Radiative β decay of the free neutron Cooper, R. L.; Chupp, T. E.; Dewey, M. S. ...
Physical review. C, Nuclear physics,
03/2010, Volume:
81, Issue:
3
Journal Article
Pair correlations between large transverse momentum neutral pion triggers (p{sub T}=4--7 GeV/c) and charged hadron partners (p{sub T}=3--7 GeV/c) in central (0%-20%) and midcentral (20%-60%) Au+Au ...collisions at {radical}(s{sub NN})=200 GeV are presented as a function of trigger orientation with respect to the reaction plane. The particles are at larger momentum than where jet shape modifications have been observed, and the correlations are sensitive to the energy loss of partons traveling through hot dense matter. An out-of-plane trigger particle produces only 26{+-}20% of the away-side pairs that are observed opposite of an in-plane trigger particle for midcentral (20%-60%) collisions. In contrast, near-side jet fragments are consistent with no suppression or dependence on trigger orientation with respect to the reaction plane. These observations are qualitatively consistent with a picture of little near-side parton energy loss either due to surface bias or fluctuations and increased away-side parton energy loss due to a long path through the medium. The away-side suppression as a function of reaction-plane angle is shown to be sensitive to both the energy loss mechanism and the space-time evolution of heavy-ion collisions.
Transverse momentum distributions and yields for {pi}{sup {+-}}, K{sup {+-}}, p, and p-bar in p+p collisions at {radical}(s) = 200 and 62.4 GeV at midrapidity are measured by the PHENIX experiment at ...the Relativistic Heavy Ion Collider (RHIC). These data provide important baseline spectra for comparisons with identified particle spectra in heavy ion collisions at RHIC. We present the inverse slope parameter T{sub inv}, mean transverse momentum <p{sub T}>, and yield per unit rapidity dN/dy at each energy, and compare them to other measurements at different {radical}(s) in p+p and p+p-bar collisions. We also present the scaling properties such as m{sub T} scaling and x{sub T} scaling on the p{sub T} spectra between different energies. To discuss the mechanism of the particle production in p+p collisions, the measured spectra are compared to next-to-leading-order or next-to-leading-logarithmic perturbative quantum chromodynamics calculations.
Measurements of electrons from the decay of open-heavy-flavor mesons have shown that the yields are suppressed in Au+Au collisions compared to expectations from binary-scaled p+p collisions. These ...measurements indicate that charm and bottom quarks interact with the hot dense matter produced in heavy-ion collisions much more than expected. Here we extend these studies to two-particle correlations where one particle is an electron from the decay of a heavy-flavor meson and the other is a charged hadron from either the decay of the heavy meson or from jet fragmentation. These measurements provide more detailed information about the interactions between heavy quarks and the matter, such as whether the modification of the away-side-jet shape seen in hadron-hadron correlations is present when the trigger particle is from heavy-meson decay and whether the overall level of away-side-jet suppression is consistent. We statistically subtract correlations of electrons arising from background sources from the inclusive electron-hadron correlations and obtain two-particle azimuthal correlations at {radical}(s{sub NN})=200 GeV between electrons from heavy-flavor decay with charged hadrons in p+p and also first results in Au+Au collisions. We find the away-side-jet shape and yield to be modified in Au+Au collisions compared to p+p collisions.
New measurements by the PHENIX experiment at the Relativistic Heavy Ion Collider for eta production at midrapidity as a function of transverse momentum (p{sub T}) and collision centrality in sq ...root(s{sub NN})=200 GeV Au+Au and p+p collisions are presented. They indicate nuclear modification factors (R{sub AA}) which are similar in both magnitude and trend to those found in earlier pi{sup 0} measurements. Linear fits to R{sub AA} as a function of p{sub T} in 5-20 GeV/c show that the slope is consistent with zero within two standard deviations at all centralities, although a slow rise cannot be excluded. Having different statistical and systematic uncertainties, the pi{sup 0} and eta measurements are complementary at high p{sub T}; thus, along with the extended p{sub T} range of these data they can provide additional constraints for theoretical modeling and the extraction of transport properties.
We report the observation at the Relativistic Heavy Ion Collider of suppression of back-to-back correlations in the direct photon+jet channel in Au+Au relative to p+p collisions. Two-particle ...correlations of direct photon triggers with associated hadrons are obtained by statistical subtraction of the decay photon-hadron ({gamma}-h) background. The initial momentum of the away-side parton is tightly constrained, because the parton-photon pair exactly balance in momentum at leading order in perturbative quantum chromodynamics, making such correlations a powerful probe of the in-medium parton energy loss. The away-side nuclear suppression factor, I{sub AA}, in central Au+Au collisions, is 0.32{+-}0.12{sup stat}{+-}0.09{sup syst} for hadrons of 3<p{sub T}{sup h}<5 in coincidence with photons of 5<p{sub T}{sup {gamma}}<15 GeV/c. The suppression is comparable to that observed for high-p{sub T} single hadrons and dihadrons. The direct photon associated yields in p+p collisions scale approximately with the momentum balance, z{sub T}{identical_to}p{sub T}{sup h}/p{sub T}{sup {gamma}}, as expected for a measurement of the away-side parton fragmentation function. We compare to Au+Au collisions for which the momentum balance dependence of the nuclear modification should be sensitive to the path-length dependence of parton energy loss.
