2,786 research outputs found
Combined Electroweak Analysis
Recent developments in the measurement of precision electroweak measurements
are summarised, notably new results on the mass of the top quark and mass and
width of the W boson. Predictions of the Standard Model are compared to the
experimental results which are used to constrain the input parameters of the
Standard Model, in particular the mass of the Higgs boson. The agreement
between measurements and expectations from theory is discussed.
Invited talk presented at the EPS HEP 2007 conference
Manchester, England, July 19th to 25th, 2007Comment: 7 pages and 6 figure
Electroweak Physics, Experimental Aspects
Collider measurements on electroweak physics are summarised. Although the
precision on some observables is very high, no deviation from the Standard
Model of electroweak interactions is observed. The data allow to set stringent
limits on some models for new physics.Comment: Plenary Talk at the UK Phenomenology Workshop on Collider Physics,
Durham, 199
Constraints on Two-Higgs Doublet Models at Large tan{beta} from W and Z decays
We study constraints on type-II two Higgs doublet models at large tan{beta}
from LEP/SLD Z-pole data and from lepton universality violation in W decay. We
perform a global fit and find that, in the context of Z decay, the LEP/SLD
experimental values for lepton universality violation, R_b, and A_b all
somewhat disfavor the model. Contributions from the neutral Higgs sector can be
used to constrain the scalar-pseudoscalar Higgs mass splittings. Contributions
from the charged Higgs sector allow us to constrain the charged Higgs mass. For
tan{beta}=100 we obtain the 1 sigma classical (Bayesian) bounds of m_{H+} > 670
GeV (370 GeV) and 1 > m_{h0}/m_{A0} > 0.68 (0.64). The 2 sigma bounds are weak.
Currently, the Tevatron experimental limits on lepton universality violation in
W decay provide no significant constraint on the Higgs sector.Comment: 26 pages, 9 postscript figures, REVTe
Searching for Anomalous Weak Couplings of Heavy Flavors at the SLC and LEP
The existence of anomalous electric() and/or
magnetic() dipole moment couplings between the heavy flavor fermions
() and the boson can cause significant shifts in the values of
several electroweak observables currently being probed at both the SLC and LEP.
Using the good agreement between existing data and the predictions of the
Standard Model we obtain strict bounds on the possible strength of these new
interactions for all of the heavy flavors. The decay ,
however, provides some possible hint of new physics. The corresponding
anomalous couplings of 's to photons is briefly examined.Comment: 21 pages, 14 figs(available on request), LaTex, SLAC-PUB-667
Higgs signals and hard photons at the Next Linear Collider: the -fusion channel in the Standard Model
In this paper, we extend the analyses carried out in a previous article for
-fusion to the case of Higgs production via -fusion within the Standard
Model at the Next Linear Collider, in presence of electromagnetic radiation due
real photon emission. Calculations are carried out at tree-level and rates of
the leading order (LO) processes e^+e^-\rightarrow e^+e^- H \ar e^+e^- b\bar b
and e^+e^-\rightarrow e^+e^- H \ar e^+e^- WW \ar e^+e^- \mathrm{jjjj} are
compared to those of the next-to-leading order (NLO) reactions
e^+e^-\rightarrow e^+e^- H (\gamma)\ar e^+e^- b\bar b \gamma and
e^+e^-\rightarrow e^+e^- H (\gamma)\ar e^+e^- WW (\gamma) \ar e^+e^-
\mathrm{jjjj}\gamma, in the case of energetic and isolated photons.Comment: 12 pages, LaTeX, 5 PostScript figures embedded using epsfig and
bitmapped at 100dpi, complete paper including high definition figures
available at ftp://axpa.hep.phy.cam.ac.uk/stefano/cavendish_9611.ps or at
http://www.hep.phy.cam.ac.uk/theory/papers
The NuTeV Anomaly, Neutrino Mixing, and a Heavy Higgs Boson
Recent results from the NuTeV experiment at Fermilab and the deviation of the
Z invisible width, measured at LEP/SLC, from its Standard Model (SM) prediction
suggest the suppression of neutrino-Z couplings. Such suppressions occur
naturally in models which mix the neutrinos with heavy gauge singlet states. We
postulate a universal suppression of the Z-nu-nu couplings by a factor of
(1-epsilon) and perform a fit to the Z-pole and NuTeV observables with epsilon
and the oblique correction parameters S and T. Compared to a fit with S and T
only, inclusion of epsilon leads to a dramatic improvement in the quality of
the fit. The values of S and T preferred by the fit can be obtained within the
SM by a simple increase in the Higgs boson mass. However, if the W mass is also
included in the fit, a non-zero U parameter becomes necessary which cannot be
supplied within the SM. The preferred value of epsilon suggests that the seesaw
mechanism may not be the reason why neutrinos are so light.Comment: 19 pages, REVTeX4, 8 postscript figures. Updated references. Typos
correcte
MS vs. Pole Masses of Gauge Bosons: Electroweak Bosonic Two-Loop Corrections
The relationship between MS and pole masses of the vector bosons Z and W is
calculated at the two-loop level in the Standard Model. We only consider the
purely bosonic contributions which represents a gauge invariant subclass of
diagrams. All calculations were performed in the linear gauge with
three arbitrary gauge parameters utilizing the method of asymptotic expansions.
The results are presented in analytic form as series in the small parameters
and mass ratio . As a byproduct we obtain the
bosonic two-loop contributions to the renormalization of the weak mixing
parameter and of the Fermi constant. The running of Fermi
constant will become important at high energy colliders.Comment: LaTeX, 36 p., 10 fig.; in v3 more technical details about
renormalization procedure are adde
WW Cross-sections and Distributions
We present the results obtained by the "WW Cross-sections and Distributions"
working group during the CERN Workshop "Physics at LEP2" (1994/1995)Comment: 61 pages, tar'ed gzip'ed uuencoded files, LaTeX, 4 Postscript
figures. To appear in "Physics at LEP2", G.Altarelli and F.Zwirner eds., CERN
Report 199
- …