Experiments with exotic atoms and exotic nuclei at GSI, recent developments and future prospects

Results and new developments with exotic atoms and exotic nuclei are presented from recent experiments at GSI. The proposed European inflight facility at GSI will open up new fields of outstanding research and will simultaneously access unknown regions of nuclei with new properties. A new generation of precision experiments will be performed with stored exotic nuclei, whereby nuclear reactions with an internal target and electron scattering in a small electron-ion collider will be a great challenge.     

Self-trapping of electrons in vortex rings in liquid helium

A model according to which “fast” and “exotic” negative ions in superfluid helium are the localized states of electrons in vortex rings has been presented. The quantization of radial and longitudinal motions of electrons inside the vortex core and the quantization of the vortex motion of liquid helium lead to the existence of a whole family of excited states of electron vortices, in qualitative agreement with the experiments on the mobility of exotic ions. The possibility of the verification of conclusions of the model in optical experiments has been considered.     

Identifying multiquark hadrons from heavy ion collisions

Identifying hadronic molecular states and/or hadrons with multiquark components either with or without exotic quantum numbers is a long-standing challenge in hadronic physics. We suggest that studying the production of these hadrons in relativistic heavy ion collisions offers a promising resolution to this problem as yields of exotic hadrons are expected to be strongly affected by their structures. Using the coalescence model for hadron production, we find that, compared to the case of a nonexotic hadron with normal quark numbers, the yield of an exotic hadron is typically an order of magnitude smaller when it is a compact multiquark state and a factor of 2 or more larger when it is a loosely bound hadronic molecule. We further find that some of the newly proposed heavy exotic states could be produced and realistically measured in these experiments.     

BESIII 实验对奇特态 X(3872) 的研究

量子色动力学允许超出夸克模型中重子和介子的奇特态的存在。对奇特态的研究是当前高能物理实验的热门话题之一。X(3872)是第一个被实验上观测到的奇特态候选者。实验和理论上对X(3872)的研究从未间断,这使得X(3872)成为了解最好的奇特态。运行在北京正负电子对撞机(BEPCII)上的北京谱仪(BESIII)实验积累了大量的质心能量从3.87 到 4.70 GeV的正负电子对撞数据样本。利用这些数据样本,得到了很多关于X(3872)的实验结果。本文将回顾BESIII上关于X(3872)所取得一系列成果及最新实验进展。对X(3872)等奇特态的研究,将有利于我们对自然界的基本相互作用的理解,也将促进标准模型理论的完善。     

Methods for organizing the interaction of circulating particle beams with internal targets in nuclear physics experiments at synchrotrons and storage rings

The first methods for using internal targets and their further development for organization of nuclear physics experiments at synchrotrons and storage rings are reviewed. With these methods, new results are obtained and discoveries are made in physics of interactions of elementary particles and nuclei. Current uses of various internal targets and circulating particle beams in ongoing and projected research in particle physics, relativistic nuclear and spin physics, and physics of interactions of exotic and radioactive nuclei and for producing fluxes of secondary particles (mesons, neutrons, exotic and radioactive nuclei, etc.) for physics experiments are described.     

Low energy study of clustering phenomena in light exotic nuclei

New experiments are proposed aimed to study the structure and cluster properties of light exotic nuclei along with specific features of the reaction mechanisms. Theoretical analysis and the calculated cross sections show that the proposed experiments can be really performed at low energies.     

奇异核的实验研究

总结了兰州放射性束实验小组在兰州放射性次级束流线上近几年来利用产生的放射性束流,轰击Si或C等靶子,测量它的反应总截面.并利用经验公式将这些结果归一到相同的能量和靶子,与其相邻的核相比较,发现了⁹C,¹¹Be,¹⁴Be,⁸B,¹⁴B 和¹²N等核素的反应总截面值有奇异增大的现象.利用微观的Glauber模型进行了计算,对有奇异结构的核采用核芯加价核子的密度分布形式,理论计算和实验结果符合得很好,可以给出奇异核的弥散的密度分布.     

In-beam gamma-ray spectroscopy with exotic beams at the NSCL

Projectile fragmentation provides radioactive beams at intermediate velocities (v/c = 0.3-0.5) by physical means of fragment separation. With the development of position-sensitive photon detectors it has become possible to measure the energies and directions of photons emitted in-flight from such fast-moving exotic beams. This allows the reconstruction of the photons' energies emitted from an exotic projectile with high accuracy. It can be advantageous to employ photon detection in experiments with exotic beams since photons can traverse matter easily and their attenuation can be calculated. Experiments with standard luminosities can be carried out at intermediate beam energies with thick secondary targets (order of g/cm²) and very low incident beam rates (order of particle/s or less). Experimental success in this field is strongly correlated with the development of photon detectors such as position-sensitive scintillation detectors or segmented germanium detectors. In-beam gamma-ray spectroscopy of fast exotic beams has been successfully used at all projectile fragmentation facilities in intermediate-energy heavy-ion inelastic scattering experiments, knockout reactions and fragmentation reactions. Here, we focus on experimental results for neutron-rich exotic nuclei in the π(sd )-shell. Measurements and detector developments carried out at the NSCL at Michigan State University during the last four years are discussed. Received: 1 May 2001 / Accepted: 4 December 2001     

Remarks on the search for exotic exchange

Triple-Regge arguments suggest that exotic exchange contributions to peripheral processes should be relatively more important for the production of massive (thus unstable) particles. Experimental evidence bearing on this idea is surveyed, and implications for new experiments are discussed.     

