The baryon-antibaryon spectrum consisting of strange, charm and bottom quarks is studied in the color flux-tube model with a multi-body confinement interaction. Numerical results indicate that many low-spin baryon-antibaryon states can form compact hexaquark states and are stable against the decay into a baryon and an antibaryon. The multi-body confinement interaction as a binding mechanism plays an important role in the formation of the states. They can be searched in the $e^+e^-$ annihilation and charmonium or bottomonium decay if they really exist. The newly reported states, X(1835), X(2370), Y(2175), Y(4360) and Y_b(10890), may be interpreted as $N\bar{N}$, $Δ\barΔ$, $Λ\barΛ$, $Λ_c\barΛ_c$ and $Λ_b\barΛ_b$ states, respectively.
The $Λ_c(2590) Σ_c$ system can exchange a pion near the mass-shell. Owing to the opposite intrinsic parity of the $Λ_c(2590)$ and $Σ_c$, the pion is exchanged in S-wave. This gives rise to a Coulomb-like force that might be able to bind the system. If one takes into account that the pion is not exactly on the mass shell, there is a shallow S-wave state, which we generically call the $Y_{cc}(5045)$ and $Y_{c\bar c}(5045)$ for the $Λ_c(2590) Σ_c$ and $Λ_c(2590) \barΣ_c$ systems respectively. For the baryon-antibaryon case this Coulomb-like force is independent of spin: the $Y_{c\bar c}(5045)$ ba…
Anti-protonic hydrogen and helium atoms are analyzed. Level shifts and width are expressed in terms of $\bar{p}$-nucleon sub-threshold scattering lengths and volumes. Experimental data are compared to results obtained from the 2009 version of the Paris $N\bar{N}$ interaction potential. Comparison with 1999 version is also made. Effects of $N\bar{N}$ quasi-bound states are discussed. Atomic 2P hyperfine structure is calculated for antiprotonic deuterium and the significance of new measurements is indicated.
By assuming certain analytic properties of the propagator, it is shown that universal features of the spectral function including threshold enhancement arise if a pole describing a particle at high temperature approaches in the complex energy plane the threshold position of its two-body decay with the variation of T. The case is considered, when one can disregard any other decay processes. The quality of the proposed description is demonstrated by comparing it with the detailed large N solution of the linear sigma model around the pole-threshold coincidence.
For the Nbar N system, the one-pion-exchange (OPE) interaction gives the largest attractive force for Nbar N with isospin I=0 and spin S=0, while a near threshold enhancement was observed for pbar p with I=0 and S=0 in J/psi -> gamma pbar p decays. With a K-matrix approach, we find that the OPE final-state-interaction (FSI) makes an important contribution to the near-threshold enhancement in the pbar p mass spectrum in J/psi -> gamma pbar p decays.
We discuss the low-mass enhancement effect in the baryon-antibaryon invariant mass in three-body baryonic B decays using final state interactions in the framework of Regge theory. We show that the rescattering between baryonic pair can reproduce the observed mass spectrum.
The scalar-isoscalar propagator of the effective linear $σ$ model of meson dynamics is investigated with the help of an expansion in the number of the Goldstone bosons. A generic scenario is suggested for the temperature and density driven evolution of its pole in the second Riemann sheet. An extended temperature range, correlated with characteristic pole locations, is found where the phenomenon of threshold enhancement takes place in the corresponding spectral function.
