4,857 research outputs found
The AMS-02 Anticoincidence Counter
The AMS-02 detector will measure cosmic rays on the International Space
Station. This contribution will cover production, testing, space qualification
and integration of the AMS-02 anticoincidence counter. The anticoincidence
counter is needed to to assure a clean track reconstruction for the charge
determination and to reduce the trigger rate during periods of high flux.Comment: IPRD08 conference proceeding. Will be published in Nuclear Physics B
(Proceedings Supplement
Determining the Sign of the Z-Penguin Amplitude
We point out that the precision measurements of the pseudo observables R_b^0,
A_b, and A_FB^0,b performed at LEP and SLC suggest that in models with
minimal-flavor-violation the sign of the Z-penguin amplitude is identical to
the one present in the standard model. We determine the allowed range for the
non-standard contribution to the Inami-Lim function C and show by analyzing
possible scenarios with positive and negative interference of standard model
and new physics contributions, that the derived bound holds in each given case.
Finally, we derive lower and upper limits for the branching ratios of K^+ ->
pi^+ nu nubar, K_L -> pi^0 nu nubar, K_L -> mu^+ mu^-, B -> X_d,s nu nubar, and
B_d,s -> mu^+ mu^- within constrained minimal-flavor-violation making use of
the wealth of available data collected at the Z-pole.Comment: 20 pages, 5 pdf figures, 5 tables, uses pdflatex; further typos
corrected, matches PRD versio
alpha_s from tau decays revisited
Being a determination at low energies, the analysis of hadronic tau decay
data provides a rather precise determination of the strong coupling alpha_s
after evolving the result to M_Z. At such a level of precision, even small
non-perturbative effects become relevant for the central value and error. While
those effects had been taken into account in the framework of the operator
product expansion, contributions going beyond it, so-called duality violations,
have previously been neglected. The following investigation fills this gap
through a finite-energy sum rule analysis of tau decay spectra from the OPAL
experiment, including duality violations and performing a consistent fit of all
appearing QCD parameters. The resulting values for alpha_s(M_tau) are 0.307(19)
in fixed-order perturbation theory and 0.322(26) in contour-improved
perturbation theory, which translates to the n_f=5 values 0.1169(25) and
0.1187(32) at M_Z, respectively.Comment: 4 pages, 3 figures. Prepared for the Proceedings of the International
Workshop on e+e- collisions from Phi to Psi (PHIPSI11), Sep. 19-22, 2011,
BINP, Novosibirsk, Russi
Constraining the Two-Higgs-Doublet-Model parameter space
We confront the Two-Higgs-Doublet Model with a variety of experimental
constraints as well as theoretical consistency conditions. The most
constraining data are the \bar B\to X_s\gamma decay rate (at low values of
M_{H^\pm}), and \Delta\rho (at both low and high M_{H^\pm}). We also take into
account the B\bar B oscillation rate and R_b, or the width \Gamma(Z\to b\bar b)
(both of which restrict the model at low values of \tan\beta), and the
B^-\to\tau\nu_\tau decay rate, which restricts the model at high \tan\beta and
low M_{H^\pm}. Furthermore, the LEP2 non-discovery of a light, neutral Higgs
boson is considered, as well as the muon anomalous magnetic moment. Since
perturbative unitarity excludes high values of \tan\beta, the model turns out
to be very constrained. We outline the remaining allowed regions in the
\tan\beta-M_{H^\pm} plane for different values of the masses of the two
lightest neutral Higgs bosons, and describe some of their properties.Comment: 17 pages, 17 figure
Further constraints on the evolution of Ks-selected galaxies in the GOODS/CDFS field
We have selected and analysed the properties of a sample of 2905 Ks<21.5
galaxies in ~ 131 sq.arcmin of the Great Observatories Origins Deep Survey
(GOODS) Chandra Deep Field South (CDFS), to obtain further constraints on the
evolution of Ks-selected galaxies with respect to the results already obtained
in previous studies. We made use of the public deep multiwavelength imaging
from the optical B through the infrared (IR) 4.5 micron bands, in conjunction
with available spectroscopic and COMBO17 data in the CDFS, to construct an
optimised redshift catalogue for our galaxy sample. We computed the Ks-band LF
and determined that its characteristic magnitude has a substantial brightening
and a decreasing total density from z=0 to =2.5. We also analysed the
colours and number density evolution of galaxies with different stellar masses.
