46,994 research outputs found
Recent Tests of QCD at SLD
We present selected results on strong interaction physics from the SLD
experiment at the SLAC Linear Collider. We report on several new studies of 3-
and 4-jet hadronic Z decays, in which jets are identified as quark, antiquark
or gluon. The 3-jet Z^0->b\bar{b}g rate is sensitive to the b-quark mass;
prospects for measuring m_b are discussed. The gluon energy spectrum is
measured over the full kinematic range, providing an improved test of QCD and
limits on anomalous bbg couplings. The parity violation in Z^0->b\bar{b}g
decays is consistent with electroweak theory plus QCD. New tests of T- and
CP-conservation at the bbg vertex are performed. A new measurement of the rate
of gluon splitting into b\bar{b} pairs yields
g_{b\bar{b}}=0.0031+-0.0007(stat.)+-0.0006(syst.) (Preliminary). We also
present a number of new results on jet fragmentation into identified hadrons.
The B hadron energy spectrum is measured over the full kinematic range using a
new, inclusive technique, allowing stringent tests of predictions for its shape
and a precise measurement of =0.714+-0.005(stat.)+-0.007(syst.)
(Preliminary). A detailed study of correlations in rapidity y between pairs of
identified pions, kaons and protons confirms that strangeness and baryon number
are conserved locally, and shows local charge conservation between meson-baryon
and strange-nonstrange pairs. Flavor-dependent long-range correlations are
observed for all combinations of these hadron species, yielding new information
on leading particle production. The first study of correlations using
rapidities signed such that y>0 corresponds to the quark direction provides
additional new insights into fragmentation, including the first direct
observation of baryon number ordering along the q\bar{q} axis.Comment: 20 pages, 12 figs.; talk given at the QCD99 meeting, Montpellier,
France, 7-13 July, 1999; a smaller-print version will appear in the
proceeding
A Multifunctional Processing Board for the Fast Track Trigger of the H1 Experiment
The electron-proton collider HERA is being upgraded to provide higher
luminosity from the end of the year 2001. In order to enhance the selectivity
on exclusive processes a Fast Track Trigger (FTT) with high momentum resolution
is being built for the H1 Collaboration. The FTT will perform a 3-dimensional
reconstruction of curved tracks in a magnetic field of 1.1 Tesla down to 100
MeV in transverse momentum. It is able to reconstruct up to 48 tracks within 23
mus in a high track multiplicity environment. The FTT consists of two hardware
levels L1, L2 and a third software level. Analog signals of 450 wires are
digitized at the first level stage followed by a quick lookup of valid track
segment patterns.
For the main processing tasks at the second level such as linking, fitting
and deciding, a multifunctional processing board has been developed by the ETH
Zurich in collaboration with Supercomputing Systems (Zurich). It integrates a
high-density FPGA (Altera APEX 20K600E) and four floating point DSPs (Texas
Instruments TMS320C6701). This presentation will mainly concentrate on second
trigger level hardware aspects and on the implementation of the algorithms used
for linking and fitting. Emphasis is especially put on the integrated CAM
(content addressable memory) functionality of the FPGA, which is ideally suited
for implementing fast search tasks like track segment linking.Comment: 6 pages, 4 figures, submitted to TN
Prospects for Higgs Boson Searches in the Channel WH -> lnbb
We present a method how to detect the WH -> lnbb in the high luminosity LHC
environment with the CMS detector. This study is performed with fast detector
response simulation including high luminosity event pile up. The main aspects
of reconstruction are pile up jet rejection, identification of b-jets and
improvement of Higgs mass resolution.
The detection potential in the SM for m(H) < 130 GeV and in the MSSM is only
encouraging for high integrated luminosity. Nevertheless it is possible to
extract important Higgs parameters which are useful to elucidate the nature of
the Higgs sector. In combination with other channels, this channel provides
valuable information on Higgs boson couplings.Comment: 8 pages, 8 figure
Searching for Higgs Bosons in Association with Top Quark Pairs in the H -> bb Decay Mode
Search for the Higgs Boson is one of the prime goals of the LHC. Higgs bosons
lighter than 130 GeV decay mainly to a b-quark pair. While the detection of a
directly produced Higgs boson in the bb channel is impossible because of the
huge QCD background, the channel ttH -> lnqqbbbb is very promising in the
Standard Model and the MSSM.
