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, with emphasis on those where strong interactions play a rôle, 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 QCDbased models. This physics input is summarized here, for areas such as hard subprocesses, initial-and final-state parton showers, beam remnants and underlying events, 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.

Results are presented from searches for the standard model Higgs boson in proton-proton collisions at root s = 7 and 8 TeV in the Compact Muon Solenoid experiment at the LHC, using data samples corresponding to integrated luminosities of up to 5.1 fb(-1) at 7 TeV and 5.3 fb(-1) at 8 TeV. The search is performed in five decay modes: gamma gamma, ZZ, W+W-, tau(+)tau(-), and b (b) over bar. An excess of events is observed above the expected background, with a local significance of 5.0 standard deviations, at a mass near 125 GeV, signalling the production of a new particle. The expected significance for a standard model Higgs boson of that mass is 5.8 standard deviations. The excess is most significant in the two decay modes with the best mass resolution, gamma gamma and ZZ; a fit to these signals gives a mass of 125.3 +/- 0.4(stat.) +/- 0.5(syst.) GeV. The decay to two photons indicates that the new particle is a boson with spin different from one. (C) 2012 CERN. Published by Elsevier B.V. All rights reserved

The fortran version of the AcerDET package has been published in [1], and used in the multiple publications on the predictions for physics at LHC. The package provides, starting from list of particles in the event, the list of reconstructed jets, isolated electrons, muons, photons and reconstructed missing transverse energy. The AcerDET represents a simplified version of the package called ATLFAST, used since several years within ATLAS Collaboration. In the fast simulation implemented in AcerDET, some functionalities of ATLFAST are absent, but the most crucial detector effects are implemented and the parametrisations are largely simplified. Therefore it is not representing details neither of ATLAS nor CMS detectors.This short paper documents a new C++ implementation of the same algorithms as used in [1]. We believe that the package can be well adequate for some feasibility studies of the high p T physics at LHC and at planned ppFCC. The further evolution of this code is planned.[1] E. Richter-Was, AcerDET: A Particle level fast simulation and reconstruction package for phenomenological studies on high p(T) physics at LHC , hep-ph/0207355. Nature of physical problem: A particle level fast simulation and reconstruction package. The package provides, starting from the list of particles in the event, list of reconstructed jets, isolated electrons, muons and photons and reconstructed missing transverse energy. The algorithmic part is just rewritten from fortran version of the package AcerDET-1.0 [1]. The default input is generated event in format of HepMC structure [2], output is in form of ROOT file [4], containing tree with reconstructed objects and set of control histograms. Distribution version includes also example of the main program for execution with PYTHIA 8.2 generator [3]. Implemented set of parametrisations is not representing in details ATLAS or CMS detectors, some of them are simple and can be considered rather as place-holders for future adaptation of any detector. Nevertheless, we believe that the package will be well adequate for some feasibility studies on the high p T physics at LHC.[1]. E. Richter-Was, AcerDET: A Particle level fast simulation and reconstruction package for phenomenological studies on high p(T) physics at LHC , hep-ph/0207355;

The Pythia program is a standard tool for the generation of events in high-energy collisions, comprising a coherent set of physics models for the evolution from a few-body hard process to a complex multiparticle final state. It contains a library of hard processes, models for initial-and final-state parton showers, matching and merging methods between hard processes and parton showers, multiparton interactions, beam remnants, string fragmentation and particle decays. It also has a set of utilities and several interfaces to external programs. Pythia 8.2 is the second main release after the complete rewrite from Fortran to C++, and now has reached such a maturity that it offers a complete replacement for most applications, notably for LHC physics studies. The many new features should allow an improved description of data. Catalogue identifier of previous version: ACTU v3 0 Journal reference of previous version: T. Sjöstrand, S. Mrenna and P. Skands, Computer Physics Commun. 178 (2008) 852 Does the new version supersede the previous version?: yes Nature of problem: high-energy collisions between elementary particles normally give rise to complex final states, with large multiplicities of hadrons, leptons, photons and neutrinos. The relation between these final states and the underlying physics description is not a simple one, for two main reasons. Firstly, we do not even in principle have a complete understanding of the physics. Secondly, any analytical approach is made intractable by the large multiplicities. Solution method: complete events are generated by Monte Carlo methods. The complexity is mastered by a subdivision of the full problem into a set of simpler separate tasks. All main aspects of the events are simulated, such as hard-process selection, initial-and final-state radiation, beam remnants, fragmentation, decays, and so on. Therefore events should be directly comparable with experimentally observable ones. The programs can be used to extract physics from comparisons with existing data, or to study physics at future experiments. Reasons for the new version: improved and expanded physics models Summary of revisions: hundreds of new features and bug fixes, allowing an improved modeling Restrictions: depends on the problem studied Unusual features: none Running time: 10-1000 events per second, depending on process studied

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