Showing papers by "Huey-Wen Lin published in 2012"
TL;DR: The most stringent limit on scalar and tensor interactions arise from 0 +! 0 + + nuclear decays and the radiative pion decay as discussed by the authors, respectively, and they have been studied in the context of collider searches.
Abstract: Scalar and tensor interactions were once competitors to the now well-established V A structure of the Standard Model weak interactions. We revisit these interactions and survey constraints from low-energy probes (neutron, nuclear, and pion decays) as well as collider searches. Currently, the most stringent limit on scalar and tensor interactions arise from 0 + ! 0 + nuclear decays and the radiative pion decay ! e , respectively. For the future, we
240 citations
TL;DR: In this article, the binding energies of the deuteron, the dineutron, the H-dibaryon, and the DQC system at a pion mass of
Abstract: Results of a high-statistics, multivolume lattice QCD exploration of the deuteron, the dineutron, the H-dibaryon, and the ${\ensuremath{\Xi}}^{\ensuremath{-}}{\ensuremath{\Xi}}^{\ensuremath{-}}$ system at a pion mass of ${m}_{\ensuremath{\pi}}\ensuremath{\sim}390\text{ }\text{ }\mathrm{MeV}$ are presented. Calculations were performed with an anisotropic ${n}_{f}=2+1$ clover discretization in four lattice volumes of spatial extent $L\ensuremath{\sim}2.0$, 2.5, 2.9, and 3.9 fm, with a lattice spacing of ${b}_{s}\ensuremath{\sim}0.123\text{ }\text{ }\mathrm{fm}$ in the spatial direction and ${b}_{t}\ensuremath{\sim}{b}_{s}/3.5$ in the time direction. Using the results obtained in the largest two volumes, the ${\ensuremath{\Xi}}^{\ensuremath{-}}{\ensuremath{\Xi}}^{\ensuremath{-}}$ is found to be bound by ${B}_{{\ensuremath{\Xi}}^{\ensuremath{-}}{\ensuremath{\Xi}}^{\ensuremath{-}}}0=14.0(1.4)(6.7)\text{ }\text{ }\mathrm{MeV}$, consistent with expectations based upon phenomenological models and low-energy effective field theories constrained by nucleon-nucleon and hyperon-nucleon scattering data at the physical light-quark masses. Further, we find that the deuteron and the dineutron have binding energies of ${B}_{d}=11(05)(12)\text{ }\text{ }\mathrm{MeV}$ and ${B}_{nn}=7.1(5.2)(7.3)\text{ }\text{ }\mathrm{MeV}$, respectively. With an increased number of measurements and a refined analysis, the binding energy of the H-dibaryon is ${B}_{H}=13.2(1.8)(4.0)\text{ }\text{ }\mathrm{MeV}$ at this pion mass, updating our previous result.
151 citations
TL;DR: In this article, a ground-state charmed-baryon spectrum using 2+1+1 flavors of dynamical quarks was calculated using a relativistic heavy-quark action for the valence charm quark, clover-Wilson fermions for valence light and strange quarks, and HISQ sea quarks.
Abstract: We present the results of a calculation of the positive-parity ground-state charmed-baryon spectrum using 2+1+1 flavors of dynamical quarks. The calculation uses a relativistic heavy-quark action for the valence charm quark, clover-Wilson fermions for the valence light and strange quarks, and HISQ sea quarks. The spectrum is calculated with a lightest pion mass around 220 MeV, and three lattice spacings (a \approx 0.12 fm, 0.09 fm, and 0.06 fm) are used to extrapolate to the continuum. The light-quark mass extrapolation is performed using heavy-hadron chiral perturbation theory up to O(m_pi^3) and at next-to-leading order in the heavy-quark mass. For the well-measured charmed baryons, our results show consistency with the experimental values. For the controversial J=1/2 Xi_{cc}, we obtain the isospin-averaged value M_{Xi_{cc}}=3595(39)(20)(6) MeV (the three uncertainties are statistics, fitting-window systematic, and systematics from other lattice artifacts, such as lattice scale setting and pion-mass determination), which shows a 1.7 sigma deviation from the experimental value. We predict the yet-to-be-discovered doubly and triply charmed baryons Xi_{cc}^*, Omega_{cc}, Omega_{cc}^* and Omega_{ccc} to have masses 3648(42)(18)(7) MeV, 3679(40)(17)(5) MeV, 3765(43)(17)(5) MeV and 4761(52)(21)(6) MeV, respectively.
