First observation of the doubly charmed baryon Ξcc +

The first experimental evidence for one of the six predicted baryon states which contain two valence charmed quarks-the doubly charmed baryons. As such, there were many predictions of the masses and other properties of these states. The properties of doubly charmed baryons provide a new window into the structure of baryonic matter.

Flavor SU(3) predictions for charmed baryon and B-meson decays

The predictions of the SU(3) flavor symmetry of the strong interactions for the weak decay of charmed baryons and B-mesons are detailed. It is hoped that comparison between these predictions and experiment will shed some light on the underlying dynamics involved in these weak decays. Although only a few decay modes of the charmed baryons and B-mesons have been studied experimentally it is hoped that the next generation of B-factories and even Z-decays at LEP will provide enough events to test these predictions.

CHARMED BARYON IN A STRING MODEL

Charmed baryon spectroscopy has been studied under a string model. In this model, charmed baryons are composed of a diquark and a charm quark which are connected by a constant tension. In this diquark picture, the quantum numbers J(P) of confirmed baryons have been well assigned. Energies of the first and second orbital excitations have been predicted and compared with the experimental data. Meanwhile, diquark masses have been extracted in the background of charm quark which satisfy a splitting relation based on spin-spin interaction.

Observation of the Ωb- baryon and measurement of the properties of the Ξb- and Ωb- baryons

We report the observation of the bottom, doubly-strange baryon Omega^-_b through the decay chain Omega^-_b -> J/psi Omega^-, where J/psi -> mu^+ mu^-, Omega^- -> Lambda K^-, and Lambda -> p pi^-, using 4.2 fb^{-1} of data from p\bar p collisions at sqrt{s}=1.96 TeV, and recorded with the Collider Detector at Fermilab. A signal is observed whose probability of arising from a background fluctuation is 4.0 * 10^{-8}, or 5.5 Gaussian standard deviations. The Omega^-_b mass is measured to be 6054.4 +/- 6.8 (stat.) +/- 0.9 (syst.) MeV/c^2. The lifetime of the Omega^-_b baryon is measured to be 1.13^{+0.53}_{-0.40}(stat.) +/- 0.02(syst.)$ ps. In addition, for the \Xi^-_b baryon we measure a mass of 5790.9 +/- 2.6(stat.) +/- 0.8(syst.) MeV/c^2 and a lifetime of 1.56^{+0.27}_{-0.25}(stat.) +/-0.02(syst.) ps. Under the assumption that the \Xi_b^- and \Omega_b^- are produced with similar kinematic distributions to the \Lambda^0_b baryon, we find sigma(Xi_b^-) B(Xi_b^- -> J/psi Xi^-)}/ sigma(Lambda^0_b) B(Lambda^0_b -> J/psi Lambda)} = 0.167^{+0.037}_{-0.025}(stat.) +/-0.012(syst.) and sigma(Omega_b^-) B(Omega_b^- -> J/psi Omega^-)/ sigma(Lambda^0_b) B(Lambda^0_b -> J/psi Lambda)} = 0.045^{+0.017}_{-0.012}(stat.) +/- 0.004(syst.) for baryons produced with transverse momentum in the range of 6-20 GeV/c.

Mass-splittings of doubly heavy baryons in QCD

We consider (for the first time) the ratios of doubly heavy baryon masses (spin 3/2 over spin 1/2 and SU(3) mass-splittings) using double ratios of sum rules (DRSR), which are more accurate than the usual simple ratios often used in the literature for getting the hadron masses. In general, our results agree and compete in precision with potential model predictions. In our approach, the alpha(s) corrections induced by the anomalous dimensions of the correlators are the main sources of the Xi(QQ)*-Xi(QQ) mass-splittings, which seem to indicate a 1/M(Q) behaviour and can only allow the electromagnetic decay Xi(QQ)* -> Xi(QQ) + gamma but not to Xi(QQ) + pi. Our results also show that the SU(3) mass-splittings are (almost) independent of the spin of the baryons and behave approximately like 1/M(Q), which could be understood from the QCD expressions of the corresponding two-point correlator. Our results can improved by including radiative corrections to the SU(3) breaking terms and can be tested, in the near future, at Tevatron and LHCb. (C) 2010 Published by Elsevier B.V.

