Heavy Quark Spin Symmetry Research Articles

Exclusive decays $\chi_{cJ}\rightarrow K^{\ast} (892)K$ χ c J → K * ( 892 ) K within the effective field theory framework

We study hadronic decays $\chi_{cJ}\rightarrow K^*(892)\bar{K} $ within the effective field theory framework. We consider the colour-singlet and colour-octet contributions and study their properties using (p)NRQCD effective theory. We show that infrared singularities in collinear integrals of the colour-singlet amplitudes can be absorbed into the renormalisation of the colour-octet matrix elements. The heavy quark spin symmetry allows us to establish a relation between the colour-octet matrix elements and to define the spin symmetry breaking corrections which are free from infrared singularities. We apply obtained results for a phenomenological description of the branching fractions.

Radiative and ρ transitions between a heavy quarkonium and isovector four-quark states

The recent observation and measurement of the decay $Z_c(3900) \to \rho \eta_c$ provides the data on the relative strength of the pion and $\rho$ coupling in the corresponding transitions between exotic resonances and pure heavy quarkonium. It is argued that using these data, the heavy quark limit for the $c$ and $b$ quarks, the heavy quark spin symmetry (HQSS) and the vector dominance for photon emission by the light quarks, one can (approximately) quantitatively estimate the rates of the radiative transitions from $\Upsilon(5S)$ to the expected $G$-odd states of molecular bottomonium $W_{bJ}$. The estimate of the cross section of the processes $e^+e^- \to \gamma W_{bJ}$ at the maximum of the $\Upsilon(5S)$ resonance comes out in the ballpark of 0.1\,pb, which sets a benchmark for a possible search for these processes at BelleII.

D*D*D¯ and D*D*D¯* three-body systems

The hidden charm $X(3872)$ resonance is usually thought to be a $D^{*0} \bar{D}^0$ meson-antimeson molecule with quantum numbers $J^{PC} = 1^{++}$. If this is the case, there is the possibility that there might be three body bound states with two charmed mesons and a charmed antimeson. Here we argue that the theoretical existence of this type of three body molecules is expected from heavy quark spin symmetry. If applied to the two body sector, this symmetry implies that the interaction of the $D^{*0} \bar{D}^{*0}$ meson-antimeson pair in the $J^{PC} = 2^{++}$ channel is the same as in the $J^{PC} = 1^{++}$ $D^{*0} \bar{D}^0$ case. From this we can infer that the $J^P = 3^{-}$ $D^{*0} D^{*0} \bar{D}^{*0}$ molecule will be able to display the Efimov effect if the scattering length of the $2^{++}$ channel is close enough to the unitary limit. Heavy quark spin symmetry also indicates that the $J^P = 2^{-}$ $D^{*0} D^{*0} \bar{D}^0$ molecule is analogous to the $J^P = 3^{-}$ $D^{*0} D^{*0} \bar{D}^{*0}$ one. That is, it can also have a geometric spectrum. If we consider these triply heavy trimers in the isospin symmetric limit, the Efimov effect disappears and we can in principle predict the fundamental state of the $2^-$ $D^*D^*\bar{D}$ and $3^-$ $D^* D^* \bar{D}^*$ systems. The same applies to the $B^*B^* \bar{B}^*$ system: if the $Z_b(10650)$ is an isovector $B^* \bar{B}^*$ molecule then the $0^-$ isodoublet and the $1^-$, $2^-$ isoquartet $B^* B^* \bar{B}^*$ trimers might bind, but do not display Efimov physics. Finally from heavy flavour symmetry it can be argued that scattering in the $B D$ two-body system might be resonant. This would in turn imply the possibility of Efimov physics in the $B B D$ three body system.

S wave hidden charm–hidden strangeness production in e+e− annihilation

It is suggested that the recently observed enhancement of the relative yield in e+e− annihilation of states with hidden charm and hidden strangeness above 4.43 GeV is associated with the S wave production of the charmed strange meson pairs Ds0(2317)D¯s⁎+c.c. and Ds1⁎(2460)D¯s+c.c. This mechanism implies a pattern of breaking of the Heavy Quark Spin Symmetry (HQSS) that can be tested in the final channels such as ηc(1S)ϕ, hc(1P)η, hc(1P)η′ produced in the same energy range.

