1,041 research outputs found
In silico single strand melting curve: a new approach to identify nucleic acid polymorphisms in Totiviridae
CpG-island promoters of developmental genes are unmethylated. DNA methylation state of CpG islands overlapping and surrounding the promoter region of Pax3 (a) and Pax7 (b) genes in myogenic (MB, MT, MF) and non-myogenic samples (ESC). CpG islands are indicated in green and regions analysed by sodium bisulphite sequencing are shown in red. Each circle represents a CpG dinucleotide and its distance to the gene TSS is indicated below. The colour gradient represents the percentage of methylation indicated in the legend. Abbreviations: ESC, embryonic stem cell; MB, myoblast; MT, myotube; MF, myofiber; TSS, transcription start site. c. DNA methylation state of -5 kb distal regulatory region for MyoD was analysed by sodium bisulphite sequencing in ESC and myoblast samples, and represented as above. (PDF 171 kb
Jet Dipolarity: Top Tagging with Color Flow
A new jet observable, dipolarity, is introduced that can distinguish whether
a pair of subjets arises from a color singlet source. This observable is
incorporated into the HEPTopTagger and is shown to improve discrimination
between top jets and QCD jets for moderate to high pT.Comment: 8 pages, 6 figures (updated to JHEP version
Explaining the t tbar forward-backward asymmetry without dijet or flavor anomalies
We consider new physics explanations of the anomaly in the top quark
forward-backward asymmetry measured at the Tevatron, in the context of flavor
conserving models. The recently measured LHC dijet distributions strongly
constrain many otherwise viable models. A new scalar particle in the
antitriplet representation of flavor and color can fit the t tbar asymmetry and
cross section data at the Tevatron and avoid both low- and high-energy bounds
from flavor physics and the LHC. An s-channel resonance in uc to uc scattering
at the LHC is predicted to be not far from the current sensitivity. This model
also predicts rich top quark physics for the early LHC from decays of the new
scalar particles. Single production gives t tbar j signatures with high
transverse momentum jet, pair production leads to t tbar j j and 4 jet final
states.Comment: 7 pages, 6 figures; v2: notation clarified, references adde
Multivariate discrimination and the Higgs + W/Z search
A systematic method for optimizing multivariate discriminants is developed
and applied to the important example of a light Higgs boson search at the
Tevatron and the LHC. The Significance Improvement Characteristic (SIC),
defined as the signal efficiency of a cut or multivariate discriminant divided
by the square root of the background efficiency, is shown to be an extremely
powerful visualization tool. SIC curves demonstrate numerical instabilities in
the multivariate discriminants, show convergence as the number of variables is
increased, and display the sensitivity to the optimal cut values. For our
application, we concentrate on Higgs boson production in association with a W
or Z boson with H -> bb and compare to the irreducible standard model
background, Z/W + bb. We explore thousands of experimentally motivated,
physically motivated, and unmotivated single variable discriminants. Along with
the standard kinematic variables, a number of new ones, such as twist, are
described which should have applicability to many processes. We find that some
single variables, such as the pull angle, are weak discriminants, but when
combined with others they provide important marginal improvement. We also find
that multiple Higgs boson-candidate mass measures, such as from mild and
aggressively trimmed jets, when combined may provide additional discriminating
power. Comparing the significance improvement from our variables to those used
in recent CDF and DZero searches, we find that a 10-20% improvement in
significance against Z/W + bb is possible. Our analysis also suggests that the
H + W/Z channel with H -> bb is also viable at the LHC, without requiring a
hard cut on the W/Z transverse momentum.Comment: 41 pages, 5 tables, 29 figure
QCD Coherence and the Top Quark Asymmetry
Coherent QCD radiation in the hadroproduction of top quark pairs leads to a
forward--backward asymmetry that grows more negative with increasing transverse
momentum of the pair. This feature is present in Monte Carlo event generators
with coherent parton showering, even though the production process is treated
at leading order and has no intrinsic asymmetry before showering. In addition,
depending on the treatment of recoils, showering can produce a positive
