Search

In this report, I discuss some of the most recent lattice spectroscopy calculations of hadrons and hadronic resonances involving charm quarks, with special emphasis on those that are relevant from an experimental perspective. [ABSTRACT FROM AUTHOR]

It has been 5 years since the data sample from the LHCb detector, the first experiment optimized for heavy-flavor physics studies at a hadronic collider, was completed. These data led to many major discoveries in exotic hadron spectroscopy, which we review in this article. We supplement the experimental results with a selection of phenomenological interpretations. As the upgraded LHCb detector is expected to collect a larger data sample starting in 2024, we also discuss the potential of the LHCb program in exotic hadron physics for the near future and beyond. [ABSTRACT FROM AUTHOR]

Motivated by the discovery of hidden-charm strange pentaquarks, we conduct a systematic study of the magnetic moments of the hidden-bottom strange pentaquarks in molecular picture. We calculate magnetic moments of hidden-bottom strange pentaquarks with strangeness-1 and 2. Magnetic moment gives valuable information about the inner structure and shape of the hadron. The obtained results may be helpful to determine the inner structure of these hypothetical states.

In recent years, many tetraquarks and pentaquarks have been discovered by various experimental groups and X (3 8 7 2) , Z c (3 9 0 0) , X (4 4 3 0) , P c + (4 3 1 2) , P c + (4 4 5 7) are some of the interesting observed tetraquark and pentaquark states. The Regge trajectories of some such states are studied in view of the flux tube model of hadrons with finite quark masses. The effect of flux tube (or string) length variation on the Regge trajectories of these states is analyzed in detail. It is observed that for a fixed angular momentum, the string length has a constant value. Some other states are also proposed and the results obtained are then compared with the studies by others. Our findings correspond rather well with those of other researchers and with those of the experiment. [ABSTRACT FROM AUTHOR]

The effective Lande splitting factor g ∗ for heavy pentaquarks has been investigated, where the pentaquarks are described as Composite Fermions (CFs). The effective Lande splitting factor for heavy pentaquarks 𝜃 c 0 , N c 0 , Ξ c 0 and 𝜃 b + , N b + , Ξ b + has been extracted. It has been suggested that due to color magnetic field, diquarks behave like CFs and effective masses of the pentaquarks m ∗ have been estimated in diquark–diquark–antiquark scheme with the input of effective diquark masses calculated in the framework of Composite Fermion model (CFM). With m ∗ g ∗ as the additional contribution to the energy expression, the variation of g ∗ with angular momentum L has been studied. The vacuum value of g ∗ has been extracted, which can be attributed to the splitting due to spin contribution of CFs and choromo-electromagnetic character of the QCD vacuum. [ABSTRACT FROM AUTHOR]

Starting with the dynamical picture of the exotic cc¯-containing states XYZ as the confinement-induced hadronization of a rapidly separating pair of a compact diquark and antidiquark, we describe the pentaquark candidates Pc+(4380) and Pc+(4450) in terms of a confined but rapidly separating color-antitriplet diquark cu and color-triplet “triquark” c¯(ud). This separation explains the relatively small Pc+ widths, despite these 5-quark systems lying far above both the J/ψp and ΛcD¯(⁎)0 thresholds. The Pc+ states are predicted to form isospin doublets with neutral partners Pc0.

Abstract We study baryo-charmonium [ η c - and J / ψ - N ⁎ , η c (2 S) -, ψ (2 S) - and χ c (1 P) - N ] and baryo-bottomonium [ η b (2 S) -, ϒ (2 S) - and χ b (1 P) - N ] bound states, where N is the nucleon and N ⁎ a nucleon resonance. In the baryo-quarkonium model, the five q q q Q Q ¯ quarks are arranged in terms of a heavy quarkonium core, Q Q ¯ , embedded in light baryonic matter, qqq , with q = u or d. The interaction between the Q Q ¯ core and the light baryon can be written in terms of the QCD multipole expansion. The spectrum of baryo-charmonium states is calculated and the results compared with the existing experimental data. In particular, we can interpret the recently discovered P c (4380) and P c (4450) pentaquarks as ψ (2 S) - N and χ c2 (1 P) - N bound states, respectively. We observe that in the baryo-bottomonium sector the binding energies are, on average, slightly larger than those of baryo-charmonia. Because of this, the hidden-bottom pentaquarks are more likely to form than their hidden-charm counterparts. We thus suggest the experimentalists to look for five-quark states in the hidden-bottom sector in the 10.4 – 10.9 GeV energy region. [ABSTRACT FROM AUTHOR]

