650 research outputs found
Do we understand the single-spin asymmetry for inclusive production in pp collisions?
The cross section data for inclusive production in collisions is
considered in a rather broad kinematic region in energy , Feynman
variable and transverse momentum . The analysis of these data is
done in the perturbative QCD framework at the next-to-leading order. We find
that they cannot be correctly described in the entire kinematic domain and this
leads us to conclude that the single-spin asymmetry, for this process,
observed several years ago at FNAL by the experiment E704 and the recent result
obtained at BNL-RHIC by STAR, are two different phenomena. This suggests that
STAR data probes a genuine leading-twist QCD single-spin asymmetry for the
first time and finds a large effect.Comment: text modified, version to be published in Eur. Phys. J. C, 6 pages, 5
figure
Rescattering effects in hadron-nucleus and heavy-ion collisions
We review the extension of the factorization formalism of perturbative QCD to
{\it coherent} soft rescattering associated with hard scattering in high energy
nuclear collisions. We emphasize the ability to quantify high order corrections
and the predictive power of factorization approach in terms of universal
nonperturbative matrix elements. Although coherent rescattering effects are
power suppressed by hard scales of the scattering, they are enhanced by the
nuclear size and could play an important role in understanding the novel
nuclear dependence observed in high energy nuclear collisions.Comment: 8 pages, 13 figures, to be published in the Proceedings of 1st
International Conference on Hard and Electromagnetic Probes of High Energy
Nuclear Collisions (Hard Probe 2004), Ericeira, Portugal, Nov. 4-10, 200
Inelastic J/psi and Upsilon hadroproduction
We consider the prompt hadroproduction of J/psi, psi' and the Upsilon
(1S,2S,3S) states caused by the fusion of a symmetric colour-octet two-gluon
state and an additional gluon. The cross sections are calculated in
leading-order perturbative QCD. We find a considerable enhancement in
comparison with previous perturbative QCD predictions. Indeed, the resulting
cross sections are found to be consistent with the values measured at the
Tevatron and RHIC, without the need to invoke non-perturbative `colour-octet'
type of contributions.Comment: 21 pages, 10 figures; several clarifying sentences and an additional
reference have been adde
Creating Ioffe-Pritchard micro-traps from permanent magnetic film with in-plane magnetization
We present designs for Ioffe-Pritchard type magnetic traps using planar
patterns of hard magnetic material. Two samples with different pattern designs
were produced by spark erosion of 40 m thick FePt foil. The pattern on the
first sample yields calculated axial and radial trap frequencies of 51 Hz and
6.8 kHz, respectively. For the second sample the calculated frequencies are 34
Hz and 11 kHz. The structures were used successfully as a magneto-optical trap
for Rb and loaded as a magnetic trap. A third design, based on
lithographically patterned 250 nm thick FePt film on a Si substrate, yields an
array of 19 traps with calculated axial and radial trap frequencies of 1.5 kHz
and 110 kHz, respectively.Comment: 8 pages, 5 figures Revised and accepted for EPJD, improved picture
Microwave traps for cold polar molecules
We discuss the possibility of trapping polar molecules in the standing-wave
electromagnetic field of a microwave resonant cavity. Such a trap has several
novel features that make it very attractive for the development of ultracold
molecule sources. Using commonly available technologies, microwave traps can be
built with large depth (up to several Kelvin) and acceptance volume (up to
several cm^3), suitable for efficient loading with currently available sources
of cold polar molecules. Unlike most previous traps for molecules, this
technology can be used to confine the strong-field seeking absolute ground
state of the molecule, in a free-space maximum of the microwave electric field.
Such ground state molecules should be immune to inelastic collisional losses.
We calculate elastic collision cross-sections for the trapped molecules, due to
the electrical polarization of the molecules at the trap center, and find that
they are extraordinarily large. Thus, molecules in a microwave trap should be
very amenable to sympathetic and/or evaporative cooling. The combination of
these properties seems to open a clear path to producing large samples of polar
molecules at temperatures much lower than has been possible previously.Comment: 10 pages, 3 figure
Electric and magnetic form factors of strange baryons
Predictions for the electromagnetic form factors of the Lambda$, Sigma and Xi
hyperons are presented. The numerical calculations are performed within the
framework of the fully relativistic constituent-quark model developed by the
Bonn group. The computed magnetic moments compare favorably with the
experimentally known values. Most magnetic form factors G_M(Q^2) can be
parametrized in terms of a dipole with cutoff masses ranging from 0.79 to 1.14
GeV.Comment: 15 pages, 8 figures, 3 tables, submitted to Eur. Phys. J.
Triangulations and Severi varieties
We consider the problem of constructing triangulations of projective planes
over Hurwitz algebras with minimal numbers of vertices. We observe that the
numbers of faces of each dimension must be equal to the dimensions of certain
representations of the automorphism groups of the corresponding Severi
varieties. We construct a complex involving these representations, which should
be considered as a geometric version of the (putative) triangulations
Decomposition of semigroup algebras
Let A \subseteq B be cancellative abelian semigroups, and let R be an
integral domain. We show that the semigroup ring R[B] can be decomposed, as an
R[A]-module, into a direct sum of R[A]-submodules of the quotient ring of R[A].
In the case of a finite extension of positive affine semigroup rings we obtain
an algorithm computing the decomposition. When R[A] is a polynomial ring over a
field we explain how to compute many ring-theoretic properties of R[B] in terms
of this decomposition. In particular we obtain a fast algorithm to compute the
Castelnuovo-Mumford regularity of homogeneous semigroup rings. As an
application we confirm the Eisenbud-Goto conjecture in a range of new cases.
Our algorithms are implemented in the Macaulay2 package MonomialAlgebras.Comment: 12 pages, 2 figures, minor revisions. Package may be downloaded at
http://www.math.uni-sb.de/ag/schreyer/jb/Macaulay2/MonomialAlgebras/html
Elliptic flow of charged particles in Pb-Pb collisions at 2.76 TeV
We report the first measurement of charged particle elliptic flow in Pb-Pb
collisions at 2.76 TeV with the ALICE detector at the CERN Large Hadron
Collider. The measurement is performed in the central pseudorapidity region
(||<0.8) and transverse momentum range 0.2< < 5.0 GeV/. The
elliptic flow signal v, measured using the 4-particle correlation method,
averaged over transverse momentum and pseudorapidity is 0.087 0.002
(stat) 0.004 (syst) in the 40-50% centrality class. The differential
elliptic flow v reaches a maximum of 0.2 near = 3
GeV/. Compared to RHIC Au-Au collisions at 200 GeV, the elliptic flow
increases by about 30%. Some hydrodynamic model predictions which include
viscous corrections are in agreement with the observed increase.Comment: 10 pages, 4 captioned figures, published version, figures at
http://aliceinfo.cern.ch/ArtSubmission/node/389
Influence of combined impact and cyclic loading on the overall fatigue life of forged steel, EA4T
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