533 research outputs found
Strange quark asymmetry in the nucleon and the NuTeV anomaly
The NuTeV anomaly of a non-universal value of the fundamental parameter
sin^2\theta_W in the electroweak theory has been interpreted as an indication
for new physics beyond the Standard Model. However, the observed quantity
depends on a possible asymmetry in the momentum distributions of strange quarks
and antiquarks in the nucleon. This asymmetry occurs naturally in a
phenomenologically successful physical model for such parton distributions,
which reduces the NuTeV result to only about two standard deviations from the
Standard Model.Comment: 4 pages, 5 figures, RevTex4. Updated with new references and extended
discussion. v.3: Minor corrections mad
A Measurement of Using Multiple Tags
A new measurement of with the ALEPH detector at LEP using five mutually exclusive hemisphere tags is presented. The preliminary result is $R_b = 0.215
Intrinsic Charm Flavor and Helicity Content in the Proton
Contributions to the quark flavor and spin observables from the intrinsic
charm in the proton are discussed in the SU(4) quark meson fluctuation model.
Our results suggest that the probability of finding the intrinsic charm in the
proton is less than 1%. The intrinsic charm helicity is small and negative,
. The fraction of the total quark helicity
carried by the intrinsic charm is less than 2%, and c_\up/c_\dw=35/67.Comment: 4 pages, 2 tables (revised version
Strange sea asymmetry in nucleons
We evaluate the medium effects in nucleon which can induce an asymmetry of
the strange sea. The short-distance effects determined by the weak interaction
can give rise to where is the medium-induced mass of strange quark by a few KeV at
most, but the long-distance effects by strong interaction could be sizable.Comment: 4 pages and no figures, Talk presented at the Third
Circum-Pan-Pacific Symposium on "High Energy Spin Physics", Oct. 8-13, 2001,
Beijing, Chin
Multi-quark components in baryons
A brief review on some recent progresses in our understanding of multi-quark
components in baryons is presented. The multi-quark components in baryons seem
to be mainly in colored quark cluster configurations rather than in ``meson
cloud'' configurations or in the form of a sea of quark-antiquark pairs. The
colored quark cluster multi-quark picture gives a natural explanation of
empirical indications for a positive strangeness magnetic moment of the
proton and the longstanding mass-reverse problem of S11(1535) and \mu_s$ of the proton is given.Comment: Contribution to the International Conference on QCD and Hadronic
Physics, June 16-20, 2005, Beijin
On the dbar/ubar Asymmetry and Parton Distributions
We discuss the impact of different measurements of the dbar/ubar asymmetry in
the extraction of parameterizations of parton distribution functions.Comment: Contributed paper to LP01, 13 pages, 4 figure
Chiral constituent quark model and the coupling strength of eta'
Using the latest data pertaining to \bar u-\bar d asymmetry and the spin
polarization functions, detailed implications of the possible values of the
coupling strength of the singlet Goldstone boson \eta' have been investigated
in the \chiCQM with configuration mixing. Using \Delta u, \Delta_3, \bar u-\bar
d and \bar u/\bar d, the possible ranges of the coupling parameters a, \alpha^
2, \beta^ 2 and \zeta^ 2, representing respectively the probabilities of
fluctuations to pions, K, \eta and \eta^{'}, are shown to be 0.10 \lesssim a
\lesssim 0.14, 0.2\lesssim \alpha \lesssim 0.5, 0.2\lesssim \beta \lesssim 0.7
and 0.10 lesssim |\zeta| \lesssim 0.70. To constrain the coupling strength of
\eta', detailed fits have been obtained for spin polarization functions, quark
distribution functions and baryon octet magnetic moments corresponding to the
following sets of parameters: a=0.1, \alpha=0.4, \beta=0.7, |\zeta|=0.65 (Case
I); a=0.1, \alpha=0.4, \beta=0.6, |\zeta|=0.70 (Case II); a=0.14, \alpha=0.4,
\beta=0.2, \zeta=0 (Case III) and a=0.13, \alpha=\beta=0.45, |\zeta|=0.10 (Case
IV). Case I represents the calculations where a is fixed to be 0.1, in
accordance with earlier calculations, whereas other parameters are treated free
and the Case IV represents our best fit. The fits clearly establish that a
small non-zero value of the coupling of \eta' is preferred over the higher
values of \eta' as well as when \zeta=0, the latter implying the absence of
\eta' from the dynamics of \chiCQM. Our best fit achieves an overall excellent
fit to the data, in particular the fit for \Delta u, \Delta d, \Delta_8 as well
as the magnetic moments \mu_{n}, \mu_{\Sigma^-}, \mu_{\Sigma^+} and \mu_{\Xi^-}
is almost perfect, the \mu_{\Xi^-} being a difficult case for most of the
similar calculations.Comment: 8 RevTeX pages, 2 Tables, Revised version to appear in Int.J.Mod.Phys
measurements using lifetime tags at LEP
/ measurements by Aleph , Delphi , and Opal using life- time tags are reviewed. These measurements currently dominate the world average value of
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