68 research outputs found
Matrix elements and Parton Shower in the event generator BABAYAGA
A new version of the event generator BABAYAGA is presented, which is based on
an original matching of the Parton Shower approach with the complete exact
O(alpha) matrix element for the inclusion of the QED radiative corrections to
the Bhabha process at flavour factories. The theoretical accuracy of the
improved generator is conservatively estimated to be 0.2%, by comparison with
independent calculations. The generator is a useful tool for precise luminosity
determination at flavour factories, for center of mass energies below 10 GeV.Comment: 4 pages, 2 figures. To appear in the proceedings of the International
Workshop e+ e- Collisions from phi to psi, Novosibirsk (Russia), 27 Feb - 2
Mar 200
Status and accuracy of the Monte Carlo generators for luminosity measurements
The status and accuracy of the precision Monte Carlo generators used for
luminosity measurements at flavour factories is reviewed. It is shown that,
thanks to a considerable, long-term effort in tuned comparisons between the
predictions of independent programs, as well as in the validation of the
generators against the presently available calculations of the
next-to-next-to-leading order QED corrections to Bhabha scattering, the
theoretical accuracy reached by the most precise tools is of about one per
mille. This error estimate is valid for realistic experimental cuts, appears to
be quite robust and is already sufficient for very accurate luminosity
measurements. However, recent progress and possible advances to further improve
it are also discussed.Comment: 6 pages, 1 table. Proceedings of the PhiPsi09 workshop, Oct. 13-16,
2009, Beijing, Chin
NNLO massive corrections to Bhabha scattering and theoretical precision of BabaYaga@NLO
We provide an exact calculation of next-to-next-to-leading order (NNLO)
massive corrections to Bhabha scattering in QED, relevant for precision
luminosity monitoring at meson factories. Using realistic reference event
selections, exact numerical results for leptonic and hadronic corrections are
given and compared with the corresponding approximate predictions of the event
generator BabaYaga@NLO. It is shown that the NNLO massive corrections are
necessary for luminosity measurements with per mille precision. At the same
time they are found to be well accounted for in the generator at an accuracy
level below the one per mille. An update of the total theoretical precision of
BabaYaga@NLO is presented and possible directions for a further error reduction
are sketched.Comment: 5 pages, 3 tables, contrib. to proceedings of International Workshop
on e+e- collisions: from Phi to Psi, PHIPSI11, BINP, Novosibirsk, Russia,
September 19-22, 201
Photon pair production at flavour factories with per mille accuracy
We present a high-precision QED calculation, with 0.1% theoretical accuracy,
of two photon production in annihilation, as required by more and
more accurate luminosity monitoring at flavour factories. The accuracy of the
approach, which is based on the matching of exact next-to-leading order
corrections with a QED Parton Shower algorithm, is demonstrated through a
detailed analysis of the impact of the various sources of radiative corrections
to the experimentally relevant observables. The calculation is implemented in
the latest version of the event generator BabaYaga, available for precision
simulations of photon pair production at colliders of moderately high
energies.Comment: 11 pages, 5 figures, 1 tabl
High-end normal adrenocorticotropic hormone and cortisol levels are associated with specific cardiovascular risk factors in pediatric obesity: a cross-sectional study.
BACKGROUND: The hypothalamic-pituitary-adrenal (HPA) axis, and in particular cortisol, has been reported to be involved in obesity-associated metabolic disturbances in adults and in selected populations of adolescents. The aim of this study was to investigate the association between morning adrenocorticotropic hormone (ACTH) and cortisol levels and cardiovascular risk factors in overweight or obese Caucasian children and adolescents.
METHODS:
This cross-sectional study of 450 obese children and adolescents (aged 4 to 18 years) was performed in a tertiary referral center. ACTH, cortisol, cardiovascular risk factors (fasting and post-challenge glucose, high-density lipoprotein (HDL)-cholesterol, low-density lipoprotein (LDL)-cholesterol, triglycerides, and hypertension) and insulin resistance were evaluated. All analyses were corrected for confounding factors (sex, age, puberty, body mass index), and odds ratios were determined.
RESULTS:
ACTH and cortisol levels were positively associated with systolic and diastolic blood pressure, triglycerides, fasting glucose and insulin resistance. Cortisol, but not ACTH, was also positively associated with LDL-cholesterol. When adjusted for confounding factors, an association between ACTH and 2 h post-oral glucose tolerance test glucose was revealed. After stratification according to cardiovascular risk factors and adjustment for possible confounding factors, ACTH levels were significantly higher in subjects with triglycerides 6590th percentile (P 5.92 pmol/l) and cortisol (>383.5 nmol/l) although within the normal range were associated with increases in cardiovascular risk factors in this population.
CONCLUSIONS:
In obese children and adolescents, high morning ACTH and cortisol levels are associated with cardiovascular risk factors. High ACTH levels are associated with high triglyceride levels and hyperglycemia, while high cortisol is associated with hypertension and high LDL-cholesterol. These specific relationships suggest complex mechanisms through which the HPA axis may contribute to metabolic impairments in obesity, and merit further investigations
The relevance of polarized bZ production at LHC
We consider the Z polarization asymmetry
A_Z=(sigma(Z_R)-sigma(Z_L))/(sigma(Z_R)+sigma(Z_L)) in the process of
associated bZ production at the LHC. We show that in the Standard Model (SM)
this quantity is essentially given by its Born approximation, remaining almost
unaffected by QCD scales and parton distribution functions variations as well
as by electroweak corrections. The theoretical quantity that appears in A_Z is
the same that provides the LEP1 Z -> b bbar forward-backward asymmetry, the
only measured observable still in some contradiction with the SM prediction. In
this sense, A_Z would provide the possibility of an independent verification of
the possible SM discrepancy, which could reach, if consistency with LEP1
measurements is imposed, values of the relative ten percent size.Comment: 10 pages, 5 eps figure
Theoretical Uncertainties in Electroweak Boson Production Cross Sections at 7, 10, and 14 TeV at the LHC
We present an updated study of the systematic errors in the measurements of
the electroweak boson cross-sections at the LHC for various experimental cuts
for a center of mass energy of 7, 10 and 14 TeV. The size of both electroweak
and NNLO QCD contributions are estimated, together with the systematic error
from the parton distributions. The effects of new versions of the MSTW, CTEQ,
and NNPDF PDFs are considered.Comment: PDFLatex with JHEP3.cls. 22 pages, 43 figures. Version 2 adds the
CT10W PDF set to analysis and updates the final systematic error table and
conclusions, plus several citations and minor wording changes. Version 3 adds
some references on electroweak and mixed QED/QCD corrections. Version 4 adds
more references and acknowledgement
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