This paper presents a new event generator, ALPGEN, dedicated to the study of multiparton hard processes in hadronic collisions. The code performs, at the leading order in QCD and EW interactions, the calculation of the exact matrix elements for a large set of parton-level processes of interest in the study of the Tevatron and LHC data. The current version of the code describes the following final states: (W → ff ′ )QQ + N jets (Q being a heavy quark, and f = ℓ, q), with N ≤ 4; (Z/γ * → ff ) QQ + N jets (f = ℓ, ν), with N ≤ 4; (W → ff ′ ) + charm + N jets (f = ℓ, q, N ≤ 5); (W → ff ′ ) + N jets (f = ℓ, q) and (Z/γ * → ff ) + N jets (f = ℓ, ν), with N ≤ 6; nW + mZ + lH + N jets, with n + m + l + N ≤ 8, N ≤ 3, including all 2-fermion decay modes of W and Z bosons, with spin correlations; QQ + N jets, with t → bff ′ decays and relative spin correlations included if Q = t, and N ≤ 6; QQQ ′ Q ′ + N jets, with Q and Q ′ heavy quarks (possibly equal) and N ≤ 4; HQQ + N jets, with t → bff ′ decays and relative spin correlations included if Q = t and N ≤ 4; N jets, with N ≤ 6. Parton-level events are generated, providing full information on their colour and flavour structure, enabling the evolution of the partons into fully hadronised final states.

We propose that the Y (4260) particle recently announced by BaBar is the first orbital excitation of a diquark-antidiquark state ([cs][cs]). Using parameters recently determined to describe the X(3872) and X(3940) we show that the Y mass is compatible with the orbital excitation picture. A crucial prediction is that Y (4260) should decay predominantly in DsDs. The Y (4260) should also be seen in B non-leptonic decays in association with one kaon. We consider the full nonet of related four-quark states and their predicted properties. Finally, we comment on a possible narrow resonance in the same channel.ROMA1 In a series of exciting experiments, BELLE and BaBar have discovered several states that, although decaying in charmonium plus pions, do not seem to fit the cc picture, in particular the X(3872) and X(3940) states.In a recent paper [1] we have pointed out that the properties of the new states can be well explained if they are S-wave diquark-antidiquark bound states with the composition (q = u, d): [(cq)(cq)] S−wave . An alternative scenario is the molecular picture where the X(3872) would be a D 0 D * 0 bound state. A crucial difference between the two alternatives is that colored objects in a rising confining potential, such as diquarks, should exhibit a series of orbital angular momentum excitations. This is clearly at variance with the molecular picture. Colorless objects bound by a short range potential should have a very limited spectrum, possibly restricted to S-wave states only.In this note we would like to propose that the first orbital excitation of a diquark-antidiquark state may have indeed been found in the state Y (4260) recently announced by the BaBar collaboration [2]. We discuss the properties of the new state in this framework and spell out a few distinctive predictions. The most revealing among them is that the dominant decay mode of Y (4260) should be in D sDs pairs. We shall also briefly discuss other states implied by the scheme and their properties. We comment on the possibility of an additional narrow state.The Y (4260) is observed by BaBar in e + e − annihilation, in association with an Initial-State-Radiation pho- * Electronic address: luciano.maiani@roma1.infn.it † Electronic address: veronica.riquer@cern.ch ‡ Electronic address: fulvio.piccinini@pv.infn.it § Electronic address: antonio.polosa@cern.ch ton, which implies J P C = 1 −− . The particle has a width of about 90 MeV and it is seen to decay in J/ψ π + π − . The π + π − mass distribution peaks around 1 GeV, consistently with a decay into J/ψ f 0 (980). BaBar reports the value [2]:(1) The diquark-antidiquark assumption together with the negative parity call for at least one unit of orbital angular momentum. In addition, the decay into f 0 (980), which fits the (

Heavy-light diquarks can be the building blocks of a rich spectrum of states which can accommodate some of the newly observed charmonium-like resonances not fitting a pure cc assignment. We examine this possibility for hidden and open charm diquark-antidiquark states deducing spectra from constituent quark masses and spin-spin interactions. Taking the X(3872) as input we predict the existence of a 2 ++ state that can be associated to the X(3940) observed by Belle and re-examine the state claimed by SELEX, X(2632). The possible assignment of the previously discovered states Ds(2317) and Ds (2457) is discussed. We predict X(3872) to be made of two components with a mass difference related to mu − m d and discuss the production of X(3872) and of its charged partner X ± in the weak decays of B +,0 .

Abstract:The discovery by the ATLAS and CMS experiments of a new boson with mass around 125 GeV and with measured properties compatible with those of a Standard-Model Higgs boson, coupled with the absence of discoveries of phenomena beyond the Standard Model at the TeV scale, has triggered interest in ideas for future Higgs factories. A new circular e + e − collider hosted in a 80 to 100 km tunnel, TLEP, is among the most attractive solutions proposed so far. It has a clean experimental environment, produces high luminosity for top-quark, Higgs boson, W and Z studies, accommodates multiple detectors, and can reach energies up to the tt threshold and beyond. It will enable measurements of the Higgs boson properties and of Electroweak Symmetry-Breaking (EWSB) parameters with unequalled precision, offering exploration of physics beyond the Standard Model in the multi-TeV range. Moreover, being the natural precursor of the VHE-LHC, a 100 TeV hadron machine in the same tunnel, it builds up a long-term vision for particle physics. Altogether, the combination of TLEP and the VHE-LHC offers, for a great cost effectiveness, the best precision and the best search reach of all options presently on the market. This paper presents a first appraisal of the salient features of the TLEP physics potential, to serve as a baseline for a more extensive design study.

We study the matching of multijet matrix elements and shower evolution in the case of top production in hadronic collisions at the Tevatron and at the LHC. We present the results of the matching algorithm implemented in the ALPGEN Monte Carlo generator, and compare them with results obtained at the parton level, and with the predictions of the MC@NLO approach. We highlight the consistency of the matching algorithm when applied to these final states, and the excellent agreement obtained with MC@NLO for most inclusive quantities. We nevertheless identify also a remarkable difference in the rapidity spectrum of the leading jet accompanying the top quark pair, and comment on the likely origin of this discrepancy.

Centre d'études et d'expertise sur les risques, l'environnement, la mobilité et l'aménagement

Abstract. We compare different procedures for combining fixed-order tree-level matrix-element generators with parton showers. We use the case of W -production at the Tevatron and the LHC to compare different implementations of the so-called CKKW and MLM schemes using different matrix-element generators and different parton cascades. We find that although similar results are obtained in all cases, there are important differences.

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