180 research outputs found
Testing the Color Charge and Mass Dependence of Parton Energy Loss with Heavy-to-light Ratios at RHIC and LHC
The ratio of nuclear modification factors of high-pT heavy-flavored mesons to
light-flavored hadrons (``heavy-to-light ratio'') in nucleus-nucleus collisions
tests the partonic mechanism expected to underlie jet quenching. Heavy-to-light
ratios are mainly sensitive to the mass and color-charge dependences of
medium-induced parton energy loss. Here, we assess the potential for
identifying these two effects in D and B meson production at RHIC and at the
LHC. To this end, we supplement the perturbative QCD factorized formalism for
leading hadron production with radiative parton energy loss. For D meson
spectra at high but experimentally accessible transverse momentum (10 < pT < 20
GeV) in Pb-Pb collisions at the LHC, we find that charm quarks behave
essentially like light quarks. However, since light-flavored hadron yields are
dominated by gluon parents, the heavy-to-light ratio of D mesons is a sensitive
probe of the color charge dependence of parton energy loss. In contrast, due to
the larger b quark mass, the medium modification of B mesons in the same
kinematical regime provides a sensitive test of the mass dependence of parton
energy loss. At RHIC energies, the strategies for identifying and disentangling
the color charge and mass dependence of parton energy loss are more involved
because of the smaller kinematical range accessible. We argue that at RHIC, the
kinematical regime best suited for such an analysis of D mesons is 7 < pT < 12
GeV, whereas the study of lower transverse momenta is further complicated due
to the known dominant contribution of additional, particle species dependent,
non-perturbative effects.Comment: 21 pages RevTex, 9 Figure
PyPWA: A Software Toolkit for Parameter Optimization and Amplitude Analysis
PyPWA is a toolkit designed to optimize parametric models describing data and
generate simulated distributions according to a model. Its software has been
written within the python ecosystem with the goal of performing Amplitude or
Partial Wave Analysis (PWA) in nuclear and particle physics experiments. We
briefly describe the general features of amplitude analysis and the PyPWA
software design and usage. We provide benchmarks of the scaling and an example
of its application
Induced scalarization in boson stars and scalar gravitational radiation
The dynamical evolution of boson stars in scalar-tensor theories of gravity
is considered in the physical (Jordan) frame. We focus on the study of
spontaneous and induced scalarization, for which we take as initial data
configurations on the well-known S-branch of a single boson star in general
relativity. We show that during the scalarization process a strong emission of
scalar radiation occurs. The new stable configurations (S-branch) of a single
boson star within a particular scalar-tensor theory are also presented.Comment: 18 pages, 11 figures. Minor changes to match the published versio
Medium-evolved fragmentation functions
Medium-induced gluon radiation is usually identified as the dominant
dynamical mechanism underling the {\it jet quenching} phenomenon observed in
heavy-ion collisions. In its actual implementation, multiple medium-induced
gluon emissions are assumed to be independent, leading, in the eikonal
approximation, to a Poisson distribution. Here, we introduce a medium term in
the splitting probabilities so that both medium and vacuum contributions are
included on the same footing in a DGLAP approach. The improvements include
energy-momentum conservation at each individual splitting, medium-modified
virtuality evolution and a coherent implementation of vacuum and medium
splitting probabilities. Noticeably, the usual formalism is recovered when the
virtuality and the energy of the parton are very large. This leads to a similar
description of the suppression observed in heavy-ion collisions with values of
the transport coefficient of the same order as those obtained using the {\it
quenching weights}.Comment: LaTeX, 18 pages, 13 figures included using epsfig, uses JHEP3; v2:
enlarged discussions, one figure replaced, some references added, final
versio
The Carnegie Supernova Project: Analysis of the First Sample of Low-Redshift Type-Ia Supernovae
We present the analysis of the first set of low-redshift Type Ia supernovae
(SNe Ia) by the Carnegie Supernova Project. Well-sampled, high-precision
optical (ugriBV) and near-infrared (NIR; YJHKs) light curves obtained in a
well-understood photometric system are used to provide light-curve parameters,
and ugriBVYJH template light curves. The intrinsic colors at maximum light are
calibrated to compute optical--NIR color excesses for the full sample, thus
allowing the properties of the reddening law in the host galaxies to be
studied. A low value of Rv~1.7, is derived when using the entire sample of SNe.