contribution to the inclusive asymmetry. We explain the origin of these
features, compare them in fixed-order calculations and the Herwig++, Pythia and
Sherpa event generators, and discuss their implications.Comment: 28 pages, 11 figures, 2 table
Heavy Squarks at the LHC
The LHC, with its seven-fold increase in energy over the Tevatron, is capable
of probing regions of SUSY parameter space exhibiting qualitatively new
collider phenomenology. Here we investigate one such region in which first
generation squarks are very heavy compared to the other superpartners. We find
that the production of these squarks, which is dominantly associative, only
becomes rate-limited at mSquark > 4(5) TeV for L~10(100) fb-1. However,
discovery of this scenario is complicated because heavy squarks decay primarily
into a jet and boosted gluino, yielding a dijet-like topology with missing
energy (MET) pointing along the direction of the second hardest jet. The result
is that many signal events are removed by standard jet/MET anti-alignment cuts
designed to guard against jet mismeasurement errors. We suggest replacing these
anti-alignment cuts with a measurement of jet substructure that can
significantly extend the reach of this channel while still removing much of the
background. We study a selection of benchmark points in detail, demonstrating
that mSquark= 4(5) TeV first generation squarks can be discovered at the LHC
with L~10(100)fb-1
Charge asymmetries of top quarks at hadron colliders revisited
A sizeable difference in the differential production cross section of top-
compared to antitop-quark production, denoted charge asymmetry, has been
observed at the Tevatron. The experimental results seem to exceed the theory
predictions based on the Standard Model by a significant amount and have
triggered a large number of suggestions for "new physics". In the present paper
the Standard Model predictions for Tevatron and LHC experiments are revisited.
This includes a reanalysis of electromagnetic as well as weak corrections,
leading to a shift of the asymmetry by roughly a factor 1.1 when compared to
the results of the first papers on this subject. The impact of cuts on the
transverse momentum of the top-antitop system is studied. Restricting the ttbar
system to a transverse momentum less than 20 GeV leads to an enhancement of the
asymmetries by factors between 1.3 and 1.5, indicating the importance of an
improved understanding of the -momentum distribution. Predictions for
similar measurements at the LHC are presented, demonstrating the sensitivity of
the large rapidity region both to the Standard Model contribution and effects
from "new physics".Comment: 23 pages. Final version to appear in JHE
RG-improved single-particle inclusive cross sections and forward-backward asymmetry in production at hadron colliders
We use techniques from soft-collinear effective theory (SCET) to derive
renormalization-group improved predictions for single-particle inclusive (1PI)
observables in top-quark pair production at hadron colliders. In particular, we
study the top-quark transverse-momentum and rapidity distributions, the
forward-backward asymmetry at the Tevatron, and the total cross section at
NLO+NNLL order in resummed perturbation theory and at approximate NNLO in fixed
order. We also perform a detailed analysis of power corrections to the leading
terms in the threshold expansion of the partonic hard-scattering kernels. We
conclude that, although the threshold expansion in 1PI kinematics is
susceptible to numerically significant power corrections, its predictions for
the total cross section are in good agreement with those obtained by
integrating the top-pair invariant-mass distribution in pair invariant-mass
kinematics, as long as a certain set of subleading terms appearing naturally
within the SCET formalism is included.Comment: 55 pages, 14 figures, 6 table
NLO QCD corrections to tW' and tZ' production in forward-backward asymmetry models
We consider Z' and W' models recently proposed to explain the top
forward-backward asymmetry at the Tevatron. We present the next-to-leading
order QCD corrections to associated production of such vector bosons together
with top quarks at the Large Hadron Collider, for centre-of-mass energies of 7
and 8 TeV. The corrections are significant, modifying the total production
cross-section by 30-50%. We consider the effects of the corrections on the top
and vector-boson kinematics. The results are directly applicable to current
experimental searches, for both the ATLAS and CMS collaborations.Comment: 62 pages, 13 figures, 36 tables. v3 Updated to correspond to Journal
version and incorporate supplementary materia
- …