the sea quark contents of other octet baryons. New experiments aimed at measuring the flavor contents of other octet baryons are needed for a more profound understanding of the non-perturbative properties of quantum chromodynamics (QCD).

Implications of CDMS-II result on Higgs sector in the MSSM

We study implications of two dark matter candidate events at CDMS-II on the neutralino dark matter scenario in the supersymmetric standard model, in light of the recent lattice simulation on the strange quark content of a nucleon. The scattering rate of neutralino–nucleon is dominated by Higgs exchange processes and the mass of heavy Higgs boson is predicted for the neutralino of Bino–Higgsino mixing state. In the case of Wino–Higgsino mixing, the Higgs sector may not be constrained.

J/ψ→VP decays and the quark and gluon content of the η and η′

The $\eta$-$\eta^\prime$ pseudoscalar mixing angle and the gluonium content of the $\eta^\prime$ meson are deduced from an updated phenomenological analysis of $J/\psi$ decays into a vector and a pseudoscalar meson. In absence of gluonium, the value of the mixing angle in the quark-flavour basis is found to be $\phi_P=(40.7\pm 2.3)^\circ$. In presence of gluonium, the values for the mixing angle and the gluonic content of the $\eta^\prime$ wave function are $\phi_P=(44.6\pm 4.4)^\circ$ and $Z^2_{\eta^\prime}=0.29^{+0.18}_{-0.26}$, respectively. The newly reported values of $B(J/\psi\to\rho\pi)$ by the BABAR and BES Collaborations are crucial to get a consistent description of data.

Strange Quark Condensate in the Nucleon in2+1Flavor QCD

We calculate the "strange quark content of the nucleon," <N|s[over]s|N>, which is important for interpreting the results of some dark matter detection experiments. The method is to evaluate quark-line disconnected correlations on the MILC lattice ensembles, which include the effects of dynamical light and strange quarks. After continuum and chiral extrapolations, the result is <N|s[over]s|N> = 0.69(7)_{stat}(9)_{syst}, in the modified minimal subtraction scheme (2 GeV) regularization, or for the renormalization scheme invariant form, m_{s} partial differentialM_{N}/ partial differentialm_{s} = 59(6)(8) MeV.

Hadronic Spectrum - Multiquark States

Many newly discovered mesons behave like c c ¯ charmonium states in that they preferentially decay into final states that contain a c- and a c ¯ -quark, but do not fit expectations for any of the unfilled levels of the conventional c c ¯ spectrum. There is a growing suspicion that at least some of these states are exotic, i.e. have a substructure that is more complex than the quark-antiquark mesons of the classical constituent quark model. Some of these candidate states have a non-zero electric charge and, thus, a minimal quark content of c c ¯ u d ¯ or c c ¯ d u ¯ . In addition, states with similar properties have been observed in the b- and s-quark sectors. In this report, the experimental situation is briefly reviewed.

New States and Charmonium Spectroscopy at BaBar

Several charmonium-like states above D D ¯ threshold have been discovered at the Belle and BaBar B -factories. Some are produced via Initial State Radiation (e.g. Y ( 4260 ) and Y ( 4350 ) ), and some are observed in B meson decays (e.g. X ( 3872 ) , Y ( 3940 ) , and Z ( 4430 ) − ). The Z ( 4430 ) − state has generated a great deal of interest, having minimum quark content ( c c ¯ d u ¯ ) and, thus, representing the unequivocal manifestation of a four-quark meson state. Here we summarize recent BaBar results on the Y ( 4260 ) , X ( 3872 ) , Y ( 3940 ) , and on a search for the Z ( 4430 ) − .

Analysis of the rare semileptonic decays ofBstof0(980)andK0*(1430)scalar mesons in QCD sum rules

We investigate the rare semileptonic decays ${B}_{s}\ensuremath{\rightarrow}[{f}_{0}(980),{K}_{0}^{*}(1430)]{l}^{+}{l}^{\ensuremath{-}}$, ($l=e$, $\ensuremath{\mu}$, $\ensuremath{\tau}$), and ${B}_{s}\ensuremath{\rightarrow}[{f}_{0}(980),{K}_{0}^{*}(1430)]\ensuremath{\nu}\overline{\ensuremath{\nu}}$ in the framework of the three-point QCD sum rules. These decays are important to study because the ${f}_{0}(980)$ and ${K}_{0}^{*}(1430)$ are the scalar mesons with total spin 0 and even parity and the quark content of them are still controversial in high energy physics. These rare decays occur at loop level by electroweak penguin and weak box diagrams in the standard model via the flavor changing neutral current transitions of $b\ensuremath{\rightarrow}d$, $s$, and not allowed by tree level. Considering the effective contributions of the nonperturbative parts of the correlation function, we calculate the relevant form factors of these transitions. The branching fractions and longitudinal lepton polarization asymmetry are also investigated.