Abstract We extend our previous study on the decay behavior of P c hadronic molecules to their strange and beauty partners. While P c (4380) and P c (4450) locate just below the D ¯ Σ c ⁎ and D ¯ ⁎ Σ c thresholds, respectively, their proposed strange partners N (1875) and N (2080) sit just below the K Σ ⁎ and K ⁎ Σ thresholds, respectively. Using the effective Lagrangian approach as the same as for the study of P c hadronic molecular states and with the couplings determined by the SU (3) flavor symmetry, the decay patterns of N (1875) and N (2080) are obtained assuming them to be the S -wave K Σ ⁎ and K ⁎ Σ molecules, respectively. It is found that the measured decay properties of N (1875) and N (2080) are reproduced well. Our results suggest that both N (1875) and N (2080) can be described as the hadronic molecular pentaquark states in the hidden strangeness sector with quantum number I (J P) = 1 / 2 (3 / 2 −). Further checks on their hadronic molecule nature by various experiments are proposed. With the same approach, we also give our predictions for the decay behavior of the possible beauty partners of the P c hadronic molecular states. The B ⁎ Λ b is found to be the largest decay mode for both B Σ b ⁎ and B ⁎ Σ b hadronic molecules, hence can be used to look for the hidden beauty pentaquark states in forthcoming experiments. [ABSTRACT FROM AUTHOR]

We discus the role of Quantum Chromodynamics (QCD) in low energy phenomena involving the color-spin symmetry of the quark model. We then combine it with orbital and isospin symmetry to obtain wave functions with the proper permutation symmetry, focusing on multi-quark systems. [ABSTRACT FROM AUTHOR]

Why do we see certain types of strongly interacting elementary particles and not others? This question was posed more than 50 years ago in the context of the quark model. M. Gell-Mann and G. Zweig proposed that the known mesons were and baryons qqq, with the quarks known at the time, u (up), d (down), and s (strange), having charges of 2/3, −1/3, and −1/3, respectively. Mesons and baryons would then have integral charges. Mesons such as and baryons such as would also have integral charges. Why weren't they seen? They have now been seen, but only with additional heavy quarks and under conditions that tell us a lot about the strong interactions and how they manifest themselves. This review describes recent progress in our understanding of such exotic mesons and baryons. [ABSTRACT FROM AUTHOR]

For many decades after the invention of the quark model in 1964 there was no evidence that hadrons are formed from anything other than the simplest pairings of quarks and antiquarks, mesons being formed of a quark–antiquark pair and baryons from three quarks. In the last decade, however, in an explosion of data from both e + e − and hadron colliders, there are many recently observed states that do not fit into this picture. These new particles are called generically “exotics”. They can be either mesons or baryons. Remarkably, they all decay into at least one meson formed of either a c c ¯ or b b ¯ pair. In this review, after the introduction, we explore each of these new discoveries in detail first from an experimental point of view, then subsequently give a theoretical discussion. These exotics can be explained if the new mesons contain two-quarks and two-antiquarks (tetraquarks), while the baryons contain four-quarks plus an antiquark (pentaquarks). The theoretical explanations for these states take three divergent tracks: tightly bound objects, just as in the case of normal hadrons, but with more constituents, or loosely bound “molecules” similar to the deuteron, but formed from two mesons, or a meson or baryon, or more wistfully, they are not multiquark states but appear due to kinematic effects caused by different rescatterings of virtual particles; most of these models have all been post-dictions. Both the tightly and loosely bound models predict the masses and related quantum numbers of new, as yet undiscovered states. Thus, future experimental discoveries are needed along with theoretical advances to elucidate the structure of these new exotic states. [ABSTRACT FROM AUTHOR]

