706 research outputs found
Tests of Power Corrections for Event Shapes in e+e- Annihilation
A study of perturbative QCD calculations combined with power corrections to
model hadronisation effects is presented. The QCD predictions are fitted to
differential distributions and mean values of event shape observables measured
in e+e- annihilation at centre-of-mass energies from 14 to 189 GeV. We
investigate the event shape observables thrust, heavy jet mass, C-parameter,
total and wide jet broadening and differential 2-jet rate and observe a good
description of the data by the QCD predictions. The strong coupling constant
alpha_S(M_Z) and the free parameter of the power correction calculations
alpha_0(2 GeV) are measured to be alpha_S(M_Z) = 0.1171 +/- 0.0032/0.0020 and
alpha_0(2 GeV) = 0.513 +/- 0.066/0.045. The predicted universality of alpha_0
is confirmed within the uncertainties of the measurements.Comment: 28 pages, LaTeX2e, 21 .eps-files included, accepted by Eur. Phys. J.
Tests of Power Corrections to Event Shape Distributions from e+e- Annihilation
A study of differential event shape distributions using e+e- data at
centre-of-mass energies of 35 to 183 GeV is presented. We investigated
non-perturbative power corrections for the thrust, C-parameter, total and wide
jet broadening observables. We observe a good description of the distributions
by the combined resummed QCD calculations plus power corrections from the
dispersive approach. The single non-perturbative parameter \alpha_0 is measured
to be \alpha_0 (2 GeV) = 0.502 +- 0.013 (stat.) ^{+0.046)_{-0.032} (exp. syst.)
^{+0.074}_{-0.053} (theo. syst.) and is found to be universal for the
observables studied within the given systematic uncertainties. Using revised
calculations of the power corrections for the jet broadening variables,
improved consistency of the individual fit results is obtained. Agreement is
also found with results extracted from the mean values of event shape
distributions.Comment: 19 pages, LaTeX2e, 8 .eps-files included, paper contributed to the
EPS-HEP99 conference in Tampere, Finlan
Comparison of hemodynamic stability in moyamoya syndrome patients under mask versus intravenous anesthetic induction
Thesis (M.A.)--Boston UniversityBackground: Moyamoya syndrome is a chronic and progressive disorder, which affects the cerebral vasculature, especially at the Circle of Willis. Pathologically, the changes occur in the vessel and wall and lead to progressive narrowing and eventual occlusion of the internal carotid artery and possibly additional vessels. As the disorder progresses, decreased cerebral blood flow leads to dangerous ischemic events in pediatric patients, especially transient ischemic attacks and stroke. Surgery is necessary to reestablish proper blood flow however; prior to this a diagnostic cerebral angiogram is performed to visualize the blood vessels affected. During this procedure, intravenous (IV) anesthetic induction is typically used. However, IV access and insertion are likely to agitate children, leading to anxiety and crying. In moyamoya patients, crying and subsequent hyperventilation is a known trigger of ischemic events. Therefore, this study is investigating the safety of mask induction compared to IV for this procedure, which would help avoid episodes of crying.
Methods: Records from moyamoya patients admitted to Boston Children’s Hospital for a diagnostic cerebral angiogram during the period of 2007-2013 were analyzed retrospectively (n=98). The main focus was data analysis between patients who underwent IV versus mask induction to determine if there was equivalence of safety based on hemodynamic parameters. An unsafe blood pressure drop is clinically deemed as a 20% or greater drop from the patient’s baseline and this criteria was used when determining if a patient was a case (who experienced this unsafe event) or control. (who did not). Additionally, other intraoperative variables were analyzed for possible correlation with hemodynamic stability. Lastly, demographic patient information was gathered to gain an understanding of the population being analyzed. Statistical analysis was performed for all results when possible to determine significance. [TRUNCATED
C-Parameter and Jet Broadening at PETRA Energies
e^+e^- annihilation data recorded by the JADE detector at PETRA were used to
measure the C-parameter for the first time at \sqrt{s}= 35 and 44 GeV. The
distributions were compared to a resummed QCD calculation.
In addition, we applied extended resummed calculations to the total and wide
jet broadening variables, B_T and B_W. We combined the results on \alpha_s with
those of our previous study of differential 2-jet rate, thrust, and heavy jet
mass, obtaining
\alpha_s(35 GeV) = 0.1448 +0.0117 -0.0070 and \alpha_s(44 GeV) = 0.1392
+0.0105 -0.0074.
Moreover power corrections to the mean values of the observables mentioned
above were investigated considering the Milan factor and the improved
prediction for the jet broadening observables.
Our study, which considered e^+e^- data of five event shape observables
between \sqrt{s}= 14 and 183 GeV, yielded \alpha_s(M_{Z^0})=0.1177 +0.0035
-0.0034.Comment: 14 pages, LaTeX2e, 9 .eps-files included, abbreviated version of the
paper contributed to the ICHEP'98 conference in Vancouver, submitted to Phys.
Lett.
