We have investigated the electronic and chemical surface properties of a Cu(In 1-x Ga x )Se 2 (CIGSe) thin-film solar cell absorber and a CdS/CIGSe interface sample taken from Nanosolar's ...manufacturing line. Using soft x-ray and UV photoelectron spectroscopy, inverse photoemission, and soft x-ray emission spectroscopy employing high-brilliance synchrotron radiation, we have determined the chemical composition of the surface and near-surface bulk, as well as some of the relevant electronic structure parameters (e.g., the surface band gap of the absorber). We find that the (previously air-exposed) surfaces show a surprisingly low degree of carbon-containing surface adsorbates, the presence of sodium and selenium oxide species on the surface of both samples, a significant S/Se intermixing at the CdS/CIGSe interface, and, as is common for high-efficiency CIGSe absorbers after surface cleaning, an electronic surface band gap (1.45 ± 0.15 eV) that is noticeably larger than the optical bulk band gap.
We present a lattice analysis of the light pseudoscalar mesons with
consideration for the mixing between the flavour-neutral states $\pi^0$, $\eta$
and $\eta^\prime$. We extract the masses and ...flavour compositions of the
pseudoscalar meson nonet in $n_f=1+1+1$ lattice QCD+QED around an SU(3)-flavour
symmetric point, and observe flavour-symmetry features of the extracted data,
along with preliminary extrapolation results for the flavour compositions at
the physical point. A key result of this work is the observed mass splitting
between the $\pi^0$ and $\eta$ on our ensembles, which is found to exhibit
behaviour that is simply related to the corresponding flavour compositions.
We present recent results on generalized parton distributions from dynamical lattice QCD calculations. Our set of twelve different combinations of couplings and quark masses allows for a preliminary ...study of the pion mass dependence of the transverse nucleon structure. PUBLICATION ABSTRACT
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Lattice QCD calculations of the nucleon electromagnetic form factors are of interest at both the high and low momentum transfer regions. For high momentum transfers especially there are open ...questions which require more intense study, such as the potential zero crossing in the proton's electric form factor. We will present recent progress from the QCDSF/UKQCD/CSSM collaboration on the calculation of these form factors using the Feynman-Hellmann method in lattice QCD. The Feynman-Hellmann method allows for greater control over excited states which we take advantage of by going to high values of the momentum transfer. In this proceeding we present results of the form factors up to \(6 \textrm{GeV}^{2}\), using \(N_{f}=2+1\) flavour fermions for three different pion masses in the range 310-470 \(\textrm{MeV}\). The results are extrapolated to the physical pion mass through the use of a flavour breaking expansion.
We determine the properties of generalised parton distributions (GPDs) from a lattice QCD calculation of the off-forward Compton amplitude (OFCA). By extending the Feynman-Hellmann relation to ...second-order matrix elements at off-forward kinematics, this amplitude can be calculated from lattice propagators computed in the presence of a background field. Using an operator product expansion, we show that the deeply-virtual part of the OFCA can be parameterised in terms of the low-order Mellin moments of the GPDs. We apply this formalism to a numerical investigation for zero-skewness kinematics at two values of the soft momentum transfer, \(t = -1.1, -2.2 \;\text{GeV}^2\), and a pion mass of \(m_{\pi}\approx 470\;\text{MeV}\). The form factors of the lowest two moments of the nucleon GPDs are determined, including the first lattice QCD determination of the \(n=4\) moments. Hence we demonstrate the viability of this method to calculate the OFCA from first principles, and thereby provide novel constraint on the \(x\)- and \(t\)-dependence of GPDs.
A major objective of lattice QCD is the computation of hadronic matrix elements. The standard method is to use three-point and four-point correlation functions. An alternative approach, requiring ...only the computation of two-point correlation functions is to use the Feynman-Hellmann theorem. In this talk we develop this method up to second order in perturbation theory, in a context appropriate for lattice QCD. This encompasses the Compton Amplitude (which forms the basis for deep inelastic scattering) and hadron scattering. Some numerical results are presented showing results indicating what this approach might achieve.
We perform a Monte Carlo calculation of the second moment of the polarised valence quark distributions in the nucleon, using quenched Wilson fermions. The special feature of this moment is that it is ...directly accessible experimentally. At a scale of μ ≈ 2 GeV we find
Δ
(1)
u = 0.198(8),
Δ
(1)
d = −0.0477(33). We compare these numbers with recent experimental results of the SMC collaboration.
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IJS, IMTLJ, KILJ, KISLJ, NUK, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Lattice calculations of hadronic observables are aggravated by short-distance fluctuations. The gradient flow, which can be viewed as a particular realisation of the coarse-graining step of momentum ...space RG transformations, proves a powerful tool for evolving the lattice gauge field to successively longer length scales for any initial coupling. Already at small flow times we find the signal-to-noise ratio of two- and three-point functions significantly enhanced and the projection onto the ground state largely improved, while the effect on the hadronic observables considered here to be negligible. A further benefit is that far fewer conjugate gradient iterations are needed for the Wilson-Dirac inverter to converge. Additionally, we find the renormalisation constants of quark bilinears to be significantly closer to unity.
The nucleon tensor charge, \(g_T\), is an important quantity in the search for beyond the Standard Model tensor interactions in neutron and nuclear \(\beta\)-decays as well as the contribution of the ...quark electric dipole moment (EDM) to the neutron EDM. We present results from the QCDSF/UKQCD/CSSM collaboration for the tensor charge, \(g_T\), using lattice QCD methods and the Feynman-Hellmann theorem. We use a flavour symmetry breaking method to systematically approach the physical quark mass using ensembles that span three lattice spacings.
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