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1. The \pi^+\pi^- Coulomb interaction study and its use in the data processing

Author

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

Subjects
High Energy Physics - Phenomenology, High Energy Physics - Experiment
Abstract

In this work the Coulomb effects (Coulomb correlations) in $\pi^+\pi^-$ pairs produced in p + Ni collisions at 24 GeV/$c$, are 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 $Q$, $Q_L$, and $Q_t$ distributions of the {\sl Coulomb pairs} in the c.m.s. have been simulated assuming they are described by the phase space modified by the known point-like Coulomb correlation function $A_C(Q)$, corrected for small effects due to the nonpoint-like pair production and the strong two-pion interaction. The same distributions of {\sl non-Coulomb pairs} have been simulated according to the phase space, but without $A_C(Q)$. It is shown that the number of {\sl Coulomb pairs} in all $Q_t$ intervals, including the small $Q_t$ (small opening angles $\theta$ in the l.s.) is calculated with the theoretical precision better than 2\%. The comparison of the simulated and experimental numbers of {\sl Coulomb pairs} at small $Q_t$ allows us to check and correct the detection efficiency for the pairs with small $\theta$ (0.06 mrad and smaller). It is shown that {\sl Coulomb pairs} can be used as a new physical tool to check and correct the quality of the simulated events. The special property of the {\sl Coulomb pairs} is the possibility of checking and correcting the detection efficiency, especially for the pairs with small opening angles.

Published
2024

2. Investigation of $K^+K^-$ pairs in the effective mass region near $2m_K$

Author

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

Subjects
High Energy Physics - Experiment, High Energy Physics - Phenomenology
Abstract

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\%. The corresponding pair distributions in $Q$ and in its longitudinal projection $Q_L$ were analyzed first in a Coulomb model, which takes into account only Coulomb final state interaction (FSI) and assuming point-like pair production. This Coulomb model analysis leads to a $K^+K^-$ yield increase of about four at $Q_L=0.5$ MeV/c compared to 100 MeV/c. In order to study contributions from strong interaction, a second more sophisticated model was applied, considering besides Coulomb FSI also strong FSI via the resonances $f_0(980)$ and $a_0(980)$ and a variable distance $r^*$ between the produced $K$ mesons. This analysis was based on three different parameter sets for the pair production. For the 70\% subsample and with best parameters, $3680\pm 370$ $K^+K^-$ pairs was found to be compared to $3900\pm 410$ $K^+K^-$ extracted by means of the Coulomb model. Knowing the efficiency of the TOF cut for background suppression, the total number of detected $K^+K^-$ pairs was evaluated to be around $40000\pm 10\%$, which agrees with the result from the 30\% subsample. The $K^+K^-$ pair number in the 50\% subsample differs from the two other values by about three standard deviations, confirming -- as discussed in the paper -- that experimental data in this subsample is less reliable.

Published
2022
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3. First measurement of a long-lived $\pi^+ \pi^-$ atom lifetime

Author

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

Subjects
High Energy Physics - Experiment, Nuclear Experiment
Abstract

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. Analysing the observed number of atomic pairs, $n_A^L= \left.436^{+157}_{-61}\right|_\mathrm{tot}$, the lifetime of the 2$p$ state is found to be ${\tau_{2p}=(\left.0.45^{+1.08}_{-0.30}\right|_\mathrm{tot}) \cdot10^{-11}}$s, not contradicting the corresponding QED $2p$ state lifetime ${\tau_{2p}^\mathrm{QED}=1.17 \cdot 10^{-11}}$s. This lifetime value is three orders of magnitude larger than our previously measured value of the $\pi^+\pi^-$ atom ground state lifetime $\tau=(\left.3.15^{+0.28}_{-0.26}\right|_\mathrm{tot})\cdot 10^{-15}$s. Further studies of long-lived $\pi^+\pi^-$ atoms will allow to measure energy differences between $p$ and $s$ atomic states and so to determine $\pi\pi$ scattering lengths with the aim to check QCD predictions., Comment: 7 pages, 8 figures

