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Item Open Access Characterization of SABRE crystal NaI-33 with direct underground counting(Springer, 2021) Antonello, M.; Arnquist, I.J.; Barberio, E.; Baroncelli, T.; Benziger, J.; Bignell, L.J.; Bolognino, I.; Calaprice, F.; Copello, S.; Dafinei, I.; D’Angelo, D.; D’Imperio, G.; D’Incecco, M.; Di Carlo, G.; Diemoz, M.; Di Giacinto, A.; Di Ludovico, A.; Dix, W.; Duffy, A.R.; Hoppe, E.; et al.Ultra-pure NaI(Tl) crystals are the key element for a model-independent verification of the long standing DAMA result and a powerful means to search for the annual modulation signature of dark matter interactions. The SABRE collaboration has been developing cutting-edge techniques for the reduction of intrinsic backgrounds over several years. In this paper we report the first characterization of a 3.4 kg crystal, named NaI-33, performed in an underground passive shielding setup at LNGS. NaI-33 has a record low ³⁹K contamination of 4.3 ± 0.2 ppb as determined by mass spectrometry. We measured a light yield of 11.1 ± 0.2 photoelectrons/keV and an energy resolution of 13.2% (FWHM/E) at 59.5 keV. We evaluated the activities of ²²⁶Ra and ²²⁸Th inside the crystal to be 5.9±0.6 μBq/kg and 1.6±0.3 μBq/kg, respectively, which would indicate a contamination from ²³⁸U and ²³²Th at part-per-trillion level. We measured an activity of 0.51 ± 0.02 mBq/kg due to ²¹⁰Pb out of equilibrium and a α quenching factor of 0.63 ± 0.01 at 5304 keV. We illustrate the analyses techniques developed to reject electronic noise in the lower part of the energy spectrum. A cut-based strategy and a multivariate approach indicated a rate, attributed to the intrinsic radioactivity of the crystal, of ∼1 count/day/kg/keV in the [5–20] keV region.Item Metadata only Instanton contributions to the low-lying hadron mass spectrum(American Physical Society, 2015) Thomas, S.; Kamleh, W.; Leinweber, D.The role of instanton-like objects in the QCD vacuum on the mass spectrum of low-lying light hadrons is explored in lattice QCD. Using overimproved stout-link smearing, tuned to preserve instanton-like objects in the QCD vacuum, the evolution of the mass spectrum under smearing is examined. The calculation is performed using a 20³×40 dynamical fat-link-irrelevant-clover (FLIC) fermion action ensemble with lattice spacing 0.126 fm. Through the consideration of a range of pion masses, the effect of the vacuum instanton content is compared at a common pion mass. While the qualitative features of ground-state hadrons are preserved on instanton-dominated configurations, the excitation spectrum experiences significant changes. The underlying physics revealed shows little similarity to the direct-instanton-interaction predictions of the instanton liquid model.Item Metadata only Magnetic properties of the nucleon in a uniform background field(American Physical Society, 2014) Primer, T.; Kamleh, W.; Leinweber, D.; Burkardt, M.We present results for the magnetic moment and magnetic polarizability of the neutron and the magnetic moment of the proton. These results are calculated using the uniform background field method on 323×64 dynamical QCD lattices provided by the PACS-CS Collaboration as part of the ILDG. We use a uniform background magnetic field quantized by the periodic spatial volume. We investigate ways to improve the effective energy plots used to calculate magnetic polarizabilities, including the use of correlation matrix techniques with various source smearings.Item Metadata only J∕Ψ mass shift and J∕Ψ‐nuclear bound state(AIP Press, 2011) Tsushima, K.; Lu, D.; Krein, G.; Thomas, A.; Tropical QCD Workshop (2nd : 2010 : Cairns, Qld.); Kizilersu, A.; Thomas, A.W.; Special Research Centre for the Subatomic Structure of MatterWe calculate mass shift of the J∕Ψ meson in nuclear matter arising from the modification of DD, DD∗ and D∗D∗ meson loop contributions to the J∕Ψ self‐energy. The estimate includes the in‐medium D and D∗ meson masses consistently. The J∕Ψ mass shift (scalar potential) calculated is negative (attractive), and is complementary to the attractive potential obtained from the QCD color van der Waals forces. Some results for the J∕Ψ‐nuclear bound state energies are also presented.Item Metadata only Wave function of the Roper from lattice QCD(Elsevier Science BV, 2013) Roberts, D.; Kamleh, W.; Leinweber, D.; Special Research Centre for the Subatomic Structure of MatterWe apply the eigenvectors from a variational analysis in lattice QCD to successfully extract the wave function of the Roper state, and a higher mass P11 state of the nucleon. We use the 2+1 flavour 323×64 PACS-CS configurations at a near-physical pion mass of 156 MeV. We find that both states exhibit a structure consistent with a