Quark-interchange Model Research Articles

Cancellation of the Sigma Mode in the Thermal Pion Gas by Quark Pauli Blocking

In this study, we calculate the pressure of the interacting pion gas using the Beth–Uhlenbeck approach to the relativistic virial expansion with Breit–Wigner phase shifts for the σ- and ϱ-meson resonances. The repulsive phase shift δ02 is taken from the quark interchange model of Barnes and Swanson, which is in very good agreement with the experimental data. In this work we show that the cancellation of the attractive (I = 0) and repulsive (I = 2) isospin channel contributions to the scalar ππ interaction in the low-energy region that is known for the vacuum phase shifts also takes place at a finite temperature. This happens despite the strong medium dependence of these phase shifts that enters our model by the temperature dependence of the σ-meson and constituent quark masses, because for these masses the relation Mσ(T)≈2mq(T) holds and the scattering length approximation is valid as long as the strong decay channel σ→ππ is open. Exploiting the Nambu–Jona-Lasinio model for describing the dynamical breaking of chiral symmetry in the vacuum and its restoration at a finite temperature, we justify with our approach that the σ-meson should be absent from the hadron resonance gas description at low temperatures because the above cancellation holds. However, since this cancellation breaks down in the vicinity of the hadronization transition, where due to chiral symmetry restoration the decay channel σ→ππ closes and the σ-meson becomes a good resonance, the latter should be included into the statistical model description of chemical freeze-out in heavy-ion collisions.

Hidden-charm pentaquarks with triple strangeness due to the Ωc(*)D¯s(*) interactions

Motivated by the successful interpretation of these observed $P_c$ and $P_{cs}$ states under the meson-baryon molecular picture, we systematically investigate the possible hidden-charm molecular pentaquark states with triple strangeness which is due to the $\Omega_{c}^{(*)}\bar{D}_s^{(*)}$ interactions. We perform a dynamical calculation of the possible hidden-charm molecular pentaquarks with triple strangeness by the one-boson-exchange model, where the $S$-$D$ wave mixing effect and the coupled channel effect are taken into account in our calculation. Our results suggest that the $\Omega_{c}\bar D_s^*$ state with $J^P={3}/{2}^{-}$ and the $\Omega_{c}^{*}\bar D_s^*$ state with $J^P={5}/{2}^{-}$ can be recommended as the candidates of the hidden-charm molecular pentaquark with triple strangeness. Furthermore, we discuss the two-body hidden-charm strong decay behaviors of these possible hidden-charm molecular pentaquarks with triple strangeness by adopting the quark-interchange model. These predictions are expected to be tested at the LHCb, which can be as a potential research issue with more accumulated experimental data in near future.

Probing hidden-charm decay properties of Pc states in a molecular scenario

The ${P}_{c}(4312)$, ${P}_{c}(4440)$, and ${P}_{c}(4457)$ observed by the LHCb collaboration are very likely to be $S$-wave ${\mathrm{\ensuremath{\Sigma}}}_{c}{\overline{D}}^{(*)}$ molecular candidates due to their near threshold character. In this work, we study the hidden-charm decay modes of these ${P}_{c}$ states, ${P}_{c}\ensuremath{\rightarrow}J/\ensuremath{\psi}p({\ensuremath{\eta}}_{c}p)$, using a quark interchange model. The decay mechanism for the ${P}_{c}\ensuremath{\rightarrow}J/\ensuremath{\psi}p({\ensuremath{\eta}}_{c}p)$ processes arises from the quark-quark interactions, where all parameters are determined by the mass spectra of mesons. We present our results in two scenarios. In scenario I, we perform the dynamical calculations and treat the ${P}_{c}$ states as pure ${\mathrm{\ensuremath{\Sigma}}}_{c}{\overline{D}}^{(*)}$ molecules. In scenario II, after considering the coupled channel effect between different flavor configurations ${\mathrm{\ensuremath{\Sigma}}}_{c}^{(*)}{\overline{D}}^{(*)}$, we calculate these partial decay widths again. The decay patterns in these two scenarios can help us to explore the molecular assignment and the inner flavor configurations for the ${P}_{c}$ states. In particular, the decay widths of $\mathrm{\ensuremath{\Gamma}}({P}_{c}(4312)\ensuremath{\rightarrow}{\ensuremath{\eta}}_{c}p)$ are comparable to the $J/\ensuremath{\psi}p$ decay widths in both of these two scenarios. Future experiments like LHCb may confirm the existence of the ${P}_{c}(4312)$ in the ${\ensuremath{\eta}}_{c}p$ channel.

