Search

Many exotic charmoniumlike mesons have already been discovered experimentally, of which the $Z_c$ mesons with isospin 1 are prominent examples. We investigate $J^{PC}=1^{+\pm}$ states with flavor $\bar cc \bar qq$ ($q=u,d$) in isospin 1 using lattice QCD. This is the first study of these mesons employing more than one volume and involving frames with nonzero total momentum. We utilize two $N_f=2+1$ CLS ensembles with $m_{\pi}\simeq 280\,$MeV. As the simulations are performed with unphysical quark masses and at a single lattice spacing of $a=0.086\,$fm, our results provide only qualitative insights. Resulting eigenenergies are compatible or just slightly shifted down with respect to noninteracting energies, where the most significant shifts occur for certain $D\bar D^*$ states. Both channels $1^{+\pm}$ have a virtual pole slightly below the threshold if $D\bar D^*$ is assumed to be decoupled from other channels. In addition, we perform a coupled channel analysis of $J/\psi \pi$ and $D\bar D^*$ scattering with $J^{PC}=1^{+-}$ within an effective field theory framework. The $J/\psi \pi$ and $D\bar D^*$ invariant-mass distributions from BESIII and finite-volume energies from several lattice QCD simulations, including this work, are fitted simultaneously. All fits yield two poles relatively close to the $D\bar D^*$ threshold and reasonably reproduce the experimental $Z_c$ peaks. They also reproduce lattice energies up to slightly above the $D\bar{D}^*$ threshold, while reproduction at even higher energies is better for fits that put more weight on the lattice data. Our findings suggest that the employed effective field theory can reasonably reconcile the peaks in the experimental line shapes and the lattice energies, although those lie close to noninteracting energies. We also study $J/\psi \pi$ scattering in s-wave and place upper bounds on the phase shift., Comment: 23 pages plus appendices, 24 figures

We present a lattice QCD study of the elastic $S$-wave $D\bar{B}$ scattering in search of tetraquark candidates with explicitly exotic flavor content $bc\bar u\bar d$ in the isospin $I\!=\!0$ and $J^P=0^+$ channel. We use four lattice QCD ensembles with dynamical $u/d$, $s$, and $c$ quark fields generated by the MILC Collaboration. A non-relativistic QCD Hamiltonian, including improvement coefficients up to $\mathcal{O}(\alpha_sv^4)$, is utilized for the bottom quarks. For the rest of the valence quarks we employ a relativistic overlap action. Five different valence quark masses are utilized to study the light quark mass dependence of the $D\bar{B}$ scattering amplitude. The finite volume energy spectra are extracted following a variational approach. The elastic $D\bar{B}$ scattering amplitudes are extracted employing L\"{u}scher's prescription. The light quark mass dependence of the continuum extrapolated amplitudes suggests an attractive interaction between the $\bar B$ and $D$ mesons. At the physical pseudoscalar meson mass ($M_{ps}=M_{\pi}$) the $D\bar{B}$ scattering amplitude has a sub-threshold pole corresponding to a binding energy of $-39(^{+4}_{-6})(^{~+8}_{-18}) \mbox{~MeV}$ with respect to the $D\bar{B}$ threshold. The critical $M_{ps}$ at which the $D\bar{B}$ scattering length diverges and the system becomes unbound corresponds to $M^*_{ps}=2.94(15)(5) \mbox{~GeV}$. This result can hold significant experimental relevance in the search for a bound scalar $T_{bc}$ tetraquark, which could well be the next "doubly heavy" bound tetraquark to be discovered with only weak decay modes., Comment: 13 pages, 10 figures

The $DD^*$ scattering phase shifts in the $T_{cc}^+=cc\bar{u}\bar{d}$ channel are extracted from lattice QCD for five different charm quark masses and a fixed light-quark mass corresponding to $m_\pi\simeq 280$~MeV. The phase shifts are analysed employing two approaches: effective range expansion and Lippmann--Schwinger equation derived in the effective field theory. In the latter case, the results imply an attraction at short range parametrised by contact terms and a slight repulsion at long range mediated by one-pion exchange with $m_\pi >m_{D^*}-m_D$. The poles in the amplitude across the complex energy plane are extracted and their trajectories are discussed as the charm quark mass is varied. Two complex conjugate poles corresponding to a resonance below threshold are found for $m_c$ close to the physical value. They turn into a pair of virtual states at the largest $m_c$ studied. With further increasing $m_c$, one virtual pole representing $T_{cc}^+$ is expected to move towards the two-body threshold and turn into a bound state. The light-quark mass dependence of the $T_{cc}^+$ pole is briefly discussed using the data on $DD^*$ scattering from other lattice collaborations., Comment: 18 pages, 17 figures, 3 tables, version to appear in Phys.Rev.D

