3,150 research outputs found
Searches for Physics Beyond the Standard Model at Colliders
All experimental measurements of particle physics today are beautifully
described by the Standard Model. However, there are good reasons to believe
that new physics may be just around the corner at the TeV energy scale. This
energy range is currently probed by the Tevatron and HERA accelerators and
selected results of searches for physics beyond the Standard Model are
presented here. No signals for new physics have been found and limits are
placed on the allowed parameter space for a variety of different particles.Comment: Proceedings for 2007 Europhysics Conference on High Energy Physics,
Manchester, July 200
Phenomenology of the Heavy Flavored spin 3/2 Baryons in Light Cone QCD
Motivated by the results of the recent experimental discoveries for charm and
bottom baryons, the masses and magnetic moments of the heavy baryons with
containing a single heavy quark are studied within light cone QCD
sum rules method. Our results on the masses of heavy baryons are in good
agreement with predictions of other approaches, as well as with the existing
experimental data.Comment: 12 Pages, 18 Figures and 3 Tables. Based on: arXiv:0807.3481v2
[hep-ph](Nucl.Phys.B808:137-154,2009). To be Published in the Proceeding of
the International Conference on New Trends in High Energy Physics, 27 Sept.-4
Oct. 2008, Yalta, Crimea, Ukrain
Measurements of the Production, Decay and Properties of the Top Quark: A Review
With the full Tevatron Run II and early LHC data samples, the opportunity for
furthering our understanding of the properties of the top quark has never been
more promising. Although the current knowledge of the top quark comes largely
from Tevatron measurements, the experiments at the LHC are poised to probe
top-quark production and decay in unprecedented regimes. Although no current
top quark measurements conclusively contradict predictions from the standard
model, the precision of most measurements remains statistically limited.
Additionally, some measurements, most notably the forward-backward asymmetry in
top quark pair production, show tantalizing hints of beyond-the-Standard-Model
dynamics. The top quark sample is growing rapidly at the LHC, with initial
results now public. This review examines the current status of top quark
measurements in the particular light of searching for evidence of new physics,
either through direct searches for beyond the standard model phenomena or
indirectly via precise measurements of standard model top quark properties
Prompt Decays of General Neutralino NLSPs at the Tevatron
Recent theoretical developments have shown that gauge mediation has a much
larger parameter space of possible spectra and mixings than previously
considered. Motivated by this, we explore the collider phenomenology of gauge
mediation models where a general neutralino is the lightest MSSM superpartner
(the NLSP), focusing on the potential reach from existing and future Tevatron
searches. Promptly decaying general neutralino NLSPs can give rise to final
states involving missing energy plus photons, Zs, Ws and/or Higgses. We survey
the final states and determine those where the Tevatron should have the most
sensitivity. We then estimate the reach of existing Tevatron searches in these
final states and discuss new searches (or optimizations of existing ones) that
should improve the reach. Finally we comment on the potential for discovery at
the LHC.Comment: 41 pages, minor changes, added refs and discussion of previous
literatur
Precision measurements of the top quark mass from the Tevatron in the pre-LHC era
The top quark is the heaviest of the six quarks of the Standard Model.
Precise knowledge of its mass is important for imposing constraints on a number
of physics processes, including interactions of the as yet unobserved Higgs
boson. The Higgs boson is the only missing particle of the Standard Model,
central to the electroweak symmetry breaking mechanism and generation of
particle masses. In this Review, experimental measurements of the top quark
mass accomplished at the Tevatron, a proton-antiproton collider located at the
Fermi National Accelerator Laboratory, are described. Topologies of top quark
events and methods used to separate signal events from background sources are
discussed. Data analysis techniques used to extract information about the top
mass value are reviewed. The combination of several most precise measurements
performed with the two Tevatron particle detectors, CDF and \D0, yields a value
of \Mt = 173.2 \pm 0.9 GeV/.Comment: This version contains the most up-to-date top quark mass averag
Diagnostiset virheet
Diagnostiset virheet ovat varsin tavallisia, vaikka eivät usein paljastukaan potilaan elinaikana, vaan vasta ruumiinavauksen yhteydessä. Lääkäri voi harhautua seuraamaan liikaa jonkin aikaisemman potilastapauksensa antamaa diagnostista esimerkkiä tai ei osaa luopua diagnoosia koskevasta ensiarviostaan, vaikka tosiseikat viittaisivatkin johonkin muuhun. Yhteen oireeseen tai löydökseen takertuminen tai sokea luotto laboratoriotuloksiin voi helposti johtaa virhediagnoosiin
Probabilistic Particle Flow Algorithm for High Occupancy Environment
Algorithms based on the particle flow approach are becoming increasingly
utilized in collider experiments due to their superior jet energy and missing
energy resolution compared to the traditional calorimeter-based measurements.
