Search results for "Strange quark"
showing 10 items of 66 documents
Determination of the strange-quark mass from QCD pseudoscalar sum rules
1998
A new determination of the strange-quark mass is discussed, based on the two-point function involving the axial-vector current divergences. This Green function is known in perturbative QCD up to order O(alpha_s^3), and up to dimension-six in the non-perturbative domain. The hadronic spectral function is parametrized in terms of the kaon pole, followed by its two radial excitations, and normalized at threshold according to conventional chiral-symmetry. The result of a Laplace transform QCD sum rule analysis of this two-point function is: m_s(1 GeV^2) = 155 pm 25 MeV.
Strange quark condensate from QCD sum rules to five loops
2007
It is argued that it is valid to use QCD sum rules to determine the scalar and pseudoscalar two-point functions at zero momentum, which in turn determine the ratio of the strange to non-strange quark condensates $R_{su} = \frac{}{}$ with ($q=u,d$). This is done in the framework of a new set of QCD Finite Energy Sum Rules (FESR) that involve as integration kernel a second degree polynomial, tuned to reduce considerably the systematic uncertainties in the hadronic spectral functions. As a result, the parameters limiting the precision of this determination are $\Lambda_{QCD}$, and to a major extent the strange quark mass. From the positivity of $R_{su}$ there follows an upper bound on the latt…
Perturbative quark mass corrections to the tau hadronic width
1998
15 páginas, 3 figuras, 2 tablas.-- arXiv:hep-ph/9804462v1
Light Quark Masses from Lattice Quark Propagators at Large Momenta
1999
We compute non-perturbatively the average up-down and strange quark masses from the large momentum (short-distance) behaviour of the quark propagator in the Landau gauge. This method, which has never been applied so far, does not require the explicit calculation of the quark mass renormalization constant. Calculations were performed in the quenched approximation, by using O(a)-improved Wilson fermions. The main results of this study are ml^RI(2GeV)=5.8(6)MeV and ms^RI(2GeV)=136(11)MeV. Using the relations between different schemes, obtained from the available four-loop anomalous dimensions, we also find ml^RGI=7.6(8)MeV and ms^RGI=177(14)MeV, and the MSbar-masses, ml^MS(2GeV)=4.8(5)MeV and …
Resonances in QCD
2015
We report on the EMMI Rapid Reaction Task Force meeting 'Resonances in QCD', which took place at GSI October 12-14, 2015. A group of 26 people met to discuss the physics of resonances in QCD. The aim of the meeting was defined by the following three key questions: What is needed to understand the physics of resonances in QCD? Where does QCD lead us to expect resonances with exotic quantum numbers? What experimental efforts are required to arrive at a coherent picture? For light mesons and baryons only those with ${\it up}$, ${\it down}$ and ${\it strange}$ quark content were considered. For heavy-light and heavy-heavy meson systems, those with ${\it charm}$ quarks were the focus. This docum…
Mass singularities in light quark correlators: the strange quark case
1995
The correlators of light-quark currents contain mass-singularities of the form log(m^2/Q^2). It has been known for quite some time that these mass- logarithms can be absorbed into the vacuum expectation values of other operators of appropriate dimension, provided that schemes without normal- ordering are used. We discuss in detail this procedure for the case of the mass logarithms m^4 log(m^2/Q^2), including also the mixing with the other dimension-4 operators to two-loop order. As an application we present an improved QCD sum rule determination of the strange-quark mass. We obtain m_s(1 GeV)=171 \pm 15 MeV.
Spin structures of the pion and nucleon
2012
We present recent studies on the transverse spin densities of the pion and nucleon within the framework of the chiral quark-(soliton) model, based on the calculation of the electromagnetic and tensor form factors of the pion and the nucleon. The results for the transverse spin densities of the quark inside a pion are in good agreement with the recent lattice data, while those of the nucleon show similar features to the lattice results. We also present the first results of the transverse spin densities of the strange quark inside a nucleon.
The leading disconnected contribution to the anomalous magnetic moment of the muon
2014
The hadronic vacuum polarization can be determined from the vector correlator in a mixed time-momentum representation. We explicitly calculate the disconnected contribution to the vector correlator, both in the $N_f = 2$ theory and with an additional quenched strange quark, using non-perturbatively $O(a)$-improved Wilson fermions. All-to-all propagators are computed using stochastic sources and a generalized hopping parameter expansion. Combining the result with the dominant connected contribution, we are able to estimate an upper bound for the systematic error that arises from neglecting the disconnected contribution in the determination of $(g-2)_\mu$.
The ALICE Collaboration
2009
The production of mesons containing strange quarks (KS, φ) and both singly and doubly strange baryons ( , , and − + +) are measured at mid-rapidity in pp collisions at √ s = 0.9 TeV with the ALICE experiment at the LHC. The results are obtained from the analysis of about 250 k minimum bias events recorded in 2009. Measurements of yields (dN/dy) and transverse momentum spectra at mid-rapidity for inelastic pp collisions are presented. For mesons, we report yields (〈dN/dy〉) of 0.184 ± 0.002(stat.) ± 0.006(syst.) for KS and 0.021 ± 0.004(stat.) ± 0.003(syst.) for φ. For baryons, we find 〈dN/dy〉 = 0.048 ± 0.001(stat.) ± 0.004(syst.) for , 0.047 ± 0.002(stat.) ± 0.005(syst.) for and 0.0101 ± 0.0…
Evidence for Strange-Quark Contributions to the Nucleon’s Form Factors atQ2=0.108 (GeV/c)2
2005
We report on a measurement of the parity violating asymmetry in the elastic scattering of polarized electrons off unpolarized protons with the A4 apparatus at MAMI in Mainz at a four momentum transfer value of ${Q}^{2}=0.108\text{ }(\mathrm{GeV}/c{)}^{2}$ and at a forward electron scattering angle of $30\ifmmode^\circ\else\textdegree\fi{}l{\ensuremath{\theta}}_{e}l40\ifmmode^\circ\else\textdegree\fi{}$. The measured asymmetry is ${A}_{LR}(\stackrel{\ensuremath{\rightarrow}}{e}p)=[\ensuremath{-}1.36\ifmmode\pm\else\textpm\fi{}0.29(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.13(\mathrm{syst})]\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}$. The expectation from the standard model as…