Producing Slow Antihydrogen for a Test of CPT Symmetry with ATHENA

The ATHENA experiment at the Antiproton Decelerator facility at CERN aims at testing CPT symmetry with antihydrogen. An overview of the experiment, together with preliminary results of development towards the production of slow antihydrogen are reported. This revised version was published online in August 2006 with corrections to the Cover Date.     

Towards antihydrogen confinement with the ALPHA antihydrogen trap

ALPHA is an international project that has recently begun experimentation at CERN’s Antiproton Decelerator (AD) facility. The primary goal of ALPHA is stable trapping of cold antihydrogen atoms with the ultimate goal of precise spectroscopic comparisons with hydrogen. We discuss the status of the ALPHA project and the prospects for antihydrogen trapping.     

Electron Magnetic Moment in Highly Charged Ions: The ARTEMIS Experiment

The magnetic moment (g‐factor) of the electron is a fundamental quantity in physics that can be measured with high accuracy by spectroscopy in Penning traps. Its value has been predicted by theory, both for the case of the free (unbound) electron and for the electron bound in a highly charged ion. Precision measurements of the electron magnetic moment yield a stringent test of these predictions and can in turn be used for a determination of fundamental constants such as the fine structure constant or the atomic mass of the electron. For the bound‐electron magnetic‐moment measurement, two complementary approaches exist, one via the so‐called “continuous Stern–Gerlach effect”, applied to ions with zero‐spin nuclei, and one a spectroscopic approach, applied to ions with nonzero nuclear spin. Here, the latter approach is detailed, and an overview of the experiment and its status is given.     

Cold and stable antimatter for fundamental physics

The field of cold antimatter physics has rapidly developed in the last 20 years, overlapping with the period of the Antiproton Decelerator (AD) at CERN. The central subjects are CPT symmetry tests and Weak Equivalence Principle (WEP) tests. Various groundbreaking techniques have been developed and are still in progress such as to cool antiprotons and positrons down to extremely low temperature, to manipulate antihydrogen atoms, to construct extremely high-precision Penning traps, etc. The precisions of the antiproton and proton magnetic moments have improved by six orders of magnitude, and also laser spectroscopy of antihydrogen has been realized and reached a relative precision of 2 × 10⁻¹² during the AD time. Antiprotonic helium laser spectroscopy, which started during the Low Energy Antiproton Ring (LEAR) time, has reached a relative precision of 8 × 10⁻¹⁰. Three collaborations joined the WEP tests inventing various unique approaches. An additional new post-decelerator, Extra Low ENergy Antiproton ring (ELENA), has been constructed and will be ready in 2021, which will provide 10–100 times more cold antiprotons to each experiment. A new era of the cold antimatter physics will emerge soon including the transport of antiprotons to other facilities.     

反物质的存在及反氢的制造

本文简述了人类寻找反物质的历程；目前产生反氢原子的方法及利用反物质的美好前景．     

Penning traps as a versatile tool for precise experiments in fundamental physics

This review article describes the trapping of charged particles. The main principles of electromagnetic confinement of various species from elementary particles to heavy atoms are briefly described. The preparation and manipulation with trapped single particles, as well as methods of frequency measurements, providing unprecedented precision, are discussed. Unique applications of Penning traps in fundamental physics are presented. Ultra-precise trap-measurements of masses and magnetic moments of elementary particles (electrons, positrons, protons and antiprotons) confirm CPT-conservation, and allow accurate determination of the fine-structure constant α and other fundamental constants. This together with the information on the unitarity of the quark-mixing matrix, derived from the trap-measurements of atomic masses, serves for assessment of the Standard Model of the physics world. Direct mass measurements of nuclides targeted to some advanced problems of astrophysics and nuclear physics are also presented.     

