17,924 research outputs found
Z+jet production at NNLO
We give a brief overview of our calculation of the next-to-next-to-leading
order (NNLO) QCD corrections to Z+jet production in hadronic collisions.
Phenomenological results are presented which comprise various differential
distributions for 8 TeV proton-proton collisions. A significant reduction of
the scale uncertainties is observed throughout as we move from NLO to NNLO. We
further discuss how this calculation can be used to describe the inclusive
Z-boson production at large transverse momentum. To this end, the theory
prediction is compared to the measurements performed by the ATLAS and CMS
collaborations at a centre-of-mass energy of 8 TeV. Here, the inclusion of NNLO
QCD effects are found to result in a substantial improvement in the agreement
between theory and data for the normalised distributions.Comment: 8 pages, 5 figures, to appear in the proceedings of Loops and Legs in
Quantum Field Theory, 24-29 April 2016, Leipzig, German
Atom-Resonant Heralded Single Photons by Interaction-Free Measurement
We demonstrate the generation of rubidium-resonant heralded single photons
for quantum memories. Photon pairs are created by cavity-enhanced
down-conversion and narrowed in bandwidth to 7 MHz with a novel atom-based
filter operating by "interaction-free measurement" principles. At least 94% of
the heralded photons are atom-resonant as demonstrated by a direct absorption
measurement with rubidium vapor. A heralded auto-correlation measurement shows
, i.e., suppression of multi-photon contributions
by a factor of 25 relative to a coherent state. The generated heralded photons
can readily be used in quantum memories and quantum networks.Comment: 5 pages, 4 figure
A macroscopic quantum state analysed particle by particle
Explaining how microscopic entities collectively produce macroscopic
phenomena is a fundamental goal of many-body physics. Theory predicts that
large-scale entanglement is responsible for exotic macroscopic phenomena, but
observation of entangled particles in naturally occurring systems is extremely
challenging. Synthetic quantum systems made of atoms in optical lattices have
been con- structed with the goal of observing macroscopic quantum phenomena
with single-atom resolution. Serious challenges remain in producing and
detecting long-range quantum correlations in these systems, however. Here we
exploit the strengths of photonic technology, including high coherence and
efficient single-particle detection, to study the predicted large-scale
entanglement underlying the macroscopic quantum phenomenon of polarization
squeezing. We generate a polarization-squeezed beam, extract photon pairs at
random, and make a tomographic reconstruction of their joint quantum state. We
present experimental evidence showing that all photons arriving within the
squeezing coherence time are entangled, that entanglement monogamy dilutes
entanglement with increasing photon density and that, counterintuitively,
increased squeezing can reduce bipartite entanglement. The results provide
direct evidence for entanglement of macroscopic numbers of particles and
introduce micro-analysis to the study of macroscopic quantum phenomena
Approaches to Automated Morphological Classification of Galaxies
There is an obvious need for automated classification of galaxies, as the
number of observed galaxies increases very fast. We examine several approaches
to this problem, utilising {\em Artificial Neural Networks} (ANNs). We quote
results from a recent study which show that ANNs can classsify galaxies
morphologically as well as humans can.Comment: 8 pages, uu-encoded compressed postscript file (containing 2 figures
Chandrasekhar's Dynamical Friction and non-extensive statistics
The motion of a point like object of mass passing through the background
potential of massive collisionless particles () suffers a steady
deceleration named dynamical friction. In his classical work, Chandrasekhar
assumed a Maxwellian velocity distribution in the halo and neglected the self
gravity of the wake induced by the gravitational focusing of the mass . In
this paper, by relaxing the validity of the Maxwellian distribution due to the
presence of long range forces, we derive an analytical formula for the
dynamical friction in the context of the -nonextensive kinetic theory. In
the extensive limiting case (), the classical Gaussian Chandrasekhar
result is recovered. As an application, the dynamical friction timescale for
Globular Clusters spiraling to the galactic center is explicitly obtained. Our
results suggest that the problem concerning the large timescale as derived by
numerical -body simulations or semi-analytical models can be understood as a
departure from the standard extensive Maxwellian regime as measured by the
Tsallis nonextensive -parameter.Comment: 16pp 5 figs, revised and extended version of arXiv:1202.1873 .
Accepted for publication by JCA
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