XYZ States Research Articles

XYZ spectroscopy at electron-hadron facilities. III. Semi-inclusive processes with vector exchange

Inclusive production processes will be important for the first observations of XYZ states at new generation electron-hadron colliders, as they generally benefit from larger cross sections than their exclusive counterparts. We make predictions of semi-inclusive photoproduction of the χc1(1P) and X(3872), whose peripheral production is assumed to be dominated by vector exchanges. We validate the applicability of vector meson dominance in the axial-vector charmonium sector and calculate production rates at center-of-mass energies relevant for future experimental facilities. We find the semi-inclusive cross sections near the threshold to be enhanced by a factor of ∼2–3 compared to the exclusive reaction and well-suited for a first observation in photoproduction. Published by the American Physical Society 2024

Nonlocal correlations dynamics of two-qubit Heisenberg XYZ states with influence of intrinsic decoherence and y-component of Dzyaloshinskii-Moriya interaction

In this paper, we explore nonlocal correlation and Bell non-locality in a two-qubit Heisenberg XYZ model by using Bell-CHSH inequality and uncertainty induced nonlocality (UIN) as well as log-negativity. We consider the effects of spin-qubits XYZ-Heisenberg couplings, the y-component of DM interaction, and intrinsic decoherence. Our results show that spin-qubits Heisenberg couplings have a strong ability to create two-qubit nonlocal correlations, enhanced by combining with DM interactions. The generated Bell-CHSH nonlocality and entanglement conform to the hierarchy principle. The UIN correlation is more resistant to intrinsic decoherence compared to Bell-CHSH inequality and log-negativity. Intrinsic decoherence causes the disappearance of Bell-CHSH non-locality and log-negativity entanglement, while leading to the appearance of partial stationary spin-qubits UIN correlation.

Search for the Y(2175) in photoproduction at GlueX

Abstract. The Y(2175), recently renamed to ϕ(2170), is one of the rare exotic candidates connected to strangeonium as compared to the heavier charmonium-like and bottomonium-like exotic states. Originally observed in initial state radiation events by the BaBar experiment in 2006, it is suggested to be a strange partner state of the charmonium-like exotic vector state Y(4230) that was one of the first of the so-called XYZ states reported in the charmonium mass region. The Y(2175) has been seen in various experiments and decay channels,but it has not yet been searched for in a photo-production experiment. In this talk we report on a measurement of the production cross section of the reaction γ + p → ϕπ+ π− + p based on data recorded by the GlueX experiment in order to search for Y(2175) → ϕπ+π−.>

Glueball-meson molecules

Experimental searches for pure glueball states have proven challenging and so far yielded no results. This is believed to occur because glueballs mix with the ordinary qq¯ states with the same quantum numbers. We will discuss an alternative mechanism, the formation of the glueball-meson molecular states. We will argue that the wave functions of already observed excited meson states may contain a significant part due to such molecular states. We discuss the phenomenology of glueball-meson molecules and comment on a possible charmless component of the XYZ states.

XYZ states: An experimental point-of-view

Since 2003, a new family of states without a clear theoretical interpretation has been measured in the heavy quarkonium spectrum, the so-called X Y Z states. While the nature of these states is so far unclear, the experimental search is one of the most active fields in the intensity frontier. In this review, the most important and representative results obtained in this field in recent years are going to be illustrated, providing insights into the nature of these exotic states. The focus will be on the experimental side, describing how it is possible to investigate their exotic nature with respect to the conventional quarkonium states.

New Experimental Results on Exotic XYZ States

New Experimental Results on Exotic XYZ States

Exotic states in the quarkonium sector — status and perspectives

The discovery of hadronic states beyond the conventional two-quark meson and three-quark baryon picture in the last two decades is one of the most amazing accomplishments in fundamental physics research. Many experiments contributed to this field despite of the original goals of the design. We review the experimental progress on the study of the quarkoniumlike states — states with at least one heavy quark-antiquark pair and possible light quarks, also known as XYZ states. We give a general review and then focus on the new experimental results on the X(3872) and its bottom-quark partner Xb, the X(3960), the Y(4260), Y(4500), Y(4660), and Y(10750), and the charged charmoniumlike Zc and Zcs states. The observations suggest that we did observe hadronic molecules and we also observed hadronic states with some other quark configurations. Possible further studies at the existing and future facilities are briefly discussed.

