3,028 research outputs found
Pauli problem for a spin of arbitrary length: A simple method to determine its wave function
The problem of determining a pure state vector from measurements is investigated for a quantum spin of arbitrary length. Generically, only a finite number of wave functions is compatible with the intensities of the spin components in two different spatial directions, measured by a Stern-Gerlach apparatus. The remaining ambiguity can be resolved by one additional well-defined measurement. This method combines efficiency with simplicity: only a small number of quantities have to be measured and the experimental setup is elementary. Other approaches to determine state vectors from measurements, also known as the ââPauli problem,ââ are reviewed for both spin and particle systems
Takagi-Taupin Description of X-ray Dynamical Diffraction from Diffractive Optics with Large Numerical Aperture
We present a formalism of x-ray dynamical diffraction from volume diffractive
optics with large numerical aperture and high aspect ratio, in an analogy to
the Takagi-Taupin equations for strained single crystals. We derive a set of
basic equations for dynamical diffraction from volume diffractive optics, which
enable us to study the focusing property of these optics with various grating
profiles. We study volume diffractive optics that satisfy the Bragg condition
to various degrees, namely flat, tilted and wedged geometries, and derive the
curved geometries required for ultimate focusing. We show that the curved
geometries satisfy the Bragg condition everywhere and phase requirement for
point focusing, and effectively focus hard x-rays to a scale close to the
wavelength.Comment: 18 pages, 12 figure
Quasi-Topological Insulator and Trigonal Warping in Gated Bilayer Silicene
Bilayer silicene has richer physical properties than bilayer graphene due to
its buckled structure together with its trigonal symmetric structure. The
buckled structure arises from a large ionic radius of silicon, and the trigonal
symmetry from a particular way of hopping between two silicenes. It is a
topologically trivial insulator since it carries a trivial
topological charge. Nevertheless, its physical properties are more akin to
those of a topological insulator than those of a band insulator. Indeed, a
bilayer silicene nanoribbon has edge modes which are almost gapless and
helical. We may call it a quasi-topological insulator. An important observation
is that the band structure is controllable by applying the electric field to a
bilayer silicene sheet. We investigate the energy spectrum of bilayer silicene
under electric field. Just as monolayer silicene undergoes a phase transition
from a topological insulator to a band insulator at a certain electric field,
bilayer silicene makes a transition from a quasi-topological insulator to a
band insulator beyond a certain critical field. Bilayer silicene is a metal
while monolayer silicene is a semimetal at the critical field. Furthermore we
find that there are several critical electric fields where the gap closes due
to the trigonal warping effect in bilayer silicene.Comment: 8 pages, 11 figures, to be published in J. Phys. Soc. Jp
Charmonium suppression in p-A collisions at RHIC
We discuss charmonium production in proton-nucleus collisions at RHIC
energies under the assumption of xF and x2 scaling. We find that all the
ambiguities due to energy loss are gone at this energy and therefore data will
reveal the scaling law, if any. These p-A data will also be crucial to
interpret nucleus-nucleus data with respect to a possible formation of a quark
gluon plasma because the extrapolations for charmonium production from the
present p-A data to RHIC energies, based on the two scaling laws, differ by a
factor of four.Comment: 6 pages, 3 figures. New section on shadowing and energy loss,
References adde
Dissociation cross sections of ground-state and excited charmonia with light mesons in the quark model
We present numerical results for the dissociation cross sections of
ground-state, orbitally- and radially-excited charmonia in collisions with
light mesons. Our results are derived using the nonrelativistic quark model, so
all parameters are determined by fits to the experimental meson spectrum.
Examples of dissociation into both exclusive and inclusive final states are
considered. The dissociation cross sections of several C=(+) charmonia may be
of considerable importance for the study of heavy ion collisions, since these
states are expected to be produced more copiously than the J/psi. The relative
importance of the productions of ground-state and orbitally-excited charmed
mesons in a pion-charmonium collision is demonstrated through the -dependent charmonium dissociation cross sections.Comment: 9 pages, 8 figure
A next-to-next-to-leading order calculation of soft-virtual cross sections
We compute the next-to-next-to-leading order (NNLO) soft and virtual QCD
corrections for the partonic cross section of colourless-final state processes
in hadronic collisions. The results are valid to all orders in the dimensional
regularization parameter \ep. The dependence of the results on a particular
process is given through finite contributions to the one and two-loop
amplitudes. To evaluate the accuracy of the soft-virtual approximation we
compare it with the full NNLO result for Drell-Yan and Higgs boson production
via gluon fusion. We also provide a universal expression for the hard
coefficient needed to perform threshold resummation up to
next-to-next-to-leading logarithmic (NNLL) accuracy.Comment: 25 pages, 4 figure
Large mass dileptons from the passage of jets through quark gluon plasma
We calculate the emission of large mass dileptons originating from the
annihilation of quark jets passing through quark gluon plasma. Considering
central collisions of heavy nuclei at SPS, RHIC and LHC energies, we find that
the yield due to the jet-plasma interaction gets progressively larger as the
collision energy increases. We find it to be negligible at SPS energies, of the
order of the Drell-Yan contribution and much larger than the normal thermal
yield at RHIC energies and up to a factor of ten larger than the Drell-Yan
contribution at LHC energies. An observation of this new dilepton source would
confirm the occurrence of jet-plasma interactions and of conditions suitable
for jet-quenching to take place.Comment: 9 pages, 11 figures; references added, improved calculation,
conclusions unchange
Synchronization of multi-phase oscillators: An Axelrod-inspired model
Inspired by Axelrod's model of culture dissemination, we introduce and
analyze a model for a population of coupled oscillators where different levels
of synchronization can be assimilated to different degrees of cultural
organization. The state of each oscillator is represented by a set of phases,
and the interaction --which occurs between homologous phases-- is weighted by a
decreasing function of the distance between individual states. Both ordered
arrays and random networks are considered. We find that the transition between
synchronization and incoherent behaviour is mediated by a clustering regime
with rich organizational structure, where some of the phases of a given
oscillator can be synchronized to a certain cluster, while its other phases are
synchronized to different clusters.Comment: 6 pages, 5 figure
Predictions for Pb Collisions at TeV: Comparison with Data
Predictions made in Albacete {\it et al} prior to the LHC Pb run at
TeV are compared to currently available data. Some
predictions shown here have been updated by including the same experimental
cuts as the data. Some additional predictions are also presented, especially
for quarkonia, that were provided to the experiments before the data were made
public but were too late for the original publication are also shown here.Comment: 55 pages 35 figure
Charm quark and D^* cross sections in deeply inelastic scattering at DESY HERA
A next-to-leading order Monte Carlo program for the calculation of heavy
quark cross sections in deeply inelastic scattering is described. Concentrating
on charm quark and D^*(2010) production at HERA, several distributions are
presented and their variation with respect to charm quark mass, parton
distribution set, and renormalization-factorization scale is studied.Comment: 15 pages including 8 figures. Uses Latex, Revtex, and psfig.
References added - others updated. Several sentences/words added for clarity.
Results/conclusions unchanged. To appear in Phys. Rev.
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