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1.
The $\pi^+\pi^-$ Coulomb interaction study and its use in the data processing / Adeva, B. (Santiago de Compostela U.) ; Afanasyev, L. (Dubna, JINR) ; Anania, A. (INFN, Messina) ; Aogaki, S. (Bucharest, IFIN-HH) ; Benelli, A. (Prague, Tech. U.) ; Brekhovskikh, V. (Serpukhov, IHEP) ; Cechak, T. (Prague, Tech. U.) ; Chiba, M. (Tokyo Metropolitan U.) ; Chliapnikov, P. (Serpukhov, IHEP) ; Drijard, D. (Prague, Tech. U. ; CERN) et al.
In this work the Coulomb effects (Coulomb correlations) were studied using experimental $\pi^+\pi^-$ pair distributions in $Q$, the relative momentum in the pair center of mass system (c.m.s), and its projections $Q_L$ (longitudinal component) and $Q_t$ (transverse component) relative to the pair direction in the laboratory system (l.s.). The major part of the pion pairs is produced by decay of $\rho, \omega$ and $\Delta$ and other short-lived sources (Coulomb pairs). [...]
arXiv:2409.12696; CERN-EP-2023-276.- Geneva : CERN, 2024-11-01 - 11 p. - Published in : Phys. Rev. D 110 (2024) 092005 Draft (restricted): PDF; Fulltext: DIRAC-Coulomb-correct - PDF; 2409.12696 - PDF;
2.
Investigation of $K^+K^-$ pairs in the effective mass region near $2m_K$ / DIRAC Collaboration
The DIRAC experiment at CERN investigated in the reaction $\rm{p}(24~\rm{GeV}/c) + Ni$ the particle pairs $K^+K^-, \pi^+ \pi^-$ and $p \bar{p}$ with relative momentum $Q$ in the pair system less than 100 MeV/c. Because of background influence studies, DIRAC explored three subsamples of $K^+K^-$ pairs, obtained by subtracting -- using time-of-flight (TOF) technique -- background from initial $Q$ distributions with $K^+K^-$ sample fractions more than 70%, 50% and 30%. [...]
arXiv:2204.01857; CERN-EP-2022-058.- 2022-08-01 - 18 p. - Published in : Phys. Rev. D 106 (2022) 032006 Fulltext: PhysRevD.106.032006 - PDF; 2204.01857 - PDF;
3.
First measurement of a long-lived $\pi^+ \pi^-$ atom lifetime / DIRAC Collaboration
The adapted DIRAC experiment at the CERN PS accelerator observed for the first time long-lived hydrogen-like $\pi^+\pi^-$ 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. [...]
arXiv:1811.08659; CERN-EP-2018-281; DIRAC-PUB-2019-01.- Geneva : CERN, 2019-03-01 - 7 p. - Published in : Phys. Rev. Lett. 122 (2019) 082003 Article from SCOAP3: PDF; Draft (restricted): PDF; Fulltext: 1811.08659 - PDF; CERN-EP-2018-281 - PDF;
4.
Measurement of the $\pi K$ atom lifetime and the $\pi K$ scattering length / DIRAC Collaboration
After having announced the statistically significant observation (5.6~$\sigma$) of the new exotic $\pi K$ atom, the DIRAC experiment at the CERN proton synchrotron presents the measurement of the corresponding atom lifetime, based on the full $\pi K$ data sample: $\tau = (5.5^{+5.0}_{-2.8}) \cdot 10^{-15}s$. By means of a precise relation ($<1\%$) between atom lifetime and scattering length, the following value for the S-wave isospin-odd $\pi K$ scattering length $a_0^{-}~=~\frac{1}{3}(a_{1/2}-a_{3/2})$ has been derived: $\left|a_0^-\right| = (0.072^{+0.031}_{-0.020}) M_{\pi}^{-1}$..
arXiv:1707.02184; CERN-EP-2017-137; DIRAC-PUB-2017-01.- Geneva : CERN, 2017-09-19 - 18 p. - Published in : Phys. Rev. D 96 (2017) 052002 Draft (restricted): PDF; Fulltext: CERN-EP-2017-137 - PDF; arXiv:1707.02184 - PDF; Fulltext from publisher: PDF;
5.
