2,721 research outputs found
Reducing combinatorial uncertainties: A new technique based on MT2 variables
We propose a new method to resolve combinatorial ambiguities in hadron
collider events involving two invisible particles in the final state. This
method is based on the kinematic variable MT2 and on the MT2-assisted-on-shell
reconstruction of invisible momenta, that are reformulated as `test' variables
Ti of the correct combination against the incorrect ones. We show how the
efficiency of the single Ti in providing the correct answer can be
systematically improved by combining the different Ti and/or by introducing
cuts on suitable, combination-insensitive kinematic variables. We illustrate
our whole approach in the specific example of top anti-top production, followed
by a leptonic decay of the W on both sides. However, by construction, our
method is also directly applicable to many topologies of interest for new
physics, in particular events producing a pair of undetected particles, that
are potential dark-matter candidates. We finally emphasize that our method is
apt to several generalizations, that we outline in the last sections of the
paper.Comment: 1+23 pages, 8 figures. Main changes in v3: (1) discussion at the end
of sec. 2 improved; (2) added sec. 4.2 about the method's dependence on mass
information. Matches journal versio
A Fast Track towards the `Higgs' Spin and Parity
The LHC experiments ATLAS and CMS have discovered a new boson that resembles
the long-sought Higgs boson: it cannot have spin one, and has couplings to
other particles that increase with their masses, but the spin and parity remain
to be determined. We show here that the `Higgs' + gauge boson invariant-mass
distribution in `Higgs'-strahlung events at the Tevatron or the LHC would be
very different under the J^P = 0+, 0- and 2+ hypotheses, and could provide a
fast-track indicator of the `Higgs' spin and parity. Our analysis is based on
simulations of the experimental event selections and cuts using PYTHIA and
Delphes, and incorporates statistical samples of `toy' experiments.Comment: 18 pages, 9 pdf figure
Intragenic DNA methylation: implications of this epigenetic mechanism for cancer research
Epigenetics is the study of all mechanisms that regulate gene transcription and genome stability that are maintained throughout the cell division, but do not include the DNA sequence itself. The best-studied epigenetic mechanism to date is DNA methylation, where methyl groups are added to the cytosine base within cytosine–guanine dinucleotides (CpG sites). CpGs are frequently clustered in high density (CpG islands (CGIs)) at the promoter of over half of all genes. Current knowledge of transcriptional regulation by DNA methylation centres on its role at the promoter where unmethylated CGIs are present at most actively transcribed genes, whereas hypermethylation of the promoter results in gene repression. Over the last 5 years, research has gradually incorporated a broader understanding that methylation patterns across the gene (so-called intragenic or gene body methylation) may have a role in transcriptional regulation and efficiency. Numerous genome-wide DNA methylation profiling studies now support this notion, although whether DNA methylation patterns are a cause or consequence of other regulatory mechanisms is not yet clear. This review will examine the evidence for the function of intragenic methylation in gene transcription, and discuss the significance of this in carcinogenesis and for the future use of therapies targeted against DNA methylation
Light hadron, Charmonium(-like) and Bottomonium(-like) states
Hadron physics represents the study of strongly interacting matter in all its
manifestations and the understanding of its properties and interactions. The
interest on this field has been revitalized by the discovery of new light
hadrons, charmonium- and bottomonium-like states. I review the most recent
experimental results from different experiments.Comment: Presented at Lepton-Photon 2011, Mumbai, India; 21 pages, 18 figures;
add more references; some correctio
Direct Evidence for Dominant Bond-directional Interactions in a Honeycomb Lattice Iridate Na2IrO3
Heisenberg interactions are ubiquitous in magnetic materials and have been
prevailing in modeling and designing quantum magnets. Bond-directional
interactions offer a novel alternative to Heisenberg exchange and provide the
building blocks of the Kitaev model, which has a quantum spin liquid (QSL) as
its exact ground state. Honeycomb iridates, A2IrO3 (A=Na,Li), offer potential
realizations of the Kitaev model, and their reported magnetic behaviors may be
interpreted within the Kitaev framework. However, the extent of their relevance
to the Kitaev model remains unclear, as evidence for bond-directional
interactions remains indirect or conjectural. Here, we present direct evidence