We study the observed enhancement of a $p\bar p$ system near the threshold in the process $J/ψ\to γp\bar p$ and $e^+ e^- \to p\bar p$. From early studies the enhancement can be explained by final state interactions, which are in general taken into account with some potential models. In this work we offer a simple approach within quantum field theory to explain the observed enhancement. We point out that among different final state interactions the rescattering in a $N\bar N$ system though exchange of $π$ is the most important. The effects of the rescattering is completely fixed by the well-kno…
Partonic cross sections for the production of massive objects in hadronic collisions receive large corrections when the invariant mass of the initial-state partons is just above the production threshold. Since typically the center-of-mass energy of the hadronic collision is much higher than the mass of the heavy objects, it is not obvious that these contributions translate into large corrections to the hadronic cross section. Using a recent approach to threshold resummation based on effective field theory, we quantify to which extent the fall-off of the parton densities at high x leads to a dy…
We discuss the simultaneous resummation of threshold and recoil enhancements to partonic cross sections due to soft radiation. Our method is based on a refactorization of the parton cross section near its partonic threshold. It avoids double counting, conserves the flow of partonic energy, and reproduces either threshold or recoil resummation when the other enhancements are neglected.
The cross sections for several $γγ\to VV$ processes exhibit strong enhancements near threshold, where $V$ denotes a vector meson. The pattern of these enhancements is not well understood; for example, $γγ\to ρ^0 ρ^0$ shows an appreciable peak, while $γγ\to ρ^+ ρ^-$ does not. Some possible mechanisms for this behavior are discussed. Tests are proposed involving production of systems containing heavier quarks, e.g., through the reaction $γγ\to J/ψρ^0$. The importance of modeling $\ell^+ \ell^- π^+ π^-$ angular distributions in decays of threshold $J/ψρ^0$ enhancements is illustrated by comparing…
We investigate effects of threshold resummation of logarithmic corrections $\ln N$ in Mellin space quantitatively. Threshold resummation leads to enhancement of next-to-leading-order QCD predictions for jet production at large jet transverse energy, which is in the trend indicated by experimental data. We show that this enhancement is completely determined by the behavior of threshold resummation at small $N$, the region where hierachy among different powers of $\ln N$ is lost and current next-to-leading-logarithm resummation is not reliable. Our analysis indicates that more accurate threshold…
We demonstrate that both the $k_T$ and threshold resummations can be performed in the Collins-Soper resummation formalism by evaluating soft gluon emissions with infrared cutoffs for the longitudinal and transverse loop momenta, respectively. The reason the $k_T$ resummation for a parton distribution function leads to suppression in the large $b$ region, $b$ being the conjugate variable of parton transverse momentum $k_T$, and the threshold resummation leads to enhancement in the large $N$ limit, $N$ being the moment of a distribution function, is a consequence of opposite directions of double…
An enhancement for the $η$ production in proton-neutron collisions as compared with that in proton-proton scattering has been recently observed. We present a calculation for the production cross section, in proton-neutron collisions near threshold, within instanton model for the QCD vacuum and show that a specific flavor dependent nonperturbative quark-gluon interaction related to instantons is able to explain the observed enhancement.
The data collected by the LHC collaborations at an energy of 13 TeV indicates the presence of an excess in the diphoton spectrum that would correspond to a resonance of a 750 GeV mass. The apparently large production cross section is nevertheless very difficult to explain in minimal models. We consider the possibility that the resonance is a pseudoscalar boson $A$ with a two--photon decay mediated by a charged and uncolored fermion having a mass at the $\frac12 M_A$ threshold and a very small decay width, $\ll 1$ MeV; one can then generate a large enhancement of the $Aγγ$ amplitude which expla…
