We discuss the production mechanism of a new state, a putative fully charm tetraquark, observed recently by the LHCb at M = 6.9 GeV in the $J/ψJ/ψ$ channel. Both single parton scattering (SPS) and double parton scattering (DPS) mechanisms are considered. We calculate the distribution in the invariant mass of the four-quark system $M_{4c}$ for SPS and DPS production of $c c \bar c \bar c$ in the $k_t$-factorization approach with modern unintegrated gluon distribution functions (UGDFs). The so-calculated contribution of DPS is almost two orders of magnitude larger than the SPS one, but the tetraquark formation mechanism is unknown at present. Imposing a mass window around the resonance position we calculate the corresponding distribution in $p_{t,4c}$ -- the potential tetraquark transverse momentum. The cross section for the $J/ψJ/ψ$ continuum is calculated in addition, again including SPS (box diagrams) and DPS contributions which are of similar size. The formation probability is estimated trying to reproduce the LHCb signal-to-background ratio. The calculation of the SPS $g g \to T_{4c}(6900)$ fusion mechanism is performed in the $k_T$-factorization approach assuming different spin scenarios ($0^+$ and $0^-$). The $0^+$ assignment is preferred over the $0^-$ one by the comparison of the transverse momentum distribution of signal and background with the LHCb preliminary data assuming the SPS mechanism dominance. There is no reliable approach for the DPS formation mechanism of tetraquarks at present as this is a complicated multi-body problem.
Inspired by the recent discovery of the $X(6900)$ meson at {\tt LHCb} experiment, we investigate the inclusive production rate of the $C$-odd fully-charmed tetraquarks associated with light hadrons at the $B$ factory within the nonrelativistic QCD (NRQCD) factorization framework. The short-distance coefficient is computed at lowest order in velocity and $α_s$. Employing the diquark-antidiquark model to roughly estimate the long-distance NRQCD matrix elements, we predict the rate for inclusive production of the $1^{+-}$ $T_{4c}$ state and discuss the observation prospects at {\tt Belle 2} exper…
We study production of the tetraquark state $T_{cc}$ via virtual photon at the B-factories in the QCD factorization framework. We predict the cross section of tetraquark state production in the leading order at the B-factories.
We investigate the production of the fully - heavy tetraquark states $T_{4Q}$ in the $γγ$ interactions present in proton-proton, proton-nucleus and nucleus-nucleus collisions at the CERN Large Hadron Collider (LHC). We focus on the $γγ\rightarrow {\cal{Q}}{\cal{Q}}$ (${\cal{Q}} = J/ψ,\, Υ$) subprocess, mediated by the $T_{4Q}$ resonance in the $s$ - channel, and present predictions for the hadronic cross sections considering the kinematical ranges probed by the ALICE and LHCb Collaborations. Our results demonstrate that the experimental study of this process is feasible and can be used to inve…
The feasibility of tetraquark detection is studied. For the cc\bar{u}\bar{d} tetraquark we show that in present (SELEX, Tevatron, RHIC) and future facilities (LHCb, ALICE) the production rate is promising and we propose some detectable decay channels.
Hadronic states composed of multi-quark flavors may exist in reality since they are not prohibited by QCD. Compact four quark systems of color singlet are classified as tetraquarks. To understand the properties of these states, more theoretical and experimental efforts are needed. In this work, we study charmed tetraquarks with three light flavors using flavor $SU(3)$ symmetry. States with three different light quarks must be in a ${\bf \bar 6 }$ or a ${\bf 15}$ multiplet. We investigate the production of charmed tetraquarks $X_c$ in $B\to X_c (\overline {X}_c) P$ and $B_c \to X_c P$ decays. W…
We develop a model to study tetraquark production in hadronic collisions. We focus on double parton scattering and formulate a version of the color evaporation model for the production of the $X(3872)$ and of the $T_{4c}$ tetraquark, a state composed by the $c \bar{c} c \bar{c}$ quarks. We find that the production cross section grows rapidly with the collision energy $\sqrt{s}$ and make predictions for the forthcoming higher energy data of the LHC.
