Non-global logarithms in inter-jet energy flow with kt clustering requirement

Recent work in inter-jet energy flow has identified a class of leading logarithms previously not considered in the literature. These so-called non-global logarithms have been shown to have significant numerical impact on gaps-between-jets calculations at the energies of current particle colliders. Here we calculate, at fixed order and to all orders, the effect of applying clustering to the gluonic final state responsible for these logarithms for a trivial colour flow 2 jet system. Such a clustering algorithm has already been used for experimental measurements at HERA. We find that the impact of the non-global logarithms is reduced, but not removed, when clustering is demanded, a result which is of considerable interest for energy flow observable calculations.Comment: 13 pages, 4 figure

Next-to-Leading order Higgs + 2 jet production via gluon fusion

We present phenomenological results for the production of a Higgs boson in association with two jets at the LHC. The calculation is performed in the limit of large top mass and is accurate to next-to-leading order in the strong coupling, i.e. ${\cal O}(\alpha_s^6)$Comment: 13 pages, 6 figures; v2: references added, modified acknowledgments, final version as published in JHE

Inclusive Jet Production, Parton Distributions, and the Search for New Physics

Jet production at the Tevatron probes some of the smallest distance scales currently accessible. A gluon distribution that is enhanced at large x compared to previous determinations provides a better description of the Run 1b jet data from both CDF and D0. However, considerable uncertainty still remains regarding the gluon distribution at high x. In this paper, we examine the effects of this uncertainty, and of the remaining uncertainties in the NLO QCD theory, on jet cross section comparisons to Run 1b data. We also calculate the range of contributions still possible from any new physics. Predictions are also made for the expanded kinematic range expected for the ongoing Run 2 at the Tevatron and for the LHC.Comment: 50 pages, 31 figures, RevTe

Next-to-leading order QCD corrections to W+W- production via vector-boson fusion

Vector-boson fusion processes constitute an important class of reactions at hadron colliders, both for signals and backgrounds of new physics in the electroweak interactions. We consider what is commonly referred to as W+W- production via vector-boson fusion (with subsequent leptonic decay of the Ws), or, more precisely, e+ nu_e mu- nubar_mu + 2 jets production in proton-proton scattering, with all resonant and non-resonant Feynman diagrams and spin correlations of the final-state leptons included, in the phase-space regions which are dominated by t-channel electroweak-boson exchange. We compute the next-to-leading order QCD corrections to this process, at order alpha^6 alpha_s. The QCD corrections are modest, changing total cross sections by less than 10%. Remaining scale uncertainties are below 2%. A fully-flexible next-to-leading order partonic Monte Carlo program allows to demonstrate these features for cross sections within typical vector-boson-fusion acceptance cuts. Modest corrections are also found for distributions.Comment: 29 pages, 14 figure

QCD radiative corrections to prompt diphoton production in association with a jet at hadron colliders

We compute the next-to-leading order corrections in $\alpha_s$ to prompt diphoton production in association with a jet at hadron colliders. We use a next-to-leading order general-purpose partonic Monte Carlo event generator that allows the computation of a rate differential in the produced photons and hadrons.Comment: 17 pages, 6 figures, JHEP3 documen

Dominant next-to-leading order QCD corrections to Higgs plus three jet production in vector-boson fusion

We present the calculation of the dominant next to leading order QCD corrections to Higgs boson production in association with three jets via vector boson fusion in the form of a NLO parton-level Monte Carlo program. QCD corrections to integrated cross sections are modest, while the shapes of some kinematical distributions change appreciably at NLO. Scale uncertainties are shown to be reduced at NLO for the total cross section and for distributions. We consider a central jet veto at the LHC and analyze the veto probability for typical vector boson fusion cuts. Scale uncertainties of the veto probability are sufficiently small at NLO for precise Higgs coupling measurements at the LHC.Comment: 40 pages, 17 figures, 2 tables, published versio

Accurate QCD predictions for heavy-quark jets at the Tevatron and LHC

Heavy-quark jets are important in many of today's collider studies and searches, yet predictions for them are subject to much larger uncertainties than for light jets. This is because of strong enhancements in higher orders from large logarithms, ln(p_t/m_Q). We propose a new definition of heavy-quark jets, which is free of final-state logarithms to all orders and such that all initial-state collinear logarithms can be resummed into the heavy-quark parton distributions. Heavy-jet spectra can then be calculated in the massless approximation, which is simpler than a massive calculation and reduces the theoretical uncertainties by a factor of three. This provides the first ever accurate predictions for inclusive b- and c-jets, and the latter have significant discriminatory power for the intrinsic charm content of the proton. The techniques introduced here could be used to obtain heavy-flavour jet results from existing massless next-to-leading order calculations for a wide range of processes. We also discuss the experimental applicability of our flavoured jet definition.Comment: 22 pages, 7 figure

The anti-k_t jet clustering algorithm

The k_t and Cambridge/Aachen inclusive jet finding algorithms for hadron-hadron collisions can be seen as belonging to a broader class of sequential recombination jet algorithms, parametrised by the power of the energy scale in the distance measure. We examine some properties of a new member of this class, for which the power is negative. This ``anti-k_t'' algorithm essentially behaves like an idealised cone algorithm, in that jets with only soft fragmentation are conical, active and passive areas are equal, the area anomalous dimensions are zero, the non-global logarithms are those of a rigid boundary and the Milan factor is universal. None of these properties hold for existing sequential recombination algorithms, nor for cone algorithms with split--merge steps, such as SISCone. They are however the identifying characteristics of the collinear unsafe plain ``iterative cone'' algorithm, for which the anti-k_t algorithm provides a natural, fast, infrared and collinear safe replacement.Comment: 12 pages, 5 figures. Small changes made for publication. Version published in JHE

PYTHIA 6.4 Physics and Manual

The PYTHIA program can be used to generate high-energy-physics `events', i.e. sets of outgoing particles produced in the interactions between two incoming particles. The objective is to provide as accurate as possible a representation of event properties in a wide range of reactions, within and beyond the Standard Model, with emphasis on those where strong interactions play a role, directly or indirectly, and therefore multihadronic final states are produced. The physics is then not understood well enough to give an exact description; instead the program has to be based on a combination of analytical results and various QCD-based models. This physics input is summarized here, for areas such as hard subprocesses, initial- and final-state parton showers, underlying events and beam remnants, fragmentation and decays, and much more. Furthermore, extensive information is provided on all program elements: subroutines and functions, switches and parameters, and particle and process data. This should allow the user to tailor the generation task to the topics of interest.Comment: 576 pages, no figures, uses JHEP3.cls. The code and further information may be found on the PYTHIA web page: http://www.thep.lu.se/~torbjorn/Pythia.html Changes in version 2: Mistakenly deleted section heading for "Physics Processes" reinserted, affecting section numbering. Minor updates to take into account referee comments and new colour reconnection option

Construction and response of a highly granular scintillator-based electromagnetic calorimeter

A highly granular electromagnetic calorimeter with scintillator strip readout is being developed for future linear collider experiments. A prototype of 21.5 푋0 depth and 180 × 180 mm2 transverse dimensions was constructed, consisting of 2160 individually read out 10 × 45 × 3 mm3 scintillator strips. This prototype was tested using electrons of 2–32 GeV at the Fermilab Test Beam Facility in 2009. Deviations from linear energy response were less than 1.1%, and the intrinsic energy resolution was determined to be (12.5±0.1(stat.)±0.4(syst.))%∕√퐸[GeV]⊕(1.2± 0.1(stat.)+0.6−0.7(syst.))%, where the uncertainties correspond to statistical and systematic sources, respectively