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Träfflista för sökning "WFRF:(Thörngren Engblom P) "

Sökning: WFRF:(Thörngren Engblom P)

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1.
  • Augustyniak, W., et al. (författare)
  • Polarization of a stored beam by spin-filtering
  • 2012
  • Ingår i: Physics Letters B. - : Elsevier. - 0370-2693 .- 1873-2445. ; 718:1, s. 64-69
  • Tidskriftsartikel (refereegranskat)abstract
    • The PAX Collaboration has successfully performed a spin-filtering experiment with protons at the COSY-ring. The measurement allowed the determination of the spin-dependent polarizing cross section, that compares well with the theoretical prediction from the nucleon-nucleon potential. The test confirms that spin-filtering can be adopted as a method to polarize a stored beam and that the present interpretation of the mechanism in terms of the proton-proton interaction is correct. The outcome of the experiment is of utmost importance in view of the possible application of the method to polarize a beam of stored antiprotons.
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2.
  • Oellers, D., et al. (författare)
  • Polarizing a stored proton beam by spin flip?
  • 2009
  • Ingår i: Physics Letters B. - : Elsevier. - 0370-2693 .- 1873-2445. ; 674:4-5, s. 269-275
  • Tidskriftsartikel (refereegranskat)abstract
    • We discuss polarizing a proton beam in a storage ring, either by selective removal or by spin flip of the stored ions. Prompted by recent, conflicting calculations, we have carried out a measurement of the spin-flip cross section in low-energy electron–proton scattering. The experiment uses the cooling electron beam at COSY as an electron target. The measured cross sections are too small for making spin flip a viable tool in polarizing a stored beam. This invalidates a recent proposal to use co-moving polarized positrons to polarize a stored antiproton beam.
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3.
  • Oellers, D., et al. (författare)
  • New experimental upper limit of the electron-proton spin-flip cross-section
  • 2014
  • Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 759, s. 6-9
  • Tidskriftsartikel (refereegranskat)abstract
    • In a previous publication, measurements of the depolarization of a stored proton beam by interaction with a co-propagating unpolarized electron beam at low relative energy have been presented and an upper limit of about 3 x 10(7) b for the electron-proton spin flip cross-section was determined. A refined analysis presented in this paper reduces the previous upper limit by a factor of three by the introduction of a new procedure that, also makes use of non-identified particles.
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4.
  • Eversmann, D., et al. (författare)
  • New Method for a Continuous Determination of the Spin Tune in Storage Rings and Implications for Precision Experiments
  • 2015
  • Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 115:9
  • Tidskriftsartikel (refereegranskat)abstract
    • A new method to determine the spin tune is described and tested. In an ideal planar magnetic ring, the spin tune-defined as the number of spin precessions per turn-is given by nu(s) = gamma G (gamma is the Lorentz factor, G the gyromagnetic anomaly). At 970 MeV/c, the deuteron spins coherently process at a frequency of approximate to 120 kHz in the Cooler Synchrotron COSY. The spin tune is deduced from the up-down asymmetry of deuteron-carbon scattering. In a time interval of 2.6 s, the spin tune was determined with a precision of the order 10(-8), and to 1 x 10(-10) for a continuous 100 s accelerator cycle. This renders the presented method a new precision tool for accelerator physics; controlling the spin motion of particles to high precision is mandatory, in particular, for the measurement of electric dipole moments of charged particles in a storage ring.
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5.
  • Guidoboni, G., et al. (författare)
  • Connection between zero chromaticity and long in-plane polarization lifetime in a magnetic storage ring
  • 2018
  • Ingår i: Physical Review Accelerators and Beams. - : American Physical Society. - 2469-9888. ; 21:2
  • Tidskriftsartikel (refereegranskat)abstract
    • In this paper, we demonstrate the connection between a magnetic storage ring with additional sextupole fields set so that the x and y chromaticities vanish and the maximizing of the lifetime of in-plane polarization (IPP) for a 0.97-GeV/c deuteron beam. The IPP magnitude was measured by continuously monitoring the down-up scattering asymmetry (sensitive to sideways polarization) in an in-beam, carbontarget polarimeter and unfolding the precession of the IPP due to the magnetic anomaly of the deuteron. The optimum operating conditions for a long IPP lifetime were made by scanning the field of the storage ring sextupole magnet families while observing the rate of IPP loss during storage of the beam. The beam was bunched and electron cooled. The IPP losses appear to arise from the change of the orbit circumference, and consequently the particle speed and spin tune, due to the transverse betatron oscillations of individual particles in the beam. The effects of these changes are canceled by an appropriate sextupole field setting.
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6.
