Multi-jet production in lepton-proton scattering at next-to-leading order accuracy

I summarize the theoretical and experimental status of multijet production in DIS. I present the state of the art theoretical predictions and compare those to the corresponding experimental results obtained by analysing the data collected by the H1 and ZEUS collaborations at HERA. I also show new predictions for three-jet event-shape distributions at the NLO accuracy.Comment: 11 pages, 8 figures. To appear in the proceedings of the Ringberg Workshop on "New Trends in HERA Physics 2005", Ringberg Castle, Tegernsee, Germany, 2-7 October 200

Hadroproduction of W+W−bbˉW^+ W^- b \bar{b} at NLO accuracy matched with shower Monte Carlo programs

We present the computation of the differential cross section for the process $pp(\bar{p}) \to (W^+\,W^-\,b\,\bar{b} \to)\;e^+\,\nu_e\,\mu^-\,\bar{\nu}_\mu\,b\, \bar{b}+X$ at NLO QCD accuracy matched to Shower Monte Carlo (SMC) simulations using PowHel, on the basis of the interface between HELAC-NLO and POWHEG-BOX. We include all resonant and non-resonant contributions. This is achieved by fully taking into account the effect of off-shell t-quarks and off-shell W-bosons in the complex mass scheme. We also present a program called DECAYER that can be used to let the t-quarks present in the event files for $pp(\bar{p}) \to {t\,\bar{t}\,X}$ processes decay including both the finite width of the t-quarks and spin correlations. We present predictions for both the Tevatron and the LHC, with emphasis on differences emerging from three different $W^+\,W^-\,b\,\bar{b}$ hadroproduction computations: (i) full implementation of the $p\,p(\bar{p}) \to W^+\,W^-\,b\,\bar{b}$ process, (ii) generating on-shell t-quarks pushed off-shell with a Breit-Wigner finite width and decayed by DECAYER, and (iii) on-shell t-quark production followed by decay in the narrow width approximation, as described by the SMC.Comment: 40 pages, 26 figures; slightly expanded version matching the one published in JHE

Physics at Large Rapidities in γ∗γ∗→\gamma^*\gamma^* \to Hadrons at LEP2

We compute the order-\as corrections to the total cross section and to jet rates in $\gamma^* \gamma^* \to$ hadrons for the process \epem\to\epem + hadrons. We use a NLO order general-purpose partonic Monte Carlo event generator that allows the computation of a rate differential in the produced leptons and hadrons. We compare our results with the experimental data for \epem\to\epem + hadrons at LEP2.Comment: 5 pages, 1 figure, presented at the LEPTRE meeting, Roma 200

Top-antitop pair hadroproduction in association with a heavy boson at the NLO QCD accuracy + Parton Shower

The PowHel framework allows to make predictions of total and differential cross-sections of multiparticle hadroproduction processes at both NLO QCD accuracy and NLO QCD matched to Parton Shower, on the basis of the interface between the POWHEG-BOX and HELAC-NLO codes. It has already been applied to study several processes involving a top-antitop pair in association with a third particle or hadronic jet. Our most recent predictions concern top-antitop-V hadroproduction (with V = W or Z), at both parton and hadron level, by considering different decay channels (hadronic and leptonic) of the heavy particles. In particular, we show the results of our phenomenological analyses under the same system of cuts also recently adopted by the CMS collaboration at LHC.Comment: 4 pages, 2 figures, Proceedings of TOP 2012 - 5th International Workshop on Top Quark Physics, September 16 - 21 2012, Winchester, U

QCD radiative corrections to γ∗γ∗→\gamma^*\gamma^* \to hadrons

We compute the order-\as corrections to the total cross section and to jet rates for the process \epem\to\epem + hadrons, where the hadrons are produced through crossed-channel quark exchange in the hard scattering of two off-shell photons originating from the incoming leptons. 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 leptons and hadrons. We compare our results with the available experimental data for \epem\to\epem + hadrons at LEP2.Comment: 25 pages Latex; 1 style file and 14 figures include

Report of the QCD Working Group

The activities of the QCD working group concentrated on improving the understanding and Monte Carlo simulation of multi-jet final states due to hard QCD processes at LEP, i.e. quark-antiquark plus multi-gluon and/or secondary quark production, with particular emphasis on four-jet final states and b-quark mass effects. Specific topics covered are: relevant developments in the main event generators PYTHIA, HERWIG and ARIADNE; the new multi-jet generator APACIC++; description and tuning of inclusive (all-flavour) jet rates; quark mass effects in the three- and four-jet rates; mass, higher-order and hadronization effects in four-jet angular and shape distributions; b-quark fragmentation and gluon splitting into b-quarks.Comment: 95 pages, 48 figures, contribution to Proceedings of the LEP2 Monte Carlo Workshop. References for NLO 4-jet matrix elements adde