J/psi Production at the LHC

We firstly examine hadroproduction of prompt J/psi's at the Fermilab Tevatron in a Monte Carlo Framework by means of the event generator PYTHIA 5.7 in which those colour-octet matrix elements processes relevant for charmonium production have been implemented accordingly. We find that colour-octet matrix elements presented in literature from p-pbar collider data are systematically overestimated due to overlooking of the effective primordial transverse momentum of partons (i.e. including higher-order QCD effects). We estimate the size of these effects using different parton distribution functions. Finally, after normalization to Tevatron data, we extrapolate up to LHC energies making a prediction on the expected pt differential cross-section for charmonium.Comment: 4 pages, LaTex, 3 Figures included in the text, Contribution to the 2nd Int. Conference on Hyperons, charm and beauty hadrons (Montreal, Aug 27-30, 1996

Compounded perturbations in coastal areas: contrasting responses to nutrient enrichment and the regime of storm-related disturbance depend on life-history traits

1. Natural systems are exposed to compounded perturbations, whose changes in temporal variance can be as important as those in mean intensity for shaping the structure of assemblages. Specifically, climate-related physical disturbances and nutrient inputs due to natural and/or anthropogenic activities occur concomitantly, but experimental tests of the simultaneous effects of changes in the regime of more than one perturbation are generally lacking. Filling this gap is the key to understand ecological responses of natural assemblages to climate-related change in the intensity and temporal patterning of physical disturbance combined with other global stressors. 2. Responses to factorial manipulations of nutrient enrichment, mean intensity and temporal variability in storm-like mechanical disturbance were examined, using benthic assemblages of tide-pools as model system. 3. Response variables were mean abundance values and temporal variances of taxa with different life-traits. Consistent negative effects of disturbance intensity were observed for the mean cover of long-living taxa (algal canopies and the polychaete Sabellaria alveolata), whose temporal fluctuations were also reduced by more severe mechanical stress. More resilient taxa (ephemeral algae, mostly green of the genus Ulva) increased under enriched conditions, particularly when low-intensity events were irregularly applied over time. Opposite effects of disturbance intensity depending on nutrient availability occurred on filamentous algae (e.g. red of the genus Ceramium). This was probably due to the fact that, although nutrient enrichment stimulated the abundance of both algal groups, when this condition was combined with relatively mild physical disturbance the competitively superior ephemeral green algae tended to become dominant over filamentous red algae. The same did not occur under high intensity of disturbance since it likely damaged large, foliose fronds of Ulva-like forms more than small, filamentous fronds of Ceramium-like forms. Grazers were positively affected by nutrients, likely responding indirectly to more food available. 4. A direct relationship between the mean abundance of most organisms and their temporal fluctuations was documented. However, all organisms persisted throughout the study, even under experimental conditions associated to the largest temporal variation in their abundance, likely due to their ability to resist to/quickly recover from, the applied perturbations. Therefore, in systems with great recovery abilities of dominant organisms (e.g. rocky intertidal, grasslands), effects of traits of the regime of disturbance and nutrient enrichment may modulate the fluctuations of populations not through the elimination and substitution of species, but through changes in relative abundances of the same species. This contrasts with the theory that temporal variation in abundance would be directly related to the risk of local extinction. Present findings enable more accurate predictions of the consequences of climatic and non-climatic scenarios on the biodiversity of marine and terrestrial systems sharing analogous functional traits of organisms. Future more intense physical disturbances are expected to exert negative effects on slow-growing/recovering species (e.g. habitat-formers) irrespectively of the temporal patterning of the same disturbances and nutrient inputs. On the contrary, more resistant species (e.g. encrusting algae on rocky shores or below-ground vegetation in grasslands) are expected to benefit from intense physical disturbance. Species whose abundance is more directly related to the availability of nutrients (e.g. filamentous and ephemeral algae or herbs) are expected to generally increase under enriched conditions, but their ability to eventually become dominant would depend on their ability to grow fast and attain cover large enough to overwhelm any possible control of concomitant disturbance intensity on their abundance. If, such as in the present examined system, virtually all organisms can persist, over the temporal scale of the experiment, under any combination of physical disturbance and nutrient availability, the resulting overall diversity is not predicted to change drastically. Nevertheless, low-intensity events evenly distributed and high-intensity events irregularly distributed appear as the conditions supporting the highest richness of taxa, independently of the availability of nutrients

