Meson Pairs Research Articles

Exclusive photoproduction of B_{c}^{pm } and bottomonia pairs

In this paper we analyze the photoproduction of heavy quarkonia pairs which include b-quarks, such as B_{c}^{+}B_{c}^{-}-mesons or charmonium-bottomonium pairs. Compared to charmonia pair production, these channels get contributions only from some subsets of diagrams, and thus allow for a better theoretical understanding of different production mechanisms. In contrast to the production of hidden-flavor quarkonia, for the production of B_{c}-meson pairs there are no restrictions on internal quantum numbers in the suggested mechanisms. Using the Color Glass Condensate approach, we estimated numerically the production cross-sections in the kinematics of the future electron–hadron colliders and the ultraperipheral collisions at LHC. We found that the production of J/psi ,eta _{c} and B_{c}^{+}B_{c}^{-} meson pairs are the most promising channels for studies of quarkonia pair production.

X(3872) , X(4014) , and their bottom partners at finite temperature

The properties of the $X(3872)$ and its spin partner, the $X(4014)$, are studied both in vacuum and at finite temperature. Using an effective hadron theory based on the hidden-gauge Lagrangian, the $X(3872)$ is dynamically generated from the $s$-wave rescattering of a pair of pseudoscalar and vector charm mesons. By incorporating the thermal spectral functions of open charm mesons, the calculation is extended to finite temperature. Similarly, the properties of the $X(4014)$ are obtained out of the scattering of charm vector mesons. By applying heavy-quark flavor symmetry, the properties of their bottom counterparts in the axial-vector and tensor channels are also predicted. All the dynamically generated states show a decreasing mass and acquire an increasing decay width with temperature, following the trend observed in their meson constituents. These results are relevant in relativistic heavy-ion collisions at high energies, in analyses of the collective medium formed after hadronization or in femtoscopic studies, and can be tested in lattice-QCD calculations exploring the melting of heavy mesons at finite temperature.

Chiral Lagrangians for strong decays K1→Kρ(ω)

A triangular quark diagram describes the vertex K1Kω with axial-vector, vector, and pseudoscalar mesons is considered in the leading order of 1NC. The application of the obtained vertex to the hadronic decays of the τ-lepton with the production of Kω, Kφ  meson pairs in the final state is discussed. Calculation of quark diagrams are considered within the  SU(3) symmetric chiral Lagrangians, which describe the interactions of four meson nonets: scalar, pseudoscalar, vector, and axial-vector in the ground and in the first radially excited states. The calculated integral decay widths of K1(1270)→K[ω,ρ] are in the agreement with the experimental data of the BES-III and Belle collaborations obtained at the BEPC II and KEK colliders. It is shown that the axial-vector channel with the intermediate meson K1A with quantum numbers  JPC=1++ plays a dominant role in describing the decay widths of τ→K[ω,ρ]ντ. In  lepton decays, the contact channel and the channel with the axial vector meson K1A are taken into account. The first of them is related with the intermediate W  boson, which products a meson pair. The second channel is related with the intermediate W boson, which transits into the axial vector state K1A and also products meson pairs. Consideration of these two channels independently of each other allows us to study the processes in more detail. The splitting of the strange axial vector state K1A into two physical mesons K1(1270) and K1(1400) due to the mixing of axial vector mesons from nonets 3P1 and  1P1 is also taken into account. The negative interference of the contact channel with the axial vector channel is established. The dependences of the integral decay widths of τ→K[ω,ρ]ντ on the value of the mixing angle of axial-vector mesons K1A and K1B are studied. A comparative analysis of the results with experimental data and theoretical estimates of other authors is carried out. The obtained theoretical predictions are in satisfactory agreement with the experimental data.