Hidden-charm strong decays of the Zc states

Inspired by BESIII's measurement of the decay $Z_c(3900)^{\pm}\rightarrow \rho^{\pm}\eta_c$, we calculate the branching fraction ratio between the $\rho\eta_c$ and $\pi J/\psi$ decay modes for the charged states $Z_c(3900)$, $Z_c(4020)$ and $Z_c(4430)$ using a quark interchange model. Our results show that (i) the ratio $R_{Z_c(3900)}=\frac{\mathcal{B}(Z_c(3900)^{\pm}\rightarrow \rho^{\pm}\eta_c)}{\mathcal{B}(Z_c(3900)^{\pm}\rightarrow \pi^{\pm}J/\psi)}$ is 1.3 and 1.6 in the molecular and tetraquark scenarios respectively, which is roughly consistent with the experimental data $R^{\mathrm{exp}}=2.2\pm0.9$. (ii) The ratios $\frac{\Gamma[Z_c(3900)\rightarrow \rho\eta_c]}{\Gamma[Z_c(4020)\rightarrow \rho\eta_c]}$ and $\frac{\Gamma[Z_c(3900)\rightarrow \pi J/\psi]}{\Gamma[Z_c(4020)\rightarrow \pi J/\psi]}$ are about 12.5 and 24.2, respectively in the molecular scenario. In contrast, these ratios are about 1.2 in the tetraquark scenario. The non-observation of the $Z_c(4020)$ signal in the $\pi J/\psi$ decay mode strongly indicates that $Z_c(3900)$ and $Z_c(4020)$ are molecule-like signals which arise from the $D^{(*)}{\bar D}^{(*)}$ hadronic interactions.

The strong decay patterns of Z_c and Z_b states in the relativized quark model

Employing the relativized quark model and the quark-interchange model, we investigate the decay of the charged heavy quarkonium-like states Z_c(3900), Z_c(4020), Z_c(4430), Z_b(10610) and Z_b(10650) into the ground and radially excited heavy quarkonia via emitting a pion meson. The Z_c and Z_b states are assumed to be hadronic molecules composed of open-flavor heavy mesons. The calculated decay ratios can be compared with the experimental data, which are useful in judging whether the molecule state assignment for the corresponding Z_c or Z_b state is reasonable or not. The theoretical framework constructed in this work will be helpful in revealing the underlying structures of some exotic hadrons.

Resolving the puzzling decay patterns of chargedZcandZbstates

We investigate the ratio of the branching fractions of the molecular candidates decaying into the ground and radially excited states within the quark interchange model. Our numerical results suggest that these molecular candidates are more likely to decay into the radially excited states than into ground states. Especially, the ratio $\Gamma[Z_c(4430)\to \pi\psi(2S)]$/$\Gamma[Z_c(4430)\to \pi J/\psi]\sim 9.8$ is close to the experimental measurement, which supports the interpretation of $Z_c(4430)$ as the $\bar{D}D^*(2S)$ molecular state. The ratios of the branching fractions of $Z_b(10610)$ and $Z_b(10650)$ to $\pi\Upsilon(2S, 3S)$ and $\pi\Upsilon(1S)$ agrees very well with Belle's measurement. We also predict the similar ratios for $Z_c(3900)$, $Z_c(4020)$, $R_{Z_c(3900)}$$\approx$1.3 and $R_{Z_c(4020)}$$\approx$$4.7$. Hopefully the $\pi\psi(2S)$ mode, and ratios $R_{Z_c(3900)}$ and $R_{Z_c(4020)}$ will be measured by the BESIII and Belle collaborations in the near future, which shall be very helpful to understand the underlying dynamics of these exotic states.

Hard breakup of the deuteron into twoΔisobars

We study high-energy photodisintegration of the deuteron into two $\ensuremath{\Delta}$ isobars at large center of mass angles within the QCD hard rescattering model (HRM). According to the HRM, the process develops in three main steps: the photon knocks a quark from one of the nucleons in the deuteron; the struck quark rescatters off a quark from the other nucleon sharing the high energy of the photon; then the energetic quarks recombine into two outgoing baryons which have large transverse momenta. Within the HRM, the cross section is expressed through the amplitude of $\mathit{pn}\ensuremath{\rightarrow}\ensuremath{\Delta}\ensuremath{\Delta}$ scattering which we evaluated based on the quark-interchange model of hard hadronic scattering. Calculations show that the angular distribution and the strength of the photodisintegration is mainly determined by the properties of the $\mathit{pn}\ensuremath{\rightarrow}\ensuremath{\Delta}\ensuremath{\Delta}$ scattering. We predict that the cross section of the deuteron breakup to ${\ensuremath{\Delta}}^{++}{\ensuremath{\Delta}}^{\ensuremath{-}}$ is 4--5 times larger than that of the breakup to the ${\ensuremath{\Delta}}^{+}{\ensuremath{\Delta}}^{0}$ channel. Also, the angular distributions for these two channels are markedly different. These can be compared with the predictions based on the assumption that two hard $\ensuremath{\Delta}$ isobars are the result of the disintegration of the preexisting $\ensuremath{\Delta}\ensuremath{\Delta}$ components of the deuteron wave function. In this case, one expects the angular distributions and cross sections of the breakup in both ${\ensuremath{\Delta}}^{++}{\ensuremath{\Delta}}^{\ensuremath{-}}$ and ${\ensuremath{\Delta}}^{+}{\ensuremath{\Delta}}^{0}$ channels to be similar.

