1,492 research outputs found
Multivariate Fitting and the Error Matrix in Global Analysis of Data
When a large body of data from diverse experiments is analyzed using a
theoretical model with many parameters, the standard error matrix method and
the general tools for evaluating errors may become inadequate. We present an
iterative method that significantly improves the reliability of the error
matrix calculation. To obtain even better estimates of the uncertainties on
predictions of physical observables, we also present a Lagrange multiplier
method that explores the entire parameter space and avoids the linear
approximations assumed in conventional error propagation calculations. These
methods are illustrated by an example from the global analysis of parton
distribution functions.Comment: 13 pages, 5 figures, Latex; minor clarifications, fortran program
made available; Normalization of Hessian matrix changed to HEP standar
Hard probes in heavy ion collisions at the LHC: PDFs, shadowing and collisions
This manuscript is the outcome of the subgroup ``PDFs, shadowing and
collisions'' from the CERN workshop ``Hard Probes in Heavy Ion Collisions at
the LHC''. In addition to the experimental parameters for collisions at
the LHC, the issues discussed are factorization in nuclear collisions, nuclear
parton distributions (nPDFs), hard probes as the benchmark tests of
factorization in collisions at the LHC, and semi-hard probes as
observables with potentially large nuclear effects. Also, novel QCD phenomena
in collisions at the LHC are considered. The importance of the
program at the LHC is emphasized.Comment: The writeup of the working group "PDFs, shadowing and
collisions" for the CERN Yellow Report on Hard Probes in Heavy Ion Collisions
at the LHC, 121 pages. Subgroup convenors: K.J. Eskola, J.w. Qiu (theory) and
W. Geist (experiment). Editor: K.J. Eskol
High Q^2 Deep Inelastic Scattering at HERA
High Q^2 NC and CC cross-sections as measured at HERA can give information on
two distinct areas of current interest. Firstly, supposing that all the
electroweak parameters are well known, these cross-sections may be used to give
information on parton distributions at high x and high Q^2. Secondly, supposing
that parton distributions are well known, after evolution in Q^2 from the
kinematic regime where they are already measured, these cross-sections can be
used to give information on electroweak parameters in a process where the
exchanged boson is `spacelike' rather than `timelike'. WG1 addressed itself to
clarifying the limits of our present and possible future knowledge on both
these areas.Comment: 26 pages, 12 figures. Uses iopart.cls, iopart12.clo, axodraw.sty.
Report of WG1 of the 3rd UK Phenomenology Workshop on HERA Physics, Durham
1998. To be published in Journal of Physics
Involvement of patients or their representatives in quality management functions in EU hospitals:implementation and impact on patient-centred care strategies
OBJECTIVE: The objective of this study was to describe the involvement of patients or their representatives in quality management (QM) functions and to assess associations between levels of involvement and the implementation of patient-centred care strategies. DESIGN: A cross-sectional, multilevel STUDY DESIGN: that surveyed quality managers and department heads and data from an organizational audit. SETTING: Randomly selected hospitals (n = 74) from seven European countries (The Czech Republic, France, Germany, Poland, Portugal, Spain and Turkey). PARTICIPANTS: Hospital quality managers (n = 74) and heads of clinical departments (n = 262) in charge of four patient pathways (acute myocardial infarction, stroke, hip fracture and deliveries) participated in the data collection between May 2011 and February 2012. MAIN OUTCOME MEASURES: Four items reflecting essential patient-centred care strategies based on an on-site hospital visit: (1) formal survey seeking views of patients and carers, (2) written policies on patients' rights, (3) patient information literature including guidelines and (4) fact sheets for post-discharge care. The main predictors were patient involvement in QM at the (i) hospital level and (ii) pathway level. RESULTS: Current levels of involving patients and their representatives in QM functions in European hospitals are low at hospital level (mean score 1.6 on a scale of 0 to 5, SD 0.7), but even lower at departmental level (mean 0.6, SD 0.7). We did not detect associations between levels of involving patients and their representatives in QM functions and the implementation of patient-centred care strategies; however, the smallest hospitals were more likely to have implemented patient-centred care strategies. CONCLUSIONS: There is insufficient evidence that involving patients and their representatives in QM leads to establishing or implementing strategies and procedures that facilitate patient-centred care; however, lack of evidence should not be interpreted as evidence of no effect
New parton distributions in fixed flavour factorization scheme from recent deep-inelastic-scattering data