Direct Higgs production and jet veto at the Tevatron and the LHC in NNLO QCD

We consider Higgs boson production through gluon--gluon fusion in hadron collisions, when a veto is applied on the transverse momenta of the accompanying hard jets. We compute the QCD radiative corrections to this process at NLO and NNLO. The NLO calculation is complete. The NNLO calculation uses the recently evaluated NNLO soft and virtual QCD contributions to the inclusive cross section. We find that the jet veto reduces the impact of the NLO and NNLO contributions, the reduction being more sizeable at the LHC than at the Tevatron.Comment: 22 pages, 12 postscript figure

Charmonia production in hadron colliders and the extraction of colour-octet matrix elements

We present the results of our analysis on charmonia ($J/\psi$ and $\psi'$) hadroproduction taking into account higher-order QCD effects induced by initial-state radiation in a Monte Carlo framework, with the colour-octet mechanism implemented in the event generation. We find that those colour-octet matrix elements extracted so far from Fermilab Tevatron data for both $J/\psi$ and $\psi'$ production have to be lowered significantly. We finally make predictions for charmonia production at the LHC, presenting a code for a fast simulation with PYTHIA based on the colour-octet model.Comment: 17 pages, LaTex, 5 Figures included in the tex

Higgs-boson production associated with a bottom quark at hadron colliders with SUSY-QCD corrections

The Higgs boson production p p (p\bar p) -> b h +X via b g -> b h at the LHC, which may be an important channel for testing the bottom quark Yukawa coupling, is subject to large supersymmetric quantum corrections. In this work the one-loop SUSY-QCD corrections to this process are evaluated and are found to be quite sizable in some parameter space. We also study the behavior of the corrections in the limit of heavy SUSY masses and find the remnant effects of SUSY-QCD. These remnant effects, which are left over in the Higgs sector by the heavy sparticles, are found to be so sizable (for a light CP-odd Higgs and large \tan\beta) that they might be observable in the future LHC experiment. The exploration of such remnant effects is important for probing SUSY, especially in case that the sparticles are too heavy (above TeV) to be directly discovered at the LHC.Comment: Results for the Tevatron adde

High-p_T pion and kaon production in relativistic nuclear collisions

High-p_T pion and kaon production is studied in relativistic proton-proton, proton-nucleus, and nucleus-nucleus collisions in a wide energy range. Cross sections are calculated based on perturbative QCD, augmented by a phenomenological transverse momentum distribution of partons (``intrinsic k_T''). An energy dependent width of the transverse momentum distribution is extracted from pion and charged hadron production data in proton-proton/proton-antiproton collisions. Effects of multiscattering and shadowing in the strongly interacting medium are taken into account. Enhancement of the transverse momentum width is introduced and parameterized to explain the Cronin effect. In collisions between heavy nuclei, the model over-predicts central pion production cross sections (more significantly at higher energies), hinting at the presence of jet quenching. Predictions are made for proton-nucleus and nucleus-nucleus collisions at RHIC energies.Comment: 26 pages in Latex, 19 EPS figure

A Student\u27s Guide to giant Viruses Infecting Small Eukaryotes: From Acanthamoeba to Zooxanthellae

The discovery of infectious particles that challenge conventional thoughts concerning “what is a virus” has led to the evolution a new field of study in the past decade. Here, we review knowledge and information concerning “giant viruses”, with a focus not only on some of the best studied systems, but also provide an effort to illuminate systems yet to be better resolved. We conclude by demonstrating that there is an abundance of new host–virus systems that fall into this “giant” category, demonstrating that this field of inquiry presents great opportunities for future research