Probing charmonium-like XYZ states in hadron\u2013hadron ultraperipheral collisions and electron\u2013proton scattering

Exclusive production of charmonium-like XYZ states in hadron–hadron ultraperipheral collisions (UPCs) and electron–proton scattering are studied employing the effective Lagrangian method. Total cross sections and rapidity distributions of charmonium-like XYZ states are obtained in hadron–hadron UPCs and the electron–proton scattering process. These predictions can be applied to estimate the observed event number of exclusive charmonium-like XYZ states in hadron–hadron UPCs and electron–proton scattering. The results indicate that it is significant to search X(3872) and Z^+_c(3900) in pA UPCs, and the Electron–Ion Collider in China will be an advantageous platform to observe XYZ states in the future.

XYZ spectroscopy at electron-hadron facilities: Exclusive processes

The next generation of electron-hadron facilities has the potential for significantly improving our understanding of exotic hadrons. The XYZ states have not been seen in photon-induced reactions so far. Their observation in such processes would provide an independent confirmation of their existence and offer new insights into their internal structure. Based on the known experimental data and the well-established quarkonium and Regge phenomenology, we give estimates for the exclusive cross sections of several XYZ states. For energies near threshold we expect cross sections of few nanobarns for the Zc(3900)+ and upwards of tens of nanobarn for the X(3872), which are well within reach of new facilities.

XYZ states in BESIII

Since the first XYZ particle X(3872) was observed in 2003, many exotic states have been found by spectroscopy studies in beauty and charm sectors. In this paper, the latest XYZ results obtained by BESIII are reviewed, mainly including X(3872), Y(4260), Y(4660), Zc (3900) and Zc (4020). The spin parties of Zc(3900) have been studied. The comparison between different final states in Y states which are helpful to understand the nature of XYZ particles has been done.

Exotic and conventional quarkonium physics prospects at Belle II

The Belle II experiment belongs to a new generation of B-factories, and it is located at the SuperKEKB collider. Its goal is to collect an integrated luminosity of 50 ab-1, corresponding to a data sample that is 50 times larger than the one collected by its predecessor Belle. From February to July 2018, the machine has completed a commissioning run, achieving a peak luminosity of 5.5 × 1033 cm-2 s-1, and a data sample of about 0.5 fb-1 has been recorded. Belle II is capable of studying the so-called XYZ states with unprecedented precision: heavy exotic hadrons consisting of more than three quarks. First discovered by Belle, these now number in the dozens, and represent the emergence of a new category within quantum chromodynamics. In this paper, a general introduction to the experiment is presented, together with the perspectives for studies of conventional and exotic quarkonium-like states.

Dynamical Approach to Decays of XYZ States

We review the existing results on the exotic XYZ states and their decays obtained within the confined covariant quark model. This dynamical approach is based on a non-local Lagrangian of hadrons with quarks, has built-in quark confinement, and is suited well for the description of different multiquark states, including the four quark ones. We focus our analysis on the various decay modes of five exotic states, X ( 3872 ) , Z c ( 3900 ) , Y ( 4260 ) , Z b ( 10610 ) , and Z b ′ ( 10650 ) , aiming to clarify their internal quark structures. By considering mostly branching fractions and decay widths using the molecular-type or the tetraquark-type interpolating currents, conclusions about the nature of these particles are drawn: the molecular structure is favored for Z c ( 3900 ) , Z b ( 10610 ) , and Z b ′ ( 10650 ) and the tetraquark for X ( 3872 ) and Y ( 4260 ) .

