45 research outputs found

    Simulated NNLO for high-pT observables in vector boson + jets production at the LHC

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    We present a study of higher order QCD corrections beyond NLO to processes with an electroweak vector boson, W or Z, in association with jets. We focus on the regions of high transverse momenta of commonly used differential distributions. We employ the LoopSim method to merge NLO samples of different multiplicity obtained from MCFM and from BLACKHAT+SHERPA in order to compute the dominant part of the NNLO corrections for high-pT observables. We find that these corrections are indeed substantial for a number of experimentally relevant observables. For other observables, they lead to significant reduction of scale uncertainties.Comment: 16 pages, 8 figures; v2: expanded discussion in a few places, added and corrected references, version accepted by Eur. Phys. J.

    Small-x single-particle distributions in jets from the coherent branching formalism

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    We calculate single parton distributions inside quark and gluon jets within the coherent branching formalism, which resums leading and next-to-leading logarithmic contributions. This formalism is at the basis of the modified leading logarithmic approximation (MLLA), and it conserves energy exactly. For a wide preasymptotic range of the evolution variable Y=ln[E\theta/Q_0], we find marked differences in the shape and norm of single parton distributions calculated in the MLLA or in the coherent branching formalism, respectively. For asymptotically large values Y>5-10, the difference in norm persists, while differences in shape disappear. In this way, our numerical study delineates the jet energy scale needed for a reliable application of both approaches. We also study the dependence of the single parton distributions on the hadronization scale Q_0 and on \Lambda_QCD, and we calculate within the coherent branching formalism the identified quark and gluon distributions inside quark and gluon jets.Comment: 23 pages, 12 figure

    Saturation model of DIS : an update

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    We present the results of new fits to the recently extracted data on F2F_2 at low xx with the GBW saturation model and its modification to cover high values of Q2Q^2. We find that the model stands the test of time and gives a good description of the data with slightly modified parameters. All the essential elements of the model, especially the saturation scale, are retained.Comment: 16 pages, 8 figures; v2: several textual changes and additions, Table 2 added, version accepted by JHEP; v3: misprint correcte

    ZZ production at high transverse momenta beyond NLO QCD

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    We study the production of the four-lepton final state l+l−l+l−l^+ l^- l^+ l^-, predominantly produced by a pair of electroweak Z bosons, ZZ. Using the LoopSim method, we merge NLO QCD results for ZZ and ZZ+jet and obtain approximate NNLO predictions for ZZ production. The exact gluon-fusion loop-squared contribution to the ZZ process is also included. On top of that, we add to our merged sample the gluon-fusion ZZ+jet contributions from the gluon-gluon channel, which is formally of N^3LO and provides approximate results at NLO for the gluon-fusion mechanism. The predictions are obtained with the VBFNLO package and include the leptonic decays of the Z bosons with all off-shell and spin-correlation effects, as well as virtual photon contributions. We compare our predictions with existing results for the total inclusive cross section at NNLO and find a very good agreement. Then, we present results for differential distributions for two experimental setups, one used in searches for anomalous triple gauge boson couplings, the other in Higgs analyses in the four charged-lepton final state channel. We find that the approximate NNLO corrections are large, reaching up to 20% at high transverse momentum of the Z boson or the leading lepton, and are not covered by the NLO scale uncertainties. Distributions of the four-lepton invariant mass are, however, stable with respect to QCD corrections at this order.Comment: 21 pages, 2 tables, 9 figure

    QCD and Jets at Hadron Colliders

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    We review various aspects of jet physics in the context of hadron colliders. We start by discussing the definitions and properties of jets and recent development in this area. We then consider the question of factorization for processes with jets, in particular for cases in which jets are produced in special configurations, like for example in the region of forward rapidities. We review numerous perturbative methods for calculating predictions for jet processes, including the fixed-order calculations as well as various matching and merging techniques. We also discuss the questions related to non-perturbative effects and the role they play in precision jet studies. We describe the status of calculations for processes with jet vetoes and we also elaborate on production of jets in forward direction. Throughout the article, we present selected comparisons between state-of-the-art theoretical predictions and the data from the LHC.Comment: 77 pages, 37 figures; v2: text developments in several places, references added, version published in Prog. Part. Nucl. Phys. 201

    Single and double inclusive forward jet production at the LHC at s\sqrt{s} = 7 and 13 TeV

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    We provide a description of the transverse momentum spectrum of single inclusive forward jets produced at the LHC, at the center-of-mass energies of 7 and 13 TeV, using the high energy factorization (HEF) framework. We subsequently study double inclusive forward jet production and, in particular, we calculate contributions to azimuthal angle distributions coming from double parton scattering. We also compare our results for double inclusive jet production to those obtained with the Pythia Monte Carlo generator. This comparison confirms that the HEF resummation acts like an initial state parton shower. It also points towards the need to include final state radiation effects in the HEF formalism.Comment: 14 pages, 5 figures, version accepted for PL