Inspired by the recent measurement of the process $e^+e^-\rightarrow Λ\barΛ$, we calculate the mass spectrum of the $ϕ$ meson with the GI model. For the excited vector strangeonium states $ϕ(3S,~4S,~5S,~6S)$ and $ϕ(2D,~3D,~4D,~5D)$, we further investigate the electronic decay width with the Van Royen-Weisskopf formula, and the partial widths of the $Λ\barΛ$, $Ξ^{-(*)}\barΞ^+$, and $Σ^{+(*)}\barΣ^{-(*)}$ decay modes with the extended quark pair creation model. We find that the electronic decay width of the $D$-wave vector strangeonium is about $3\sim8$ times larger than that of the $S$-wave vec…
We investigate in detail the "triangle singularity" regions of meson loops where the corresponding intermediate mesons are nearly-on-shell and have relatively small momenta, and the two heavy mesons strongly interact with each other in an $S$ wave. This $S$-wave interaction will make such kind of meson loops always enhanced and can explain experimental observations of threshold enhancements. We show that the production of the $Y(4260)$ and the recently observed $Z_c(3900)$ can be related to each other by this mechanism which will allow for a possible understanding of the nature of these thresh…
Supersymmetric extensions of the standard model contain additional heavy neutral Higgs bosons that are coupled to heavy scalar top quarks (stops). This system exhibits interesting field theoretic phenomena when the Higgs mass is close to the stop-antistop production threshold. Existing work in the literature has examined the digluon-to-diphoton cross section near threshold and has focused on enhancements in the cross section that might arise either from the perturbative contributions to the Higgs-to-digluon and Higgs-to-diphoton form factors or from mixing of the Higgs boson with stoponium sta…
We present a simple interpretation of the recently observed near-threshold proton-antiproton enhancement. It is described by a set of low-energy parameters deduced from the analysis of NantiN experiments at LEAR. We predict a related effect in photoproduction reaction under study by CLAS collaboration.
We have analyzed the reaction $χ_{c0}\to \bar{p} K^+Λ$ reported by the BESIII Collaboration, taking into account the contributions from the intermediate $K(1830)$, $N(2300)$, and $Λ(1520)$ resonances. Our results are in good agreement with the BESIII measurements, and it is found that the anomalous enhancement near the $\bar{p}Λ$ threshold is mainly due to the contribution of the $K(1830)$ resonance. We also show that the interference of the high-mass $N^*$ and $Λ^*$ can not produce the anomalous enhancement near the $\bar{p}Λ$ threshold.
We demonstrate that triangle singularity (TS) and box singularity (BS) mechanisms can produce unique narrow enhancements at the $Λ_c\bar{D}$ and $Λ_c\bar{D}^*$ thresholds in the invariant mass spectra of $J/ψp$ and $J/ψpπ$, respectively. Taking into account that such mechanisms only depend on the initial $Σ_c^{(*)}\bar{D}^{(*)}$ interactions near threshold within the TS or BS kinematic regimes, the $Λ_c\bar{D}$ and $Λ_c\bar{D}^*$ threshold enhancements can be regarded as a feed-down phenomenon originated from both the heavier pentaquark decays and the $Σ_c^{(*)}\bar{D}^{(*)}$ scatterings from …
We study the energy dependence of the e^+e^- to ppbar cross section close to the two-nucleon threshold, recently reported by the BaBar collaboration. Our analysis also includes the pbarp to e^+e^- data collected by PS170 collaboration and the e^+e^- to NNbar data from the FENICE collaboration. We show that the near-threshold enhancement in the e^+e^- to ppbar cross section can be explained by the final-state interaction between proton and antiproton in the 3S1 partial wave, utilizing the Juelich nucleon-antinucleon model. As a consequence, the strong dependence of the proton electromagnetic fo…
In this letter we study a novel effect of a hidden sector coupling to the standard model Higgs boson: an enhancement of the Higgs pair production cross section near threshold due to bound state effects. After summing the ladder contributions of the hidden sector to the effective $ggHH$ coupling, we find the amplitude for gluon-gluon scattering via a Higgs loop. We relate this amplitude to the double Higgs production cross section via the optical theorem. We find that enhancements of the order of 100 for the partonic cross section near the threshold region can be obtained for a hidden sector st…
The nature of low-mass baryon-antibaryon enhancements seen in B decays is explored. Three possibilities include (i) states near threshold as found in a model by Nambu and Jona-Lasinio, (ii) isoscalar states with $J^{PC} = 0^{\pm +}$ coupled to a pair of gluons, and (iii) low-mass enhancements favored by the fragmentation process. Ways of distinguishing these mechanisms using angular distributions and flavor symmetry are proposed.