Spin degeneracy of Hadronic molecules in the heavy quark region

Hadronic molecules have been considered to appear close to the hadron-hadron threshold. For the heavy mesons, and B, the one pion exchange potential is enhanced by the mass degeneracy of heavy pseudoscalar and vector mesons, caused by the heavy quark spin symmetry. In this study, we investigate new hadronic molecules formed by the heavy meson and a nucleon N, being P(*)N. As the interaction between P(*) and N, the pion and vector meson (ρ and ω) exchanges are considered. By solving the coupled-channel Schrödinger equations for P N and P*N, we obtain the bound and resonant states in the charm and bottom sectors, and in the in nite heavy quark mass limit. In the molecular states, the PN − P*N mixing effect is important, where the tensor force of the one pion exchange potential generates the strong attraction. In the heavy quark limit, we obtain the degeneracy of the states for JP = 1/2− and 3/2−.

Omega _c excited states within a mathrm{SU(6)}_{mathrm{lsf}}times \xa0HQSS model

We have reviewed the renormalization procedure used in the unitarized coupled-channel model of Romanets et al. (Phys Rev D 85:114032, 2012), and its impact in the C=1, S=-,2, and I=0 sector, where five Omega _c^{(*)} states have been recently observed by the LHCb Collaboration. The meson-baryon interactions used in the model are consistent with both chiral and heavy-quark spin symmetries, and lead to a successful description of the observed lowest-lying odd parity resonances Lambda _c(2595) and Lambda _c(2625), and Lambda _b(5912) and Lambda _b(5920) resonances. We show that some (probably at least three) of the states observed by LHCb will also have odd parity and J=1/2 or J=3/2, belonging two of them to the same mathrm{SU(6)}_{mathrm{light}text {-}mathrm{spin}text {-}mathrm{flavor}}times HQSS multiplets as the latter charmed and beauty Lambda baryons.

X(4260) revisited: A coupled channel perspective

We calculate the probabilities of various charmed meson molecules for $X(4260)$ under the framework of ${}^3P_0$ model. The results indicate that even though heavy quark spin symmetry forbids $S$ wave coupling of $D_1\bar{D}$ to the ${}^3S_1$ charmonia ($\psi(nS)$), the $D$ wave coupling is allowed and not negligible. Under this symmetry, the $D_1\bar{D}$ can couple to ${}^3D_1$ charmonia ($\psi(nD)$) via both $S$ and $D$ wave, and the overall coupling is around three times larger than that of $\psi(nS)$. The $X(4260)$ cannot be a pure molecule but a mixture of a charmonium and various charmed meson components. Since the $D_1\bar{D}$ couples strongly to $\psi(nD)$, our results suggest that in the $D_1\bar{D}$ molecular picture, the charmonium core of $X(4260)$ is $\psi(nD)$ instead of $\psi(nS)$. As a result, the experimental fact that the $R$ ratio has a dip around 4.26 GeV can be understood in the $D_1\bar{D}$ molecular picture of the $X(4260)$.

Charm-beauty meson bound states from B(B*)D(D*) and B(B*)D¯(D¯*) interaction

We evaluate the s-wave interaction of pseudoscalar and vector mesons with both charm and beauty to investigate the possible existence of molecular $BD$, $B^*D$, $BD^*$, $B^*D^*$, $B\bar D$, $B^*\bar D$, $B\bar D^*$ or $B^* \bar D^*$ meson states. The scattering amplitude is obtained implementing unitarity starting from a tree level potential accounting for the dominant vector meson exchange. The diagrams are evaluated using suitable extensions to the heavy flavor sector of the hidden gauge symmetry Lagrangians involving vector and pseudoscalar mesons{, respecting heavy quark spin symmetry}. We obtain bound states at energies above 7 GeV for $BD$ ($J^P=0^+$), $B^*D$ ($1^+$), $BD^*$ ($1^+$) and $B^*D^*$ ($0^+$, $1^+$, $2^+$), all in isospin 0. For $B\bar D$ ($0^+$), $B^*\bar D$ ($1^+$), $B\bar D^*$ ($1^+$) and $B^*\bar D^*$ ($0^+$, $1^+$, $2^+$) we also find similar bound states in $I=0$, but much less bound, which would correspond to exotic meson states with $\bar b$ and $\bar c$ quarks, and for the $I=1$ we find a repulsive interaction. We also evaluate the scattering lengths in all cases, which can be tested in current investigations of lattice QCD.

