共查询到20条相似文献,搜索用时 15 毫秒
1.
Between 10(4) and 10(6) 9Be+ ions were trapped in a Penning trap and laser cooled to approximately 1 mK, where they formed a crystalline plasma. We measured the ion temperature as a function of time after turning off the laser cooling and observed a rapid temperature increase as the plasma underwent the solid-liquid phase transition at T approximately 10 mK (Gamma approximately 170). We present evidence that this rapid heating is due to a sudden release of energy from weakly cooled degrees of freedom involving the cyclotron motion of trapped impurity ions. This equilibration of cyclotron motion with motion parallel to the magnetic field is more than 10 orders of magnitude faster than that predicted by currently available theory, which is valid only in the absence of correlations (Gamma<1). 相似文献
2.
In the energy domain of 1?C2 GeV kinetic energy per nucleon, HADES has measured rare and penetrating probes in elementary and heavy ion collisions. Our results demonstrate that electron pair emission in C+C collisions can essentially be explained as a superposition of independent N+N collisions. HADES results on e+e? production in Ar+KCl collisions, however, show a strong enhancement of the dilepton yield relative to a reference spectrum obtained from elementary nucleon-nucleon reactions, signal the onset of medium effects beyond the superposition of individual N+N collisions. Intriguing results where also obtained from the reconstruction of hadrons with open and hidden strangeness. Analyses of the experimentally obtained hadronic yields measured in Ar+KCl allows to extract the chemical freeze-out conditions in the T -??B phase diagram of strongly interacting matter. While the measured abundance of all reconstructed particles are well described assuming thermalization, the also reconstructed double strange baryon ??? appears about ten times more abundant than expected. This result will be discussed in the context of the exploration of the nuclear matter phase diagram in the region of finite density. Further investigations to search for significant medium effects, will be followed over the coming years with an upgraded HADES detector. 相似文献
3.
Lee Kai Fong Chan Kat Fu 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1977,5(3):141-145
The stability of left-hand circularly polarized waves propagating along an external magnetic field with wavelengths much larger than the ion Larmor radius is studied for fully-ionized collisional plasmas carrying a field-aligned current. It is found that, in the presence of electron-ion collisions, this "kink-like" instability has two branches of unstable wavenumbers: a main branch and a resistive branch. The resistive branch owes its existence to electron-ion collisions, but its growth rate is much smaller than that of the main branch, which is typically some fraction of the ion cyclotron frequency. The effect of collisions on the main branch is to reduce its maximum growth rate while extending the range of unstable wavenumbers to larger values. However, these changes are significant only when the electron-ion collision frequency is comparable to the electron cyclotron frequency. The dispersion relation is solved numerically for plasma and magnetic field parameters appropriate to the UCLA arcjet plasma. The results show that, within the framework of an infinite and homogeneous theory, the kink-like instability should occur in this plasma device. 相似文献
4.
《Physics Reports》1986,142(4):167-262
Abundances of strange antibaryons formed in nuclear collisions at above 10 GeV/A are considered as a most accessible diagnostic tool for the study of the possible formation and physical properties of the quark-gluon plasma phase of hadronic matter. In this report we describe the current status and develop a dynamical approach in order to describe strange particle formation in nuclear collisions at high energy. 相似文献
5.
考虑到核碰撞几何,我们推导出高能诱发核反应中二阶阶乘矩与参加反应核子数涨落之间的关系.分析表明,在高能碰撞的射弹碎裂区,强子-核反应末态粒子的间歇性质决定于其强子-强子子过程的间歇特征;而在靶碎裂区,它却主要依赖于参加反应核子数的涨落.推广到核-核反应(B<相似文献
6.
《Waves in Random and Complex Media》2013,23(3):356-369
In this paper, the dissipative instabilities in the interaction of an ion beam with unmagnetized and strongly magnetized plasmas are investigated. In both cases, relevant dispersion equations of high-frequency and ion acoustic waves are obtained. In addition, the resonance frequencies and growth rates of the instabilities are derived. It is shown that the thermal motion of charged particles has positive effects on the resonance frequency but its influence on the growth rate of an instability depends on the plasma conditions. Although in all cases the collisions are found to have a stabilizing effect, it is shown that the dominant type of collisions (electron-neutral or ion-neutral collisions) depends on the frequency range. It is also indicated that the resonance frequency and the growth rate of an instability in the unmagnetized plasma is higher than in the strongly magnetized plasma for non-zero propagation angles. 相似文献
7.
