arXiv subjects

Parikshit Junnarkar

Publications and source records attributed to Parikshit Junnarkar.

12 recordsLinked to original sources

arXiv2022

Study of three-flavored heavy dibaryons using lattice QCD

We present results of the first lattice QCD calculation of three-flavored heavy dibaryons both in the flavor-symmetric and antisymmetric channels. These dibaryons have spin zero, and are constructed using various possible combinations of quark flavors with at least one of them as the charm or the bottom quark, i.e., namely, $H_c(cudcud), H_b(budbud), H_{bcs}(bcsbcs)$, $H_{csl}(cslcsl), H_{bsl}(bslbsl)$ and $H_{bcl}(bclbcl)$; $l\in u,d$. We compute the ground state masses of these dibaryons and the calculations are performed on three $N_f=2+1+1$ HISQ gauge ensembles of the MILC collaboration, with lattice spacings $a =$ 0.1207, 0.0888 and 0.0582 fm. A relativistic overlap action is employed for the valence light to charm quarks while a non-relativistic-QCD Hamiltonian with improved coefficients is used for the bottom quarks. Unlike the doubly heavy tetraquarks, one and two-flavored heavy dibaryons, for which lattice QCD calculations have predicted deeply bound strong-interactions-stable states, for these $H_c, H_b, H_{csl},H_{bsl}$ dibaryons we do not find any such deeply bound state. However, for $H_{bcs}$, our results indicate the presence of an energy level $29\pm 24$ MeV below the lowest two-baryon threshold, which could be relevant for its future experimental searches. Moreover, we find that the energy difference between the ground state of $H_{bcl}$ and its lowest threshold increases when $m_l>m_s$. Taken together, our findings indicate the possibility of the existence of the $H_{bcs}$ dibaryon while all other physical three-flavored dibaryons are much closer to their thresholds suggesting either they are weakly bound or unbound, resolving which requires further detail study. Our results also point that the binding of a dibaryon configuration becomes stronger with the increase of its valence quark masses which suggests an interesting aspect of strong interactions at multiple scales.

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arXiv2021

$H$ dibaryon away from the $SU(3)_f$ symmetric point

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.

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arXiv2019

Deuteron-like heavy dibaryons from Lattice QCD

We report the first lattice quantum chromodynamics (QCD) study of deuteron($np$)-like dibaryons with heavy quark flavours. These include particles with following dibaryon structures and valence quark contents: $Σ_cΞ_{cc} (uucucc)$, $Ω_cΩ_{cc} (sscscc)$, $Σ_bΞ_{bb} (uububb)$, $Ω_bΩ_{bb} (ssbsbb)$ and $Ω_{ccb}Ω_{cbb} (ccbcbb)$, and with spin ($J$)-parity ($P$), $J^{P} \equiv 1^{+}$. Using a state-of-the art lattice QCD calculation, after controlling relevant systematic errors, we unambiguously find that the ground state masses of dibaryons $Ω_cΩ_{cc} (sscscc)$, $Ω_bΩ_{bb} (ssbsbb)$ and $Ω_{ccb}Ω_{cbb} (ccbcbb)$ are below their respective two-baryon thresholds, suggesting the presence of bound states which are stable under strong and electromagnetic interactions. We also predict their masses precisely. For dibaryons $Σ_cΞ_{cc} (uucucc)$, and $Σ_bΞ_{bb} (uububb)$, we could not reach to a definitive conclusion about the presence of any bound state due to large systematics associated with these states. We also find that the binding of these dibaryons becomes stronger as they become heavier in mass. This study also opens up the possibility of the existence of many other exotic nuclei, which can be formed through the fusion of heavy baryons, similar to the formation of nuclei of elements in the Periodic Table.

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arXiv2019

Nucleon isovector charges and twist-2 matrix elements with $N_f=2+1$ dynamical Wilson quarks

We present results from a lattice QCD study of nucleon matrix elements at vanishing momentum transfer for local and twist-2 isovector operator insertions. Computations are performed on gauge ensembles with non-perturbatively improved $N_f=2+1$ Wilson fermions, covering four values of the lattice spacing and pion masses down to $M_π\approx200$MeV. Several source-sink separations (typically ~1.0fm to ~1.5fm) allow us to assess excited-state contamination. Results on individual ensembles are obtained from simultaneous two-state fits across all observables and all available source-sink separations with the energy gap as a common fit parameter. Renormalization has been performed non-perturbatively using the Rome-Southampton method for all but the finest lattice spacing for which an extrapolation has been used. Physical results are quoted in the $\overline{MS}$ scheme at a scale of $μ=2$GeV and are obtained from a combined chiral, continuum and finite-size extrapolation. For the nucleon isovector axial, scalar and tensor charges we find physical values of $g_A^{u-d}=1.242(25)_\text{stat}(\genfrac{}{}{0pt}{2}{+00}{-31})_\text{sys}$, $g_S^{u-d}=1.13(11)_\text{stat}(\genfrac{}{}{0pt}{2}{+07}{-06})_\text{sys}$ and $g_T^{u-d}=0.965(38)_\text{stat}(\genfrac{}{}{0pt}{2}{+13}{-41})_\text{sys}$, respectively, where individual systematic errors in each direction from the chiral, continuum and finite-size extrapolation have been added in quadrature. Our final results for the isovector average quark momentum fraction and the isovector helicity and transversity moments are given by $\langle x\rangle_{u-d}=0.180(25)_\text{stat}(\genfrac{}{}{0pt}{2}{+14}{-06})_\text{sys}$, $\langle x\rangle_{Δu-Δd}=0.221(25)_\text{stat}(\genfrac{}{}{0pt}{2}{+10}{-00})_\text{sys}$ and $\langle x\rangle_{δu-δd}=0.212(32)_\text{stat}(\genfrac{}{}{0pt}{2}{+20}{-10})_\text{sys}$, respectively.