We investigate the nature of the near-threshold enhancement in the ppbar invariant mass spectrum of the reaction J/Psi -> gamma ppbar reported recently by the BES Collaboration. Using the Juelich NNbar model we show that the mass dependence of the ppbar spectrum close to the threshold can be reproduced by the S-wave ppbar final state interaction in the isospin I=1 state within the Watson-Migdal approach. However, because of our poor knowledge of the NNbar interaction near threshold and of the J/Psi -> gamma ppbar reaction mechanism and in view of the controversal situation in the decay J/Psi -…
We investigate the possibility of producing the enhancement observed in $J/ψ\to γX$ with $X\to ωϕ$ at BES by intermediate meson rescatterings through $f_0(1710)\to PP\to ωϕ$, $f_0(1710)\to VV\to ωϕ$, and $f_0(1710)\to SS\to ωϕ$. We find that intermediate meson rescatterings can produce some enhancement near the $ωϕ$ threshold. Implications about the property of this enhancement are discussed.
We find model-independent upper limits on rates of dark matter annihilation in galactic halos. The Born approximation generally fails, while exotic threshold enhancements akin to "Sommerfeld factors" also turn out to be baseless The most efficient annihilation mechanism involves perturbatively small decay widths that have largely been ignored. Widths that are very small compared to TeV mass scales suffice to effectively saturate unitarity bounds on annihilation rates. Bound state formation in weakly coupled theories produces small effects due to wave function normalizations. Unitarity shows th…
We study the threshold enhancement effects of baryon-anti-baryon systems in $J/ψ$ decays at BES using parity $P$, charge conjugation $C$, and flavor SU(3) symmetries. The $P$ and $C$ symmetries restrict the $p\bar p$ in $J/ψ\to γp\bar p$ to be in a state with $C=+1$, while the $p\bar p$ in $J/ψ\to π^0 p\bar p$ to be with $C=-1$. Combining the $C$ and $P$ symmetries with flavor SU(3) symmetry, i.e. the CPS symmetry, we find that the $Λ\bar p$ system cannot be in $0^+$ and $0^-$ states in $J/ψ\to K^+ Λ\bar p$. We provide a consistent explanation of observation and non-observation of near thresho…
The near-threshold behavior of the ppbar invariant mass spectrum from the J/psi -> omega ppbar decay reported recently by the BES Collaboration is analyzed. Contrary to the statement made by the BES Collaboration itself our study demonstrates that there is indeed a noticeable enhancement in the ppbar invariant mass spectrum near threshold. Moreover, this enhancement is nicely reproduced by the final state interaction in the relevant 11S0 ppbar partial wave as given by the Julich nucleon--antinucleon model. Therefore, and again contrary to the statement by the BES Collaboration, their new data …
We calculate open charm production in $Pb+Pb$ reactions at SPS energies within the HSD transport approach - which is based on string, quark, diquark ($q, \bar{q}, qq, \bar{q}\bar{q}$) and hadronic degrees of freedom - including the production of open charm pairs from secondary 'meson'-'baryon' (or quark-diquark and antiquark-diquark) collisions. It is argued that at collision energies close to the $c\bar{c}$ pair threshold the dominant production mechanism is related to the two body (or quasi two body) reactions $πN \to \bar{D} (\bar{D^*}) Λ_c, (Σ_c)$. Estimates within the framework of the Qua…
The observed enhancement of $p\bar p$-production near the threshold in radiative decays of $J/ψ$ and $e^+e^-$-annihilations can be explained with final state interactions among the produced $N\bar N$ system, where the enhancement is essentially determined by $N\bar N$ elastic scattering amplitudes. We propose to use an effective theory for interactions in a $N\bar N$ system near its threshold. The effective theory is similar to the well-known one for interactions in a $NN$ system but with distinctions. It is interesting to note that in the effective theory some corrections to scattering amplit…
