5,650 research outputs found
Small x Behavior of Parton Distributions from the Observed Froissart Energy Dependence of the Deep Inelastic Scattering Cross Section
We fit the reduced cross section for deep-inelastic electron scattering data
to a three parameter ln^2 s fit, A + beta ln^2 (s/s_0), where s= [Q^2/x] (1-x)
+ m^2, and Q^2 is the virtuality of the exchanged photon. Over a wide range in
Q^2 (0.11 < Q^2 < 1200 GeV^2) all of the fits satisfy the logarithmic energy
dependence of the Froissart bound. We can use these results to extrapolate to
very large energies and hence to very small values of Bjorken x -- well beyond
the range accessible experimentally. As Q^2 --> infinity, the structure
function F_2^p(x, Q^2) exhibits Bjorken scaling, within experimental errors. We
obtain new constraints on the behavior of quark and antiquark distribution
functions at small x.Comment: 10 pages, 2 figure
Diffusion of oxygen in niobium during bake-out
Bake-outs at temperatures between 100 C and 150 C for a duration up to two days have become customary for optimising the performance of bulk niobium cavities. This treatment results in the diffusion of oxygen, originating from the surface oxide, into the niobium. The theoretical oxygen profile has been simulated using the diffusion equations, and compared with some experimental results
Ultimate pressures achieved in TiZrV sputter-coated vacuum chambers
Two metre long, cylindrical vacuum chambers of diameter ranging from 34 to 100 mm, coated with TiZrV getter films by sputtering, have been baked for about 24 h at temperatures from 120 to 250 degrees C. The ultimate pressures achieved after bakeout were found to correspond to the ratio of the pressure gauge degassing to the effective pumping speed provided by the chamber at the location of the gauge. The results covering a pressure range from 10/sup -11/ Torr down to 10 /sup -13/ Torr are presented and discussed. (6 refs)
On QCD -evolution of Deuteron Structure Function for
The deep-inelastic deuteron structure function (SF) in the
covariant approach in light-cone variables is considered. The and
-dependences of SF are calculated. The QCD analysis of generated data both
for non-cumulative ranges was performed. It was
shown that -evolution of SF is valid for ranges and
for the same value of QCD scale parameter . It was
found the -dependence of SF for the ranges is essentially different.Comment: LaTeX, 10 pages, 2 Postscript figure
D-brane probes on L^{abc} Superconformal Field Theories
We study supersymmetric embeddings of D-brane probes of different
dimensionality in the AdS_5xL^{abc} background of type IIB string theory. In
the case of D3-branes, we recover the known three-cycles dual to the dibaryonic
operators of the gauge theory and we also find a new family of supersymmetric
embeddings. Supersymmetric configurations of D5-branes, representing fractional
branes, and of spacetime filling D7-branes (which can be used to add flavor)
are also found. Stable non supersymmetric configurations corresponding to fat
strings and domain walls are found as well.Comment: 20 pages, LaTeX;v2: minor improvements, references adde
Zonotopes and four-dimensional superconformal field theories
The a-maximization technique proposed by Intriligator and Wecht allows us to
determine the exact R-charges and scaling dimensions of the chiral operators of
four-dimensional superconformal field theories. The problem of existence and
uniqueness of the solution, however, has not been addressed in general setting.
In this paper, it is shown that the a-function has always a unique critical
point which is also a global maximum for a large class of quiver gauge theories
specified by toric diagrams. Our proof is based on the observation that the
a-function is given by the volume of a three dimensional polytope called
"zonotope", and the uniqueness essentially follows from Brunn-Minkowski
inequality for the volume of convex bodies. We also show a universal upper
bound for the exact R-charges, and the monotonicity of a-function in the sense
that a-function decreases whenever the toric diagram shrinks. The relationship
between a-maximization and volume-minimization is also discussed.Comment: 29 pages, 15 figures, reference added, typos corrected, version
published in JHE
An electromagnetic shashlik calorimeter with longitudinal segmentation
A novel technique for longitudinal segmentation of shashlik calorimeters has
been tested in the CERN West Area beam facility. A 25 tower very fine samplings
e.m. calorimeter has been built with vacuum photodiodes inserted in the first 8
radiation lengths to sample the initial development of the shower. Results
concerning energy resolution, impact point reconstruction and electron/pion
separation are reported.Comment: 13 pages, 12 figure
Cumulative structure function in terms of nucleonic wave function of the nucleus
The structure function of the nucleus in the cumulative region is
studied in terms of nucleon degrees of freedom. At high the resulting
expressions are presented as a sum of contributions from few-nucleon
correlations. Two-nucleon correlations are studied in some detail. Spin
variables are averaged out. In the region the structure functions are
calculated for the relativistic interaction proposed by F.Gross {\it et al}.
They are found to fall with faster than the exponential. For Carbon at
, where the method is not rigorously applicable, they turn out to be
rougly twice larger than the experimental data.Comment: text and 2 figures in LaTex, 7 figures in P
On the pulsating strings in AdS_5 x T^{1,1}
We study the class of pulsating strings in AdS_5 x T^{1,1}. Using a
generalized ansatz for pulsating string configurations we find new solutions of
this class. Further we semiclassically quantize the theory and obtain the first
correction to the energy. The latter, due to AdS/CFT correspondence, is
supposed to give the anomalous dimensions of operators in the dual N=1
superconformal gauge field theory.Comment: 12 pages, improvements made, references adde
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