arXiv subjects
Publications and source records attributed to Z. Xu.
A $ρ(770)^0$ mass shift of about -40 MeV/$c^2$ was measured in $p+p$ collisions at $\sqrt{s_{_{NN}}} = $ 200 GeV at RHIC. Previous mass shifts have been observed at CERN-LEBC-EHS and CERN-LEP. We will show that phase space does not account for the $ρ(770)^0$ mass shift measured at RHIC, CERN-LEBC-EHS and CERN-LEP and conclude that there are significant scattering interactions in $p+p$ collisions.
Within a pQCD inspired kinetic parton cascade we simulate the space time evolution of gluons which are produced initially in a heavy ion collision at RHIC energy. The inelastic gluonic interactions $gg \leftrightarrow ggg$ do play an important role: For various initial conditions it is found that thermalization and the close to ideal fluid dynamical behaviour sets in at very early times. Special emphasis is put on color glass condensate initial conditions and the `bottom up thermalization' scenario. Off-equilibrium $3\to 2$ processes make up the very beginning of the evolution leading to an initial decrease in gluon number and a temporary avalanche of the gluon momentum distribution to higher transversal momenta.
We propose a genuine multi-party correlation measure for a multi-party quantum system as the trace norm of the cumulant of the state. The legitimacy of our multi-party correlation measure is explicitly demonstrated by proving it satisfies the five basic conditions required for a correlation measure. As an application we construct an efficient algorithm for the calculation of our measures for all stabilizer states.
Motivated by the recent experimental observation of multi-component spinor condensates via a time-dependent quadrupole-Ioffe-configuration trap (QUIC trap), we provide a general framework for the investigation of nonadiabatic Landau-Zener dynamics of a hyperfine spin, e.g., from an atomic magnetic dipole moment coupled to a weak time-dependent magnetic (B-) field. The spin flipped population distribution, or the so-called Majorona formula is expressed in terms of system parameters and experimental observables; thus, provides much needed insight into the underlying mechanism for the production of spinor condensates due to nonadiabatic level crossings.
We demonstrate the occurrence of canonical suppression associated with the conservation of an U(1)-charge in current transport models. For this study a pion gas is simulated within two different transport approaches by incorporating inelastic and volume-limited collisions $ππ\leftrightarrow K\bar{K}$ for the production of kaon pairs. Both descriptions can dynamically account for the suppression in the yields of rare strange particles in a limited box, being in full accordance with a canonical statistical description.
We investigate quantum correlations of the $N$-qubit states via a collective pseudo-spin interaction ($\propto J_y^2$) on arbitrary pure separable states for a given interval of time. Based on this dynamical generation of the $N$-qubit maximal entangled states, a quantum secret sharing protocol with $N$ continuous classical secrets is developed.
We investigate the temperature-dependent effective size of a trapped interacting atomic Bose gas within a mean field theory approximation. The sudden shrinking of the average length, as observed in an earlier experiment by Wang {\it et al.} [Chin. Phys. Lett. {\bf 20}, 799 (2003)], is shown to be a good indication for Bose-Einstein condensation (BEC). Our study also supports the use of the average width of a trapped Bose gas for a nondestructive calibration of its temperature.
Employing a newly developed pQCD inspired parton cascade we simulate the space time evolution of gluons which are produced initially in a heavy ion collision at RHIC energy. The inelastic $gg \leftrightarrow ggg$ interactions are for the first time implemented obeying full detailed balance. The numerical results show that thermalization of gluons is mainly driven by the inelastic gluonic interactions and reaches equilibrium at $1\sim 2$ fm/c. In simulations for noncentral collisions considerable partonic elliptic flow $v_2$ is generated being comparable with the experimental data.
A number of promising results of a new 3+1 dimensional Monte Carlo parton cascade including inelastic multiplication processes (gg <--> ggg) are elaborated: (1) thermalization and chemical saturation; (2) the onset of longitudinal hydrodynamical expansion; (3) the build up of elliptic flow. We first briefly outline the basic idea of the algorithm. Full simulations are done with initial conditions for the kinetic partons via minijets or with ones stemming from a color glass condensate. The inclusion of the inelastic channels leads to a very fast kinetic equilibration and also to an early creation of pressure.
Particle identification (PID) capabilities are studied by using the Time Projection Chamber (TPC) and a Time-Of-Flight (TOF) detector together at STAR. The identification capability of charged hadrons is greatly extended compared with that achieved by TPC and TOF separately. Particle spectra from p+p, d+Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV and Au+Au collisions at $\sqrt{s_{_{NN}}}=62.4$ GeV are used to develop the methods. The transverse momentum ($p_T$) ranges of $π$, and $p(\bar{p})$ identification are from $\sim0.3$ GeV/$c$ to $\sim10$ GeV/$c$. The high $p_T$ reach is limited by statistics in current data sets. An important conceptual advance was developed to identify electrons by using a combination of dE/dx in TPC and velocity information from the TOF detectors, which is important for future low-mass dilepton program at STAR.
