6,081 research outputs found

### Running of the QED coupling in small-angle Bhabha scattering at LEP

Using the OPAL detector at LEP, the running of the effective QED coupling
alpha(t) is measured for space-like momentum transfer, 2 \leq -t \leq 6 GeV^2,
from the angular distribution of small-angle Bhabha scattering. This is
currently the most significant direct observation of the running of the QED
coupling in a single experiment and the first clear evidence of the hadronic
contribution to the running in the space-like region. Our result is in good
agreement with standard evaluations of alpha(t), based on data in the time-like
region.Comment: Talks given at the 19th Rencontres De Physique De La Vallee D'Aoste
(27.2-5.3.05), La Thuile, Italy and at the 40th Rencontres De Moriond On
Electroweak Interactions And Unified Theories (5.3-12.3.05), La Thuile,
Italy. Added 1 figure and related text wrt vers.

### A Framework to Simultaneously Explain Tiny Neutrino Mass and Huge Missing Mass Problem of the Universe

Recently a minimalistic scenario has been developed to explain dark matter
and tiny but nonzero neutrino masses. In this scenario, a new scalar called
SLIM plays the role of the dark matter. Neutrinos achieve Majorana mass through
a one-loop diagram. This scenario can be realized for both real and complex
SLIM. Simultaneously explaining the neutrino mass and dark matter abundance
constrains the scenario. In particular for real SLIM, an upper bound of a few
MeV on the masses of the new particles and a lower bound on their coupling are
obtained which make the scenario testable. The low energy scenario can be
embedded within various $SU(2)\times U(1)$ symmetric models. I shall briefly
review the scenario and a specific model that embeds the scenario, with special
emphasis on the effects in the charged Kaon decay which might be observable at
the KLOE and NA62 experiments.Comment: 7 pages, 1 figur

### Quark mixing and CP violation - the CKM matrix

I present the status of the elements and parameters of the
Cabibbo-Kobayashi-Maskawa (CKM) matrix and summarise the related theoretical
progress since "Lepton-Photon 2003". One finds |V_{us}| = 0.2227 +/- 0.0017
from K and tau decays and |V_{cb}| = (41.6 +/- 0.5) * 10^{-3} from inclusive
semileptonic B decays. The unitarity triangle can now be determined from
tree-level quantities alone and the result agrees well with the global fit
including flavour-changing neutral current (FCNC) processes, which are
sensitive to new physics. From the global fit one finds the three CKM angles
theta_{12}=12.9 +/- 0.1 degrees, theta_{23}= 2.38 +/- 0.03 degrees and
theta_{13}= 0.223 +/- 0.007 degrees in the standard PDG convention. The CP
phase equals delta_{13} = gamma = (58.8 +5.3/-5.8) degrees at 1 sigma CL and
gamma=(58.8 +11.2/-15.4) degrees at 2 sigma CL. A major progress are first
results from fully unquenched lattice QCD computations for the hadronic
quantities entering the UT fit. I further present the calculation of three-loop
QCD corrections to the charm contribution in K+ -> pi+ nu nu-bar decays, which
removes the last relevant theoretical uncertainty from the K -> pi nu nu-bar
system. Finally I discuss mixing-induced CP asymmetries in b -> s q-bar q
penguin decays, whose naive average is below its Standard Model value by 3
sigma.Comment: 14 pages, 12 figures, plenary talk at "Lepton-Photon 2005

### Performance of the OPAL Si-W luminometer at LEP I-II

A pair of compact Silicon-Tungsten calorimeters was operated in the OPAL
experiment at LEP to measure the integrated luminosity from detection of Bhabha
electrons scattered at angles between 25 and 58 mrad from the beam line. In the
eight years from 1993 to 2000 the detector worked first at the Z mass peak and
then at center of mass energies up to 209 GeV. The fine radial and longitudinal
segmentation (2.5mm x 1X0) allowed the radial position of electron and photon
showers to be measured with a resolution of 130-170 microns and a residual
radial bias as small as 7 microns. Reducing the bias in the definition of the
inner acceptance radius was the key element in obtaining an experimental
systematic error on the integrated luminosity of only 3.4 10^-4. The
performance of the detector at both LEP-I and LEP-II is reviewed. Energy
resolution, sensitivity to overlapping electromagnetic showers and sensitivity
to minimum ionizing particles are discussed.Comment: 9 pages, 7 figures, 10th International Conference on Calorimetry in
High Energy Physics. http://3w.hep.caltech.edu/calor02

### Renormalization of the EWCL and its Application to LEP2

We perform a systematic one-loop renormalization on the electroweak chiral
Lagrangian (EWCL) up to $O(p^4)$ 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
$S-T$ parameter at the $\Lambda=1 TeV$, and find that the uncertainty in the
TGC measurements can shift $S(\Lambda)$ at least $3.3 \sigma$.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

### Cosmo-Particle Searches for Supersymmetry at the Collider Detector at Fermilab

Some theories of particle physics are so compelling that it is worth doing a
comprehensive and systematic set of experimental searches to see if they are
realized in nature. Supersymmetry is one such theory. This review focuses on
the motivation for a broad set of cosmology-inspired search strategies at the
Tevatron and on their implementation and results at the Collider Detector at
Fermilab (CDF) with the first few fb$^{-1}$ of integrated luminosity of data.Comment: 15 Pages, 23 figure

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