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1.
Spectroscopy of antiprotonic helium atoms and its contribution to the fundamental physical constants
Ryugo S. Hayano 《Proceedings of the Japan Academy. Series B, Physical and biological sciences》2010,86(1):1-10
Antiprotonic helium atom, a metastable neutral system consisting of an antiproton, an electron and a helium nucleus, was serendipitously discovered, and has been studied at CERN’s antiproton decelerator facility. Its transition frequencies have recently been measured to nine digits of precision by laser spectroscopy. By comparing these experimental results with three-body QED calculations, the antiproton-to-electron massratio was determined as 1836.152674(5). This result contributed to the CODATA recommended values of the fundamental physical constants. 相似文献
2.
Eberhard Widmann 《Hyperfine Interactions》1999,119(1-4):195-200
This paper discusses the level splitting of the antiprotonic helium atomcule, an exotic atom consisting of a helium nucleus,
an electron, and an antiproton which occupies highly excited states with angular momentum of L ≈ 30–35. The observation of a splitting in a laser transition between two levels is presented, and an experiment in preparation
at the forthcoming AD facility at CERN is described which aims at directly measuring the level splitting by using a 2-laser
microwave triple resonance technique. This experiment has the potential to determine the magnetic moment of the antiproton
with higher precision than currently known.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
3.
Dániel Barna 《Hyperfine Interactions》2012,212(1-3):159-165
The mass of the antiproton (the antiproton-electron mass ratio $m_{\overline{p}}/m_e$ ) can be deduced from laser spectroscopy measurements of antiprotonic helium, compared to 3-body QED calculations. The most precise spectroscopy measurements have so far been limited by Doppler-broadening at finite temperatures. The status of our ongoing precision measurements is presented, within the framework of the Asacusa experiment at CERN. 相似文献
4.
C. J. G. Onderwater 《Hyperfine Interactions》2012,209(1-3):9-14
Twenty years ago, we published a paper entitled “Discovery of antiproton trapping by long-lived metastable states in liquid helium”. In retrospect, this was the discovery of antiprotonic helium atoms, the study of which is actively being done at CERN’s antiproton decelerator. A brief overview of this interesting exotic atom is given, together with some historical background. 相似文献
5.
Dániel Barna 《Hyperfine Interactions》2014,229(1-3):89-95
The precision of laser spectroscopy of antiprotonic helium (a helium atom with one of its electrons replaced by an antiproton) has improved by almost 4 orders of magnitude over its 20 years of history. Experimental transition frequencies can be compared to 3-body QED calculations to derive the antiproton-electron mass ratio. In the latest measurements of the Asacusa experiment at CERN, two-photon transitions of antiprotonic helium were excited using two counter-propagating laser beams. This method reduces the Doppler-broadening caused by the thermal motion of the atoms, and allowed us to measure the transition frequencies with a fractional precision of 2.5–5 parts in 109. From these frequencies, we derived an antiproton-electron mass ratio of 1836.1526736(23). Our precision approaches that of the experimental value of the proton-electron mass ratio, and agrees with the latter within errors. Assuming CPT symmetry (i.e. \(m_{p}=m_{\overline {p}}\) ), we further derived the electron’s atomic mass as m e = 0.0005485799091(7)u from the more accurately known atomic mass of the proton. 相似文献
6.
Cross-beam atomic collision experiment between ultra-low-energy antiprotons and a supersonic gas jet
H. A. Torii Y. Nagata H. Toyoda H. Imao N. Kuroda V. L. Varentsov Y. Yamazaki 《Hyperfine Interactions》2009,194(1-3):37-43
The antiproton is a unique projectile in the study of atomic collision physics. With an aim to produce an antiproton beam at atomic-physics energies for ‘pure’ collision experiments, we have so far developed techniques to decelerate, cool and confine antiprotons in vacuo. Our recent success in stable extraction of the beam has opened up the possibility to study ionization and atomic capture processes between an antiproton and an atom at an unprecedented low energy from 10 eV to 1 keV under the single-collision condition. We have prepared a powerful supersonic helium gas jet to be crossed with the antiproton beam. The reaction rate is of the order of 10???4, and rigorous identification of particles is required for reduction of huge background counts. The reaction events are recognized by an electron signal followed by antiproton annihilation with an appropriate interval in the time of flight. Our design and strategy of the experiment are presented. 相似文献
7.