However, when the two highly reddened SNe in the sample are excluded, a value
Galactic standard of Rv~3.2 is obtained. The colors of these two events are
well matched by a reddening model due to circumstellar dust. The peak
luminosities are calibrated using a two-parameter linear fit to the decline
rates and the colors, or alternatively, the color excesses. In both cases,
dispersions in absolute magnitude of 0.12--0.16 mag are obtained, depending on
the filter-color combination. In contrast to the results obtained from color
excesses, these fits give Rv~1--2, even when the two highly reddened SNe are
excluded. This discrepancy suggests that, beyond the "normal" interstellar
reddening produced in the host galaxies, there is an intrinsic dispersion in
the colors of SNe Ia which is correlated with luminosity but independent of the
decline rate. Finally, a Hubble diagram is produced by combining the results of
the fits for each filter. The resulting scatter of 0.12 mag appears to be
limited by peculiar velocities as evidenced by the strong correlation between
the distance-modulus residuals among the different filters. The implication is
that the actual precision of SN Ia distances is 3--4%.Comment: 76 pages, 20 figures, accepted for publication in A
Whisker spot patterns: a noninvasive method of individual identification of Australian sea lions (Neophoca cinerea)
Reliable methods for identification of individual animals are advantageous for ecological studies of population demographics and movement patterns. Photographic identification, based on distinguishable patterns, unique shapes, or scars, is an effective technique already used for many species. We tested whether photographs of whisker spot patterns could be used to discriminate among individual Australian sea lion (Neophoca cinerea). Based on images of 53 sea lions, we simulated 5,000 patterns before calculating the probability of duplication in a study population. A total of 99% (± 1.5 SD) of patterns were considered reliable for a population of 50, 98% (± 1.7 SD) for 100, 92% (± 4.7 SD) for 500, and 88% (± 5.7 SD) for 1,000. We tested a semiautomatic approach by matching 16 known individuals at 3 different angles (70°, 90°, and 110°), 2 distances (1 and 2 m), and 6 separate times over a 1-year period. A point-pattern matching algorithm for pairwise comparisons produced 90% correct matches of photographs taken on the same day at 90°. Images of individuals at 1 and 2 m resulted in 89% correct matches, those photographed at different angles and different times (at 90°) resulted in 48% and 73% correct matches, respectively. Our results show that the Chamfer distance transform can effectively be used for individual identification, but only if there is very little variation in photograph angle. This point-pattern recognition application may also work for other otariid species
The Carnegie Supernova Project: First Photometry Data Release of Low-Redshift Type Ia Supernovae
The Carnegie Supernova Project (CSP) is a five-year survey being carried out
at the Las Campanas Observatory to obtain high-quality light curves of ~100
low-redshift Type Ia supernovae in a well-defined photometric system. Here we
present the first release of photometric data that contains the optical light
curves of 35 Type Ia supernovae, and near-infrared light curves for a subset of
25 events. The data comprise 5559 optical (ugriBV) and 1043 near-infrared
(YJHKs) data points in the natural system of the Swope telescope. Twenty-eight
supernovae have pre-maximum data, and for 15 of these, the observations begin
at least 5 days before B maximum. This is one of the most accurate datasets of
low-redshift Type Ia supernovae published to date. When completed, the CSP
dataset will constitute a fundamental reference for precise determinations of
cosmological parameters, and serve as a rich resource for comparison with
models of Type Ia supernovae.Comment: 93 pages, 8 figures, accepted for publication in A
Nuclear shadowing in Glauber-Gribov theory with Q2-evolution
We consider deep inelastic scattering off nuclei in the Regge limit within
the Glauber-Gribov model. Using unitarized parton distribution functions for
the proton, we find sizeable shadowing effects on the nuclear total and
longitudinal structure functions, and , in the low-x limit.
Extending a fan-diagram analysis for the large-mass region of coherent
diffraction off nuclei to high Q2, we also find significant shadowing effects
in this kinematical regime. Finally, we discuss shortcomings of our approach
and possible extensions of the model to other kinematical regimes.Comment: 16 pages, 9 figure
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