重味粒子是新的物质形态——夸克胶子等离子体的敏感探针。 利用相对论流体力学描述夸克胶子等离子体的时空演化, 采用输运方程模拟重味粒子在夸克胶子等离子体中的运动, 既考虑重味粒子的热胶子离解, 也通过细致平衡原理包含重味粒子在热密媒质中的重产生。 正是由于离解与重产生之间的竞争以及竞争对于碰撞能量、 横动量和快度的依赖性, 自然解释了在RHIC能区的J/ψ疑难, 预言了在LHC能区由于重产生取得主导地位, J/ψ的核修正因子在中心和半中心碰撞中将随着参与反应核子数的增大而升高, 同时其平均横动量会受到强烈的压低。 Heavy quarkonium is a sensitive signature of the new state of matter-quark gluon plasma produced in high energy nuclear collisions. We describe the space time evolution of the quark gluon plasma by relativistic hydrodynamic equations and the quarkonium motion by transport equation. We found that the competition between the gluon dissociation and regeneration can explain naturally the J/ψ puzzles at RHIC energy. We predict the increase of the nuclear modification factor in semi central and central collisions and the related transverse momentum suppression at LHC energy. 相似文献
8.
B. Borderie M. F. Rivet C. Cabot H. Fuchs D. Gardes F. Hanappe D. Jouan M. Montoya 《Zeitschrift für Physik A Hadrons and Nuclei》1991,338(3):369-370
The dynamics of the two partners produced in dissipative collisions has been experimentally studied for the system40Ar + Ag at 27 MeV per nucleon. Primary masses of the fragments can then be calculated; the excitation energy partition between the two fragments is derived from the number of particles evaporated by each fragment. We found that this division evolves from equipartition to a repartition close to thermal equilibrium in the excitation energy range 300–350 MeV or interaction times 5-10×l0?22 s. 相似文献
9.
V. S. Pantuev 《Physics of Atomic Nuclei》2008,71(9):1625-1631
We argue that, on the basis of recent experimental data, there is possible existence of a finite formation time of strongly
interacting plasma in nuclear collisions at RHIC. To show this, we construct a simple model based on a Monte Carlo simulation
of nucleus—nucleus collisions with a realistic nuclear density distribution. The most striking feature of the experimental
data—an absence of absorption of high-transverse-momentum pions in the reaction-plane direction for midperipheral collisions—points
to the presence of a surface zone with no absorption and strong suppression in the inner core. A natural interpretation of
such a zone could be the plasma formation time T ≃ 2–3 fm/c. With this assumption, we describe the angular anisotropy of high-transverse-momentum pions with respect to the reaction
plane and the centrality dependence of the nuclear modification factor in Au + Au and Cu + Cu collisions.We present predictions
for LHC.
The text was submitted by the author in English. 相似文献
10.
We propose a unified space-time picture of baryon stopping and quark-gluon plasma creation in ultrarelativistic heavy-ion collisions. It is assumed that the highly Lorentz contracted nuclei are decelerated by the coherent color field which is formed between them after they pass through each other. This process continues until the field is neutralized by the Schwinger mechanism. Conservation of energy and momentum allow us to calculate the energy losses of the nuclear slabs and the initial energy density of the quark-gluon plasma. 相似文献
11.
We analyze the azimuthal anisotropy of jet spectra due to energy loss of hard partons in quark-gluon plasma, created initially
in nuclear overlap zone in collisions with non-zero impact parameter. The calculations are performed for semi-central Pb-Pb
collisions at LHC energy. 相似文献
12.
Tim Schuster 《Progress in Particle and Nuclear Physics》2009,62(2):373-374
Two experimental programs are aiming to study nuclear collisions in the energy regime in order to explore an essential part of the phase diagram of strongly interacting matter. The programs are motivated by observations that indicate a phase transition to take place in this energy domain: the onset of deconfinement. The STAR collaboration proposes an energy scan in the Relativistic Heavy Ion Collider (RHIC) at BNL. The ongoing program of the NA61/SHINE experiment consists of a two-dimensional energy-system size scan in nuclear and elementary collisions. The goal of both programs is to study the properties of the onset of deconfinement and to eventually discover the conjectured critical point of strongly interacting matter. A comparison of the strengths and limitations reveals the complementarity of the two programs. 相似文献
13.