We perform a lattice simulation to investigate the doubly charmed tetraquark $T^+_{cc}$ observed by the LHCb collaboration, slightly below the $D^{*+}D^0$ threshold, with flavor content $cc\bar{u}\bar{d}$ and isospin-$0$. Two-meson interpolators are implemented to explore the isospin quantum numbers $I=0$ and $I=1$. We observe attraction near the $DD^*$ threshold for $I=0$ and repulsion for $I=1$. Moreover, we also include diquark-antidiquark interpolators to study their effect on the energy spectrum. There is no significant shift in the ground state energy when adding diquark-antidiquark interpolators to the interpolator basis when the heavy quark mass is close to the physical charm quark mass. However, we observe a non-negligible shift in the second energy level. This effect has to be taken into account to extract the scattering amplitude of the $T^+_{cc}$. Finally, with a higher mass (close to the bottom quark), the ground state is shifted down significantly. The simulation is performed on $N_f=2+1$ CLS ensembles with $m_\pi \simeq 280$ MeV., Comment: IMSc/2023/06

We report a lattice QCD study of the heavy-light meson-meson interactions with an explicitly exotic flavor content $bc\bar u\bar d$, isospin $I\!=\!0$, and axialvector $J^P=1^+$ quantum numbers in search of possible tetraquark bound states. The calculation is performed at four values of lattice spacing, ranging $\sim$0.058 to $\sim$0.12 fm, and at five different values of valence light quark mass $m_{u/d}$, corresponding to pseudoscalar meson mass $M_{ps}$ of about 0.5, 0.6, 0.7, 1.0, and 3.0 GeV. The energy eigenvalues in the finite-volume are determined through a variational procedure applied to correlation matrices built out of two-meson interpolating operators as well as diquark-antidiquark operators. The continuum limit estimates for $D\bar B^*$ elastic $S$-wave scattering amplitude are extracted from the lowest finite-volume eigenenergies, corresponding to the ground states, using amplitude parametrizations supplemented by a lattice spacing dependence. Light quark mass $m_{u/d}$ dependence of the $D\bar B^*$ scattering length ($a_0$) suggests that at the physical pion mass $a_0^{phys} = +0.57(^{+4}_{-5})(17)$ fm, which clearly points to an attractive interaction between the $D$ and $\bar B^*$ mesons that is strong enough to host a real bound state $T_{bc}$, with a binding energy of $-43(_{-7}^{+6})(_{-24}^{+14})$ MeV with respect to the $D\bar B^*$ threshold. We also find that the strength of the binding decreases with increasing $m_{u/d}$ and the system becomes unbound at a critical light quark mass $m^{*}_{u/d}$ corresponding to $M^{*}_{ps} = 2.73(21)(19)$ GeV., Comment: 8 pages, 6 figures, 1 table, plus supplemental material (4 pages, 5 figures, 1 table). v2: version accepted to be published in Physical Review Letters. Results and conclusions unchanged

Many mesons with properties incompatible with a $\bar cc$ structure have already been discovered, e.g. the $Z_c$ mesons with isospin 1. We investigate the spectrum of exotic charmonium-like mesons using lattice QCD. The focus is on $\bar cc \bar qq$ states with $J^{PC}=1^{+\pm}$ and isospin 1. This is the first study of four-quark states with these quantum numbers, a non-zero total momentum and two different lattice volumes. We extract the energy levels and determine the scattering length for $D\bar D^*$ scattering close to the threshold using L\"uscher's formalism. Our preliminary results show that the energy shifts for eigenstates dominated by $D\bar{D}^*$ are very small in the $1^{++}$ channel and consistent with zero in the $1^{+-}$ channel., Comment: 9 pages, 2 figures, contribution to the 39th International Symposium on Lattice Field Theory (LATTICE2022)

We present the first lattice study of dibaryons with highest bottom number. Utilizing a set of state-of-the-art lattice QCD ensembles and methodologies, we determine the ground state of dibaryon composed of two $\Omega_{bbb}$ baryons. We extract the related scattering amplitude in the $^1S_0$ channel and find a sub-threshold pole, which signifies an unambiguous evidence for a deeply bound $\Omega_{bbb}-\Omega_{bbb}$ dibaryon. The binding energy of such a state as dictated by this pole singularity is found to be -81($^{+14}_{-16}$) MeV. We quantify various systematic uncertainties involved in this determination, including those related to the excited state contamination and Coulomb repulsion between the bottom quarks., Comment: 7 pages, 4 figures, 2 tables, contribution for the 39th International Symposium on Lattice Field Theory, 8th-13th August, 2022, Bonn, Germany

We report the first lattice QCD study of the heavy dibaryons in which all six quarks have the bottom (beauty) flavor. Performing a state-of-the-art lattice QCD calculation we find clear evidence for a deeply bound $\Omega_{bbb}$-$\Omega_{bbb}$ dibaryon in the $^1S_0$ channel, as a pole singularity in the $S$-wave $\Omega_{bbb}$-$\Omega_{bbb}$ scattering amplitude with a binding energy $-81(_{-16}^{+14})$ MeV. With such a deep binding, Coulomb repulsion serves only as a perturbation on the ground state wave function of the parameterized strong potential and may shift the strong binding only by a few percent. Considering the scalar channel to be the most bound for single flavored dibaryons, we conclude this state is the heaviest possible most deeply bound dibaryon in the visible universe., Comment: 4 figures, 1 table

