6,984 research outputs found
Collider Inclusive Jet Data and the Gluon Distribution
Inclusive jet production data are important for constraining the gluon
distribution in the global QCD analysis of parton distribution functions. With
the addition of recent CDF and D0 Run II jet data, we study a number of issues
that play a role in determining the up-to-date gluon distribution and its
uncertainty, and produce a new set of parton distributions that make use of
that data. We present in detail the general procedures used to study the
compatibility between new data sets and the previous body of data used in a
global fit. We introduce a new method in which the Hessian matrix for
uncertainties is ``rediagonalized'' to obtain eigenvector sets that
conveniently characterize the uncertainty of a particular observable.Comment: Published versio
Implications of Hadron Collider Observables on Parton Distribution Function Uncertainties
Standard parton distribution function sets do not have rigorously quantified
uncertainties. In recent years it has become apparent that these uncertainties
play an important role in the interpretation of hadron collider data. In this
paper, using the framework of statistical inference, we illustrate a technique
that can be used to efficiently propagate the uncertainties to new observables,
assess the compatibility of new data with an initial fit, and, in case the
compatibility is good, include the new data in the fit.Comment: 22 pages, 5 figure
kt Effects in Direct-Photon Production
We discuss the phenomenology of initial-state parton-kt broadening in
direct-photon production and related processes in hadron collisions. After a
brief summary of the theoretical basis for a Gaussian-smearing approach, we
present a systematic study of recent results on fixed-target and collider
direct-photon production, using complementary data on diphoton and pion
production to provide empirical guidance on the required amount of kt
broadening. This approach provides a consistent description of the observed
pattern of deviation of next-to-leading order QCD calculations relative to the
direct-photon data, and accounts for the shape and normalization difference
between fixed-order perturbative calculations and the data. We also discuss the
uncertainties in this phenomenological approach, the implications of these
results on the extraction of the gluon distribution of the nucleon, and the
comparison of our findings to recent related work.Comment: LaTeX, uses revtex and epsf, 37 pages, 15 figure
Huddle test measurement of a near Johnson noise limited geophone
In this paper, the sensor noise of two geophone configurations (L-22D and L-4C geophones from Sercel with custom built amplifiers) was measured by performing two huddle tests. It is shown that the accuracy of the results can be significantly improved by performing the huddle test in a seismically quiet environment and by using a large number of reference sensors to remove the seismic foreground signal from the data. Using these two techniques, the measured sensor noise of the two geophone configurations matched the calculated predictions remarkably well in the bandwidth of interest (0.01 Hz–100 Hz). Low noise operational amplifiers OPA188 were utilized to amplify the L-4C geophone to give a sensor that was characterized to be near Johnson noise limited in the bandwidth of interest with a noise value of 10−11 m/Hz⎯⎯⎯⎯⎯√10−11 m/Hz at 1 Hz
Unique Residues Involved in Activation of the Multitasking Protease/Chaperone HtrA from Chlamydia trachomatis
DegP, a member of the HtrA family of proteins, conducts critical bacterial protein quality control by both chaperone and proteolysis activities. The regulatory mechanisms controlling these two distinct activities, however, are unknown. DegP activation is known to involve a unique mechanism of allosteric binding, conformational changes and oligomer formation. We have uncovered a novel role for the residues at the PDZ1:protease interface in oligomer formation specifically for chaperone substrates of Chlamydia trachomatis HtrA (DegP homolog). We have demonstrated that CtHtrA proteolysis could be activated by allosteric binding and oligomer formation. The PDZ1 activator cleft was required for the activation and oligomer formation. However, unique to CtHtrA was the critical role for residues at the PDZ1:protease interface in oligomer formation when the activator was an in vitro chaperone substrate. Furthermore, a potential in vivo chaperone substrate, the major outer membrane protein (MOMP) from Chlamydia, was able to activate CtHtrA and induce oligomer formation. Therefore, we have revealed novel residues involved in the activation of CtHtrA which are likely to have important in vivo implications for outer membrane protein assembly
Examination of direct-photon and pion production in proton-nucleon collisions
We present a study of inclusive direct-photon and pion production in hadronic
interactions, focusing on a comparison of the ratio of gamma/pi0 yields with
expectations from next-to-leading order perturbative QCD (NLO pQCD). We also
examine the impact of a phenomenological model involving k_T smearing (which
approximates effects of additional soft-gluon emission) on absolute predictions
for photon and pion production and their ratio.Comment: 20 pages, 12 figures. Minor changes in wording and in figure
A simplified structure for the second order cosmological perturbation equations
Increasingly accurate observations of the cosmic microwave background and the
large scale distribution of galaxies necessitate the study of nonlinear
perturbations of Friedmann-Lemaitre cosmologies, whose equations are
notoriously complicated. In this paper we present a new derivation of the
governing equations for second order perturbations within the framework of the
metric-based approach that is minimal, as regards amount of calculation and
length of expressions, and flexible, as regards choice of gauge and
stress-energy tensor. Because of their generality and the simplicity of their
structure our equations provide a convenient starting point for determining the
behaviour of nonlinear perturbations of FL cosmologies with any given
stress-energy content, using either the Poisson gauge or the uniform curvature
gauge.Comment: 30 pages, no figures. Changed title to the one in published version
and some minor changes and addition
A GLOBAL QCD STUDY OF DIRECT PHOTON PRODUCTION
A global QCD analysis of the direct photon production process from both fixed
target and collider experiments is presented. These data sets now completely
cover the parton range from 0.01 to 0.6, thereby providing a stringent test
of perturbative QCD and parton distributions. Previous detailed studies of
direct photons emphasized fixed target data. We find most data sets have a
steeper distribution than the QCD prediction. Neither global fits with
new parton distributions nor improved photon fragmentation functions can
resolve this problem since the deviation occurs at different values for
experiments at different energies. A more likely explanation is the need for
additional broadening of the of the initial state partons. The magnitude
and the possible physical origin of this effect are investigated and discussed.Comment: 8 page Latex file using epsf.sty for figures. 6 eps figures submitted
separately in uuencoded file
Leptoquark Contribution to the Higgs Boson Production at the LHC Collider
In this report we study how a light-scalar leptoquark could affect the Higgs
boson production cross-section at the LHC collider. We construct the most
general renormalizable and gauge invariant effective Lagrangian involving the
standard model particles and a scalar, isoscalar leptoquark, \eta.
The total cross-section for pp -> H+X is then calculated for different values
of the unknown parameters \lambda_eta, m_eta and m_H.(Here \lambda_eta is the
coupling associated with the Higgs-leptoquark interaction.)
We find that if \lambda_eta is moderately large and m_eta is around a few
hundred GeV, then the cross-section is significantly larger than the standard
model value.Comment: 9 pages, 4 postscript figure
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