Strong decay widths and mass spectra of charmed baryons

The total decay widths of the charmed baryons are calculated by means of the $^{3}{P}_{0}$ model. Our calculations consider in the final states: the charmed baryon-(vector/pseudoscalar) meson pairs and the (octet/decuplet) baryon-(pseudoscalar/vector) charmed meson pairs, within a constituent quark model. Furthermore, we calculate the masses of the charmed baryon ground states and their excitations up to the $D$-wave in a constituent quark model both in the three-quark and in the quark-diquark schemes, utilizing a Hamiltonian model based on a harmonic oscillator potential plus a mass splitting term that encodes the spin, spin-orbit, isospin, and flavor interactions. The parameters of the Hamiltonian model are fitted to the experimental data of the charmed baryon masses and decay widths. As the experimental uncertainties of the data affect the fitted model parameters, we have thoroughly propagated these uncertainties into our predicted charmed baryon masses and decay widths via a Monte Carlo bootstrap approach, which is often absent in other theoretical studies on this subject. Our quantum number assignments and predictions of the masses and strong partial decay widths are in reasonable agreement with the available data. Thus, our results show the ability to guide future measurements in LHCb, Belle and Belle II experiments. Finally, the appendices provide some details of our calculations, in which we include the flavor coupling coefficients, which are useful for further theoretical investigations.

Measurements of the branching fractions B(B¯0→D*+π−) and B(B¯0→D*+K−) and tests of QCD factorization

Using (771.6±10.6)×106 BB¯ meson pairs recorded by the Belle experiment at the KEKB e+e− collider, we report the branching fractions B(B¯0→D*+π−)=(2.62±0.02±0.09)×10−3 and B(B¯0→D*+K−)=(2.22±0.06±0.08)×10−4; the quoted uncertainties are statistical and systematic, respectively. A measurement of the ratio of these branching fractions is also presented, RK/π=B(B¯→D*+K−)/B(B¯→D*+π−)=(8.41±0.24±0.13)×10−2, where systematic uncertainties due to the D*+ meson reconstruction cancel out. Furthermore, we report a new QCD factorization test based on the measured ratios for B¯→D*+h− and B¯→D*+ℓ−ν decays at squared momentum transfer values equivalent to the mass of the h=π or K hadron. The parameters |a1(h)| are measured to be |a1(π)|=0.884±0.004±0.003±0.016 and |a1(K)|=0.913±0.019±0.008±0.013, where the last uncertainties account for all external inputs. These values are approximately 15% lower than those expected from theoretical predictions. Subsequently, flavor SU(3) symmetry is tested by measuring the ratios for pions and kaons, |a1(K)|2/|a1(π)|2=1.066±0.042±0.018±0.023, as well as for different particle species. The ratio is consistent with unity and therefore no evidence for SU(3) symmetry breaking effects is found at the 5% precision level.Received 3 July 2022Accepted 10 October 2022DOI:https://doi.org/10.1103/PhysRevD.107.012003Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP3.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasBranching fractionPhysical SystemsBottom mesonsParticles & Fields

Accessing GPDs Through the Exclusive Photoproduction of a Photon–Meson Pair with a Large Invariant Mass

Accessing GPDs Through the Exclusive Photoproduction of a Photon–Meson Pair with a Large Invariant Mass

Fully Heavy Tetraquark Spectroscopy in the Relativistic Quark Model

Masses of the ground and excited (1P, 2S, 1D, 2P, 3S) states of the fully heavy tetraquarks, composed of charm (c) and bottom (b) quarks and antiquarks, are calculated in the diquark–antidiquark picture within the relativistic quark model based on the quasipotential approach and quantum chromodynamics. The quasipotentials of the quark–quark and diquark–antidiquark interactions are constructed similarly to the previous consideration of mesons and baryons. Relativistic effects are consistently taken into account. A tetraquark is considered a bound state of a diquark and an antidiquark. The finite size of the diquark is taken into account, using the form factors of the diquark–gluon interaction. It is shown that most of the investigated states of tetraquarks lie above the decay thresholds into a meson pair; as a result, they can be observed only as broad resonances. The narrow state X(6900) recently discovered in the di-J/ψ production spectrum by the LHCb, CMS and ATLAS Collaborations corresponds to an excited state of the fully charmed tetraquark. Other recently discovered exotic heavy resonances, X(6200), X(6400), X(6600), X(7200), and X(7300), can also be interpreted as the different excitations of the fully charmed tetraquark.

