Showing papers by "Chang-Hwan Lee published in 2006"

Direct observation of dijets in central Au+Au collisions at sNN=200GeV

Abstract: The STAR Collaboration at the Relativistic Heavy Ion Collider reports measurements of azimuthal correlations of high transverse momentum (p(T)) charged hadrons in Au+Au collisions at higher p(T) than reported previously. As p(T) is increased, a narrow, back-to-back peak emerges above the decreasing background, providing a clear dijet signal for all collision centralities studied. Using these correlations, we perform a systematic study of dijet production and suppression in nuclear collisions, providing new constraints on the mechanisms underlying partonic energy loss in dense matter.

Longitudinal double-spin asymmetry and cross section for inclusive jet production in polarized proton collisions at s=200GeV

Abstract: We report a measurement of the longitudinal double-spin asymmetry A(LL) and the differential cross section for inclusive midrapidity jet production in polarized proton collisions at s=200 GeV. The cross section data cover transverse momenta 5 < p(T)< 50 GeV/c and agree with next-to-leading order perturbative QCD evaluations. The A(LL) data cover 5 < p(T)< 17 GeV/c and disfavor at 98% C.L. maximal positive gluon polarization in the polarized nucleon.

Strange baryon resonance production in sNN=200GeV p+p and Au+Au collisions

Abstract: We report the measurements of Σ(1385) and Λ(1520) production in p+p and Au+Au collisions at √sNN=200 GeV from the STAR Collaboration. The yields and the p_T spectra are presented and discussed in terms of chemical and thermal freeze-out conditions and compared to model predictions. Thermal and microscopic models do not adequately describe the yields of all the resonances produced in central Au+Au collisions. Our results indicate that there may be a time span between chemical and thermal freeze-out during which elastic hadronic interactions occur.

Strangeness condensation by expanding about the fixed point of the Harada-Yamawaki vector manifestation.

Abstract: Building on, and extending, the result of a higher-order in-medium chiral perturbation theory combined with renormalization group arguments and a variety of observations of the vector manifestation of Harada-Yamawaki hidden local symmetry theory, we obtain a surprisingly simple description of kaon condensation by fluctuating around the 'vector manifestation' fixed point identified to be the chiral restoration point. Our development establishes that strangeness condensation takes place at {approx}3n{sub 0} where n{sub 0} is nuclear matter density. This result depends only on the renormalization-group (RG) behavior of the vector interactions, other effects involved in fluctuating about the bare vacuum in so many previous calculations being irrelevant in the RG about the fixed point. Our results have major effects on the collapse of neutron stars into black holes.

Late Hadronization and Matter Formed at RHIC: Vector Manifestation, Brown-Rho Scaling and Hadronic Freedom

Abstract: Recent developments in our description of RHIC and related heavy-ion phenomena in terms of hidden local symmetry theories are reviewed with a focus on the novel nearly massless states in the vicinity of -- both below and above -- the chiral restoration temperature T_c. We present complementary and intuitive ways to understand both Harada-Yamawaki's vector manifestation structure and Brown-Rho scaling -- which are closely related -- in terms of "melting" of soft glues observed in lattice calculations and join the massless modes that arise in the vector manifestation (in the chiral limit) just below T_c to tightly bound massless states above T_c. This phenomenon may be interpreted in terms of the Beg-Shei theorem. It is suggested that hidden local symmetry theories arise naturally in holographic dual QCD from string theory, and a clear understanding of what really happens near the critical point could come from a deeper understanding of the dual bulk theory. Other matters discussed are the relation between Brown-Rho scaling and Landau Fermi-liquid fixed point parameters at the equilibrium density, its implications for "low-mass dileptons" produced in heavy-ion collisions, the reconstruction of vector mesons in peripheral collisions, the pion velocity in the vicinity of the chiral transition point, kaon condensation viewed from the VM fixed point, nuclear physics with Brown-Rho scaling, and the generic feature of dropping masses at the RGE fixed points in generalized hidden local symmetry theories.

Deformed conformal and super-Poincaré symmetries in the non- (anti-) commutative spaces

Abstract: Generators of the super-Poincare algebra in the non- (anti-) commutative superspace are represented using appropriate higher derivative operators defined in this quantum superspace. Also discussed are the analogous representations of the conformal and superconformal symmetry generators in the deformed spaces. This construction is obtained by generalizing the recent work of Wess et al. on the Poincare generators in the θ-deformed Minkowski space, or by using the substitution rules we derived on the basis of the phase-space structures of non- (anti-) commutative-space variables. Even with the non-zero deformation parameters the algebras remain unchanged although the comultiplication rules are deformed. The transformation of the fields under deformed symmetry is also discussed. Our construction can be used for systematic development of field theories in the deformed spaces.

