986 research outputs found
The Sources of b-Quarks at the Tevatron and their Correlations
The leading-log order QCD hard scattering Monte-Carlo models of HERWIG,
ISAJET, and PYTHIA are used to study the sources of b-quarks at the Tevatron.
The reactions responsible for producing b and bbar quarks are separated into
three categories; flavor creation, flavor excitation, and
parton-shower/fragmentation. Flavor creation corresponds to the production of a
b-bbar pair by gluon fusion or by annihilation of light quarks, while flavor
excitation corresponds to a b or bbar quark being knocked out of the
initial-state by a gluon or a light quark or antiquark. The third source occurs
when a b-bbar pair is produced within a parton shower or during the
fragmentation process of a gluon or a light quark or antiquark (includes gluon
splitting). The QCD Monte-Carlo models indicate that all three sources of
b-quarks are important at the Tevatron and when combined they qualitatively
describe the inclusive cross-section data. Correlations between the b and bbar
quark are very different for the three sources and can be used to isolate the
individual contributions.Comment: RevTex4, 14 pages, 20 figures, submitted to Phys. Rev.
Event Reconstruction with MarlinReco at the ILC
After an overview of the modular analysis and reconstruction framework Marlin
an introduction on the functionality of the Marlin-based reconstruction package
MarlinReco is given. This package includes a full set of modules for event
reconstruction based on the Particle Flow approach. The status of the software
is reviewed and recent results using this software package for event
reconstruction are presented.Comment: 6 pages, 2 .eps figures, to appear in Proc. LCWS06, Bangalore, March
200
Anomalous behavior of pion production in high energy particle collisions
A shape of invariant differential cross section for charged hadron production
as function of transverse momentum measured in various collider experiments is
analyzed. Contrary to the behavior of produced charged kaons, protons and
antiprotons, the pion spectra require an anomalously high contribution of an
exponential term to describe the shape.Comment: 4 pages, 6 figure
Measuring the Charged Particle Multiplicity with ALICE
The charged particle multiplicity distribution is one of the first
measurements that ALICE will be able to perform. The knowledge of this basic
property at a new energy is needed to configure Monte Carlo generators
correctly with the aim of understanding the background of other, especially
rare, processes including new physics. It allows to study the scaling behaviour
and to verify model predictions. The unfolding of the measurement is a
non-trivial task due to the finite precision and acceptance of the detector.
Solutions are based on chi2 minimization or iteratively using Bayes' theorem.
Both approaches to unfold the spectrum are presented. Furthermore, the
capabilities of the SPD fast OR trigger are shown that enable physics at very
high multiplicities.Comment: Proceedings of poster presentation at Quark Matter 2008, 20th
International Conference on Ultra-Relativistic Nucleus-Nucleus Collisions in
Jaipur, India; to be published in Indian Journal of Physics; 4 pages, 4
figure
Proposal for Higgs and Superpartner Searches at the LHCb Experiment
The spectrum of supersymmetric theories with R-parity violation are much more
weakly constrained than that of supersymmetric theories with a stable
neutralino. We investigate the signatures of supersymmetry at the LHCb
experiment in the region of parameter space where the neutralino decay leaves a
displaced vertex. We find sensitivity to squark production up to squark masses
of order 1 TeV. We note that if the Higgs decays to neutralinos in this
scenario, LHCb should see the lightest Higgs boson before ATLAS and CMS.Comment: 7 pages, 5 figure
Langevin dynamics of heavy flavors in relativistic heavy-ion collisions
We study the stochastic dynamics of c and b quarks, produced in hard initial
processes, in the hot medium created after the collision of two relativistic
heavy ions. This is done through the numerical solution of the relativistic
Langevin equation. The latter requires the knowledge of the friction and
diffusion coefficients, whose microscopic evaluation is performed treating
separately the contribution of soft and hard collisions. The evolution of the
background medium is described by ideal/viscous hydrodynamics. Below the
critical temperature the heavy quarks are converted into hadrons, whose
semileptonic decays provide single-electron spectra to be compared with the
current experimental data measured at RHIC. We focus on the nuclear
modification factor R_AA and on the elliptic-flow coefficient v_2, getting, for
sufficiently large p_T, a reasonable agreement.Comment: Talk given at the workshop "Jets in Proton-Proton and Heavy-Ion
Collisions", Prague, 12th-14th August 201
Strangeness production in jets from p+p \sqrt{s} = 200 GeV collisions
Measurements of strangeness production in jets help illuminate the QCD
mechanisms in fragmentation. Furthermore, they provide a crucial baseline for
heavy-ion studies where modifications in jet chemistry have recently been
predicted. We present new results on strange particle production in jets from
p+p \sqrt{s} = 200 GeV collisions measured by the STAR experiment. The momentum
distributions of the \Lambda, \bar{\Lambda} and K0Short particles are obtained
using various jet finding algorithms, and then compared to various models.
Strange particle ratios in jets are obtained and compared to values obtained
from the inclusive spectra. Finally, we show jets tagged with leading strange
baryons and mesons, in order to investigate whether gluon or quark jets can be
isolated in this way.Comment: 5 pages, 4 figures, Winter Workshop on Nuclear Dynamics 2010, Jamaic
t' at the LHC: the physics of discovery
A search for a fourth family at the LHC is presently a low priority, but we
argue that an effective search can be conducted early with only a few inverse
femtobarns of data. We discuss a method based on invariant masses of single
jets for identifying the 's originating from heavy quark decays. This can
significantly increase signal to background in the reconstruction of the
mass. We also study the various types of physics that can impact the background
estimate, most notably higher order effects, initial state radiation, and
models of the underlying event.Comment: 16 pages, 12 figures, small improvements, version to appear in JHE
Heavy-quark Langevin dynamics and single-electron spectra in nucleus-nucleus collision
The stochastic dynamics of heavy quarks in the fireball produced in heavy-ion
collisions is followed through numerical simulations based on the Langevin
equation. The modification of the final p_T spectra (R_AA) of c and b quarks,
hadrons and single-electrons with respect to pp collisions is studied. The
transport coefficients are evaluated treating separately the contribution of
soft and hard collisions. The initial heavy-quark spectra are generated
according to NLO-pQCD, accounting for nuclear effects through recent nPDFs. The
evolution of the medium is obtained from the output of two hydro-codes (ideal
and viscous). The heavy-quark fragmentation into hadrons and their final
semileptonic decays are implemented according to up to date experimental data.
A comparison with RHIC data for non-photonic electron spectra is given.Comment: 4 pages, 3 figures, Talk given at "Hot Quarks 2010", 21th-26th June
201
Higgs mediated Double Flavor Violating top decays in Effective Theories
The possibility of detecting double flavor violating top quark transitions at
future colliders is explored in a model-independent manner using the effective
Lagrangian approach through the () decays. A
Yukawa sector that contemplates invariants of up to
dimension six is proposed and used to derive the most general flavor violating
and CP violating and vertices of renormalizable type.
Low-energy data, on high precision measurements, and experimental limits are
used to constraint the and vertices and then used to
predict the branching ratios for the decays. It is found
that this branching ratios may be of the order of , for a
relative light Higgs boson with mass lower than , which could be more
important than those typical values found in theories beyond the standard model
for the rare top quark decays () or . %% LHC experiments, by using a total integrated luminosity of of data, will be able to rule out, at 95% C.L., DFV top quark
decays up to a Higgs mass of 155 GeV/ or discover such a process up to a
Higgs mass of 147 GeV/.Comment: 24 pages, 11 figure
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