Results from PS185 Johansson, T.; Barnes, P.D.; Bassalleck, B. ...
Nuclear physics. A,
08/1999, Letnik:
655, Številka:
1
Journal Article
Recenzirano
The PS185 experiment at LEAR/CERN has studied strangeness production in antiproton-proton collisions. Exclusive final states of antihyperon-hyperon pairs have been measured in order to investigate ...strange-quark production dynamics. A comprehensive data set is available for the
ΛΛ
channel and observables include total and differential cross sections, polarisations and spin correlations. Data from other hyperon channels, such as
Σ
0Λ + c.c.
,
Σ
+Σ
+
and
Σ
−Σ
−
, are also available. The analysis of a spin transfer measurement for the
pp →
ΛΛ
reaction using a polarised proton target is in progress.
New data were taken at the Triangle Universities Nuclear Laboratory to investigate the plausibility of using low energy deuterons and the {sup 10}B(d,n){sup 11}C reaction as a portable source of 6.3 ...MeV neutrons. Analysis of the data at and below incident deuteron energies of 160 keV indicates an n{sub 0} neutron cross section that is lower than previous estimates by at least three orders of magnitude. In separate runs, deuterons with two different energies (160 and 140 keV) were stopped in a {sup 10}B target. The resulting n{sub 0} neutrons of approximately 6.3 MeV were detected at angles between 0 deg. and 150 deg. The angle integrated yields were used to determine the astrophysical S factor for this reaction assuming a constant value for the S factor below 160 keV. The cross sections reported between 130 and 160 keV were calculated using the extracted value of the S factor. The measured n{sub 0} cross section is several orders of magnitude smaller than previous results, thus eliminating {sup 10}B(d,n){sup 11}C as a portable source of intense neutrons with low energy deuteron beams on the order of tens of microamps. In order to gain insight into the reaction dynamics at these low energies the cross section results have been compared with results from calculations using the distorted wave Born approximation (DWBA) and a detailed Hauser-Feshbach calculation performed by the authors. The angular distribution is consistent with the Hauser-Feshbach calculation suggesting a statistical compound nucleus reaction rather than a direct reaction.
The reaction (p) over barp -> (Lambda) over bar Lambda -> (p) over bar pi(+)p pi(-) has been measured with high statistics at a beam momentum of p((p) over bar)=1.637GeV/c. The use of a ...transversely polarized frozen-spin target combined with the self-analyzing property of Lambda/(Lambda) over bar decay allows access to unprecedented information on the spin structure of the interaction. The most general spin-scattering matrix can be written in terms of 11 real parameters for each bin of scattering angle; each of these parameters is determined with reasonable precision. From these results, all conceivable spin correlations are determined with inherent self-consistency. Good agreement is found with the few previously existing measurements of spin observables in (p) over barp ->(Lambda) over bar Lambda near this energy. Existing theoretical models do not give good predictions for those spin observables that had not been previously measured.
Phys.Rev.Lett.106:162303,2011 High precision measurements of the differential cross sections for $\pi^0$
photoproduction at forward angles for two nuclei, $^{12}$C and $^{208}$Pb, have
been performed ...for incident photon energies of 4.9 - 5.5 GeV to extract the
${\pi^0 \to \gamma\gamma}$ decay width. The experiment was done at Jefferson
Lab using the Hall B photon tagger and a high-resolution multichannel
calorimeter. The ${\pi^0 \to \gamma\gamma}$ decay width was extracted by
fitting the measured cross sections using recently updated theoretical models
for the process. The resulting value for the decay width is $\Gamma{(\pi^0 \to
\gamma\gamma)} = 7.82 \pm 0.14 ~({\rm stat.}) \pm 0.17 ~({\rm syst.}) ~{\rm
eV}$. With the 2.8% total uncertainty, this result is a factor of 2.5 more
precise than the current PDG average of this fundamental quantity and it is
consistent with current theoretical predictions.
