Combined NLO EW and QCD corrections to off-shell $$\text {t} \overline{\text {t}}\text {W} $$ production at the LHC

The high luminosity that will be accumulated at the LHC will enable precise differential measurements of the hadronic production of a top–antitop-quark pair in association with a $$\text {W} $$ W boson. Therefore, an accurate description of this process is needed for realistic final states. In this work we combine for the first time the NLO QCD and electroweak corrections to the full off-shell $$\text {t} \overline{\text {t}}\text {W} ^+$$ t t ¯ W + production at the LHC in the three-charged-lepton channel, including all spin correlations, non-resonant effects, and interferences. To this end, we have computed the NLO electroweak radiative corrections to the leading QCD order as well as the NLO QCD corrections to both the QCD and the electroweak leading orders.

Universality-breaking effects in $$e^+e^-$$ hadronic production processes

Recent BELLE measurements provide the cross section for single hadron production in $$e^+e^-$$ e + e - annihilations, differential in thrust and in the hadron transverse momentum with respect to the thrust axis. Universality breaking effects due to process-dependent soft factors make it very difficult to relate this cross sections to those corresponding to hadron-pair production in $$e^+e^-$$ e + e - annihilations, where transverse momentum dependent (TMD) factorization can be applied. The correspondence between these two cross sections is examined in the framework of the Collins-Soper-Sterman factorization, in the collinear as well as in the TMD approach. We propose a scheme that allows to relate the TMD parton densities defined in 1-hadron and in 2-hadron processes, neatly separating, within the soft and collinear parts, the non-perturbative terms from the contributions that can be calculated perturbatively. The regularization of rapidity divergences introduces cut-offs, the arbitrariness of which will be properly reabsorbed by means of a mechanism closely reminiscent of a gauge transformation. In this way, we restore the possibility to perform global phenomenological studies of TMD physics, simultaneously analyzing data belonging to different hadron classes.

Event Generators for Multi Hadronic Production in e+e− Collisions

An event generator for multi hadron production is presented for measuring the R value in the τ-charm energy region with e+e− collisions. The initial state radiation effects are considered up to second order accuracy, and the radiative correction factor is calculated with hadronic Born cross sections. The established exclusive processes are generated according to their measured cross sections, while the missing processes are generated using the LUND Area Law model, and its parameters are tuned with data collected at $ \sqrt s $ = 3.08 GeV. The optimized values are validated with data in the range $ \sqrt s $= 2.2324 ∼ 3.671 GeV. These optimized parameters are universally valid for event generation below the DD¯threshold.