New data for X(3872) production in B decays provide a separation between X production and decay, sharpen several experimental puzzles and impose serious constraints on all models. Both charged and neutral B decays produce a narrow neutral resonant state that decays to both J/ψρand J/ψω, while no charged resonances in the same multiplet are found. This suggests that the X is an isoscalar resonance whose production conserves isospin, while isospin is violated only in the decay by an electromagnetic interaction allowing the isospin-forbidden J/ψρdecay. A tetraquark isoscalar X model is proposed w…
We apply the newly developed NRQCD factorization formula to analyze the exclusive production of the fully-charmed tetraquark $T_{4c}$ plus a hard photon at $B$ factory. For simplicity, in this work we have concentrated on the associated production of the $0^{++}$ and $2^{++}$ tetraquarks with a photon. With some rough estimates about the size of the unknown nonperturbative NRQCD matrix elements, we predict the production rates of these types of exclusive channels at $\sqrt{s}=10.6$ GeV and also assess their observation prospect at {\tt Belle 2} experiment.
Inclusive production cross sections of the possible exotic state X(3872) in proton-proton, pionp-roton and proton-antiproton collisions are calculated using a statistical based model, which is previously used to describe inclusive charmed and bottomed hadron production cross sections in the low energy region. With the extensions made here, the model is capable to include tetraquarks as well, using the diquark picture of tetraquarks. The evaluated cross section ratio of $Ψ(2S)$ and $X(3872)$ at $\sqrt{s}=7$ TeV agrees well with the measured value.
In the paper we discuss contribution of the doubly intrinsic heavy mechanism into the production of $B_c$ meson, the doubly heavy baryons and the all-charm tetraquark at a future fixed-target experiment at the LHC (AFTER@LHC). The production cross sections and the mean values of Feynman-x for the finale states are presented.
During recent years, the study of exotic hadrons including tetraquarks and pentaquarks has attracted a lot of interests and more studies are in progress experimentally and theoretically. It is well-known that at sufficiently large transverse momentum the dominant production mechanism for standard heavy hadrons (mesons/baryons) is actually the fragmentation so that the same mechanism is also proposed for the production of heavy exotic hadrons. This work is the first attempt to study the direct fragmentation of a heavy quark into ground state heavy tetraquarks in leading order of perturbative QC…
We use the twist dimensions of the operators underlying the dynamical behavior of exclusive production processes as a tool for determining the structure of exotic heavy-quark states such as the $Z_c^+(4430)$ tetraquark. The resulting counting rules predict distinctive fall-offs of the cross sections in center-of-mass energy, thus distinguishing whether the tetraquarks are segregated into di-meson molecules, diquark-antidiquark pairs, or more democratically arranged four-quark states. In addition, we propose straightforward methods of experimentally producing additional exotic multiquark states…
In this study, we investigate the discovery potential of double-charm tetraquarks $T^{\{cc\}}_{[\bar{q}\bar{q}']}$. We find that their production cross sections at the LHCb with $\sqrt{s} = 13$ TeV reach $\mathcal{O}(10^4)$ pb, which indicates that the LHCb has collected $\mathcal{O}(10^8)$ such particles. Through the decay channels of $T^{\{cc\}}_{[\bar{u}\bar{d}]}\to D^{+}K^{-}π^{+}$ or $D^0D^+γ$ (if stable) or $T^{\{cc\}}_{[\bar{u}\bar{d}]}\to D^0D^{*+}\to D^0D^0π^+$ (if unstable), it is highly expected that they get discovered at the LHCb in the near future. We also discuss the productions…
The $X(6900)$ resonance, very recently discovered in the double-$J/ψ$ channel at LHCb experiment, has spurred intensive interest in unravelling the nature of the fully charmed tetraquark state. The aim of this paper is to present a model-independent theoretical framework to study the inclusive production of this novel species of exotic hadrons, the resonances composed of four heavy quark (commonly referred to as $T_{4c}$), at large $p_T$ in hadron collision experiments. Appealing to asymptotic freedom and the fact $m_c\gg Λ_{\rm QCD}$, we propose that the nonpertubative yet universal gluon-to-…
