13 research outputs found

    First πK\pi K atom lifetime and πK\pi K scattering length measurements

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    The results of a search for hydrogen-like atoms consisting of πK±\pi^{\mp}K^{\pm} mesons are presented. Evidence for πK\pi K atom production by 24 GeV/c protons from CERN PS interacting with a nickel target has been seen in terms of characteristic πK\pi K pairs from their breakup in the same target (178±49178 \pm 49) and from Coulomb final state interaction (653±42653 \pm 42). Using these results the analysis yields a first value for the πK\pi K atom lifetime of τ=(2.51.8+3.0)\tau=(2.5_{-1.8}^{+3.0}) fs and a first model-independent measurement of the S-wave isospin-odd πK\pi K scattering length a0=13a1/2a3/2=(0.110.04+0.09)Mπ1\left|a_0^-\right|=\frac{1}{3}\left|a_{1/2}-a_{3/2}\right|= \left(0.11_{-0.04}^{+0.09} \right)M_{\pi}^{-1} (aIa_I for isospin II).Comment: 14 pages, 8 figure

    Determination of ππ\pi\pi scattering lengths from measurement of π+π\pi^+\pi^- atom lifetime

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    The DIRAC experiment at CERN has achieved a sizeable production of π+π\pi^+\pi^- atoms and has significantly improved the precision on its lifetime determination. From a sample of 21227 atomic pairs, a 4% measurement of the S-wave ππ\pi\pi scattering length difference a0a2=(.0.25330.0078+0.0080stat.0.0073+0.0078syst)Mπ+1|a_0-a_2| = (.0.2533^{+0.0080}_{-0.0078}|_\mathrm{stat}.{}^{+0.0078}_{-0.0073}|_\mathrm{syst})M_{\pi^+}^{-1} has been attained, providing an important test of Chiral Perturbation Theory.Comment: 6 pages, 6 figure

    Ratio between proton-antiproton and pi+pi- pairs

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    Search for Long-Lived States of π+π\pi^+\pi^- Atoms : Addendum to the DIRAC Proposal

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    The proposed experiment is a further development of the DIRAC experiment already running at CERN PS. The observation of long-lived (metastable) states of π+π\pi^+\pi^- atoms (A2πA_{2\pi}) will be performed with the same setup. This observation opens a possibility to measure the energy difference between nsns and npnp states and to determine the value of the combination 2a0+a22a_0+a_2 of S-wave ππ\pi\pi scattering lengths in a model-independent way. In combination with the A2πA_{2\pi} lifetime measurement providing the value a0a2|a_0-a_2| DIRAC is in the position to get a0a_0 and a2a_2 separately on the basis of A2πA_{2\pi} data only