H+4形成机制的初步研究

利用Penningiontrap存储和累积离子的功能,获得不同延时（即反应时间）的离子谱H+n(n≤4),不仅进一步证实了H+4具有稳定结构的理论预言,而且经分析得出,H+4是经碰撞反应H+2+H2→H+4;H+3+H+H2→H+4+H2产生的。     

ATRAP antihydrogen experiments and update

Antihydrogen (Hbar) was first produced at CERN in 1995. Over the past decade our ATRAP collaboration has made massive progress toward our goal of producing large numbers of cold Hbar atoms that will be captured in a magnetic gradient trap for precise comparison between the atomic spectra of matter and antimatter. The AD at CERN provides bunches of 3 × 10⁷ low energy antiprotons approximately every 90 s. We capture and cool to 4 K, 0.1% of these in a cryogenic Penning trap. By stacking many bunches we are able to do experiments with 3 × 10⁵ Antiprotons. Approximately 100 positrons (e+)/s from a 22 Na radioactive source are captured and cooled in the trap, with 5 × 10⁶ available experiments. We have developed two ways to make Hbar from these cold ingredients, namely three-body collisions, and two-stage Rydberg charge exchange. We have also developed techniques to measure the excited-state distribution of the Hbar and measure their velocity. A new apparatus is being used this year that includes a e+ accumulator built at York University providing many more e+. The new antiproton annihilation detector provides spatial information of annihilations. Windows allow lasers to enter the trap for spectroscopic measurements and for laser cooling of the Hbar. Possibly the most exciting inclusion in this new apparatus is the inclusion of a neutral particle trap which may, for the first time, capture the Hbar and lead to the first atomic spectrum from antimatter.     

The LEBIT facility at MSU

The low-energy beam and ion trap facility LEBIT at the NSCL at MSU has demonstrated that rare isotopes produced by fast-beam fragmentation can be slowed down and prepared such that precision experiments with low-energy beams are possible. For this purpose high-pressure gas-stopping is employed combined with advanced ion manipulation techniques. Penning trap mass measurements on short-lived rare isotopes have been performed with a 9.4 T Penning trap mass spectrometer. Examples include ⁶⁶As, which has a half-live of only 96 ms, and the super-allowed Fermi-emitter ³⁸Ca, for which a mass accuracy of 8 ppb (280 eV) has been achieved. The high accuracy of this new mass value makes ³⁸Ca a new candidate for the test of the conserved vector current hypothesis.      

Excitation of 31,3 P and 31,3 D states of helium from the ground 11 S state by electrons and positrons

A systematic theoretical study is carried out for the electron and positron impact excitation of the 3^1,3 P and 3^1,3 D states of helium from the ground 1¹ S state. The results are reported for the differential cross sections, Stokes parameters and alignment and orientation parameters. To calculate the scattering amplitude which relate these parameters, a distorted wave approximation theory with different choices of distortion potential has been used. The results are compared with available theoretical and experimental data in the energy range of 40–100eV.     

A gauge theory of CPT transformations to first order

The CPT symmetry is made local for the Dirac field and an analogous local symmetry is proposed for curved spacetime. A nontrivial, infinitesimal variation of the Dirac action is thus induced. It is shown that the metric spin connection of general relativity cannot accommodate this symmetry. A new gauge field is therefore introduced, which turns out to be a real pseudovector field, and its equations of motion are derived.     

Theory of X-ray grazing incidence reflection in the presence of nuclear resonance excitation

ATHENA, one of the three approved experiments at the new facility for low energy antiprotons (AD) at CERN, has the primary goal to test CPT invariance by comparing the atomic energy levels of antihydrogen to those of hydrogen. The extended experimental program also contains studies on differences in gravitational acceleration of antimatter and matter. The production of antihydrogen atoms and their spectral response to laser light will be monitored by a sophisticated detector for the end products of antiproton and positron annihilations. This revised version was published online in August 2006 with corrections to the Cover Date.     

Fundamental weak interaction studies using polarised nuclei and ion traps

Two experiments to search for new physics beyond the standard model for electroweak interactions by measuring correlations between different spin and momentum vectors in nuclear β-decay are discussed. In the first experiment the correlation between the emission asymmetry and the longitudinal polarisation of positrons emitted by polarised nuclei is determined. This type of measurement is sensitive to the presence of right-handed currents but also to possible scalar and tensor-type currents in the weak interaction. The aim of the second experiment is to determine the βν-correlation in β-decay by measuring the energy spectrum of the recoil ions, using a Penning trap and a retardation spectrometer. In this case the focus is on the search for scalar currents in the weak interaction. The results of the experiments presented here are complementary to results from experiments in muon decay and at high-energy colliders. This revised version was published online in July 2006 with corrections to the Cover Date.     