The doubly charm tetraquark with flavor $cc\bar u\bar d$ and isospin $I\!=\!0$ is investigated by calculating the $DD^*$ scattering amplitude with lattice QCD. The simulation is done on CLS ensembles with dynamical $u/d,s$ quarks and $m_\pi\simeq 280~$MeV for two charm quark masses, one slightly larger and one slightly lower than the physical value. The scattering amplitudes for partial waves $l=0,1$ are extracted near-threshold via the L\"uscher's method by considering systems with total momenta $PL/(2\pi)=0,1,\sqrt{2},2$ on two spatial volumes. A virtual bound state pole in the $DD^*$ scattering amplitude with $l=0$ is found $9.9_{-7.1}^{+3.6}~$MeV below $DD^*$ threshold for the charm quark mass closer to the physical value. This pole is likely related to the doubly charm tetraquark discovered by LHCb less than $1~$MeV below $D^0D^{*+}$ threshold. Future lattice simulations closer to the continuum limit and physical quark masses would be valuable to establish this connection systematically., Comment: version to appear in Phys.Rev.Lett. 6(+6) pages; 4(+6) figures; 2(+1) tables; Modified and extended discussions, supplemental material and video file. Results and conclusions unchanged

We present the current status of our efforts in search of $H$ dibaryon on $N_f$=2+1 CLS ensembles away from the $SU(3)$ flavor symmetric point. Utilizing the distillation framework (also known as LapH) in its exact and stochastic forms, we calculate two-point correlation matrices using large bases of bi-local two-baryon interpolators to reliably determine the low-energy spectra. We report the low lying spectrum on several moving frames for multiple ensembles with different lattice spacing and physical volumes. The status of finite-volume analysis to extract the scattering amplitudes is also discussed., Comment: 9 pages, 5 figures. Talk presented at the 38th International Symposium on Lattice Field Theory (Lattice 2021), 26-30 July, 2021, Zoom/Gather@Massachusetts Institute of Technology

Charmonium-like resonances and bound states with isospin zero and $J^{PC}=0^{++},~1^{--},~2^{++},~3^{--}$ are extracted on the lattice. Coupled $D\bar D$ and $D_s\bar D_s$ scattering suggests three charmonium-like states with $J^{PC}=0^{++}$ in addition to $\chi_{c0}(1P)$: a so far unobserved $D\bar D$ bound state just below threshold, a conventional resonance likely related to $\chi_{c0}(3860)/\chi_{c0}(2P)$ and a narrow resonance just below the $D_s\bar D_s$ threshold with a large coupling to $D_s\bar D_s$ likely related to $X(3915)/\chi_{c0}(3930)$. One-channel $D\bar D$ scattering renders resonances and bound states with $J^{PC}= 1^{--},~2^{++},~3^{--}$ related to the observed conventional charmonia. Lattice QCD ensembles from the CLS consortium with $m_{\pi}\simeq 280$ MeV are utilized., Comment: 9 pages, talk presented at LATTICE2021, July 2021, v2: affiliations modified

We present the results of a lattice calculation of four-quark states with the quark contents $\bar{b}\bar{c}q_1q_2$ where $q_1,q_2 \in u,d,s$. For the spin 1 states, when the light quark ($q_1, q_2$) masses are lighter, we find at least one energy level below the possible elastic threshold energy levels. These calculations are performed on three dynamical $N_f = 2+1+1$ highly improved staggered quark ensembles at lattice spacings of about 0.12, 0.09, and 0.06 fm. We use the overlap action for light to charm quarks while a non-relativistic action with non-perturbatively improved coefficients is employed for the bottom quark., Comment: 9 pages, 6 figures. Proceedings of the 38th International Symposium on Lattice Field Theory (LATTICE2021)

This report discusses some recent investigations of the heavy hadron spectra using lattice QCD. The first half addresses multiple precision determinations of the masses of charm (and bottom) baryons. Recent lattice results in the tetraquark and the dibaryon sectors are also presented. The second half focuses on new exploratory studies of the excited charmonium spectra in the vector and scalar channels. Along the way, lattice results are compared with the experimental results, wherever they are available., Comment: Contribution to the Proceedings for 10th International Workshop on Charm Physics (CHARM 2020), May 31-June 5 2021, Mexico City, Mexico

