Y. G. Ma

Elliptic flow of phi mesons and strange quark collectivity

Based on a multiphase transport model, we have studied the elliptic flow v{sub 2} of {phi} mesons from the reconstructed K{sup +}K{sup -} decay channel at the top Relativistic Heavy Ion Collider energy at Brookhaven National Laboratory. The dependences of v{sub 2} on transverse momentum p{sub T} and collision centrality are presented and the rescattering effect of {phi} mesons in the hadronic phase is also investigated. The results show that experimental measurement of v{sub 2} for {phi} mesons can retain the early collision information before the {phi} decays and that the {phi} v{sub 2} value obeys the constituent quark number scaling that has been observed for other mesons and baryons. Our study indicates that the {phi} v{sub 2} mostly reflects partonic-level collectivity developed during the early stage of the nucleus-nucleus collision and the strange and light up/down quarks have developed similar angular anistropy properties at the hadronization.

Study of halo nuclei with phenomenological relativistic mean field approach

Abstract The properties of halo nuclei are studied in the framework of the relativistic mean field approach. Single particle wave functions for last neutron configurations are obtained by using renormalized mean field potentials which reproduce experimental rms radii of halo nuclei. The extracted experimental density distributions and separation energies of loosely-bound neutrons of halo nuclei 11Li and 11Be are well described by the calculated results.

Examining the exotic structure of the proton-rich nucleus {sup 23}Al

The longitudinal momentum distribution (P{sub //}) of fragments after one-proton removal from {sup 23}Al and reaction cross sections ({sigma}{sub R}) for {sup 23,24}Al on a carbon target at 74A MeV have been measured. The {sup 23,24}Al ions were produced through projectile fragmentation of 135A MeV {sup 28}Si primary beam using the RIPS fragment separator at RIKEN. P{sub parallel} is measured by a direct time-of-flight (TOF) technique, while {sigma}{sub R} is determined using a transmission method. An enhancement in {sigma}{sub R} is observed for {sup 23}Al compared with {sup 24}Al. The P{sub parallel} for {sup 22}Mg fragments from {sup 23}Al breakup has been obtained for the first time. FWHM of the distributions has been determined to be 232 {+-} 28 MeV/c. The experimental data are discussed by using the Few-Body Glauber model. Analysis of P{sub //} demonstrates a dominant d-wave configuration for the valence proton in ground state of {sup 23}Al, indicating that {sup 23}Al is not a proton halo nucleus.

Different mechanism of two-proton emission from proton-rich nuclei 23 Al and 22 Mg

Two-proton relative momentum (q(pp)) and opening angle (theta(pp)) distributions from the three-body decay of two excited proton-rich nuclei, namely Al-23 --> p + p + Na-21 and Mg-22 --> p + p + Ne-20, have been measured with the projectile fragment separator (RIPS) at the RIKEN RI Beam Factory. An evident peak at q(pp) similar to 20 MeV/c as well as a peak in theta(pp) around 30 degrees are seen in the two-proton break-up channel from a highly-excited Mg-22. In contrast, such peaks are absent for the Al-23 case. It is concluded that the two-proton emission mechanism of excited Mg-22 is quite different from the Al-23 case, with the former having a favorable diproton emission component at a highly excited state and the latter dominated by the sequential decay process

Giant Dipole Resonance as a Fingerprint of a Clustering Configurations in C-12 and O-16

It is studied how the α cluster degrees of freedom, such as α clustering configurations close to the α decay threshold in (12)C and (16)O, including the linear chain, triangle, square, kite, and tetrahedron, affect nuclear collective vibrations with a microscopic dynamical approach, which can describe properties of nuclear ground states well across the nuclide chart and reproduce the standard giant dipole resonance (GDR) of (16)O quite nicely. It is found that the GDR spectrum is highly fragmented into several apparent peaks due to the α structure. The different α cluster configurations in (12)C and (16)O have corresponding characteristic spectra of GDR. The number and centroid energies of peaks in the GDR spectra can be reasonably explained by the geometrical and dynamical symmetries of α clustering configurations. Therefore, the GDR can be regarded as a very effective probe to diagnose the different α cluster configurations in light nuclei.