91 citations
University of New Hampshire1, University of Barcelona2, University of Washington3, Thomas Jefferson National Accelerator Facility4, College of William & Mary5, Massachusetts Institute of Technology6, Lawrence Livermore National Laboratory7, Lawrence Berkeley National Laboratory8, University of California, Berkeley9
TL;DR: In this article, the 1 S 0 and 3 S 1 spinchannels calculated with Lattice QCD (LQCD) were used to quantify the energy shift of the hyperon in dense neutron matter, as might occur in the interior of a neutron star.
Abstract: eld theory. The interactions determined from QCD are consistent with those extracted from hyperon-nucleon experimental data within uncertainties, and strengthen theoretical arguments that the strange quark is a crucial component of dense nuclear matter. The interactions between hyperons and nucleons are important for understanding the composition of dense nuclear matter. In high-density baryonic systems, the large values of the Fermi energies may make it energetically advantageous for some of the nucleons to transform into hyperons via the weak interactions, with the increase in rest mass being more than compensated for by the decrease in combined Fermi energy of the baryon-lepton system. This is speculated to occur in the interior of neutron stars, but a quantitative understanding of this phenomenon depends on knowledge of the hyperon-nucleon (YN) interactions in the medium. In this letter we use n scattering phase shifts in the 1 S0 and 3 S1 spinchannels calculated with Lattice QCD (LQCD) to quantify the energy shift of the hyperon in dense neutron matter, as might occur in the interior of a neutron star. Our results strongly suggest an important role for strangeness in such environments. Precise nucleon-nucleon (NN) interactions constrained by experiment and chiral symmetry, together with numerically small but important three-nucleon interactions, have served as input to rened many-body techniques for
78 citations
TL;DR: In this paper, the π+π+ s-wave scattering phase-shift is determined below the inelastic threshold using Lattice QCD, at a pion mass of mπ ≈ 390 MeV with an anisotropic nf = 2+1 clover fermion discretization in four lattice volumes, with spatial extent L ≈ 2.0, 2.5, 3.0 and 3.9 fm.
Abstract: The π+π+ s-wave scattering phase-shift is determined below the inelastic threshold using Lattice QCD. Calculations were performed at a pion mass of mπ ≈ 390 MeV with an anisotropic nf = 2+1 clover fermion discretization in four lattice volumes, with spatial extent L ≈ 2.0, 2.5, 3.0 and 3.9 fm, and with a lattice spacing of bs ≈ 0.123 fm in the spatial direction and bt bs/3.5 in the time direction. The phase-shift is determined from the energy-eigenvalues of π+π+ systems with both zero and non-zero total momentum in the lattice volume using Luscher's method. Our calculations are precise enough to allow for a determination of the threshold scattering parameters, the scattering length a, the effective range r, and the shape-parameter P, in this channel and to examine the prediction of two-flavor chiral perturbation theory: mπ2 a r = 3+O(mπ2/Λχ2). Chiral perturbation theory is used, with the Lattice QCD results as input, to predict the scattering phase-shift (and threshold parameters) at the physical pion mass. Our results are consistent with determinations from the Roy equations and with the existing experimental phase shift data.
74 citations
TL;DR: In this article, it was shown that the correlation functions on the lattice with a gauge-invariant nucleon interpolation field and replacing the gauge link in the quark lattice momentum operator with unity corresponds to the partial derivative in the continuum.
Abstract: It is argued by the author that the canonical form of the quark energy-momentum tensor with a partial derivative instead of the covariant derivative is the correct definition for the quark momentum and angular momentum fraction of the nucleon in covariant quantization. Although it is not manifestly gauge invariant, its matrix elements in the nucleon will be non-vanishing and are gauge invariant. We test this idea in the path-integral quantization by calculating correlation functions on the lattice with a gauge-invariant nucleon interpolation field and replacing the gauge link in the quark lattice momentum operator with unity, which corresponds to the partial derivative in the continuum. We find that the ratios of three-point to two-point functions are zero within errors for both the u and d quarks, contrary to the case without setting the gauge links to unity.
