First observation of long-lived $\pi^+ \pi^-$ atoms

Adeva, B; Tauscher, L; Prusa, P; Gugiu, M; Hansroul, M; Iwashita, Y; Dumitriu, D; Gorin, A; Nemenov, L; Kuptsov, A; Smolik, J; Kulikov, A; Pentia, M; Sidorov, A; Afanasyev, L; Zrelov, P; Hons, Z; Lednicky, R; Takeutchi, F; Horikawa, S; Rappazzo, G; Schacher, J; Trusov, S; Saborido, J; Karpukhin, V; Kruglova, L; Benelli, A; Chliapnikov, P; Lamberto, A; Gorchakov, O; Nikitin, M; Fluerasu, D; Olchevskii, V; Kruglov, V; Ryazantsev, A; Brekhovskikh, V; Anania, A; Marinas, C; Doskarova, P; Martincik, J; Zhabitsky, M; Chiba, M; Cechak, T; Kluson, J; Gritsay, K; Penzo, A; Yazkov, V; Romero Vidal, A; Guaraldo, C; Kulish, E; Vrba, T; Aogaki, S; Dudarev, A; Yoshimura, Y; Drijard, D; Plo, M; Ovsiannikov, V; Kobayashi, M; Rykalin, V; Lanaro, A; Trojek, T; Duma, M; Urban, T; Okada, K

doi:10.1016/j.physletb.2015.09.060

Article
Report number	arXiv:1508.04712 ; CERN-PH-EP-2015-175 ; DIRAC-PUB-2015-02 ; CERN-PH-EP-2015-175
Title	First observation of long-lived $\pi^+ \pi^-$ atoms
Author(s)	Adeva, B (U. Santiago de Compostela (main)) ; Afanasyev, L (Dubna, JINR) ; Anania, A (INFN, Trieste ; U. Messina (main)) ; Aogaki, S (Bucharest, IFIN-HH) ; Benelli, A (CTU, Prague) ; Brekhovskikh, V (Serpukhov, IHEP) ; Cechak, T (CTU, Prague) ; Chiba, M (Tokyo Metropolitan U. (main)) ; Chliapnikov, P (Serpukhov, IHEP) ; Doskarova, P (CTU, Prague) ; Drijard, D (CERN) ; Dudarev, A (Dubna, JINR) ; Duma, M (Bucharest, IFIN-HH) ; Dumitriu, D (Bucharest, IFIN-HH) ; Fluerasu, D (Bucharest, IFIN-HH) ; Gorin, A (Serpukhov, IHEP) ; Gorchakov, O (Dubna, JINR) ; Gritsay, K (Dubna, JINR) ; Guaraldo, C (Frascati) ; Gugiu, M (Bucharest, IFIN-HH) ; Hansroul, M (CERN) ; Hons, Z (Rez, Nucl. Phys. Inst.) ; Horikawa, S (U. Zurich (main)) ; Iwashita, Y (Kyoto U. (main)) ; Karpukhin, V (Dubna, JINR) ; Kluson, J (CTU, Prague) ; Kobayashi, M (KEK, Tsukuba) ; Kruglov, V (Dubna, JINR) ; Kruglova, L (Dubna, JINR) ; Kulikov, A (Dubna, JINR) ; Kulish, E (Dubna, JINR) ; Kuptsov, A (Dubna, JINR) ; Lamberto, A (INFN, Trieste ; U. Messina (main)) ; Lanaro, A (U. Wisconsin, Madison (main)) ; Lednicky, R (Prague, Inst. Phys.) ; Marinas, C (U. Santiago de Compostela (main)) ; Martincik, J (CTU, Prague) ; Nemenov, L (Dubna, JINR ; CERN) ; Nikitin, M (Dubna, JINR) ; Okada, K (Kyoto Sangyo U.) ; Olchevskii, V (Dubna, JINR) ; Ovsiannikov, V (Voronezh State U.) ; Pentia, M (Bucharest, IFIN-HH) ; Penzo, A (INFN, Trieste) ; Plo, M (U. Santiago de Compostela (main)) ; Prusa, P (CTU, Prague) ; Rappazzo, G (INFN, Trieste ; U. Messina (main)) ; Romero Vidal, A (U. Santiago de Compostela (main)) ; Ryazantsev, A (Serpukhov, IHEP) ; Rykalin, V (Serpukhov, IHEP) ; Saborido, J (U. Santiago de Compostela (main)) ; Schacher, J (Bern U., LHEP) ; Sidorov, A (Serpukhov, IHEP) ; Smolik, J (CTU, Prague) ; Takeutchi, F (Kyoto Sangyo U.) ; Tauscher, L (Basel U. (main)) ; Trojek, T (CTU, Prague) ; Trusov, S (SINP, Moscow) ; Urban, T (CTU, Prague) ; Vrba, T (CTU, Prague) ; Yazkov, V (SINP, Moscow) ; Yoshimura, Y (KEK, Tsukuba) ; Zhabitsky, M (Dubna, JINR) ; Zrelov, P (Dubna, JINR)
Publication	2015-09-26
Imprint	30 Jun 2015
Number of pages	13
Note	13 pages, 7 figures
In:	Phys. Lett. B 751 (2015) 12-18
DOI	10.1016/j.physletb.2015.09.060
Subject category	Detectors and Experimental Techniques ; Nuclear Physics - Experiment ; Particle Physics - Experiment
Accelerator/Facility, Experiment	CERN PS ; DIRAC PS212
Free keywords	QCD ; lifetime ; experimental results
Abstract	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. This observation opens a new possibility to measure energy differences between $p$ and $s$ atomic states and so to determine $\pi \pi$ scattering lengths.
Copyright/License	preprint: © 2015-2024 CERN (License: arXiv nonexclusive-distrib. 1.0) publication: © 2015-2024 CERN (License: CC-BY-4.0), sponsored by SCOAP³

$Method to observe long-lived $A_{2\pi}^L$ by means of a breakup foil (Pt).$ $General view of the DIRAC setup: 1 -- target station with insertion, showing the Be target, magnetic field and Pt breakup foil; 2 -- first shielding; 3 -- microdrift chambers (MDC); 4 -- scintillating fiber detector (SFD); 5 -- ionisation hodoscope (IH); 6 -- second shielding; 7 -- vacuum tube; 8 -- spectrometer magnet; 9 -- vacuum chamber; 10 -- drift chambers (DC); 11 -- vertical hodoscope (VH); 12 -- horizontal hodoscope (HH); 13 -- aerogel Cherenkov; 14 -- heavy gas Cherenkov; 15 -- nitrogen Cherenkov; 16 -- preshower (PSh); 17 -- muon detector. (The plotted symmetric and asymmetric events are a $\pi \pi$ and $\pi K$ pair, respectively.)$