119710149
Decay distribution of tau produced by neutrino-nucleon scattering☆
We studied the decay distributions of τ leptons produced in neutrino-nucleon scattering via charged current interaction, taking into account the τ polarization, for the long baseline neutrino oscillation experiments which aim to observe ν τ appearance. The information on the τ polarization is essential for measuring ν τ appearance since the decay particle distributions depend crucially on the τ spin. We show that τ produced via neutrino has high degree of polarization, and its spin direction depends non-trivially on the energy and the scattering angle of τ in the laboratory frame. We also show that the subsequent decay distributions are significantly affected by the produced τ polarization.
17215723
Higgs characterisation via vector-boson fusion and associated production: NLO and parton-shower effects
Vector-boson fusion and associated production at the LHC can provide key information on the strength and structure of the Higgs couplings to the Standard Model particles. Using an effective field theory approach, we study the effects of next-to-leading order (NLO) QCD corrections matched to a parton shower on selected observables for various spin-0 hypotheses. We find that inclusion of NLO corrections is needed to reduce the theoretical uncertainties on the total rates as well as to reliably predict the shapes of the distributions. Our results are obtained in a fully automatic way via FeynRules and MadGraph5_aMC@NLO.
18756329
Higgs characterisation at NLO in QCD: CP properties of the top-quark Yukawa interaction
At the LHC the CP properties of the top-quark Yukawa interaction can be probed through Higgs production in gluon fusion or in association with top quarks. We consider the possibility for both CP-even and CP-odd couplings to the top quark to be present, and study CP-sensitive observables at next-to-leading order (NLO) in QCD, including parton-shower effects. We show that the inclusion of NLO corrections sizeably reduces the theoretical uncertainties, and confirm that di-jet correlations in $$H+2$$H+2 jet production through gluon fusion and correlations of the top-quark decay products in $$t\bar{t}H$$tt¯H production can provide sensitive probes of the CP nature of the Higgs interactions.
17463150
T-odd asymmetries in radiative top-quark decays
We study the angular distribution of the charged lepton in the top-quark decay into a bottom quark and a W boson which subsequently decays into lνl, when a hard gluon is radiated off. The absorptive part of the t → bWg decay amplitudes, which gives rise to T-odd asymmetries in the distribution, is calculated at the one-loop level in perturbative QCD. The asymmetries at a few percent level are predicted, which may be observable at future colliders.
55904501
MadGolem: automated NLO predictions for Beyond-the-Standard Model searches
TeV-scale new physics is already at the spotlight of the current experimental LHC program. In this context, particle phenomenologists are urged to develop automated tools aiming at fast, flexible and accurate theoretical predictions for the major new physics discovery channels. In this contribution we provide a summarized description of the MADGOLEM package, a fully automated tool that enables to evaluate next-to-leading order (NLO) cross sections and distributions for generic heavy particle pair production beyond the Standard Model (BSM). We concisely portray the structure and inner architecture of the code, with our main emphasis on the strategies by which we handle the genuine building blocks of a NLO calculation ‐ the evaluation of the one-loop amplitudes, the renormalization of the ultraviolet singularities, and the subtraction of infrared and on-shell divergences. We discuss the performance of the tool, its multiple functionalities and analysis options, and the attentive cross-checks of all these features. Finally, we present some sample applications to BSM heavy particle production at the LHC.
54513709
Probing top-philic sgluons with LHC Run I data
Many theories beyond the Standard Model predict the existence of colored scalar states, known as sgluons, lying in the adjoint representation of the QCD gauge group. In scenarios where they are top-philic, sgluons are expected to be copiously pair-produced at the LHC via strong interactions with decays into pairs of top quarks or gluons. Consequently, sgluons can be sought in multijet and multitop events at the LHC. We revisit two LHC Run I analyses in which events featuring either the same-sign dileptonic decay of a four-top-quark system or its single leptonic decay are probed. Adopting a simplified model approach, we show how this reinterpretation allows us to extract simultaneous bounds on the sgluon mass and couplings.
117769943
An H-alpha search for over-dense regions at z=2.23
We present the results of a narrow-band (H2S1, 2.121/0.021um) imaging search with WFCAM/UKIRT for H-alpha emitters around several potential signposts of rare (10^-7-10^-8 Mpc^-3) over-dense regions at z=2.23: an over-density of QSOs (2QZ cluster), a powerful, high-redshift radio galaxy (HzRG), and a concentration of submillimetre galaxies (SMGs) and optically faint radio galaxies (OFRGs). In total, we detect 137 narrow-band emitter candidates down to emission-line fluxes of 0.5-1 x 10^-16 erg s^-1 cm^-2, across a total area of 0.56 sq. degrees (2.1 x 10^5 comoving Mpc at z=2.23) in these fields. The BzK colours of the emitters suggest that at least 80% of our sample are likely to be H-alpha emitters (HAEs) at z=2.23. This is one of the largest HAE samples known at z>2. We find modest (~3-sigma) local over-densities of emitters associated with all the three targets. In the 2QZ cluster field, the emitters show a striking filamentary structure connecting four of the z=2.23 QSOs extending over 30Mpc (comoving). In the HzRG and SMG/OFRG fields, the structures appear to be smaller and seen only in the vicinities of the targets. The K-band magnitudes and the H-alpha equivalent widths of the emitters are weakly correlated with the over-density of the emitters: emitters in over-dense region are more evolved systems compared to those in under-dense regions at z=2.23. We find several examples of extended HAEs in our target fields, including a striking example with a spatial extent of 7.5 arcsec (60 kpc at z=2.23) in the 2QZ field, suggesting that these are relatively common in high-density regions. We conclude that narrow-band H-alpha surveys are efficient routes to map over-dense regions at high-z and thus to understand the relation between the growth of galaxies and their surrounding large-scale structures.