21 research outputs found
Simultaneous Projectile-Target Excitation in Heavy Ion Collisions
We calculate the lowest-order contribution to the cross section for
simultaneous excitation of projectile and target nuclei in relativistic heavy
ion collisions. This process is, to leading order, non-classical and adds
incoherently to the well-studied semi-classical Weizs\"acker-Williams cross
section. While the leading contribution to the cross section is down by only
from the semiclassical process, and consequently of potential
importance for understanding data from light projectiles, we find that phase
space considerations render the cross section utterly negligible.Comment: 9 pages, LA-UR-94-247
A Quantum-Mechanical Equivalent-Photon Spectrum for Heavy-Ion Physics
In a previous paper, we calculated the fully quantum-mechanical cross section
for electromagnetic excitation during peripheral heavy-ion collisions. Here, we
examine the sensitivity of that cross section to the detailed structure of the
projectile and target nuclei. At the transition energies relevant to nuclear
physics, we find the cross section to be weakly dependent on the projectile
charge radius, and to be sensitive to only the leading momentum-transfer
dependence of the target transition form factors. We exploit these facts to
derive a quantum-mechanical ``equivalent-photon spectrum'' valid in the
long-wavelength limit. This improved spectrum includes the effects of
projectile size, the finite longitudinal momentum transfer required by
kinematics, and the response of the target nucleus to the off-shell photon.Comment: 19 pages, 5 figure
Electromagnetic Dissociation of Nuclei in Heavy-Ion Collisions
Large discrepancies have been observed between measured Electromagnetic
Dissociation(ED) cross sections and the predictions of the semiclassical
Weiz\"acker-Williams-Fermi(WWF) method. In this paper, the validity of the
semiclassical approximation is examined. The total cross section for
electromagnetic excitation of a nuclear target by a spinless projectile is
calculated in first Born approximation, neglecting recoil. The final result is
expressed in terms of correlation functions and convoluted densities in
configuration space. The result agrees with the WWF approximation to leading
order(unretarded electric dipole approximation), but the method allows an
analytic evaluation of the cutoff, which is determined by the details of the
electric dipole transition charge density. Using the Goldhaber-Teller model of
that density, and uniform charge densities for both projectile and target, the
cutoff is determined for the total cross section in the nonrelativistic limit,
and found to be smaller than values currently used for ED calculations. In
addition, cross sections are calculated using a phenomenological momentum space
cutoff designed to model final state interactions. For moderate projectile
energies, the calculated ED cross section is found to be smaller than the
semiclassical result, in qualitative agreement with experiment.Comment: 28 page
Nuclear absorption of Charmoniums in pA and AA collisions
We have analysed the latest NA50 data on production in pA and AA
collisions. The production is assumed to be a two step process, (i)
formation of pairs, perturbatively calculable, and (ii) formation of
from the pair, a non-perturbative process, which is conviniently
parametrized. In a nuclear medium, as the pair passes through the
nuclear medium, it gain relative square momentum and some of the pairs can gain
enough square momentum to cross the threshold for open charm meson, leading to
suppression in nuclear medium. Few parameters of the model were fixed from the
latest high statistics NA50 pA and NA38 SU total cross sectional data.
The model then reproduces the centrality dependence of over Drell-Yan
ration in 200 GeV/c S+U and 158 GeV/c Pb+Pb collisions. We also discuss the
centrality dependence of suppression at RHIC energy.Comment: 4 pages including 3 figures, Revised version, to be published in
Phys.Rev.
suppression in Pb+Pb collisions and broadening
We have analysed the NA50 data, on the centrality dependence of
broadening of 's, in Pb+Pb collisions, at the CERN-SPS. The data were
analysed in a QCD based model, where 's are suppressed in 'nuclear'
medium. Without any free parameter, the model could explain the NA50
broadening data. The data were also analysed in a QGP based threshold model,
where suppression is 100% above a critical density. The QGP based
model could not explain the NA50 broadening data. We have also predicted
the centrality dependence of suppression and broadening at RHIC
energy. Both the models, the QGP based threshold model and the QCD based
nuclear absorption model, predict broadening very close to each other.Comment: The paper was completely revised. The conclusion is also changed. 5
pages, 4 figure
J/psi suppression in heavy ion collisions by quark momentum diffusion
The momentum diffusion effect of the quark pair due to the multiple
scattering in a nuclear medium is studied to explain the observed J/psi yields
in SPS experiments. The resulting suppression is found to be insufficient to
reproduce the J/psi yield in Pb-Pb collisions at SPS energy.Comment: 2 pages (1 figure
Improved Measurement of the Asymmetry in the Nucleon Sea
Measurements of the ratio of Drell-Yan yields from an 800 \rm{GeV/c} proton
beam incident on liquid hydrogen and deuterium targets are reported.
Approximately 360,000 Drell-Yan muon pairs remained after all cuts on the data.
From these data, the ratio of anti-down () to anti-up ()
quark distributions in the proton sea is determined over a wide range in
Bjorken-. These results confirm previous measurements by E866 and extend
them to lower . From these data, and
are evaluated for . These results are
compared with parameterizations of various parton distribution functions,
models and experimental results from NA51, NMC, and HERMES.Comment: 17 pages, 15 figure
Tocilizumab in patients admitted to hospital with COVID-19 (RECOVERY): a randomised, controlled, open-label, platform trial
Background:
In this study, we aimed to evaluate the effects of tocilizumab in adult patients admitted to hospital with COVID-19 with both hypoxia and systemic inflammation.