for dominant bond-directional interactions in antiferromagnetic Na2IrO3 and
show that they lead to strong magnetic frustration. Diffuse magnetic x-ray
scattering reveals broken spin-rotational symmetry even above Neel temperature,
with the three spin components exhibiting nano-scale correlations along
distinct crystallographic directions. This spin-space and real-space
entanglement directly manifests the bond-directional interactions, provides the
missing link to Kitaev physics in honeycomb iridates, and establishes a new
design strategy toward frustrated magnetism.Comment: Nature Physics, accepted (2015
Scratch lottery tickets are a poor incentive to respond to mailed questionnaires
BACKGROUND: It has been demonstrated that the enclosure of money with a mailed questionnaire increases the response rate significantly. We evaluated scratch lottery tickets as an alternative to cash. METHODS: 1500 randomly selected Norwegians between the ages of 40 and 65 years were sent a short questionnaire. 250 received one lottery scratch ticket worth 20 Norwegian kroner (approximately 3 US$) together with the questionnaire, 250 received two scratch tickets, and 250 were promised two scratch tickets if they replied within one week. A fourth group of 250 persons received a 50 kroner banknote with the questionnaire. The remaining 500 letters served as controls. RESULTS: The overall response rate after 6 weeks was 77%. Logistic regression analysis showed that only the 50 kroner group had a response rate that was statistically significantly higher than the controls (p < 0.0001). It was also significantly higher than that in any of the other incentive groups (p < 0.0001, p < 0.004 and p < 0.0001 respectively). Female sex (p < 0.001) and age (p < 0.002) increased the response rate significantly. CONCLUSION: It is possible that the recipients scratched their cards before completing the questionnaire, and that it was a disincentive for the majority that they did not win anything. Lottery scratch tickets are no substitute for cash as an incentive to respond to a questionnaire
Testing the gaugino AMSB model at the Tevatron via slepton pair production
Gaugino AMSB models-- wherein scalar and trilinear soft SUSY breaking terms
are suppressed at the GUT scale while gaugino masses adopt the AMSB form--
yield a characteristic SUSY particle mass spectrum with light sleptons along
with a nearly degenerate wino-like lightest neutralino and quasi-stable
chargino. The left- sleptons and sneutrinos can be pair produced at
sufficiently high rates to yield observable signals at the Fermilab Tevatron.
We calculate the rate for isolated single and dilepton plus missing energy
signals, along with the presence of one or two highly ionizing chargino tracks.
We find that Tevatron experiments should be able to probe gravitino masses into
the ~55 TeV range for inoAMSB models, which corresponds to a reach in gluino
mass of over 1100 GeV.Comment: 14 pages including 6 .eps figure
Signal transducer and activator of transcription 3-mediated CD133 up-regulation contributes to promotion of hepatocellular carcinoma
published_or_final_versio
Axion-mediated dark matter and Higgs diphoton signal
We consider axion-mediated dark matter models motivated by Fermi gamma ray
line at 130 GeV, where anomaly interactions of an axion-like scalar mediate a
singlet Dirac fermion dark matter (DM) to electroweak gauge bosons. In these
models, extra vector-like leptons generate anomaly interactions for the axion
and can also couple to the SM Higgs boson to modify the Higgs-to-diphoton rate.
We can distinguish models by the branching fraction of the DM annihilation into
a photon pair, favoring the model with a triplet fermion. From the condition
that the lighter charged extra lepton must be heavier than dark matter for no
tree-level DM annihilations, we also show that the ratio of Higgs-to-diphoton
rate to the SM value is constrained by vacuum stability to 1.4(1.5) for the
cutoff scale of 10(1) TeV.Comment: 29 pages, 6 figures, references adde
Multi-Photon Signals from Composite Models at LHC
We analyze the collider signals of composite scalars that emerge in certain
little Higgs models and models of vectorlike confinement. Similar to the decay
of the pion into photon pairs, these scalars mainly decay through
anomaly-induced interactions into electroweak gauge bosons, leading to a
distinct signal with three or more photons in the final state. We study the
standard model backgrounds for these signals, and find that the LHC can
discover these models over a large range of parameter space with 30 fb
at 14 TeV. An early discovery at the current 7 TeV run is possible in some
regions of parameter space. We also discuss possibilities to measure the spin
of the particles in the and decay channels.Comment: 18 pages, LaTe
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