Quark Structure of the Nucleon and Angular Asymmetry of Proton-Neutron Hard Elastic Scattering

We investigate an asymmetry in the angular distribution of hard elastic proton-neutron scattering with respect to the 90 degrees center of mass scattering angle and demonstrate that it's magnitude is related to the helicity-isospin symmetry of the quark wave function of the nucleon. Our estimate of the asymmetry within the quark-interchange model of hard scattering demonstrates that the quark wave function of a nucleon based on the exact SU(6) symmetry predicts an angular asymmetry opposite to that of experimental observations. We found that the quark wave function based on the diquark picture of the nucleon produces a correct asymmetry. Comparison with the data allowed us to show that the vector diquarks contribute around 10% in the nucleon wave function and they are in negative phase relative to the scalar diquarks. These observations are essential in constraining QCD models of a nucleon.

J/ψabsorption by nucleons in the meson-exchange model

We reinvestigate the $J/\ensuremath{\psi}$ dissociation processes induced by the reactions with nucleons, $J/\ensuremath{\psi}+N\ensuremath{\rightarrow}{\overline{D}}^{(*)}+{\ensuremath{\Lambda}}_{c}$, in the meson-exchange model. Main constraints used in this work are vector-meson dominance and charm vector-current conservation. We show that the cross section for $J/\ensuremath{\psi}+N\ensuremath{\rightarrow}\overline{D}+{\ensuremath{\Lambda}}_{c}$ can be larger than that for $J/\ensuremath{\psi}+N\ensuremath{\rightarrow}{\overline{D}}^{*}+{\ensuremath{\Lambda}}_{c}$ when these constraints are imposed. The dependence of the cross sections on the coupling constants is analyzed in detail, and the comparison with the recent quark-interchange model predictions is also made.

Meson-meson scattering in relativistic constraint dynamics

Dirac's relativistic constraint dynamics have been successfully applied to obtain a covariant nonperturbative description of QED and QCD bound states. We use this formalism to describe a microscopic theory of meson-meson scattering as a relativistic generalization of the nonrelativistic quark-interchange model developed by Barnes and Swanson.

AnomalousJ/ψsuppression and charmonium dissociation cross sections

We study $J/\psi$ suppression in Pb+Pb collisions at CERN-SPS energies in hadronic matter with energy- and temperature-dependent charmonium dissociation cross sections calculated in the quark-interchange model of Barnes and Swanson. We find that the variation of J/$\psi$ survival probability from peripheral to central collisions can be explained as induced by hadronic matter absorption in central collisions.

Erratum: Heavy quarkonium dissociation cross sections in relativistic heavy-ion collisions [Phys. Rev. C65, 014903 (2002)

Many of the hadron-hadron cross sections required for the study of the dynamics of matter produced in relativistic heavy-ion collisions can be calculated using the quark-interchange model. Here we evaluate the low-energy dissociation cross sections of $J/\psi$, $\psi'$, $\chi$, $\Upsilon$, and $\Upsilon'$ in collision with $\pi$, $\rho$, and $K$, which are important for the interpretation of heavy-quarkonium suppression as a signature for the quark gluon plasma. These comover dissociation processes also contribute to heavy-quarkonium suppression, and must be understood and incorporated in simulations of heavy-ion collisions before QGP formation can be established through this signature.

Dissociation of a heavy quarkonium at high temperatures

We examine three different ways a heavy quarkonium can dissociate at high temperatures. The heavy quarkonium can dissociate spontaneously when it becomes unbound at a temperature above its dissociation temperature. Following the recent work of Digal, Petreczky, and Satz, we calculate the dissociation temperatures of heavy quarkonia taking into account the angular momentum selection rules and using a temperature-dependent potential inferred from lattice gauge calculations. We find that the selection rules change the dissociation temperatures substantially for charmonia but only slightly for bottomia. A quarkonium system in thermal equilibrium with the medium can dissociate by thermalization. The fraction of quarkonium lying above the dissociation threshold increases as temperature increases. A quarkonium can also dissociate by colliding with light hadrons. We evaluate the cross sections for the dissociation of $J/\psi$ and $\Upsilon$ in collision with $\pi$ as a function of the temperature of the hadron medium, using the quark-interchange model of Barnes and Swanson. We find that as the temperature increases, the threshold energy decreases and the dissociation cross section increases.