Kerr parameters for stellar mass black holes and their consequences for grbs and hypernovae

Abstract: Recent measurements of the Kerr parameters a⋆ for two black-hole binaries in our Galaxy (Shafee et al. 2006), GRO J1655−40 and 4U 1543−47 of a⋆ = 0.65 − 0.75 and a⋆ = 0.75 − 0.85, respectively, fitted well the predictions of Lee et al. (2002), of a⋆ ∼ 0.8. In this report we also note that Lee et al. (2002) predicted a⋆ > 0.5 for 80% of the Soft X-ray Transient Sources. The maximum available energy in the Blandford-Znajek formalism for a⋆ > 0.5 gives E > 3 × 10 53 ergs, orders of magnitude larger than the energy needed for the GRB and hypernova explosion. We interpret the Soft X-ray Transients to be relics of GRBs and Hypernovae, but most of them were subluminous ones which could use only a small part of the available rotational energy. Subject headings: binaries: close — gamma rays: bursts — black hole physics — supernovae: general — X-rays: binaries

Hans Bethe And His Physics

Abstract: When Hans Bethe, at the age of 97, asked his long-term collaborator, Gerry Brown, to explain his scientific work to the world, the latter knew that this was a steep task As the late John Bahcall famously remarked: "If you know his (Bethe's) work, you might be inclined to think he is really several people, all of whom are engaged in a conspiracy to sign their work with the same name" Almost eight decades of original research, hundreds of scientific papers, numerous books, countless reports spanning the key areas of 20th century physics are the impressive record of Hans Bethe's academic work In answering Bethe's request, the editors enlisted the help of experts in the different research fields, collaborators and friends of this "last giant" of 20th century physics "Hans Bethe and His Physics" is the result It contains discussions of Hans Bethe's work in solid state physics, nuclear physics and astrophysics; it explains his contributions as a science advisor and his stance on energy and nuclear weapons; and it demonstrates his impact as a teacher and mentor to generations of young scientists While the book's primary aim is to explain the science behind the man, the different articles also allow the reader to take a glimpse at the man behind the science

ΔS = 0 effective weak chiral Lagrangianfrom the instanton vacuum

Abstract: We investigate the ΔS = 0 effective chiral Lagrangian from the instanton vacuum. Based on the ΔS = 0 effective weak Hamiltonian from the operator product expansion and renormalization group equations, we derive the strangeness-conserving effective weak chiral Lagrangian from the instanton vacuum to order ${{\mathcal{O}}}(p^2)$ and the next-to-leading order in the 1/N c expansion at the quark level. We find that the quark condensate and a dynamical term which arise from the QCD and electroweak penguin operators appear in the next-to-leading order in the 1/N c expansion for the ΔS = 0 effective weak chiral Lagrangian, while they are in the leading order terms in the ΔS = 1 case. Three different types of form factors are employed and we find that the dependence on the different choices of the form factor is rather insensitive. The low-energy constants of the Gasser-Leutwyler type are determined and discussed in the chiral limit.

Mergers of Binary Compact Objects

Abstract: We work out the effects of hypercritical accretion, which transfers mass from the secondary to the primary (first-born) neutron star (NS) in a binary, showing that the mass of the primary would end up 0.6 M_sun greater than the secondary NS in contradiction with the very nearly equal masses of the two NS's in binaries measured to date. We discuss that the primary NS evolves into a low-mass black-hole (LMBH) due to the hypercritical accretion. Using a flat distribution in the mass ratio q (q = M_secondary/M_primary), we calculated a ratio of LMBH-NS and NS-NS systems to be 5, in rough agreement with Pinsonneault and Stanek (2006). These authors emphasize the importance of "twins", which we discuss. The two NS's in the twins would be close in mass and further increase the number of mergings.

Sub-Bandgap Photonic Base Current Method for Extracting the Trap Density at Heterointerfaces in Heterojunction Bipolar Transistors

Abstract: In this paper, we propose a novel photonic base current analysis method to extract the energy-dependent distribution of interface states in heterojunction bipolar transistors (HBTs) using the photonic current-voltage characteristics under sub-bandgap (Eph