Mesic nuclei with a heavy antiquark

The binding of a hadron and a nucleus is a topic of great interest for investigating hadron properties. In the heavy-flavor region, attraction between a |$P(=\bar{D},B)$| meson and a nucleon |$N$| can appear, where |$PN$|–|$P^\ast N$| mixing plays an important role in relation to the heavy-quark spin symmetry. The attraction can produce exotic heavy mesic nuclei that are stable against strong decay. We study an exotic system where the |$\bar{D}$| (⁠|$B$|⁠) meson and nucleus are bound. The meson–nucleus interaction is given by a folding potential with single-channel |$PN$| interaction and the nucleon number distribution function. By solving the Schrödinger equations of the heavy meson and the nucleus, we obtain several bound and resonant states for nucleon number |$A=16,\ldots,208$|⁠. The results indicate the possible existence of exotic mesic nuclei with a heavy antiquark.

Hidden-charm pentaquarks as a meson-baryon molecule with coupled channels for D¯(*)Λc and D¯(*)Σc(*)

The recent observation of two hidden-charm pentaquark states by LHCb collaborations prompted us to investigate the exotic states close to the $\bar{D}\Lambda_{\rm c}$, $\bar{D}^{\ast}\Lambda_{\rm c}$, $\bar{D}\Sigma_{\rm c}$, $\bar{D}\Sigma^{\ast}_{\rm c}$, $\bar{D}^{\ast}\Sigma_{\rm c}$ and $\bar{D}^{\ast}\Sigma^{\ast}_{\rm c}$ thresholds. We therefore studied the hadronic molecules that form the coupled-channel system of $\bar{D}^{(\ast)}\Lambda_{\rm c}$ and $\bar{D}^{(\ast)}\Sigma^{(\ast)}_{\rm c}$. As the heavy quark spin symmetry manifests the mass degenerations of $\bar{D}$ and $\bar{D}^\ast$ mesons, and of $\Sigma_{\rm c}$ and $\Sigma^\ast_{\rm c}$ baryons, the coupled channels of $\bar{D}^{(\ast)}\Sigma^{(\ast)}_{\rm c}$ are important in these molecules. In addition, we consider the coupling to the $\bar{D}^{(\ast)}\Lambda_{\rm c}$ channel whose thresholds are near the $\bar{D}^{(\ast)}\Sigma^{(\ast)}_{\rm c}$ thresholds, and the coupling to the state with nonzero orbital angular momentum mixed by the tensor force. This full coupled channel analysis of $\bar{D}^{(\ast)}\Lambda_{\rm c}-\bar{D}^{(\ast)}\Sigma^{(\ast)}_{\rm c}$ with larger orbital angular momentum has never been performed before. By solving the coupled-channel Schr\"odinger equations with the one meson exchange potentials that respected to the heavy quark spin and chiral symmetries, we studied the hidden-charm hadronic molecules with $I(J^P)=1/2(3/2^\pm)$ and $1/2(5/2^\pm)$. We conclude that the $J^P$ assignment of the observed pentaquarks is $3/2^+$ for $P^+_{\rm c}(4380)$ and $5/2^-$ for $P^+_{\rm c}(4450)$, which is agreement with the results of the LHCb analysis. In addition, we give predictions for other $J^P=3/2^\pm$ states at 4136.0, 4307.9 and 4348.7 MeV in $J^P=3/2^-$, and 4206.7 MeV in $J^P=3/2^+$, which can be further investigated by means of experiment.

