5,262 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
Influence of Charge Order on the Ground States of TMTTF Molecular Salts
(TMTTF)2AsF6 and (TMTTF)2SbF6 are both known to undergo a charge ordering
phase transition, though their ground states are different. The ground state of
the first is Spin-Peierls, and the second is an antiferromagnet. We study the
effect of pressure on the ground states and the charge-ordering using 13C NMR
spectroscopy. The experiments demonstrate that the the CO and SP order
parameters are repulsive, and consequently the AF state is stabilized when the
CO order parameter is large, as it is for (TMTTF)2SbF6. An extension of the
well-known temperature/pressure phase diagram is proposed.Comment: 5pages, 5 figures, Proceeding of ISCOM2003, to appear in Journal de
Physique I
Events with Isolated Charged Leptons and Large Missing Transverse Momentum at HERA
Striking events with isolated charged leptons, large missing transverse
momentum and large transverse momentum of the hadronic final state were
observed at the electron proton collider HERA in a data sample corresponding to
a luminosity of about 130 pb-1. The H1 collaboration observed 11 events with
isolated electrons or muons and with transverse momentum above 25 GeV. Only
3.4+-0.6 events were expected from Standard Model (SM) processes. Six of these
events have a transverse momentum of greater than 40 GeV, while 1.3+-0.3 events
were expected. The ZEUS collaboration observed good agreement with the SM.
However, ZEUS found two events with a similar event topology, but tau leptons
instead of electrons or muons in the final state. Only 0.2+-0.05 events were
expected from SM processes. For various hypotheses the compatibility of the
experimental results was investigated with respect to the SM and with respect
to possible explanations beyond the SM. Prospects for the high-luminosity
HERA-II data taking period are given
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
Hysteresis of Backflow Imprinted in Collimated Jets
We report two different types of backflow from jets by performing 2D special
relativistic hydrodynamical simulations. One is anti-parallel and
quasi-straight to the main jet (quasi-straight backflow), and the other is bent
path of the backflow (bent backflow). We find that the former appears when the
head advance speed is comparable to or higher than the local sound speed at the
hotspot while the latter appears when the head advance speed is slower than the
sound speed bat the hotspot. Bent backflow collides with the unshocked jet and
laterally squeezes the jet. At the same time, a pair of new oblique shocks are
formed at the tip of the jet and new bent fast backflows are generated via
these oblique shocks. The hysteresis of backflow collisions is thus imprinted
in the jet as a node and anti-node structure. This process also promotes
broadening of the jet cross sectional area and it also causes a decrease in the
head advance velocity. This hydrodynamic process may be tested by observations
of compact young jets.Comment: 9 pages, 5 figures, accepted for publication in ApJ
Electron-lattice coupling and the broken symmetries of the molecular salt (TMTTF)SbF
(TMTTF)SbF is known to undergo a charge ordering (CO) phase
transition at and another transition to an
antiferromagnetic (AF) state at . Applied pressure causes a
decrease in both and . When , the CO is largely
supressed, and there is no remaining signature of AF order. Instead, the ground
state is a singlet. In addition to establishing an expanded, general phase
diagram for the physics of TMTTF salts, we establish the role of
electron-lattice coupling in determining how the system evolves with pressure.Comment: 4 pages, 5 figure
Hadronic Production with QCD Corrections and Leptonic Decays
The process , where
denotes a lepton, is calculated to order . Total and differential
cross sections, with acceptance cuts imposed on the leptons and photon, are
given for the Tevatron and LHC center of mass energies. In general, invariant
mass and angular distributions are simply scaled up in magnitude by the QCD
radiative corrections, whereas in transverse momentum distributions, the QCD
radiative corrections increase with the transverse momentum.Comment: 16 pages + 9 figures, UCD-94-29. A postscript version and 9
postscript figures are available via anonymous ftp to UCDHEP.UCDAVIS.EDU in
the directory [.ohnemus.ucd-94-29
Electroweak radiative corrections to W-boson production at hadron colliders
The complete set of electroweak O(alpha) corrections to the Drell--Yan-like
production of W bosons is calculated and compared to an approximation provided
by the leading term of an expansion about the W-resonance pole. All relevant
formulae are listed explicitly, and particular attention is paid to issues of
gauge invariance and the instability of the W bosons. A detailed discussion of
numerical results underlines the phenomenological importance of the electroweak
corrections to W-boson production at the Tevatron and at the LHC. While the
pole expansion yields a good description of resonance observables, it is not
sufficient for the high-energy tail of transverse-momentum distributions,
relevant for new-physics searches.Comment: 29 pages, latex, 17 postscript files, revised version that is to
appear in Phys.Rev.D, some explanations added and results extended by a
discussion of the QED factorization scale dependenc
Top Pair Production Beyond Double-Pole Approximation: pp, pp~ --> 6 Fermions and 0, 1 or 2 Additional Partons
Hadron collider cross sections for tt~ production and di-lepton,
single-lepton and all-jet decays with up to 2 additional jets are calculated
using complete LO matrix elements with 6-, 7- and 8-particle final states. The
fixed-width, complex-mass and overall-factor schemes (FWS, CMS & OFS) are
employed and the quality of narrow-width and double-pole approximations (NWA &
DPA) is investigated for inclusive production and suppressed backgrounds to new
particle searches. NWA and DPA cross sections differ by 1% or less. The
inclusion of sub- and non-resonant amplitudes effects a cross section increase
of 5-8% at pp supercolliders, but only minor changes at the Tevatron. On-shell
tt~/Wtb backgrounds for the H --> WW decay in weak boson fusion, the hadronic
\tau decay of a heavy H^\pm and the \phi --> hh --> \tau\tau bb~ radion decay
at the LHC are updated, with corrections ranging from 3% to 30%. FWS and CMS
cross sections are uniformly consistent, but OFS cross sections are up to 6%
smaller for some backgrounds.Comment: 20 pages, 6 tables, 1 figur
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