NUCLEON RESONANCES AND QUARK STRUCTURE

A review of the past 50 years of study of resonances, leading to our understanding of the quark content of baryons and mesons. The quark structure of the proton as revealed through deep inelastic scattering. Structure functions and what they reveal about proton structure. Prospects for further studies with new and upgraded facilities, particularly a proposed electron-ion collider.

Electroweak symmetry breaking and singlino dark matter with deflected anomaly mediation

We investigate the phenomenology of the Nearly Minimal Supersymmetric Standard Model (nMSSM) in the deflected anomaly mediation scenario. We also include the Fayet-Iliopoulos D-term of the standard model gauge group. In the nMSSM, the mu term is replaced by the vacuum expectation value of the gauge singlet; therefore, there is no difficulty in generating the B-term of the SUSY breaking scale. Although the messenger sector is introduced, direct couplings between nMSSM fields and messenger sector fields are forbidden by the discrete symmetry. Therefore, the phenomenology at the weak scale does not depend on the detail of the messenger sector. We show that there are regions of parameter space in which electroweak symmetry breaking occurs successfully and the lightest Higgs is heavier than the LEP bound. We show that the gluino is light in this scenario. The lightest neutralino, which is mainly composed of a singlino, is a candidate for dark matter. The relic density explains the observed abundance of dark matter. The dark matter-nucleon scattering cross section satisfies the current limit from CDMS and XENON10 with a small value for the strange quark content of a nucleon.

Formula omitted] in lattice QCD

We present a search for the possible I ( J P ) = 0 ( 2 + ) tetraquark state with s s s ¯ s ¯ quark content in quenched improved anisotropic lattice QCD. Using various local and non-local interpolating fields we determine the energies of ground-state and second ground state using variational method. The state is found to be consistent with two-particle scattering state, which is checked to exhibit the expected volume dependence of the spectral weights. In the physical limit, we obtain for the ground state, a mass of 2123 ( 33 ) ( 58 ) MeV which is higher than the mass of experimentally observed f ( 2010 ) . The lattice resonance signal obtained in the physical region does not support a localized J P = 2 + tetraquark state in the pion mass region of 300 – 800 MeV . We conclude that the 4 q system in question appears as a two-particle scattering state in the quark mass region explored here.

Global aspects of the scalar meson puzzle

A generalized linear sigma model for low-energy QCD is employed to study the quark structure of eight low-lying scalar isomultiplets as well as eight low-lying pseudoscalar isomultiplets. The model, building on earlier work, assumes the possible mixing of quark antiquark states with others made of two quarks and two antiquarks. No a priori assumption is made about the quark contents of the states, which emerge as predictions. An amusing and contrasting pattern for the quark structure is found; the lighter conventional pseudoscalars are, as expected, primarily of two-quark type whereas the lighter scalars have very large four-quark admixtures. The new feature of the present paper compared to earlier ones in this series involves the somewhat subtle and complicated effects of SU(3) flavor breaking. They do not alter the general pattern of two-quark vs four-quark mixing obtained in the SU(3)symmetric case but, of course, give a more detailed picture.

Line shapes of theZ(4430)

The Belle Collaboration recently discovered the first manifestly exotic meson: ${Z}^{+}(4430)$, which decays into ${\ensuremath{\psi}}^{\ensuremath{'}}{\ensuremath{\pi}}^{+}$ and therefore has quark content $c\overline{c}u\overline{d}$. The proximity of its mass to the ${D}_{1}{\overline{D}}^{*}$ threshold has motivated the interpretation of the ${Z}^{+}$ as a charm meson molecule whose constituents are an $S$-wave superposition of ${D}_{1}^{+}{\overline{D}}^{*0}$ and ${D}^{*+}{\overline{D}}_{1}^{0}$. If this interpretation is correct, the small ratio of the binding energy of the ${Z}^{+}$ to the width ${\ensuremath{\Gamma}}_{1}$ of its constituent ${D}_{1}$ can be exploited to predict properties of its line shapes. Its full width at half maximum in the channel ${\ensuremath{\psi}}^{\ensuremath{'}}{\ensuremath{\pi}}^{+}$ should be approximately $\sqrt{3}{\ensuremath{\Gamma}}_{1}\ensuremath{\approx}35\text{ }\text{ }\mathrm{MeV}$, which is consistent with the measured width of the ${Z}^{+}$. The ${Z}^{+}$ should also decay into ${D}^{*}{\overline{D}}^{*}\ensuremath{\pi}$ through decay of its constituent ${D}_{1}$. The peak in the line shape for ${D}^{*}{\overline{D}}^{*}\ensuremath{\pi}$ should be at a higher energy than the peak in the line shape for ${\ensuremath{\psi}}^{\ensuremath{'}}{\ensuremath{\pi}}^{+}$ by about ${\ensuremath{\Gamma}}_{1}/\sqrt{12}\ensuremath{\approx}6\text{ }\text{ }\mathrm{MeV}$. The line shape in ${D}^{*}{\overline{D}}^{*}\ensuremath{\pi}$ should also be broader and asymmetric, with a shoulder on the high energy side that can be attributed to a threshold enhancement in the production of ${D}_{1}{\overline{D}}^{*}$.

