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Register a new userStudies of Higher Twist and Higher Order Effects in NLO and NNLO QCD Analysis of Lepton-Nucleon Scattering Data on F_2 and R =sigma_L/sigma_T
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We report on the extraction of the higher twist contributions to F_2 and R = sigma_L/sigma_T from the global NLO and NNLO QCD fits to lepton nucleon scattering data over a wide range of Q^2. The NLO fits require both target mass and higher twist contributions at low Q^2. However, in the NNLO analysis, the data are described by the NNLO QCD predictions (with target mass corrections) without the need for any significant contributions from higher twist effects. An estimate of the difference between NLO and NNLO parton distribution functions is obtained.
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The partonic structure of hadrons plays an important role in a vast array of high-energy and nuclear physics experiments. It also underpins the theoretical understanding of hadron structure. Recent developments in lattice QCD offer new opportunities for reliably studying partonic structure from first principles. Here we report on the use of the Feynman-Hellmann theorem to study the forward Compton amplitude in the unphysical region. We demonstrate how this amplitude provides direct constraint on hadronic inelastic structure functions. The use of external momentum transfer allows us to study the $Q^2$ evolution to explore the onset of asymptotic scaling and reveal higher-twist effects in partonic structure.
We report on a detailed study of longitudinal strength in the nucleon resonance region, presenting new results from inclusive electron-proton cross sections measured at Jefferson Lab Hall C in the four-momentum transfer range 0.2 < Q^2 < 5.5 GeV^2. The data have been used to accurately perform 167 Rosenbluth-type longitudinal / transverse separations. The precision R = sigma_L / sigma_T data are presented here, along with the first separate values of the inelastic structure functions F_1 and F_L in this regime. The resonance longitudinal component is found to be significant, both in magnitude and in the existence of defined mass peaks. Additionally, quark-hadron duality is here observed above Q^2 = 1 GeV^2 in the separated structure functions independently.
We report on the extraction of R=sigam_L/sigma_T from CCFR neutrino and antineutrino-Iron differential cross sections. R as measured in neutrno scattering is in agreement with $R$ as measured in muon and electron scattering. All data on R for Q2 > 1 GeV2 are in agreement with a NNLO QCD calculation which uses NNLO PDFs and includes target mass effects. We report on the first measurements of R in the low x and Q2 < 1 GeV2 region (where an anomalous large rise in R for nuclear targets has been observed by the HERMES collaboration).
We present a determination of nucleon-nucleon scattering phase shifts for l >= 0. The S, P, D and F phase shifts for both the spin-triplet and spin-singlet channels are computed with lattice Quantum ChromoDynamics. For l > 0, this is the first lattice QCD calculation using the Luscher finite-volume formalism. This required the design and implementation of novel lattice methods involving displaced sources and momentum-space cubic sinks. To demonstrate the utility of our approach, the calculations were performed in the SU(3)-flavor limit where the light quark masses have been tuned to the physical strange quark mass, corresponding to m_pi = m_K ~ 800 MeV. In this work, we have assumed that only the lowest partial waves contribute to each channel, ignoring the unphysical partial wave mixing that arises within the finite-volume formalism. This assumption is only valid for sufficiently low energies; we present evidence that it holds for our study using two different channels. Two spatial volumes of V ~ (3.5 fm)^3 and V ~ (4.6 fm)^3 were used. The finite-volume spectrum is extracted from the exponential falloff of the correlation functions. Said spectrum is mapped onto the infinite volume phase shifts using the generalization of the Luscher formalism for two-nucleon systems.
We report on the extraction of R=sigma_L/sigma_T from CCFR nu_mu-Fe and nubar_mu-Fe differential cross sections. The CCFR differential cross sections do not show the deviations from the QCD expectations that are seen in the CDHSW data at very low and very high x. R as measured in nu_mu scattering is in agreement with R as measured in muon and electron scattering. All data on R for Q^2 > 1 GeV^2 are in agreement with a NNLO QCD calculation which includes target mass effects. We report on the first measurements of R in the low x and Q^2 < 1 GeV^2 region (where an anomalous large rise in R for nuclear targets has been observed by the HERMES collaboration).
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