Formation of η\eta-mesic Nuclei Using the Recoilless (d,3^3He) Reaction

We propose to use the recoilless (d,$^3$He) reaction to produce $\eta$-mesic nuclei. This reaction has been used to observe deeply bound pionic states and proven to be powerful recently. We calculate $\eta$-mesic bound states in the nucleus using an optical potential and their formation cross section with the Green function method. Then, we carefully check the experimental feasibility. We find that $\eta$-mesic nuclei can be observed experimentally using the (d,$^3$He) reaction. We also mention the possibility to study the formation of $\omega$-mesic nuclei.Comment: 15 pages, 6 eps figures, Late

Extracting the depolarization coefficient D_NN from data measured with a full acceptance detector

The spin transfer from vertically polarized beam protons to Lambda or Sigma hyperons of the associated strangeness production pp -> pK Lambda (Sigma) is described with the depolarization coefficient D_NN. As the polarization of the hyperons is determined by their weak decays, detectors, which have a large acceptance for the decay particles, are needed. In this paper a formula is derived, which describes the depolarization coefficient D_NN by count rates of a 4 pi detector. It is shown, that formulas, which are given in publications for detectors with restricted acceptance, are specific cases of this formula for a 4 pi detector.Comment: Accepted for publication by Nuclear Instruments and Methods in Physics Research Section

Precision spectroscopy of pionic 1s states of Sn nuclei and evidence for partial restoration of chiral symmetry in the nuclear medium

Deeply bound 1s states of $\pi^-$ in $^{115,119,123}$Sn were preferentially observed using the Sn($d$,$^3$He) pion-transfer reaction under the recoil-free condition. The 1s binding energies and widths were precisely determined, and were used to deduce the isovector parameter of the s-wave pion-nucleus potential to be $b_1 =-0.115\pm 0.007 ~m_{\pi}^{-1}$. The observed enhancement of $|b_1|$ over the free $\pi N$ value ($b_1^{\rm free}/b_1 = 0.78 \pm 0.05$) indicates a reduction of the chiral order parameter, $f^{*}_{\pi} (\rho)^2/f_{\pi}^2 \approx 0.64$, at the normal nuclear density, $\rho = \rho_0$.Comment: 4 pages including 3 postscript figures, RevTeX 4 with multirow.sty, submitted to Physical Review Letter

High precision measurement of the associated strangeness production in proton proton interactions

A new high precision measurement of the reaction pp -> pK+Lambda at a beam momentum of 2.95 GeV/c with more than 200,000 analyzed events allows a detailed analysis of differential observables and their inter-dependencies. Correlations of the angular distributions with momenta are examined. The invariant mass distributions are compared for different regions in the Dalitz plots. The cusp structure at the N Sigma threshold is described with the Flatt\'e formalism and its variation in the Dalitz plot is analyzed.Comment: accepted for publication in Eur. Phys. J.

First Model-Independent Measurement of the Spin Triplet pΛp\Lambda Scattering Length from Final State Interaction in the p⃗p→pK+Λ\vec{p}p \rightarrow pK^{+}\Lambda Reaction

The $\vec{p}p \rightarrow pK^{+}\Lambda$ reaction has been measured with the COSY-TOF detector at a beam momentum of $2.7\,\mathrm{GeV}/c$. The polarized proton beam enables the measurement of the beam analyzing power by the asymmetry of the produced kaon ($A_N^{K}$). This observable allows the $p\Lambda$ spin triplet scattering length to be extracted for the first time model independently from the final-state interaction in the reaction. The obtained value is $a_{t} = (-2.55 ^{+0.72}_{-1.39} {}_{\textrm{stat.}} \pm 0.6_{\textrm{syst.}} \pm 0.3_{\textrm{theo.}})\mathrm{fm}$. This value is compatible with theoretical predictions and results from model-dependent analyses.Comment: Revised version as accepted for publication in PR

Single-Pion Production in pp Collisions at 0.95 GeV/c (II)

The single-pion production reactions $pp\to d\pi^+$, $pp\to np\pi^+$ and $pp\to pp\pi^0$ were measured at a beam momentum of 0.95 GeV/c ($T_p \approx$ 400 MeV) using the short version of the COSY-TOF spectrometer. The central calorimeter provided particle identification, energy determination and neutron detection in addition to time-of-flight and angle measurements from other detector parts. Thus all pion production channels were recorded with 1-4 overconstraints. Main emphasis is put on the presentation and discussion of the $np\pi^+$ channel, since the results on the other channels have already been published previously. The total and differential cross sections obtained are compared to theoretical calculations. In contrast to the $pp\pi^0$ channel we find in the $np\pi^+$ channel a strong influence of the $\Delta$ excitation already at this energy close to threshold. In particular we find a $(3 cos^2\Theta + 1)$ dependence in the pion angular distribution, typical for a pure s-channel $\Delta$ excitation and identical to that observed in the $d\pi^+$ channel. Since the latter is understood by a s-channel resonance in the $^1D_2$ $pn$ partial wave, we discuss an analogous scenario for the $pn\pi^+$ channel