  • Hempelmann, N., et al. (författare)
  • Locking the Spin Precession in a Storage Ring
  • 2017
  • Ingår i: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 119:1
  • Tidskriftsartikel (refereegranskat)abstract
    • This Letter reports the successful use of feedback from a spin polarization measurement to the revolution frequency of a 0.97 GeV= c bunched and polarized deuteron beam in the Cooler Synchrotron (COSY) storage ring in order to control both the precession rate (approximate to 121 kHz) and the phase of the horizontal polarization component. Real time synchronization with a radio frequency (rf) solenoid made possible the rotation of the polarization out of the horizontal plane, yielding a demonstration of the feedback method to manipulate the polarization. In particular, the rotation rate shows a sinusoidal function of the horizontal polarization phase (relative to the rf solenoid), which was controlled to within a 1 standard deviation range of sigma= 0.21 rad. The minimum possible adjustment was 3.7 mHz out of a revolution frequency of 753 kHz, which changes the precession rate by 26 mrad/s. Such a capability meets a requirement for the use of storage rings to look for an intrinsic electric dipole moment of charged particles.
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7.
  • Hempelmann, N., et al. (författare)
  • Phase measurement for driven spin oscillations in a storage ring
  • 2018
  • Ingår i: Physical Review Accelerators and Beams. - : American Physical Society. - 2469-9888. ; 21:4
  • Tidskriftsartikel (refereegranskat)abstract
    • This paper reports the first simultaneous measurement of the horizontal and vertical components of the polarization vector in a storage ring under the influence of a radio frequency (rf) solenoid. The experiments were performed at the Cooler Synchrotron COSY in Julich using a vector polarized, bunched 0.97 GeV/c deuteron beam. Using the new spin feedback system, we set the initial phase difference between the solenoid field and the precession of the polarization vector to a predefined value. The feedback system was then switched off, allowing the phase difference to change over time, and the solenoid was switched on to rotate the polarization vector. We observed an oscillation of the vertical polarization component and the phase difference. The oscillations can be described using an analytical model. The results of this experiment also apply to other rf devices with horizontal magnetic fields, such as Wien filters. The precise manipulation of particle spins in storage rings is a prerequisite for measuring the electric dipole moment (EDM) of charged particles.
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8.
  • Saleev, A., et al. (författare)
  • Spin tune mapping as a novel tool to probe the spin dynamics in storage rings
  • 2017
  • Ingår i: Physical Review Accelerators and Beams. - : American Physical Society. - 2469-9888. ; 20:7
  • Tidskriftsartikel (refereegranskat)abstract
    • Precision experiments, such as the search for electric dipole moments of charged particles using storage rings, demand for an understanding of the spin dynamics with unprecedented accuracy. The ultimate aim is to measure the electric dipole moments with a sensitivity up to 15 orders in magnitude better than the magnetic dipole moment of the stored particles. This formidable task requires an understanding of the background to the signal of the electric dipole from rotations of the spins in the spurious magnetic fields of a storage ring. One of the observables, especially sensitive to the imperfection magnetic fields in the ring is the angular orientation of stable spin axis. Up to now, the stable spin axis has never been determined experimentally, and in addition, the JEDI collaboration for the first time succeeded to quantify the background signals that stem from false rotations of the magnetic dipole moments in the horizontal and longitudinal imperfection magnetic fields of the storage ring. To this end, we developed a new method based on the spin tune response of a machine to artificially applied longitudinal magnetic fields. This novel technique, called spin tune mapping, emerges as a very powerful tool to probe the spin dynamics in storage rings. The technique was experimentally tested in 2014 using polarized deuterons stored in the cooler synchrotron COSY, and for the first time, the angular orientation of the stable spin axis at two different locations in the ring has been determined to an unprecedented accuracy of better than 2.8 mu rad.
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9.
  • Schönning, Karin, et al. (författare)
  • Production of the omega meson in the pd -> He-3 omega reaction at 1450 MeV and 1360 MeV
  • 2009
  • Ingår i: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 79:4, s. 044002-
  • Tidskriftsartikel (refereegranskat)abstract
    • The production of omega mesons in the pd -> He-3 omega reaction has been studied at two energies near the kinematic threshold, T-p = 1450 MeV and T-p = 1360 MeV. The differential cross section was measured as a function of the omega c.m. angle at both energies over the whole angular range. Whereas the results at 1360 MeV are consistent with isotropy, strong rises are observed near both the forward and backward directions at 1450 MeV. Calculations made using a two-step model with an intermediate pion fail to reproduce the shapes of the measured angular distributions and also underestimate the total cross sections.
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10.
