Determining the BDMPS transport coefficient via medium-modified fragmentation functions

In nucleus-nucleus collisions at RHIC and LHC, partons produced at high transverse momentum can undergo multiple scattering within the collision region prior to fragmenting into hadrons. We have studied the resulting medium-modified fragmentation function based on a calculation of the BDMPS-Z medium-induced gluon radiation for a dense, expanding medium of small finite extension. Here we explain how the BDMPS transport coefficient which measures the energy density attained in the collision, can be extracted from the observed modification of high-pt hadroproduction. We also comment on the significant remaining uncertainties in extracting the transport coefficient from data.Comment: 4 pages, 4 postscript figures. Proceedings for Quark Matter 200

Toric K\"ahler metrics seen from infinity, quantization and compact tropical amoebas

We consider the metric space of all toric K\"ahler metrics on a compact toric manifold; when "looking at it from infinity" (following Gromov), we obtain the tangent cone at infinity, which is parametrized by equivalence classes of complete geodesics. In the present paper, we study the associated limit for the family of metrics on the toric variety, its quantization, and degeneration of generic divisors. The limits of the corresponding K\"ahler polarizations become degenerate along the Lagrangian fibration defined by the moment map. This allows us to interpolate continuously between geometric quantizations in the holomorphic and real polarizations and show that the monomial holomorphic sections of the prequantum bundle converge to Dirac delta distributions supported on Bohr-Sommerfeld fibers. In the second part, we use these families of toric metric degenerations to study the limit of compact hypersurface amoebas and show that in Legendre transformed variables they are described by tropical amoebas. We believe that our approach gives a different, complementary, perspective on the relation between complex algebraic geometry and tropical geometry.Comment: v1: 32 pages, 5 figures; v2: 1 figure added; v3: 1 reference added; v4: some reorganization, 1 theorem (now 1.1) added; v5: final version, to appear in JD

Medium-induced gluon radiation and jet quenching in heavy ion collisions

In this brief review, I summarize the new developments on the description of gluon radiation by energetic quarks traversing a medium as well as the observable consequences in high-energy heavy ion collisions. Information about the initial state is essential for a reliable interpretation of the experimental results and will also be reviewed. Comparison with experimental data from RHIC and expectation for the future LHC will be given.Comment: 16 pages, 9 postscript figures. Invited brief review for Modern Physics Letters

Diseño y construcción de un convertidor multinivel en cascada basado en celdas monofásicas de corriente

91 p.En este trabajo se presenta el desarrollo de la topología de un convertidor multinivel en cascada basado en celdas monofásicas de corriente. El trabajo de esta memoria consta de simular esta topología de convertidor multinivel en cascada, con el fin de obtener la base del desarrollo posterior del convertidor, el diseño de las celdas de corriente, la construcción de las tarjetas electrónicas correspondientes al rectificador e inversor, así como su interconexión y el montaje sobre el set-up para conformar las celdas a fin de conectarlas en cascada y la realización de pruebas de estas celdas monofásicas de corriente y ver el desempeño global del convertidor. Este informe muestra los aspectos fundamentales en las etapas correspondientes del desarrollo del convertidor, así como la comparación de los resultados proporcionados por las simulaciones y por las pruebas experimentale