Exploration of a physical picture for the QCD scalar channel

A generalized linear sigma model is employed to study the quark structure of low lying scalar as well as pseudoscalar states. The model allows the possible mixing of quark anti-quark states with others made of two quarks and two antiquarks but no a priori assumption is made about the quark contents of the predicted physical states. Effects of SU(3) symmetry breaking are included. The lighter conventional pseudoscalars turn out to be primarily of two quark type whereas the lighter scalars have very large four quark admixtures.

Nucleon sigma term and strange quark content from lattice QCD with exact chiral symmetry

We calculate the nucleon sigma term in two-flavor lattice QCD utilizing the Feynman-Hellman theorem. Both sea and valence quarks are described by the overlap fermion formulation, which preserves exact chiral and flavor symmetries on the lattice. We analyze the lattice data for the nucleon mass using the analytical formulae derived from the baryon chiral perturbation theory. From the data at valence quark mass set different from sea quark mass, we may extract the sea quark contribution to the sigma term, which corresponds to the strange quark content. We find that the strange quark content is much smaller than the previous lattice calculations and phenomenological estimates.

Neutral-Current Neutrino-Nucleus Scattering in the Quasielastic Region

The neutral-current neutrino-nucleus scattering is calculated through the neutrino-induced knocked-out nucleon process in the quasielastic region by using a relativistic single particle model for the bound and continuum states. The incident energy range between 500 MeV and 1.0 GeV is used for the neutrino (antineutrino) scattering on the 12 C target nucleus. The effects of the final state interaction of the knocked-out nucleon are studied not only on the cross section but also on the asymmetry due to the difference between neutrinos and antineutrinos, within a relativistic optical potential. We also investigate the sensitivity of the strange quark contents in the nucleon on the asymmetry. (Some figures in this article are in colour only in the electronic version)

The thermal production of strange and non-strange hadrons in e + e − collisions

The thermal multihadron production observed in different high energy collisions poses two basic problems. (1) Why do even elementary collisions with comparatively few secondaries (e + e − annihilation) show thermal behavior? (2) Why is there in such interactions a suppression of strange particle production? We show that the recently proposed mechanism of thermal hadron production through Hawking–Unruh radiation can naturally account for both. The event horizon of color confinement leads to thermal behavior, but the resulting temperature depends on the strange quark content of the produced hadrons, causing a deviation from full equilibrium and hence a suppression of strange particle production. We apply the resulting formalism to multihadron production in e + e − annihilation over a wide energy range and make a comprehensive analysis of the data in the conventional statistical hadronization model and the modified Hawking–Unruh formulation. We show that this formulation provides a very good description of the measured hadronic abundances, fully determined in terms of the string tension and the bare strange quark mass; it contains no adjustable parameters.

Two chiral nonet model with massless quarks

We present a detailed study of a linear sigma model containing one chiral nonet transforming under $\mathrm{U}(1{)}_{\mathrm{A}}$ as a quark-antiquark composite and another chiral nonet transforming as a diquark-antidiquark composite (or, equivalently from a symmetry point of view, as a two meson molecule). The model provides an intuitive explanation of a current puzzle in low energy QCD: Recent work has suggested the existence of a lighter than 1 GeV nonet of scalar mesons which behave like four quark composites. On the other hand, the validity of a spontaneously broken chiral symmetric description would suggest that these states be chiral partners of the light pseudoscalar mesons, which are two quark composites. The model solves the problem by starting with the two chiral nonets mentioned and allowing them to mix with each other. The input of physical masses in the SU(3) invariant limit for two scalar octets and an excited pion octet results in a mixing pattern wherein the light scalars have a large four quark content while the light pseudoscalars have a large two quark content. One light isosinglet scalar is exceptionally light. In addition, the pion pion scattering is also studied and the current algebra theorem is verified for massless pions which contain some four quark admixture.

The neutral-current neutrino-nucleus scattering in the quasielastic region

The neutral-current neutrino-nucleus scattering is calculated through the neutrino-induced knocked-out nucleon process in the quasielastic region by using a relativistic single particle model for the bound and continuum states. The incident energy range between 500 MeV and 1.0 GeV is used for the neutrino (antineutrino) scattering on the 12C target nucleus. The effects of the final state interaction of the knocked-out nucleon are studied not only on the cross section but also on the asymmetry due to the difference between neutrinos and antineutrinos, within a relativistic optical potential. We also investigate the sensitivity of the strange quark contents in the nucleon on the asymmetry.