  • Lenisa, P., et al. (författare)
  • Low-energy spin-physics experiments with polarized beams and targets at the COSY storage ring
  • 2019
  • Ingår i: EPJ TECHNIQUES AND INSTRUMENTATION. - : Springer. - 2195-7045. ; 6:1
  • Tidskriftsartikel (refereegranskat)abstract
    • A low-energy spin-physics program is being developed at the COSY storage ring. To support the planned experimental activities, several experimental tools for polarized beams and targets have been developed. The paper presents the physics case and the readiness of the setup for its realization.
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11.
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12.
  • Andersson, Gabriella, et al. (författare)
  • Kvinnor i fysik
  • 2004
  • Ingår i: KOSMOS.
  • Tidskriftsartikel (populärvet., debatt m.m.)
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13.
  • Bagdasarian, Z., et al. (författare)
  • Measuring the polarization of a rapidly precessing deuteron beam
  • 2014
  • Ingår i: Physical Review Special Topics - Accelerators and Beams. - 1098-4402. ; 17:5, s. 052803-
  • Tidskriftsartikel (refereegranskat)abstract
    • This paper describes a time-marking system that enables a measurement of the in-plane (horizontal) polarization of a 0.97-GeV/c deuteron beam circulating in the Cooler Synchrotron (COSY) at the Forschungszentrum Julich. The clock time of each polarimeter event is used to unfold the 120-kHz spin precession and assign events to bins according to the direction of the horizontal polarization. After accumulation for one or more seconds, the down-up scattering asymmetry can be calculated for each direction and matched to a sinusoidal function whose magnitude is proportional to the horizontal polarization. This requires prior knowledge of the spin tune or polarization precession rate. An initial estimate is refined by resorting the events as the spin tune is adjusted across a narrow range and searching for the maximum polarization magnitude. The result is biased toward polarization values that are too large, in part because of statistical fluctuations but also because sinusoidal fits to even random data will produce sizable magnitudes when the phase is left free to vary. An analysis procedure is described that matches the time dependence of the horizontal polarization to templates based on emittance-driven polarization loss while correcting for the positive bias. This information will be used to study ways to extend the horizontal polarization lifetime by correcting spin tune spread using ring sextupole fields and thereby to support the feasibility of searching for an intrinsic electric dipole moment using polarized beams in a storage ring. This paper is a combined effort of the Storage Ring EDM collaboration and the JEDI collaboration.
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14.
  • Bargholtz, Chr., et al. (författare)
  • Measurement of the eta -> pi(+)pi(-)e(+)e(-) decay branching ratio
  • 2007
  • Ingår i: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 644:5-6, s. 299-303
  • Tidskriftsartikel (refereegranskat)abstract
    • The reaction pd -> He-3 eta at threshold was used to provide a clean source of eta mesons for decay studies with the WASA detector at CELSIUS. The branching ratio of the decay eta -> pi(+)pi(-)e(+)e(-) is measured to be (4.3 +/- 1.3 +/- 0.4) x 10(-4).
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15.
  • Bashkanov, M., et al. (författare)
  • Double-Pionic Fusion of Nuclear Systems and the "ABC" Effect : Approaching a Puzzle by Exclusive and Kinematically Complete Measurements
  • 2009
  • Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 102:5, s. 052301-
  • Tidskriftsartikel (refereegranskat)abstract
    • The ABC effect-a puzzling low-mass enhancement in the pi pi invariant mass spectrum, first observed by Abashian, Booth, and Crowe-is well known from inclusive measurements of two-pion production in nuclear fusion reactions. Here we report on the first exclusive and kinematically complete measurements of the most basic double-pionic fusion reaction pn -> d pi(0)pi(0) at beam energies of 1.03 and 1.35 GeV. The measurements, which have been carried out at CELSIUS-WASA, reveal the ABC effect to be a (pi pi)(I=L=0) channel phenomenon associated with both a resonancelike energy dependence in the integral cross section and the formation of a Delta Delta system in the intermediate state. A corresponding simple s-channel resonance ansatz provides a surprisingly good description of the data.
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16.
  • Daehnick, W.W, et al. (författare)
  • Spin correlations in polarized p polarized p -> p n pi+ production near threshold
  • 2002
  • Ingår i: Physical Review C. Nuclear Physics. - : American Physical Society. - 0556-2813 .- 1089-490X. ; 65, s. 024003-1
  • Tidskriftsartikel (refereegranskat)abstract
    • A first measurement of longitudinell as well as transverse spin correlation coefficients for the reaction pp->pn pi+ is made using a polarized proton target and a polarized proton beam. We report kinematically complete measurements for this reaction at 32
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17.