Focusing on recent measurement of $B^+ \to D_s^+D_s^-K^+$ process given by the LHCb Collaboration, we propose that this newly observed near the $D_s^+D_s^-$ threshold enhancement can be due to the contribution of the $χ_{c0}(2P)$, which is a $P$-wave charmonium below the $D_s^+D_s^-$ threshold. By performing a combined fit to the measured $D_s^+D_s^-$, $D_s^+K^+$, and $D_s^-K^+$ invariant mass spectra, introducing the $χ_{c0}(2P)$ can well reproduce the near threshold enhancement in the $D_s^+D_s^-$ invariant mass spectrum. When depicting the whole $D_s^+D_s^-$ invariant mass spectrum, the con…
The near-threshold $e^+e^- \to Λ\barΛ$ reaction is studied with the assumption that the production mechanism is due to a near-$Λ\barΛ$-threshold bound state. The cross section of $e^+e^- \to Λ\barΛ$ reaction is parametrized in terms of the electromagnetic form factors of $Λ$ hyperon, which are obtained with the vector meson dominance model. It is shown that the contribution to the $e^+e^- \to Λ\barΛ$ reaction from a new narrow state with quantum numbers $J^{PC}=1^{--}$ is dominant for energies very close to threshold. The mass of this new state is around 2231 MeV, which is very close to the ma…
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 investigate the enhancement in the D^0\bar{D}^0π^0 final state with the mass M=3875.2\pm 0.7^{+0.3}_{-1.6}\pm 0.8 MeV found recently by the Belle Collaboration in the B\to K D^0\bar{D}^0π^0 decay and test the possibility that this is yet another manifestation of the well-established resonance X(3872). We perform a combined Flatte analysis of the data for the D^0\bar{D}^0π^0 mode, and for the π^+π^- J/ψmode of the X(3872). Only if the X(3872) is a virtual state in the D^0\bar{D}^{*0} channel, the data on the new enhancement comply with those on the X(3872). In our fits, the mass distribution…
In the $J/ψ$ radiative decay channels $J/ψ\to γV\bar{V}$, the result of partial wave analysis indicates that the $V\bar{V}$ systems are predominately pseudoscalar component, and most of these channels have relatively large branching ratios at an order of $10^{-3}$. Meanwhile, vector mesons, such as $ρ$, $ω$ and $K^*$, have strong couplings with nucleons and/or hyperons. This suggests a dynamical mechanism describing the $ηp\bar{p}$ form factors for higher $η$ mesons, such as $η(1405/1475)$ and $η(1760)$. It is thus natural to expect that rescatterings of these vector meson pairs into $p\bar{p}…
One of the main issues in hadron spectroscopy is to identify the origin of threshold or near-threshold enhancement. Prior to our study, there is no straightforward way of distinguishing even the lowest channel threshold-enhancement of the nucleon-nucleon system using only the cross-sections. The difficulty lies in the proximity of either a bound or virtual state pole to the threshold which creates an almost identical structure in the scattering region. Identifying the nature of the pole causing the enhancement falls under the general classification problem and supervised machine learning using…
The excitation function for the $pp\to ppK^+K^-$ reaction revealed a significant enhancement close to threshold which may plausibly be assigned to the influence of the $pK^-$ and $K^+K^-$ final state interactions. In an improved reanalysis of COSY-11 data for the $pp\to ppK^+K^-$ reaction at excess energies of Q = 10 MeV and 28 MeV including the proton-K- interaction the enhancement is confirmed. Invariant mass distributions for the two- and three-particle subsystems allow to test at low excess energies the ansatz and parameters for the description of the interaction in the ppK+K- system as de…
The anomalous behavior of the spin-spin correlation at large momentum transfer in pp elastic scattering is described in terms of the degrees of freedom associated with the onset of the charm threshold. A non-perturbative analysis based on the symmetries of QCD is used to extract the relevant dynamics of the charmonium-proton interaction. The enhancement to pp amplitudes and their phase follow from analyticity and unitarity, giving a plausible explanation of the spin anomaly. The interaction between charmonium and light quarks in nuclei may form a distinct kind of nuclear matter, nuclear bound …
We present a simple explanation for the recently observed near-threshold proton-antiproton enhancement. It is described by a set of low-energy parameters deduced from the analysis of NantiN experiments at LEAR. We predict a related effect in photoproduction reaction under study by CLAS collaboration.
