1,373 research outputs found
Fundamental Symmetries and Interactions - Some Aspects
In the framework of nuclear physics and at nuclear physics facilities a large
number of different experiments can be performed which render the possibility
to investigate fundamental symmetries and interactions in nature. In
particular, the precise measurements of properties of fundamental fermions,
searches for new interactions in -decays, and violations of discrete
symmetries have a robust discovery potential for physics beyond standard
theory. Precise measurements of fundamental constants can be carried out as
well. Low energy experiments allow probing of New Physics models at mass scales
far beyond the reach of present accelerators or such planned for the future in
the domain of high energy physics and at which predicted new particles could be
produced directly.Comment: Review Talk ENAM'0
On Observing Top Quark Production at the Tevatron
A technique for separating top quark production from Standard Model
background events is introduced. It is applicable to the channel in which one
top quark decays semi-leptonically and its anti-quark decays hadronically into
three jets, or vice versa. The method is shown to discriminate dramatically
between Monte Carlo generated events with and without simulated top quarks of
mass around 120 GeV and above. The simulations were performed with CDF detector
characteristics incorporated, showing that the method is applicable to existing
data.Comment: 8 pages, TUFTS-TH-92-G01 (Two minor TeX mistakes corrected
The Neutralino Relic Density in Minimal N=1 Supergravity
We compute the cosmic relic (dark matter) density of the lightest
supersymmetric particle (LSP) in the framework of minimal Supergravity
models with radiative breaking of the electroweak gauge symmetry. To this end,
we re--calculate the cross sections for all possible annihilation processes for
a general, mixed neutralino state with arbitrary mass. Our analysis includes
effects of all Yukawa couplings of third generation fermions, and allows for a
fairly general set of soft SUSY breaking parameters at the Planck scale. We
find that a cosmologically interesting relic density emerges naturally over
wide regions of parameter space. However, the requirement that relic
neutralinos do not overclose the universe does not lead to upper bounds on SUSY
breaking parameters that are strictly valid for all combinations of parameters
and of interest for existing or planned collider experiments; in particular,
gluino and squark masses in excess of 5 TeV cannot strictly be excluded. On the
other hand, in the ``generic'' case of a gaugino--like neutralino whose
annihilation cross sections are not ``accidentally'' enhanced by a nearby Higgs
or pole, all sparticles should lie within the reach of the proposed
and supercolliders. We also find that requiring the LSP to provide all
dark matter predicted by inflationary models imposes a strict lower bound of 40
GeV on the common scalar mass at the Planck scale, while the lightest
sleptons would have to be heavierComment: 53 pages(8figs are not included), Latex file; DESY 92-101,
SLAC-PUB-586
Azimuthal and Single Spin Asymmetries in Hard Scattering Processes
In this article we review the present understanding of azimuthal and single
spin asymmetries for inclusive and semi-inclusive particle production in
unpolarized and polarized hadronic collisions at high energy and moderately
large transverse momentum. After summarizing the experimental information
available, we discuss and compare the main theoretical approaches formulated in
the framework of perturbative QCD. We then present in some detail a
generalization of the parton model with inclusion of spin and intrinsic
transverse momentum effects. In this context, we extensively discuss the
phenomenology of azimuthal and single spin asymmetries for several processes in
different kinematical configurations. A comparison with the predictions of
other approaches, when available, is also given. We finally emphasize some
relevant open points and challenges for future theoretical and experimental
investigation.Comment: 70 pages, 34 ps figures. Invited review paper to be published in
Progress in Particle and Nuclear Physic
Observation of the Baryonic Flavor-Changing Neutral Current Decay Lambda_b -> Lambda mu+ mu-
We report the first observation of the baryonic flavor-changing neutral
current decay Lambda_b -> Lambda mu+ mu- with 24 signal events and a
statistical significance of 5.8 Gaussian standard deviations. This measurement
uses ppbar collisions data sample corresponding to 6.8fb-1 at sqrt{s}=1.96TeV
collected by the CDF II detector at the Tevatron collider. The total and
differential branching ratios for Lambda_b -> Lambda mu+ mu- are measured. We
find B(Lambda_b -> Lambda mu+ mu-) = [1.73+-0.42(stat)+-0.55(syst)] x 10^{-6}.
