5,790 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
Vector Boson Pair Production in Hadronic Collisions at Order : Lepton Correlations and Anomalous Couplings
We present cross sections for production of electroweak vector boson pairs,
, and , in and collisions, at next-to-leading
order in . We treat the leptonic decays of the bosons in the
narrow-width approximation, but retain all spin information via decay angle
correlations. We also include the effects of and anomalous
couplings.Comment: 23 pages, 8 figures, 3 table
Electroweak-correction effects in gauge-boson pair production at the LHC
We have studied the effect of one-loop logarithmic electroweak radiative
corrections on WZ and production processes at the LHC. We present
analytical results for the leading-logarithmic electroweak corrections to the
corresponding partonic processes du -> WZ, Wgamma. Using the leading-pole
approximation we implement these corrections into Monte Carlo programs for
. We find that electroweak corrections
lower the predictions by 5-20% in the physically interesting region of large
transverse momentum and small rapidity separation of the gauge bosons.Comment: 28 pages, LaTex, 13 eps figures included; references added and
corrected typo
Higher-order QED corrections to W-boson mass determination at hadron colliders
The impact of higher-order final-state photonic corrections on the precise
determination of the W-boson mass at the Tevatron and LHC colliders is
evaluated. In the presence of realistic selection criteria, the shift in the W
mass from a fit to the transverse mass distribution is found to be about 10 MeV
in the channel and almost negligible in the
channel. The calculation, which is implemented in a Monte Carlo event generator
for data analysis, can contribute to reduce the uncertainty associated to the W
mass measurement at future hadron collider experiments.Comment: 9 pages, 2 figures, 1 table, RevTe
Heavy ion beam lifetimes at relativistic and ultrarelativistic colliders
The effects of higher order corrections in ultra-relativistic nuclear
collisions are considered. It is found that higher order contributions are
small at low energy, large at intermediate energy and small again at very high
energy. An explanation for this effect is given. This means that the
Weizsacker-Williams formula is a good approximation to use in calculating cross
sections and beam lifetimes at energies relevant to RHIC and LHC.Comment: 10 pages, 2 tables, 4 figure
Amplitude Zeros in Production
We demonstrate that the Standard Model amplitude for at the Born-level exhibits an approximate zero located at
at
high energies, where the () are the left-handed couplings
of the -boson to fermions and is the center of mass scattering
angle of the -boson. The approximate zero is the combined result of an exact
zero in the dominant helicity amplitudes and strong gauge
cancelations in the remaining amplitudes. For non-standard couplings
these cancelations no longer occur and the approximate amplitude zero is
eliminated.Comment: 11 pages, 4 figures submitted separately as uuencoded tar-ed
postscript files, FSU-HEP-940307, UCD-94-
Exclusive W + photon production in proton-antiproton collisions I: general formalism
We present a detailed computation of the fully exclusive cross section of p +
antip --> W + photon + X with X = 0 and 1 jet in the framework of the
factorization theorem and dimensional regularization. Order alpha-strong and
photon bremsstrahlung contributions are discussed in the MS-bar mass
factorization scheme. The resulting expressions are ready to be implemented
numerically using Monte Carlo techniques to compute single and double
differential cross sections and correlations between outgoing pairs of
particles.Comment: ITP-SB-93-72, 40 pages, LateX. 3*4 figures in separate file.
([email protected]) ([email protected]
Probing Electroweak Top Quark Couplings at Hadron Colliders
We consider QCD t\bar{t}\gamma and t\bar{t}Z production at hadron colliders
as a tool to measure the tt\gamma and ttZ couplings. At the Tevatron it may be
possible to perform a first, albeit not very precise, test of the tt\gamma
vector and axial vector couplings in t\bar{t}\gamma production, provided that
more than 5 fb^{-1} of integrated luminosity are accumulated. The t\bar{t}Z
cross section at the Tevatron is too small to be observable. At the CERN Large
Hadron Collider (LHC) it will be possible to probe the tt\gamma couplings at
the few percent level, which approaches the precision which one hopes to
achieve with a next-generation e^+e^- linear collider. The LHC's capability of
associated QCD t\bar{t}V (V=\gamma, Z) production has the added advantage that
the tt\gamma and ttZ couplings are not entangled. For an integrated luminosity
of 300 fb^{-1}, the ttZ vector (axial vector) coupling can be determined with
an uncertainty of 45-85% (15-20%), whereas the dimension-five dipole form
factors can be measured with a precision of 50-55%. The achievable limits
improve typically by a factor of 2-3 for the luminosity-upgraded (3 ab^{-1})
LHC.Comment: Revtex3, 30 pages, 9 Figures, 6 Table
Secants of Lagrangian Grassmannians
We study the dimensions of secant varieties of the Grassmannian of Lagrangian
subspaces in a symplectic vector space. We calculate these dimensions for third
and fourth secant varieties. Our result is obtained by providing a normal form
for four general points on such a Grassmannian and by explicitly calculating
the tangent spaces at these four points
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