Observation of $\pi^- K^+$ and $\pi^+ K^-$ atoms / DIRAC Collaboration
The observation of hydrogen-like $\pi K$ atoms, consisting of $\pi^- K^+$ or $\pi^+ K^-$ mesons, is presented. The atoms have been produced by 24 GeV/$c$ protons from the CERN PS accelerator, interacting with platinum or nickel foil targets. [...]
arXiv:1605.06103; CERN-EP-2016-128; DIRAC-PUB-2016-02.- Geneva : CERN, 2016-09-08 - 6 p. - Published in : Phys. Rev. Lett. 117 (2016) 112001 Draft (restricted): PDF; Fulltext: arXiv:1605.06103 - PDF; 10.1103_PhysRevLett.117.112001 - PDF; PhysRevLett.117.112001 - PDF; Preprint: PDF; External link: Fulltext
6.
First observation of long-lived $\pi^+ \pi^-$ atoms / DIRAC Collaboration
After observing and investigating the double-exotic $\pi^+\pi^-$ atom with the ground state lifetime $\tau$ of about $3 \times 10^{-15}$~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 $\pi^+\pi^-$ atoms amounts to $436\pm61$, corresponding to a signal-to-error ratio of better than 7 standard deviations. [...]
arXiv:1508.04712; CERN-PH-EP-2015-175; DIRAC-PUB-2015-02; CERN-PH-EP-2015-175.- Geneva : CERN, 2015-09-26 - 13 p. - Published in : Phys. Lett. B 751 (2015) 12-18 Article from SCOAP3: plb-751-12 - PDF; scoap3-fulltext - PDF; Fulltext: PDF; External link: Preprint
7.
Updated DIRAC spectrometer at CERN PS for the investigation of ππ and πK atoms / PS212 collaboration
The DIRAC spectrometer installed at CERN PS was redesigned and upgraded in order to study simultaneously Aππ and AπK atoms, namely the bound states of π+π–, and π+K–, π–K+ mesons. The detector system which is able to accept a high intensity beam such as 2 - 6 × 1011 primary protons per second, the electronics and the data-acquisition system adapted to handle very large amount of data actually allowed to identify successfully π, K, p, e and µ and to give the possibility to select π-π and π-K pairs in the off-line analysis. [...]
CERN-PH-EP-2015-147; DIRAC-PUB-2016-03.- Geneva : CERN, 2016 - 34 p. - Published in : Nucl. Instrum. Methods Phys. Res., A 839 (2016) 52-85 Draft (restricted): PDF; Fulltext: PDF;
8.
First $\pi K$ atom lifetime and $\pi K$ scattering length measurements / DIRAC Collaboration
The results of a search for hydrogen-like atoms consisting of $\pi^{\mp}K^{\pm}$ mesons are presented. Evidence for $\pi K$ atom production by 24 GeV/c protons from CERN PS interacting with a nickel target has been seen in terms of characteristic $\pi K$ pairs from their breakup in the same target ($178 \pm 49$) and from Coulomb final state interaction ($653 \pm 42$). [...]
arXiv:1403.0845; CERN-PH-EP-2014-030; DIRAC-PUB-2014-01; CERN-PH-EP-2014-030.- Geneva : CERN, 2014-07-30 - 7 p. - Published in : Phys. Lett. B 735 (2014) 288-294 Article from SCOAP3: PDF; Draft (restricted): PDF; Fulltext: PDF; Preprint: PDF;
9.
Search for Long-Lived States of $\pi^+\pi^-$ Atoms : Addendum to the DIRAC Proposal / DIRAC Collaboration
The proposed experiment is a further development of the DIRAC experiment already running at CERN PS. [...]
CERN-SPSC-2012-001 ; SPSC-P-284-ADD-6 ; DIRAC-DOC-2012-01.
- 2012.
Original Document (SPSC-P-284-ADD-5) - SPSC-P-284-ADD-6
10.
A permanent Magnet to search for long-lived $\pi^{+}\pi^{-}$ atoms / Aogaki, S (Kyoto Sangyo U.) ; Chiba, M (Tokyo Metropolitan U., Math. Dept.) ; Iwashita, Y (Kyoto U.) ; Kobayashi, M (KEK, Tsukuba) ; Okada, K (Kyoto Sangyo U.) ; Takeutchi, F (Kyoto Sangyo U.)
DIRAC-NOTE-2011-06.
- 2011. - 31 p.
Full text

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2 Okada, Kazushi
1 Okada, Kenichi
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1 Okada, Kensuke
1 Okada, Kiyoshi
1 Okada, Kunihiro
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