A.D. Polosa

ALPGEN, a generator for hard multiparton processes in hadronic collisions

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→f)Q+N jets (Q being a heavy quark, and f = l,q), with N ≤ 4;(Z/γ*→f)Q+N jets (f = l,ν), with N ≤ 4; W→f)+charm+N jets (f = l,q,N ≤ 5;W→f)+N jets (f = l,q and Z/γ*→f)+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; Q+N jets, with t→bf decays and relative spin correlations included where relevant, and N ≤ 6; QQ+N jets, with Q and Q heavy quarks (possibly equal) and N ≤ 4; HQ+N jets, with t→bf decays and relative spin correlations included where relevant 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.

The new pentaquarks in the diquark model

Abstract Pentaquark baryons are a natural expectation of an extended picture of hadrons where quarks and diquarks are the fundamental units. The parity/mass pattern observed, when compared to that of exotic mesons, appears as the footprint of a compact five-quark structure. What has been learned from the X, Y, Z phenomenology informs about the newly found pentaquark structure and suggests further experimental tests and directions to be explored.

Higgs boson self-couplings at the LHC as a probe of extended Higgs sectors

A study of two-Higgs-doublet models (2HDM) in the decoupling limit reveals the existence of parameter configurations with a large triple-Higgs self-coupling as the only low-energy trace of the departure from a Standard Model (SM) Higgs sector. This observation encourages attempts to search for double Higgs production at the Large Hadron Collider (LHC) even in mass regions which have been shown to be very hard to probe in the context of SM-like Higgs self-couplings. In this document we consider the case of an Intermediate Mass Higgs (IMH) boson, with 120 GeVMH140 GeV, produced in pairs via vector-vector fusion, Higgs-strahlung and associate production with heavy-quarks and decaying into b pairs. After a detailed signal-to-background analysis, we confirm that the observation of a Higgs-pair signal is very challenging in the framework of the SM, even at the LHC with upgraded luminosity. In contrast, we verify that the sensitivity is sufficient to detect departures from the SM which would escape detection in the measurements of the single-Higgs production channels.

Heavier Higgs particles: Indications from Minimal Supersymmetry

Abstract We use the most recent data on the Higgs-like resonance h observed at 125 GeV to derive information about the mass of the heavier Higgs particles predicted by Minimal Supersymmetry. We treat as independent parameters the couplings of h to top quark, beauty and massive vector bosons and, in this three-dimensional space, we locate the point realizing the best fit to data and compare it to the position of the Standard Model point and to the region of coupling values accommodating heavier Higgs particles in Minimal Supersymmetry. We conclude that mass values 320 ≲ M H ≲ 360 GeV are compatible at 2 σ with the best fit of couplings to present data, larger values being compatible at the 1 σ level. Values of 1 ≲ tan β ≲ 6 are compatible with data.

bb̄ final states in Higgs production via weak boson fusion at the LHC

We present a study of the Higgs production at the LHC via Weak Boson Fusion, with the Higgs boson decaying into a b-quark pair. A detailed partonic LO calculation of all the potential backgrounds is performed. We conclude that this channel for Higgs production can be extracted from the backgrounds, and present our estimates of the accuracy in the determination of the Hbb Yukawa coupling.Abstract We present a study of the Higgs production at the LHC via weak boson fusion, with the Higgs boson decaying into a b b pair. A detailed partonic LO calculation of all the potential backgrounds is performed. We conclude that this channel for Higgs production can be extracted from the backgrounds, and present our estimates of the accuracy in the determination of the Hb b Yukawa coupling.

Bounds to the Higgs sector masses in minimal supersymmetry from LHC data

Abstract We update our analysis of the Higgs sector masses in minimal supersymmetry and in the Two Higgs Doublet Model to the final ATLAS and CMS data from the 2011–2012 LHC run.

Counting valence quarks at RHIC and LHC

Abstract We consider the nuclear modification ratios in heavy ion collisions, R C P and R A A , in the region of intermediate transverse momentum, and study the dependency upon the constituent quark composition of the observed hadron. Adopting a two component recombination/fragmentation model, validated by experimental information from STAR and PHENIX, we show that a clear distinction is predicted for the f 0 ( 980 ) between the assumptions of s s ¯ or diquark–antidiquark content.

Tetraquarks in the 1/N expansion and meson-meson resonances

A bstractDiquarks are found to have the right degrees of freedom to describe the tetraquark poles in hidden-charm to open-charm meson-meson amplitudes. Compact tetraquarks result as intermediate states in non-planar diagrams of the 1/N expansion and the corresponding resonances are narrower than what estimated before. The proximity of tetraquarks to meson-thresholds has an apparent role in this analysis and, in the language of meson molecules, an halving rule in the counting of states is obtained.

Structure of light scalar mesons from Ds and D0 non-leptonic decays

Abstract Non-leptonic D meson decays may provide a reliable testbed for the multiquark interpretation of light scalar mesons. In this Letter we consider D s decay and show that a 4-quark f 0 ( 980 ) meson could induce a decay pattern, which is forbidden for a q q ¯ constituent structure. Experimental tests to probe such possibilities are within reach in the near future.

arXiv : A Theory of X and Z Multiquark Resonances

Abstract We introduce the hypothesis that diquarks and antidiquarks in tetraquarks are separated by a potential barrier. We show that this notion can answer satisfactorily long standing questions challenging the diquark–antidiquark model of exotic resonances. The tetraquark description of X and Z resonances is shown to be compatible with present limits on the non-observation of charged partners X ± , of the X ( 3872 ) and the absence of a hyperfine splitting between two different neutral states. In the same picture, Z c and Z b particles are expected to form complete isospin triplets plus singlets. It is also explained why the decay rate into final states including quarkonia are suppressed with respect to those having open charm/beauty states.