Semiclassical description of antiproton capture on atomic helium

Beck, W.; Wilets, L.; Alberg, Mary

doi:10.1103/physreva.48.2779

Cited by 49 publications

(34 citation statements)

References 31 publications

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“…7). Relatively little metastable populations were detected in states with n ജ 41, whereas theoretical calculations [21][22][23][24][25][26][27][28] predict significant populations in states up to n ജ 50. As these theoretical populations do not take the effect of collisions between pHe + and helium atoms into account, however, they may not be directly comparable with the experimental results presented here which refer to atoms thermalized by many collisions.…”

Section: A Primary Populationsmentioning

confidence: 99%

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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
35
2
23
0
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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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Section: A Primary Populationsmentioning

confidence: 99%

“…(i) Capture: when an antiproton collides with a helium atom at electron-volt energies, it may replace one of the electrons orbiting the helium nucleus, and become captured into a pHe + state. This occurs [12,[20][21][22][23][24][25][26][27][28] with the highest probability into states with n-values of about n ϳ n 0 ϵ ͱ M * /m e = 38.3…”

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
35
2
23
0
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“…The description of the p interaction with the atomic or molecular electrons, however, is based on quantummechanical calculations with the atomic electrons usually assumed to be a degenerate electron gas; for the lightest elements the kinematics of the individual electrons may be calculated directly. Although few calculations have been performed for antiprotons (Beck et al, 1993;Cohen, 1997), the results for muons can easily be transferred to p by appropriate kinematic scaling factors.…”

Section: The Formation Of Antiprotonic Atomsmentioning

confidence: 99%

“…The (Leon and Miller, 1977). most recent include a calculation based on quantum coupling equations performed by Dolinov et al (1989) and two quasiclassical approaches: Beck et al (1993) have developed a theory for the atomic capture of p in He and very recently Cohen (1997) devised a corresponding theory for p capture in hydrogen molecules.…”

Section: The Formation Of Antiprotonic Atomsmentioning

confidence: 99%

Forty years of antiprotons

Eades

Hartmann

1999

Rev. Mod. Phys.

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The discovery of the antiproton some 40 years ago and the almost synchronous fall of parity (P) and charge conjugation (C) symmetries were soon followed by the realization that CPT rather than C invariance is the fundamental symmetry connecting matter and antimatter, and that consequently any measurement of the antiproton's properties can be interpreted as a test of that symmetry. It is the latter view of the antiproton, as an object of study in its own right, rather than as a means to such other ends as the production of gauge bosons and meson resonances, that is presented here. The authors review the technical steps that have led from the handful of antiprotons observed by Chamberlain, Segrè , Wiegand, and Ypsilantis to the intense, high-quality beams available today and show how the state of rest and isolation required for high precision measurements of their properties can be achieved by confining them in electromagnetic traps or in their microscopic counterparts, exotic atoms. The test bench role of antiprotons and antihydrogen atoms for both CPT symmetry and the gravitational weak equivalence principle is discussed, and the body of experimental results obtained since 1955 critically reviewed from this standpoint. Future experiments are then discussed in the light of the closure of the CERN Low Energy Antiproton Ring (LEAR), its replacement in 1999 by the Antiproton Decelerator (AD), and the likely antiproton source at the Japan Hadron Facility.[S0034-6861(99)00401-8] CONTENTS

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“…Several theoretical calculations [20][21][22][23][24][25] (two such results are shown in Fig. 5) predict that T e is small with respect to I 0 .…”

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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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Semiclassical description of antiproton capture on atomic helium

Cited by 49 publications

References 31 publications

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
35
2
23
0
View full text Add to dashboard Cite

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
35
2
23
0
View full text Add to dashboard Cite

Forty years of antiprotons

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

et al. 2002
Phys. Rev. Lett.

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Semiclassical description of antiproton capture on atomic helium

Cited by 49 publications

References 31 publications

Populations and lifetimes in thev=n−ℓ−1=2and 3 metastable cascades ofp¯Hori1, Eades2, Widmann3 et al. 2004Phys. Rev. A352230View full textAdd to dashboardCite

Populations and lifetimes in thev=n−ℓ−1=2and 3 metastable cascades ofp¯Hori1, Eades2, Widmann3 et al. 2004Phys. Rev. A352230View full textAdd to dashboardCite

Forty years of antiprotons

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

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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
35
2
23
0
View full text Add to dashboard Cite

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
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.