1,249 research outputs found
System Tests of the ATLAS Pixel Detector
The innermost part of the ATLAS (A Toroidal LHC ApparatuS) experiment at the
LHC (Large Hadron Collider) will be a pixel detector, which is presently under
construction. Once installed into the experimental area, access will be
extremely limited. To ensure that the integrated detector assembly operates as
expected, a fraction of the detector which includes the power supplies and
monitoring system, the optical readout, and the pixel modules themselves, has
been assembled and operated in a laboratory setting for what we refer to as
system tests. Results from these tests are presented.Comment: 5 Pages, 9 Figures, to appear in Proceedings of the Eleventh Workshop
on Electronics for LHC and Future Experiment
A Serendipitous Galaxy Cluster Survey with XMM: Expected Catalogue Properties and Scientific Applications
This paper describes a serendipitous galaxy cluster survey that we plan to
conduct with the XMM X-ray satellite. We have modeled the expected properties
of such a survey for three different cosmological models, using an extended
Press-Schechter (Press & Schechter 1974) formalism, combined with a detailed
characterization of the expected capabilities of the EPIC camera on board XMM.
We estimate that, over the ten year design lifetime of XMM, the EPIC camera
will image a total of ~800 square degrees in fields suitable for the
serendipitous detection of clusters of galaxies. For the presently-favored
low-density model with a cosmological constant, our simulations predict that
this survey area would yield a catalogue of more than 8000 clusters, ranging
from poor to very rich systems, with around 750 detections above z=1. A
low-density open Universe yields similar numbers, though with a different
redshift distribution, while a critical-density Universe gives considerably
fewer clusters. This dependence of catalogue properties on cosmology means that
the proposed survey will place strong constraints on the values of Omega-Matter
and Omega-Lambda. The survey would also facilitate a variety of follow-up
projects, including the quantification of evolution in the cluster X-ray
luminosity-temperature relation, the study of high-redshift galaxies via
gravitational lensing, follow-up observations of the Sunyaev-Zel'dovich effect
and foreground analyses of cosmic microwave background maps.Comment: Accepted to ApJ. Minor changes, e.g. presentation of temperature
errors as a figure (rather than as a table). Latex (20 pages, 6 figures, uses
emulateapj.sty
Optical and X-ray clusters as tracers of the supercluster-void network. I Superclusters of Abell and X-ray clusters
We study the distribution of X-ray selected clusters of galaxies with respect
to superclusters determined by Abell clusters of galaxies and show that the
distribution of X-ray clusters follows the supercluster-void network determined
by Abell clusters. We find that in this network X-ray clusters are more
strongly clustered than other clusters. Poor, non-Abell X-ray clusters follow
the supercluster-void network as well: these clusters are embedded in
superclusters determined by rich clusters and populate filaments between them.
We present a new catalog of superclusters of Abell clusters out to a redshift
of z_{lim}=0.13, a catalog of X-ray clusters located in superclusters
determined by Abell clusters, and a list of additional superclusters of X-ray
clusters.Comment: LaTex (sty files added), 16 pages, 3 ps figures, submitted to
Astronomical Journal. Animations of the 3D distribution of superclusters of
Abell and X-ray clusters at http://www.aai.ee/~maret/SCLVnet.ht
Neutrino Masses in the Composite Little Higgs Model
The composite little Higgs model, a UV completion for the
little Higgs model, incorporates supersymmetry into strong gauge dynamics. We
extend the study of flavor physics in the model, and find that it is similar to
the bosonic technicolor model. Lepton flavor violations and neutrino mass
matrix arise once R-parity violating superpotential is introduced to the model,
as in the MSSM. We identify various low-energy effective lepton
flavor violating operators, and find that most of them are similar to those of
the R-parity violating MSSM. There is a new operator which involves only
leptons and the pseudo-Nambu Goldstone bosons of the little Higgs model. We
further study a possibility that this operator gives a dominant contribution to
the neutrino mass matrix.Comment: 17 pages, 4 figures; Changed contents;v3 corrected typos, to appear
in JHE
The Effects of Inhomogeneities on Evaluating the mass parameter and the cosmological constant
Analytic expressions for distance-redshift relations which have been
corrected for the effects of inhomogeneities in the
Friedmann-Lema\^itre-Robertson-Walker (FLRW) mass density are given in terms of
Heun functions and are used to illustrate the significance of inhomogeneities
on a determination of the mass parameter and the cosmological
constant . The values of these parameters inferred from a given set of
observations depend on the fractional amount of matter in inhomogeneities and
can significantly differ from those obtained by using the standard
magnitude-redshift (-) result for pure dust FLRW models. As an example a
determination of made by applying the homogeneous distance-redshift
relation to SN 1997ap at could be as much as 50% lower than its true
value.Comment: 39 pages including 8 figures and captions. To appear in ApJ 507 (Nov.
