13 research outputs found
First atom lifetime and scattering length measurements
The results of a search for hydrogen-like atoms consisting of
mesons are presented. Evidence for atom production
by 24 GeV/c protons from CERN PS interacting with a nickel target has been seen
in terms of characteristic pairs from their breakup in the same target
() and from Coulomb final state interaction (). Using
these results the analysis yields a first value for the atom lifetime
of fs and a first model-independent measurement of
the S-wave isospin-odd scattering length
( for isospin ).Comment: 14 pages, 8 figure
Determination of scattering lengths from measurement of atom lifetime
The DIRAC experiment at CERN has achieved a sizeable production of
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 scattering length difference
has been attained, providing an important test of Chiral Perturbation Theory.Comment: 6 pages, 6 figure
Search for Long-Lived States of Atoms : Addendum to the DIRAC Proposal
The proposed experiment is a further development of the DIRAC experiment already running at CERN PS. The observation of long-lived (metastable) states of atoms () will be performed with the same setup. This observation opens a possibility to measure the energy difference between and states and to determine the value of the combination of S-wave scattering lengths in a model-independent way. In combination with the lifetime measurement providing the value DIRAC is in the position to get and separately on the basis of data only
First measurement of a long-lived atom lifetime
The adapted DIRAC experiment at the CERN PS accelerator observed for the first time long-lived hydrogen-like 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, , the lifetime of the 2 state is found to be s, not contradicting the corresponding QED state lifetime s. This lifetime value is three orders of magnitude larger than our previously measured value of the atom ground state lifetime s. Further studies of long-lived atoms will allow to measure energy differences between and atomic states and so to determine 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 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, , the lifetime of the 2 state is found to be s, not contradicting the corresponding QED state lifetime s. This lifetime value is three orders of magnitude larger than our previously measured value of the atom ground state lifetime s. Further studies of long-lived atoms will allow to measure energy differences between and atomic states and so to determine scattering lengths with the aim to check QCD predictions
First observation of long-lived π+π− atoms
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 and atoms
The observation of hydrogen-like atoms, consisting of or mesons, is presented. The atoms have been produced by 24 GeV/ protons from the CERN PS accelerator, interacting with platinum or nickel foil targets. The breakup (ionisation) of atoms in the same targets yields characteristic pairs, called ``atomic pairs'', with small relative momenta in the pair centre-of-mass system. The upgraded DIRAC experiment has observed such atomic pairs, corresponding to a signal of 5.6 standard deviations