  • Keleta, S, et al. (författare)
  • Exclusive measurement of two-pion production in the dd -> He-4 pi pi reaction
  • 2009
  • Ingår i: Nuclear Physics A. - : Elsevier BV. - 0375-9474 .- 1873-1554. ; 825:1-2, s. 71-90
  • Tidskriftsartikel (refereegranskat)abstract
    • The results from the first kinematically complete measurement of the dd -> He-4 pi pi reaction are reported. The aim was to investigate a long standing puzzle regarding the origin of the peculiar pi pi-invariant mass distributions appearing in double pion production in light ion collisions, the so-called ABC effect. The measurements were performed at the incident deuteron energies of 712 MeV and 1029 MeV. with the WASA detector assembly at CELSIUS in Uppsala, Sweden. We report the observation of a characteristic enhancement at low pi pi-invariant mass at 712 MeV, the lowest energy yet. At the higher energy, in addition to confirming previous experimental observations, Our results reveal a strong angular dependence of the pions in the overall centre of mass system. The results are qualitatively reproduced by a theoretical model, according to which the ABC effect is described as resulting from a kinematical enhancement in the production of the pion pairs from two parallel and independent NN -> d pi sub-processes. (C) 2009 Elsevier B.V. All rights reserved.
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18.
  • Kren, F., et al. (författare)
  • Exclusive measurements of pp -> d pi(+)pi(0) : Double-pionic fusion without ABC effect
  • 2010
  • Ingår i: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 684:2-3, s. 110-113
  • Tidskriftsartikel (refereegranskat)abstract
    • Exclusive measurements of the reaction pp -> d pi(+)pi(0) have been carried out at T-p = 1.1 GeV at the CELSIUS storage ring using the WASA detector. The isovector pi(+)pi(0) channel exhibits no enhancement at low invariant pi pi masses, i.e. no ABC effect. Therefore this most basic isovector double-pionic fusion reaction qualifies as an ideal test case for the conventional t-channel Delta Delta excitation process. Indeed, the obtained differential distributions reveal the conventional t-channel Delta Delta mechanism as the appropriate reaction process, which also accounts for the observed energy dependence of the total cross section.
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19.
  • Kren, F., et al. (författare)
  • THE pp -> d pi(+)pi(0) REACTION - A CASE OF Delta Delta EXCITATION WITHOUT ABC-EFFECT
  • 2009
  • Ingår i: International Journal of Modern Physics A. - 0217-751X .- 1793-656X. ; 24:2-3, s. 561-563
  • Tidskriftsartikel (refereegranskat)abstract
    • The ABC effect, a low-mass enhancement in the invariant pp mass, is observed in double-pionic fusion reactions leading to a bound nuclear system in the final state. From previous measurements there have been indications that this phenomenon is resctricted to the sigma channel of the pp system. With exclusive measurements of the pp -> d pi(+)pi(0) reaction at T-p = 1.1 GeV we demonstrate that, indeed, the ABC effect does not occur in the vector-isovector Delta Delta channel (rho channel) despite the fact that the Delta Delta excitation is oberved to be the dominant reaction process. We also show that this reaction is well described by a t-channel Delta Delta excitation with the subsequent decay into the vector-isovector Delta Delta channel given by the rho channel operator.
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20.
  • Meyer, H.O, et al. (författare)
  • Complete set of polarization observables in (pol)p(pol)p->pp pi0 clos to threshold
  • 2001
  • Ingår i: Phys. Rev. C. - : The American Physical Society. ; 63:6, s. 064002-1
  • Tidskriftsartikel (refereegranskat)abstract
    • In a kinematically complete experiment we have measured the two analyzing powers and the five spin correlation coefficients of the reaction (pol)p pol(p) -> p p pi0 as a function of all five parameters of the three-body final state for bombarding energies
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21.
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22.
  • Schonning, K., et al. (författare)
  • The pd -> He-3 eta pi(0) reaction at T-p=1450 MeV CELSIUS/WASA Collaboration
  • 2010
  • Ingår i: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 685:1, s. 33-37
  • Tidskriftsartikel (refereegranskat)abstract
    • The cross section for the pd -> He-3 eta pi(0) reaction has been measured at a beam energy of 1450 MeV using the WASA detector at the CELSIUS storage ring. The He-3 was detected in coincidence with four photons from the decays of the two mesons. The data indicate that the production mechanism involves the formation of the Delta(1232) isobar. Although the beam energy does not allow the full peak of this resonance to be seen, the invariant mass distributions Of all three pairs of final particles are well reproduced by a phase space Monte Carlo simulation weighted with the p-wave factor of the square of the pi(0) momentum in the He-3 pi(0) system.
