3,554 research outputs found
p p -> j j e+/- mu+/- nu nu and j j e+/- mu-/+ nu nu at O(\alpha_{em}^6) and O(\alpha_{em}^4 \alpha_s^2) for the Study of the Quartic Electroweak Gauge Boson Vertex at LHC
We analyze the potential of the CERN Large Hadron Collider (LHC) to study the
structure of quartic vector-boson interactions through the pair production of
electroweak gauge bosons via weak boson fusion q q -> q q W W. In order to
study these couplings we have performed a partonic level calculation of all
processes p p -> j j e+/- mu+/- nu nu and pp -> j j e+/- mu-/+ nu nu at the LHC
using the exact matrix elements at O(\alpha_{em}^6) and O(\alpha_{em}^4
\alpha_s^2) as well as a full simulation of the t tbar plus 0 to 2 jets
backgrounds. A complete calculation of the scattering amplitudes is necessary
not only for a correct description of the process but also to preserve all
correlations between the final state particles which can be used to enhance the
signal. Our analyses indicate that the LHC can improve by more than one order
of magnitude the bounds arising at present from indirect measurements.Comment: 26 pages, 8 figures, revised version with some typos corrected, and
some comments and references adde
Photon Structure and Quantum Fluctuation
Photon structure derives from quantum fluctuation in quantum field theory to
fermion and anti-fermion, and has been an experimentally established feature of
electrodynamics since the discovery of the positron. In hadronic physics, the
observation of factorisable photon structure is similarly a fundamental test of
the quantum field theory Quantum Chromodynamics (QCD). An overview of
measurements of hadronic photon structure in e+e- and ep interactions is
presented, and comparison made with theoretical expectation, drawing on the
essential features of photon fluctuation into quark and anti-quark in QCD.Comment: 29 pages, 15 figures, to appear in Philosophical Transactions of the
Royal Society of London (Series A: Mathematical, Physical and Engineering
Sciences
Chaotic Phase Synchronization in Bursting-neuron Models Driven by a Weak Periodic Force
We investigate the entrainment of a neuron model exhibiting a chaotic
spiking-bursting behavior in response to a weak periodic force. This model
exhibits two types of oscillations with different characteristic time scales,
namely, long and short time scales. Several types of phase synchronization are
observed, such as 1 : 1 phase locking between a single spike and one period of
the force and 1 : l phase locking between the period of slow oscillation
underlying bursts and l periods of the force. Moreover, spiking-bursting
oscillations with chaotic firing patterns can be synchronized with the periodic
force. Such a type of phase synchronization is detected from the position of a
set of points on a unit circle, which is determined by the phase of the
periodic force at each spiking time. We show that this detection method is
effective for a system with multiple time scales. Owing to the existence of
both the short and the long time scales, two characteristic phenomena are found
around the transition point to chaotic phase synchronization. One phenomenon
shows that the average time interval between successive phase slips exhibits a
power-law scaling against the driving force strength and that the scaling
exponent has an unsmooth dependence on the changes in the driving force
strength. The other phenomenon shows that Kuramoto's order parameter before the
transition exhibits stepwise behavior as a function of the driving force
strength, contrary to the smooth transition in a model with a single time
scale
Unique Identification of Graviton Exchange Effects in e^+ e^- Collisions
Many types of new physics can lead to contact interaction-like modifications
in e^+ e^- processes below direct production threshold. We examine the
possibility of uniquely identifying the effects of graviton exchange, which are
anticipated in many extra dimensional theories, from amongst this large set of
models by using the moments of the angular distribution of the final state
particles. In the case of the e^+ e^- --> f bar{f} process we demonstrate that
this technique allows for the unique identification of the graviton exchange
signature at the 5 sigma level for mass scales as high as 6 sqrt(s). The
extension of this method to the e^+ e^- --> W^+ W^- process is also discussed.Comment: 21 pages, 3 figs, LaTe
The performance of thin NaI(Tl) scintillator plate for dark matter search
A thin (0.05cm) and wide area (5cmX5cm) NaI(Tl) scintillator was developed.
