Search results for "Sst"
showing 10 items of 538 documents
TandFasymmetries inπ0photoproduction on the proton
2016
The γp→π0p reaction was studied at laboratory photon energies from 425 to 1445 MeV with a transversely polarized target and a longitudinally polarized beam. The beam-target asymmetry F was measured for the first time and new high precision data for the target asymmetry T were obtained. The experiment was performed at the photon tagging facility of the Mainz Microtron (MAMI) using the Crystal Ball and TAPS photon spectrometers. The polarized cross sections were expanded in terms of associated Legendre functions and compared to recent predictions from several partial-wave analyses. The impact of the new data on our understanding of the underlying partial-wave amplitudes and baryon resonance c…
Beam Asymmetry of Coherentπ° Photoproduction on4Hein theΔ(1232) Range Measured using Coherent Bremsstrahlung
1997
Using coherent bremsstrahlung at MAMI (Mainz), the beam asymmetry of the differential cross sections for coherent $\ensuremath{\pi}\ifmmode^\circ\else\textdegree\fi{}$ photoproduction on ${}^{4}\mathrm{He}$ has been measured in the energy interval from 200 to 500 MeV at an angle of ${\ensuremath{\theta}}_{\mathrm{lab}}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}37\ifmmode^\circ\else\textdegree\fi{}$. The coherent ( $\ensuremath{\gamma},\ensuremath{\pi}\ifmmode^\circ\else\textdegree\fi{}$) reaction is used as a precise linear polarimeter for the first time. Agreement with predictions has been obtained on a $\ensuremath{\gtrsim}3%$ level of precision.
Kaon Tagging at 0° Scattering Angle for High-Resolution Decay-Pion Spectroscopy
2014
At the Mainz Microtron hypernuclei can be studied by (e,e'K) reactions. By detecting the kaon which is emitted in forward direction, with the KAOS spectrometer placed at 0 scattering angle, reactions involving open strangeness production are tagged. High-resolution magnetic spectrometers are then used to coincidentally detect the mono- energetic decay-pions from mesonic two-body weak decays of light hypernuclei at rest. As a pioneering experiment has confirmed, the KAOS spectrometer is exposed to a large flux of background particles, mostly positrons from bremsstrahlung pair production. In order to increase the e ciency of kaon identification the KAOS spectrometer was modi- fied to suppress…
Evaluation of high-energy brachytherapy source electronic disequilibrium and dose from emitted electrons
2009
Purpose: The region of electronic disequilibrium near photon-emitting brachytherapysources of high-energy radionuclides ( C 60 o , C 137 s , I 192 r , and Y 169 b ) and contributions to total dose from emitted electrons were studied using the GEANT4 and PENELOPEMonte Carlo codes. Methods: Hypothetical sources with active and capsule materials mimicking those of actual sources but with spherical shape were examined. Dose contributions due to sourcephotons, x rays, and bremsstrahlung; source β − , Auger electrons, and internal conversionelectrons; and water collisional kerma were scored. To determine if conclusions obtained for electronic equilibrium conditions and electrondose contribution t…
Helicity-dependent cross sections for the photoproduction of π0 pairs from nucleons
2020
The double-polarization observable $E$ and helicity-dependent cross sections $\sigma_{1/2}$, $\sigma_{3/2}$ have been measured for the photoproduction of $\pi^0$ pairs off quasi-free protons and neutrons at the Mainz MAMI accelerator with the Crystal Ball/TAPS setup. A circularly polarized photon beam was produced by bremsstrahlung from longitudinally polarized electrons and impinged on a longitudinally polarized deuterated butanol target. The reaction products were detected with an almost $4\pi$ covering calorimeter. The results reveal for the first time the helicity- and isospin-dependent structure of the $\gamma N\rightarrow N\pi^0\pi^0$ reaction. They are compared to predictions from re…
Transverse momenta of partons and dimuons in QCD
1978
Abstract Intrinsic (primordial) transverse momenta of quarks and gluons are calculated as well as those arising from recoil (bremsstrahlung) effects, using only the well-known parton distributions as input. The intrinsic kT's lie typically in the range of 150–250 MeV. Recent approaches using heuristic integro-differential equations for kT distributions of partons are shown to disagree with the results obtained by rigorous QCD calculations. The transverse momenta of dimuon pairs produced in pp → μ+μ− + X at the ISR can be solely explained by dynamical recoil effects, i.e., q q →(μ + μ − ) g and gq →(μ + μ − ) q , and no significant intrinsic transverse parton momenta are required. These dimu…
Spectral distribution and Coulomb correction for nuclear bremsstrahlung induced by heavy targets
2021
Abstract Bremsstrahlung spectra below 250 MeV have been measured colliding 500 MeV–electrons with Cu, Ag, and Au targets. The experimental intensity ratios relative to Cu are well described by an accurate analytical high-energy theory, which accounts both for Coulomb distortion and screening. This represents the first experimental verification of the discovery by Bethe-Maximon that leading-order quantum mechanical calculations, equivalent to quasiclassical approximations, become exact at high energies and small angles. It also shows that radiative QED effects play a minor role in the covered part of the spectral distribution within the accuracy (1.6%) of the present measurements.
O(alpha_s) Spin-Spin Correlations for Top and Bottom Quark Production in e+ e- Annihilation
1997
We present the full O(alpha_s) longitudinal spin-spin correlations for heavy-quark pair production at e+ e- high-energy colliders in closed analytical form. In such reactions, quark and antiquark have strongly correlated spins, and the longitudinal components are dominant. For the explicit computation of the QCD bremsstrahlung contributions, new phase-space integrals are derived. Explicit numerical estimates are given for t t_bar and b b_bar production. Around the Z-peak, QCD one-loop corrections depolarize the spin-spin asymmetry for bottom quark pairs by approximately -4%. For top pair production, we find at 350GeV a 0.6% increased polarization over a value of 0.4 in the longitudinal corr…
Evaluation using m.c.n.p. code of the bremsstrahlung energy spectrum produced by interactions between structural materials and accelerated electrons
2004
Abstract In order to design the biological shield of industrial accelerator plants, it is needed to have a good knowledge of the bremsstrahlung energy spectrum and the intensity of the bremsstrahlung produced by electron interactions with both products (usually water equivalent) and structural materials such as concrete, iron, aluminium. Using the MCNP code, a normalized bremsstrahlung energy spectrum was obtained for materials with average atomic number lower than or equal to 13 and irradiated with 5 and 10 Mev electrons, respectively; multiplying the spectrum by suitable coefficients, it was possible to obtain the real spectrum for materials such as water, concrete, aluminium and iron. Th…
SU-FF-T-180: Dosimetric Characteristics of Tm-170 as a Radionuclide for Its Possible Use in Brachytherapy
2006
In clinical brachytherapy several types of photon sources are used, mainly Cs‐137, Ir‐192, I‐125, and Pd‐103. The Tm‐170 is a promising radionuclide for use in brachytherapy because of the low mean‐energy (46.75 keV or 66.39 keV if the lines below 10 keV are removed) and the possible high specific activity (2.21×1014 Bq/g for a half life of 128.6 days). Tm‐170 is produced in a nuclear reactor by neutron absorption of the natural Tm‐169 and decays mainly via β‐emission. The maximum energies of the β‐rays are 0.290 and 0.323 MeV. These β particles are thus absorbed in the source core and in the encapsulation cover producing bremsstrahlung that contributes significantly to the dose. These fact…