Discovery of antiproton trapping by long-lived metastable states in liquid helium

Iwasaki, M.; Nakamura, Seitaro; Shigaki, K.; Shimizu, Y.; Tamura, H.; Ishikawa, Takashi; Hayano, R.; Takada, E.; Widmann, E.; Outa, H.; Aoki, M.; Kitching, P.; Yamazaki, T.

doi:10.1103/physrevlett.67.1246

Cited by 236 publications

(110 citation statements)

References 12 publications

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“…[7,9] are plotted in megahertz. The imaginary part plotted here is the half Auger width with negative sign, − 1 2 ͑␥ A /2 ͒. The values used for the comparison of the real part are the transition frequencies from metastable states, where the theoretical uncertainty should be very small.…”

Section: Resultsmentioning

confidence: 99%

“…The antiprotonic helium atom ͑pHe + ͒ is an exotic threebody system consisting of an antiproton, an electron, and a helium nucleus [1][2][3]. Detailed studies have been done for its metastable-state region, where the principal quantum number n and angular momentum l are both around 38, and where lifetimes against annihilation can be as long as several microseconds.…”

Section: Introductionmentioning

confidence: 99%

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Systematic study of the decay rates of antiprotonic helium states

Yamaguchi

Hayano²,

Ishikawa³

et al. 2004

Phys. Rev. A

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A systematic study of the decay rates of antiprotonic helium (p 4 He + and p 3 He + ) at CERN Antiproton Decelerator has been made by a laser spectroscopic method. The decay rates of some of its short-lived states, namely those for which the Auger rates ␥ A are much larger than their radiative decay rates ͑␥ rad ϳ 1 s −1 ͒, were determined from the time distributions of the antiproton annihilation signals induced by laser beams, and the widths of the atomic resonance lines. The magnitude of the decay rates, especially their relation with the transition multipolarity, is discussed and compared with theoretical calculations.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Systematic study of the decay rates of antiprotonic helium states

Yamaguchi

Hayano²,

Ishikawa³

et al. 2004

Phys. Rev. A

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“…When antiprotons are stopped in a helium target, a 3% fraction survive with an average lifetime avg =3-4 s [1][2][3][4][5][6] by forming metastable antiprotonic helium ͑pHe + ϵ p − +He 2+ + e − ͒ atoms [7,8]. In this paper, we study the initial distributions of these atoms over principal ͑n͒ and orbital angular momentum ͑ᐉ͒ quantum numbers in the v ϵ n − ᐉ −1=2 and 3 metastable cascades using a laser spectroscopic method.…”

Section: Introductionmentioning

confidence: 99%

Populations and lifetimes in thev=n−ℓ−1=2and 3 metastable cascades ofp¯
Hori
¹
,
Eades
²
,
Widmann
³

et al. 2004
Phys. Rev. A
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The time evolution of the state populations in the v ϵ n − ᐉ −1=2 and 3 metastable cascades of antiprotonic helium (p 4 He + ) atoms were studied using laser spectroscopy. The antiprotonic states ͑n , ᐉ͒ = ͑39, 35͒, (40,36), and (41,37) in the v = 3 cascade were estimated to initially contain, respectively, ͑0.28± 0.04͒%, ͑0.06± 0.02͒%, and ͑0.02± 0.01͒% of the antiprotons stopped in the helium target, while the corresponding values for states ͑37, 34͒, ͑38, 35͒, and ͑39, 36͒ in the v = 2 cascade were ͑0.21± 0.04͒%, ͑0.49± 0.07͒%, and ͑0.19± 0.07͒%. The shortening of the state lifetimes due to collisions between pHe + and helium atoms was studied. As the atomic density of the target was increased from =2ϫ 10 20 to 2 ϫ 10 21 cm −3 , the lifetime of state ͑37, 34͒ decreased by an order of magnitude, whereas the higher states ͑38, 35͒ and ͑39, 35͒ were relatively unaffected. Between densities =6ϫ 10 20 and 2 ϫ 10 22 cm −3 , a short-lived component with a time constant ϳ 0.2 s appeared at early times in the delayed annihilation time spectrum of pHe + , while the total fraction of long-lived antiprotons decreased from 3.0 to 2.5%. These effects were caused by the lifetime-shortening of specific pHe + states such as ͑37, 34͒.

