5,568 research outputs found
Hadron collider limits on anomalous couplings
A next-to-leading log calculation of the reactions and
is presented including a tri-boson
gauge coupling from non-Standard Model contributions. Two approaches are made
for comparison. The first approach considers the tri-boson coupling
as being uniquely fixed by tree level unitarity at high energies to its
Standard Model form and, consequently, suppresses the non-Standard Model
contributions with form factors. The second approach is to ignore such
considerations and calculate the contributions to non-Standard Model tri-boson
gauge couplings without such suppressions. It is found that at Tevatron
energies, the two approaches do not differ much in quantitative results, while
at Large Hadron Collider (LHC) energies the two approaches give significantly
different predictions for production rates. At the Tevatron and LHC, however,
the sensitivity limits on the anomalous coupling of are too weak to
usefully constrain parameters in effective Lagrangian models.Comment: Revtex 23 pages + 8 figures, UIOWA-94-1
Experimental Evaluation of Steady-State Control Properties of an Electron-Bombardment Ion Thrustor
Examined in this report are the experimental steady-state gains, or changes, in beam-current output with changes in thrustor inputs for a 10-centimeter-diameter electron-bombardment ion thrustor. A general leveling off of beam current as a function of an input variable was found at the upper range of each variable, At the design operating point, the filament-heating current exhibited the greatest sensitivity, or percentage beam-current output change for a percentage change in the input (2 to 4). Accelerator voltage showed the least effect (0.04) while discharge voltage, magnetic field, and neutral propellant flow exhibited about the same sensitivity (0.4 to 0.5). Some effects of nonlinearity are shown that may require consideration in the design of a closed-loop control system
Higgs Boson Discovery Potential of LHC in the Channel
We discuss the SM Higgs discovery potential of LHC in the reaction when the jet is observed at sufficiently high to
be reliably identified. We conclude that this channel gives promising discovery
possibilities for the Higgs boson mass range 100-140 GeV, during LHC operation
at a low luminosity. With 30 fb of accumulated data and for
GeV about 100 signal events could be observed with the number of background
events larger by a factor of 2 only, showing a signal significance
. We use the difference of distributions in the partonic
subprocess energy for the signal and background for a better
separation of the signal.Comment: 15 pages including 6 figures, LaTeX, use epsfig.sty. To appear in
Phys.Lett.B. In this replacement minor LaTeX improvements are mad
and couplings in collision with polarized beams
The potential of e mode of linear collider to probe
and vertices is investigated through the Z boson
production from the procees . Considering the longitudinal and
transverse polarization states of the Z boson and incoming polarized beams we
find the 95% C.L. limits on the form factors , ,
and with integrated luminosity 500
and 0.5, 1, 1.5 TeV energies. It is shown that the polarization can
improve sensitivities by factors 2-3 depending on the energy.Comment: 12 pages, 8 EPS figure
The Semiclassical Coulomb Interaction
The semiclassical Coulomb excitation interaction is at times expressed in the
Lorentz gauge in terms of the electromagnetic fields and a contribution from
the scalar electric potential. We point out that the potential term can make
spurious contributions to excitation cross sections, especially when the the
decay of excited states is taken into account. We show that, through an
appropriate gauge transformation, the excitation interaction can be expressed
in terms of the electromagnetic fields alone.Comment: 12 pages. Phys. Rev. C, Rapid Communication, in pres
Kinematical Limits on Higgs Boson Production via Gluon Fusion in Association with Jets
In this paper, we analyze the high-energy limits for Higgs boson plus two jet
production. We consider two high-energy limits, corresponding to two different
kinematic regions: a) the Higgs boson is centrally located in rapidity between
the two jets, and very far from either jet; b) the Higgs boson is close to one
jet in rapidity, and both of these are very far from the other jet. In both
cases the amplitudes factorize into impact factors or coefficient functions
connected by gluons exchanged in the t channel. Accordingly, we compute the
coefficient function for the production of a Higgs boson from two off-shell
gluons, and the impact factors for the production of a Higgs boson in
association with a gluon or a quark jet. We include the full top quark mass
dependence and compare this with the result obtained in the large top-mass
limit.Comment: 35 pages, 6 figure
Searching for a heavy Higgs boson via the H --> l nu jj decay mode at the CERN LHC
The discovery of a heavy Higgs boson with mass up to m_H = 1 TeV at the CERN
LHC is possible in the H--> W^+W^- --> l nu jj decay mode. The weak boson
scattering signal and backgrounds from t\bar tjj and from W+jets production are
analyzed with parton level Monte Carlo programs which are built on full tree
level amplitudes for all subprocesses. The use of double jet tagging and the
reconstruction of the W invariant mass reduce the combined backgrounds to the
same level as the Higgs signal. A central mini-jet veto, which distinguishes
the different gluon radiation patterns of the hard processes, further improves
the signal to background ratio to about 2.5:1, with a signal cross section of 1
fb. The jet energy asymmetry of the W --> jj decay will give a clear signature
of the longitudinal polarization of the W's in the final event sample.Comment: 23 pages (with 7 embedded figures), Revtex, uses epsf.sty.
Z-compressed postscript version also available at
http://phenom.physics.wisc.edu/pub/preprints/1997/madph-97-1017.ps.Z or at
ftp://phenom.physics.wisc.edu/pub/preprints/1997/madph-97-1017.ps.
W+W-, WZ and ZZ production in the POWHEG BOX
We present an implementation of the vector boson pair production processes
ZZ, W+W- and W Z within the POWHEG framework, which is a method that allows the
interfacing of NLO calculations to shower Monte Carlo programs. The
implementation is built within the POWHEG BOX package. The Z/\gamma^*
interference, as well as singly resonant contributions, are properly included.
We also considered interference terms arising from identical leptons in the
final state. As a result, all contributions leading to the desired four-lepton
system have been included in the calculation, with the sole exception of the
interference between ZZ and W+W- in the production of a pair of same-flavour,
oppositely charged fermions and a pair of neutrinos, which we show to be fully
negligible. Anomalous trilinear couplings can be also set in the program, and
we give some examples of their effect at the LHC. We have made the relevant
code available at the POWHEG BOX web site.Comment: 20 pages, 9 figures, 2 tables. Minor corrections and updated
references in revised versio
Weak Boson Production Amplitude Zeros; Equalities of the Helicity Amplitudes
We investigate the radiation amplitude zeros exhibited by many Standard Model
amplitudes for triple weak gauge boson production processes. We show that
production amplitudes have especially rich structure in terms of
zeros, these amplitudes have zeros originating from several different sources.
It is also shown that TYPE I current null zone is the special case of the
equality of the specific helicity amplitudes.Comment: 27 pages, 12 figures, 2 table
The t->WZb decay in the Standard Model: A Critical Reanalysis
We compute the t->WZb decay rate, in the Standard Model, at the leading order
in perturbation theory, with special attention to the effects of the finite
widths of the W and Z bosons. These effects are extremely important, since the
t->WZb decay occurs near its kinematical threshold. They increase the value of
the decay rate by orders of magnitude near threshold or allow it below the
nominal threshold. We discuss a procedure to take into account the finite-width
effects and compare the results with previous studies of this decay. Within the
Standard Model, for a top quark mass in the range between 170 and 180 GeV, we
find BR(t->WZb) ~ 2 x 10^{-6}, which makes the observation at the LHC very
difficult if at all possible.Comment: 10 pages, 4 eps figures, LaTeX. Few references added and minor
changes in the text. Results unchanged. Final version to appear on PL
- …