Published
2018
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5. Measurement of the $\pi K$ atom lifetime and the $\pi K$ scattering length

Author

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

Subjects
High Energy Physics - Experiment, Nuclear Experiment
Abstract

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: $\left|a_0^-\right| = (0.072^{+0.031}_{-0.020}) M_{\pi}^{-1}$., Comment: 18 pages, 17 figures

Published
2017
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10. First $\pi K$ atom lifetime and $\pi K$ scattering length measurements

Author

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

Subjects
Nuclear Experiment, High Energy Physics - Experiment
Abstract

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 ($653 \pm 42$). Using these results the analysis yields a first value for the $\pi K$ atom lifetime of $\tau=(2.5_{-1.8}^{+3.0})$ fs and a first model-independent measurement of the S-wave isospin-odd $\pi K$ scattering length $\left|a_0^-\right|=\frac{1}{3}\left|a_{1/2}-a_{3/2}\right|= \left(0.11_{-0.04}^{+0.09} \right)M_{\pi}^{-1}$ ($a_I$ for isospin $I$)., Comment: 14 pages, 8 figures

Published
2014
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11. Determination of $\pi\pi$ scattering lengths from measurement of $\pi^+\pi^-$ atom lifetime

Author

Adeva, B., Afanasyev, L., Benayoun, M., Benelli, A., Berka, Z., Brekhovskikh, V., Caragheorgheopol, G., Cechak, T., Chiba, M., Chliapnikov, P. V., Ciocarlan, C., Constantinescu, S., Costantini, S., Curceanu, C., Doskarova, P., Dreossi, D., Drijard, D., Dudarev, A., Ferro-Luzzi, M., Pazos, J. L. Fungueiriño, Torreira, M. Gallas, Gerndt, J., Gianotti, P., Goldin, D., Gomez, F., Gorin, A., Gorchakov, O., Guaraldo, C., Gugiu, M., Hansroul, M., Hons, Z., Hosek, R., Iliescu, M., Karpukhin, V., Kluson, J., Kobayashi, M., Kokkas, P., Komarov, V., Kruglov, V., Kruglova, L., Kulikov, A., Kuptsov, A., Kuroda, K. I., Lamberto, A., Lanaro, A., Lapshin, V., Lednicky, R., Leruste, P., Sandri, P. Levi, Aguera, A. Lopez, Lucherini, V., Maki, T., Manuilov, I., Marin, J., Narjoux, J. L., Nemenov, L., Nikitin, M., Pardo, T. Nunez, Okada, K., Olchevskii, V., Pazos, A., Pentia, M., Penzo, A., Perreau, J. M., Plo, M., Ponta, T., Rappazzo, G. F., Riazantsev, A., Rodriguez, J. M., Fernandez, A. Rodriguez, Vidal, A. Romero, Ronjin, V. M., Rykalin, V., Saborido, J., Santamarina, C., Schacher, J., Schuetz, C., Sidorov, A., Smolik, J., Takeutchi, F., Tarasov, A., Tauscher, L., Tobar, M. J., Trojek, T., Trusov, S., Utkin, V., Doce, O. Vázquez, Vlachos, S., Voskresenskaya, O., Vrba, T., Willmott, C., Yazkov, V., Yoshimura, Y., Zhabitsky, M., and Zrelov, P.

Subjects
High Energy Physics - Experiment, High Energy Physics - Phenomenology
Abstract

The DIRAC experiment at CERN has achieved a sizeable production of $\pi^+\pi^-$ 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 $\pi\pi$ scattering length difference $|a_0-a_2| = (.0.2533^{+0.0080}_{-0.0078}|_\mathrm{stat}.{}^{+0.0078}_{-0.0073}|_\mathrm{syst})M_{\pi^+}^{-1}$ has been attained, providing an important test of Chiral Perturbation Theory., Comment: 6 pages, 6 figures

Published
2011
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12. Evidence for $\pi K$-atoms with DIRAC