We also report the first measurement of the differential branching ratio of B_s
-> phi mu+ mu- using 49 signal events. In addition, we report branching ratios
for B+ -> K+ mu+ mu-, B0 -> K0 mu+ mu-, and B -> K*(892) mu+ mu- decays.Comment: 8 pages, 2 figures, 4 tables. Submitted to Phys. Rev. Let
Observation of Exclusive Gamma Gamma Production in p pbar Collisions at sqrt{s}=1.96 TeV
We have observed exclusive \gamma\gamma production in proton-antiproton
collisions at \sqrt{s}=1.96 TeV, using data from 1.11 \pm 0.07 fb^{-1}
integrated luminosity taken by the Run II Collider Detector at Fermilab. We
selected events with two electromagnetic showers, each with transverse energy
E_T > 2.5 GeV and pseudorapidity |\eta| < 1.0, with no other particles detected
in -7.4 < \eta < +7.4. The two showers have similar E_T and azimuthal angle
separation \Delta\phi \sim \pi; 34 events have two charged particle tracks,
consistent with the QED process p \bar{p} to p + e^+e^- + \bar{p} by two-photon
exchange, while 43 events have no charged tracks. The number of these events
that are exclusive \pi^0\pi^0 is consistent with zero and is < 15 at 95% C.L.
The cross section for p\bar{p} to p+\gamma\gamma+\bar{p} with |\eta(\gamma)| <
1.0 and E_T(\gamma) > 2.5$ GeV is
2.48^{+0.40}_{-0.35}(stat)^{+0.40}_{-0.51}(syst) pb.Comment: 7 pages, 4 figure
Measurement of the Bottom-Strange Meson Mixing Phase in the Full CDF Data Set
We report a measurement of the bottom-strange meson mixing phase \beta_s
using the time evolution of B0_s -> J/\psi (->\mu+\mu-) \phi (-> K+ K-) decays
in which the quark-flavor content of the bottom-strange meson is identified at
production. This measurement uses the full data set of proton-antiproton
collisions at sqrt(s)= 1.96 TeV collected by the Collider Detector experiment
at the Fermilab Tevatron, corresponding to 9.6 fb-1 of integrated luminosity.
We report confidence regions in the two-dimensional space of \beta_s and the
B0_s decay-width difference \Delta\Gamma_s, and measure \beta_s in [-\pi/2,
-1.51] U [-0.06, 0.30] U [1.26, \pi/2] at the 68% confidence level, in
agreement with the standard model expectation. Assuming the standard model
value of \beta_s, we also determine \Delta\Gamma_s = 0.068 +- 0.026 (stat) +-
0.009 (syst) ps-1 and the mean B0_s lifetime, \tau_s = 1.528 +- 0.019 (stat) +-
0.009 (syst) ps, which are consistent and competitive with determinations by
other experiments.Comment: 8 pages, 2 figures, Phys. Rev. Lett 109, 171802 (2012
Combined search for the standard model Higgs boson decaying to a bb pair using the full CDF data set
We combine the results of searches for the standard model Higgs boson based
on the full CDF Run II data set obtained from sqrt(s) = 1.96 TeV p-pbar
collisions at the Fermilab Tevatron corresponding to an integrated luminosity
of 9.45/fb. The searches are conducted for Higgs bosons that are produced in
association with a W or Z boson, have masses in the range 90-150 GeV/c^2, and
decay into bb pairs. An excess of data is present that is inconsistent with the
background prediction at the level of 2.5 standard deviations (the most
significant local excess is 2.7 standard deviations).Comment: To be published in Phys. Rev. Lett (v2 contains minor updates based
on comments from PRL
Shrinking a large dataset to identify variables associated with increased risk of Plasmodium falciparum infection in Western Kenya
Large datasets are often not amenable to analysis using traditional single-step approaches. Here, our general objective was to apply imputation techniques, principal component analysis (PCA), elastic net and generalized linear models to a large dataset in a systematic approach to extract the most meaningful predictors for a health outcome. We extracted predictors for Plasmodium falciparum infection, from a large covariate dataset while facing limited numbers of observations, using data from the People, Animals, and their Zoonoses (PAZ) project to demonstrate these techniques: data collected from 415 homesteads in western Kenya, contained over 1500 variables that describe the health, environment, and social factors of the humans, livestock, and the homesteads in which they reside. The wide, sparse dataset was simplified to 42 predictors of P. falciparum malaria infection and wealth rankings were produced for all homesteads. The 42 predictors make biological sense and are supported by previous studies. This systematic data-mining approach we used would make many large datasets more manageable and informative for decision-making processes and health policy prioritization
Search for Kaluza-Klein Graviton Emission in Collisions at TeV using the Missing Energy Signature
We report on a search for direct Kaluza-Klein graviton production in a data
sample of 84 of \ppb collisions at = 1.8 TeV, recorded
by the Collider Detector at Fermilab. We investigate the final state of large
missing transverse energy and one or two high energy jets. We compare the data
with the predictions from a -dimensional Kaluza-Klein scenario in which
gravity becomes strong at the TeV scale. At 95% confidence level (C.L.) for
=2, 4, and 6 we exclude an effective Planck scale below 1.0, 0.77, and 0.71
TeV, respectively.Comment: Submitted to PRL, 7 pages 4 figures/Revision includes 5 figure
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