Such methods have been shown to work well in environments with low occupancy of
particles per unit of calorimeter granularity. However, at higher instantaneous
luminosity or in detectors with coarse calorimeter segmentation, the overlaps
of calorimeter energy deposits from charged and neutral particles significantly
complicate particle energy reconstruction, reducing the overall energy
resolution of the method. We present a technique designed to resolve
overlapping energy depositions of spatially close particles using a
statistically consistent probabilistic procedure. The technique is nearly free
of ad-hoc corrections, improves energy resolution, and provides new important
handles that can improve the sensitivity of physics analyses: the uncertainty
of the jet energy on an event-by-event basis and the estimate of the
probability of a given particle hypothesis for a given detector response. When
applied to the reconstruction of hadronic jets produced in the decays of tau
leptons using the CDF-II detector at Fermilab, the method has demonstrated
reliable and robust performance.Comment: Accepted by Nuclear Instruments and Methods
Diagnostiset virheet
Diagnostiset virheet ovat varsin tavallisia, vaikka eivät usein paljastukaan potilaan elinaikana, vaan vasta ruumiinavauksen yhteydessä. Lääkäri voi harhautua seuraamaan liikaa jonkin aikaisemman potilastapauksensa antamaa diagnostista esimerkkiä tai ei osaa luopua diagnoosia koskevasta ensiarviostaan, vaikka tosiseikat viittaisivatkin johonkin muuhun. Yhteen oireeseen tai löydökseen takertuminen tai sokea luotto laboratoriotuloksiin voi helposti johtaa virhediagnoosiin
A Fast Track towards the `Higgs' Spin and Parity
The LHC experiments ATLAS and CMS have discovered a new boson that resembles
the long-sought Higgs boson: it cannot have spin one, and has couplings to
other particles that increase with their masses, but the spin and parity remain
to be determined. We show here that the `Higgs' + gauge boson invariant-mass
distribution in `Higgs'-strahlung events at the Tevatron or the LHC would be
very different under the J^P = 0+, 0- and 2+ hypotheses, and could provide a
fast-track indicator of the `Higgs' spin and parity. Our analysis is based on
simulations of the experimental event selections and cuts using PYTHIA and
Delphes, and incorporates statistical samples of `toy' experiments.Comment: 18 pages, 9 pdf figure
Supersymmetric Decays of the Z' Boson
The decay of the Z' boson into supersymmetric particles is studied. We
investigate how these supersymmetric modes affect the current limits from the
Tevatron and project the expected sensitivities at the LHC. Employing three
representative supersymmetric Z' models, namely, E_6, U(1)_{B-L}, and the
sequential model, we show that the current limits of the Z' mass from the
Tevatron could be reduced substantially due to the weakening of the branching
ratio into leptonic pairs. The mass reach for the E_6 Z' bosons is about
1.3-1.5 TeV at the LHC-7 (1 fb^{-1}), about 2.5 - 2.6 TeV at the LHC-10 (10
fb^{-1}), and about 4.2 - 4.3 TeV at the LHC-14 (100 fb^{-1}). A similar mass
reach for the U(1)_{B-L} Z' is also obtained. We also examine the potential of
identifying various supersymmetric decay modes of the Z' boson because it may
play a crucial role in the detailed dynamics of supersymmetry breaking.Comment: 30 pages, including 13 figures. improvements to the presentation and
references adde
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