A technique is presented for precision measurements of the area densities, density * T, of approximately 5% radiation length carbon and 208Pb targets used in an experiment at Jefferson Laboratory to ...measure the neutral pion radiative width. The precision obtained in the area density for the carbon target is +/- 0.050%, and that obtained for the lead target through an x-ray attenuation technique is +/- 0.43%.
Phys.Rev.C74:015206,2006 The reaction anti-proton + proton -> anti-\Lambda + \Lambda -> anti-proton +
\pi^+ + proton + \pi^- has been measured with high statistics at anti-proton
beam momentum of ...1.637 GeV/c. The use of a transversely-polarized frozen-spin
target combined with the self-analyzing property of \Lambda/anti-\Lambda decay
allows access to unprecedented information on the spin structure of the
interaction. The most general spin-scattering matrix can be written in terms of
eleven real parameters for each bin of scattering angle, each of these
parameters is determined with reasonable precision. From these results all
conceivable spin-correlations are determined with inherent self-consistency.
Good agreement is found with the few previously existing measurements of spin
observables in anti-proton + proton -> anti-\Lambda + \Lambda near this energy.
Existing theoretical models do not give good predictions for those
spin-observables that had not been previously measured.
High precision measurements of the differential cross sections for \(\pi^0\) photoproduction at forward angles for two nuclei, \(^{12}\)C and \(^{208}\)Pb, have been performed for incident photon ...energies of 4.9 - 5.5 GeV to extract the \({\pi^0 \to \gamma\gamma}\) decay width. The experiment was done at Jefferson Lab using the Hall B photon tagger and a high-resolution multichannel calorimeter. The \({\pi^0 \to \gamma\gamma}\) decay width was extracted by fitting the measured cross sections using recently updated theoretical models for the process. The resulting value for the decay width is \(\Gamma{(\pi^0 \to \gamma\gamma)} = 7.82 \pm 0.14 ~({\rm stat.}) \pm 0.17 ~({\rm syst.}) ~{\rm eV}\). With the 2.8% total uncertainty, this result is a factor of 2.5 more precise than the current PDG average of this fundamental quantity and it is consistent with current theoretical predictions.
Phys.Rev.Lett.89:212302,2002 Spin transfer observables for the strangeness-production reaction
Antiproton-Proton -> Antilambda-Lambda have been measured by the PS185
collaboration using a ...transversely-polarized frozen-spin target with an
antiproton beam momentum of 1.637 GeV/c at the Low Energy Antiproton Ring at
CERN. This measurement investigates observables for which current models of the
reaction near threshold make significantly differing predictions. Those models
are in good agreement with existing measurements performed with unpolarized
particles in the initial state. Theoretical attention has focused on the fact
that these models produce conflicting predictions for the spin-transfer
observables D_{nn} and K_{nn}, which are measurable only with polarized target
or beam. Results presented here for D_{nn} and K_{nn} are found to be in
disagreement with predictions from existing models. These results also
underscore the importance of singlet-state production at backward angles, while
current models predict complete or near-complete triplet-state dominance.
The reaction anti-proton + proton -> anti-\Lambda + \Lambda -> anti-proton + \pi^+ + proton + \pi^- has been measured with high statistics at anti-proton beam momentum of 1.637 GeV/c. The use of a ...transversely-polarized frozen-spin target combined with the self-analyzing property of \Lambda/anti-\Lambda decay allows access to unprecedented information on the spin structure of the interaction. The most general spin-scattering matrix can be written in terms of eleven real parameters for each bin of scattering angle, each of these parameters is determined with reasonable precision. From these results all conceivable spin-correlations are determined with inherent self-consistency. Good agreement is found with the few previously existing measurements of spin observables in anti-proton + proton -> anti-\Lambda + \Lambda near this energy. Existing theoretical models do not give good predictions for those spin-observables that had not been previously measured.
PDF
