361 research outputs found
Higher-Order QCD Corrections to Inclusive Particle Production in p anti-p Collisions
Inclusive single-particle production cross sections have been calculated
including higher-order QCD corrections. Transverse-momentum and rapidity
distributions are presented and the scale dependence is studied. The results
are compared with experimental data from the CERN S(p anti-p)S Collider and the
Fermilab Tevatron.Comment: 28 pages, [12 uuencoded PS figures, 3 available under request].
Preprint DESY 92-13
QCD Factorized Drell-Yan Cross Section at Large Transverse Momentum
We derive a new factorization formula in perturbative quantum chromodynamics
for the Drell-Yan massive lepton-pair cross section as a function of the
transverse momentum of the pair. When is much larger than the
pair's invariant mass , this factorization formula systematically resums the
logarithmic contributions of the type to all
orders in the strong coupling . When , our formula yields
the same Drell-Yan cross section as conventional fixed order QCD perturbation
theory. We show that resummation is important when the collision energy
is large enough and , and we argue that perturbative
expansions are more stable and reliable in terms of the modified factorization
formula.Comment: 36 pages, latex, including 16 figure
Virtual photon fragmentation functions
We introduce operator definitions for virtual photon fragmentation functions,
which are needed for reliable calculations of Drell-Yan transverse momentum
() distributions when is much larger than the invariant mass . We
derive the evolution equations for these fragmentation functions. We calculate
the leading order evolution kernels for partons to fragment into a unpolarized
as well as a polarized virtual photon. We find that fragmentation functions to
a longitudinally polarized virtual photon are most important at small , and
the fragmentation functions to a transversely polarized virtual photon dominate
the large region. We discuss the implications of this finding to the
J/ mesons' polarization at large transverse momentum.Comment: Latex, 19 pages including 6 figures. An error in the first version
has been corrected, and references update
Azimuthal correlation in DIS
We introduce the azimuthal correlation for the deep inelastic scattering
process. We present the QCD prediction to the level of next-to-leading log
resummation, matching to the fixed order prediction. We also estimate the
leading non-perturbative power correction. The observable is compared with the
energy-energy correlation in e+e- annihilation, on which it is modelled. The
effects of the resummation and of the leading power correction are both quite
large. It would therefore be particularly instructive to study this observable
experimentally.Comment: 33 pages, 4 figures, JHEP class included. One figure and some
clarifications adde
Recoil and Threshold Corrections in Short-distance Cross Sections
We identify and resum corrections associated with the kinematic recoil of the
hard scattering against soft-gluon emission in single-particle inclusive cross
sections. The method avoids double counting and conserves the flow of partonic
energy. It reproduces threshold resummation for high-p_T single-particle cross
sections, when recoil is neglected, and Q_T-resummation at low Q_T, when
higher-order threshold logarithms are suppressed. We exhibit explicit resummed
cross sections, accurate to next-to-leading logarithm, for electroweak
annihilation and prompt photon inclusive cross sections.Comment: minor modifications of the text, some references added. 51 pages,
LaTeX, 6 figures as eps file
Three-nucleon mechanisms in photoreactions
The C reaction has been measured for
E=150-800 MeV in the first study of this reaction in a target
heavier than He. The experimental data are compared to a microscopic many
body calculation. The model, which predicts that the largest contribution to
the reaction arises from final state interactions following an initial pion
production process, overestimates the measured cross sections and there are
strong indications that the overestimate arises in this two-step process. The
selection of suitable kinematic conditions strongly suppresses this two-step
contribution leaving cross sections in which up to half the yield is predicted
to arise from the absorption of the photon on three interacting nucleons and
which agree with the model. The results indicate measurements on
nuclei may be a valuable tool for obtaining information on the nuclear
three-body interaction.Comment: 5 pages, 3 figure
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
Double Photoproduction off the Proton at Threshold
The reaction has been measured using the TAPS
BaF calorimeter at the tagged photon facility of the Mainz Microtron
accelerator. Chiral perturbation theory (ChPT) predicts that close to threshold
this channel is significantly enhanced compared to double pion final states
with charged pions. In contrast to other reaction channels, the lower order
tree terms are strongly suppressed in 2 photoproduction. The consequence
is the dominance of pion loops in the 2 channel close to threshold - a
result that opens new prospects for the test of ChPT and in particular its
inherent loop terms. The present measurement is the first which is sensitive
enough for a conclusive comparison with the ChPT calculation and is in
agreement with its prediction. The data also show good agreement with a
calculation in the unitary chiral approach.Comment: Submitted to PL
Deuteron photodisintegration cross-sections 50-155 MeV
The study of the photodisintegration of the deuteron should be a rewarding area over the next few years both as a result of the increased sophistication of recent theoretical treatments and also because of the potential, which has only just begun to be realised, of much more accurate and reliable photoreaction data
Haloperidol and Ziprasidone for Treatment of Delirium in Critical Illness
BACKGROUND:
There are conflicting data on the effects of antipsychotic medications on delirium in patients in the intensive care unit (ICU).
METHODS:
In a randomized, double-blind, placebo-controlled trial, we assigned patients with acute respiratory failure or shock and hypoactive or hyperactive delirium to receive intravenous boluses of haloperidol (maximum dose, 20 mg daily), ziprasidone (maximum dose, 40 mg daily), or placebo. The volume and dose of a trial drug or placebo was halved or doubled at 12-hour intervals on the basis of the presence or absence of delirium, as detected with the use of the Confusion Assessment Method for the ICU, and of side effects of the intervention. The primary end point was the number of days alive without delirium or coma during the 14-day intervention period. Secondary end points included 30-day and 90-day survival, time to freedom from mechanical ventilation, and time to ICU and hospital discharge. Safety end points included extrapyramidal symptoms and excessive sedation.
RESULTS:
Written informed consent was obtained from 1183 patients or their authorized representatives. Delirium developed in 566 patients (48%), of whom 89% had hypoactive delirium and 11% had hyperactive delirium. Of the 566 patients, 184 were randomly assigned to receive placebo, 192 to receive haloperidol, and 190 to receive ziprasidone. The median duration of exposure to a trial drug or placebo was 4 days (interquartile range, 3 to 7). The median number of days alive without delirium or coma was 8.5 (95% confidence interval [CI], 5.6 to 9.9) in the placebo group, 7.9 (95% CI, 4.4 to 9.6) in the haloperidol group, and 8.7 (95% CI, 5.9 to 10.0) in the ziprasidone group (P=0.26 for overall effect across trial groups). The use of haloperidol or ziprasidone, as compared with placebo, had no significant effect on the primary end point (odds ratios, 0.88 [95% CI, 0.64 to 1.21] and 1.04 [95% CI, 0.73 to 1.48], respectively). There were no significant between-group differences with respect to the secondary end points or the frequency of extrapyramidal symptoms.
CONCLUSIONS:
The use of haloperidol or ziprasidone, as compared with placebo, in patients with acute respiratory failure or shock and hypoactive or hyperactive delirium in the ICU did not significantly alter the duration of delirium. (Funded by the National Institutes of Health and the VA Geriatric Research Education and Clinical Center; MIND-USA ClinicalTrials.gov number, NCT01211522 .)
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