The two-channel exotic charmonium-like resonances in the mass region (3900–4700) MeV

Numerous resonances in the c{{bar{c}}} and 4q systems, containing c{{bar{c}}} plus s{{bar{s}}} quarks (or light q{{bar{q}}}) were observed during last decades and recently the LHCb has found a remarkable narrow peak T_{cc}(3875) in the D D^* system. Besides there are several highly excited charmonium-like resonances, which can be treated as the shifted standard charmonium states. We analyze all these groups of the resonances in the mass region (3900–4700) MeV, using relativistic strong coupling theory with possible channel coupling phenomena. For the shifted charmonium states conventional charmonium spectrum is presented, being calculated with the relativistic string Hamiltonian, which does not contain fitting parameters, while for high excitations the universal flattened confining potential is used. It is shown that X(4274), X(4500), X(4700) can be identified as 3,^3P_1, 4,^3P_0, 5,^3P_0 states. The group of exotic states are considered using the Extended Recoupling Model, where two mesons m_1,m_2 transfer into another pair of mesons m_3, m_4 and back (infinite number of times), creating the four-quark resonance. Within this approach the resonances – T_{cc}(3875), Z_c(3900), X(3915), Z_{cs}(3985), X(4014), and X(4140) – can be explained as the exotic four-quark states in the S-wave decay channels.

Role of meson interactions in the Ds+→π+π+π−η decay

We perform a theoretical study of the $D_s^{+}\to \pi^{+}\pi^{+}\pi^{-}\eta$ decay. We look first at the basic $D_s^{+}$ decay at the quark level from external and internal emission. Then hadronize a pair or two pairs of $q\bar{q}$ states to have mesons at the end. Posteriorly the pairs of mesons are allowed to undergo final state interaction, by means of which the $a_0(980)$, $f_0(980)$, $a_1(1260)$, and $b_1(1235)$ resonances are dynamically generated. The $G$-parity is used as a filter of the possible channels, and from those with negative $G$-parity only the ones that can lead to $\pi^{+}\pi^{+}\pi^{-}\eta$ at the final state are kept. Using transition amplitudes from the chiral unitary approach that generates these resonances, and a few free parameters, we obtain a fair reproduction of the six mass distributions reported in BESIII experiment.

A new group of doubly charmed molecule with T-doublet charmed meson pair

Inspired by the observation of the doubly charmed tetraquark state Tcc+ at the LHCb Collaboration, we systematically study the S-wave interactions between a pair of charmed mesons (D1,D2⁎) in the T-doublet, where we adopt the one-boson-exchange model and consider both the S-D wave mixing and coupled channel effects. Our numerical results suggest that the prime doubly charmed molecular tetraquark candidates are the S-wave D1D1 state with I(JP)=0(1+), the S-wave D1D2⁎ states with I(JP)=0(1+,2+,3+), and the S-wave D2⁎D2⁎ states with I(JP)=0(1+,3+). The S-wave D1D1 state with I(JP)=1(2+), the S-wave D1D2⁎ state with I(JP)=1(3+), and the S-wave D2⁎D2⁎ state with I(JP)=1(4+) may be the possible isovector doubly charmed molecular tetraquark candidates. We expect the experiments like the LHCb or Belle II collaborations to search for these predicted doubly charmed molecular tetraquarks near the D1D1, D1D2⁎, and D2⁎D2⁎ thresholds in the future.

Scalar resonances in the final state interactions of the decays D0→π0π0π0,π0π0η,π0ηη

We investigate the scalar resonances in the processes of $D^{0} \rightarrow \pi^{0}\pi^{0}\pi^{0}, \pi^{0}\pi^{0}\eta, \pi^{0}\eta\eta$ decays based on the chiral unitary approach for the final state interaction. We start from singly Cabibbo-suppressed production diagrams which provide a primary quark pair to hadronize two pseudoscalar mesons in $D^{0}$ decays. The resonances $f_{0}(500)$, $f_{0}(980)$ and $a_{0}(980)$ are dynamically produced from the final state interactions of the meson pairs. In our results, the experimental data for the $\pi^{0}\eta$ invariant mass spectrum of the $D^{0} \rightarrow \pi^{0}\eta\eta$ decay can be described well. We also make the predictions for the $\pi^{0}\pi^{0}$ invariant mass spectrum of the $D^{0} \rightarrow \pi^{0}\pi^{0}\pi^{0}$, where the $f_{0}(980)$ can be found, and for the $\pi^{0}\pi^{0}$, $\pi^{0}\eta$ invariant mass spectrum of the $D^{0} \rightarrow \pi^{0}\pi^{0}\eta$, where the $f_{0}(500)$, $f_{0}(980)$ and $a_{0}(980)$ appear. Furthermore, the branching ratios of each decay channel are predicted. We expect more accurate measurements of these decays to better understand the nature of the states $f_{0}(500)$, $f_{0}(980)$ and $a_{0}(980)$.