    First measurement of a long-lived π+π\pi^+ \pi^- atom lifetime

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    The adapted DIRAC experiment at the CERN PS accelerator observed for the first time long-lived hydrogen-like π+π\pi^+\pi^- atoms, produced by protons hitting a beryllium target. A part of these atoms crossed the gap of 96~mm and got broken up in the 2.1~\textmu{}m thick platinum foil. Analysing the observed number of atomic pairs, nAL=43661+157totn_A^L= \left.436^{+157}_{-61}\right|_\mathrm{tot}, the lifetime of the 2pp state is found to be τ2p=(0.450.30+1.08tot)1011{\tau_{2p}=(\left.0.45^{+1.08}_{-0.30}\right|_\mathrm{tot}) \cdot10^{-11}}s, not contradicting the corresponding QED 2p2p state lifetime τ2pQED=1.171011{\tau_{2p}^\mathrm{QED}=1.17 \cdot 10^{-11}}s. This lifetime value is three orders of magnitude larger than our previously measured value of the π+π\pi^+\pi^- atom ground state lifetime τ=(3.150.26+0.28tot)1015\tau=(\left.3.15^{+0.28}_{-0.26}\right|_\mathrm{tot})\cdot 10^{-15}s. Further studies of long-lived π+π\pi^+\pi^- atoms will allow to measure energy differences between pp and ss atomic states and so to determine ππ\pi\pi scattering lengths with the aim to check QCD predictions.The adapted DIRAC experiment at the CERN PS accelerator observed for the first time long-lived hydrogenlike π+π- atoms, produced by protons hitting a beryllium target. A part of these atoms crossed the gap of 96 mm between the target and a 2.1  μm thick platinum foil, in which most of them dissociated. Analyzing the observed number of atomic pairs, nAL=436-61+157|tot, the lifetime of the 2p state is found to be τ2p=(0.45-0.30+1.08|tot)×10-11  s, not contradicting the corresponding QED 2p state lifetime τ2pQED=1.17×10-11  s. This lifetime value is three orders of magnitude larger than our previously measured value of the π+π- atom ground state lifetime τ=(3.15-0.26+0.28|tot)×10-15  s. Further studies of long-lived π+π- atoms will allow us to measure energy differences between p and s atomic states and so to discriminate between the isoscalar and isotensor ππ scattering lengths with the aim to check QCD predictions.The adapted DIRAC experiment at the CERN PS accelerator observed for the first time long-lived hydrogen-like π+π\pi^+\pi^- atoms, produced by protons hitting a beryllium target. A part of these atoms crossed the gap of 96~mm and got broken up in the 2.1~\textmu{}m thick platinum foil. Analysing the observed number of atomic pairs, nAL=43661+157totn_A^L= \left.436^{+157}_{-61}\right|_\mathrm{tot}, the lifetime of the 2pp state is found to be τ2p=(0.450.30+1.08tot)1011{\tau_{2p}=(\left.0.45^{+1.08}_{-0.30}\right|_\mathrm{tot}) \cdot10^{-11}}s, not contradicting the corresponding QED 2p2p state lifetime τ2pQED=1.171011{\tau_{2p}^\mathrm{QED}=1.17 \cdot 10^{-11}}s. This lifetime value is three orders of magnitude larger than our previously measured value of the π+π\pi^+\pi^- atom ground state lifetime τ=(3.150.26+0.28tot)1015\tau=(\left.3.15^{+0.28}_{-0.26}\right|_\mathrm{tot})\cdot 10^{-15}s. Further studies of long-lived π+π\pi^+\pi^- atoms will allow to measure energy differences between pp and ss atomic states and so to determine ππ\pi\pi scattering lengths with the aim to check QCD predictions

    First observation of long-lived π+π− atoms

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    After observing and investigating the double-exotic (a double-exotic atom is a bound system, in which both oppositely charged components are unstable particles like μ,π,K,…) π+π− atom with the ground state lifetime τ of about 3×10−15 s, the upgraded DIRAC experiment at the CERN PS accelerator observes for the first time long-lived states of the same atom with lifetimes of about 10−11 s and more. The number of characteristic pion pairs resulting from the breakup (ionisation) of long-lived π+π− atoms amounts to 436±61, corresponding to a signal-to-error ratio of better than 7 standard deviations. This observation opens a new possibility to measure energy differences between p and s atomic states and so to determine ππ scattering lengths

    Observation of πK+\pi^- K^+ and π+K\pi^+ K^- atoms

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    The observation of hydrogen-like πK\pi K atoms, consisting of πK+\pi^- K^+ or π+K\pi^+ K^- mesons, is presented. The atoms have been produced by 24 GeV/cc protons from the CERN PS accelerator, interacting with platinum or nickel foil targets. The breakup (ionisation) of πK\pi K atoms in the same targets yields characteristic πK\pi K pairs, called ``atomic pairs'', with small relative momenta in the pair centre-of-mass system. The upgraded DIRAC experiment has observed 349±62349\pm62 such atomic πK\pi K pairs, corresponding to a signal of 5.6 standard deviations
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