Heavy quarkonium dissociation cross sections in relativistic heavy-ion collisions

Many of the hadron-hadron cross sections required for the study of the dynamics of matter produced in relativistic heavy-ion collisions can be calculated using the quark-interchange model. Here we evaluate the low-energy dissociation cross sections of $J/\ensuremath{\psi},$ ${\ensuremath{\psi}}^{\ensuremath{'}},$ \ensuremath{\chi}, $\ensuremath{\Upsilon},$ and ${\ensuremath{\Upsilon}}^{\ensuremath{'}}$ in collision with \ensuremath{\pi}, \ensuremath{\rho}, and K. These are important for the interpretation of heavy-quarkonium suppression as a signature for the quark gluon plasma, as such comover dissociation processes also contribute to heavy-quarkonium suppression, and must be understood and incorporated in simulations of heavy-ion collisions before QGP formation can be established through this signature.

Meson-meson scattering in the quark model: Spin dependence and exotic channels

We apply a quark interchange model to spin-dependent and exotic meson-meson scattering. The model includes the complete set of standard quark model forces, including OGE spin-orbit and tensor and scalar confinement spin-orbit. Scattering amplitudes derived assuming SHO and Coulomb plus linear plus hyperfine meson wavefunctions are compared. In I=2 pi pi we find approximate agreement with the S-wave phase shift from threshold to 1.5 GeV, where we predict an extremum that is supported by the data. Near threshold we find rapid energy dependence that may reconcile theoretical estimates of small scattering lengths with experimental indications of larger ones based on extrapolation of measurements at moderate kpi^2. In PsV scattering we find that the quark-quark L*S and T forces map into L*S and T meson-meson interactions, and the P-wave L*S force is large. Finally we consider scattering in J^PC-exotic channels, and note that some of the Deck effect mechanisms suggested as possible nonresonant origins of the pi_1(1400) signal are not viable in this model.

Cross sections forπ- andρ-induced dissociation ofJ/ψandψ′

We evaluate the cross sections for the dissociation of $J/\psi$ and $\psi'$ by $\pi$ and $\rho$ at low collision energies, using the quark-interchange model of Barnes and Swanson. The dissociation cross section for $J/\psi$ by $\pi$ is found to be relatively small with a maximum of about 1 mb and a kinetic energy threshold of 0.65 GeV. The pion-induced $\psi'$ dissociation cross section is found to be much larger, with a maximum of about 5 mb and a lower threshold. Dissociation cross sections for $J/\psi$ and $\psi'$ by $\rho$ mesons are also evaluated and are found to be large near threshold.

Meson exchanges in the harmonic-oscillator quark model

Meson exchanges are introduced into the harmonic oscillator quark model along with a lower quark wave function. The mechanism is based on quark correlations that derive from quark exchange scattering via gluon exchange at short distances. This method allows avoiding spurious van der Waals forces at long range. Meson-baryon coupling constants and vertex form factors are calculated. They are found to be in agreement with those obtained from other quark models, phenomenological potentials, and the broken SU(3) flavor symmetry. The resulting $S$-wave NN phase shifts are compared with those from quark-molecular models.NUCLEAR REACTIONS Meson exchanges, ${E}_{\mathrm{lab}}\ensuremath{\le}300$ MeV. Coupling constants, vertex form factors calculated from harmonic-oscillator quark interchange model. Comparison of NN $S$-wave phase shifts with those of potential models.

High-energy pp elastic scattering and evidence for a nucleon core of valence quarks

High-energy pp elastic scattering is analyzed in a model that incorporates a hard mechanism besides diffraction. The hard process is responsible for large-momentum-transfer scattering, while diffraction dominates the small-momentum-transfer region. Orear fall-off (dσ/dt∼exp[−bp⊥]) is taken as the basic characteristic behavior of the large-t scattering. The origin of this behavior is explored and is attributed to a smoothed Yukawa potential. The form of this potential indicates that each nucleon has a core and the two cores interact via meson exchange. The model provides an overall quantitative picture of pp elastic scattering that extends over the energy rangeEL≅(15÷1500) GeV and |t|≅(0÷15) (GeV)2, where dσ/dt drops more than ten decades. This is regarded as evidence for the existence of the nucleon core. Diffraction, as a by-product, is found to be well represented by as-channel pomeron pole. Physical implications of the core are explored. The core is interpreted as originating from the distribution of valence quarks in a nucleon. The valence quarks, being confined in a small region, are found to have large average transverse momentum consistent with the values indicated by large-p⊥ inelastic processes. The core is also identified with the repulsive nucleon core known in low-energyNN interaction. The model is found to join smoothly with the quark interchange model of pp high-energy large-angle scattering.