Hadronic weak decay Bb(12+)→B(12+, 32+)+V

It is shown that for the effective Lagrangian with the factorization ansatz considered here, in the two-body hadronic decay ${\mathcal{B}}_{b}({\frac{1}{2}}^{+})\ensuremath{\rightarrow}\mathcal{B}({\frac{1}{2}}^{+},{\frac{3}{2}}^{+})+V$, with ${\mathcal{B}}_{b}({\frac{1}{2}}^{+})$ belonging to the representation $\overline{3}$, the only allowed decay channel is ${\mathcal{B}}_{b}({\frac{1}{2}}^{+})\ensuremath{\rightarrow}\mathcal{B}({\frac{1}{2}}^{+})+V$, where $\mathcal{B}({\frac{1}{2}}^{+})$ belongs to the representation 8 of $SU(3)$. However, for ${\mathcal{B}}_{b}({\frac{1}{2}}^{+})$ belonging to the sextet representation 6, the allowed decay channels are ${\mathcal{B}}_{b}({\frac{1}{2}}^{+})\ensuremath{\rightarrow}\mathcal{B}({\frac{1}{2}}^{+},{\frac{3}{2}}^{+})+V$, where $\mathcal{B}({\frac{1}{2}}^{+})$ and $\mathcal{B}({\frac{3}{2}}^{+})$ belong to the octet representation ${8}^{\ensuremath{'}}$ and the decuplet 10 of $SU(3)$, respectively. The decay channel ${\mathcal{B}}_{b}({\frac{1}{2}}^{+})\ensuremath{\rightarrow}\mathcal{B}({\frac{1}{2}}^{+})+V$ is analyzed in detail. The decay rate ($\mathrm{\ensuremath{\Gamma}}$) and the asymmetry parameters $\ensuremath{\alpha},{\ensuremath{\alpha}}^{\ensuremath{'}},\ensuremath{\beta},\ensuremath{\gamma}$, and ${\ensuremath{\gamma}}^{\ensuremath{'}}$ are expressed in terms of four amplitudes. In particular, for the decay ${\mathrm{\ensuremath{\Lambda}}}_{b}\ensuremath{\rightarrow}\mathrm{\ensuremath{\Lambda}}+J/\ensuremath{\psi}$ it is shown that within the factorization framework, using heavy quark spin symmetry, the decay rate and the asymmetry parameters can be expressed in terms of two form factors ${F}_{1}$ and ${F}_{2}/{F}_{1}$, which are to be evaluated in some model. By using the values of these form factors calculated in a quark model, the branching ratio and the asymmetry parameters $\ensuremath{\alpha}$ and ${\ensuremath{\alpha}}^{\ensuremath{'}}$ are calculated numerically. For other heavy quarks belonging to the triplet and sextet representations, the results can be easily obtained by using $SU(3)$ symmetry and a phase-space factor. Finally, the decay ${\mathrm{\ensuremath{\Omega}}}_{b}^{\ensuremath{-}}\ensuremath{\rightarrow}{\mathrm{\ensuremath{\Omega}}}^{\ensuremath{-}}+J/\ensuremath{\psi}$ is analyzed within the factorization framework. It is shown that the asymmetry parameter $\ensuremath{\alpha}$ in this particular decay is zero. The branching ratio obtained in the first approximation is compared with the experimental value.

Spin partners of the Zb(10610) and Zb(10650) revisited

We study the implications of the heavy-quark spin symmetry for the possible spin partners of the exotic states Zb(10610) and Zb(10650) in the spectrum of bottomonium. We formulate and solve numerically the coupled-channel equations for the Zb states that allow for a dynamical generation of these states as hadronic molecules. The force includes short-range contact terms and the one-pion exchange potential, both treated full nonperturbatively. The strength of the potential at leading order is fixed completely by the pole positions of the Zb states so that the mass and the most prominent contributions to the width of the isovector heavy-quark spin partner states WbJ with the quantum numbers J++ (J = 0, 1, 2) come out as predictions. In particular, we predict the existence of an isovector 2++ tensor state lying a few MeV below the {B}^{ast }{overline{B}}^{ast } threshold which should be detectable in the experiment. Since the accuracy of the present experimental data does not allow one to fix the pole positions of the Zb’s reliably enough, we also study the pole trajectories of their spin partner states as functions of the Zb binding energies. It is shown that, once the heavy-quark spin symmetry is broken by the physical B and B∗ mass difference, especially the pion tensor force has a significant impact on the location of the partner states clearly demonstrating the need of a coupled-channel treatment of pion dynamics to understand the spin multiplet pattern of hadronic molecules.

Some properties of the states at the hidden-strangeness mixed 12++12− heavy meson pair threshold in e+e− annihilation

The threshold behavior of $e^+ e^-$ annihilation is considered in the channels $B_{s0} \bar B_s^* + c.c.$, $B_{s1} \bar B_s + c.c.$, and $B_{s1} \bar B_s^* +c.c.$, where $B_{s0}$ and $B_{s1}$ are the excited bottom-strange $J^P=0^+$ and $J^P = 1^+$ mesons. It is argued that due to the heavy quark spin symmetry (HQSS) only one coherent combination of the first two channels is produced in the $S$ wave as well as the third channel. Thus, if there exist threshold molecular peaks in the considered channels, only two of such peaks can be formed in the annihilation. The properties of such threshold states are discussed, including the heavy-light spin structure and the related transitions to bottomonium plus light mesons, as well as mixing with the channels with and without hidden strangeness.