15 citations
18 Apr 2012
TL;DR: In this article, the authors give an overview of the latest progress in lattice-QCD calculations of the Roper resonance and Roper-nucleon electromagnetic and axial transition form factors using dynamical gauge ensembles.
Abstract: In this proceeding, I give an overview of the latest progress in lattice-QCD calculations of the Roper resonance, and Roper-nucleon electromagnetic and axial transition form factors using dynamical gauge ensembles.
14 citations
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Abstract: We report a complete calculation of the quark and glue momenta and angular momenta in the proton. These include the quark contributions from both the connected and disconnected insertions. The calculation is carried out on a $16^3 \times 24$ quenched lattice at $\beta = 6.0$ and for Wilson fermions with $\kappa = 0.154, 0.155,$ and 0.1555 which correspond to pion masses at 650, 538, and 478 MeV. The quark loops are calculated with $Z_4$ noise and signal-to-noise is improved further with unbiased subtractions. The glue operator is comprised of gauge-field tensors constructed from the overlap operator. The $u$ and $d$ quark momentum/angular momentum fraction is 0.66(5)/0.72(5), the strange momentum/angular momentum fraction is 0.024(6)/0.023(7), and that of the glue is 0.31(6)/0.25(8). The orbital angular momenta of the quarks are obtained from subtracting the angular momentum component from its corresponding spin. As a result, the quark orbital angular momentum constitutes 0.50(2) of the proton spin, with almost all it coming from the disconnected insertion. The quark spin carries a fraction 0.25(12) and glue carries a fraction 0.25(8) of the total proton spin.
13 citations
20 Dec 2012
TL;DR: In this paper, the authors revisited the systematic uncertainties in recent calculations of gA and review prospects for future calculations, and proposed higher-order operators in the neutron electric dipole moment Lagrangian, which would be useful when combined with effective theory to probe BSM.
Abstract: Study of the hadronic matrix elements can provide not only tests of the QCD sector of the Standard Model (in comparing with existing experiments) but also reliable low-energy hadronic quantities applicable to a wide range of beyond-the-Standard Model scenarios where experiments or theoretical calculations are limited or difficult. On the QCD side, progress has been made in the notoriously difficult problem of addressing gluonic structure inside the nucleon, reaching higherQ2 region of the form factors, and providing a complete picture of the proton spin. However, even further study and improvement of systematic uncertainties are needed. There are also proposed calculations of higher-order operators in the neutron electric dipole moment Lagrangian, which would be useful when combined with effective theory to probe BSM. Lattice isovector tensor and scalar charges can be combined with upcoming neutron beta-decay measurements of the Fierz interference term and neutrino asymmetry parameter to probe new interactions in the effective theory, revealing the scale of potential new TeV particles. Finally, I revisit the systematic uncertainties in recent calculations of gA and review prospects for future calculations.
9 citations
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TL;DR: In this paper, the authors study low-energy hadronic quantities applicable to a wide range of beyond-the-Standard Model scenarios where experiments or theoretical calculations are limited or difficult.
Abstract: Study of the hadronic matrix elements can provide not only tests of the QCD sector of the Standard Model (in comparing with existing experiments) but also reliable low-energy hadronic quantities applicable to a wide range of beyond-the-Standard Model scenarios where experiments or theoretical calculations are limited or difficult. On the QCD side, progress has been made in the notoriously difficult problem of addressing gluonic structure inside the nucleon, reaching higher-$Q^2$ region of the form factors, and providing a complete picture of the proton spin. However, even further study and improvement of systematic uncertainties are needed. There are also proposed calculations of higher-order operators in the neutron electric dipole moment Lagrangian, which would be useful when combined with effective theory to probe BSM. Lattice isovector tensor and scalar charges can be combined with upcoming neutron beta-decay measurements of the Fierz interference term and neutrino asymmetry parameter to probe new interactions in the effective theory, revealing the scale of potential new TeV particles. Finally, I revisit the systematic uncertainties in recent calculations of $g_A$ and review prospects for future calculations.
6 citations
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TL;DR: In this article, the authors describe the status of their Lattice QCD program of using valence clover fermions on dynamical N_f=2+1+1 + 1 HISQ configurations generated by the MILC Collaboration.