In terms of P c 1 , c 2 = P c ( 4380 , 4450 ) + as the hidden charm pentaquark states to consist of c c ̄ u u d , we study the semileptonic Λ b → ( P c 1 , c 2 → ) J ∕ ψ p ℓ − ν ̄ ℓ decays. In our discussion, while the main contribution to Λ b → K − J ∕ ψ p is from the non-perturbative process via the doubly charmful b → c c ̄ s transition, we propose that the Λ b → P c 1 , c 2 → J ∕ ψ p transitions partly contribute to the Λ b → K − ( P c 1 , c 2 → ) J ∕ ψ p decays, in which the required c c ̄ pair is formed by the sea quarks, intrinsic charm, or both. We predict that B ( Λ b → J ∕ ψ p ℓ − ν ̄ ℓ ) = ( 2 . 0 4 − 1 . 57 + 4 . 82 , 1 . 7 5 − 1 . 35 + 4 . 14 ) × 1 0 − 6 for ℓ = ( e , μ ) , which are about two orders of magnitude smaller than the observed decay of Λ b → p μ ν ̄ μ . We also explore the angular correlations for the J ∕ ψ p and ℓ − ν ̄ ℓ pairs. Our results of the decay branching ratios and angular asymmetries in Λ b → J ∕ ψ p ℓ − ν ̄ ℓ , accessible to the ongoing experiments at the LHCb, can be used to improve the understanding of the hidden charm pentaquark states. [ABSTRACT FROM AUTHOR]

Multiquark resonances are undoubtedly experimentally observed. The number of states and the amount of details on their properties have been growing over the years. It is very recent the discovery of two pentaquarks and the confirmation of four tetraquarks, two of which had not been observed before. We mainly review the theoretical understanding of this sector of particle physics phenomenology and present some considerations attempting a coherent description of the so called X and Z resonances. The prominent problems plaguing theoretical models, like the absence of selection rules limiting the number of states predicted, motivate new directions in model building. Data are reviewed going through all of the observed resonances with particular attention to their common features and the purpose of providing a starting point to further research. [ABSTRACT FROM AUTHOR]

We have investigated the Regge trajectories of exotic hadrons by considering different possible pentaquark configurations with finite quark mass in the flux tube model. Significant deviation is observed in the linear behavior of the Regge trajectories for pentaquark systems in view of the universal value of the Regge slope parameter for hadrons. The modified Regge trajectories are also compared with the available experimental and lattice data. It is observed that the nonlinear Regge trajectories of such pentaquark systems can be well described by the relativistic corrections in view of the current quark masses and the high rotational speed of the quarks at the end of flux tube structure. [ABSTRACT FROM AUTHOR]

QCD-motivated models for hadrons predict an assortment of 'exotic' hadrons that have structures that are more complex than the quark-antiquark mesons and three-quark baryons of the original quark-parton model. These include pentaquark baryons, the six-quark H-dibaryon, and tetraquark, hybrid and glueball mesons. Despite extensive experimental searches, no unambiguous candidates for any of these exotic configurations have been identified. On the other hand, a number of meson states, one that seems to be a proton-antiproton bound state, and others that contain either charmed-anticharmed quark pairs or bottom-antibottom quark pairs, have been recently discovered that neither fit into the quark-antiquark meson picture nor match the expected properties of the QCD-inspired exotics. Here I briefly review results from a recent search for the H-dibaryon, and discuss some properties of the newly discovered states -the proton-antiproton state and the so-called XY Z mesons- and compare them with expectations for conventional quark-antiquark mesons and the predicted QCD-exotic states. [ABSTRACT FROM AUTHOR]

