Fixed target Drell-Yan data and NNLO QCD fits of parton distribution functions

We discuss the influence of fixed target Drell-Yan data on the extraction of parton distribution functions at next-to-next-to-leading order (NNLO) in QCD. When used in a parton distribution fit, the Drell-Yan (DY) data constrain sea quark distributions at large values of Bjorken x. We find that not all available DY data are useful for improving the precision of parton distribution functions (PDFs) obtained from a fit to the deep inelastic scattering (DIS) data. In particular, some inconsistencies between DIS-based parton distribution functions and DY data for large values of dilepton rapidity are found. However, by selecting a sample of the DY data that is both representative and consistent with the DIS data, we are able to perform a combined PDF fit that significantly improves the precision of non-strange quark distributions at large values of x. The NNLO QCD corrections to the DY process are crucial for improving the precision. They reduce the uncertainty of the theoretical prediction, making it comparable to the experimental uncertainty in DY cross-sections over a broad range of x.Comment: 12 pages, revte

Puusta valmistettujen tuotteiden hiilivaraston muutoksen laskenta kasvihuonekaasuinventaariossa : Menetelmäkehitys Suomen kasvihuonekaasuinventaarioon

Tämän tutkimuksen päätavoite oli kehittää puutuotelaskentamenetelmä, jolla voidaan tuottaa estimaatit Suomen kasvihuonekaasujen inventaarioraportointiin. Laskentamenetelmän oli perustuttava ilmastosopimuksen ja Kioton pöytäkirjan osapuolikokousten päätöksiin. Tässä tutkimuksessa puutuotteilla tarkoitetaan puusta valmistettuja puolivalmisteita, joita ovat sahatavara, puulevyt, paperi ja kartonki sekä muut puolivalmisteet, kuten hirret ja puhelinpylväät. Kioton pöytäkirjan laskennassa puutuotteiden alkuperän selvittäminen oli yksi tärkeimmistä tavoitteista. Alkuperällä tarkoitetaan tässä tapauksessa sitä, onko puutuotteisiin käytetty puu peräisin Kioton pöytäkirjan aktiviteeteistä (metsänhoito, metsitys, metsänhävitys) vai näiden kolmen luokan ulkopuolisilta alueilta. Tavoitteena oli arvioida hakkuupoistumat näissä luokissa vuodesta 1990 alkaen. Tutkimuksessa tuotettiin erilaisilla laskentavaihtoehdoilla aikasarjat ilmastosopimuksen ja Kioton pöytäkirjan mukaisiin laskentoihin käyttäen tuotantoon perustuvaa laskentaa, jossa huomioidaan kotimaassa tuotetut ja vientiin menneet puutuotteet, jotka on valmistettu kotimaisesta puusta. Laskennan luotettavuutta saatiin parannettua kokoamalla vuosia 1900–1960 koskeva kansallinen aineisto sekä selvittämällä suomalaisille puutuotteille soveltuvat kansalliset hiilenmuuntokertoimet. Sahatavara, puulevyt ja puumassat (paperin ja kartongin hiilitaseiden arvioimiseksi) jaettiin laskennassa mielekkäisiin alaryhmiin, jotta puutuotteiden hiilitaseista saataisiin luotettavammat tulokset. Laskennassa käytettiin kullekin alaryhmälle sopivia hiilenmuuntokertoimia, ja kullekin puutuoteryhmälle omia kotimaisuusasteitaan. Tutkimuksen tulokset antavat tietoa siitä, kuinka puutuotteet on tarkoituksenmukaisinta laskea Suomen kasvihuonekaasuinventaariossa ottaen huomioon ilmastosopimuksen päätösten ja IPCC:n raportointiohjeiden asettamat vaatimukset.201

Direct collider signatures of large extra dimensions

The realization of low (TeV) scale strings usually requires the existence of large (TeV) extra dimensions where gauge bosons live. The direct production of Kaluza-Klein excitations of the photon and Z-boson at present and future colliders is studied in this work. At the LEPII, NLC and Tevatron colliders, these Kaluza-Klein modes lead to deviations from the standard model cross-sections, which provide lower bounds on their mass. At the LHC the corresponding resonances can be produced and decay on-shell, triggering a characteristic pattern in the distribution of the dilepton invariant mass.Comment: 14 pages, LateX, 5 figure