The intensity of spectral lines in the light emitted by stars gives information about the thermodynamic state of stellar matter. Similarly, the intensity of charmonium and bottonium lines in the spectrum of dileptons emitted in nuclear collisions can provide information about the early thermodynamic state of any strongly interacting matter created in such collisions. TheJ/? suppression found in centralO-U andS-U collisions is a first instance of a change in spectral intensity. We develop a full spectral analysis for the production of \(c\bar c\) and \(b\bar b\) resonances and discuss how it can be used to explore the primordial state of matter produced in high energy heavy ion collisions. 相似文献
14.
Volker Metag 《Pramana》2010,75(2):195-206
Properties of hadrons in strongly interacting matter provide a link between quantum chromodynamics in the strong coupling
regime and experimental observables. QCD sum rules show that changes in chiral and higher-order condensates, partially associated
with a restoration of chiral symmetry in the nuclear medium, will lead to significant changes in the low-energy spectrum of
hadrons. Heavy-ion collisions and reactions with elementary probes have been used to extract experimental information on in-medium
properties of hadrons. Results on the light vector mesons ρ, ω, and ϕ, are summarized and compared. Almost all experiments report a softening of the spectral functions with increases in width
depending on the density and temperature of the hadronic environment. No evidence for mass shifts is found in majority of
the experiments. Remaining inconsistencies among experimental results demonstrate the need for further measurements with higher
statistics and inrceased acceptance in particular for low-momentum vector mesons. 相似文献
15.
Wave damping has been observed for the fast (compressional) wave at frequencies that are about 10 percent above the second and third harmonics of the ion cyclotron frequency. Preliminary calculations indicate that this shift is the result of collisions. The waves were launched by a 1-turn loop around the cylindrical plasma column and damped in a magnetic beach. The highly ionized hydrogen or deuterium plasma had an average temperature of 2 eV and an average density of about 2.5 × 1020 m-3. 相似文献
16.
The interplay of nuclear effects on the p(T)>2 GeV inclusive hadron spectra in d+Au and Au+Au reactions at sqrt[s(NN)]=17, 200, and 5500 GeV is compared to leading order perturbative QCD calculations for elementary p+p (p+p) collisions. The competition between nuclear shadowing, Cronin effect, and jet energy loss due to medium-induced gluon radiation is predicted to lead to a striking energy dependence of the nuclear suppression/enhancement pattern in A+A reactions. We show that future d+Au data can be used to disentangle the initial and final state effects. 相似文献
17.
W. Cassing 《Zeitschrift für Physik A Hadrons and Nuclei》1987,327(4):447-460
The Uehling-Uhlenbeck collision term is derived from coupled equations of motion for the one-body density matrix and the two-body correlation function as obtained from the density-matrix hierarchy. The respective approximations introduced are related with energy and momentum conservation in single nucleon-nucleon collisions and found numerically to be approximately valid for energetic nucleon-nucleon collisions in case of intermediate energy heavy-ion reactions. Primary collision times of nucleons in the dinuclear reaction zone are calculated for various laboratory energies and the approach to local equilibrium is followed in time. Average relaxation times for highly excited finite nuclear systems are found to be considerably shorter than for related infinite nuclear matter problems, however, still too large as to allow for the formation of hot spots in nuclei. 相似文献
18.
M. Ostrick 《The European Physical Journal A - Hadrons and Nuclei》2006,30(1):81-108
Dynamical and thermal characterizations of excited nuclear systems produced during the collisions between two heavy ions at
intermediate incident energies are presented by means of a review of experimental and theoretical work performed in the last
two decades. Intensity interferometry, applied to both charged particles (light particles and intermediate mass fragments)
and to uncharged radiation (gamma rays and neutrons) has provided relevant information about the space-time properties of
nuclear reactions. The volume, lifetime, density and relative chronology of particle emission from decaying nuclear sources
have been extensively explored and have provided valuable information about the dynamics of heavy-ion collisions. Similar
correlation techniques applied to coincidences between light particles and complex fragments are also presented as a tool
to determine the internal excitation energy of excited primary fragments as it appears in secondary-decay phenomena. 相似文献
19.
20.
《Physics letters. [Part B]》1988,215(2):375-380
A calculation is made for charm quark production in a longitudinally expanding quark-gluon plasma. A comparison is made with hadronic charm production in ultra-relativistic nuclear collisions assuming an extrapolation from p-p collisions and no plasma formation. The charm yield from a QGP begins to dominate purely hadronic production for plasma temperatures above 315–440 MeV, depending on the bombarding energy of the colliding nuclei and the value assumed for the charm quark mass. Implications for plasma signals, most notably dilepton emission and J/ψ suppression, are discussed. 相似文献