The performance of the thin NaI(Tl) plate, energy resolution, single
photoelectron energy and position sensitivity were tested. An excellent energy
resolution of 20% (FWHM) at 60keV was obtained. The single photoelectron energy
was calculated to be approximately 0.42 0.02keV. Position information in the
5cmx5cm area of the detector was also obtained by analyzing the ratio of the
number of photons collected at opposite ends of the detector. The position
resolution was obtained to be 1cm (FWHM) in the 5cmx5cm area.Comment: 10 pages. Accepted to Journal of Physical Society of Japa
Clocking hadronization in relativistic heavy ion collisions with balance functions
A novel state of matter has been hypothesized to exist during the early stage
of relativistic heavy ion collisions, with normal hadrons not appearing until
several fm/c after the start of the reaction. To test this hypothesis,
correlations between charges and their associated anticharges are evaluated
with the use of balance functions. It is shown that late-stage hadronization is
characterized by tightly correlated charge/anticharge pairs when measured as a
function of relative rapidity.Comment: 5 pages, 3 figure
A Two-Year Time Delay for the Lensed Quasar SDSS J1029+2623
We present 279 epochs of optical monitoring data spanning 5.4 years from 2007
January to 2012 June for the largest image separation (22.6 arcsec)
gravitationally lensed quasar, SDSS J1029+2623. We find that image A leads the
images B and C by dt_AB = (744+-10) days (90% confidence); the uncertainty
includes both statistical uncertainties and systematic differences due to the
choice of models. With only a ~1% fractional error, the interpretation of the
delay is limited primarily by cosmic variance due to fluctuations in the mean
line-of-sight density. We cannot separate the fainter image C from image B, but
since image C trails image B by only 2-3 days in all models, the estimate of
the time delay between image A and B is little affected by combining the fluxes
of images B and C. There is weak evidence for a low level of microlensing,
perhaps created by the small galaxy responsible for the flux ratio anomaly in
this system. Interpreting the delay depends on better constraining the shape of
the gravitational potential using the lensed host galaxy, other lensed arcs and
the structure of the X-ray emission.Comment: Accepted for publication in The Astrophysical Journal. Changes in
response to referee's comment
Automated user modeling for personalized digital libraries
Digital libraries (DL) have become one of the most typical ways of accessing any kind of digitalized information. Due to this key role, users welcome any improvements on the services they receive from digital libraries. One trend used to
improve digital services is through personalization. Up to now, the most common approach for personalization in digital libraries has been user-driven. Nevertheless, the design of efficient personalized services has to be done, at least in part, in
an automatic way. In this context, machine learning techniques automate the process of constructing user models. This paper proposes a new approach to construct digital libraries that satisfy user’s necessity for information: Adaptive Digital Libraries, libraries that automatically learn user preferences and goals and personalize their interaction using this information
Optical photometric GTC/OSIRIS observations of the young massive association Cygnus OB2
In order to fully understand the gravitational collapse of molecular clouds,
the star formation process and the evolution of circumstellar disks, these
phenomena must be studied in different Galactic environments with a range of
stellar contents and positions in the Galaxy. The young massive association
Cygnus OB2, in the Cygnus-X region, is an unique target to study how star
formation and the evolution of circumstellar disks proceed in the presence of a
large number of massive stars. We present a catalog obtained with recent
optical observations in r,i,z filters with OSIRIS, mounted on the GTC
telescope, which is the deepest optical catalog of Cyg OB2 to date.
The catalog consist of 64157 sources down to M=0.15 solar masses at the
adopted distance and age of Cyg OB2. A total of 38300 sources have good
photometry in all three bands. We combined the optical catalog with existing
X-ray data of this region, in order to define the cluster locus in the optical
diagrams. The cluster locus in the r-i vs. i-z diagram is compatible with an
extinction of the optically selected cluster members in the 2.64<AV<5.57 range.
We derive an extinction map of the region, finding a median value of AV=4.33 in
the center of the association, decreasing toward the north-west. In the
color-magnitude diagrams, the shape of the distribution of main sequence stars
is compatible with the presence of an obscuring cloud in the foreground at
about 850+/-25 pc from the Sun.Comment: Accepted for publication ApJS 201
Topological charge density renormalization in the presence of dynamical fermions
We study the renormalization group behaviour of the topological charge
density in full QCD on the lattice. We propose a way of extracting the
necessary renormalization functions from Monte Carlo simulations.Comment: 8 pages, Revte
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