Observed evidence of microwave-background formation by thermal radiation of metagalaxy stars

In the opinion of the majority of scientists, to disprove the validity of the Big Bang cosmology, it suffices to demonstrate another convincing mechanism of microwave-background formation, which leads to the conclusion that the background is not a strictly black-body one and/or is not associated with the matter in early epoch [1].Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 39, No. 7, pp. 817–843, July, 1996.     

Beyond the Chandrasekhar limit: Structure and formation of compact stars

The concept of limiting mass, introduced by Chandrasekhar in case of white dwarfs, plays an important role in the formation and stability of compact objects such as neutron stars and black holes. Like white dwarfs, neutron stars have their own mass limit, and a compact configuration would progress from one family to the next, more dense one once a mass limit is crossed. The mass limit of neutron stars depends on the nature of nuclear forces at very high density, which has so far not been determined conclusively. This article reviews how observational determinations of the properties of neutron stars are starting to impose significant constraints on the state of matter at high density.     

The Zoo of neutron stars

In these lecture notes, I briefly discuss the present day situation and new discoveries in astrophysics of neutron stars focusing on isolated objects. The latter include soft gamma repeaters, anomalous x-ray pulsars, central compact objects in supernova remnants, the Magnificent Seven, and rotating radio transients. In the last part of the paper, I describe available tests of cooling curves of neutron stars and discuss different additional constraints that can help to confront theoretical calculations of cooling with observational data. The text was submitted by the author in English.     

用离子阱经H2++H2碰撞反应碰撞反应制备H4+

用Ｐｅｎｎｉｎｇ型离子阱经碰撞反应Ｈ２＾＋＋Ｈ２→Ｈ４＾＋产生稳定的Ｈ４＾＋,主要的反应产物是Ｈ３＾＋,但十分明显地观测到Ｈ４＾＋信号。Ｈ４＾＋在阱中稳定存在时间长达０．１ｓ量级,远比Ｋｉｒｃｈｎｅｒ等人测量的１０＾－６ｓ量级长,最后讨论了生成Ｈ４＾＋的反应过程机制。     

The Canadian Penning Trap Spectrometer at Argonne

The Canadian Penning Trap (CPT) mass spectrometer is a device used for high-precision mass measurements on short-lived isotopes. It is located at the ATLAS superconducting heavy-ion linac facility where a novel injection system, the RF gas cooler, allows fast reaction products to be decelerated, thermalized and bunched for rapid and efficient injection into the CPT. The CPT spectrometer and its injection system will be described in detail and its unique capabilities with respect to its initial physics program, concentrating on isotopes around the N=Z line with particular emphasis on isotopes of interest to low-energy tests of the electroweak interaction and the rp-process, will be highlighted. This revised version was published online in July 2006 with corrections to the Cover Date.     

潘宁源放电的全三维电磁粒子模拟/蒙特卡罗碰撞数值算法研究

深入研究潘宁放电的物理机制, 研制了全三维高品质算法粒子模拟软件(PIC), 设计并添加了相应物理情景的蒙特卡罗碰撞模块(MCC), 并对电子、氢分子离子(H₂⁺)、氢正离子(H⁺)、氢三正离子(H₃⁺)同时进行了跟踪, 成功研制了全三维电磁PIC/MCC数值算法. 结合国内研究较热的潘宁放电模型, 对该算法进行模拟验证. 模拟结果显示: 采用有效的滤波算法能抑制电磁数值噪声, 电子能量呈麦克斯韦分布, 由于电子的径向漂移和加速导致离子源顶端H₂⁺产量较大. 关键词： 潘宁离子源 高品质算法 粒子模拟/蒙特卡罗