Fungicides and insecticides efficiency on wheat and triticale

Foi avaliada, durante três anos, a eficiência de fungicidas e inseticidas em trigo (Triticum aestivum L.) e triticale (Triticosecale Wittmack), e demonstrada a eficácia destes defensivos sobre o rendimento, peso específico, degradação de área foliar verde, incidência de septória, giberela, ferrugem-da-folha, oídio, afídeos e amarelidão. Nos anos chuvosos, 1977 e 1979, pode-se observar a grande eficiência dos fungicidas no controle de doenças e da degradação da área foliar verde, além do aumento de rendimento e de peso específico do trigo e do triticale. Os maiores aumentos de rendimento, em ambas as culturas, foram obtidas quando pulgões e doenças foram controlados combinadamente. O peso específico aumentou de 1 a 7 kg por hectolitro. No triticale conseguiu-se superar o mínimo de 65 kg/hl. A aplicação de fungicidas antes do espigamento em triticale produziu aumentos menores do que em trigo, mas ainda significativos. No ano pouco chuvoso, 1978, durante a fase final do ciclo da cultura, os tratamentos com fungicidas após o espigamento não aumentaram o rendimento.The fungicides and insecticides efficiency for control of wheat (Triticum aestivum L.) and triticale (Triticasecale Wittmack) diseases and aphids was tested during three years. The chemical action of these pesticides on yield, test weight, degradation of green leaf area, incidence of septoria, scab, leaf rust, mildew, aphids and leaf yellowing is demonstrated. During rainy years, like 1977 and 1979, a high fungicidal efficiency in controlling diseases, slowing leaf degradation, and increasing yield and test weight was observed in wheat and triticale. The highest yield increases were obtained in both crops when diseases and aphids were controlled simultaneously. Test weight was increased from 1 to 7 kg per hectoliter. In triticale, duo to the pesticides, more than the minimum of 65 kg/hl was obtained. Significant yield increases, doe to the fungicide treatment prior heading, were lower in triticale. In the favorable year of 1978, the fungicide treatment after heading did not increase yield

RHIC results from LHC perspectives

RHIC data opens new ways of characterizing the medium created in a heavy ion collision by measuring particles with high transverse momentum. In addition to the observation of the predicted jet quenching, the new data on particle correlations indicate that a strong modification of the jet-like shapes is driven by the dynamical properties of the medium. I will review the lessons we are learning from RHIC and outline some new directions which could become of primary importance at the LHC.Comment: 10 pages, 5 figures. Plenary talk given at Quark Matter 2005 Conference, Budapest, Hungary, 4-9 Aug 200

Jets in QCD media: from color coherence to decoherence

We investigate soft gluon radiation off a quark-antiquark antenna in both color singlet and octet configurations traversing a dense medium. We demonstrate that, in both cases, multiple scatterings lead to a gradual decoherence of the antenna radiation as a function of the medium density. In particular, in the limit of an completely opaque medium, total decoherence is obtained, i.e., the quark and the antiquark radiate as independent emitters in vacuum, thus losing memory of their origin. We comment on possible implications on intrajet observables in heavy-ion collisions.Comment: 4 pages, 1 figur

Calculating Quenching Weights

We calculate the probability (``quenching weight'') that a hard parton radiates an additional energy fraction due to scattering in spatially extended QCD matter. This study is based on an exact treatment of finite in-medium path length, it includes the case of a dynamically expanding medium, and it extends to the angular dependence of the medium-induced gluon radiation pattern. All calculations are done in the multiple soft scattering approximation (Baier-Dokshitzer-Mueller-Peign\'e-Schiff--Zakharov ``BDMPS-Z''-formalism) and in the single hard scattering approximation (N=1 opacity approximation). By comparison, we establish a simple relation between transport coefficient, Debye screening mass and opacity, for which both approximations lead to comparable results. Together with this paper, a CPU-inexpensive numerical subroutine for calculating quenching weights is provided electronically. To illustrate its applications, we discuss the suppression of hadronic transverse momentum spectra in nucleus-nucleus collisions. Remarkably, the kinematic constraint resulting from finite in-medium path length reduces significantly the transverse momentum dependence of the nuclear modification factor, thus leading to consistency with the data measured at the Relativistic Heavy Ion Collider (RHIC).Comment: 45 pages LaTeX, 20 eps-figure

Suppression of heavy flavors at RHIC & LHC

Some of the open questions on jet quenching are expected to be clarified by measuring heavy-flavored mesons at high transverse momentum. The formalism based on radiative in-medium energy-loss, which describes other high-pt results at RHIC, gives definite predictions for the suppression of charm and beauty quarks. However, the uncertainties from both contributions to the observed electrons make the interpretation of the data difficult due to the absence of a well calibrated benchmark. We review the present situation as well as the consequences for the future LHC. We also comment on the use of heavy flavored jet angular correlations as an additional tool to study the underline dynamics of jet quenching.Comment: Plenary talk at the Conference Hard Probes 2006, Asilomar (California) June 2006. 8 page