We present the first lattice investigation of coupled-channel $D\bar D$ and $D_s\bar D_s$ scattering in the $J^{PC}=0^{++}$ and $2^{++}$ channels. The scattering matrix for partial waves $l=0,2$ and isospin zero is determined using multiple volumes and inertial frames via L\"uscher's formalism. Lattice QCD ensembles from the CLS consortium with $m_{\pi}\simeq280$ MeV, $a \simeq 0.09 $ fm and $L/a=24,~32$ are utilized. The resulting scattering matrix suggests the existence of three charmonium-like states with $J^{PC}=0^{++}$ in the energy region ranging from slightly below $2m_D$ up to 4.13 GeV. We find a so far unobserved $D\bar D$ bound state just below threshold and a $D\bar D$ resonance likely related to $\chi_{c0}(3860)$, which is believed to be $\chi_{c0}(2P)$. In addition, there is an indication for a narrow $0^{++}$ resonance just below the $D_s\bar D_s$ threshold with a large coupling to $D_s\bar D_s$ and a very small coupling to $D\bar D$. This resonance is possibly related to the narrow $X(3915)$/$\chi_{c0}(3930)$ observed in experiment also just below $D_s\bar D_s$. The partial wave $l=2$ features a resonance likely related to $\chi_{c2}(3930)$. We work with several assumptions, such as the omission of $J/\psi\omega$, $\eta_c\eta$ and three-particle channels. Only statistical uncertainties are quantified, while the extrapolations to the physical quark-masses and the continuum limit are challenges for the future., Comment: 41 pages, 16 figures; JHEP version, corrected typo concerning the uncertainty in Fig 5c

In this report, the most recent and precise estimates of masses of ground state baryons using lattice QCD are discussed. Considering the prospects in the heavy baryon sector, lattice estimates for these are emphasized. The first and only existing lattice determination of the highly excited $\Omega_c$ excitations in relation to the recent LHCb discovery is also discussed., Comment: 5 pages, 3 figures, Proceedings of talk at the Mini-Workshop on Doubly-charm baryons and dimesons, Bled Slovenia, June 17-23, 2018

I review recent results on hadron spectroscopy using lattice QCD. In light of the discoveries in heavy baryon sector at LHCb over the past few years, lattice calculations in this regard are emphasized. Investigations on light baryon, heavy-heavy and heavy-light meson resonances are also discussed., Comment: 20 pages, 10 figures, Proceedings of the 36th Annual International Symposium on Lattice Field Theory, LATTICE2018 22-28 July, 2018

We present a lattice QCD study of charmonium resonances and bound states with $J^{PC}=1^{--}$ and $3^{--}$ near the open-charm threshold, taking into account their strong transitions to $\bar DD$. Vector charmonia are the most abundant in the experimentally established charmonium spectrum, while recently LHCb reported also the first discovery of a charmonium with likely spin three. The $\bar DD$ scattering amplitudes for partial waves $l=1$ and $l=3$ are extracted on the lattice by means of the L\"uscher formalism, using multiple volumes and inertial frames. Parameterizations of the scattering amplitudes provide masses and widths of the resonances, as well as the masses of bound states. CLS ensembles with 2+1 dynamical flavors of non-perturbatively $O(a)$ improved Wilson quarks are employed with $m_\pi\simeq 280$ MeV, a single lattice spacing of $a\simeq0.086$ fm and two lattice spatial extents of $L=24$ and $32$. Two values of the charm quark mass are considered to examine the influence of the position of the $\bar{D}D$ threshold on the hadron masses. For the lighter charm quark mass we find the vector resonance $\psi(3770)$ with mass $m=3780(7)$ MeV and coupling $g=16.0(^{+2.1}_{-0.2})$ (related to the width), both consistent with their experimental values. The vector $\psi(2S)$ appears as a bound state with $m=3666(10)$ MeV. The charmonium resonance with $J^{PC}=3^{--}$ is found at $m=3831(^{+10}_{-16})$ MeV, consistent with the $X(3842)$ recently discovered by LHCb. At our heavier charm-quark mass the $\psi(2S)$ as well as the $\psi(3770)$ are bound states and the $X(3842)$ remains a resonance. We stress that all quoted uncertainties are only statistical, while lattice spacing effects and the approach to the physical point still need to be explored. This study of conventional charmonia sets the stage for more challenging future studies of unconventional charmonium-like states., Comment: 21 pages, 17 figures. Version 2: Added Appendix B and Figure 12, improved text and figures

Many exotic charmonium resonances have been identified recently in experiment, however their nature and properties are mostly unknown. Algorithmic and theoretical progress in lattice calculations has enabled reliable numerical investigation of the spectrum below the strong decay threshold, while the study of charmonium resonances remains an open challenge. The main difficulty to overcome is the presence of many open decay channels which are coupled together, resulting in a complex finite volume quantization condition. We report on our recent progress towards the determination of single-channel and coupled-channel scattering matrices in the scalar and vector channels on CLS ensembles. We also present an update concerning the study of the charmonium spectrum in moving frames., Comment: Talk presented at Lattice 2018 by S. Piemonte and at Confinement 2018 by D. Mohler