Author

Adeva, B., Afanasyev, L., Allkofer, Y., Amsler, C., Anania, A., Benelli, A., Brekhovskikh, V., Caragheorgheopol, G., Cechak, T., Chiba, M., Chliapnikov, P., Ciocarlan, C., Constantinescu, S., Curceanu, C., Detraz, C., Dreossi, D., Drijard, D., Dudarev, A., Duma, M., Dumitriu, D., Fungueiriño, J. L., Gerndt, J., Gorin, A., Gorchakov, O., Gritsay, K., Guaraldo, C., Gugiu, M., Hansroul, M., Hons, Z., Horikawa, S., Iliescu, M., Karpukhin, V., Kluson, J., Kobayashi, M., Komarov, V., Kruglov, V., Kruglova, L., Kulikov, A., Kuptsov, A., Kurochkin, I., Lamberto, A., Lanaro, A., Lapshin, V., Lednicky, R., Sandri, P. Levi, Aguera, A. Lopez, Lucherini, V., Manuilov, I., Mariñas, C., Nemenov, L., Nikitin, M., Okada, K., Olchevskii, V., Pentia, M., Penzo, A., Pló, M., Rappazzo, G. F., Regenfus, C., Rochet, J., Romero, A., Ronjin, V., Ryazantsev, A., Rykalin, V., Saborido, J., Schacher, J., Sidorov, A., Smolik, J., Sugimoto, S., Takeutchi, F., Tarasov, A., Tauscher, L., Trojek, T., Trusov, S., Utkin, V., Doce, O. Vázquez, Vrba, T., Yazkov, V., Yoshimura, Y., Zhabitsky, M., and Zrelov, P.

Subjects
High Energy Physics - Experiment
Abstract

We present evidence for the first observation of electromagnetically bound $\pi^\pm K^\mp$-pairs ($\pi K$-atoms) with the DIRAC experiment at the CERN-PS. The $\pi K$-atoms are produced by the 24 GeV/c proton beam in a thin Pt-target and the $\pi^\pm$ and $K^\mp$-mesons from the atom dissociation are analyzed in a two-arm magnetic spectrometer. The observed enhancement at low relative momentum corresponds to the production of 173 $\pm$ 54 $\pi K$-atoms. The mean life of $\pi K$-atoms is related to the s-wave $\pi K$-scattering lengths, the measurement of which is the goal of the experiment. From these first data we derive a lower limit for the mean life of 0.8 fs at 90% confidence level., Comment: 15 pages, 9 figures

Published
2009
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13. Upgraded DIRAC spectrometer at CERN PS for the investigation of ππ and πK atoms

Author

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

Published
2016
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15. Investigation of <math><msup><mi>K</mi><mo>+</mo></msup><msup><mi>K</mi><mo>−</mo></msup></math> pairs in the effective mass region near <math><mn>2</mn><msub><mi>m</mi><mi>K</mi></msub></math>

Author

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

Abstract

The DIRAC experiment at CERN investigated in the reaction p(24 GeV/c)+Ni the particle pairs K+K−,π+π−, and pp¯ 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 the time-of-flight (TOF) technique-the background from initial Q distributions with K+K− sample fractions more than 70%, 50%, and 30%. The corresponding pair distributions in Q and in its longitudinal projection QL were analyzed first in a Coulomb model, which takes into account only the Coulomb final-state interaction (FSI) and assuming pointlike pair production. This Coulomb model analysis leads to a K+K− yield increase of about four at QL=0.5 MeV/c compared to 100 MeV/c. In order to study contributions from strong interaction, a second more sophisticated model was applied, considering also strong FSI via the resonances f0(980) and a0(980) and a variable distance r* between the produced K mesons besides Coulomb FSI. This analysis was based on three different parameter sets for the pair production. For the 70% subsample and with the best parameters, 3680±370 K+K− pairs were found to be compared to 3900±410 K+K− extracted by means of the Coulomb model. Knowing the efficiency of the TOF cut for background suppression, the total number of detected K+K− pairs was evaluated to be around 40000±10%, which agrees with the result from the 30% subsample. The K+K− pair number in the 50% subsample differs from the two other values by about three standard deviations, confirming—as discussed in the paper—that experimental data in this subsample is less reliable. In summary, the upgraded DIRAC experiment observed increased K+K− production at small relative momentum Q. The pair distribution in Q is well described by Coulomb FSI, whereas a potential influence from strong interaction in this Q region is insignificant within experimental errors.