We analyze the Belle data [K. F. Chen {\it et al.} (Belle Collaboration), Phys.\ Rev.\ Lett.\ {\bf 100}, 112001 (2008); I. Adachi {\it et al.} (Belle Collaboration), arXiv:0808.2445] on the processes $e^+ e^- \to Υ(1S)\; π^+π^-, Υ(2S)\; π^+π^-$ near the peak of the $Υ(5S)$ resonance, which are found to be anomalously large in rates compared to similar dipion transitions between the lower $Υ$ resonances. Assuming these final states arise from the production and decays of the $J^{PC}=1^{--}$ state $Y_b(10890)$, which we interpret as a bound (diquark-antidiquark) tetraquark state $[bq][\bar{b}\ba…
Motivated by the observation of exotic structure around 6900MeV in the $J/ψ$-pair mass spectrum using proton-proton collision data by the LHCb collaboration, we study the spectra of fully-heavy tetraquarks within Bethe-Salpeter equation and Regge trajectory relation. The $X(6900)$ may be explained as a radially excited state with quark content $cc\bar{c}\bar{c}$ and spin-parity $0^{++}(3S)$ or $2^{++}(3S)$ or an orbitally excited $2P$ state. New $cc\bar{c}\bar{c}$ structures around 6.0GeV, 6.5GeV, and 7.1GeV are predicted together. Other $bb\bar{b}\bar{b}$ and $bc\bar{b}\bar{c}$ structures whi…
Fully charmed tetraquark production in forward rapidity $pp$ collisions at LHC and FCC energies
Universidad de Alcalá (UAH)（阿尔卡拉大学）；Federal University of Grande Dourados（大杜拉多联邦大学）；Universidade do Estado de Santa Catarina（圣卡塔琳娜州立大学）；Federal University of Pelotas（佩洛塔斯联邦大学）；Universidade de São Paulo（圣保罗大学）
The article is devoted to double J/psi-meson production at LHC. Theoretical predictions for pp -> 2J/psi+X cross section at sqrt{s}=7 TeV for different kinematical restrictions are presented. Special attention is payed to possible contribution of novel particles -- tetraquarks build from four c-quarks. According to presented in our article estimates, it is quietly possible to observe at least one of these state (tensor meson) experimentally.
We discuss the production of the exotic doubly-charmed tetraquark mesons ${\rm T}_{{\rm c}{\rm c}}({\rm c}{\rm c}\bar{\rm u}\bar{\rm d})$ from electron-positron collisions. ${\rm T}_{{\rm c}{\rm c}}({\rm c}{\rm c}\bar{\rm u}\bar{\rm d})$ is a compact exotic hadron whose binding energy is provided by the diquark correlations. We evaluate the production cross section in the electron-positron collisions using the nonrelativistic QCD framework, and investigate the difference of the production cross section for different color configurations in two charm quarks (antitriplet and sextet), where the m…
We investigate the production of exotic tetraquarks, $QQ\bar{q}\bar{q} \equiv T_{QQ}$ ($Q=c$ or $b$ and $q=u$ or $d$), in relativistic heavy-ion collisions using the quark coalescence model. The $T_{QQ}$ yield is given by the overlap of the density matrix of the constituents in the emission source with the Wigner function of the produced tetraquark. The tetraquark wave function is obtained from exact solutions of the four-body problem using realistic constituent models. The production yields are typically one order of magnitude smaller than previous estimations based on simplified wave functio…
The high prompt production cross section of X(3872) at hadron colliders has shown to be very informative about the quark nature of the X, Y, Z states. We present here a number of results on X production in pp(pbar) collisions obtained with Monte Carlo hadronization methods and illustrate what can be learned from their use to improve our understanding of exotic states. In particular, a comparison between antideuteron and X production cross sections is proposed. Hadronization might be the key to solve the problem of the extra states expected in diquark-antidiquark models which are naturally favo…