Abstract: We motivate undertaking precision analyses of neutron decays to look for signatures of new scalar and tensor interactions that can arise in extensions of the Standard Model at the TeV scale. The key ingrediant needed to connect experimental data with theoretical analysis are high-precision calculations of matrix elements of isovector bilinear operators between the decaying neutron and final state proton. We describe the status of our Lattice QCD program of using valence clover fermions on dynamical N_f=2+1+1 HISQ configurations generated by the MILC Collaboration. On the theoretical side we use the effective field theory method and provide both model independent and dependent analyses to obtain bounds on possible scalar and tensor interactions, both from low energy experiments and LHC data.
20 Apr 2012
TL;DR: In this article, the authors discuss a few representative areas in which lattice QCD can contribute to the search for BSM physics, emphasizing suppressed operators in neutron decay, and outline prospects for future development.
Abstract: Precision measurements of nucleons provide constraints on the Standard Model and can discern the signatures predicted for particles beyond the Standard Model (BSM). Knowing the Standard Model inputs to nucleon matrix elements will be necessary to constrain the couplings of dark matter candidates such as the neutralino, to relate the neutron electric dipole moment to the CP-violating theta parameter, or to search for new TeV-scale particles though non-V–A interactions in neutron beta decay. However, these matrix elements derive from the properties of quantum chromodynamics (QCD) at low energies, where perturbative treatments fail. Using lattice gauge theory, we can nonperturbatively calculate the QCD path integral on a supercomputer. In this proceeding, I will discuss a few representative areas in which lattice QCD (LQCD) can contribute to the search for BSM physics, emphasizing suppressed operators in neutron decay, and outline prospects for future development.
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TL;DR: In this article, the authors present an update on the calculation of matrix elements of iso-vector scalar, axial and tensor charges between a neutron and a proton state.
Abstract: We present an update on the calculation of matrix elements of iso-vector scalar, axial and tensor charges between a neutron and a proton state. These matrix elements are needed to probe novel scalar and tensor interactions in neutron beta-decay that can arise in extensions of the Standard Model at the TeV scale. Our calculations are being done using valence clover fermions on dynamical N_f=2+1+1 HISQ configurations generated by the MILC Collaboration. We provide preliminary estimates of the dependence of these matrix elements on the light quark masses, lattice spacing, and the time separation between the source and sink of the nucleons. We also find that the renormalization constants calculated using the RI-sMOM scheme are close to unity for the HYP smeared HISQ lattices.
20 Dec 2012
TL;DR: In this article, the authors present an update on the calculation of matrix elements of iso-vector scalar, axial and tensor charges between a neutron and a proton state.
Abstract: We present an update on the calculation of matrix elements of iso-vector scalar, axial and tensor charges between a neutron and a proton state. These matrix elements are needed to probe novel scalar and tensor interactions in neutron beta-decay that can arise in extensions of the Standard Model at the TeV scale. Our calculations are being done using valence clover fermions on dynamical N f = 2+ 1+ 1 HISQ configurations generated by the MILC Collaboration. We provide preliminary estimates of the dependence of these matrix elements on the light quark masses, lattice spacing, and the time separation between the source and sink of the nucleons. We also find that the renormalization constants calculated using the RI-sMOM scheme are close to unity for the HYP smeared HISQ lattices.
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TL;DR: In this article, the authors review the constraints on weak interactions from nuclear and hadronic decays, as well as from collider searches, and show that the most stringent bounds come from the analysis of the 0+ to 0+ nuclear and the pi to e nu gamma radiative pion decays.
Abstract: The standard model weak interactions can be described by four-fermion V-A operators at low energies. New physics at the TeV scale can, however, generate the other Lorentz structures. In this talk, we review the constraints on such interactions from nuclear and hadronic decays, as well as from collider searches. Currently the most stringent bounds come from the analysis of the 0+ to 0+ nuclear and the pi to e nu gamma radiative pion decays. In the near future, the ultracold neutron beta decay experiments and the direct LHC measurements will compete in setting the most stringent bounds, provided, however, that the neutron-to-proton non-perturbative transition matrix elements can be calculated to a level of 10-20% accuracy.