constituent quark model. The Roper d-quark wave function contains a single node consistent with a 2S state, and the third state wave function contains two, consistent with a 3S state. A detailed comparison with constituent quark model wave functions is carried out, obtained from a Coulomb plus ramp potential. These results validate the approach of accessing these states by constructing a variational basis composed of different levels of fermion source and sink smearing. Furthermore, significant finite volume effects are apparent for these excited states which mix with multi-particle states, driving their masses away from physical values and enabling the extraction of resonance parameters from lattice QCD simulations. © 2013 .Item Metadata only Finite-volume corrections to charge radii(Elsevier Science BV, 2013) Hall, J.; Leinweber, D.; Owen, B.; Young, R.; Special Research Centre for the Subatomic Structure of MatterThe finite-volume nature of lattice QCD entails a variety of effects that must be handled in the process of performing chiral extrapolations. Since the pion cloud that surrounds hadrons becomes distorted in a finite volume, hadronic observables must be corrected before one can compare with the experimental values. The electric charge radius of the nucleon is of particular interest when considering the implementation of finite-volume corrections. It is common practice in the literature to transform electric form factors from the lattice into charge radii prior to analysis. However, there is a fundamental difficulty with using these charge radii in a finite-volume extrapolation. The subtleties are a consequence of the absence of a continuous derivative on the lattice. A procedure is outlined for handling such finite-volume corrections, which must be applied directly to the electric form factors themselves rather than to the charge radii. © 2013 Elsevier B.V.Item Metadata only Production of Ξ⁻-hypernuclei via the (K⁻, K⁺) reaction in a quark-meson coupling model(Springer-Verlag Wien, 2013) Tsushima, K.; Shyam, R.; Thomas, A.; Special Research Centre for the Subatomic Structure of MatterWe study the production of Ξ⁻-hypernuclei, ¹²Ξ⁻ Be and ²⁸Ξ⁻ Mg, via the (K⁻, K⁺) reaction within a covariant effective Lagrangian model, employing the bound Ξ⁻ and proton spinors calculated by the latest quark-meson coupling model. The present treatment yields the 0° differential cross sections for the formation of simple s-state Ξ− particle-hole states peak at a beam momentum around 1.0 GeV/c with a value in excess of 1 μb.Item Metadata only Chiral extrapolations for nucleon electric charge radii(American Physical Soc, 2013) Hall, J.; Leinweber, D.; Young, R.; Special Research Centre for the Subatomic Structure of MatterLattice simulations for the electromagnetic form factors of the nucleon yield insights into the internal structure of hadrons. The logarithmic divergence of the charge radius in the chiral limit poses an interesting challenge in achieving reliable predictions from finite-volume lattice simulations. Recent results near the physical pion mass (m(π)∼180 MeV) are examined in order to confront the issue of how the chiral regime is approached. The electric charge radius of the nucleon isovector presents a forum for achieving consistent finite-volume corrections. Newly developed techniques within the framework of chiral effective field theory (χEFT) are used to achieve a robust extrapolation of the electric charge radius to the physical pion mass and to infinite volume. The chiral extrapolations exhibit considerable finite-volume dependence; lattice box sizes of L≳7 fm are required in order to achieve a direct lattice simulation result within 2% of the infinite-volume value at the physical point. Predictions of the volume dependence are provided to guide the interpretation of future lattice results.Item Open Access Resonant phase shift from finite volume interactions(Proceedings of Science, 2012) Hsu, A.; Hall, J.; Young, R.; Thomas, A.; International Symposium on Lattice Field Theory (30th : 2012 : Cairns, Australia)A scattering process can be modelled by a finite volume lattice with appropriate boundary conditions. Such lattices have intermediate states with discretized energy spectrum. With Lüscher’s formula we can obtain the phase shifts of these states. We constructed a three dimensional, non-relativistic model for the scattering of two scalar mesons on a lattice. The resonant energy spectra at different lattice sizes were obtained. Using Lüscher’s formula, the corresponded phase shifts were calculated. Then, we compared the infinite volume phase shifts with the finite volume phase shifts acquired by Lüscher’s formula.Item Open Access Baryon resonances and hadronic interactions in a finite volume(Proceedings