The spectrum of charmonium resonances contains a number of unanticipated states along with several conventional quark-model excitations. The hadrons of different quantum numbers $J^P$ appear in a fairly narrow energy band, where $J^P$ refers to the spin-parity of a hadron at rest. This poses a challenge for Lattice QCD studies of (coupled-channel) meson-meson scattering aimed at the determination of scattering amplitudes and resonance pole positions. A wealth of information for this purpose can be obtained from the lattice spectra in frames with nonzero total momentum. These are particularly dense since hadrons with different $J^P$ contribute to any given lattice irreducible representation. This is because $J^P$ is not a good quantum number in flight, and also because the continuum symmetry is reduced on the lattice. In this paper we address the assignment of the underlying continuum $J^P$ quantum numbers to charmonia in flight using a $N_f = 2 + 1$ CLS ensemble. As a first step, we apply the single-hadron approach, where only interpolating fields of quark-antiquark type are used. The approach follows techniques previously applied to the light meson spectrum by the Hadron Spectrum Collaboration. The resulting spectra of charmonia with assigned $J^P$ will provide valuable information for the parameterization of (resonant) amplitudes in future determinations of resonance properties with lattice QCD., Comment: 19 pages, 17 figures, Version published in Physical Review D

We present results of a lattice calculation of tetraquark states with quark contents $q_1q_2\bar{Q}\bar{Q}, \, q_1,q_2 \subset u,d,s,c$ and $Q \equiv b,c$ in both spin zero ($J=0$) and spin one ($J=1$) sectors. These calculations are performed on three dynamical $N_f = 2 + 1 + 1$ highly improved staggered quark ensembles at lattice spacings of about 0.12, 0.09 and 0.06 fm. We use the overlap action for light to charm quarks while a non-relativistic action with non-perturbatively improved coefficients with terms up to $\mathcal{O}(\alpha_s v^4)$ is employed for the bottom quark. While considering two heavy quarks as charm or bottom, we calculate the energy levels of various four-quark configurations with light quark masses ranging from the physical strange quark mass to that of the corresponding physical pion mass. Results for the spin one states show the presence of ground state energy levels which are below their respective thresholds for all the light flavor combinations with both doubly heavy quarks and particularly for the bottom quarks. Further, we identify a trend that the energy splittings, defined as the energy difference between the ground state energy levels and their respective thresholds, increase with decreasing the light quark masses and are maximum at the physical point for all the spin one states. The rate of increase is however dependent on the light quark configuration of the particular spin one state. We also present a study of hadron mass relations involving tetraquarks, baryons and mesons arising in the limit of infinitely heavy quark and find that these relations are more compatible with the heavy quark limit in the bottom sector but deviate substantially in the charm sector. The ground state spectra of the spin zero tetraquark states with various flavor combinations are seen to lie above their respective thresholds., Comment: 19 pages, 9 figures. Version accepted for publication in PRD

We present the energy spectra of the low lying doubly-charmed baryons using lattice quantum chromodynamics. We precisely predict the ground state mass of the charmed-strange Omega(cc) (1/2+) baryon to be 3712(11)(12) MeV which could well be the next doubly-charmed baryon to be discovered at the LHCb experiment at CERN. We also predict masses of other doubly-charmed strange baryons with quantum numbers 3/2+, 1/2-, and 3/2-., Comment: 7 pages, 8 figures, accepted for publication in PRD Rapid Communications

We report the ground state masses of hadrons containing at least one charm and one bottom quark using lattice quantum chromodynamics. These include mesons with spin (J)-parity (P) quantum numbers J(P): 0(-), 1(-), 1(+) and 0(+) and the spin-1/2 and 3/2 baryons. Among these hadrons only the ground state of 0(-) is known experimentally and therefore our predictions provide important information for the experimental discovery of all other hadrons with these quark contents., Comment: 7 pages 5 figures, version published in Phys. Rev. Lett

The nature of resonances and excited states near decay thresholds is encoded in scattering amplitudes, which can be extracted from single-particle and multiparticle correlators in finite volumes. Lattice calculations have only recently reached the precision required for a reliable study of such correlators. The distillation method represents a significant improvement insofar as it simplifies quark contractions and allows one to easily extend the operator basis used to construct interpolators. We present preliminary results on charmonium bound states and resonances on the Nf=2+1 CLS ensembles. The long term goal of our investigation is to understand the properties of the X resonances that do not fit into conventional models of quark-antiquark mesons. We tune various parameters of the distillation method and the charm quark mass. As a first result, we present the masses of the ground and excited states in the 0++ and 1-- channels., Comment: 10 pages, 5 figures, talk and poster presented at the 35th International Symposium on Lattice Field Theory, 18-24 June 2017, Granada, Spain

We present a lattice QCD study of the puzzling positive-parity nucleon channel, where the Roper resonance $N^*(1440)$ resides in experiment. The study is based on an ensemble of gauge configurations with $N_f=2+1$ Wilson-clover fermions with a pion mass of $156$ MeV and lattice size $L=2.9$ fm. We use several $qqq$ interpolating fields combined with $N\pi$ and $N\sigma$ two-hadron operators in calculating the energy spectrum in the rest frame. Combining experimental $N\pi$ phase shifts with elastic approximation and the L\"uscher formalism suggests in the spectrum an additional energy level near the Roper mass $m_R=1.43$ GeV for our lattice. We do not observe any such additional energy level, which implies that $N\pi$ elastic scattering alone does not render a low-lying Roper resonance. The current status indicates that the $N^*(1440)$ might arise as dynamically generated resonance from coupling to other channels, most notably the $N\pi\pi$., Comment: updated references

