2,916 research outputs found
Measurements of the top-antitop production cross section at the Tevatron Run II CDF experiment using b-tagging
We present measurements of the top-antitop production cross section in
b-tagged lepton + jets events from proton-antiproton collisions at 1.96 TeV
using the CDF detector at Fermilab. B-jets are tagged with either a secondary
vertex algorithm, or a soft lepton tagger that identifies muons from B hadron
semileptonic decays. With Tevatron Run II data, we estimate the top-antitop
signal fraction in two different ways: by estimating the various background
contributions, and by fitting directly the leading jet transverse energy
spectrum for the signal and background contributions. A subset of the sample
with two secondary vertex tagged jets yields a production cross section
consistent with the inclusive measurements. Results are consistent with a
Standard Model top-antitop signal and current measurements of the top quark
mass.Comment: 3 pages, 4 figures, DPF 2004 proceedin
Measurements of Masses in SUGRA Models at LHC
This paper presents new measurements in a case study of the minimal SUGRA
model with m_0=100 GeV, mhalf=300 GeV, A_0=0, tan(beta)=2.1, and mu=+1 based on
four-body distributions from three-step decays and on minimum masses in such
decays. These measurements allow masses of supersymmetric particles to be
determined without relying on a model. The feasibility of testing slepton
universality at the ~0.1% level at high luminosity is discussed. In addition,
the effect of enlarging the parameter space of the minimal SUGRA model is
discussed. The direct production of left handed sleptons and the
non-observation of additional structure in the dilepton invariant mass
distributions is shown to provide additional constraints.Comment: 30 pages, 22 figure
Constrained invariant mass distributions in cascade decays. The shape of the "-threshold" and similar distributions
Considering the cascade decay in which
are massive particles and are massless particles, we
determine for the first time the shape of the distribution of the invariant
mass of the three massless particles for the sub-set of decays in
which the invariant mass of the last two particles in the chain is
(optionally) constrained to lie inside an arbitrary interval, . An example of an experimentally
important distribution of this kind is the `` threshold'' -- which is
the distribution of the combined invariant mass of the visible standard model
particles radiated from the hypothesised decay of a squark to the lightest
neutralino via successive two body decay,: \squark \to q \ntlinoTwo \to q l
\slepton \to q l l \ntlinoOne , in which the experimenter requires
additionally that be greater than . The
location of the ``foot'' of this distribution is often used to constrain
sparticle mass scales. The new results presented here permit the location of
this foot to be better understood as the shape of the distribution is derived.
The effects of varying the position of the cut(s) may now be seen more
easily.Comment: 12 pages, 3 figure
Probing the SM with Dijets at the LHC
The LHC has started to explore the TeV energy regime, probing the SM beyond
LEP and Tevatron. We show how the dijet measurements at the LHC are able to
test certain sectors of the SM at an unprecedented level. We provide the best
bounds on all possible four-quark interactions and translate them into limits
on the compositeness scale of the quarks and gluons. We also provide
constraints on extra gauge bosons, Z', W' and G', and on new interactions
proposed to explain the present measurement of the forward-backward asymmetry
of the top.Comment: 22 pages, 6 figures. v2: New bounds derived from the 2011 CMS dijet
data se
Low mass neutralino dark matter in mSUGRA and more general models in the light of LHC data
The b\tau j \etslash signal at the ongoing LHC experiments is simulated
with Pythia in the mSUGRA and other models of SUSY breaking. Special attention
is given on the compatibility of this signature with the low mass neutralino
dark matter (LMNDM) scenario consistent with WMAP data. In the mSUGRA model the
above signal as well as the LMNDM scenario are strongly disfavoured due to the
constraints from the on going SUSY searches at the LHC. This tension, however,
originates from the model dependent correlations among the parameters in the
strong and electroweak sectors of mSUGRA. That there is no serious conflict
between the LMNDM scenario and the LHC data is demonstrated by constructing
generic phenomenological models such that the strong sector is unconstrained or
mildly constrained by the existing LHC data and parameters in the electroweak
sector, unrelated to the strong sector,yield DM relic density consistent with
the WMAP data. The proposed models, fairly insensitive to the conventional SUSY
searches in the jets + \etslash and other channels, yield observable signal
in the suggested channel for \lum \gsim 1 \ifb of data. They are also
consistent with the LMNDM scenario and can be tested by the direct dark matter
search experiments in the near future. Some of these models can be realized by
non-universal scalar and gaugino masses at the GUT scale.Comment: 33 pages, 2 figures, analyses updated for 1 fb^{-1} of LHC data and
presented in a new section, some new references have been added, published in
Phys. Rev.
Measurement of the Superparticle Mass Spectrum in the Long-Lived Stau Scenario at the LHC
In supersymmetric scenarios with a long-lived stau, the LHC experiments
provide us with a great environment for precise mass measurements of
superparticles. We study a case in which the mass differences between the
lightest stau and other sleptons are about 10 GeV or larger, so that the decay
products of heavier sleptons are hard enough to be detected. We demonstrate
that the masses of neutralinos, sleptons, and squarks can be measured with a
good accuracy.Comment: 20 pages, 6 figure
SUSY Parameter Analysis at TeV and Planck Scales
Coherent analyses at future LHC and LC experiments can be used to explore the
breaking mechanism of supersymmetry and to reconstruct the fundamental theory
at high energies, in particular at the grand unification scale. This will be
exemplified for minimal supergravity.Comment: 7 pages, 3 figures, uses espcrc2.sty (included), Proceedings, Loops
and Legs 2004, Zinnowitz on Usedo
Searches for phenomena beyond the Standard Model at the LHC with the ATLAS and CMS detectors
The LHC has delivered several fb-1 of data in spring and summer 2011, opening
new windows of opportunity for discovering phenomena beyond the Standard Model.
A summary of the searches conducted by the ATLAS and CMS experiments based on
about 1 fb-1 of data is presented.Comment: Presented at Lepton-Photon 2011, Mumbai, India; 10 pages, 11 figure
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