新奇粒子和奇特物质的实验探索

根据理论预言及实验兴趣,我们设计了一系列实验,对轴子、重中微子、磁单极子、小电荷粒子和超重核块进行寻找。本文系统地报告这一系列实验工作,并且给出这些新奇粒子和奇特物质的限。     

From kaonic atoms to kaonic nuclei: A search for antikaon-mediated bound nuclear systems

Strong interaction processes were intensively studied at low energy with exotic atoms, touching one of the fundamental problems in hadron physic today — the still unsolved question of how hadron masses are generated. The question of the origin of the large hadron masses made up of light quarks, the current mass of the up (u) and down (d) quarks (m_u,d≈5 MeV) is two orders of magnitude smaller than a typical hadron mass of about 1 GeV, will be discussed in the context with the experimental work done in the field of exotic atoms expanded to exotic nuclei.An overview of the properties of exotic hydrogen atoms made of pions and kaons are presented, using high precision experiments unrevealing the nature of strong interaction physics at low energy. A new field which contributes to the understanding of the origin of the large hadron mass is the study of the mass modification in a nuclear medium. Antikaon mediated bound nuclear systems would be an ideal tool, if they exist, to look for chiral restoration at high density and zero temperature or even more exotic to look for phase transitions.     

Stability diagram of higher modes of the Fabry-Perot resonator

We have numerically calculated the stability diagram of the higher modes of the Fabry-Perot resonator by direct diagonalization of the Fox-Li equation. The diagram has an exotic behavior in the small Fresnel number region and its higher modes in our numerical experiments.     

Recent experiments with radioactive ion beams at GSI

A review is given over recent experiments performed by means of A·keV to A·GeV radioactive ion beams at GSI Darmstadt. Nuclear structure information on exotic nuclei is discussed as obtained by using an online isotope separator, a velocity filter or a magnetic beam-line spectrometer.     

Development of Polarized HD Target for Future LEPS Experiments at Spring-8

We are carrying out hadron photoproduction experiments by using polarized photon beams at SPring-8 in Japan.In 2005,we started developing a polarized HD target for future experiments using both the polarized photon beams and the polarized target.The polarized HD target is an idealistic target for experiments observing reactions with small cross sections because the HD does not include heavy nuclei which produce many background events.The measurement of double polarization asymmetries is expected to give much important information to investigate the nucleon hidden structure,hadron photoproduction dynamics,and exotic hadron property.We report on the present status of the development of the polarized HD target al RCNP.     

A naturally occurring trap for antiprotons

The phenomenon of delayed annihilation of antiprotons in helium is the first instance of a naturally occurring trap for antimatter in ordinary matter. Recent studies of this effect at CERN are summarised, and plans are described for laser excitation experiments to test its interpretation in terms of metastable exotic helium atom formation.     

Warped unification, proton stability, and dark matter

We show that solving the problem of baryon-number violation in nonsupersymmetric grand unified theories (GUT's) in warped higher-dimensional spacetime can lead to a stable Kaluza-Klein particle. This exotic particle has gauge quantum numbers of a right-handed neutrino, but carries fractional baryon number and is related to the top quark within the higher-dimensional GUT. A combination of baryon number and SU(3) color ensures its stability. Its relic density can easily be of the right value for masses in the 10 GeV-few TeV range. An exciting aspect of these models is that the entire parameter space will be tested at near future dark matter direct detection experiments. Other exotic GUT partners of the top quark are also light and can be produced at high energy colliders with distinctive signatures.     

Experiments on the solution of the helmholtz equation using the finite element method and a variational approach in the case of domains of complicated boundary shape

Domains of ‘exotic’ boundary shape are of interest in several technological applications—acoustic and electromagnetic waveguides, solid propellant rocket cross-sections, printed circuit boards, etc.The present paper describes some experiments performed to determine the eigenvalues of a vibrating, ideal membrane.It is shown that the finite element method yields results which are in very good agreement with values determined by means of an analytical approach in the case of a membrane of a cardioidal shape.     

Search for topological defect of axionlike model with cesium atomic comagnetometer

Many terrestrial experiments have been designed to detect domain walls composed of axions or axionlike particles(ALPs), which are promising candidates of dark matter. When the domain wall crosses over the Earth, the pseudoscalar field of ALPs could couple to the atomic spins. Such exotic spin-dependent couplings can be searched for by monitoring the transient-in-time change of the atomic spin precession frequency in the presence of a magnetic field. We propose here a single-species cesium atomic comagnetometer, which measures the spin precession frequencies of atoms in different ground-state hyperfine levels, to eliminate the common-mode magnetic-field variations and search for the exotic nonmagnetic couplings solely between protons and ALPs. With the single-species atomic comagnetometer, we experimentally rule out the possibility that the decay constant of the linear pseudoscalar couplings of ALPs to protons is f_p■ 3.71 ×10~7 Ge V. The advanced system has the potential to constrain the constant to be f_p■ 10.7 × 10~9 Ge V, promising to improve astrophysical constraint level by at least one order of magnitude. Our system could provide a sensitive detection method for the global network of optical magnetometers to search for exotic physics.     

Constraining Exotic Interactions

Beyond‐the‐standard‐model interactions mediated by an exchange of virtual “new” bosons result in a finite set of possible effective interaction potentials between standard‐model particles such as electrons and nucleons. The classification of such potentials is discussed and recent experiments searching for such exotic interactions at spatial scales from sub‐nanometers to tens of thousand kilometers are briefly reviewed.     

X-ray spectroscopy at PSI

Crystal spectroscopy of the X-rays of exotic atoms started with a series of experiments using transmission spectrometers. Experiments at lower energies were made possible by the development of reflection spectroscopy. The progress made is illustrated with a measurement of the pion mass and the determination of strong interaction effects in pionic hydrogen isotopes. Modern developments aim at a determination of the strong interaction width on the level of %. The way to reach this goal is presented and the limits of the method and possible future experiments are discussed. This revised version was published online in August 2006 with corrections to the Cover Date.