Recoil and Threshold Corrections in Short-distance Cross Sections

We identify and resum corrections associated with the kinematic recoil of the hard scattering against soft-gluon emission in single-particle inclusive cross sections. The method avoids double counting and conserves the flow of partonic energy. It reproduces threshold resummation for high-p_T single-particle cross sections, when recoil is neglected, and Q_T-resummation at low Q_T, when higher-order threshold logarithms are suppressed. We exhibit explicit resummed cross sections, accurate to next-to-leading logarithm, for electroweak annihilation and prompt photon inclusive cross sections.Comment: minor modifications of the text, some references added. 51 pages, LaTeX, 6 figures as eps file

Soil nutrients and beta diversity in the Bornean Dipterocarpaceae: evidence for niche partitioning by tropical rain forest trees

1   The relative importance of niche- and dispersal-mediated processes in structuring diverse tropical plant communities remains poorly understood. Here, we link mesoscale beta diversity to soil variation throughout a lowland Bornean watershed underlain by alluvium, sedimentary and granite parent materials ( c . 340 ha, 8–200 m a.s.l.). We test the hypothesis that species turnover across the habitat gradient reflects interspecific partitioning of soil resources. 2   Floristic inventories (≥ 1 cm d.b.h.) of the Dipterocarpaceae, the dominant Bornean canopy tree family, were combined with extensive soil analyses in 30 (0.16 ha) plots. Six samples per plot were analysed for total C, N, P, K, Ca and Mg, exchangeable K, Ca and Mg, extractable P, texture, and pH. 3   Extractable P, exchangeable K, and total C, N and P varied significantly among substrates and were highest on alluvium. Thirty-one dipterocarp species ( n  = 2634 individuals, five genera) were recorded. Dipterocarp density was similar across substrates, but richness and diversity were highest on nutrient-poor granite and lowest on nutrient-rich alluvium. 4   Eighteen of 22 species were positively or negatively associated with parent material. In 8 of 16 abundant species, tree distribution (≥ 10 cm d.b.h.) was more strongly non-random than juveniles (1–10 cm d.b.h.), suggesting higher juvenile mortality in unsuitable habitats. The dominant species Dipterocarpus sublamellatus (> 50% of stems) was indifferent to substrate, but nine of 11 ‘subdominant’ species (> 8 individuals ha −1 ) were substrate specialists. 5   Eighteen of 22 species were significantly associated with soil nutrients, especially P, Mg and Ca. Floristic variation was significantly correlated with edaphic and geographical distance for all stems ≥ 1 cm d.b.h. in Mantel analyses. However, juvenile variation (1–10 cm d.b.h.) was more strongly related to geographical distance than edaphic factors, while the converse held for established trees (≥ 10 cm d.b.h.), suggesting increased importance of niche processes with size class. 6   Pervasive dipterocarp associations with soil factors suggest that niche partitioning structures dipterocarp tree communities. Yet, much floristic variation unrelated to soil was correlated with geographical distance between plots, suggesting that dispersal and niche processes jointly determine mesoscale beta diversity in the Bornean Dipterocarpaceae. Journal of Ecology (2005) doi: 10.1111/j.1365-2745.2005.01077.xPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72822/1/j.1365-2745.2005.01077.x.pd

Global Search for New Physics with 2.0/fb at CDF

Data collected in Run II of the Fermilab Tevatron are searched for indications of new electroweak-scale physics. Rather than focusing on particular new physics scenarios, CDF data are analyzed for discrepancies with the standard model prediction. A model-independent approach (Vista) considers gross features of the data, and is sensitive to new large cross-section physics. Further sensitivity to new physics is provided by two additional algorithms: a Bump Hunter searches invariant mass distributions for "bumps" that could indicate resonant production of new particles; and the Sleuth procedure scans for data excesses at large summed transverse momentum. This combined global search for new physics in 2.0/fb of ppbar collisions at sqrt(s)=1.96 TeV reveals no indication of physics beyond the standard model.Comment: 8 pages, 7 figures. Final version which appeared in Physical Review D Rapid Communication