100 research outputs found

    Upper limits for a narrow resonance in the reaction p + p -> K^+ + (Lambda p)

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    The reaction pp -> K^+ + (Lambda p) has been measured at T_p = 1.953 GeV and \Theta = 0 deg with a high missing mass resolution in order to study the Lambda p final state interaction. Narrow S = -1 resonances predicted by bag model calculations are not visible in the missing mass spectrum. Small structures observed in a previous experiment are not confirmed. Upper limits for the production cross section of a narrow resonance are deduced for missing masses between 2058 and 2105 MeV/c^2.Comment: 8 pages, 5 figure

    Detailed comparison of the pp -> \pi^+pn and pp -> \pi^+d reactions at 951 MeV

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    The positively charged pions produced in proton-proton collisions at a beam momentum of 1640 MeV/c were measured in the forward direction with a high resolution magnetic spectrograph. The missing mass distribution shows the bound state (deuteron) clearly separated from the pnpn continuum. Despite the very good resolution, there is no evidence for any significant production of the pnpn system in the spin-singlet state. However, the σ(ppπ+pn)/σ(ppπ+d)\sigma(pp\to \pi^+pn)/\sigma(pp\to \pi^+d) cross section ratio is about twice as large as that predicted from SS-wave final-state-interaction theory and it is suggested that this is due to DD-state effects in the pnpn system.Comment: 8 pages, 3 figure

    Cross section of the ppK+Σ+npp\to K^+\Sigma^+n reaction close to threshold

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    We have measured inclusive data on K+K^+-meson production in pppp collisions at COSY J\"ulich close to the hyperon production threshold and determined the hyperon-nucleon invariant mass spectra. The spectra were decomposed into three parts: Λp\Lambda p, Σ0p\Sigma^0p and Σ+n\Sigma^+n. The cross section for the Σ+n\Sigma^+n channel was found to be much smaller than a previous measurement in that excess energy region. The data together with previous results at higher energies are compatible with a phase space dependence.Comment: accepted by Phys. lett. B some typos correcte

    High resolution study of the Lambda p final state interaction in the reaction p + p -> K+ + (Lambda p)

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    The reaction pp -> K+ + (Lambda p) was measured at Tp=1.953 GeV and Theta = 0 deg with a high missing mass resolution in order to study the Lambda p final state interaction. The large final state enhancement near the Lambda p threshold can be described using the standard Jost-function approach. The singlet and triplet scattering lengths and effective ranges are deduced by fitting simultaneously the Lambda p invariant mass spectrum and the total cross section data of the free Lambda p scattering.Comment: submitted to Physics Letters B, 10 pages, 3 figure

    Study of the p+6\bm{p+^6}Liη+7\bm{\to\eta+^7}Be reaction 11.3 MeV above threshold

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    The cross section for the reaction p+6Liη+7Bep+^6\text{Li}\to\eta+^7\text{Be} was measured at an excess energy of 11.28 MeV above threshold by detecting the recoiling 7^7Be nuclei. A dedicated set of focal plane detectors was built for the magnetic spectrograph Big Karl and was used for identification and four momentum measurement of the 7^7Be. A differential cross section of dσdΩ=(0.69±0.20(stat.)±0.20(syst.))nb/sr\frac{d\sigma}{d\Omega}=(0.69\pm{0.20}\text{(stat.)}\pm 0.20\text{(syst.)})\text{nb/sr} for the ground state plus the 1/2^- was measured. The result is compared to model calculations.Comment: accepted by Phys. Rev. C as rapid communicatio

    A precision determination of the mass of the η\eta meson

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    Several processes of meson production in proton-deuteron collisions have been measured simultaneously using a calibrated magnetic spectrograph. Among these processes, the η\eta meson is seen clearly as a sharp missing--mass peak on a slowly varying background in the p+d3He+Xp+d\to ^3\textrm{He} +X reaction. Knowing the kinematics of the other reactions with well determined masses, it is possible to deduce a precise mass for the η\eta meson. The final result, m(η)=547.311±0.028(stat)±0.032(syst) MeV/c2m(\eta)=547.311\pm 0.028 \textrm{(stat)} \pm 0.032 \textrm{(syst) MeV/c}^2, is significantly lower than that found by the recent NA48 measurement, though it is consistent with values obtained in earlier counter experiments.Comment: 10 pages, 6 figures, Fig. 3 change

    Technical Design Report for the PANDA Solenoid and Dipole Spectrometer Magnets

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    This document is the Technical Design Report covering the two large spectrometer magnets of the PANDA detector set-up. It shows the conceptual design of the magnets and their anticipated performance. It precedes the tender and procurement of the magnets and, hence, is subject to possible modifications arising during this process.Comment: 10 pages, 14MB, accepted by FAIR STI in May 2009, editors: Inti Lehmann (chair), Andrea Bersani, Yuri Lobanov, Jost Luehning, Jerzy Smyrski, Technical Coordiantor: Lars Schmitt, Bernd Lewandowski (deputy), Spokespersons: Ulrich Wiedner, Paola Gianotti (deputy

    Search for η\eta-mesic nuclei in recoil-free transfer reaction

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    We have studied the reaction p+27Al3He+p+π+Xp+{^{27}Al}\to {^3{He}}+p+\pi^-+X at recoil-free kinematics. An η\eta meson possibly produced in this reaction would be thus almost at rest in the laboratory system and could therefore be bound with high probability, if nuclear η\eta states exist. The decay of such a state through the N(1535)N^*(1535) resonance would lead to a proton-π\pi^- pair emitted in opposite directions. For these conditions we find some indication of such a bound state. An upper limit of \approx 0.5 nb is found.Comment: 3 figure

    Cross Section and Tensor Analysing Power of the ddηα\vec{d}d\to \eta\alpha Reaction Near Threshold

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    The angular distributions of the unpolarised differential cross section and tensor analysing power AxxA_{xx} of the ddαη\vec{d}d\to\alpha \eta reaction have been measured at an excess energy of 16.6 MeV. The ambiguities in the partial-wave description of these data are made explicit by using the invariant amplitude decomposition. This allows the magnitude of the s-wave amplitude to be extracted and compared with results published at lower energies. In this way, firmer bounds could be obtained on the scattering length of the ηα\eta \alpha system. The results do not, however, unambiguously prove the existence of a quasi-bound ηα\eta \alpha state.Comment: 20 pages, 11 figure
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