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23.
  • Schönning, Karin, et al. (författare)
  • Production of eta and 3 pi mesons in the pd -> (HeX)-He-3 reaction at 1360 and 1450 MeV
  • 2010
  • Ingår i: European Physical Journal A. - : Springer Science and Business Media LLC. - 1434-6001 .- 1434-601X. ; 45:1, s. 11-21
  • Tidskriftsartikel (refereegranskat)abstract
    • The cross-sections of the pd -> He-3 eta, pd -> He-3 pi(0)pi(0)pi(0) and pd -> He-3 pi(+)pi(-)pi(0) reactions have been measured at the beam kinetic energies T-p = 1360 MeV and T-p = 1450 MeV using the CELSIUS/WASA detector setup. At both energies, the differential cross-section d sigma/d Omega of the eta meson in the pd -> He-3 eta reaction shows a strong forward-backward asymmetry in the CMS. The ratio between the pd -> He-3 pi(+)pi(-)pi(0) and pd -> He-3 pi(0)pi(0)pi(0) cross-sections has been analysed in terms of isospin amplitudes. The reconstructed invariant-mass distributions of the pi pi, He-3 pi and (3)He2 pi systems provide hints on the role of nucleon resonances in the 3 pi production process.
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24.
  • Schönning, Karin, et al. (författare)
  • The pd →3Heηπ0 reaction at Tp = 1450 MeV
  • 2010
  • Ingår i: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 685:1, s. 33-37
  • Tidskriftsartikel (refereegranskat)abstract
    • The cross section for the pd→3Heηπ0 reaction has been measured at a beam energy of 1450 MeV using the WASA detector at the CELSIUS storage ring and detecting one 3He and four photons from the decays of the two mesons. The data indicate that the production mechanism involves the formation of the Δ(1232) isobar. Although the beam energy does not allow the full peak of this resonance to be seen, the invariant masses of all three pairs of final particles are well reproduce dby a phase space Monte Carlo simulation weighted with the p-wave factor of the square of the π0 momentum in the 3He π0 system.
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25.
  • Thörngren Engblom, Pia, et al. (författare)
  • Experimental search for evidence of the three-nucleon force and a new analysis method
  • 2004
  • Ingår i: FEW-BODY PROBLEMS IN PHYSICS. - : AIP. - 0735402531 ; , s. 65-68
  • Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
    • A research program with the aim of investigating the spin dependence of the three-nucleon continuum in pd collisions at intermediate energies was carried out at IUCF using the Polarized INternal Target EXperiments (PINTEX) facility. In the elastic scattering experiment at 135 and 200 MeV proton beam energies a total of 15 independent spin observables were obtained. The breakup experiment was done with a vector and tensor polarized beam of 270 MeV and an internal polarized hydrogen gas target. We developed a novel technique for the analysis of the breakup observables, the sampling method. The new approach takes into account acceptance and non-uniformities of detection efficiencies and is suitable for any kinematically complete experiment with three particles in the final state.
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26.
  • Thörngren Engblom, Pia, et al. (författare)
  • Extensive high-precision studies of proton deuteron breakup reactions at COSY
  • 2011
  • Ingår i: Proceedings of Science. - : Sissa Medialab Srl.
  • Konferensbidrag (refereegranskat)abstract
    • We plan to measure the spin dependence of proton deuteron breakup at 30 and 49 MeV proton beam energy where previous measurements are few and limited. The physics objective is to test the predictive power of the chiral effective field theory in the three nucleon continuum by measuring analyzing powers and double spin observables with high precision over large areas of phase space at relevant energies for the theoretical interpretation. The experiment will be done at a newly installed and commissioned low-b section and interaction point in the COSY ring utilizing the PAX Multipurpose Detection System that is presently in the design stage. 
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27.
  • v. Przewoski, B., et al. (författare)
  • Analyzing powers and spin correlation coefficients for p+d elastic scattering at 135 and 200 MeV
  • 2006
  • Ingår i: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 74:6
  • Tidskriftsartikel (refereegranskat)abstract
    • The proton and deuteron analyzing powers and ten of the possible 12 spin correlation coefficients have been measured for p+d elastic scattering at proton bombarding energies of 135 and 200 MeV. The results are compared with Faddeev calculations using two different NN potentials. The qualitative features of the extensive data set on the spin dependence in p+d elastic scattering over a wide range of angles presented here are remarkably well explained by two-nucleon force predictions without inclusion of a three-nucleon force. The remaining discrepancies are, in general, not alleviated when theoretical three-nucleon forces are included in the calculations.
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