Exploring new possibilities to discover a light pseudo-scalar at LHCb

We study the possibility of observing a light pseudo-scalar a at LHCb. We target the mass region 2.5,mathrm{GeV}lesssim m_alesssim 60,mathrm{GeV} and various decay channels, some of which have never been considered before: muon pairs, tau pairs, D meson pairs, and di-photon. We interpret the results in the context of models of 4D Composite Higgs and Partial Compositeness in particular.

Analysis of coupled-channel potentials with quark and hadron degrees of freedom

The quark-antiquark potentials are known to be confining in the absence of the q̅q pair creation. On the other hand, the inter-hadron potentials vanish at large distance, because the interaction range is limited by the inverse pion mass. When the q̅q pair creation and annihilation are switched on, the channel coupling occurs between the quark and hadron degrees of freedom, modifying the behavior of potentials. In this work, we investigate the properties of the effective potentials obtained by eliminating one of the channels. We show that the coupling to the eliminated channel induces a non-local and energy dependent effective potential, irrespective of the properties of the transition potential. In addition, when the hadron channel having continuous scattering eigenstates is eliminated, the resulting inter-quark potential contains an imaginary part above the threshold to describe the decay effect into the meson pair.

Tcc+ decays: Differential spectra and two-body final states

The recently discovered tetraquark, $T_{cc}^+$, has quark content $cc\bar{u}\bar{d}$ and a mass that lies just below open charm thresholds. Hence it is reasonable to expect the state to have a significant molecular component. We calculate the decay of the $T_{cc}^+$ in a molecular interpretation using effective field theory. In addition we calculate differential spectra as a function of the invariant mass of the final state charm meson pair. These are in good agreement with spectra measured by LHCb. We also point out that if shallow bound states of two pseudoscalar charm mesons exist, then two-body decays to those bound states and a single pion or photon can significantly enhance the width of the $T_{cc}^+$.

Pure annihilation decay of strange beauty meson into two charm heavy mesons

In this study, the heavy to heavy decay of is evaluated through the factorization approach by using the final state interaction as an effective correction. Under the factorization approach, this decay mode occurs only through the annihilation process, so a small amount is produced. Feynman's rules state that six meson pairs can be assumed for the intermediate states before the final meson pairs are produced. By taking into account the effects of twelve final state interaction diagrams in the calculations, a significant correction is obtained. These effects correct the value of the branching ratio obtained by the pure factorization approach from to . The value obtained for the branching ratio of the decay is consistent with the experimental results.

Global determination of two-meson distribution amplitudes from three-body B decays in the perturbative QCD approach

We perform a global analysis of three-body charmless hadronic decays $B\to VP_3\to P_1P_2P_3$ in the perturbative QCD (PQCD) approach, where $V$ denotes an intermediate vector resonance, and $P_i$, $i=1,2,3$, denote final-state pseudoscalar mesons. Fitting the PQCD factorization formulas at leading order in the strong coupling $\alpha_s$ to measured branching ratios and direct $CP$ asymmetries, we determine the Gegenbauer moments in the two-meson distribution amplitudes (DAs) for the meson pairs $P_1P_2=\pi\pi, K\pi, KK$. The fitted Gegenbauer moments are then employed to make predictions for those observables, whose data are excluded in the fit due to larger experimental uncertainties. A general consistency between our predictions and data is achieved, which hints the validity of the PQCD formalism for the above three-body $B$ meson decays and the universality of the nonperturbative two-meson DAs. The obtained two-meson DAs can be applied to PQCD studies of other multi-body $B$ meson decays involving the same meson pairs. We also attempt to determine the dependence of the Gegenbauer moments on the meson-pair invariant mass, and demonstrate that this determination is promising, when data become more precise.