Methods:
This randomised, controlled, open-label, platform trial (Randomised Evaluation of COVID-19 Therapy [RECOVERY]), is assessing several possible treatments in patients hospitalised with COVID-19 in the UK. Those trial participants with hypoxia (oxygen saturation <92% on air or requiring oxygen therapy) and evidence of systemic inflammation (C-reactive protein ≥75 mg/L) were eligible for random assignment in a 1:1 ratio to usual standard of care alone versus usual standard of care plus tocilizumab at a dose of 400 mg–800 mg (depending on weight) given intravenously. A second dose could be given 12–24 h later if the patient's condition had not improved. The primary outcome was 28-day mortality, assessed in the intention-to-treat population. The trial is registered with ISRCTN (50189673) and ClinicalTrials.gov (NCT04381936).
Findings:
Between April 23, 2020, and Jan 24, 2021, 4116 adults of 21 550 patients enrolled into the RECOVERY trial were included in the assessment of tocilizumab, including 3385 (82%) patients receiving systemic corticosteroids. Overall, 621 (31%) of the 2022 patients allocated tocilizumab and 729 (35%) of the 2094 patients allocated to usual care died within 28 days (rate ratio 0·85; 95% CI 0·76–0·94; p=0·0028). Consistent results were seen in all prespecified subgroups of patients, including those receiving systemic corticosteroids. Patients allocated to tocilizumab were more likely to be discharged from hospital within 28 days (57% vs 50%; rate ratio 1·22; 1·12–1·33; p<0·0001). Among those not receiving invasive mechanical ventilation at baseline, patients allocated tocilizumab were less likely to reach the composite endpoint of invasive mechanical ventilation or death (35% vs 42%; risk ratio 0·84; 95% CI 0·77–0·92; p<0·0001).
Interpretation:
In hospitalised COVID-19 patients with hypoxia and systemic inflammation, tocilizumab improved survival and other clinical outcomes. These benefits were seen regardless of the amount of respiratory support and were additional to the benefits of systemic corticosteroids.
Funding:
UK Research and Innovation (Medical Research Council) and National Institute of Health Research
Convalescent plasma in patients admitted to hospital with COVID-19 (RECOVERY): a randomised controlled, open-label, platform trial
Background:
Many patients with COVID-19 have been treated with plasma containing anti-SARS-CoV-2 antibodies. We aimed to evaluate the safety and efficacy of convalescent plasma therapy in patients admitted to hospital with COVID-19.
Methods:
This randomised, controlled, open-label, platform trial (Randomised Evaluation of COVID-19 Therapy [RECOVERY]) is assessing several possible treatments in patients hospitalised with COVID-19 in the UK. The trial is underway at 177 NHS hospitals from across the UK. Eligible and consenting patients were randomly assigned (1:1) to receive either usual care alone (usual care group) or usual care plus high-titre convalescent plasma (convalescent plasma group). The primary outcome was 28-day mortality, analysed on an intention-to-treat basis. The trial is registered with ISRCTN, 50189673, and ClinicalTrials.gov, NCT04381936.
Findings:
Between May 28, 2020, and Jan 15, 2021, 11558 (71%) of 16287 patients enrolled in RECOVERY were eligible to receive convalescent plasma and were assigned to either the convalescent plasma group or the usual care group. There was no significant difference in 28-day mortality between the two groups: 1399 (24%) of 5795 patients in the convalescent plasma group and 1408 (24%) of 5763 patients in the usual care group died within 28 days (rate ratio 1·00, 95% CI 0·93–1·07; p=0·95). The 28-day mortality rate ratio was similar in all prespecified subgroups of patients, including in those patients without detectable SARS-CoV-2 antibodies at randomisation. Allocation to convalescent plasma had no significant effect on the proportion of patients discharged from hospital within 28 days (3832 [66%] patients in the convalescent plasma group vs 3822 [66%] patients in the usual care group; rate ratio 0·99, 95% CI 0·94–1·03; p=0·57). Among those not on invasive mechanical ventilation at randomisation, there was no significant difference in the proportion of patients meeting the composite endpoint of progression to invasive mechanical ventilation or death (1568 [29%] of 5493 patients in the convalescent plasma group vs 1568 [29%] of 5448 patients in the usual care group; rate ratio 0·99, 95% CI 0·93–1·05; p=0·79).
Interpretation:
In patients hospitalised with COVID-19, high-titre convalescent plasma did not improve survival or other prespecified clinical outcomes.
Funding:
UK Research and Innovation (Medical Research Council) and National Institute of Health Research
Recommended from our members
A quantum mechanical equivalent photon spectrum for heavy ion reactions
Radioactive nuclear beams are rapidly coming to the fore as an important alternative to traditional measurements in nuclear astrophysics. Radioactive nuclei are scattered off the strong electromagnetic fields of a heavy ion, such as lead, providing an independent measurement of electromagnetic cross sections that are difficult to measure otherwise. In this paper, we examine the corrections to the semi-classical ``equivalent photon spectrum`` used to analyze these experiments, and derive an improved spectrum, valid in the long wavelength limit, that includes the effects of the size of the heavy ion, the non-zero longitudinal momentum transfer required by kinematics, and the response of the target nucleus to be off-shell photon