8.
J. Révai N. Shevchenko 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2006,37(1):83-92
A consistent quantum mechanical calculation of partial
cross-sections leading to different final states of antiprotonic
helium atom was performed. For the four-body scattering wave
function, corresponding to the initial state, as well as for the
antiprotonic helium wave function, appearing in the final state,
adiabatic approximations were used. Further, symmetric and
non-symmetric effective charge (SEC, NEC) approximations were
introduced for the two-electron wave functions in the field of the
two fixed charges of the He nucleus and the antiproton.
Calculations were carried out for a wide range of antiprotonic
helium states and incident energies of the antiproton below the
first ionization threshold of the He atom. The origin of the
rich low-energy structure of certain cross-sections is discussed
in detail. 相似文献
9.
Hori M Eades J Hayano RS Ishikawa T Sakaguchi J Widmann E Yamaguchi H Torii HA Juhász B Horváth D Yamazaki T 《Physical review letters》2001,87(9):093401
Six laser-resonant transitions have been detected in metastable antiprotonic helium atoms produced at the CERN Antiproton Decelerator. They include UV transitions from the last metastable states in the v = n-l-1 = 0 and 1 cascades. Zero-density frequencies were obtained from measured pressure shifts with fractional precisions between 1.3 x 10(-7) and 1.6 x 10(-6). By comparing these with QED calculations and the antiproton cyclotron frequency, we deduce that the antiproton and proton charges and masses agree to within 6 x 10(-8) with a confidence level of 90%. 相似文献
10.
M. Hori 《Hyperfine Interactions》2014,227(1-3):17-22
The ASACUSA collaboration of CERN has carried out two-photon laser spectroscopy of antiprotonic helium atoms using counter-propagating ultraviolet laser beams. This excited some non-linear transitions of the antiproton at the wavelengths λ = 139.8–197.0 nm, in a way that reduced the thermal Doppler broadening of the observed resonances. The resulting narrow spectral lines allowed the measurement of three transition frequencies with fractional precisions of 2.3–5 parts in 109. By comparing these values with three-body QED calculations, the antiproton-to-electron mass ratio was derived as 1836.1526736(23). We briefly review these results. 相似文献
11.
激光氦离子源产生的MeV能量的氦离子因有望用于聚变反应堆材料辐照损伤的模拟研究而得到关注.目前激光驱动氦离子源的主要方案是采用相对论激光与氦气射流作用加速高能氦离子,但这种方案在实验上难以产生具有前向性和准单能性、数MeV能量、高产额的氦离子束,而这些氦离子束特性是材料辐照损伤研究中十分关注的.不同于上述激光氦离子产生方法,我们提出了一种利用超强激光与固体-气体复合靶作用产生氦离子的新方法.利用这种方法,在实验上,采用功率密度5×10~(18)W/cm~2的皮秒脉宽的激光脉冲与铜-氦气复合靶作用,产生了前向发射的2.7 MeV的准单能氦离子束,能量超过0.5 MeV的氦离子产额约为10~(13)/sr.二维粒子模拟显示,氦离子在靶背鞘场加速和类无碰撞冲击波加速两种加速机理共同作用下得到加速.同时粒子模拟还显示氦离子截止能量与超热电子温度成正比. 相似文献
12.
M. Hori A. Sótér D. Barna A. Dax R. S. Hayano S. Friedreich B. Juhász T. Pask E. Widmann D. Horváth L. Venturelli N. Zurlo 《Few-Body Systems》2013,54(7-10):917-922
The ASACUSA collaboration of CERN has recently irradiated antiprotonic helium atoms with two counter-propagating laser beams. This excited some non-linear two-photon transitions of the antiproton at the deep UV wavelengths λ = 139.8–197.0 nm. The counterpropagating geometry of the laser beams reduced the thermal Doppler broadening of the observed resonances. Their narrow spectral lines allowed the measurement of three transition frequencies with fractional precisions of 2.3–5 parts in 109. By comparing the results with three-body QED calculations, the antiproton-to-electron mass ratio was derived as 1836.1526736(23). 相似文献
13.
14.