A laser-Compton scattering prototype experiment at 100 MeV linac of Shanghai Institute of Applied Physics

As a prototype of the Shanghai Laser Electron Gamma Source in the Shanghai Synchrotron Radiation Facility, an x-ray source based on laser-Compton scattering (LCS) has been installed at the terminal of the 100 MeV linac of the Shanghai Institute of Applied Physics. LCS x-rays are generated by interactions between Q-switched Nd:yttrium aluminum garnet laser pulses [with wavelength of 1064 nm and pulse width of 21 ns (full width at half maximum)] and electron bunches [with energy of 108 MeV and pulse width of 0.95 ns (rms)] at an angle of 42 degrees between laser and electron beam. In order to measure the energy spectrum of LCS x-rays, a Si(Li) detector along the electron beam line axis is positioned at 9.8 m away from a LCS chamber. After background subtraction, the LCS x-ray spectrum with the peak energy of 29.1+/-4.4|(stat)+/-2.1|(syst) keV and the peak width (rms) of 7.8+/-2.8|(stat)+/-0.4|(syst) keV is observed. Normally the 100 MeV linac operates with the electron macropulse charge of 1.0 nC/pulse, and the electron and laser collision repetition rate of 20 Hz. Therefore, the total LCS x-ray flux of (5.2+/-2.0) x 10(2) Hz can be achieved.

A Future Laser Compton Scattering (LCS) γ-Ray Source: SLEGS at SSRF

The Shanghai Synchrotron Radiation Facility (SSRF) is a third-generation synchrotron radiation light source and will come into commission in April 2009. The project Shanghai Laser Electron Gamma Source (SLEGS), which is a high intensity γ-ray beamline based on Laser Compton Scattering (LCS) between relativistic electron bunches and a laser, has been proposed at the SSRF. According to our simulations, the SLEGS is expected to generate a polarized γ-ray beam of up to 22 MeV and 109–10 photons/s if using 3.5 GeV, 200–300 mA relativistic electrons and a 500 W CO2 polarized laser. Here we describe the status and the application prospects of SLEGS and its developed prototype.

Parameterization of deformed nuclei for Glauber modeling in relativistic heavy ion collisions

The density distributions of large nuclei are typically modeled with a Woods-Saxon distribution characterized by a radius R-0 and skin depth a. Deformation parameters beta are then introduced to describe non-spherical nuclei using an expansion in spherical harmonics R-0(1 + beta Y-2(2)0 + beta Y-4(4)0). But when a nucleus is non-spherical, the R-0 and a inferred from electron scattering experiments that integrate over all nuclear orientations cannot be used directly as the parameters in the Woods-Saxon distribution. In addition, the beta(2) values typically derived from the reduced electric quadrupole transition probability B(E2)up arrow are not directly related to the beta(2) values used in the spherical harmonic expansion. B(E2). is more accurately related to the intrinsic quadrupole moment Q(0) than to beta(2). One can however calculate Q(0) for a given beta(2) and then derive B(E2). from Q(0). In this paper we calculate and tabulate the R-0, a, and beta(2) values that when used in a Woods-Saxon distribution, will give results consistent with electron scattering data. We then present calculations of the second and third harmonic participant eccentricity (epsilon(2) and epsilon(3)) with the new and old parameters. We demonstrate that epsilon(3) is particularly sensitive to a and argue that using the incorrect value of a has important implications for the extraction of viscosity to entropy ratio (eta/s) from the QGP created in Heavy Ion collisions

Thermodynamic properties and shear viscosity over entropy-density ratio of the nuclear fireball in a quantum-molecular dynamics model

Thermodynamic and transport properties of nuclear fireball created in the central region of heavy-ion collisions below 400 MeV/nucleon are investigated within the isospin-dependent quantum molecular dynamic (IQMD) model. These properties, including the density, temperature, chemical potential, entropy density (s), and shear viscosity (eta), are calculated by a generalized hot Thomas Fermi formulism and a parametrized function, which was developed by Danielewicz. As the collision goes on, a transient minimal eta/s = 5/4 pi - 10/4 pi occurs in the largest compression stage. Besides, the relationship of eta/s to temperature (T) in the freeze-out stage displays a local minimum which is about 9-20 times 1/4 pi around T = 8-12 MeV, which can be argued as indicative of a liquid gas phase transition. In addition, the influences of nucleon-nucleon (NN) cross section (sigma(NN)) and symmetry energy coefficient (C-s) are also discussed, and it is found that the results are sensitive to sNN but not to C-s.

Hindered proton collectivity in 16(28)S12: possible magic number at Z=16.

The reduced transition probability B(E2;0(gs)(+)→2(1)(+)) for (28)S was obtained experimentally using Coulomb excitation at 53 MeV/nucleon. The resultant B(E2) value 181(31) e(2)fm(4) is smaller than the expectation based on empirical B(E2) systematics. The double ratio |M(n)/M(p)|/(N/Z) of the 0(gs)(+)→2(1)(+) transition in (28)S was determined to be 1.9(2) by evaluating the M(n) value from the known B(E2) value of the mirror nucleus (28)Mg, showing the hindrance of proton collectivity relative to that of neutrons. These results indicate the emergence of the magic number Z=16 in the |T(z)|=2 nucleus (28)S.