We analyze two recent reactions of Belle, producing $D\bar D$ and $D\bar D^*$ states that have an enhancement of the invariant $D\bar D$, $D\bar D^*$ mass distribution close to threshold, from the point of view that they might be indicative of the existence of a hidden charm scalar and an axial vector meson states below $D\bar D$ or $D\bar D^*$ thresholds, respectively. We conclude that the data is compatible with the existing prediction of a hidden charm scalar meson with mass around 3700 MeV, though other possibilities cannot be discarded. The peak seen in the $D\bar D^*$ spectrum above thre…
The near-threshold enhancement in the ppbar invariant mass spectrum from the B^+ -> K^+ ppbar decay reported recently by the BaBar Collaboration is studied within the Jülich NNbar model. We illustrate that the invariant mass dependence of the ppbar spectrum close to the threshold can be reproduced by the final state interactions. This explanation is in line with our previous analysis of the ppbar invariant mass spectrum from the J/Psi -> gamma ppbar decay measured by the BES Collaboration. We also comment on a structure found recently in the pi^+ pi^- eta' mass spectrum of the radiative J/Psi …
A systematic analysis of the near-threshold enhancement in the $\bar pp$ invariant mass spectrum seen in the decay reactions $J/ψ\to x \bar pp$ and $ψ(3686) \to x \bar pp$ $(x = γ,\, ω,\, ρ,\, π,\, η)$ is presented. The enhancement is assumed to be due to the $\bar NN$ final-state interaction (FSI) and the pertinent FSI effects are evaluated in an approach that is based on the distorted-wave Born approximation. For the $\bar NN$ interaction a recent potential derived within chiral effective field theory and fitted to results of a partial-wave analysis of $\bar pp$ scattering data is considered…
The near-threshold behavior of the ppbar invariant mass spectrum from the psi(3686) -> gamma ppbar decay reported recently by the BESIII Collaboration is analyzed. The enhancement in the ppbar invariant mass spectrum near threshold is nicely reproduced by the ppbar final-state interaction based on the isospin averaged 1S0 partial-wave amplitude as predicted by the Julich nucleon--antinucleon model. Contributions from the f_2(1910) or f_2(1950) mesons, as promoted in earlier works, are not needed.
By assuming that Y(4260) either is a $D_1\bar{D}$ molecular state, or has sizeable couplings with $D_0 \bar{D}^*$ and $D_1^\prime \bar{D}$, we investigate several decay modes of Y(4260). Under the special kinematic configurations, triangle singularity (TS) may occur in the rescattering amplitude, which will significantly change the threshold behavior. Obvious threshold enhancements or narrow cusp structures appear quite naturally without introducing a genuine resonance. We emphasize that the radiative decay modes may be useful for studying $D^{(*)}\bar{D}$ $S$-wave scattering.