We report on preliminary results from a systematic study of the hyperfine (HF) structure of antiprotonic helium. This precise measurement which was commenced in 2006, has now been completed. Our initial analysis shows no apparent density or power dependence and therefore the results can be averaged. The statistical error of the individual lines is a factor of 60 smaller than that of three body quantum electrodynamic (QED) calculations, while the difference has been resolved to a precision comparable to theory (a factor of 10 better than our first measurement). Agreement between theory and experiment would lead to an increased precision of the measurement for the antiproton magnetic moment and provide a test of CPT invariance. 相似文献
15.
We present total cross sections for single and double ionization of helium by antiproton impact over a wide range of impact energies from 10 keV/amu to 1 MeV/amu. A nonperturbative time-dependent close-coupling method is applied to fully treat the correlated dynamics of the ionized electrons. Excellent agreement is obtained between our calculations and experimental measurements of total single and double ionization cross sections at high impact energies, whereas for lower impact energies, some discrepancies with experiment are found. At an impact energy of 1 MeV we also find that the double-to-single ionization ratio is twice as large for antiproton impact as for proton impact, confirming a long-standing unexpected experimental measurement. 相似文献
16.
An electron lens is capable of producing focusing fields of controllable profile separately for proton and antiproton bunches.
This makes it possible to neutralize collision effects. The pioneering experiments with this lens demonstrated that the antiproton
lifetime can be reduced from several hundreds to several tens of hours. In this work, we experimentally study processes arising
when a high-intensity proton bunch meets an electron beam. Two physical mechanisms that may diminish the lifetime of the antiproton
bunch are suggested. 相似文献
17.
Potential energy curves for excited leptonic states of the helium-antihydrogen system are calculated within the Ritz variational approach. An explicitly correlated ansatz for the leptonic wave function is employed describing accurately the motion of the leptons (two electrons and positron) in the field of the helium nucleus and of the antiproton with an arbitrary orbital angular momentum projection Lambda onto the internuclear axis. Results for Lambda=0, 1, and 30 are presented. For quasibound states with large values of Lambda and rotational quantum numbers J>Lambda no annihilation and rearrangement decay channels occur; i.e., they are metastable. 相似文献
18.
We argue that the observed antiproton production in heavy-ion collisions at CERN-SPS energies can be understood if (contrary to most sequential scattering approaches) the backward direction in the process pP<-->n(pi) (with n = 5-6) is consistently accounted for within a thermal framework. Employing the standard picture of subsequent chemical and thermal freezeout, which induces an oversaturation of pion number with associated chemical potentials of mu(pi) approximately 60-80 MeV, enhances the backward reaction substantially. The resulting rates turn out to be large enough to maintain an antiproton abundance at thermal freezeout in accordance with the measured p/p ratio in Pb(158A GeV)+Pb collisions. 相似文献
19.
S.N. Abdulmadjid M.M. Suliyanti K.H. Kurniawan T.J. Lie M. Pardede R. Hedwig K. Kagawa M.O. Tjia 《Applied physics. B, Lasers and optics》2006,82(1):161-166
We report in this paper the results of an experimental study on hydrogen analysis of solid samples in high pressure helium
ambient gas employing the basic scheme of laser induced breakdown spectroscopy (LIBS). It is shown that the metastable excited
state of helium atom can be utilized to induce delayed excitation of the ablated hydrogen atoms, and thereby avoid the Stark
broadening effect as well as overcoming the undesirable mismatch effect, which are responsible for inefficient excitation
respectively. It is further demonstrated that for samples of high boiling-point materials such as zircaloy, successful hydrogen
analysis can be achieved by a newly introduced double excitation technique employing single laser realized in a modified configuration
of the conventional LIBS method.
PACS 51-52 相似文献
20.
E. Widmann 《Hyperfine Interactions》2001,138(1-4):121-129
New results of the laser and microwave spectroscopy of antiprotonic helium “atomcules” obtained in the first year of operation
of the Antiproton Decelerator (AD) facility of CERN are presented. They include the discovery of three new resonant transitions
and the determination of the zero-density wavelength of six transitions with an accuracy of 130 ppb in the best case. Auger
rates of those states were also determined, and two of them were found to be several orders of magnitude larger than expected
from a simple estimate based on the multipolarity Δl, i.e., the jump in angular momentum required for the antiproton to reach the next lower-lying state of ionized
He++. Furthermore, a first signal of a two-laser microwave triple resonance to measure the hyperfine splitting in antiprotonic
helium was observed.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献