1,419 research outputs found
Five-loop renormalization group functions of -symmetric -theory and \ep-expansions of critical exponents up to \ep^5
Motivated by the discovery of errors in six of the 135 diagrams in the
published five-loop expansions of the -function and the anomalous
dimensions of the -symmetric -theory in D=4-\ep dimensions we
present the results of a full analytic reevaluation of all diagrams. The
divergences are removed by minimal subtraction and \ep-expansions are given
for the critical exponents , , and up to order
.Comment: LaTeX file. For related work see the www address
http://www.physik.fu-berlin.de/kleiner_re.html on our www homepage
http://www.physik.fu-berlin.de/kleinert.htm
Higher moments of nucleon spin structure functions in heavy baryon chiral perturbation theory and in a resonance model
The third moment of the twist-3 part of the nucleon spin structure
function is generalized to arbitrary momentum transfer and is
evaluated in heavy baryon chiral perturbation theory (HBChPT) up to order
and in a unitary isobar model (MAID). We show how to link
as well as higher moments of the nucleon spin structure functions
and to nucleon spin polarizabilities. We compare our results with the
most recent experimental data, and find a good description of these available
data within the unitary isobar model. We proceed to extract the twist-4 matrix
element which appears in the suppressed term in the twist
expansion of the spin structure function for proton and neutron.Comment: 30 pages, 7 figure
Observation of a narrow baryon resonance with positive strangeness formed in Xe collisions
The charge-exchange reaction K^+ Xe --> K^0 p Xe' is investigated using the
data of the DIANA experiment. The distribution of the pK^0 effective mass shows
a prominent enhancement near 1538 MeV formed by \sim 80 events above the
background, whose width is consistent with being entirely due to the
experimental resolution. Under the selections based on a simulation of K^+Xe
collisions, the statistical significance of the signal reaches 5.5\sigma. We
interpret this observation as strong evidence for formation of a pentaquark
baryon with positive strangeness, \Theta^+(uudd\bar{s}), in the charge-exchange
reaction K^+ n --> K^0 p on a bound neutron. The mass of the \Theta^+ baryon is
measured as m(\Theta^+) = 1538+-2 MeV. Using the ratio between the numbers of
resonant and non-resonant charge-exchange events in the peak region, the
intrinsic width of this baryon resonance is determined as \Gamma(\Theta^+) =
0.34+-0.10 MeV.Comment: 19 pages, 8 figure
Observation of a baryon resonance with positive strangeness in K+ collisions with Xe nuclei
The status of our investigation of low-energy Xe collisions in the Xenon
bubble chamber DIANA is reported. In the charge-exchange reaction the spectrum of effective mass shows a resonant enhancement
with MeV/c and ^24.4\sigma$. The mass and width of the
observed resonance are consistent with expectations for the lightest member of
the anti-decuplet of exotic pentaquark baryons, as predicted in the framework
of the chiral soliton model.Comment: 9 pages, 4 figure
Further evidence for formation of a narrow baryon resonance with positive strangeness in K+ collisions with Xe nuclei
We have continued our investigation of the charge-exchange reaction K^+ Xe
--> K^0 p Xe' in the bubble chamber DIANA. In agreement with our previous
results based on part of the present statistics, formation of a narrow p K^0
resonance with mass of 1537+-2 MeV/c^2 is observed in the elementary transition
K^+ n --> K^0 p on a neutron bound in the Xenon nucleus. Visible width of the
peak is consistent with being entirely due to instrumental resolution and
allows to place an upper limit on its intrinsic width: \Gamma < 9 MeV/c^2. A
more precise estimate of the resonance intrinsic width, \Gamma = 0.36+-0.11
MeV/c^2, is obtained from the ratio between the numbers of resonant and
non-resonant charge-exchange events. The signal is observed in a restricted
interval of incident K^+ momentum, that is consistent with smearing of a narrow
p K^0 resonance by Fermi motion of the target neutron. Statistical significance
of the signal is some 7.3, 5.3, and 4.3 standard deviations for the estimators
S/sqrt{B}, S/sqrt{S+B}, and S/sqrt{S+2B}, respectively. This observation
confirms and reinforces our earlier results, and offers strong evidence for
formation of a pentaquark baryon with positive strangeness in the
charge-exchange reaction K^+ n --> K^0 p on a bound neutron.Comment: 13 pages, 8 figures, some chenges in text and references, more
precise estimate of Theta(1540) to add, submitted to Phys.Atom.Nucl(Yad.Fiz.
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