We present preliminary results from a lattice calculation of tetraquark states in the charm and bottom sector of the type $ud\bar{b}\bar{b}$, $us\bar{b}\bar{b}$, $ud\bar{c}\bar{c}$ and $sc\bar{b}\bar{b}$. These calculations are performed on $N_f = 2 + 1 + 1$ MILC ensembles with lattice spacing of $a = 0.12~\mathrm{fm} $ and $a=0.06~\mathrm{fm} $. A relativistic action with overlap fermions is employed for the light and charm quarks while a non-relativistic action with non-perturbatively improved coefficients is used in the bottom sector. Preliminary results provide a clear indication of presence of energy levels below the relevant thresholds of different tetraquark states. While in double charm sector we find shallow bound levels, our results suggest deeply bound levels with double bottom tetraquarks., Comment: Corrected threshold for the $ud\bar{c}\bar{c}$ tetraquark state. Proceedings of the 35th International Symposium on Lattice Field Theory, 18-24 June 2017, Granada, Spain. TIFR preprint no : TIFR/TH/17-39

We present preliminary results on the light, charmed and bottom baryon spectra using overlap valence quarks on the background of 2+1+1 flavours HISQ gauge configurations of the MILC collaboration. These calculations are performed on three different gauge ensembles at three lattice spacings (a ~ 0.12 fm, 0.09 fm and 0.06 fm) and for physical strange, charm and bottom quark masses. The SU(2) heavy baryon chiral perturbation theory is used to extrapolate baryon masses to the physical pion mass and the continuum limit extrapolations are also performed. Our results are consistent with the well measured charmed baryons. We predict the masses of many other states which are yet to be discovered., Comment: 8 pages, Proceedings of the 35th International Symposium on Lattice Field Theory (Lattice 2017)

We present results from our recent lattice QCD study of $N\pi$ scattering in the positive-parity nucleon channel, where the puzzling Roper resonance $N^*(1440)$ resides in experiment. Using a variety of hadron operators, that include $qqq$-like, $N\pi$ in $p$-wave and $N\sigma$ in $s$-wave, we systematically extract the excited lattice spectrum in the nucleon channel up to 1.65 GeV. Our lattice results indicate that N$\pi$ scattering in the elastic approximation alone does not describe a low-lying Roper. Coupled channel effects between $N\pi$ and $N\pi\pi$ seem to be crucial to render a low-lying Roper in experiment, reinforcing the notion that this state could be a dynamically generated resonance. After giving a brief motivation for studying the Roper channel and the relevant technical details to this study, we will discuss the results and the conclusions based on our lattice investigation and in comparison with other lattice calculations., Comment: 8 pages, 5 figures, presented at the 35th International Symposium on Lattice Field Theory, 18-24 June 2017, Granada, Spain

Lattice simulation of charmonium resonances with non-zero momentum provides additional information on the two-meson scattering matrices. However, the reduced rotational symmetry in a moving frame renders a number of states with different $J^P$ in the same lattice irreducible representation. The identification of $J^P$ for these states is particularly important, since quarkonium spectra contain a number of states with different $J^P$ in a relatively narrow energy region. Preliminary results concerning spin-identification are presented in relation to our study of charmonium resonances in flight on the Nf=2+1 CLS ensembles., Comment: 6 pages, presented at the 35th International Symposium on Lattice Field Theory, 18-24 June 2017, Granada, Spain

We present the ground and excited state spectra of $\Omega^{0}_{c}$ baryons with spin up to 7/2 from lattice quantum chromodynamics with dynamical quark fields. Based on our lattice results, we predict the quantum numbers of five $\Omega^{0}_{c}$ baryons, which have recently been observed by the LHCb Collaboration. Our results strongly indicate that the observed states $\Omega_c(3000)^0$ and $\Omega_c(3050)^0$ have spin-parity $J^P = 1/2^{-}$, the states $\Omega_c(3066)^0$ and $\Omega_c(3090)^0$ have $J^P = 3/2^{-}$, whereas $\Omega_c(3119)^0$ is possibly a $5/2^{-}$ state., Comment: Version accepted for publication in Physical Review Letters

We present ground state spectra of mesons containing a charm and a bottom quark. For the charm quark we use overlap valence quarks while a non-relativistic formulation is utilized for the bottom quark on a background of 2+1+1 flavors HISQ gauge configurations generated by the MILC collaboration. The hyperfine splitting between $1S$ states of $B_c$ mesons is found to be $56^{+4}_{-3}$ MeV. We also study the baryons containing only charm and bottom quarks and predict their ground state masses. Results are obtained at three lattice spacings., Comment: 7 pages, 5 figures. Talk presented at Lattice 2016, Southampton, UK