of Science, 2012) Hall, J.; Hsu, A.; Leinweber, D.; Thomas, A.; Young, R.; International Symposium on Lattice Field Theory (30th : 2012 : Cairns, Australia)In a finite volume, resonances and multi-hadron states are identified by discrete energy levels. When comparing the results of lattice QCD calculations to scattering experiments, it is important to have a way of associating the energy spectrum of the finite-volume lattice with the asymptotic behaviour of the S-matrix. A new technique for comparing energy eigenvalues with scattering phase shifts is introduced, which involves the construction of an exactly solvable matrix Hamiltonian model. The model framework is applied to the case of ∆ → Nπ decay, but is easily generalized to include multi-channel scattering. Extracting resonance parameters involves matching the energy spectrum of the model to that of a lattice QCD calculation. The resulting fit parameters are then used to generate phase shifts. Using a sample set of pseudodata, it is found that the extraction of the resonance position is stable with respect to volume for a variety of regularization schemes, and compares favorably with the well-known Lüscher method. The model-dependence of the result is briefly investigated.Item Open Access The influence of instantons on the quark propagator(Proceedings of Science, 2012) Trewartha, D.; Kamleh, W.; Leinweber, D.; Moran, P.; International Symposium on Lattice Field Theory (30th : 2012 : Cairns, Australia)We use over-improved stout-link smearing to investigate the presence and nature of instantons on the lattice. We find that smearing can remove short-range effects with little damage to the longrange structure of the gauge field, and that after around 50 sweeps this process is complete. There are more significant risks for very high levels of smearing beyond 100 sweeps. We are thus able to produce gauge configurations dominated by instanton effects. We then calculate the overlap quark propagator on these configurations, and thus the non-perturbative mass function. We find that smeared configurations preserve the majority of dynamical mass generation, and conclude that instantons are primarily responsible for the dynamical generation of mass.Item Open Access Scale setting, sigma terms and the Feynman-Hellman theorem(Proceedings of Science, 2012) Shanahan, P.; Thomas, A.; Young, R.; International Symposium on Lattice Field Theory (30th : 2012 : Cairns, Australia)The authors recently presented new values for the octet baryon sigma terms. These were extracted using the Feynman-Hellman theorem from a chiral perturbation theory fit to octet baryon mass data from the PACS-CS collaboration. Of particular interest is the precise determination of the strangeness sigma term δs = 21±6 MeV. In this work, we elaborate on the critical effect which the choice of scale setting has on this value. We discuss the prospect that the comparison of direct and 'spectrum' determinations of the sigma terms from the lattice can provide insight not only into scale setting on the lattice, but into QCD itself.Item Open Access Magnetic properties of the neutron in a uniform background field(Proceedings of Science, 2012) Primer, T.; Kamleh, W.; Leinweber, D.; Burkardt, M.; International Symposium on Lattice Field Theory (30th : 2012 : Cairns, Australia)We present calculations of the magnetic moment and magnetic polarisability of the neutron from the background field method. The calculations are performed on 32³ × 64 dynamical lattices generated by the PACS-CS collaboration and made available via the ILDG. We consider uniform fields quantised by the periodic spatial volume. We explore different approaches for improving the quality of the fits used in the results. Also included are initial results for the magnetic moment of the lowest lying negative parity nucleon states.Item Open Access Instanton contributions to the low-lying hadronic mass spectrum(Proceedings of Science, 2012) Thomas, S.; Kamleh, W.; Leinweber, D.; International Symposium on Lattice Field Theory (30th : 2012 : Cairns, Australia)The masses of the light hadrons are calculated on in lattice QCD at various stages of stout-link smearing tuned specifically to preserve instanton-like objects. The calculation is performed using a 20³ × 40 dynamical FLIC ensemble with lattice spacing 0.126 fm at a range of pion masses; the effect of vacuum instanton content is compared at a common pion mass of 350 MeV. We find little evidence that the instanton effect is as significant as models would suggest. In fact, the direct instanton-induced effect cannot be seen at all.Item Open Access Odd-parity nucleon eigenstates in full QCD(Proceedings of Science, 2012) Mahbub, M.; Kamleh, W.; Leinweber, D.; Moran, P.; Williams, A.; International