We discuss an event reconstruction and selection method based on likelihood
functions. The CMS detector response is performed with parametrisations
obtained from detailed simulations. Various physics and detector performance
scenarios are investigated and the results are presented. It turns out that
excellent b-tagging performance and good mass resolution are essential for this
channel.Comment: 10 pages, 6 figure
Microscopic Description of Deeply Virtual Compton Scattering off Spin-0 Nuclei
We evaluate within a microscopic calculation the contributions of both
coherent and incoherent deeply virtual Compton scattering from a spin-0
nucleus. The coherent contribution is obtained when the target nucleus recoils
as a whole, whereas for incoherent scattering break-up configurations for the
final nucleus into a an outgoing nucleon and an system are considered.
The two processes encode different characteristics of generalized parton
distributions.Comment: 7 pages, 3 figure
Cerenkov counters for high energy nuclei: Some new developments
A method to determine with gas Cerenkov counters the Lorentz factor, gamma = E/mc, of cosmic ray nuclei with high accuracy over the range gamma approx. 20 to 100 is discussed. The measurement of the Cerenkov emission angle theta, by use of a suitable imaging system is considered. Imaging counters, the ring imaging Cerenkov counters (RICH), were developed for use on accelerators. The image of off-axis particles to determine the amount of image distortion as a function of the direction of the incoming nucleus is examined and an acceptance solid angle, relative to the optical axis, within which the nucleus produces an image with an acceptable level of distortion is defined. The properties of the image, which becomes elliptical, for off-axis particles are analyzed
The attainable superconducting Tc in a model of phase coherence by percolation
The onset of macroscopic phase coherence in superconducting cuprates is
considered to be determined by random percolation between mesoscopic
Jahn-Teller pairs, stripes or clusters. The model is found to predict the onset
of superconductivity near 6% doping, maximum Tc near 15% doping and Tc= T* at
optimum doping, and accounts for the destruction of superconductivity by Zn
doping near 7%. The model also predicts a relation between the pairing
(pseudogap) energy and Tc in terms of experimentally measurable quantities.Comment: 3 pages + 3 postscript figure
Neutron Star Kicks from Asymmetric Collapse
Many neutron stars are observed to be moving with spatial velocities, in
excess of 500km/s. A number of mechanisms have been proposed to give neutron
stars these high velocities. One of the leading classes of models proposed
invokes asymmetries in the core of a massive star just prior to collapse. These
asymmetries grow during the collapse, causing the resultant supernova to also
be asymmetric. As the ejecta is launched, it pushes off (or ``kicks'') the
newly formed neutron star. This paper presents the first 3-dimensional
supernova simulations of this process. The ejecta is not the only matter that
kicks the newly-formed neutron star. Neutrinos also carry away momentum and the
asymmetric collapse leads also to asymmetries in the neutrinos. However, the
neutrino asymmetries tend to damp out the neutron star motions and even the
most extreme asymmetric collapses presented here do not produce final neutron
star velocities above 200km/s.Comment: 7 pages, 4 figures, see http://qso.lanl.gov/~clf/papers/kick.ps.gz
for full figure
Regularized adaptive long autoregressive spectral analysis
This paper is devoted to adaptive long autoregressive spectral analysis when
(i) very few data are available, (ii) information does exist beforehand
concerning the spectral smoothness and time continuity of the analyzed signals.
The contribution is founded on two papers by Kitagawa and Gersch. The first one
deals with spectral smoothness, in the regularization framework, while the
second one is devoted to time continuity, in the Kalman formalism. The present
paper proposes an original synthesis of the two contributions: a new
regularized criterion is introduced that takes both information into account.
The criterion is efficiently optimized by a Kalman smoother. One of the major
features of the method is that it is entirely unsupervised: the problem of
automatically adjusting the hyperparameters that balance data-based versus
prior-based information is solved by maximum likelihood. The improvement is
quantified in the field of meteorological radar
Comment on ``Intensity correlations and mesoscopic fluctuations of diffusing photons in cold atoms''
In a recent Letter (Phys. Rev. Lett. \textbf{98}, 083601 (2007),
arXiv:cond-mat/0610804), O. Assaf and E. Akkermans claim that the angular
correlations of the light intensity scattered by a cloud of cold atoms with
internal degeneracy (Zeeman sublevels) of the ground state overcome the usual
Rayleigh law. More precisely, they found that they become exponentially large
with the size of the sample. In what follows, we will explain why their results
are wrong and, in contrary, why the internal degeneracy leads to lower
intensity correlations.Comment: 1 page. Comment submitted to PR
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