We discuss the production mechanism of fully charm tetraquark, observed recently by the LHCb at M = 6.9 GeV in the $J/ψJ/ψ$ channel. Both single parton scattering (SPS) and double parton scattering (DPS) mechanisms are considered. We calculate the distribution in the invariant mass of the four-quark system $M_{4c}$ for SPS and DPS production of $c c \bar c \bar c$ in the $k_t$-factorization approach. We present transverse momentum distribution in $p_{t,4c}$ for $c \bar c c \bar c$ system in a mass window around tetraquark mass. The calculation of the SPS $g^* g^* \to T_{4c}(6900)$ fusion mecha…
Recently, the Belle Collaboration has updated the analysis of the cross sections for the processes $e^+ e^- \to Υ(nS)\, π^+ π^-$ ($n = 1,\, 2,\, 3$) in the $e^+ e^-$ center-of-mass energy range from 10.52 to 11.02~GeV. A new structure, called $Y_b (10750)$, with the mass $M (Y_b) = (10752.7 \pm 5.9^{+0.7}_{-1.1})$~MeV and the Breit-Wigner width $Γ(Y_b) = (35.5^{+17.6 +3.9}_{-11.3 -3.3})$~MeV was observed. We interpret $Y_b (10750)$ as a compact $J^{PC} = 1^{--}$ state with a dominant tetraquark component. The mass eigenstate $Y_b (10750)$ is treated as a linear combination of the diquark-antid…
Background: A resonance has been observed by the ANDY Collaboration at the Relativistic Heavy-Ion Collider at Brookhaven National Laboratory in Cu+Au collisions at center-of-mass energy $\sqrt{s} = 200$ GeV and at forward rapidity with an average mass of 18.15 GeV. The Collaboration suggests that it is a $b \overline b b \overline b$ tetraquark state decaying to two $Υ$(1S) states, each measured through the $Υ\rightarrow ggg$ channel. Purpose: Their suggestion is investigated assuming that the two $Υ$ states are produced through the materialization of a $|uud b\overline b b \overline b \rangle…
Structure and production of doubly charmed tetraquarks T_cc (cc ubar dbar) are studied from the viewpoint of color configurations. Based on the diquark correlation, the tetraquark T_cc with I(JP)=0(1+) is considered to be stable against strong decay. We discuss that the mixing probability of color antitriplet and sextet cc components in T_cc is suppressed by 1/m_c^2, so the two configurations are separately realized in the heavy quark limit. Utilizing the nonrelativistic QCD framework, we evaluate the production cross sections of T_cc in electron-positron collisions. The momentum dependence of…
Recently, the Belle Collaboration has updated the analysis of the cross sections for the processes $e^+ e^- \to Υ(nS)\, π^+ π^-$ ($n = 1,\, 2,\, 3$) in the $e^+ e^-$ center-of-mass energy range from 10.52 to 11.02 GeV. A new structure, called here $Y_b (10750)$, with the mass $M (Y_b) = (10752.7 \pm 5.9^{+0.7}_{-1.1})$ MeV and the Breit-Wigner width $Γ(Y_b) = (35.5^{+17.6 +3.9}_{-11.3 -3.3})$ MeV was observed \cite{Abdesselam:2019gth}. We interpret $Y_b (10750)$ as a compact $J^{PC} = 1^{--}$ state with a dominant tetraquark component. The mass eigenstate $Y_b (10750)$ is treated as a linear c…
We propose to search for a tetraquark candidate $X(ud\bar{s}\bar{s})$ in $pn\to ΛΛX(ud\bar{s}\bar{s})\to ΛΛK^+K^0$ or $ΛΛKK^*$. The existence of tetraquark state $X(ud\bar{s}\bar{s})$ with $J^P=0^+$, $1^-$ or $1^+$ was predicted in the literature based on specific diquark effective degrees of freedom inside hadrons. In order to understand the underlying dynamics for exotic hadrons, a search for the tetraquark $X(ud\bar{s}\bar{s})$ is strongly recommended. The proposed reaction involves two $Λ$ production, of which the narrow widths make it a great advantage in the analysis of the final state m…
We consider the production and decay of multiquark systems in the framework of string models where the hadron structure is determined by valence quarks together with string junctions. We show that the low mass multiquark resonances can be very narrow.
In the LHC collider a significant rate of events with double parton scattering is expected. This will be the leading mechanism for production of two b-bbar pairs. We estimate the probability of binding two b quarks into a diquark and the probability of dressing this diquark into a b-b-ubar-dbar ISP=01+ tetraquark. Calculations shows that that this bound state of two B mesons is stable against the strong interaction and has a life time of the order of ps. We estimate that the production rate at luminosity L=0.1 events per second will be about 6 tetraquarks per hour or more.