Symposium on Lattice Field Theory (30th : 2012 : Cairns, Australia)The results for the odd-parity nucleon spectrum at light quark masses are presented. The 2+1 flavor gauge configurations generated by the PACS-CS collaboration are used and the analysis is performed at the lightest pion mas of 156 MeV. The energy eigenstates are tracked by following the evolution of the eigenvector as the quark mass changes. The two lowest-energy odd-parity states revealed are found to be in accord with the physical N½⁻ spectrum of Nature.Item Open Access Correlation matrix methods for excited meson form factors in full QCD(Proceedings of Science, 2012) Owen, B.; Kamleh, W.; Leinweber, D.; Mahbub, M.; Menadue, B.; International Symposium on Lattice Field Theory (30th : 2012 : Cairns, Australia)In recent years, there has been increasing interest in hadronic excitations. So how would one go about exploring hadron resonances and their structure in the context of Lattice QCD? We outline how the variational method can be utilised for form factor calculations. This variational approach not only provides us with a method for extracting excited state hadron form factors, but also results in dramatic improvement in ground state calculations through the removal of excited state contaminations. Here we present both these aspects in the context of π and ρ meson form factors.Item Open Access Electromagnetic form factors of the Λ(1405) in (2+1)-flavour lattice QCD(Proceedings of Science, 2012) Menadue, B.; Kamleh, W.; Leinweber, D.; Mahbub, M.; Owen, B.; International Symposium on Lattice Field Theory (30th : 2012 : Cairns, Australia)The Λ(1405) is unusual in that it lies surprisingly low in mass. At 1405.1 MeV, it lies lower than the lowest-lying odd-parity state of the nucleon, even though it contains a valence strange quark. We build on our recent success in isolating this otherwise elusive state in lattice QCD using correlation matrix techniques coupled with source and sink smearing, and present first results from our world-first calculation of the electromagnetic form factors of this unusual state. We use the PACS-CS (2+1)-flavour full-QCD ensembles, available through the ILDG.Item Open Access Light meson transition form factors on the lattice(Proceedings of Science, 2012) Owen, B.; Kamleh, W.; Leinweber, D.; El Bakry Mahmoud, A.; Moran, P.; International Symposium on Lattice Field Theory (30th : 2012 : Cairns, Australia)Here we present exploratory calculations of the light meson radiative transition moment ρ → γπ from lattice QCD. We observe interesting chiral curvature in the form factor and a definite environment sensitivity in the quark sector contributions. Results are compared with the simple quark model and experiment.Item Open Access The wave function of the Roper resonance(Proceedings of Science, 2012) Roberts, D.; Kamleh, W.; Leinweber, D.; International Symposium on Lattice Field Theory (30th : 2012 : Cairns, Australia)We apply the eigenvectors from a variational analysis to successfully extract the wave function of the Roper state, and the next P₁₁ state of the nucleon, associated with the N*(1710). We find that both states exhibit a structure consistent with a constituent quark model. The Roper d-quark wave function contains a single node consistent with a 2S state, and the N*(1710) contains two, consistent with a 3S state. A detailed investigation of the mass dependence of the wave functions of these states is carried out at four quark masses. The lightest mass provides a pion mass of 156 MeV, just slightly above the physical mass of 139.6 MeV. The ground state wave function shows little mass dependence, consistent with prior wave function investigations. The wave functions of the Roper and second excited state show finite volume effects which become prominent at heavier quark masses than for the ground state.Item Open Access Multi-particle baryon spectroscopy(Proceedings of Science, 2012) Kiratidis, A.; Kamleh, W.; Leinweber, D.; Moran, P.; International Symposium on Lattice Field Theory (30th : 2012 : Cairns, Australia)In Nature the excited states of the hadron spectrum appear as resonances. Consequently, there has been significant interest in studying the excited baryon spectrum using lattice QCD.With this in mind we perform spectroscopic calculations with five-quark interpolating fields. Stochastic estimation techniques are used in order to calculate the loop propagators, with dilution in spin, colour and time implemented as a means of variance reduction. We present effective mass plots extracted from these five-quark interpolators, and examine the contributions from fully-connected and loop-containing pieces of the correlation function, keeping in mind their use in future correlation matrix studies.