6,521 research outputs found
Renormalization of the EWCL and its Application to LEP2
We perform a systematic one-loop renormalization on the electroweak chiral
Lagrangian (EWCL) up to operators and construct the renormalization
group equations (RGE) for the anomalous couplings. We examine the impact of the
triple gauge coupling (TGC) measurement from LEP2 to the uncertainty of the
parameter at the , and find that the uncertainty in the
TGC measurements can shift at least .Comment: 4 pages, 1 eps figure, uses ws-ijmpa.cls. Paralell talk given at
"International Conference on QCD and hadronic Physics", Beijing, China, 16-20
June, 200
Search for Higgs and New Phenomena at Colliders
The present status of searches for the Higgs boson(s) and new phenomena is
reviewed. The focus is on analyses and results from the current runs of the
HERA and Tevatron experiments. The LEP experiments have released their final
combined MSSM Higgs results for this conference. Also included are results from
sensitivity studies of the LHC experiments and lepton flavour violating
searches from the B factories, KEKB and PEP-II.Comment: XXII International Symposium on Lepton-Photon Interactions at High
Energy (11 pages, 16 figures, 2 tables
Probing the Higgs Field Using Massive Particles as Sources and Detectors
In the Standard Model, all massive elementary particles acquire their masses
by coupling to a background Higgs field with a non-zero vacuum expectation
value. What is often overlooked is that each massive particle is also a source
of the Higgs field. A given particle can in principle shift the mass of a
neighboring particle. The mass shift effect goes beyond the usual perturbative
Feynman diagram calculations which implicitly assume that the mass of each
particle is rigidly fixed. Local mass shifts offer a unique handle on Higgs
physics since they do not require the production of on-shell Higgs bosons. We
provide theoretical estimates showing that the mass shift effect can be large
and measurable, especially near pair threshold, at both the Tevatron and the
LHC.Comment: 6 pages, no figures; Version 2 corrects some typographical errors of
factors of 2 in equations 14, 17, 18 and 19 (all of the same origin) and
mentions a linear collider as an interesting place to test the results of
this pape
Bounds on the Simplest Little Higgs Model Mass Spectrum Through Z Leptonic Decay
We derive the leptonic neutral current in the simplest little Higgs model and
compute the contribution of the model to the decay width . Using
the precision electroweak data we obtain a strong lower bound TeV
at 95% C.L. on the characteristic energy scale of the model. It results in a
lower bound for the new gauge bosons and as being
TeV and TeV, respectively.
We also present the allowed values of the which is the parameter
relating the two vacuum expectation values of the scalar triplets in the model,
and the parameter of a quadratic term, involving the triplets, necessary
to provide an acceptable mass range for the standard Higgs boson.Comment: New references added, 13 pages. Version to be publishe
Global analysis of fragmentation functions for pions and kaons and their uncertainties
We present new sets of pion and kaon fragmentation functions obtained in NLO
combined analyses of single-inclusive hadron production in electron-positron
annihilation, proton-proton collisions, and deep-inelastic lepton-proton
scattering with either pions or kaons identified in the final state. At
variance with all previous fits, the present analyses take into account data
where hadrons of different electrical charge are identified, which allow to
discriminate quark from anti-quark fragmentation functions without the need of
non trivial flavor symmetry assumptions. The resulting sets are in good
agreement with all data analyzed, which cover a much wider kinematical range
than in previous fits. An extensive use of the Lagrange multiplier technique is
made in order to assess the uncertainties in the extraction of the
fragmentation functions and the synergy from the complementary data sets in our
global analysis.Comment: 28 pages, 25 figure
Finite-width effects in the near-threshold ZZZ and ZWW production at ILC
We calculate the cross-section of the near-threshold off-shell and
production at the International Linear Collider taking into account
their instability and the principal part of NLO corrections. The calculations
are performed in the framework of the model of unstable particles with smeared
mass-shell. We show that the contribution of the finite and widths
(their instability) is large in the Higgs resonance range and should be taken
into account in the Higgs boson searches at future colliders.Comment: 5 pages, 6 figure
Constraining Nonstandard Neutrino-Electron Interactions
We present a detailed analysis on nonstandard neutrino interactions (NSI)
with electrons including all muon and electron (anti)-neutrino data from
existing accelerators and reactors, in conjunction with the ``neutrino
counting'' data (e- e+ -> nu nu gamma) from the four LEP collaborations. First
we perform a one-parameter-at-a-time analysis, showing how most constraints
improve with respect to previous results reported in the literature. We also
present more robust results where the NSI parameters are allowed to vary freely
in the analysis. We show the importance of combining LEP data with the other
experiments in removing degeneracies in the global analysis constraining
flavor-conserving NSI parameters which, at 90 % and 95 % C.L., must lie within
unique allowed regions. Despite such improved constraints, there is still
substantial room for improvement, posing a big challenge for upcoming
experiments.Comment: 19 pages, 4 figures. Final version to appear in Phys. Rev.
Double fermiophobic Higgs boson production at the LHC and LC
We consider the phenomenology of a fermiophobic Higgs boson (h_f) at the
Large Hadron Collider (LHC) and a e+e- Linear Collider (LC). At both machines
the standard production mechanisms which rely on the coupling h_fVV (V=W,Z) can
be very suppressed at large tan beta. In such cases the complementary channels
pp to H^\pm h_f, A^0 h_f and e+e- to A^0 h_f offer promising cross-sections.
Together with the potentially large branching ratios for H^\pm to h_fW* and A^0
to h_fZ*, these mechanisms would give rise to double h_f production, leading to
signatures of gamma gamma gamma gamma, gamma gamma VV and VVVV.Comment: 19 pages, 9 figures, expanded discussion, fig.1 changed slightly,
version to appear in Phys.Rev.
Gamma(*)Gamma(*) reaction at high energies
The energy available for gamma(*)gamma(*) physics at LEP2 is opening a new
window on the study of diffractive phenomena, both non-perturbative and
perturbative. We discuss some of the uncertainties and problems connected with
the experimental measurements and their interpretation.Comment: 6 pages, 6 figures, submitted to proceedings of the Durham Collider
Workshop, 22-26 September 199
Determination of the Strong Coupling \boldmath{\as} from hadronic Event Shapes and NNLO QCD predictions using JADE Data
Event Shape Data from annihilation into hadrons collected by the
JADE experiment at centre-of-mass energies between 14 GeV and 44 GeV are used
to determine the strong coupling . QCD predictions complete to
next-to-next-to-leading order (NNLO), alternatively combined with resummed
next-to-leading-log-approximation (NNLO+NLLA) calculations, are used. The
combined value from six different event shape observables at the six JADE
centre-of-mass energies using the NNLO calculations is
= 0.1210 +/- 0.0007(stat.) +/- 0.0021(expt.) +/- 0.0044(had.)
+/- 0.0036(theo.) and with the NNLO+NLLA calculations the combined value is
= 0.1172 +/- 0.0006(stat.) +/- 0.0020(expt.) +/- 0.0035(had.) +/-
0.0030(theo.) . The stability of the NNLO and NNLO+NLLA results with respect to
missing higher order contributions, studied by variations of the
renormalisation scale, is improved compared to previous results obtained with
NLO+NLLA or with NLO predictions only. The observed energy dependence of
agrees with the QCD prediction of asymptotic freedom and excludes
absence of running with 99% confidence level.Comment: 9 pages, EPHJA style, 4 figures, corresponds to published version
with JADE author lis
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