Planar two-loop corrections to Higgs+jet production in QCD

• Roberto Bonciani (ROMA1)

Room: Aula Seminari We will review the calculation of the two-loop QCD amplitudes that contribute to the NLO cross section for the production of a Higgs boson with a jet (or to Higgs decay to three partons). In particular we concentrate on planar corrections, we discuss the structure of the amplitude in terms of helicity amplitudes, their expression in terms of dimensionally regularized Feynman integrals and, finally, the reduction to the master integrals and their calculation with the differential equations method. We show a class of four-point functions that show an elliptic behaviour, i.e. whose differential equation can be solved in terms of complete elliptic integrals.

Massless dark-photon phenomenology at colliders

• Barbara Mele (ROMA1)

Room: Aula Seminari A prediction of recent models possibly explaining the fermion-mass hierarchy is the existence of a massless dark photon. Its interaction is restricted to a hidden sector made up of massive dark fermions (which are promising dark-matter candidates), and heavier scalar messengers connecting the SM with the dark fields. Thanks to the nondecoupling properties of the Higgs boson, exotic Higgs interactions with the invisible dark photon can show up at present and future colliders with measurable rates. Predictions for new Higgs signatures and corresponding rates are presented. A new class of FCNC’s mediating SM fermion decays into massless dark photons  are also discussed.

Top B physics with the ATLAS experiment

• Lucio Cerrito (ROMA2)

Room: Aula Seminari The violation of the combined charge conjugation (C) and parity transformation (P) of particles and antiparticles implies that the laws of physics are not the same for matter and antimatter. Observations of CP violation are not sufficient to explain the matter–antimatter asymmetry in the universe, and it is believed that a source of new physics is required. The abundance of top quarks at the Large Hadron Collider are usually exploited to explore top properties or search for heavy resonances, however top decay products also provide a unique window for measurements of CP violation in b- and c-quarks. Utilising semileptonic b-decays, CP sensitive asymmetries may be built from lepton-pairs in the l+jets channel. The first analysis to use this technique is presented using data collected by the ATLAS detector.

The Structure of the proton: global analyses in QCD and LHC precision physics

• Marco Guzzi (University of Manchester)

Room: Aula Seminari Parton distribution functions (PDFs) provide detailed information about the nonperturbative structure of the proton and are the core input for QCD theory predictions and simulations for the Large Hadron Collider. Modern PDFs are determined from large-scale analyses of high-energy hadronic data and account for a rich variety of experimental and theoretical factors. I will review the current status of new generation of PDFs, in particular the CT14 PDFs, by the Coordinated Theoretical-Experimental project on QCD (CTEQ). PDF implications for predictions of importance for LHC processes, (Higgs boson, top-quark pair production, etc.) will also be discussed.

Theory uncertainty from missing higher orders

• Marco Bonvini

Room: Aula Seminari In the precision era of the LHC, it is of utmost importance having a good control on the theoretical uncertainties. With particular attention to the inclusive Higgs cross section in gluon fusion, where scale variation notoriously underestimates the theory error, I will discuss alternative options, trying to provide a statistical interpretation.