We present a lattice QCD study of $N\pi$ scattering in the positive-parity nucleon channel, where the puzzling Roper resonance $N^*(1440)$ resides in experiment. The study is based on the PACS-CS ensemble of gauge configurations with $N_f=2+1$ Wilson-clover dynamical fermions, $m_\pi \simeq 156~$MeV and $L\simeq 2.9~$fm. In addition to a number of $qqq$ interpolating fields, we implement operators for $N\pi$ in $p$-wave and $N\sigma$ in $s$-wave. In the center-of-momentum frame we find three eigenstates below 1.65 GeV. They are dominated by $N(0)$, $N(0)\pi(0)\pi(0)$ (mixed with $N(0)\sigma(0)$) and $N(p)\pi(-p)$ with $p\simeq 2\pi/L$, where momenta are given in parentheses. This is the first simulation where the expected multi-hadron states are found in this channel. The experimental $N\pi$ phase-shift would -- in the approximation of purely elastic $N\pi$ scattering -- imply an additional eigenstate near the Roper mass $m_R\simeq 1.43~$GeV for our lattice size. We do not observe any such additional eigenstate, which indicates that $N\pi$ elastic scattering alone does not render a low-lying Roper. Coupling with other channels, most notably with $N\pi\pi$, seems to be important for generating the Roper resonance, reinforcing the notion that this state could be a dynamically generated resonance. Our results are in line with most of previous lattice studies based just on $qqq$ interpolators, that did not find a Roper eigenstate below $1.65~$GeV. The study of the coupled-channel scattering including a three-particle decay $N\pi\pi$ remains a challenge., Comment: 14 pages, 9 figures, version published in Phys. Rev. D plus additional footnote and reference

We discuss a recent lattice study of charmonium-like mesons with $J^{PC}=1^{++}$ and three quark contents $\bar cc\bar du$, $\bar cc(\bar uu + \bar dd)$ and $\bar cc\bar ss$, where the latter two can mix with $\bar cc$. In this quantum channel, the long known exotic candidate, X(3872), resides. This simulation employs $N_f=2$, $m_\pi=266~$MeV and a large basis of $\bar cc$, two-meson and diquark-antidiquark interpolating fields, with diquarks in both anti-triplet and sextet color representations. It aims at the possible signatures of four-quark exotic states. Along the way, we discuss the relations between the diquark-antidiquark operators and the two-meson operators via the Fierz transformations., Comment: 7 pages, Talk given at the 33rd International Symposium on Lattice Field Theory (Lattice 2015), 14-18 July 2015, Kobe International Conference Center, Kobe, Japan

We discuss the significance of charm baryon spectroscopy in hadron physics and review the recent developments of the spectra of charmed baryons in lattice calculations. Special emphasis is given on the recent studies of highly excited charm baryon states. Recent precision lattice measurements of the low lying charm and bottom baryons are also reviewed., Comment: 11 pages, 6 figures, To be published in the proceedings of CHARM-2015, Detroit, MI, 18-22 May 2015

We present the ground and excited state spectra of doubly charmed baryons from lattice QCD with dynamical quark fields. Calculations are performed on anisotropic lattices of size 16^3 X 128, with inverse spacing in temporal direction 1/a_t = 5.67(4) GeV and with a pion mass of about 390 MeV. A large set of baryonic operators that respect the symmetries of the lattice yet which retain a memory of their continuum analogues are used. These operators transform as irreducible representations of SU(3) symmetry for flavor, SU(4) symmetry for Dirac spins of quarks and O(3) for spatial symmetry. The distillation method is utilized to generate baryon correlation functions which are analysed using the variational fitting method to extract excited states. The lattice spectra obtained have baryonic states with well-defined total spins up to 7/2 and the pattern of low lying states does not support the diquark picture for doubly charmed baryons. On the contrary the calculated spectra are remarkably similar to the expectations from models with an SU(6)X O(3) symmetry. Various spin dependent energy splittings between the extracted states are also evaluated., Comment: 20 pages, 17 figures. arXiv admin note: text overlap with arXiv:1307.7022

We present results of our continuing study on mixed-action hadron spectra and decay constants using overlap valence quarks on MILC's 2+1+1 flavor HISQ gauge configurations. This study is carried out on three lattice spacings, with charm and strange masses tuned to their physical values, and with m_l/m_s = 1/5. We present results of an ongoing determination of the mixed-action parameter Delta_{mix}, which enters into chiral formulae for the masses and decay constants., Comment: 7 pages, 4 figures. v2 updated discussion and references. Contribution to the 32nd International Symposium on Lattice Field Theory, 23-28 June 2014, Columbia University New York, NY, USA