重子磁矩及粲重子谱研究

强子内部的有效自由度是强子物理研究的一个重要内容。本文利用含有五夸克成份的重子波函数计算了重子八重态的磁矩；利用含有偶夸克的弦模型研究单粲夸克重子谱。计算结果显示，在由轻夸克组成的重子八重态中，五夸克成分对粒子自旋磁矩有很大贡献；在含有重味夸克的重子中，将两个轻夸克近似看作偶夸克能得出合理的结果。磁矩和 衰变率的计算常常是检验重子模型是否合理的第一步。三夸克重子模型无法解释近些年来实验上发现的核子自旋丢失以及海夸克的非对称性等现象。三个价夸克与核子内的海夸克对可以形成瞬时稳定的五夸克态。邹冰松等在其模型中构造出这样一个态，它能同时给出奇异夸克对质子负的自旋贡献和正的磁矩贡献。而且该模型也能很好的解释夸克海中 被压低的实验结果。基于此模型，我们把奇异夸克的贡献推广到所有夸克贡献得出质子磁矩，然后由对称性构造其他八重态波函数并计算它们的磁矩。通过拟合实验，我们分析了重子内多夸克成分的几率，然后计算了 衰变系数以及轨道角动量对核子自旋的贡献等。含有重味夸克的重子是研究重子结构的一个非常理想的场所。近些年来，实验上发现了大量含粲夸克的重子，但是没有给出这些重子的宇称和角动量。通过分析单粲夸克重子谱，我们发现能级图中出现的劈裂可以分成宽度不同的两类。这可由引入两类偶夸克与粲夸克不同的的耦合给出解释。我们首先对含粲夸克重子按不同偶夸克进行了分类，进而给出部分粒子的宇称和角动量；然后利用A. Selem等推广的弦模型，计算了单粲夸克重子谱。 我们预测了实验上发现的一些高激发态的宇称和角动量同时给出了各种偶夸克的质量，并对其作了定性分析。我们还计算了含有粲夸克的五夸克态重子能谱。最后，对取得的结果作了讨论以及指出未来工作的方向

The reaction (p)over-barp -> (Lambda)over-bar(c)(-)Lambda(+)(c) close to threshold

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Observation of the Doubly Strange b Baryon Omega(-)(b)

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Charmed-meson scattering on nucleons in a QCD Coulomb gauge quark model

The scattering of charmed mesons on nucleons is investigated within a chiral quark model inspired on the QCD Hamiltonian in Coulomb gauge. The microscopic model incorporates a longitudinal Coulomb confining interaction derived from a self-consistent quasi-particle approximation to the QCD vacuum, and a traverse hyperfine interaction motivated from lattice simulations of QCD in Coulomb gauge. From the microscopic interactions at the quark level, effective meson-baryon interactions are derived using a mapping formalism that leads to quark-Born diagrams. As an application, the total cross-section of heavy-light D-mesons scattering on nucleons is estimated.

Production of charmed pseudoscalar mesons in antiproton-proton annihilation

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Charmed

Charmed is a tangible interactive media artwork that explores aspects of daily life in urban environments. The work was commissioned by Experimenta MEdia Arts for the Experimenta Playground Biennial of Media Art (2007) held at Black Box Melbourne Victoria. The work also shown in Play ++ at the International Symposium of Electronic Art July - August 2008

New exact solutions for Hele-Shaw flow in doubly connected regions

Radial Hele-Shaw flows are treated analytically using conformal mapping techniques. The geometry of interest has a doubly-connected annular region of viscous fluid surrounding an inviscid bubble that is either expanding or contracting due to a pressure difference caused by injection or suction of the inviscid fluid. The zero-surface-tension problem is ill-posed for both bubble expansion and contraction, as both scenarios involve viscous fluid displacing inviscid fluid. Exact solutions are derived by tracking the location of singularities and critical points in the analytic continuation of the mapping function. We show that by treating the critical points, it is easy to observe finite-time blow-up, and the evolution equations may be written in exact form using complex residues. We present solutions that start with cusps on one interface and end with cusps on the other, as well as solutions that have the bubble contracting to a point. For the latter solutions, the bubble approaches an ellipse in shape at extinction.