寿命长的π+π-原子寿命的首次测量
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First Measurement of a Long-Lived π
+
π
−
Atom Lifetime
B. Adeva,
1
L. Afanasyev,
2
A. Anania,
3
S. Aogaki,
4
A. Benelli,
7
V. Brekhovskikh,
6
T. Cechak,
7
M. Chiba,
8
P. V. Chliapnikov,
6
P. Doskarova,
7
D. Drijard,
9
A. Dudarev,
2
D. Dumitriu,
4
D. Fluerasu,
4
A. Gorin,
6
O. Gorchakov,
2,†
K. Gritsay,
2
C. Guaraldo,
10
M. Gugiu,
4
M. Hansroul,
9
Z. Hons,
11
S. Horikawa,
5
Y. Iwashita,
12
V. Karpukhin,
2
J. Kluson,
7
M. Kobayashi,
13
V. Kruglov,
2
L. Kruglova,
2
A. Kulikov,
2
E. Kulish,
2
A. Lamberto,
3
A. Lanaro,
9,14
R. Lednicky,
15
C. Mariñas,
1
J. Martincik,
7
L. Nemenov,
2,9
M. Nikitin,
2
K. Okada,
16
V. Olchevskii,
2
V. Ovsiannikov,
17
M. Pentia,
4
A. Penzo,
18
M. Plo,
1
P. Prusa,
7
G. F. Rappazzo,
3
A. Romero Vidal,
1
A. Ryazantsev,
6
V. Rykalin,
6
J. Saborido,
1
J. Schacher,
19,*
A. Sidorov,
6
J. Smolik,
7
F. Takeutchi,
16
T. Trojek,
7
S. Trusov,
20
T. Urban,
7
T. Vrba,
7
V. Yazkov,
20,†
Y. Yoshimura,
13
and P. Zrelov
2
1
Santiago de Compostela University, Santiago de Compostela, Spain
2
JINR, Dubna, Russia
3
INFN, Sezione di Trieste and Messina University, Messina, Italy
4
IFIN-HH, National Institute for Physics and Nuclear Engineering, Bucharest, Romania
5
Zurich University, Zurich, Switzerland
6
IHEP, Protvino, Russia
7
Czech Technical University in Prague, Prague, Czech Republic
8
Tokyo Metropolitan University, Tokyo, Japan
9
CERN, Geneva, Switzerland
10
INFN, Laboratori Nazionali di Frascati, Frascati, Italy
11
Nuclear Physics Institute ASCR, Rez, Czech Republic
12
Kyoto University, Kyoto, Japan
13
KEK, Tsukuba, Japan
14
University of Wisconsin, Madison, Wisconsin USA
15
Institute of Physics ASCR, Prague, Czech Republic
16
Kyoto Sangyo University, Kyoto, Japan
17
Voronezh State University, Voronezh, Russia
18
INFN, Sezione di Trieste, Trieste, Italy
19
Albert Einstein Center for Fundamental Physics, LHEP, Bern, Switzerland
20
Skobeltsin Institute for Nuclear Physics of Moscow State University, Moscow, Russia
(Received 29 November 2018; published 1 March 2019)
The adapted DIRAC experiment at the CERN PS accelerator observed for the first time lon g-lived
hydrogenlike π
þ
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, n
L
A
¼ 436
þ157
−61
j
tot
, the lifetime of the 2p state is found to be
τ
2p
¼ð0.45
þ1.08
−0.30
j
tot
Þ × 10
−11
s, not contradicting the correspo nding QED 2p state lifetime τ
QED
2p
¼
1.17 × 10
−11
s. This lifetime value is three orders of magnitude larger than our pr eviously measured value
of the π
þ
π
−
atom ground state lifetime τ ¼ð3.15
þ0.28
−0.26
j
tot
Þ × 10
−15
s. Further studies of long-lived π
þ
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.
DOI: 10.1103/PhysRevLett.122.082003
Introduction.—The DIRAC collaboration aims to check
low-energy QCD predictions using double-exotic π
þ
π
−
and π
K
∓
atoms, which have been observed and studied
[1–7]. In strong inclusive processes, these atoms are
produced in s states and are distributed according to
n
−3
, n being the principal quantum number [8].
The decay probability of short-lived π
þ
π
−
atoms (A
2π
,
pionium) in s states is dominated (99.6%) by the annihi-
lation process [9–13] π
þ
þ π
−
→ π
0
þ π
0
and is given by
the ππ s-wave scattering lengths combination ja
0
− a
2
j (a
I
is the ππ scattering length for isospin I):
Published by the American Phys ical Society under the terms of
the Creative Commons Attribution 4.0 International license.
Further distribution of this work must maintain attribution to
the author(s) and the published article’s title, journal citation,
and DOI. Funded by SCOAP
3
.
PHYSICAL REVIEW LETTERS 122, 082003 (2019)
0031-9007=19=122(8)=082003(7) 082003-1 Published by the American Physical Society
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