We present the ground and excited state spectra of singly, doubly and triply charmed baryons by using dynamical lattice QCD. A large set of baryonic operators that respect the symmetries of the lattice and are obtained after subduction from their continuum analogues are utilized. Using novel computational techniques correlation functions of these operators are generated and the variational method is exploited to extract excited states. The lattice spectra that we obtain have baryonic states with well-defined total spins up to 7/2 and the low lying states remarkably resemble the expectations of quantum numbers from SU(6) $\otimes$ O(3) symmetry. Various energy splittings between the extracted states, including splittings due to hyperfine as well as spin-orbit coupling, are considered and those are also compared against similar energy splittings at other quark masses., Comment: 7 pages, 3 tables, 4 figures; Contribution to the 32nd International Symposium on Lattice Field Theory, 23-28 June, 2014, Columbia University New York, NY

Adopting a mixed action approach, we report here results on hadron spectra containing one or more charm quarks. We use overlap valence quarks on a background of 2+1+1 flavor HISQ gauge configurations generated by the MILC collaboration. We also study the ratio of leptonic decay constants, f_Ds*/f_Ds. Results are obtained at two lattice spacings., Comment: 7 pages, 4 figures; presented at the 31st International Symposium on Lattice Field Theory (Lattice 2013), 29 July - 3 August 2013, Mainz, Germany

We present the ground and excited state spectra of singly, doubly and triply-charmed baryons by using dynamical lattice QCD. A large set of baryonic operators that respect the symmetries of the lattice and are obtained after subduction from their continuum analogues are utilized. These operators transform as irreducible representations of SU(3)$_F$ symmetry for flavour, SU(4) symmetry for Dirac spins of quarks and O(3) symmetry for orbital angular momenta. Using novel computational techniques correlation functions of these operators are generated and the variational method is exploited to extract excited states. The lattice spectra that we obtain have baryonic states with well-defined total spins up to 7/2 and the low lying states remarkably resemble the expectations of quantum numbers from SU(6)$\otimes$O(3) symmetry., Comment: to appear in the proceedings of The 6th International Workshop on Charm Physics (CHARM 2013)

We present the ground and excited state spectra of doubly and triply-charmed baryons by using lattice QCD with dynamical clover fermions. A large set of baryonic operators that respect the symmetries of the lattice and are obtained after subduction from their continuum analogues are utilized. Using novel computational techniques correlation functions of these operators are generated and the variational method is exploited to extract excited states. The lattice spectra that we obtain have baryonic states with well-defined total spins up to 7/2 and the low lying states remarkably resemble the expectations of quantum numbers from SU(6) $\otimes$ O(3) symmetry. Various energy splittings between the extracted states, including splittings due to hyperfine as well as spin-orbit coupling, are considered and those are also compared against similar energy splittings at other quark masses. Using those splittings for doubly-charmed baryons, and taking input of experimental $B_c$ meson mass, we predict the mass splittings of $B^*_c - B_c$ to be about 80 $\pm$ 8 MeV and $m_{\Omega_{ccb}} = 8050\pm10$ MeV., Comment: Presented at the 31st International Symposium on Lattice Field Theory (Lattice 2013), 29 July - 3 August 2013, Mainz, Germany

The spectrum of excitations of triply-charmed baryons is computed using lattice QCD including dynamical light quark fields. Calculations are performed on anisotropic lattices with temporal and spatial spacings a_t = 0.0351(2) and a_s ~ 0.12 fm respectively and with pion mass of about 390 MeV. The spectrum obtained has baryonic states with well-defined total spin up to 7/2 and the low-lying states closely resemble the expectation from models with an SU(6)X O(3) symmetry. Energy splittings between extracted states, including those due to spin-orbit coupling in the heavy quark limit are computed and compared against data at other quark masses., Comment: Version published in PRD

Using non-perturbative lattice method we studied hadronic screening correlators above and immediately below the deconfinement transition temperature, Tc, in the quenched approximation with lattice spacing of 1/(8T) using clover improved Wilson fermions. Simulations were performed at temperatures T /Tc = 0, 0.95 and 1.5. Mesonic screening correlators show no statistically significant thermal effects below Tc, and clear evidence for weakly interacting quarks above Tc . Baryon screening correlators yield similar physics above Tc, but show precursor effects for chiral symmetry restoration below Tc ., Comment: 12 pages, 8 figures, typos corrected

We report here results on charm and strange hadron spectra. Adopting a mixed action approach, we use overlap fermions for valence quarks, on a background of 2+1+1 flavours HISQ gauge configurations of MILC collaboration. Two lattice spacings (0.09 fm and 0.06 fm) are used. We find the hyperfine splitting of 1S charmonia to be 114(3)(-2) MeV and 109(4)(-3) MeV, and the splitting (m(Omega_ccc)-3/2 m(J\Psi)) is found to be 110(20)(-10) MeV and 120(10) MeV, corresponding to lattices with spacings a = 0.09 and 0.06 fm respectively. We also look at the ratio of the leptonic decay constant f_Ds*/f_Ds., Comment: 7 pages, 5 figures, Proceedings of the 30th International Symposium on Lattice Field Theory, June 24 - 29, 2012, Cairns, Australia, to appear as PoS(Lattice 2012)141