5,442 research outputs found
Precision Probes of QCD at High Energies
New physics, that is too heavy to be produced directly, can leave measurable
imprints on the tails of kinematic distributions at the LHC. We use energetic
QCD processes to perform novel measurements of the Standard Model (SM)
Effective Field Theory. We show that the dijet invariant mass spectrum, and the
inclusive jet transverse momentum spectrum, are sensitive to a dimension 6
operator that modifies the gluon propagator at high energies. The dominant
effect is constructive or destructive interference with SM jet production. We
compare differential next-to-leading order predictions from POWHEG to public 7
TeV jet data, including scale, PDF, and experimental uncertainties and their
respective correlations. We constrain a New Physics (NP) scale of 3.5 TeV with
current data. We project the reach of future 13 and 100 TeV measurements, which
we estimate to be sensitive to NP scales of 8 and 60 TeV, respectively. As an
application, we apply our bounds to constrain heavy vector octet colorons that
couple to the QCD current. We project that effective operators will surpass
bump hunts, in terms of coloron mass reach, even for sequential couplings.Comment: 40 pages, 13 figures, 8 tables. Minor changes. Accepted on JHE
Catching a New Force by the Tail
The Large Hadron Collider (LHC) is sensitive to new heavy gauge bosons that
produce narrow peaks in the dilepton invariant mass spectrum up to about
TeV. s that are too heavy to produce directly can reveal
their presence through interference with Standard Model dilepton production. We
show that the LHC can significantly extend the mass reach for such s by
performing precision measurements of the shape of the dilepton invariant mass
spectrum. The high luminosity LHC can exclude, with 95 confidence, new
gauge bosons as heavy as TeV that couple with gauge
coupling strength of .Comment: 8 pages, 7 figure
New Physics from High Energy Tops
Precision measurements of high energy top quarks at the LHC constitute a
powerful probe of new physics. We study the effect of four fermion operators
involving two tops and two light quarks on the high energy tail of the invariant mass distribution. We use existing measurements at a center of
mass energy of 13 TeV, and state of the art calculations of the Standard Model
contribution, to derive bounds on the coefficients of these operators. We
estimate the projected reach of the LHC at higher luminosities and discuss the
validity of these limits within the Effective Field Theory description. We find
that current measurements constrain the mass scale of these operators to be
larger than about 1-2 TeV, while we project that future LHC data will be
sensitive to mass scales of about 3-4 TeV. We apply our bounds to constrain
composite Higgs models with partial compositeness and models with approximate
flavor symmetries. We find our limits to be most relevant to flavor
non-universal models with a moderately large coupling of the heavy new physics
states to third generation quarks.Comment: 13 pages, 2 appendices, 5 figures, references adde
A Finite Element Model for Describing the Effect of Muscle Shortening on Surface EMG
A finite-element model for the generation of single fiber action potentials in a muscle undergoing various degrees of fiber shortening is developed. The muscle is assumed fusiform with muscle fibers following a curvilinear path described by a Gaussian function. Different degrees of fiber shortening are simulated by changing the parameters of the fiber path and maintaining the volume of the muscle constant. The conductivity tensor is adapted to the muscle fiber orientation. In each point of the volume conductor, the conductivity of the muscle tissue in the direction of the fiber is larger than that in the transversal direction. Thus, the conductivity tensor changes point-by-point with fiber shortening, adapting to the fiber paths. An analytical derivation of the conductivity tensor is provided. The volume conductor is then studied with a finite-element approach using the analytically derived conductivity tensor. Representative simulations of single fiber action potentials with the muscle at different degrees of shortening are presented. It is shown that the geometrical changes in the muscle, which imply changes in the conductivity tensor, determine important variations in action potential shape, thus affecting its amplitude and frequency content. The model provides a new tool for interpreting surface EMG signal features with changes in muscle geometry, as it happens during dynamic contractions
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