Within our sample, and in contrast to what is observed for less massive
systems, the vast majority (~ 85-90%) of the most massive (M>2.5x10^11 Msun)
local galaxies appear to be in place before redshift z ~1. Around 65-70% of the
total assemble between redshifts z=1 and z=3 and most of them display extremely
red colours, suggesting that plausible star formation in these very massive
systems should mainly proceed in obscured, short-timescale bursts. The
remaining fraction (up to ~ 20%) could be in place at even higher redshifts
z=3-4, pushing the first epoch of formation of massive galaxies beyond the
limits of current near-IR surveys.Comment: Accepted for publication in MNRAS. 16 pages, 15 figure
Construction and Test of MDT Chambers for the ATLAS Muon Spectrometer
The Monitored Drift Tube (MDT) chambers for the muon spectrometer of the AT-
LAS detector at the Large Hadron Collider (LHC) consist of 3-4 layers of
pressurized drift tubes on either side of a space frame carrying an optical
monitoring system to correct for deformations. The full-scale prototype of a
large MDT chamber has been constructed with methods suitable for large-scale
production. X-ray measurements at CERN showed a positioning accuracy of the
sense wires in the chamber of better than the required 20 ?microns (rms). The
performance of the chamber was studied in a muon beam at CERN. Chamber
production for ATLAS now has started
Trilinear Higgs couplings in the two Higgs doublet model with CP violation
We carry out a detailed analysis of the general two Higgs doublet model with
CP violation. We describe two different parametrizations of this model, and
then study the Higgs boson masses and the trilinear Higgs couplings for these
two parametrizations. Within a rather general model, we find that the trilinear
Higgs couplings have a significant dependence on the details of the model, even
when the lightest Higgs boson mass is taken to be a fixed parameter. We include
radiative corrections in the one-loop effective potential approximation in our
analysis of the Higgs boson masses and the Higgs trilinear couplings. The
one-loop corrections to the trilinear couplings of the two Higgs doublet model
also depend significantly on the details of the model, and can be rather large.
We study quantitatively the trilinear Higgs couplings, and show that these
couplings are typically several times larger than the corresponding Standard
Model trilinear Higgs coupling in some regions of the parameter space. We also
briefly discuss the decoupling limit of the two Higgs doublet model.Comment: 23 pages, 15 figures. v2: References added, version to appear in PR
Supersymmetric large tan(beta) corrections to DeltaM_(d,s) and B_(d,s) -> mu+mu- revisited
We point out that in the minimal supersymmetric standard model terms from the
mixing of Higgs and Goldstone bosons which are connected to the renormalization
of tan(beta) via Slavnov-Taylor identities give rise to corrections that do not
vanish in the limit where the supersymmetric particles are much heavier than
the Higgs bosons. These additional contributions have important
phenomenological implications as they can lead to potentially large
supersymmetric effects in DeltaM_d and to a significant increase of DeltaM_s
relative to the standard model prediction for a light pseudoscalar Higgs A0. We
calculate all the missing one-loop pieces and combine them with the known
effective non-holomorphic terms to obtain improved predictions for the
B_(d,s)-anti-B_(d,s) mass differences DeltaM_(d,s) and the branching ratios of
B_(d,s) -> mu+mu- in the large tan(beta) regime of the minimal supersymmetric
standard model with minimal flavor violation.Comment: 8 pp; few typos corrected; version to appear in Phys. Rev.
Issues in determining alpha_s from hadronic tau decay and electroproduction data
We discuss some key issues associated with duality-violating and
non-perturbative OPE contributions to the theoretical representations of light
quark current-current two-point functions and relevant to precision
determinations of alpha_s from hadronic tau decay and electroproduction
cross-section data. We demonstrate that analyses with an explicit
representation of duality-violating effects are required to bring theoretical
errors in such extractions under control, motivating the accompanying paper in
these proceedings, which presents the results of such an analysis.Comment: 5 pages, 4 figures. Prepared for the Proceedings of the International
Workshop on e+e- collisions from Phi to Psi (PHIPSI11), Sep. 19-22, 2011,
BINP, Novosibirsk, Russi
Construction and Test of the Precision Drift Chambers for the ATLAS Muon Spectrometer
The Monitored Drift Tube (MDT) chambers for the muon spectrometer of the
ATLAS detector at the Large Hadron Collider (LHC) consist of 3-4 layers of
pressurised drift tubes on either side of a space frame carrying an optical
deformation monitoring system. The chambers have to provide a track position
resolution of 40 microns with a single-tube resolution of at least 80 microns
and a sense wire positioning accu- racy of 20 ?microns (rms). The feasibility
was demonstrated with the full-scale prototype of one of the largest MDT
chambers with 432 drift tubes of 3.8 m length. For the ATLAS muon spectrometer,
88 chambers of this type have to be built. The first chamber has been completed
with a wire positioning accuracy of 14 microns (rms)
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