Study of moments of event shapes in e+e- annihilation using JADE data
Data from e+e- annihilation into hadrons collected by the JADE experiment at
centre-of-mass energies between 14 GeV and 44 GeV were used to study moments of
event shape distributions. The data were compared with Monte Carlo models and
with predictions from QCD NLO order calculations. The strong coupling constant
measured from the moments is alpha_S(M_Z) = 0.1286 +/- 0.0007 (stat) +/- 0.0011
(expt) +/- 0.0022 (had) +/- 0.0068 (theo), alpha_S(M_Z) = 0.1286 +/- 0.0072
(total error), consistent with the world average. However, systematic
deficiencies in the QCD NLO order predictions are visible for some of the
higher moments.Comment: JADE note 147 submitted as contributed paper to ICHEP 2004, corrected
statistical error of 6 observable average and several typo
A Study of Event Shapes and Determinations of alpha_s using data of e^+e^- Annihilations at sqrt{s} = 22 to 44 GeV
Data recorded by the JADE experiment at the PETRA e^+e^- collider were used
to measure the event shape observables thrust, heavy jet mass, wide and total
jet broadening and the differential 2-jet rate in the Durham scheme. For the
latter three observables, no experimental results have previously been
presented at these energies. The distributions were compared with resummed QCD
calulations (O(alpha_s^2)+NLLA), and the strong coupling constant alpha_s(Q)
was determined at different energy scales Q=sqrt{s}. The results,
\alpha_s(22 GeV) = 0.161 ^{+0.016}_{-0.011},
\alpha_s(35 GeV) = 0.143 ^{+0.011}_{-0.007},
\alpha_s(44 GeV) = 0.137 ^{+0.010}_{-0.007}, are in agreement with previous
combined results of PETRA albeit with smaller uncertainties. Together with
corresponding data from LEP, the energy dependence of alpha_s is significantly
tested and is found to be in good agreement with the QCD expectation.
Similarly, mean values of the observables were compared to analytic QCD
predictions where hadronisation effects are absorbed in calculable power
corrections.Comment: 36 pages, LaTeX2e, 34 .eps-files included, submitted to Z. Phys. C,
revised version, with comments of referee included and some typos corrected,
accepted for publicatio
Measurement of the Strong Coupling Constant alpha_S from the Four-Jet Rate in e+e- Annihilation using JADE data
Data from e+e- annihilation into hadrons collected by the JADE experiment at
centre-of-mass energies between 14 GeV and 44 GeV were used to study the
four-jet rate as a function of the Durham algorithm's resolution parameter
y_cut. The four-jet rate was compared to a QCD NLO order calculations including
NLLA resummation of large logarithms. The strong coupling constant measured
from the four-jet rate is alpha_S(M_Z) = 0.1169 +/- 0.0004 (stat) +/- 0.0012
(expt) +/- 0.0021 (had) +/- 0.0007 (theo), alpha_S(M_Z) = 0.1169 +/- 0.0026
(total error) in agreement with the world average.Comment: JADE note 146 submitted as contributed paper to ICHEP 200
Measurement of the longitudinal and transverse cross-section in e^+e^- annihilation at sqrt(s)=35-44 GeV
An investigation of the polar angle distribution of charged hadrons is
presented using data taken by the JADE experiment at the PETRA e^+e^- collider
at centre-of-mass energies of 35 and 44 GeV. From fits to the polar angle
distribution the longitudinal, sigma_L, and transverse, sigma_T, cross-section
relative to the total hadronic are determined at an average energy scale of
36.6 GeV. The results are sigma_L/sigma_tot = 0.067 +/- 0.013,
sigma_T/sigma_tot = 0.933 -/+ 0.013 where total errors are given and the
results are exactly anti-correlated. Using the next-to-leading order QCD
prediction for the longitudinal cross-section, the value alpha_S(36.6 GeV) =
0.150 +/- 0.025 of the strong coupling constant is obtained in agreement with
the world average value of alpha_S evolved to an energy scale of 36.6 GeV.Comment: 12 pages, LaTeX2e, 5 .eps-files included, pennames.sty included,
submitted to Phys. Lett.
A Measurement of the QCD Colour Factors using Event Shape Distributions at sqrt(s)=14 GeV to 189 GeV
Measurements of the QCD colour factors C_A and C_F and of the number of
active quark flavours n_f in the process e+e- -> hadrons at high energy are
presented. They are based on fits of O(alpha_S**2)+NLLA QCD calculations to
distributions of the event shape observables 1-T, C, B_T and B_W measured at
centre-of-mass energies from 14 GeV to 189 GeV. Hadronisation effects are
approximated with power correction calculations which also depend on the QCD
gauge structure. In this approach potential biases from hadronisation models
are reduced. Our results for individually measured quantities are n_f = 5.64 +-
1.35, C_A = 2.88 +- 0.27 and C_F = 1.45 +- 0.27 in good agreement with QCD
based on the SU(3) symmetry group where n_f=5 for the energies considered here,
C_A=3 and C_F=4/3. From simultaneous fits of C_A and C_F we find C_A = 2.84 +-
0.24 and C_F = 1.29 +- 0.18, which is also in good agreement with the QCD
expectation.Comment: accepted by European Journal of Physics
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