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Phi meson production in relativistic heavy ion collisions

Within a multiphase transport model we study phi meson production in relativistic heavy ion collisions from both superposition of initial multiple proton-proton interactions and the secondary collisions in the produced hadronic matter. The yield of phi mesons is then reconstructed from their decaying product of either the kaon-antikaon pairs or the dimuon pairs. Since the kaon-antikaon pairs at midrapidity with low transverse momenta are predominantly rescattered or absorbed in the hadronic medium, they can not be used to reconstruct the phi meson and lead thus to a smaller reconstructed phi meson yield than that reconstructed from the dimuon channel. With in-medium mass modifications of kaons and phi mesons, the phi yield from dimuons is further enhanced compared to that from the kaon-antikaon pairs. The model result is compared with the experimental data at the CERN/SPS and RHIC energies and its implications to quark-gluon plasma formation are discussed.Comment: Revised version, to appear in Nucl. Phys.

Cascade production in heavy-ion collisions at SIS energies

Production of the doubly strange $\Xi$ baryon in heavy-ion collisions at \textrm{SIS} energies is studied in a relativistic transport model that includes perturbatively the strangeness-exchange reactions $\bar{K}\Lambda \to \pi \Xi$ and $\bar{K}\Sigma \to \pi \Xi$. Taking the cross sections for these reactions from the predictions of a hadronic model, we find that the $\Xi$ yield is about $10^{-4}$ in central collisions of $$Ni + $^{58}$Ni at $E/A=1.93$ \textrm{GeV}. The $\Xi$ yield is further found to be more sensitive to the magnitude of the cross sections for strangeness-exchange reactions than to the medium effects due to modified kaon properties. We have also made predictions for $\Xi$ production in Au+Au collisions at energies from 1 to 2 GeV/nucleon.Comment: 13 pages, 5 figures, typos fixed and discussions added, to appear in PL

Quantum Lattice Fluctuations and Luminescence in C_60

We consider luminescence in photo-excited neutral C_60 using the Su-Schrieffer-Heeger model applied to a single C_60 molecule. To calculate the luminescence we use a collective coordinate method where our collective coordinate resembles the displacement of the carbon atoms of the Hg(8) phonon mode and extrapolates between the ground state "dimerisation" and the exciton polaron. There is good agreement for the existing luminescence peak spacing and fair agreement for the relative intensity. We predict the existence of further peaks not yet resolved in experiment. PACS Numbers : 78.65.Hc, 74.70.Kn, 36.90+

Information-theoretic classification of SNOMED improves the organization of context-sensitive excerpts from Cochrane Reviews

The emphasis on evidence based medicine (EBM) has placed increased focus on finding timely answers to clinical questions in presence of patients. Using a combination of natural language processing for the generation of clinical excerpts and information theoretic distance based clustering, we evaluated multiple approaches for the efficient presentation of context-sensitive EBM excerpts

Strange Particles in Dense Matter and Kaon Condensates

We discuss the role of strangeness in dense matter and especially in neutron stars. The early (in density) introduction of hyperons found in many calculations is probably delayed by the decrease in vector mean field acting on the neutron. The decrease results from both conventional many-body rescattering effects and from the movement towards asymptotic freedom at high densities. Subthreshold $K^-$-meson production by the KaoS collaboration at GSI shows that the $K^-$-mass must be substantially lowered, by $\gtrsim$ 200 MeV at $\rho\sim 2\rho_0$. It is shown that explicit chiral symmetry breaking through the kaon mass may be responsible for $\Sigma^-$-nucleon and $\Xi^-$-nucleon scalar attraction being weaker than obtained by simple quark scaling. The normal mode of the strangeness minus, charge $e^-$, excitation is constructed as a linear combination of $K^-$-meson and $\Sigma^-$, neutron-hole state. Except for zero momentum, where the terms are unmixed the "kaesobar" is a linear combination of these two components.Comment: 10 pages, 8 postscript figures, Talk given at the International Conference on Hypernuclear and Strange Particle Physics (HYP97), Brookhaven Nat'l Lab., USA, October 13-18, 1997, to be published in Nucl. Phys.

Antikaon Production and Medium Effects in Heavy Ion Collisions at AGS

Antikaon production from heavy ion collisions at energies available from the Alternating Gradient Synchrotron (AGS) at the Brookhaven National Laboratory is studied in a relativistic transport (ART) model. We include contributions from the baryon-baryon, meson-baryon, and meson-meson interactions. The final-state interaction of antikaons via both absorption and elastic scattering by nucleons and pions are also considered. To compare with presently available or future experimental data, we have calculated the antikaon rapidity and transverse momentum distributions as well as its collective flow. Medium effects on these observables due to mean field potentials have also been investigated. It is found that the ratio of antikaon transverse momentum spectrum to that of kaon and their transverse flow are most sensitive to the in-medium properties of kaons and antikaons.Comment: 19 pages, 13 figure

Asymmetric Totally-corrective Boosting for Real-time Object Detection

Real-time object detection is one of the core problems in computer vision. The cascade boosting framework proposed by Viola and Jones has become the standard for this problem. In this framework, the learning goal for each node is asymmetric, which is required to achieve a high detection rate and a moderate false positive rate. We develop new boosting algorithms to address this asymmetric learning problem. We show that our methods explicitly optimize asymmetric loss objectives in a totally corrective fashion. The methods are totally corrective in the sense that the coefficients of all selected weak classifiers are updated at each iteration. In contract, conventional boosting like AdaBoost is stage-wise in that only the current weak classifier's coefficient is updated. At the heart of the totally corrective boosting is the column generation technique. Experiments on face detection show that our methods outperform the state-of-the-art asymmetric boosting methods.Comment: 14 pages, published in Asian Conf. Computer Vision 201

Heterotic Non-Kahler Geometries via Polystable Bundles on Calabi-Yau Threefolds

In arXiv:1008.1018 it is shown that a given stable vector bundle $V$ on a Calabi-Yau threefold $X$ which satisfies $c_2(X)=c_2(V)$ can be deformed to a solution of the Strominger system and the equations of motion of heterotic string theory. In this note we extend this result to the polystable case and construct explicit examples of polystable bundles on elliptically fibered Calabi-Yau threefolds where it applies. The polystable bundle is given by a spectral cover bundle, for the visible sector, and a suitably chosen bundle, for the hidden sector. This provides a new class of heterotic flux compactifications via non-Kahler deformation of Calabi-Yau geometries with polystable bundles. As an application, we obtain examples of non-Kahler deformations of some three generation GUT models.Comment: 12 pages, late