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arXiv2019

Study of doubly heavy tetraquarks in Lattice QCD

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 $\mathcal{O}(α_s v^4)$ 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.

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arXiv2018

The $H$ dibaryon from lattice QCD with SU(3) flavor symmetry

We show recent results from the Mainz group using $N_f = 2 + 1$ CLS ensembles generated at the $SU(3)$ symmetric point. Temporal correlation functions using two-baryon interpolating operators are calculated with the distillation method. In addition to the spin-0 operators relevant for studying the $H$ dibaryon, we added spin-1 operators to our basis, thereby extending our results to other flavor sectors. These preliminary results show a finite-volume energy below the $ΛΛ$ threshold. Further calculations are necessary to establish whether the $H$ dibaryon is bound at the physical point.

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arXiv2018

Heavy light tetraquarks from Lattice QCD

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.

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arXiv2017

Nucleon form factors and couplings with $N_\mathrm{f} = 2 + 1$ Wilson fermions

We present updated results on the nucleon electromagnetic form factors and axial coupling calculated using CLS ensembles with $N_\mathrm{f}=2+1$ dynamical flavours of Wilson fermions. The measurements are performed on large, fine lattices with a pseudoscalar mass reaching down to 200 MeV. The truncated-solver method is employed to reduce the variance of the measurements. Estimation of the matrix elements is challenging due to large contamination from excited states and further investigation is necessary to bring these effects under control.

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arXiv2015

Nucleon electromagnetic form factors and axial charge from CLS $N_\mathrm{f}=2+1$ ensembles

We present preliminary results on the electromagnetic form factors and axial charge of the nucleon from ensembles generated by the CLS effort with $N_\mathrm{f}=2+1$ flavours of non-perturbatively $\mathrm{O}(a)$-improved Wilson fermions and open temporal boundary conditions. Systematic effects due to excited-state contamination are accounted for using both two-state fits and the method of summed operator insertions. This exploratory analysis demonstrates the viability of obtaining precision baryon observables with $N_\mathrm{f}=2+1$ flavours of Wilson fermions on fine lattices, aiming towards controlled chiral and continuum limits in the future.

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arXiv2015

Search for the H-Dibaryon in two flavor Lattice QCD

We present preliminary results from a lattice QCD calculation of the H-dibaryon using two flavors of $\mathcal{O}(a)$ improved Wilson fermions. We employ local six-quark interpolating operators at the source with a combination of local six-quark and two-baryon operators at the sink with the appropriate quantum numbers of the H-dibaryon and its coupling to the two-baryon channels. We find that the two-baryon operators provide an improved overlap onto the ground state in comparison to the local six-quark operators. We also apply Lüscher's finite volume formalism to obtain information on the nature of the infinite-volume interaction of two particles. Further, the momentum projection to three moving frames enables the isolation of the pole in the infinite-volume scattering amplitude. Preliminary results at pion masses of 450 MeV and 1 GeV clearly indicate the presence of states below the $ΛΛ$ threshold while a finite-volume analysis fails to conclusively show the existence of an infinite-volume bound state.

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arXiv2014

Search for a bound H-dibaryon using local six-quark interpolating operators

We present early results from a lattice QCD study seeking a bound $H$-dibaryon using $N_f=2$ flavors of $O(a)$ improved Wilson fermions and a quenched strange quark. We compute a matrix of two-point functions using operators consisting of the two independent local products of six positive-parity-projected quarks with the appropriate quantum numbers, which belong to the singlet and 27-plet irreducible representations of flavor SU(3). To expand this basis, we also independently vary the quark-field smearing, and apply a new scheme to reduce the noise caused by smearing. We then find the ground-state mass by solving the generalized eigenvalue problem. We show results from ensembles with pion masses 451 MeV and 1 GeV, and compare with other lattice calculations.

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arXiv2013

The Scalar Strange Content of the Nucleon from Lattice QCD

The scalar strange-quark matrix element of the nucleon is computed with lattice QCD. A mixed-action scheme is used with domain-wall valence fermions computed on the staggered MILC sea-quark configurations. The matrix element is determined by making use of the Feynman-Hellmann theorem which relates this strange matrix element to the change in the nucleon mass with respect to the strange-quark mass. The final result of this calculation is m_s < N | s-bar s| N > = 49 +-10 +- 15 MeV and, correspondingly f_s = m_s < N | s-bar s |N > / m_N = 0.051 +- 0.011 +- 0.016. Given the lack of a quantitative comparison of this phenomenologically important quantity determined from various lattice QCD calculations, we take the opportunity to present such an average. The resulting conservative determination is f_s = 0.043 +- 0.011.

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