Charming synergies: the role of charm-threshold studies in the search for physics beyond the Standard Model

Measurements performed with pairs of charm mesons produced at threshold from the decay of the $\psi(3770)$ resonance are of great value in flavour physics. The quantum correlation that exists between the two mesons allows unique access to strong-phase information, which is essential input to flavour-physics studies conducted in other environments. An excellent example from the BESIII collaboration is a recent determination of the strong-phase difference between $D^0$ and $\bar{D}^0$ mesons in the decay $D^0 \to K^0_S\pi^+\pi^-$, which has enabled recent measurements to be performed of the $C\!P$-violating phase $\gamma$ and $D^0-\bar{D}^0$ oscillations by the LHCb experiment at CERN. These $\psi(3770)$ data, and also those collected just above the thresholds for $D_s^+$ and $\Lambda_c^+$ production, can also be exploited in many other ways that are of benefit to flavour-physics studies. These synergies are reviewed, and the need for larger threshold data samples in the near future is emphasised.

Continuum approach to real time dynamics of(1+1)Dgauge field theory: Out of horizon correlations of the Schwinger model

We develop a truncated Hamiltonian method to study nonequilibrium real time dynamics in the Schwinger model - the quantum electrodynamics in D=1+1. This is a purely continuum method that captures reliably the invariance under local and global gauge transformations and does not require a discretisation of space-time. We use it to study a phenomenon that is expected not to be tractable using lattice methods: we show that the 1+1D quantum electrodynamics admits the dynamical horizon violation effect which was recently discovered in the case of the sine-Gordon model. Following a quench of the model, oscillatory long-range correlations develop, manifestly violating the horizon bound. We find that the oscillation frequencies of the out-of-horizon correlations correspond to twice the masses of the mesons of the model suggesting that the effect is mediated through correlated meson pairs. We also report on the cluster violation in the massive version of the model, previously known in the massless Schwinger model. The results presented here reveal a novel nonequilibrium phenomenon in 1+1D quantum electrodynamics and make a first step towards establishing that the horizon violation effect is present in gauge field theory.

Pi ^-prightarrow eta ^{(prime )}, pi ^- p in the double-Regge region

The production of eta ^{(prime )}pi pairs constitutes one of the golden channels to search for hybrid exotics, with explicit gluonic degrees of freedom. Understanding the dynamics and backgrounds associated to eta ^{(prime )}pi production above the resonance region is required to impose additional constraints to the resonance extraction. We consider the reaction pi ^-prightarrow eta ^{(prime )} pi ^- ,p measured by COMPASS. We show that the data in 2.4< m_{eta ^{(prime )}pi } < 3.0{mathrm {,GeV}} can be described by amplitudes based on double-Regge exchanges. The angular distribution of the meson pairs, in particular in the eta ' pi channel, can be attributed to flavor singlet exchanges, suggesting the presence of a large gluon content that couples strongly to the produced mesons.

Computation of the quarkonium and meson-meson composition of the ϒ(nS) states and of the new ϒ(10753) Belle resonance from lattice QCD static potentials

We compute the composition of the bottomonium $\mathrm{\ensuremath{\Upsilon}}(nS)$ states [including $\mathrm{\ensuremath{\Upsilon}}(10860)$] and the new $\mathrm{\ensuremath{\Upsilon}}(10753)$ resonance reported by Belle in terms of quarkonium and meson-meson components. We use a recently developed novel approach utilizing lattice QCD string breaking potentials for the study of resonances. This approach is based on the diabatic extension of the Born-Oppenheimer approximation and the unitary emergent wave method and allows us to compute the poles of the $\mathrm{S}$ matrix. We focus on $I=0$ bottomonium $S$ wave bound states and resonances, where the Schr\"odinger equation is a set of coupled differential equations. One of the channels corresponds to a confined heavy quark-antiquark pair $\overline{b}b$, and the others correspond to pairs of heavy-light mesons. In a previous study, only one meson-meson channel ${\overline{B}}^{(*)}{B}^{(*)}$ was considered. Now, we also include the closed strangeness channel ${\overline{B}}_{s}^{(*)}{B}_{s}^{(*)}$, extending our formalism significantly to have a more realistic description of bottomonium. We confirm the new Belle resonance $\mathrm{\ensuremath{\Upsilon}}(10753)$ as a dynamical meson-meson resonance with around 76% meson-meson content. Moreover, we identify $\mathrm{\ensuremath{\Upsilon}}(4S)$ and $\mathrm{\ensuremath{\Upsilon}}(10860)$ as states with both sizable quarkonium and meson-meson contents. With these results, we contribute to the clarification of ongoing controversies in the vector bottomonium spectrum.