Published
2022

25. First Measurement of a Long-Lived π^{+}π^{-} Atom Lifetime

Author

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

Abstract

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.

Published
2018

26. First measurement of a long-lived $��^+ ��^-$ atom lifetime

Author

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

Subjects
High Energy Physics - Experiment (hep-ex), FOS: Physical sciences, Physics::Atomic Physics, Nuclear Experiment (nucl-ex)
Abstract

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, $n_A^L= \left.436^{+157}_{-61}\right|_\mathrm{tot}$, the lifetime of the 2$p$ state is found to be ${��_{2p}=(\left.0.45^{+1.08}_{-0.30}\right|_\mathrm{tot}) \cdot10^{-11}}$s, not contradicting the corresponding QED $2p$ state lifetime ${��_{2p}^\mathrm{QED}=1.17 \cdot 10^{-11}}$s. This lifetime value is three orders of magnitude larger than our previously measured value of the $��^+��^-$ atom ground state lifetime $��=(\left.3.15^{+0.28}_{-0.26}\right|_\mathrm{tot})\cdot 10^{-15}$s. Further studies of long-lived $��^+��^-$ atoms will allow to measure energy differences between $p$ and $s$ atomic states and so to determine $����$ scattering lengths with the aim to check QCD predictions., 7 pages, 8 figures

Published
2018
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27. First Measurement of a Long-Lived π+π− Atom Lifetime

Author

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

Published
2019
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30. Measurement of the $��K$ atom lifetime and the $��K$ scattering length

Author

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

Subjects
High Energy Physics - Experiment (hep-ex), FOS: Physical sciences, Nuclear Experiment (nucl-ex)
Abstract

After having announced the statistically significant observation (5.6~$��$) of the new exotic $��K$ atom, the DIRAC experiment at the CERN proton synchrotron presents the measurement of the corresponding atom lifetime, based on the full $��K$ data sample: $��= (5.5^{+5.0}_{-2.8}) \cdot 10^{-15}s$. By means of a precise relation ($, 18 pages, 17 figures

Published
2017
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33. First observation of long-lived π+π− atoms

Author

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

Published
2015
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41. First $��K$ atom lifetime and $��K$ scattering length measurements

Author

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

Subjects
High Energy Physics - Experiment (hep-ex), FOS: Physical sciences, Nuclear Experiment (nucl-ex)
Abstract

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

Published
2014
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45. Search for Long-Lived States of $\pi^+\pi^-$ Atoms : Addendum to the DIRAC Proposal

Author

Adeva, B, Afanasyev, L, Anania, A, Aogaki, S, Augsten, K, Batyuk, P, Benelli, A, Brekhovskikh, V, Cechak, T, Chiba, M, Ciortea, C, Curceanu, C, Doskarova, P, Dudarev, A, Dumitriu, D, Drijard, D, Fluerasu, D, Gortchakov, O, Gritsay, K, Guaraldo, C, Gugiu, M, Hansroul, M, Hosek, R, Hons, Z, Iwashita, Y, Karpukhin, V, Kluson, J, Kobayashi, M, Kruglov, V, Kruglova, L, Kulikov, A, Kulish, E, Kuptsov, A, Lamberto, A, Lednicky, R, Martincik, J, Nemenov, L, Nikitin, M, Okada, K, Pentia, M, Plo, M, Prusa, P, Rappazzo, G, Ryazantsev, A, Romero, A, Ronzhin, V, Rykalin, V, Saborido, J, Schacher, J, Shlyapnikov, P, Smolik, J, Takeutchi, F, Trojek, T, Urban, T, Vrba, T, Vazquez, P, Yazkov, V, Yoshimura, Y, Zhabitsky, M, and Zrelov, P