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“…In this paper, we describe measurements of the n; ' distributions of antiprotons captured into atomic states in metastable antiprotonic helium [5][6][7][8], including the isotopes p 4 He for which n 0 38:3 and p 3 He for which n 0 37:1. These pHe states (see Fig.…”

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confidence: 99%

Primary Populations of Metastable AntiprotonicH4eandH
Hori
¹
,
Eades
²
,
Hayano
³

et al. 2002
Phys. Rev. Lett.
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Initial distributions of metastable antiprotonic 4 He and 3 He atoms over principal (n) and angular momentum (') quantum numbers have been deduced using laser spectroscopy experiments. The regions n 37-40 and n 35-38 in the two atoms account for almost all of the observed fractions [ 3:0 0:1 % and 2:4 0:1 %] of antiprotons captured into metastable states. DOI: 10.1103/PhysRevLett.89.093401 PACS numbers: 36.10.-k, 25.43.+t, 34.90.+q A negatively charged particle X ÿ (such as ÿ , ÿ , or p) approaching an atom at electron-volt energies can displace one of its electrons, thereby forming an exotic atom [1]. Little is known about the principal (n) and angular momentum (') quantum numbers of the atom's primordial (i.e., initially occupied) states. It has been widely believed since the 1950s [2-4] that in exotic hydrogen and helium atoms, n will be distributed around the value(M being the reduced mass of the X ÿ -nucleus system, and m e the electron mass), which corresponds to the X ÿ orbital with the same radius and binding energy as that of the displaced 1s electron. In this paper, we describe measurements of the n; ' distributions of antiprotons captured into atomic states in metastable antiprotonic helium [5][6][7][8], including the isotopes p 4 He for which n 0 38:3 and p 3 He for which n 0 37:1. These pHe states (see Fig. 1) have microsecond-scale lifetimes against annihilation, because their large ' values (' n ÿ 1) do not permit them to deexcite by Auger emission of the electron. Instead, the atoms slowly undergo a series of constant v n ÿ ' ÿ 1 radiative transitions (i.e., n ' ÿ1). They finally reach states which proceed rapidly to pHe 2 ions, which are immediately destroyed by collisional Stark effects. So far, the numbers of antiprotons populating two metastable states in p 4 He [namely, n; ' 39; 35 and 37; 34 ] have been measured [9,10] using laser spectroscopic methods [11] at the former LEAR facility at CERN. The two states represent only a small fraction of the totality of metastable states shown in Fig. 1; moreover, since for technical reasons [9] the populations could be measured only after a minimum delay of t 1:8 s following atomic formation, the primary populations (those at t 0) could not be reliably estimated. We study here a total of 20 transitions in p 4 He and p 3 He atoms starting at t 300 ns, and estimate the primary populations in nearly all the metastable states.These experiments were made at the Antiproton Decelerator at CERN, the setup [12] being an extension of our former one. Metastable pHe atoms were produced

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Discovery of antiproton trapping by long-lived metastable states in liquid helium

Cited by 236 publications

References 12 publications

Systematic study of the decay rates of antiprotonic helium states

Systematic study of the decay rates of antiprotonic helium states

Populations and lifetimes in thev=n−ℓ−1=2and 3 metastable cascades ofp¯
Hori
¹
,
Eades
²
,
Widmann
³

et al. 2004
Phys. Rev. A
Self Cite
35
2
23
0
View full text Add to dashboard Cite

Primary Populations of Metastable AntiprotonicH4eandH
Hori
¹
,
Eades
²
,
Hayano
³

et al. 2002
Phys. Rev. Lett.
Self Cite

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Discovery of antiproton trapping by long-lived metastable states in liquid helium

Cited by 236 publications

References 12 publications

Systematic study of the decay rates of antiprotonic helium states

Systematic study of the decay rates of antiprotonic helium states

Populations and lifetimes in thev=n−ℓ−1=2and 3 metastable cascades ofp¯Hori1, Eades2, Widmann3 et al. 2004Phys. Rev. ASelf Cite352230View full textAdd to dashboardCite

Primary Populations of Metastable AntiprotonicH4eandHHori1, Eades2, Hayano3 et al. 2002Phys. Rev. Lett.Self Cite

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Populations and lifetimes in thev=n−ℓ−1=2and 3 metastable cascades ofp¯
Hori
¹
,
Eades
²
,
Widmann
³

et al. 2004
Phys. Rev. A
Self Cite
35
2
23
0
View full text Add to dashboard Cite

Primary Populations of Metastable AntiprotonicH4eandH
Hori
¹
,
Eades
²
,
Hayano
³

et al. 2002
Phys. Rev. Lett.
Self Cite