We consider an imaginary time functional integral formulation of a two-flavor, 3+1 lattice QCD model with Wilson's action and in the strong coupling regime (with a small hopping parameter, κ > 0, and a much smaller plaquette coupling, $\beta=1/g_0^2>0$, so that the quarks and glueballs are heavy). The model has local SU(3)c gauge and global SU(2)f flavor symmetries, and incorporates the corresponding part of the eightfold way particles: baryons (mesons) of asymptotic mass ≈-3 ln κ(≈-2 ln κ). We search for pentaquark states as meson-baryon bound states in the energy-momentum spectrum of the model, using a lattice Bethe-Salpeter equation. This equation is solved within a ladder approximation, given by the lowest nonvanishing order in κ and β of the Bethe-Salpeter kernel. It includes order κ2 contributions with a $q\bar q$ exchange potential together with a contribution that is a local-in-space, energy-dependent potential. The attractive or repulsive nature of the exchange interaction depends on the spin of the meson-baryon states. The Bethe-Salpeter equation presents integrable singularities, forcing the couplings to be above a threshold value for the meson and the baryon to bind in a pentaquark. We analyzed all the total isospin sectors, I = 1/2, 3/2, 5/2, for the system. For all I, the net attraction resulting from the two sources of interaction is not strong enough for the meson and the baryon to bind. Thus, within our approximation, these pentaquark states are not present up to near the free meson-baryon energy threshold of ≈-5 ln κ. This result is to be contrasted with the spinless case for which our method detects meson-baryon bound states, as well as for Yukawa effective baryon and meson field models. A physical interpretation of our results emerges from an approximate correspondence between meson-baryon bound states and negative energy states of a one-particle lattice Schrödinger Hamiltonian. [ABSTRACT FROM AUTHOR]

The relativistic five-quark equations are found in the framework of the dispersion relation technique. The five-quark amplitude for the N*(1688) resonance including u- and d-quarks is calculated. The pole of this amplitude determines the mass of nonstrange pentaquark M=1686 MeV and the width about 7 MeV. The results are in good agreement with the evidence for a narrow N*(1688) resonance. [ABSTRACT FROM AUTHOR]

FOCUS is a photoproduction experiment designed to reconstruct charm particles and to study their decays. Data was collected at Fermilab during the 1996-97 fixed-target run. We present recent results on semileptonic meson decays and a search for pentaquarks. [ABSTRACT FROM AUTHOR]

The results of pentaquark searches at the B-factories are reviewed. No pentaquark signal has been seen; the resulting bounds (on pentaquark production rates, branching fractions, and widths) vary in strength, and in their relationship to positive results from other experiments. [ABSTRACT FROM AUTHOR]

We review lattice calculations of pentaquarks and discuss issues pertaining to interpolation fields, distinguishing the signal of pentaquarks from those of the KN scattering states, chiral symmetry, and ghost state contaminations. [ABSTRACT FROM AUTHOR]

The relativistic five-quark equations are found in the framework of the dispersion relation technique. The five-quark amplitudes for the low-lying pentaquarks including the u, d, s-quarks are calculated. The poles of these amplitudes determine the masses of the nucleon and the Ξ–– pentaquarks. The mass spectra of the lowest pentaquarks with the $J^P=\frac{1}{2}^+, \frac{1}{2}^-, \frac{3}{2}^+$ are calculated. The mass values of the positive and negative parity pentaquarks are determined by the mixing of both 0+ and 1+ diquarks. [ABSTRACT FROM AUTHOR]

The relativistic five-quark equations are found in the framework of the dispersion relation technique. The five-quark amplitudes for the low-lying pentaquarks including u, d quarks are calculated. The poles of the five-quark amplitudes determine the masses of the ududţ and uuuuţ pentaquarks. The calculated of pentaquark amplitudes estimates the contributions of four subamplitudes. The main contributions to the pentaquark amplitude are determined by the subamplitudes, which include the meson states M. [ABSTRACT FROM AUTHOR]

Based on an assumed mass formula for the spectrum of the Y=2 pentaquarks, where the chromo-magnetic interaction plays an important role, and identifying the lightest state with the Θ+(1540), we predict a spectrum in good agreement with the few I=0 and I=1 candidates proposed in the past. [ABSTRACT FROM AUTHOR]

The relativistic generalization of Faddeev–Yakubovsky approach is constructed in the form of the dispersion relations. The five-quark amplitudes for the low-lying pentaquarks including the u-, d-, s-quarks are calculated. The poles of these amplitudes determine the masses and widths of θ-pentaquarks. [ABSTRACT FROM AUTHOR]