In this paper we report the growth and superconductivity of $Na_xTaS_2$ crystals. The structural data deduced from X-ray diffraction pattern shows that the sample has the same structure as $2H-TaS_2$. A series of crystals with different superconducting transition temperatures ($T_c$) ranging from 2.5 K to 4.4 K were obtained. It is found that the $T_c$ rises with the increase of $Na$ content determined by Energy-Dispersive x-ray microanalysis(EDX) of Scanning Electron Microscope (SEM) on these crystals. Compared with the resistivity curve of un-intercalated sample $2H-TaS_2$ ($T_c$ = 0.8 K, $T_{CDW} \approx$ 70 K), no signal of charge density wave (CDW) was observed in samples $Na_{0.1}TaS_2$ and $Na_{0.05}TaS_2$. However, in some samples with lower $T_c$, the CDW appears again at about 65 K. Comparison between the anisotropic resistivity indicates that the anisotropy becomes smaller in samples with more $Na$ intercalation (albeit a weak semiconducting behavior along c-axis) and thus higher $T_c$. It is thus concluded that there is a competition between the superconductivity and the CDW. With the increase of sodium content, the rise of $T_c$ in $Na_xTaS_2$ is caused mainly by the suppression to the CDW in $2H-TaS_2$, and the conventional rigid band model for layered dichalcogenide may be inadequate to explain the changes induced by the slight intercalation of sodium in $2H-TaS_2$.
It is investigated whether canonical suppression associated with the exact conservation of an U(1)-charge can be reproduced correctly by current transport models. Therefore a pion-gas having a volume-limited cross section for kaon production and annihilation is simulated within two different transport prescriptions for realizing the inelastic collisions. It is found that both models can indeed dynamically account for the canonical suppression in the yields of rare strange particles.
We discuss the canonical form for a pure state of three identical bosons in two modes, and classify its entanglement correlation into two types, the analogous GHZ and the W types as well known in a system of three distinguishable qubits. We have performed a detailed study of two important entanglement measures for such a system, the concurrence $\mathcal{C}$ and the triple entanglement measure $τ$. We have also calculated explicitly the spin squeezing parameter $ξ$ and the result shows that the W state is the most ``anti-squeezing'' state, for which the spin squeezing parameter cannot be regarded as an entanglement measure.
We propose two protocols to encode a logical qubit into physical qubits relying on common types of qubit-qubit interactions in as simple forms as possible. We comment on its experimental implementation in several quantum computing architectures, e.g. with trapped atomic ion qubits, atomic qubits inside a high Q optical cavity, solid state Josephson junction qubits, and Bose-Einstein condensed atoms.
We present the elliptic flow $v_2$ of pions produced from resonance decays. The transverse momentum $p_T$ spectra of the parent particles are taken from thermal model fits and their $v_2$ are fit under the assumption that they follow number-of-constituent-quark (NCQ) scaling expected from quark-coalescence models. The $v_2$ of pions from resonance particle decays is found to be similar to the measured pion $v_2$. We also propose the measurement of electron $v_2$ as a means to extract open-charm $v_2$ and investigate whether a thermalized system of quarks and gluons (a quark-gluon plasma) is created in collisions of Au nuclei at RHIC.
We elaborate on a new 3+1 dimensional Monte Carlo parton cascade solving kinetic Boltzmann processes including - for the first time - inelastic multiplication processes (gg <-->ggg) in a unified manner. The back reaction channel is treated fully consistently, exactly obeying detailed balance. The algorithm can handle, in principle, any specified initial conditions for the freed partons, the latter being on their kinetic mass shell. First full simulations with minijet initial conditions demonstrate that the inclusion of the inelastic channels leads to a very fast kinetic and chemical equilibration and also to an early creation of pressure.
In this lecture we review recent progress in various aspects of non-equilibrium QFT with respect to relativistic heavy ion collisions. As a first and rather general study we summarize our (numerical) investigations for a dissipative quantum time evolution of $ϕ^4$-field theory for a spatially homogeneous system in 2+1 space-time dimensions on the basis of the Kadanoff-Baym equations. The initial conditions can be chosen arbitrarily and far from equilibrium. The calculations demonstrate how thermalization and chemical equilibration is achieved ab initio from the underlying QFT. As a possible candidate for a non-equilibrium phase transition phenomena we then adress the stochastic formation of disoriented chiral condensates. Finally we elaborate on a new 3+1 dimensional Monte Carlo parton cascade solving kinetic Boltzmann processes including inelastic multiplication processes (gg<->ggg) in an unified manner, where the back reaction channel is treated for the first time fully consistently.
Typically the materialization of high energetic transverse partons to hadronic jets is assumed to occur outside the reaction zone in a relativistic heavy ion collision. In contrast, a quantum mechanical estimate yields a time on the order of only a few fm/c for building up the hadronic wavefunction for jets with typical transverse momenta of pT < 10 GeV as accessible at RHIC facilities. The role of possible elastic or inelastic collisions of these high pT particles with the bulk of hadrons inside the fireball is addressed by means of an opacity expansion in the number of collisions. This analysis shows that the hadronic final state interactions can in principle account for the modification of the (moderate) high pT spectrum observed for central collisions at RHIC.