The dark matter annihilation rate at small relative velocities can be amplified by a large boost factor using various mechanisms, including Sommerfeld enhancement, resonance enhancement, and Breit-Wigner enhancement. These mechanisms all involve a resonance near the threshold for a pair of dark matter particles. We point out that if the resonance is in the S-wave channel, the mechanisms are equivalent sufficiently near the resonance and they are constrained by universal two-body physics. The amplified annihilation rate requires a corresponding amplification of the elastic scattering cross sect…
A mixing of near-threshold quarkonium-like resonances with heavy meson-antimeson pairs results in an enhancement of heavy quark spin symmetry breaking, since the meson pairs are not eigenstates of the heavy quark spin. The decomposition of $P$-wave states of meson pairs in terms of the heavy-quark-pair spin states is considered in the channel with $J^{PC}=1^{--}$, which is directly produced in $e^+e^-$ annihilation. Specific processes are suggested for experimental study of the effects of the mixing with heavy meson pairs and of the internal spin structure of bottomonium and charmonium resonan…
The BES data on the $J/ψ\to ηK^{*0}\bar{K}^{*0}$ reaction show a clear enhancement in the $K^{*0}\bar{K}^{*0}$ mass distribution close to the threshold of this channel. Such an enhancement is usually a signature of a L=0 resonance around threshold, which in this case would correspond to an $h_1$ state with quantum numbers $I^G(J^{PC})=0^-(1^{+-})$. A state around $1800\ \text{MeV}$ results from the interaction of the $K^* \bar{K}^*$ using the local hidden gauge approach. We show that the peak observed in $J/ψ\to ηK^{*0}\bar{K}^{*0}$ naturally comes from the creation of this $h_1$ state with ma…
Indications of the existence of quasi-bound states in the N-Nbar system are presented. Measurements by BES discovered a broad enhancement close to the p-pbar threshold in the S wave, isospin 0 state formed in radiative decays of J/psi. Another enhancement located about 50 MeV below the threshold was found in mesonic decays of J/psi. In terms of the Paris potential model it was shown that these are likely to represent the same state. Antiprotonic atomic data provide some support for this interpretation and indicate the existence of another fairly narrow quasi-bound state in a P wave.
The cross sections for the reactions pp -> p Lambda^0K^+ and pn -> n Lambda^0K^+ are calculated near threshold of the final states. The theoretical ratio of the cross sections R = sigma(pn -> n Lambda^0K^+)/ sigma(pp ->pΛ^0K^+) = 3 shows the enhancement of the pn interaction with respect to the pp interaction near threshold of the strangeness production N Lambda^0K^+. Such an enhancement is caused by the contribution of the np interaction in the isospin-singlet state, which is stronger than the $pn$ interaction in the isospin-triplet state. For the confirmation of this result we calculate the …
Very recently, the LHCb Collaboration reported the first observation of the hidden charm pentaquark with strangeness, $P_{ψs}^Λ(4338)^0$. Considering this state is very close to the $Ξ_c^0\bar{D}^0$ and $Ξ_c^+D^-$ thresholds, we explore the possible bias of the Breit-Wigner parameterization, with emphasis on the effect of its coupling to the double thresholds $Ξ_c^0\bar{D}^0$ and $Ξ_c^+D^-$. We first use a qualitative picture based on the ``uniformization" of the Riemann surface of the two-channel system to understand the positions of the enhancement. Then we use the Lippmann-Schwinger equatio…
A new mechanism of baryon-antibaryon production via nonperturbative double pair creation in intermediate mesons is proposed and the theory contains no fitting parameters. It is shown, that near-threshold resonances are responsible for enhancements in electroproduction cross sections: $ψ(4S)$ for $Λ^+_c Λ^-_c, Υ(6S)$ for $Λ_b \bar Λ_b$. An admixture of intermediate $D$- wave resonances produces angular dependence in differential cross section and can explain unusual behavior of the ratio $G_E/G_M$ for the proton.
We revisit the compositeness theorem proposed by Weinberg in an effective field theory (EFT) and explore criteria which are sensitive to the structure of $S$-wave threshold states. On a general basis, we show that the wave function renormalization constant $Z$, which is the probability of finding an elementary component in the wave function of a threshold state, can be explicitly introduced in the description of the threshold state. As an application of this EFT method, we describe the near-threshold line shape of the $D^{\ast 0}\bar D^0$ invariant mass spectrum in $B\rightarrow D^{\ast 0}\bar…