Future Physics Programme of BESIII * * Supported in part by National Key Basic Research Program of China (2015CB856700); National Natural Science Foundation of China (NSFC) (11335008, 11425524, 11625523, 11635010, 11735014, 11822506, 11935018); the Chinese Academy of Sciences (CAS) Large-Scale Scientific Facility Program; the CAS Center for Excellence in Particle Physics (CCEPP); Joint Large-Scale Scientific Facility Funds of the NSFC

There has recently been a dramatic renewal of interest in hadron spectroscopy and charm physics. This renaissance has been driven in part by the discovery of a plethora of charmonium-like XYZ states at BESIII and B factories, and the observation of an intriguing proton-antiproton threshold enhancement and the possibly related X(1835) meson state at BESIII, as well as the threshold measurements of charm mesons and charm baryons. We present a detailed survey of the important topics in tau-charm physics and hadron physics that can be further explored at BESIII during the remaining operation period of BEPCII. This survey will help in the optimization of the data-taking plan over the coming years, and provides physics motivation for the possible upgrade of BEPCII to higher luminosity.

XYZ states at BESIII

In this proceeding, I report the most recent experimental results from BESIII about the XYZ sates. Two new X(3872) decay modes are observed, which is X(3872) → ωJ/ψ and X(3872) → π0χc1(1P). Precise measurement of cross sections of various channels reveal more fine structure about Y states. To study the property of Zc states, the Jp of Zc(3900) is determined with partial wave analysis, and a hint of new decay mode of Zc±(3900) → ρ±ηc are observed.

XYZ at Belle

Recent results of exotic states with heavy quarks, denoted as XYZ states, are presented. The results include searches for the Y(4260) in B meson decays, a spin partner of Y(4630), and the strange Pentaquark $ P_s^ + $. An addition, the measurements of the absolute branching fraction of X(3872) and search for double Zc production is dicussed.

XYZ states as hadronic molecules

In the past decade, a lot of new hadrons containing heavy quarks were discovered which do not fit into the scheme provided by the traditional quark models. Such states are known as the XYZ states and they are conventionally referred to as exotic ones. At present, there is no consensus on their nature, and different models and approaches have been suggested to explain their unusual properties. The talk is devoted to a brief overview of the molecule model for such exotic states.

Exotic hadrons from BESIII

We report the progress in the study of the exotic hadrons, also called XYZ states, at BESIII experiment with its unique data samples in e+ e− annihilation at center-of-mass energies of 3.8–4.6 GeV. The talk covers the observation of the Zc(3900) and Zc(4020) and new measurements related to them; updated measurement of the resonant parameters of the Y(4260) in e+ e−→ π+π− J/ψ and discovery of its new decay modes π+π−ψ(2S), ωχc0, π+π−hc, and D0D∗−π++c.c.; and observation of X(3872) in e+e− annihilation.

Theory of hadronic molecules applied to the XYZ states

In recent years data have been accumulated at various experiments about states in the heavy quarkonium mass range that seem to be inconsistent with the most simple variants of the quark model. In this contribution it is demonstrated that most of those data are consistent with a dominant molecular nature of those states. It is also discussed which kind of observables are sensitive to the molecular component and which are not.

The XYZ states revisited

The BESIII and the LHCb became the leading experiments in the study of the exotic states after the Belle and BaBar experiments finished their data taking in the first decade of this century. We review the progress in the study of the XYZ states at BESIII and LHCb experiments with their unique data samples in [Formula: see text] annihilation at center-of-mass energies of 3.8–4.6 GeV and in [Formula: see text] collision at center-of-mass energies 7, 8, and 13 TeV, respectively. With these data samples, we have deepened our understanding of the most famous charmonium-like states [Formula: see text], [Formula: see text], [Formula: see text], and [Formula: see text], as well as other similar states like the [Formula: see text] and [Formula: see text]. We review the progress in the study of these states and also discuss perspectives at future experiments.

XYZ states at BESIII

The BESIII experiment at the Beijing Electron Positron Collider (BEPCII) provided a significant contribution to the charmonium-like state spectroscopy thanks to the large data samples collected in the center of mass energy region between 3.8 and 4.6 GeV. New and surprising resonant states have been discovered. Their interpretation goes beyond the traditional quark and anti-quark model paradigm of the charmonium: for example, the two isospin triplets Zc(3900) and Zc(4020) that are electrically charged quarkonium-like states. In this proceeding, it will be reported recent studies on XYZ states made by BESIII in particular the radiative transition between various states, i.e. in the channel Y(4260) → γX(3872).