F. Piccinini

The 2-+ assignment for the X(3872)

Very recently the BABAR collaboration has put forward a claim that the X(3872) is not a 1{sup ++} resonance, as most of the phenomenological work on the subject was relying on, but rather a 2{sup -+} one. We examine the consequences of this quantum number assignment for the solution of the X(3872) puzzle. The molecular interpretation appears less likely, and the conventional charmonium interpretation should be reconsidered. There are several well-known difficulties with this interpretation, to which we add a new one: the production cross section at CDF is predicted to be much smaller than that observed. We also confirm, using a relativistic string model, the conclusion from potential models that the mass of the state is not consistent with expectations. In the tetraquark interpretation the 2{sup -+} assignment implies a rich spectrum of partner states, although the X(3872) may be among the few which are narrow enough to be observable.

Precision physics at LEP

1 - Introduction 2 - Small-Angle Bhabha Scattering and the Luminosity Measurement 3 - Z^0 Physics 4 - Fits to Precision Data 5 - Physics at LEP2 6 - Conclusions

Complete one-loop calculation of electroweak supersymmetric effects in t-channel single top production at CERN LHC

We have computed the complete one-loop electroweak effects in the minimal supersymmetric standard model for single top (and single antitop) production in the t channel at hadron colliders, generalizing a previous analysis performed for the dominant dt final state and fully including QED effects. The results are quite similar for all processes. The overall standard model one-loop effect is small, of the few percent size. This is due to a compensation of weak and QED contributions that are of opposite sign. The genuine supersymmetry contribution is generally quite modest in the minimal supergravity scenario. The experimental observables would therefore only practically depend, in this framework, on the Cabibbo-Kobayashi-Maskawa Wtb coupling.

WWGENPV — A Monte Carlo event generator for four-fermion production in e+e− → W+W− → 4f

The Monte Carlo program {\tt WWGENPV}, designed for computing distributions and generating events for the four-fermion process

Precision studies of observables in pp → W → lνl and pp → γ , Z → l+l− processes at the LHC.

e^+ e^- \to W^+ W^- \to 4f

SABSPV: A Monte Carlo integrator for small angle Bhabha scattering

, is described. It is based on the calculation of the exact tree-level matrix element of the four-fermion reaction and includes initial-state radiation in the leading-log approximation within the structure function approach. The program can be used in a two-fold way: as a Monte Carlo integrator for weighted events, providing predictions for the total cross section, the

Radiative Events as a Probe of Dark Forces at GeV-Scale

W

e^+ e^-

invariant-mass distribution, the radiative energy and invariant-mass loss; as a true event generator of unweighted events, useful for simulation purposes.Abstract The Monte Carlo program WWGENPV, designed for computing distributions and generating events for the four-fermion process e + e − → W + W − → 4 f is described. It is based on the calculation of the exact tree-level matrix element of the four-fermion reaction and includes initial-state radiation in the leading-log approximation within the structure function approach. The program can be used in a two-fold way: as a Monte Carlo integrator for weighted events, providing predictions for the total cross section, the W invariant-mass distribution, the radiative energy and invariant-mass loss; and as a true event generator of unweighted events, useful for simulation purposes.

Colliders

This report was prepared in the context of the LPCC Electroweak Precision Measurements at the LHC WG (https://lpcc.web.cern.ch/lpcc/index.php?page=electroweak_wg) and summarizes the activity of a subgroup dedicated to the systematic comparison of public Monte Carlo codes, which describe the Drell–Yan processes at hadron colliders, in particular at the CERN Large Hadron Collider (LHC). This work represents an important step towards the definition of an accurate simulation framework necessary for very high-precision measurements of electroweak (EW) observables such as the W boson mass and the weak mixing angle. All the codes considered in this report share at least next-to-leading-order (NLO) accuracy in the prediction of the total cross sections in an expansion either in the strong or in the EW coupling constant. The NLO fixed-order predictions have been scrutinized at the technical level, using exactly the same inputs, setup and perturbative accuracy, in order to quantify the level of agreement of different implementations of the same calculation. A dedicated comparison, again at the technical level, of three codes that reach next-to-next-to-leading-order (NNLO) accuracy in quantum chromodynamics (QCD) for the total cross section has also been performed. These fixed-order results are a well-defined reference that allows a classification of the impact of higher-order sets of radiative corrections. Several examples of higher-order effects due to the strong or the EW interaction are discussed in this common framework. Also the combination of QCD and EW corrections is discussed, together with the ambiguities that affect the final result, due to the choice of a specific combination recipe. All the codes considered in this report have been run by the respective authors, and the results presented here constitute a benchmark that should be always checked/reproduced before any high-precision analysis is conducted based on these codes. In order to simplify these benchmarking procedures, the codes used in this report, together with the relevant input files and running instructions, can be found in a repository at https://twiki.cern.ch/twiki/bin/view/Main/DrellYanComparison.

More loosely bound hadron molecules at CDF

SABSPV is a code designed to perform a theoretical evaluation of small-angle Bhabha scattering cross sections by suitably matching fixed-order perturbative calculations and structure-function techniques. The implementation of realistic experimental triggering conditions is achieved by using Monte Carlo integration.SABSPV is a code designed to perform a theoretical evaluation of small-angle Bhabha scattering cross sections by suitably matching fixed-order perturbative calculations and structure-function techniques. The implementation of realistic experimental triggering conditions is achieved by using Monte Carlo integration.