Lowest-lying even-parity {bar{B}}_s mesons: heavy-quark spin-flavor symmetry, chiral dynamics, and constituent quark-model bare masses

The discovery of the D^*_{s0}(2317) and D_{s1}(2460) resonances in the charmed-strange meson spectra revealed that formerly successful constituent quark models lose predictability in the vicinity of two-meson thresholds. The emergence of non-negligible effects due to meson loops requires an explicit evaluation of the interplay between Q{bar{q}} and (Q{bar{q}})(q{bar{q}}) Fock components. In contrast to the c{bar{s}} sector, there is no experimental evidence of J^P=0^+,1^+ bottom–strange states yet. Motivated by recent lattice studies, in this work the heavy-quark partners of the D_{s0}^*(2317) and D_{s1}(2460) states are analyzed within a heavy meson chiral unitary scheme. As a novelty, the coupling between the constituent quark-model P-wave {bar{B}}_s scalar and axial mesons and the {bar{B}}^{(*)}K channels is incorporated employing an effective interaction, consistent with heavy-quark spin symmetry, constrained by the lattice energy levels.

Molecular partners of the X(3872) from heavy-quark spin symmetry: a fresh look

The heavy-quark spin symmetry (HQSS) partners of the X(3872) molecule are investigated in a chiral effective field theory (EFT) approach which incorporates contact and one-pion exchange interactions. The integral equations of the Lippmann-Schwinger type are formulated and solved for the coupled-channel problem for the DD , DD *, and D*D * systems with the quantum numbers J PC = 1 ++ , 1+− , 0 ++ , and 2 ++ . We confirm that, if the X (3872) is a 1 ++ DD * molecular state then, in the strict heavy-quark limit, there exist three partner states, with the quantum numbers 1 +− , 0 ++ , and 2 ++ , which are degenerate in mass. At first glance, this result looks natural only for the purely contact pionless theory since pions contribute differently to different transition potentials and, therefore, may lift the above degeneracy. Nevertheless, it is shown that, by an appropriate unitary transformation, the Lippmann-Schwinger equation in each channel still can be brought to a block-diagonal form, with the same blocks for all quantum numbers, so that the degeneracy of the bound states in different channels is preserved. We stress that neglecting some of the coupled-channel transitions in an inconsistent manner leads to a severe violation of HQSS and yields regulator-dependent results for the partner states. The effect of HQSS violation in combination with nonperturbative pion dynamics on the pole positions of the partner states is discussed.

ηcHadroproduction at Large Hadron Collider Challenges NRQCD Factorization

We report on our analysis [1] of prompt ηc meson production, measured by the LHCb Collaboration at the Large Hadron Collider, within the framework of non-relativistic QCD (NRQCD) factorization up to the sub-leading order in both the QCD coupling constant αs and the relative velocity v of the bound heavy quarks. We thereby convert various sets of J/ψ and χc,J long-distance matrix elements (LDMEs), determined by different groups in J/ψ and χc,J yield and polarization fits, to ηc and hc production LDMEs making use of the NRQCD heavy quark spin symmetry. The resulting predictions for ηc hadroproduction in all cases greatly overshoot the LHCb data, while the color-singlet model contributions alone would indeed be sufficient. We investigate the consequences for the universality of the LDMEs, and show how the observed tensions remain in follow-up works by other groups.

P -wave coupled channel effects in electron-positron annihilation

$P$-wave coupled channel effects arising from the $D\overline{D}$, $D{\overline{D}}^{*}+\mathrm{c}.\mathrm{c}.$, and ${D}^{*}{\overline{D}}^{*}$ thresholds in ${e}^{+}{e}^{\ensuremath{-}}$ annihilations are systematically studied. We provide an exploratory study by solving the Lippmann-Schwinger equation with short-ranged contact potentials obtained in the heavy quark limit. These contact potentials can be extracted from the $P$-wave interactions in the ${e}^{+}{e}^{\ensuremath{-}}$ annihilations, and then be employed to investigate possible isosinglet $P$-wave hadronic molecules. In particular, such an investigation may provide information about exotic candidates with quantum numbers ${J}^{\mathrm{PC}}={1}^{\ensuremath{-}+}$. In the mass region of the $D\overline{D}$, $D{\overline{D}}^{*}+\mathrm{c}.\mathrm{c}.$, and ${D}^{*}{\overline{D}}^{*}$ thresholds, there are two quark model bare states, i.e. the $\ensuremath{\psi}(3770)$ and $\ensuremath{\psi}(4040)$, which are assigned as $({1}^{3}{D}_{1})$ and $({3}^{1}{S}_{1})$ states, respectively. By an overall fit of the cross sections of ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}D\overline{D}$, $D{\overline{D}}^{*}+\mathrm{c}.\mathrm{c}.$, ${D}^{*}{\overline{D}}^{*}$, we determine the physical coupling constants to each channel and extract the pole positions of the $\ensuremath{\psi}(3770)$ and $\ensuremath{\psi}(4040)$. The deviation of the ratios from that in the heavy quark spin symmetry (HQSS) limit reflects the HQSS breaking effect due to the mass splitting between the $D$ and the ${D}^{*}$. Besides the two poles, we also find a pole a few MeV above the $D{\overline{D}}^{*}+\mathrm{c}.\mathrm{c}.$ threshold which can be related to the so-called $G(3900)$ observed earlier by BABAR and Belle. This scenario can be further scrutinized by measuring the angular distribution in the ${D}^{*}{\overline{D}}^{*}$ channel with high luminosity experiments.