Z-prime Gauge Bosons at the Tevatron

We study the discovery potential of the Tevatron for a Z-prime gauge boson. We introduce a parametrization of the Z-prime signal which provides a convenient bridge between collider searches and specific Z-prime models. The cross section for p pbar -> Z-prime X -> l^+ l^- X depends primarily on the Z-prime mass and the Z-prime decay branching fraction into leptons times the average square coupling to up and down quarks. If the quark and lepton masses are generated as in the standard model, then the Z-prime bosons accessible at the Tevatron must couple to fermions proportionally to a linear combination of baryon and lepton numbers in order to avoid the limits on Z--Z-prime mixing. More generally, we present several families of U(1) extensions of the standard model that include as special cases many of the Z-prime models discussed in the literature. Typically, the CDF and D0 experiments are expected to probe Z-prime-fermion couplings down to 0.1 for Z-prime masses in the 500--800 GeV range, which in various models would substantially improve the limits set by the LEP experiments.Comment: 34 pages, 13 figure

Early root growth and architecture of fast- and slow-growing Norway spruce (Picea abies) families differ-potential for functional adaptation

The relationship between the growth rate of aboveground parts of trees and fine root development is largely unknown. We investigated the early root development of fast-and slow-growing Norway spruce (Picea abies (L.) H. Karst.) families at a developmental stage when the difference in size is not yet observed. Seedling root architecture data, describing root branching, were collected with the WinRHIZO (TM) image analysis system, and mixed models were used to determine possible differences between the two growth phenotypes. A new approach was used to investigate the spatial extent of root properties along the whole sample root from the base of 1-year-old seedlings to the most distal part of a root. The root architecture of seedlings representing fastgrowing phenotypes showed similar to 30% higher numbers of root branches and tips, which resulted in larger root extensions and potentially a better ability to acquire nutrients. Seedlings of fast-growing phenotypes oriented and allocated root tips and bio-mass further away from the base of the seedling than those growing slowly, a possible advantage in nutrient-limited and heterogeneous boreal forest soils. We conclude that a higher long-term growth rate of the aboveground parts in Norway spruce may relate to greater allocation of resources to explorative roots that confers a competitive edge during early growth phases in forest ecosystems.Peer reviewe

Production of Kaluza-Klein States at Future Colliders

Perturbative breaking of supersymmetry in four-dimensional string theories predict in general the existence of new large dimensions at the TeV scale. Such large dimensions lie in a domain of energies accessible to particle accelerators. Their main signature is the production of Kaluza-Klein excitations which can be detected at future colliders. We study this possibility for hadron colliders (TEVATRON, LHC) and $e^+ e^-$ colliders (LEP-200, NLC-500).Comment: 13 pages, LATEX, 4 postscript figures appended at the end, CPTH-A293.0294 and IEM-FT-84/9

Threshold Corrections in Precision LHC Physics: QED otimes QCD

With an eye toward LHC processes in which theoretical precisions of 1 percent are desired, we introduce the theory of the simultaneous YFS resummation of QED and QCD to compute the size of the expected resummed soft radiative threshold effects in precision studies of heavy particle production at the LHC. Our results show that both QED and QCD soft threshold effects must be controlled to be on the conservative side to achieve such precision goals.Comment: 4 pages, no figures; presented by B.F.L. Ward in DPF200

Genotypes exhibit no variation in precision foraging in mycorrhizal Norway spruce seedlings

Aims Fine roots, that comprise the adjustable part of the root system, are important in spatially heterogeneous boreal forest soils. We investigated the soil exploring patterns of Norway spruce (Picea abies) seedlings of equal height belonging to families representing two contrasting growth phenotypes that have shown fast and slow growth rates in long-term experiments. We hypothesised that seedlings of the fast-growing phenotype would show a more explorative root growth strategy, intense branching, and root proliferation in response to the nutrient patch, and that slow-growing phenotypes would be more tolerant to drought stress. Methods Seedlings were grown in flat Perspex microcosms with a clod of humus placed in the mid-bottom part of each microcosm for eight months. The order-based and functional classification, branching topology, and size of seedling root systems were studied with WinRHIZO (TM) image-analysis software and root exploration patterns with LIGNUM-model simulations. In addition, transpiration, stomatal conductance, net assimilation rate responses were measured. Results No differences were found in the early foraging of roots for the humus clod nor net assimilation rate and transpiration between the phenotype groups. Seedlings were favouring exploitation over exploration in the early phases of development regardless of growth phenotype group. However, in fast-growing phenotypes, the main roots were longer, and the lateral root pool favoured long and bifurcated laterals that formed larger absorptive root area. Conclusions Our results indicate that in nutrient-poor conditions, better growth of lateral roots precedes future differences in the aboveground growth rate of Norway spruce.Peer reviewe

Three-loop non-diagonal current correlators in QCD and NLO corrections to single-top-quark production

The non-diagonal correlators of vector and scalar currents are considered at three-loop order in QCD. The full mass dependence is computed in the case where one of the quarks is massless and the other one carries the mass $M$. As applications we consider the single-top-quark production via the process $q\bar{q}\to t\bar{b}$ and the decay rate of a charged Higgs into hadrons. In both cases the computed NLO corrections are shown to be numerically much less important than the leading ones.Comment: 13 page