1,427 research outputs found
Electroweak Measurements
The measurements of electroweak sector of the Standard Model are presented,
including most recent results from LEP, Tevatron and HERA colliders. The
robustness of the Standard Model is illustrated with the precision
measurements, the electroweak fits and the comparisons to the results obtained
from low energy experiments. The status of the measurements of the boson
properties and rare production processes involving weak bosons at colliders is
examined, together with the measurements of the electroweak parameters in
collisions.Comment: 12 pages, Proceedings of "Lepton-Photon 2005", Upsalla, Swede
Transverse Lepton Polarization in Polarized W Decays
Calculations of transverse polarization of leptons in the decay with polarized 's are presented. Planned accelerators will produce
enough 's for observation of the Standard Model contributions to this
polarization. One loop corrections to the polarization are given; these are too
small to be seen at presently available sources. The exchange of Majorons
will contribute to these polarizations; these may provide limits on the
couplings of these particles to leptons.Comment: 8 pages set in RevTex III and 4 uucompressed figures. This revised
version studies polarization effects due to the exchange of charged Majoron
doublet
Higher-Order Corrections in Threshold Resummation
We extend the threshold resummation exponents G^N in Mellin-N space to the
fourth logarithmic (N^3LL) order collecting the terms alpha_s^2 (alpha_s ln
N)^n to all orders in the strong coupling constant as. Comparing the results to
our previous three-loop calculations for deep-inelastic scattering (DIS), we
derive the universal coefficients B_q and B_g governing the final-state jet
functions to order alpha_s^3, extending the previous quark and gluon results by
one and two orders. A curious relation is found at second order between these
quantities, the splitting functions and the large-angle soft emissions in
Drell-Yan type processes. We study the numerical effect of the N^3LL
corrections using both the fully exponentiated form and the expansion of the
coefficient function in towers of logarithms.Comment: 20 pages, LaTeX, 6 eps-figures. Misprints in equations and fig. 5
correcte
Higher-Order Soft Corrections to Lepton Pair and Higgs Boson Production
Utilizing recent three-loop results on the quark and gluon splitting
functions and form factors, we derive the complete threshold-enhanced
third-order (N^3LO) QCD corrections to the total cross sections for the
production of lepton pairs and the Higgs boson in hadron collisions. These
results, for the latter case obtained in the heavy top-quark limit, are
employed to extend the threshold resummation for these processes to the fourth
logarithmic order. We investigate the numerical impact of the higher-order
corrections for Higgs boson production at the Tevatron and the LHC. Our
results, suitably treated in Mellin N-space, provide a sufficiently accurate
approximation to the full N^3LO contributions. Corrections of about 5% at the
LHC and 10% at the Tevatron are found for typical Higgs masses. The N^3LO
predictions exhibit a considerably reduced dependence on the renormalization
scale with, for the first time, stationary points close to the Higgs mass.Comment: 11 pages, LaTeX, 2 eps-figures. Slightly revised text of journal
version, with two new references. Misprint in eq. (13) correcte
Threshold Corrections in Precision LHC Physics: QED otimes QCD
With an eye toward LHC processes in which theoretical precisions of 1 percent
are desired, we introduce the theory of the simultaneous YFS resummation of QED
and QCD to compute the size of the expected resummed soft radiative threshold
effects in precision studies of heavy particle production at the LHC. Our
results show that both QED and QCD soft threshold effects must be controlled to
be on the conservative side to achieve such precision goals.Comment: 4 pages, no figures; presented by B.F.L. Ward in DPF200
Parton distribution functions from the precise NNLO QCD fit
We report the parton distribution functions (PDFs) determined from the NNLO
QCD analysis of the world inclusive DIS data with account of the precise NNLO
QCD corrections to the evolution equations kernel. The value of strong coupling
constant \alpha_s^{NNLO}(M_Z)=0.1141(14), in fair agreement with one obtained
using the earlier approximate NNLO kernel by van Neerven-Vogt. The intermediate
bosons rates calculated in the NNLO using obtained PDFs are in agreement to the
latest Run II results.Comment: 8 pages, LATEX, 2 figures (EPS
Z-prime Gauge Bosons at the Tevatron
We study the discovery potential of the Tevatron for a Z-prime gauge boson.
We introduce a parametrization of the Z-prime signal which provides a
convenient bridge between collider searches and specific Z-prime models. The
cross section for p pbar -> Z-prime X -> l^+ l^- X depends primarily on the
Z-prime mass and the Z-prime decay branching fraction into leptons times the
average square coupling to up and down quarks. If the quark and lepton masses
are generated as in the standard model, then the Z-prime bosons accessible at
the Tevatron must couple to fermions proportionally to a linear combination of
baryon and lepton numbers in order to avoid the limits on Z--Z-prime mixing.
More generally, we present several families of U(1) extensions of the standard
model that include as special cases many of the Z-prime models discussed in the
literature. Typically, the CDF and D0 experiments are expected to probe
Z-prime-fermion couplings down to 0.1 for Z-prime masses in the 500--800 GeV
range, which in various models would substantially improve the limits set by
the LEP experiments.Comment: 34 pages, 13 figure
Next-to-Next-to-Leading Order Higgs Production at Hadron Colliders
The Higgs boson production cross section at pp and p\bar{p} colliders is
calculated in QCD at next-to-next-to-leading order (NNLO). We find that the
perturbative expansion of the production cross section is well behaved and that
scale dependence is reduced relative to the NLO result. These findings give us
confidence in the reliability of the prediction. We also report an error in the
NNLO correction to Drell-Yan production.Comment: 5 pages, 4 figures, minor change
Complexity of the Ruminococcus flavefaciens FD-1 cellulosome reflects an expansion of family-related protein-protein interactions
This work was supported in part by the European Union, Area NMP.2013.1.1â2: Self-assembly of naturally occurring nanosystems: CellulosomePlus Project number: 604530, and by the EU Seventh Framework Programme (FP7 2007â2013) under the WallTraC project (Grant Agreement no 263916), and BioStruct-X (grant agreement no 283570). This paper reflects the authorâs views only. The European Community is not liable for any use that may be made of the information contained herein. CMGAF is also supported by Fundação para a CiĂȘncia e a Tecnologia (Lisbon, Portugal) through grants PTDC/BIA-PRO/103980/2008 and EXPL/BIA-MIC/1176/2012. EAB is also funded by a grant (No. 1349/13) from the Israel Science Foundation (ISF), Jerusalem, Israel and by a grant (No. 2013284) from the U.S.-Israel Binational Science Foundation (BSF). E.A.B. is the incumbent of The Maynard I. and Elaine Wishner Chair of Bio-organic Chemistry.Peer reviewedPublisher PD
Subtraction Terms for Hadronic Production Processes at Next-to-Next-to-Leading Order
I describe a subtraction scheme for the next-to-next-to-leading order
calculation of single inclusive production at hadron colliders. Such processes
include Drell-Yan, W^{+/-}, Z and Higgs Boson production. The key to such a
calculation is a treatment of initial state radiation which preserves the
production characteristics, such as the rapidity distribution, of the process
involved. The method builds upon the Dipole Formalism and, with proper
modifications, could be applied to deep inelastic scattering and e^+ e^-
annihilation to hadrons.Comment: 4 page
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