Heavy-quark spin symmetry partners of the X(3872) revisited

We revisit the consequences of the heavy-quark spin symmetry for the possible spin partners of the $X(3872)$. We confirm that, if the $X(3872)$ were a $D\bar{D}^*$ molecular state with the quantum numbers $J^{PC}=1^{++}$, then in the strict heavy-quark limit there should exist three more hadronic molecules degenerate with the $X(3872)$, with the quantum numbers $0^{++}$, $1^{+-}$, and $2^{++}$ in line with previous results reported in the literature. We demonstrate that this result is robust with respect to the inclusion of the one-pion exchange interaction between the $D$ mesons. However, this is true only if all relevant partial waves as well as particle channels which are coupled via the pion-exchange potential are taken into account. Otherwise, the heavy-quark symmetry is destroyed even in the heavy-quark limit. Finally, we solve the coupled-channel problem in the $2^{++}$ channel with nonperturbative pions beyond the heavy-quark limit and, contrary to the findings of previous calculations with perturbative pions, find for the spin-2 partner of the $X(3872)$ a significant shift of the mass as well as a width of the order of 50 MeV.

Production ofY(4260)as a hadronic molecule state ofD¯D1+c.c.ine+e−annihilations

We study the $Y(4260)$ production mechanism in $e^+e^-$ annihilations in the framework of hadronic molecules and investigate the consequence of such a picture in different decay channels. In the hadronic molecule picture the $Y(4260)$ is described as a mixture state composed of a long-ranged $\bar{D}D_1(2420)+c.c.$ molecule state and a compact $c\bar{c}$ component. We show that the compositeness relation can still provide a reasonable constraint on the wavefunction renormalization parameter due to the dominance of the molecular component. Such a mechanism can be regarded as a natural consequence of the heavy quark spin symmetry (HQSS) breaking. This study elaborates the molecular picture for the $Y(4260)$ in the $e^+e^-$ annihilations and affirms that the cross section lineshape of $e^+e^-\to \bar{D}D^*\pi+c.c.$ in the vicinity of the $Y(4260)$ should have a nontrivial behavior. In this framework we predict that the upper limit of the $Y(4260)$ leptonic decay width is about 500 eV. We also investigate the coupling for $D_1(2420)\to D^*\pi$ in the $^3P_0$ quark model and examine the possible HQSS breaking effects due to the deviation from the $|^1P_1\rangle$ and $|^3P_1\rangle$ ideal mixing. This will in turn provide a constraint on the HQSS breaking coupling for the $Y(4260)$ to $\bar{D}D_1(2420)+c.c.$ via its $c\bar{c}$ component.

Bottomonium physics at Υ(4S, 5S, 6S) energies with the Belle detector

The description of quarkonia as pure quark anti-quark bound states has been recently challenged by the observation of charged states in both the charmonium and bottomonium region and large violations of the heavy quark spin symmetry in hadronic transitions. All these effects can be ascribable to non-negligible contributions from the light quark degrees of freedom in the description of both charmonia and bottomonia. We will report the most recent experimental measurements performed by the Belle collaboration in the Y(4S), Y(5S) and Y(6S) regions, including the measurement of the ratio σ[e+e- → bb̅]/σ[e+e- → μ+ μ-], the search for neutral states near the B0B̅0 threshold, the first observation of the transition ϒ(4S) → ηhb(lP) and the study of the η transitions at the ϒ(5S) energy. The contribution to the study of the structure of these states coming from the measurement of hadronic transitions will be discussed.