Subjects
Detectors and Experimental Techniques
Abstract

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

Published
2012

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

Author

Adeva, B, Afanasyev, L, Amsler, C, Anania, A, Aogaki, S, Augsten, K, Benelli, A, Brekhovskikh, V, Cechak, T, Chiba, M, Ciortea, C, Ciocarlan, C, Constantinescu, S, Curceanu, C, Doskarova, P, Dudarev, A, Dumitriu, D, Drijard, D, Enulescu, A, Fluerasu, D, Gortchakov, O, Gritsay, K, Guaraldo, C, Gugiu, M, Hansroul, M, Hosek, R, Hons, Z, Karpukhin, V, Kluson, J, Kobayashi, M, Kulikov, A, Kulish, E, Kuptsov, A, Kruglov, V, Kruglova, L, Kuroda, K, Lamberto, A, Lednicky, R, Martincik, J, Nemenov, L, Nikitin, M, Okada, K, Pentia, M, Plo, M, Prusa, P, Rappazzo, G, Ryazantsev, A, Romero, A, Ronzhin, V, Rykalin, V, Saborido, J, Schacher, J, Shlyapnikov, P, Smolik, J, Takeutchi, F, Tarasov, A, Trojek, T, Urban, T, Vrba, T, Vazquez, P, Yazkov, V, Yoshimura, Y, Zhabitsky, M, and Zrelov, P

Subjects
Detectors and Experimental Techniques
Abstract

The proposed experiment is a further development of the DIRAC experiment already running at CERN PS. Up to now more than 21000 $\pi^+\pi^-$ pairs originated from the $\pi^+\pi^-$ atom ($A_{2\pi}$) breakup were identified and the overall accuracy of the $A_{2\pi}$ lifetime is about 9% in accordance with the DIRAC proposal. This measurement allowed to extract the difference $|a_0-a_2|$ of $s$-wave $\pi\pi$-scattering length with accuracy of 4.3%. The observation of long-lived (metastable) $A_{2\pi}$ states will be performed with the same setup. This observation opens a possibility to measure the energy difference between $ns$ and $np$ states and to determine the value of another combination $2a_0+a_2$ of $\pi\pi$ scattering length in a model-independent way. In combination with the first measurement it allows to get $a_0$ and $a_2$ separately. An additional measurement of the multiple scattering angles in different materials with accuracy better than 1% will be performed in parallel with the observation. This measurement is needed to improve the systematic accuracy in the $A_{2\pi}$ lifetime for the data already collected in 2008--2010.

Published
2011

47. Determination of pi pi scattering lengths from measurement of pi(+)pi(-) atom lifetime

Author

Adeva, B., Afanasyev, L., Benayoun, M., Benelli, A., Berka, Z., Brekhovskikh, V., Caragheorgheopol, G., Cechak, T., Chiba, M., Chliapnikov, P. V., Ciocarlan, C., Constantinescu, S., Costantini, S., Curceanu, C., Doskarova, P., Dreossi, D., Drijard, D., Dudarev, A., Ferro-Luzzi, M., Pazos, J. L. F., Torreira, M. G., Gerndt, J., Gianotti, P., Goldin, D., Gomez, F., Gorin, A., Gorchakov, O., Guaraldo, C., Gugiu, M., Hansroul, M., Hons, Z., Hosek, R., Iliescu, M., Karpukhin, V., Kluson, J., Kobayashi, M., Kokkas, P., Komarov, V., Kruglov, V., Kruglova, L., Kulikov, A., Kuptsov, A., Kuroda, K. I., Lamberto, A., Lanaro, A., Lapshin, V., Lednicky, R., Leruste, P., Sandri, P. L., Aguera, A. L., Lucherini, V., Maki, T., Manuilov, I., Marin, J., Narjoux, J. L., Nemenov, L., Nikitin, M., Pardo, T. N., Okada, K., Olchevskii, V., Pazos, A., Pentia, M., Penzo, A., Perreau, J. M., Plo, M., Ponta, T., Rappazzo, G. F., Riazantsev, A., Rodriguez, J. M., Fernandez, A. R., Vidal, A. R., Ronjin, V. M., Rykalin, V., Saborido, J., Santamarina, C., Schacher, J., Schuetz, C., Sidorov, A., Smolik, J., Takeutchi, F., Tarasov, A., Tauscher, L., Tobar, M. J., Trojek, T., Trusov, S., Utkin, V., Doce, O. V., Vlachos, S., Voskresenskaya, O., Vrba, T., Willmott, C., Yazkov, V., Yoshimura, Y., Zhabitsky, M., and Zrelov, P.