1998
The Rest-Frame Extreme Ultraviolet Spectral Properties of QSOs
We use a sample of 332 Hubble Space Telescope spectra of 184 QSOs with z >
0.33 to study the typical ultraviolet spectral properties of QSOs, with
emphasis on the ionizing continuum. Our sample is nearly twice as large as that
of Zheng et al. (1997) and provides much better spectral coverage in the
extreme ultraviolet (EUV). The overall composite continuum can be described by
a power law with index alpha_EUV = -1.76 +/- 0.12 (f_nu ~ nu^alpha) between 500
and 1200 Angstroms. The corresponding results for subsamples of radio-quiet and
radio-loud QSOs are alpha_EUV = -1.57 +/- 0.17 and alpha_EUV = -1.96 +/- 0.12,
respectively. We also derive alpha_EUV for as many individual objects in our
sample as possible, totaling 39 radio-quiet and 40 radio-loud QSOs. The typical
individually measured values of alpha_EUV are in good agreement with the
composites. We find no evidence for evolution of alpha_EUV with redshift for
either radio-loud or radio-quiet QSOs. However, we do find marginal evidence
for a trend towards harder EUV spectra with increasing luminosity for
radio-loud objects. An extrapolation of our radio-quiet QSO spectrum is
consistent with existing X-ray data, suggesting that the ionizing continuum may
be represented by a single power law. The resulting spectrum is roughly in
agreement with models of the intergalactic medium photoionized by the
integrated radiation from QSOs.Comment: 14 pages using emulateapj, 15 figures, accepted for publication in
Ap
Tracing cosmic evolution with clusters of galaxies
The most successful cosmological models to date envision structure formation
as a hierarchical process in which gravity is constantly drawing lumps of
matter together to form increasingly larger structures. Clusters of galaxies
currently sit atop this hierarchy as the largest objects that have had time to
collapse under the influence of their own gravity. Thus, their appearance on
the cosmic scene is also relatively recent. Two features of clusters make them
uniquely useful tracers of cosmic evolution. First, clusters are the biggest
things whose masses we can reliably measure because they are the largest
objects to have undergone gravitational relaxation and entered into virial
equilibrium. Mass measurements of nearby clusters can therefore be used to
determine the amount of structure in the universe on scales of 10^14 to 10^15
solar masses, and comparisons of the present-day cluster mass distribution with
the mass distribution at earlier times can be used to measure the rate of
structure formation, placing important constraints on cosmological models.
Second, clusters are essentially ``closed boxes'' that retain all their gaseous
matter, despite the enormous energy input associated with supernovae and active
galactic nuclei, because the gravitational potential wells of clusters are so
deep. The baryonic component of clusters therefore contains a wealth of
information about the processes associated with galaxy formation, including the
efficiency with which baryons are converted into stars and the effects of the
resulting feedback processes on galaxy formation. This article reviews our
theoretical understanding of both the dark-matter component and the baryonic
component of clusters. (Abridged)Comment: 54 pages, 15 figures, Rev. Mod. Phys. (in press
Measurements of Flavour Dependent Fragmentation Functions in Z^0 -> qq(bar) Events
Fragmentation functions for charged particles in Z -> qq(bar) events have
been measured for bottom (b), charm (c) and light (uds) quarks as well as for
all flavours together. The results are based on data recorded between 1990 and
1995 using the OPAL detector at LEP. Event samples with different flavour
compositions were formed using reconstructed D* mesons and secondary vertices.
The \xi_p = ln(1/x_E) distributions and the position of their maxima \xi_max
are also presented separately for uds, c and b quark events. The fragmentation
function for b quarks is significantly softer than for uds quarks.Comment: 29 pages, LaTeX, 5 eps figures (and colour figs) included, submitted
to Eur. Phys. J.
Bose-Einstein Correlations in e+e- to W+W- at 172 and 183 GeV
Bose-Einstein correlations between like-charge pions are studied in hadronic
final states produced by e+e- annihilations at center-of-mass energies of 172
and 183 GeV. Three event samples are studied, each dominated by one of the
processes W+W- to qqlnu, W+W- to qqqq, or (Z/g)* to qq. After demonstrating the
existence of Bose-Einstein correlations in W decays, an attempt is made to
determine Bose-Einstein correlations for pions originating from the same W
boson and from different W bosons, as well as for pions from (Z/g)* to qq
events. The following results are obtained for the individual chaoticity
parameters lambda assuming a common source radius R: lambda_same = 0.63 +- 0.19
+- 0.14, lambda_diff = 0.22 +- 0.53 +- 0.14, lambda_Z = 0.47 +- 0.11 +- 0.08, R
= 0.92 +- 0.09 +- 0.09. In each case, the first error is statistical and the
second is systematic. At the current level of statistical precision it is not
established whether Bose-Einstein correlations, between pions from different W
bosons exist or not.Comment: 24 pages, LaTeX, including 6 eps figures, submitted to European
Physical Journal
TESLA Technical Design Report Part III: Physics at an e+e- Linear Collider
The TESLA Technical Design Report Part III: Physics at an e+e- Linear
ColliderComment: 192 pages, 131 figures. Some figures have reduced quality. Full
quality figures can be obtained from http://tesla.desy.de/tdr. Editors -
R.-D. Heuer, D.J. Miller, F. Richard, P.M. Zerwa
- …