arXiv subjects

W. Eyrich

Publications and source records attributed to W. Eyrich.

100 records · Page 6Linked to original sources

arXiv2004

Evidence for a narrow resonance at 1530 MeV/c2 in the K0 p - system of the reaction pp --> Sigma+ K0 p from the COSY-TOF experiment

The hadronic reaction pp --> Sigma+ K0 p was measured exclusively at a beam momentum of 2.95 GeV/c using the TOF detector at the COSY storage ring. A narrow peak was observed in the invariant mass spectrum of the K0 p subsystem at 1530 +- 5 MeV/c2 with a significance of 4 - 6 standard deviations, depending on background assumptions. The upper limit of 18 +- 4 MeV/c2 (FWHM) for its width is given by the experimental resolution. The corresponding total cross section is estimated to be about 0.4 +- 0.1(stat) +- 0.1(syst) microbarn. Since a resonance in this subsystem must have strangeness S = + 1 we claim it to be the Theta+ state for which very recently evidence was found in various experiments.

hep-ex↗

arXiv2004

How to measure the parity of the $Θ^+$ in $\vec p\vec p$ collisions

Triggered by a recent paper by Thomas, Hicks and Hosaka, we investigate which observables can be used to determine the parity of the $Θ^+$ from the reaction $\vec p\vec p \to Σ^+Θ^+$ near its production threshold. In particular, we show that the sign of the spin correlation coefficient $A_{xx}$ for small excess energies yields the negative of the parity of the $Θ^+$. The argument relies solely on the Pauli principle and parity conservation and is therefore model--independent.

hep-ph↗

arXiv2002

Measurement of Spin Transfer Observables in Antiproton-Proton -> Antilambda-Lambda at 1.637 GeV/c

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.

nucl-ex↗

arXiv2001

Measurement of the $\overline{p}p \to K_S K_S η$ cross section at beam momenta in the regions of 1.45 and 1.7 GeV/c

The PS185 experiment at LEAR/CERN has investigated strangeness production in antiproton-proton collisions with final states such as $\overlineΛ Λ$, $\overlineΣ^0 Λ+ c.c$, $\overline{Σ^+} Σ^+$, $\overline{Σ^-} Σ^-$ and $K_S K_S$. Results are presented from a study of about 32,000 {$K_S K_S X$} events obtained at several antiproton momenta in the regions of 1.45 and 1.7 GeV/c. The $\overline{p} p \to K_S K_S η$ cross sections extracted at these momenta constitute the first measurement of this reaction in flight and are broadly consistent with expectations of a phase-space extrapolation of branching ratios from annihilation at rest.

hep-ex↗

arXiv1998

Comparison of Lambda and Sigma(0) Threshold Production in Proton-Proton Collisions

Threshold measurements of the associated strangeness production reactions pp --> p K(+) Lambda and pp --> p K(+) Sigma(0) are presented. Although slight differences in the shapes of the excitation functions are observed, the most remarkable feature of the data is that at the same excess energy the total cross section for the Sigma(0) production appears to be about a factor of 28 smaller than the one for the Lambda particle. It is concluded that strong Sigma(0)-p final state interactions, and in particular the Sigma-N --> Lambda-p conversion reaction, are the likely cause of the depletion for the yield in the Sigma signal. This hypothesis is in line with other experimental evidence in the literature.

nucl-ex↗

arXiv1998

Total Cross Section of the Reaction pp \to pK^+ΛClose to Threshold

The energy dependence of the total cross section for the pp \to pK^+Λreaction was measured in the threshold region covering the excess energy range up to 7MeV. Existing model calculations describe the slope of the measured cross sections well, but are too low by a factor of two to three in rate. The data were used for a precise determination of the beam momentum of the COSY-synchrotron.

nucl-ex↗

arXiv1998

Study of the reaction pbar p -> phi phi from 1.1 to 2.0 GeV/c

A study has been performed of the reaction pbar p -> 4K using in-flight antiprotons from 1.1 to 2.0 GeV/c incident momentum interacting with a hydrogen jet target. The reaction is dominated by the production of a pair of phi mesons. The pbar p -> phi phi cross section rises sharply above threshold and then falls continuously as a function of increasing antiproton momentum. The overall magnitude of the cross section exceeds expectations from a simple application of the OZI rule by two orders of magnitude. In a fine scan around the xi/f_J(2230) resonance, no structure is observed. A limit is set for the double branching ratio B(xi -> pbar p) * B(xi -> phi phi) < 6e-5 for a spin 2 resonance of M = 2.235 GeV and Width = 15 MeV.

hep-ex↗

arXiv1998

Search for narrow pbar p resonances in the reaction pbar p>pbar p pi+pi-

The reaction pbar p -> pbar p pi+ pi- has been studied with high statistics at CERN-LEAR with incident pbar momenta from 1.65 to 2.0 GeV/c by the JETSET (PS202) experiment. The aim of this paper is to search for narrow resonances decaying to pbar p. No evidence for such structures is found. In particular, an upper limit for the production of a 2.02 GeV state with a width of Gamma = 20 MeV, having been seen in other hadroproduction experiments, is established. Our results restrict the cross section for such a peak to be below 200 nb at the 95% confidence level.

hep-ex↗

arXiv1997

Measurement of the pbar p -> Ks Ks Reaction from 0.6 to 1.9 GeV/c

The pbar p -> Ks Ks -> 4pi+/- cross section was measured at incident antiproton momenta between 0.6 and 1.9 GeV/c using the CERN Low Energy Antiproton Ring (LEAR). This investigation was part of a systematic study of in-flight antiproton-proton annihilations into two-neutral-meson final states in a search for hadronic resonances. A coarse scan of the pbar p -> Ks Ks cross section as a function of center-of-mass energy between 1.964 and 2.395 GeV/c^2 and a fine scan of the region surrounding the Xi(2220) are presented. Upper limits on the product branching ratio BR(Xi -> pbar p)BR(Xi -> Ks Ks) are determined for a wide range of mass and width assumptions based on the non-observation of the Xi(2220). A rise in the pbar p -> Ks Ks cross section is observed near 2.15 GeV/c^2, which is consistent with the f2(2150) resonance.

hep-ex↗

arXiv1995

Analysis of data on low energy piN-->pipiN reaction. I. Total cross sections

This is the first of a series of papers on a consistent model independent analysis of the complete experimental information on the reaction $πN \rightarrow ππN$ at pion momenta up to 500 MeV/c. The paper summarizes the theoretical approach and details of the computational procedure. The complete database on total cross sections in 5 $ππN$ channels is given together with a critical discussion of their model independent analysis.

hep-ph↗