We present the first study of the cusp effect (the movement of resonant poles due to the proximity of multiparticle thresholds) caused by the creation of diquark-antidiquark pairs. The cusp profile for such states is obtained from constituent counting rules. We compare the effectiveness of diquark cusps in moving resonant poles with that from a phenomenological form commonly used for meson-pair creation, and find that mesons tend to be more effective at lower energies $({\it e.g.}$, the $K\overline{K}$ threshold), while diquarks tend to be more effective at the charm [$X(3872)$] scales and abo…
Beauty tetraquark states $X(\bar b q'q'' \bar q )$ composed of $ \bar b s u \bar d$, $\bar b d s \bar u$, and $\bar b u d \bar s$, are unique that all the four valence quarks are different. Although the claim of existence of the first two states by D0 was not confirmed by data from LHCb, the possibility of such states still generated a lot of interests and should be pursued further. Non-observation of $X(\bar b q'q'' \bar q )$ states by LHCb may be just due to a still lower production rate than the limit of LHCb or at some different mass ranges. In this work we use light quark $SU(3)$ flavor s…
We study the properties of fully-heavy tetraquarks at finite temperature and their production in high-energy nuclear collisions. We obtain the masses and wave functions of the exotic hadron states $cc\bar c\bar c$ and $bb\bar b\bar b$ by solving the four-body Schrödinger equation in vacuum and strongly interacting matter. In vacuum, the tetraquarks are above the corresponding meson-meson mass threshold, and the newly observed exotic state $X(6900)$ might be a $cc\bar c\bar c$ state with quantum number $J^{PC}=0^{++}$ or $1^{+-}$. In hot medium, the temperature dependence of the tetraquark mass…
Prospects for discovering strongly decaying doubly heavy $T_{bc}$ tetraquark states at LHCb
Institute of High Energy Physics, Chinese Academy of Science（中国科学院高能物理研究所）；University of Chinese Academy of Science（中国科学院大学）；Laboratoire de Physique Théorique et Hautes Energies (LPTHE), UMR 7589, Sorbonne Université et CNRS（索邦大学与法国国家科学研究中心联合理论物理与高能物理实验室）
Lindblad-driven recombination of the X(3872) tetraquark
Instituto Galego de Física de Altas Enerxías IGFAE, Universidade de Santiago de Compostela（加利西亚高等物理研究所、圣地亚哥-德孔波斯特拉大学）；Departament de Física Quàntica i Astrofísica and Institut de Ciències del Cosmos, Universitat de Barcelona（量子天体物理学系与宇宙科学研究所、巴塞罗那大学）
The present work reviews the various aspects of the extension of the large-$N_c$ approach, as had been proposed and developed by 't Hooft, to the case of tetraquark states, which are a category of the general class of exotic states, also called multiquark states, whose internal valence-quark structure does not match with that of ordinary hadrons, and which have received, in recent years, many experimental confirmations. The primary question of describing, or probing, on theoretical grounds, multiquark states is first examined. The signature of such states inside Feynman diagrams in relation wi…
We present a study of the isospin-violating one-pion strong decays of single heavy tetraquarks $X_Q = X(s q \bar q \bar Q)$, $Q=c, b$, and $q=u, d$ with spin-parity $J^P = 0^+$. We assume that the tetraquarks have the configuration of a color diquark and a antidiquark. Three mechanisms of isospin violation can contribute to the decay rate: (1) mixing of the $X(s u \bar u \bar Q)$ and $X(s d \bar d \bar Q)$ tetraquark currents, (2) an explicit $m_d-m_u$ quark mass difference in the quark diagrams describing the corresponding decay transitions and (3) $π^0-η$ mixing in the final state. Our main …
Inspired by the observation of the fully-charm tetraquark $X(6900)$ state at LHCb, the production of $X(6900)$ in $\bar{p}p\rightarrow J/ψJ/ψ$ reaction is studied within an effective Lagrangian approach and Breit-Wigner formula. The numerical results show that the cross section of $X(6900)$ at the c.m. energy of 6.9 GeV is much larger than that from the background contribution. Moreover, we estimate dozens of signal events can be detected by D0 experiment, which indicates that searching for the $X(6900)$ via antiproton-proton scattering may be a very important and promising way. Therefore, rel…
Heavy-ion collisions provide a unique opportunity to study the nature of X(3872) compared with electron-positron and proton-proton (antiproton) collisions. We investigate the centrality and momentum dependence of X(3872) in heavy-ion collisions via the Langevin equation and instant coalescence model (LICM). When X(3872) is treated as a compact tetraquark state, the tetraquarks are produced via the coalescence of heavy and light quarks near the quantum chromodynamic (QCD) phase transition due to the restoration of the heavy quark potential at $T\rightarrow T_c$. In the molecular scenario, loose…
Verifying the existence of bound states of gluons and distinguishing them from conventional quark-antiquark, hybrid or tetraquark states has remained a key problem in QCD. We show that QCD counting rules for the power-law fall-off of production cross sections at high momentum transfer can be used to distinguish gluonium states from conventional hadrons. The valence two-gluon contribution to a 0^+ gluonium bound state has L=0 and thus twist (dimension minus spin of their minimum interpolating operators) tau=2. The competing twist assignments for scalar f_0 mesons have twist tau = 3 for the vale…
