206 research outputs found
Correlation Time-of-flight Spectrometry of Ultracold Neutrons
The fearures of the correlation method used in time-of-flight spectrometry of
ultracold neutrons are analyzed. The time-of-flight spectrometer for the energy
range of ultracold neutrons is described, and results of its testing by
measuring spectra of neutrons passing through interference filters are
presented.Comment: 16 pages, 5 figure
Updated NNLO QCD predictions for the weak radiative B-meson decays
Weak radiative decays of the B mesons belong to the most important flavor
changing processes that provide constraints on physics at the TeV scale. In the
derivation of such constraints, accurate standard model predictions for the
inclusive branching ratios play a crucial role. In the current Letter we
present an update of these predictions, incorporating all our results for the
O(alpha_s^2) and lower-order perturbative corrections that have been calculated
after 2006. New estimates of nonperturbative effects are taken into account,
too. For the CP- and isospin-averaged branching ratios, we find B_{s gamma} =
(3.36 +_ 0.23) * 10^-4 and B_{d gamma} = 1.73^{+0.12}_{-0.22} * 10^-5, for
E_gamma > 1.6GeV. Both results remain in agreement with the current
experimental averages. Normalizing their sum to the inclusive semileptonic
branching ratio, we obtain R_gamma = ( B_{s gamma} + B_{d gamma})/B_{c l nu} =
(3.31 +_ 0.22) * 10^-3. A new bound from B_{s gamma} on the charged Higgs boson
mass in the two-Higgs-doublet-model II reads M_{H^+} > 480 GeV at 95%C.L.Comment: journal version, 5 pages, no figure
The NNLO gluon fusion Higgs production cross-section with many heavy quarks
We consider extensions of the Standard Model with a number of additional
heavy quarks which couple to the Higgs boson via top-like Yukawa interactions.
We construct an effective theory valid for a Higgs boson mass which is lighter
than twice the lightest heavy quark mass and compute the corresponding Wilson
coefficient through NNLO. We present numerical results for the gluon fusion
cross-section at the Tevatron for an extension of the Standard Model with a
fourth generation of heavy quarks. The gluon fusion cross-section is enhanced
by a factor of roughly 9 with respect to the Standard Model value. Tevatron
experimental data can place stringent exclusion limits for the Higgs mass in
this model.Comment: 14 pages, 1 tabl
Analytic Results for Virtual QCD Corrections to Higgs Production and Decay
We consider the production of a Higgs boson via gluon-fusion and its decay
into two photons. We compute the NLO virtual QCD corrections to these processes
in a general framework in which the coupling of the Higgs boson to the external
particles is mediated by a colored fermion and a colored scalar. We present
compact analytic results for these two-loop corrections that are expressed in
terms of Harmonic Polylogarithms. The expansion of these corrections in the low
and high Higgs mass regimes, as well as the expression of the new Master
Integrals which appear in the reduction of the two-loop amplitudes, are also
provided. For the fermionic contribution, we provide an independent check of
the results already present in the literature concerning the Higgs boson and
the production and decay of a pseudoscalar particle.Comment: 19 pages, 3 figures, version accepted by JHE
Two-loop light fermion contribution to Higgs production and decays
We compute the electroweak corrections due to the light fermions to the
production cross section and to the partial decay widths
and . We present analytic
results for these corrections that are expressed in terms of Generalized
Harmonic Polylogarithms. We find that for the gluon fusion production cross
section and for the decay width the corrections are large
in the Higgs mass region below 160 GeV where they reach up to 9% of the lowest
order term. For the decay width the corrections
for Higgs mass above 160 GeV can reach 10% of the lowest order term.Comment: 12 pages, 4 figure
HUMID ENVIRONMENT STABILITY OF LPCVD ZNO:B USED AS TRANSPARENT ELECTRODES IN THIN FILM SILICON SOLAR CELLS
The stability in humid environment of low pressure chemical vapor deposited boron doped zinc oxide (LPCVD ZnO:B) used as transparent conductive oxide in thin film silicon solar cells is investigated. Damp heat treatment (exposition to humid and hot atmosphere) induces a degradation of the electrical properties of unprotected LPCVD ZnO:B layers. By combining analyses of the electrical and optical properties of the films, we are able to attribute this behavior to an increase of electron grain boundary scattering. This is in contrast to the intragrain scattering mechanisms, which are not affected by damp heat exposure. The ZnO stability is enhanced for heavily doped films due to easier tunneling through potential barrier at grain boundaries
The SUSY-QCD beta function to three loops
A number of DR-bar renormalization constants in softly broken SUSY-QCD are
evaluated to three-loop level: the wave function renormalization constants for
quarks, squarks, gluons, gluinos, ghosts, and epsilon-scalars, and the
renormalization constants for the quark and gluino mass as well as for all
cubic vertices. The latter allow us to derive the corresponding beta functions
through three loops, all of which we find to be identical to the expression for
the gauge beta function obtained by Jack, Jones, and North [Jack:1996vg] (see
also Ref. [Pickering:2001aq]). This explicitely demonstrates the consistency of
DRED with SUSY and gauge invariance, an important pre-requisite for precision
calculations in supersymmetric theories.Comment: Latex, 16 pages, reference added; v2: matches published version in
Eur.Phys.J.
Symmetries and Asymmetries of B -> K* mu+ mu- Decays in the Standard Model and Beyond
The rare decay B -> K* (-> K pi) mu+ mu- is regarded as one of the crucial
channels for B physics as the polarization of the K* allows a precise angular
reconstruction resulting in many observables that offer new important tests of
the Standard Model and its extensions. These angular observables can be
expressed in terms of CP-conserving and CP-violating quantities which we study
in terms of the full form factors calculated from QCD sum rules on the
light-cone, including QCD factorization corrections. We investigate all
observables in the context of the Standard Model and various New Physics
models, in particular the Littlest Higgs model with T-parity and various MSSM
scenarios, identifying those observables with small to moderate dependence on
hadronic quantities and large impact of New Physics. One important result of
our studies is that new CP-violating phases will produce clean signals in
CP-violating asymmetries. We also identify a number of correlations between
various observables which will allow a clear distinction between different New
Physics scenarios.Comment: 56 pages, 18 figures, 14 tables. v5: Missing factor in eqs. (3.31-32)
and fig. 6 corrected. Minor misprints in eq. (2.10) and table A corrected.
Conclusions unchange
Top-mass effects in differential Higgs production through gluon fusion at order \alpha_s^4
Effects from a finite top quark mass on differential distributions in the
Higgs+jet production cross section through gluon fusion are studied at
next-to-leading order in the strong coupling, i.e. . Terms
formally subleading in are calculated, and their influence on the
transverse momentum and rapidity distribution of the Higgs boson are evaluated.
We find that, for the differential K-factor, the heavy-top limit is valid at
the 2-3% level as long as the transverse momentum of the Higgs remains below
about 150 GeV.Comment: 21 pages, 12 figure
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