We present our QCD analysis of the proton structure function
to determine the parton distributions at the next-to-leading order (NLO). The
heavy quark contributions to , with = , have been
included in the framework of the `fixed flavour number scheme' (FFNS). The
results obtained in the FFNS are compared with available results such as the
general-mass variable-flavour-number scheme (GM-VFNS) and other prescriptions
used in global fits of PDFs. In the present QCD analysis, we use a wide range
of the inclusive neutral-current deep-inelastic-scattering (NC DIS) data,
including the most recent data for charm , bottom , longitudinal
structure functions and also the reduced DIS cross sections
from HERA experiments. The most recent HERMES data for
proton and deuteron structure functions are also added. We take into account
ZEUS neutral current DIS inclusive jet cross section data from HERA
together with the recent Tevatron Run-II inclusive jet cross section data from
CDF and D{\O}. The impact of these recent DIS data on the PDFs extracted from
the global fits are studied. We present two families of PDFs, {\tt KKT12} and
{\tt KKT12C}, without and with HERA `combined' data sets on DIS. We
find these are in good agreement with the available theoretical models.Comment: 23 pages, 26 figures and 4 tables. V3: Only few comments and
references added in the replaced version, results unchanged. Code can be
found at http://particles.ipm.ir/links/QCD.ht
Phase-space dependence of particle-ratio fluctuations in Pb+Pb collisions from 20A to 158A GeV beam energy
A novel approach, the identity method, was used for particle identification
and the study of fluctuations of particle yield ratios in Pb+Pb collisions at
the CERN Super Proton Synchrotron (SPS). This procedure allows to unfold the
moments of the unknown multiplicity distributions of protons (p), kaons (K),
pions () and electrons (e). Using these moments the excitation function of
the fluctuation measure [A,B] was measured, with A and
B denoting different particle types. The obtained energy dependence of
agrees with previously published NA49 results on the related
measure . Moreover, was found to depend
on the phase space coverage for [K,p] and [K,] pairs. This feature most
likely explains the reported differences between measurements of NA49 and those
of STAR in central Au+Au collisions
Production of deuterium, tritium, and He in central Pb+Pb collisions at 20A, 30A, 40A, 80A, and 158A GeV at the CERN SPS
Production of , , and He nuclei in central Pb+Pb interactions was
studied at five collision energies ( 6.3, 7.6, 8.8, 12.3, and
17.3 GeV) with the NA49 detector at the CERN SPS. Transverse momentum spectra,
rapidity distributions, and particle ratios were measured. Yields are compared
to predictions of statistical models. Phase-space distributions of light nuclei
are discussed and compared to those of protons in the context of a coalescence
approach. The coalescence parameters and , as well as coalescence
radii for and He were determined as a function of transverse mass at
all energies.Comment: 22 pages, 29 figures, 8 tables, for submission to Phys. Rev.
Parton-Hadron Duality in Unpolarised and Polarised Structure Functions
We study the phenomenon of parton-hadron duality in both polarised and
unpolarised electron proton scattering using the HERMES and the Jefferson Lab
data, respectively. In both cases we extend a systematic perturbative QCD based
analysis to the integrals of the structure functions in the resonance region.
After subtracting target mass corrections and large x resummation effects, we
extract the remaining power corrections up to order 1/Q^2. We find a sizeable
suppression of these terms with respect to analyses using deep inelastic
scattering data. The suppression appears consistently in both polarised and
unpolarised data, except for the low Q^2 polarised data, where a large negative
higher twist contribution remains. Possible scenarios generating this behavior
are discussed.Comment: 17 pages, 9 figure
Models for the Polarized Parton Distributions of the Nucleon
Polarized deep inelastic scattering (DIS) data are analyzed in leading and
next-to-leading order of QCD within the common `standard' scenario of polarized
parton distributions with a flavor-symmetric light sea (antiquark) distribution
, and a completely SU(3) broken `valence' scenario with
totally flavor-asymmetric light sea densities
. The latter flavor-broken
light sea distributions are modelled with the help of a Pauli-blocking ansatz
at the low radiative/dynamical input scales of
(0.40) GeV which complies with predictions of the chiral quark-soliton
model and expectations based on the statistical parton model as well as with
the corresponding, well established, flavor-broken unpolarized sea
(). Present semi-inclusive DIS data cannot yet uniquely
discriminate between those two flavor-symmetric and flavor-broken polarized
light sea scenarios.Comment: 39 pages, LaTe
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