A brief review of the latest developments in the spectroscopy of heavy quarks is presented. The current status of the recently 'discovered' pentaquarks is also discussed. [ABSTRACT FROM AUTHOR]

Abstract: After a quick look at the present status of experiments we briefly review in a first step the ongoing discussions on some of the basic theoretical approaches to pentaquarks: Chiral solitons, large- considerations, quark models, and lattice gauge approaches. In a second step we apply the chiral quark–soliton approach including linear -corrections to the calculation of magnetic moments of the baryons of the antidecuplet. In this approach the parameters are fixed solely by experimental data for the magnetic moments of the baryon octet and for the masses of the octet, decuplet and of . The magnetic moment of depends rather strongly on the pion–nucleon sigma term and reads −1.19 to −0.33 nm for and 75 MeV respectively. As a by-product the strange magnetic moment of the nucleon is obtained with a value of . [Copyright &y& Elsevier]

A model for nuclei described directly in terms of quarks has been developed in both relativistic and non-relativistic forms. It describes nuclear binding energy and structure for small nuclei (A = 3,4) systematically correctly, including the EMC effect. With one free parameter each for strange and for nonstrange states, it also well describes low energy baryon-nucleon scattering, phase shifts and potentials. It predicts low mass, narrow dibaryon and pentaquark states. To be consistent with reported states, new physics may be required that is not included in any quark model to date. [ABSTRACT FROM AUTHOR]

Light and heavy pentaquarks are described within a constituent quark model based on a spin-flavor hyperfine interaction. In this model the lowest state acquires positive parity. The masses of the light antidecuplet members are calculated dynamically using a variational method. It is shown that the octet and antidecuplet states with the same quantum numbers mix ideally due to SU(3)F breaking. Masses of the charmed antisextet pentaquarks are predicted within the same model. [ABSTRACT FROM AUTHOR]

Glueballs and hybrids are predicted to exist but searches for them have failed to provide conclusive evidence. One-gluon exchange is not an important part of strong interactions in this energy regime. Instead% quarks seem to interact indirectly, via changes of the QCD vacuum. Strong interactions seem to be governed by instanton-induced interactions; the chiral soliton model gives a more suitable interpretation of the ϴ+(1540) than models based on the dynamics of four quarks and one antiquark. [ABSTRACT FROM AUTHOR]

Recent results on the study of the electromagnetic structure of nucleon resonances, the spin structure of protons and neutrons at small and intermediate photon virtuality, and the search for exotic pentaquark baryons are presented. [ABSTRACT FROM AUTHOR]

I discuss the recent experimental and theoretical developments following the discovery of the Θ+ pentaquark – an exotic $uudd\bar{s}$ baryon resonance observed in the KN channel by several experiments, and an exotic Ξ*-- (ddssū) reported by NA49 at CERN. I focus on the theoretical interpretation of the data, both in terms of quark and chiral degrees of freedom, on the predictions for related exotic states, and on several unresolved questions raised by the experimental data, such why some experiments observe the pentaquarks and other don't, the apparently extremely narrow width of the Θ+ and the determination of its parity. I also describe the likely properties of the proposed heavy-quark pentaquarks – an anticharmed exotic baryon $\Theta_c\ (uudd\bar{c})$ and $\Theta_b^+$, $(uudd\bar{b})$, which are expected to be extremely narrow or even stable against strong decays. H1 recently reported observation of a possible Θc candidate in D*-p channel. Pentaquarks are also being searched for in e+e- annihilation and γγ collisions in the LEP data and at B-factories. [ABSTRACT FROM AUTHOR]

The pentaquarks are exotic baryons formed of four quarks and an antiquarks. Their existence has been discussed in the literature over the last 30 years or more, first in connection with kaon nucleon scattering data. The subject has been revived by the end of 2002 when experimental evidence of a narrow baryon of strangeness S=+1, and mass M≃1530 MeV has been found. This is interpreted as the lightest member of an SU(3)-flavor antidecuplet. Here we shall mainly review the predictions of pentaquark properties as e.g. mass, spin and parity, within constituent quark models. Both light and heavy pentaquarks will be presented. [ABSTRACT FROM AUTHOR]