Search results for "RULE"
showing 10 items of 1403 documents
Results on longitudinal spin physics at COMPASS
2016
Abstract The COMPASS experiment at the CERN SPS has taken data for deep inelastic scattering of polarised muons off a polarised NH3 target in 2007 and 2011 and off a polarised 6LiD target in 2002–2004 and 2006. We present our new results on the longitudinal double spin asymmetry A 1 p and the spin-dependent structure function g 1 p obtained from the 2011 data set. These results are used in a NLO QCD fit to the world data to obtain the polarised parton distributions. Also an update on our results on the Bjorken sum rule, connecting the integral of the non-singlet spin-dependent structure function with the ratio of the weak coupling constants, is given. The gluon polarisation can be accessed …
A Quark model analysis of the Sivers function.
2008
We develop a formalism to evaluate the Sivers function. The approach is well suited for calculations which use constituent quark models to describe the structure of the nucleon. A non-relativistic reduction of the scheme is performed and applied to the Isgur-Karl model of hadron structure. The results obtained are consistent with a sizable Sivers effect and the signs for the u and d flavor contributions turn out to be opposite. This pattern is in agreement with the one found analyzing, in the same model, the impact parameter dependent generalized parton distributions. The Burkardt Sum Rule turns out to be fulfilled to a large extent. We estimate the QCD evolution of our results from the mom…
New results on the spin structure function g1 of the proton and the deuteron from SMC
1998
Abstract New results from a measurement of the spin-dependent structure function g 1 p by the SMC are presented. A next-to-leading order QCD analysis of all published data is used to compute g 1 p at a fixed Q 2 of 10 GeV 2 . Two methods for the extrapolation towards x = 0 to determine the first moment are discussed. In both cases the violation of the Ellis-Jaffe sum rule is confirmed. Using the deuteron data in addition the Bjorken sum rule is tested.
The pion polarisability from QCD sum rules
1994
Abstract The electromagnetic polarisability of charged pions, α E , has recently attracted both theoretical and experimental attention. Unfortunately the experimental results disagree with each other. We have investigated this polarisation via a QCD sum rule approach and find α E = 5.6 ± 0.5 × 10 −4 fm 3 , which is in agreement with one experiment and disagrees with the result of chiral perturbation theory.
Charm quark mass determined from a pair of sum rules
2016
In this paper, we present preliminary results of the determination of the charm quark mass $\hat{m}_c$ from QCD sum rules of moments of the vector current correlator calculated in perturbative QCD at ${\cal O} (\hat \alpha_s^3)$. Self-consistency between two different sum rules allow to determine the continuum contribution to the moments without requiring experimental input, except for the charm resonances below the continuum threshold. The existing experimental data from the continuum region is used, then, to confront the theoretical determination and reassess the theoretic uncertainty.
Pinched weights and duality violation in QCD sum rules: A critical analysis
2010
We analyze the so-called pinched weights, that are generally thought to reduce the violation of quarkhadron duality in finite-energy sum rules. After showing how this is not true in general, we explain how to address this question for the left-right correlator and any particular pinched weight, taking advantage of our previous work [1], where the possible high-energy behavior of the left-right spectral function was studied. In particular, we show that the use of pinched weights allows to determine with high accuracy the dimension six and eight contributions in the operator-product expansion, O-6 = (-4.3(-0.7)(+0.9)) x 10(-3) GeV6 and O-8 = (-7.2(-5.3)(+4.2)) x 10(-3) GeV8.
Bottom-quark mass from finite energy QCD sum rules
2011
Finite energy QCD sum rules involving both inverse and positive moment integration kernels are employed to determine the bottom quark mass. The result obtained in the $\bar{\text {MS}}$ scheme at a reference scale of $10\, {GeV}$ is $\bar{m}_b(10\,\text{GeV})= 3623(9)\,\text{MeV}$. This value translates into a scale invariant mass $\bar{m}_b(\bar{m}_b) = 4171 (9)\, {MeV}$. This result has the lowest total uncertainty of any method, and is less sensitive to a number of systematic uncertainties that affect other QCD sum rule determinations.
The strange-quark mass from QCD sum rules in the pseudoscalar channel
1997
QCD Laplace transform sum rules, involving the axial-vector current divergences, are used in order to determine the strange quark mass. The two-point function is known in QCD up to four loops in perturbation theory, and up to dimension-six in the non-perturbative sector. The hadronic spectral function is reconstructed using threshold normalization from chiral symmetry, together with experimental data for the two radial excitations of the kaon. The result for the running strange quark mass, in the $\bar{MS}$ scheme at a scale of 1 ${GeV}^{2}$ is: ${\bar m}_{s}(1 GeV^{2}) = 155 \pm 25 {MeV}$.
Order-$\alpha_s^3$ determination of the strange quark mass
1996
We present a QCD sum rule calculation of the strange-quark mass including four-loop QCD corrections to the correlator of scalar currents. We obtain $\bar m_s(1$ GeV$)=205.5\pm 19.1$ MeV.
Improved determination of the mass of the1−+light hybrid meson from QCD sum rules
2003
We calculate the next-to-leading order (NLO) ${\ensuremath{\alpha}}_{s}$ corrections to the contributions of the condensates $〈\ensuremath{\alpha}{G}^{2}〉$ and $〈\overline{q}q{〉}^{2}$ in the current-current correlator of the hybrid current $g\overline{q}(x){\ensuremath{\gamma}}_{\ensuremath{\nu}}{\mathrm{iF}}_{\ensuremath{\mu}\ensuremath{\nu}}^{a}{T}^{a}q(x)$ using the external field method in the Feynman gauge. After incorporating these NLO contributions into the Laplace sum rules, the mass of the ${J}^{\mathrm{PC}}{=1}^{\ensuremath{-}+}$ light hybrid meson is recalculated using the QCD sum rule approach. We find that the sum rules exhibit enhanced stability when the NLO ${\ensuremath{\alp…