Jet coherence in QCD media: the antenna radiation spectrum

We study the radiation of a highly energetic partonic antenna in a colored state traversing a dense QCD medium. Resumming multiple scatterings of all involved constituents with the medium we derive the general gluon spectrum which encompasses both longitudinal color coherence between scattering centers in the medium, responsible for the well known Landau-Pomeranchuk-Migdal (LPM) effect, and transverse color coherence between partons inside a jet, leading, in vacuum, to angular ordering of the parton shower. We discuss shortly the onset of transverse decoherence which is reached in opaque media. In this regime, the spectrum consists of independent radiation off the antenna constituents.Comment: 15 pages, 2 figures, paper shortened and partly rewritten, references added, results unchange

Jet quenching and broadening: the transport coefficient q^\hat{q} in an anisotropic plasma

The jet quenching parameter $\hat{q}$ is analyzed for a quark jet propagating in an anisotropic plasma. The momentum anisotropy is calculated at high temperature of the underlying quark-gluon plasma. $\hat{q}$ is explicitly estimated in leading-logarithmic approximation by the broadening of the massless quark interacting via gluon exchange. A plasma instability is present. Strong indications are found that $\hat{q}$ is increasing with increasing anisotropy. Possible implications for the saturation scale $Q_s$ in $A-A$ collisions are pointed out.Comment: 1

Costs and process of in-patient tuberculosis management at a central academic hospital, Cape Town, South Africa

Publication of this article was funded by the Stellenbosch University Open Access Fund.The original publication is available at http://www.ingentaconnect.com/journals/browse/iuatld/Setting: South Africa reports more cases of tuberculosis (TB) than any other country, but an up-to-date, precise estimate of the costs associated with diagnosing, treating and preventing TB at the in-patient level is not available. Objective: To determine the costs associated with TB management among in-patients and to study the use of personal protective equipment (PPE) at a central academic hospital in Cape Town. Design: Retrospective and partly prospective cost analysis of TB cases diagnosed between May 2008 and October 2009. Results: The average daily in-patient costs were US$238; the average length of stay was 9.7 days. Mean laboratory and medication costs per stay were respectively US$26.82 and US$8.68. PPE use per day cost US$0.99. The average total TB management costs were US$2373 per patient. PPE was not always properly used. Discussion: The costs of in-patient TB management are high compared to community-based treatment; the main reason for the high costs is the high number of in-patient days. An efficiency assessment is needed to reduce costs. Cost reduction per TB case prevented was approximately US$2373 per case. PPE use accounted for the lowest costs. Training is needed to improve PPE use.Stellenbosch University Open Access FundPublishers' versio

Unexplained HIV-1 infection in children — documenting cases and assessing for possible risk factors

Background. In the year 2000 we reported possible horizontal transmission of HIV-1 infection between two siblings. An investigation of three families, each with an HIV-infected child but seronegative parents, permitted this finding. Sexual abuse and surrogate breast-feeding were thought unlikely. The children had overlapping hospitalisation in a regional hospital. Since then several cases of unexplained HIV infection in children have been reported. A registry was established at Tygerberg Children’s Hospital for collection of data on the extent of horizontal or unexplained transmission of HIV in children. Study design. Retrospective chart review. Results. Fourteen children were identified, 12 from the Western Cape and 1 each from the Eastern Cape and KwaZulu-Natal. Thirteen (92%) had been hospitalised previously. In the Western Cape, children had been hospitalised in 8 hospitals. Ten of 13 (77%) were admitted as neonates and 9 of 13 (69%) had 2 or more admissions. Intravascular cannulation and intravenous drug administration occurred in all but 2 children before HIV diagnosis. Conclusion. We have confirmed HIV infection in a number of cases where the source of infection has been inadequately explained. Circumstantial evidence supports but does not prove nosocomial transmission. Further studies and identification of medical procedures conducive to the spread of HIV are urgently needed

The contribution of medium-modified color flow to jet quenching

Multiple interactions between parton showers and the surrounding QCD matter are expected to underlie the strong medium-modifications of jet observables in ultra-relativistic heavy ion collisions at RHIC and at the LHC. Here, we note that such jet-medium interactions alter generically and characteristically the color correlations in the parton shower. We characterize these effects in a color-differential calculation of the medium-induced gluon radiation spectrum to first and second order in opacity. By interfacing simple branching histories of medium-modified color flow with the Lund hadronization model, we analyze how the medium modification of color correlations can affect the distribution of hadronic fragments in jets. Importantly, we observe that jet-medium interactions give rise to the medium-induced color decoherence of gluons from the parton shower. Since hadronization respects color flow and since each color singlet in a parton shower is hadronized separately, this medium-induced color decoherence leaves characteristic signatures in the jet fragmentation pattern. In particular, it can contribute to the quenching of leading hadron spectra. Moreover, it can increase strongly the yield of soft hadronic fragments from a jet, while the distribution of more energetic hadrons follows naturally the shape of a vacuum-like fragmentation pattern of lower total energy

Jet Quenching via Jet Collimation

The ATLAS Collaboration recently reported strong modifications of dijet properties in heavy ion collisions. In this work, we discuss to what extent these first data constrain already the microscopic mechanism underlying jet quenching. Simple kinematic arguments lead us to identify a frequency collimation mechanism via which the medium efficiently trims away the soft components of the jet parton shower. Through this mechanism, the observed dijet asymmetry can be accomodated with values of $\hat{q}\, L$ that lie in the expected order of magnitude.Comment: 6 pages, 4 figure