Radiative {beta} decay of the free neutron Cooper, R. L.; Chupp, T. E.; Dewey, M. S. ...
Physical review. C, Nuclear physics,
03/2010, Volume:
81, Issue:
3
Journal Article
The theory of quantum electrodynamics predicts that the {beta} decay of the neutron into a proton, electron, and antineutrino is accompanied by a continuous spectrum of emitted photons described as ...inner bremsstrahlung. While this phenomenon has been observed in nuclear {beta} decay and electron-capture decay for many years, it has only been recently observed in free-neutron decay. We present a detailed discussion of an experiment in which the radiative decay mode of the free neutron was observed. In this experiment, the branching ratio for this rare decay was determined by recording photons that were correlated with both the electron and proton emitted in neutron decay. We determined the branching ratio for photons with energy between 15 and 340 keV to be (3.09+-0.32)x10{sup -3} (68% level of confidence), where the uncertainty is dominated by systematic effects. This value for the branching ratio is consistent with theoretical predictions. The characteristic energy spectrum of the radiated photons, which differs from the uncorrelated background spectrum, is also consistent with the theoretical spectrum.
Effective management of freshwater fish habitat is essential to supporting healthy aquatic ecosystems and sustainable fisheries. In Canada, recent changes to the Fisheries Act enhanced the protection ...of fish habitat, but application of those provisions relies on sound scientific evidence. We employed collaborative research prioritization methods to identify scientific research questions that, if addressed, would significantly advance the management of freshwater fish habitat in Canada. This list was generated by a diverse group of freshwater fish experts, including substantial contributions from practitioners who administer provisions of the Fisheries Act. The research questions generated in this study identify priority topics for future research, while highlighting issues that could be addressed with different funding models. As a result, this study should support evidence-based management of Canada’s aquatic resources by identifying scientific knowledge gaps faced by practitioners, and suggesting mechanisms to address them. Given the important contribution of Canadian freshwater systems to global ecosystem values, and the similar scientific challenges facing fish habitat managers in other jurisdictions, this study is likely to have broad applicability.
The theory of quantum electrodynamics (QED) predicts that beta decay of the neutron into a proton, electron and antineutrino should be accompanied by a continuous spectrum of soft photons. While this ...inner bremsstrahlung branch has been previously measured in nuclear beta and electron capture decay, it has never been observed in free neutron decay. Recently, the photon energy spectrum and branching ratio for neutron radiative decay have been calculated using two approaches: a standard QED framework and heavy baryon chiral perturbation theory (an effective theory of hadrons based on the symmetries of quantum chromodynamics). The QED calculation treats the nucleons as point-like, whereas the latter approach includes the effect of nucleon structure in a systematic way. Here we observe the radiative decay mode of free neutrons, measuring photons in coincidence with both the emitted electron and proton. We determined a branching ratio of (3.13 ± 0.34) × 10-3 (68 per cent level of confidence) in the energy region between 15 and 340 keV, where the uncertainty is dominated by systematic effects. The value is consistent with the predictions of both theoretical approaches; the characteristic energy spectrum of the radiated photons, which differs from the uncorrelated background spectrum, is also consistent with the calculated spectrum. This result may provide opportunities for more detailed investigations of the weak interaction processes involved in neutron beta decay.
Using the INTEGRA Dermal Regeneration Template requires the outer silastic layer to be replaced with an autograft. We followed the manufacturer's directions for epidermal autografting and frequently ...obtained shredded, useless grafts, therefore, it seemed important to determine the proper dermatome setting. We evaluated dermatome settings from 0.002 to 0.012 inches. First, with feeler gauges, we verified the dermatome settings. Second, we harvested skin at various dermatome settings and measured the thickness histologically. We found that 1) the dermatome settings are reasonably accurate; 2) harvesting useful sheets at 0.002 and 0.004 inches is virtually impossible; 3) the variability of histologic graft thickness is enormous; and 4) a dermatome setting of 0.006 inches yields useful grafts. We no longer use the term epidermal autografting but rather ultrathin split-thickness grafting. To harvest these grafts, we now merely set the dermatome to 0.006 inches and make whatever midcourse corrections are necessary to obtain translucent grafts.
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