Subjects
pion scattering, probability, pionium, elementary atom, dirac experiment, pionium atom, cross-sections, qcd, target
Abstract

The DIRAC experiment at CERN has achieved a sizeable production of pi(+)pi(-) atoms and has significantly improved the precision on its lifetime determination. From a sample of 21 227 atomic pairs, a 4% measurement of the S-wave pi pi scattering length difference |a(0) - a(2)| = (0.2533(-0.0078)(+0.0080)|stat(-0.0073)(+0.0078)|syst)M(pi+)(-1) has been attained, providing an important test of Chiral Perturbation Theory. (C) 2011 Elsevier B.V. All rights reserved. Physics Letters B

Published
2011

50. Evidence for $��K$-atoms with DIRAC

Author

Adeva, B., Afanasyev, L., Allkofer, Y., Amsler, C., Anania, A., Benelli, A., Brekhovskikh, V., Caragheorgheopol, G., Cechak, T., Chiba, M., Chliapnikov, P., Ciocarlan, C., Constantinescu, S., Curceanu, C., Detraz, C., Dreossi, D., Drijard, D., Dudarev, A., Duma, M., Dumitriu, D., Fungueiri��o, J. L., Gerndt, J., Gorin, A., Gorchakov, O., Gritsay, K., Guaraldo, C., Gugiu, M., Hansroul, M., Hons, Z., Horikawa, S., Iliescu, M., Karpukhin, V., Kluson, J., Kobayashi, M., Komarov, V., Kruglov, V., Kruglova, L., Kulikov, A., Kuptsov, A., Kurochkin, I., Lamberto, A., Lanaro, A., Lapshin, V., Lednicky, R., Sandri, P. Levi, Aguera, A. Lopez, Lucherini, V., Manuilov, I., Mari��as, C., Nemenov, L., Nikitin, M., Okada, K., Olchevskii, V., Pentia, M., Penzo, A., Pl��, M., Rappazzo, G. F., Regenfus, C., Rochet, J., Romero, A., Ronjin, V., Ryazantsev, A., Rykalin, V., Saborido, J., Schacher, J., Sidorov, A., Smolik, J., Sugimoto, S., Takeutchi, F., Tarasov, A., Tauscher, L., Trojek, T., Trusov, S., Utkin, V., Doce, O. V��zquez, Vrba, T., Yazkov, V., Yoshimura, Y., Zhabitsky, M., and Zrelov, P.

Subjects
High Energy Physics - Experiment (hep-ex), FOS: Physical sciences
Abstract

We present evidence for the first observation of electromagnetically bound $��^\pm K^\mp$-pairs ($��K$-atoms) with the DIRAC experiment at the CERN-PS. The $��K$-atoms are produced by the 24 GeV/c proton beam in a thin Pt-target and the $��^\pm$ and $K^\mp$-mesons from the atom dissociation are analyzed in a two-arm magnetic spectrometer. The observed enhancement at low relative momentum corresponds to the production of 173 $\pm$ 54 $��K$-atoms. The mean life of $��K$-atoms is related to the s-wave $��K$-scattering lengths, the measurement of which is the goal of the experiment. From these first data we derive a lower limit for the mean life of 0.8 fs at 90% confidence level., 15 pages, 9 figures

Published
2009
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