1,721,013 research outputs found
Deconstructing resonant Higgs pair production at the LHC: effects of coloured and neutral scalars in the NMSSM test case
No full textWe study resonant production of pairs of Standard Model (SM)-like Higgs bosons, in the presence of new neutral Higgs states together with new coloured scalars (stops or sbottoms) in loops within the Next-to-Minimal Supersymmetric SM (NMSSM). This is used as a test case to prove that the Large Hadron Collider has sensitivity to a variety of effects stemming from interferences between resonant (heavy) Higgs diagrams and/or among these and non-resonant topologies involving loops of both tops and stops. These effects can alter significantly the naive description of individual s-channel Breit-Wigner resonances, leading to distortions of the latter which, on the one hand, maymask their presence but, on the other hand, could enable one to extract features of the underlying new physics scenario. This last aspect is made possible through a decomposition of the gg → hh signal process into all its amplitude components, each of which has a well-defined coupling structure. Ultimately, such effects can be traced back to the relevant Feynman diagrams and can enable a detailed interpretation of this process. To illustrate this, we introduce various Benchmark Points that exhibit potentially observable features during the current and/or upcoming runs of the LHC in one or more of the three customary di-Higgs decay channels: b¯bb¯b, b¯bτ +τ− and b¯bγγ
The 750 GeV threshold to a new particle world
No full textWe show how an excess in the diphoton channel can be the effect of neither a resonance nor an end-point in a cascade decay, but rather of a threshold for virtual production of a pair of extra quarks, each with half of peak invariant mass, onsetting in both the -initiated production and the -induced decay of an off-shell boson. For our analysis we consider as paradigmatic example the 750 GeV excess previously seen at the end of 2015 with the Run 2 data of the LHC but not confirmed with 2016 data
Deconstructing squark contributions to di-Higgs production at the LHC
No full textWe present a novel approach to the study of di-Higgs production via gluon-gluon fusion at the LHC. The relevant Feynman diagrams involving two Standard Model-like Higgs bosons are computed within a simplified model approach that enables one to interpret possible signals of new physics in a model-independent way as well as to map these onto specific theories. This is possible thanks to a decomposition of such a signal process into all its squared amplitudes and their relative interferences, each of which has a well-defined coupling structure. We illustrate the power of this procedure for the case of both a minimal and next-to-minimal representation of Supersymmetry, for which the new physics effects are due to top squarks entering the loops of . The squarks yield both a change of the integrated cross section and peculiar kinematic features in its differential distributions with respect to the Standard Model. These effects can in turn be traced back to the relevant diagrammatic and coupling structures and allow for a detailed analysis of the process. In order to do so, we perform systematic scans of the parameter spaces of such new physics scenarios and identify benchmark points which exhibit potentially observable features during the current and upcoming runs of the LHC
Extra quarks decaying to dark matter beyond the narrow width approximation
No full textWe explore the effects induced by a finite width in processes of pair production of a heavy top-quark partner and its subsequent decay into a bosonic Dark Matter (DM) candidate -- either scalar or vector -- and a SM up-type quark at the Large Hadron Collider (LHC). We discuss the configurations of masses, widths and couplings where this phenomenology can be important in a simple model with just one such objects. Finally, we emphasise the correct definition of signal and background to be adopted as well as stress the importance of new dedicated experimental searches
Single production of vectorlike quarks with large width at the Large Hadron Collider
No full textVectorlike quarks (VLQs) are predicted by several theoretical scenarios of new physics and having colour quantum numbers they can copiously be produced at the Large Hadron Collider (LHC) so long that their mass is within the testable kinematic regime of this machine. While it would be convenient to assume that such objects are narrow and can be treated in the so-called narrow width approximation (NWA), this is not always possible: non-minimal new physics scenarios can predict VLQs with potentially large couplings and/or exotic decays, which can contribute to generate a large decay width for such extra quarks without being constrained by current bounds. In this analysis we consider single production of VLQs, which is rapidly becoming a channel of choice in experimental searches owing to the ever increasing limits on their mass, and we describe an approach to treat the large width regime which retains to a large extent a degree of model independence. We also consider the role of potentially sizable and model-dependent interference effects between different VLQ production and decay channels as well as between these and the corresponding irreducible background.</p
Dark Matter characterization at the LHC in the Effective Field Theory approach
No full textWe have studied the complete set of dimension 5 and dimension 6 effective operators involving the interaction of scalar, fermion and vector Dark Matter (DM) with SM quarks and gluons, to explore the possibility to distinguish these operators and characterise the spin of DM at the LHC. We have found that three factors — the effective dimension of the operator, the structure of the SM part of the operator and the parton densities of the SM particles connected to the operator — uniquely define the shape of the (unobservable) invariant mass distribution of the DM pair and, consequently, the shape of the (observable) E missT distribution related to it. Using χ2 analysis, we found that at the LHC, with a luminosity of 300 fb−1, certain classes of EFT operators can be distinguished from each other. Hence, since DM spin is partly correlated with the factors defining the shape of E missT , the LHC can potentially shed a light also on DM spin. We have also observed a drastic difference in the efficiencies (up to two orders of magnitude) for large E missT cuts scenarios with different DM spin, thus indicating that the DM discovery potential strongly depends on it. The study we perform here can be applied more generally than within the EFT paradigm, where the DM mediator is not produced on-the-mass-shell, such as the case of t-channel mediator or mediator with mass below 2M DM, where the invariant mass of the DM pair is not fixed
Effective theory of a doubly charged singlet scalar: complementarity of neutrino physics and the LHC
No full textWe consider a rather minimal extension of the Standard Model involving just one extra particle, namely a single singlet scalar and its antiparticle . We propose a model independent effective operator, which yields an effective coupling of to pairs of same sign weak gauge bosons, . We also allow tree-level couplings of to pairs of same sign right-handed charged leptons of the same or different flavour. We calculate explicitly the resulting two-loop diagrams in the effective theory responsible for neutrino mass and mixing. We propose sets of benchmark points for various masses and couplings which can yield successful neutrino masses and mixing, consistent with limits on charged lepton flavour violation (LFV) and neutrinoless double beta decay. We discuss the prospects for discovery at the LHC, for these benchmark points, including single and pair production and decay into same sign leptons plus jets and missing energy. The model represents a minimal example of the complementarity between neutrino physics (including LFV) and the LHC, involving just one new particle, the
Large width effects in processes of production of extra quarks decaying to Dark Matter at the LHC
No full textThis paper explores the effects of finite width in processes of pair production of a heavy eXtra Quark (XQ) with charge 2/3 and its subsequent decay into a Dark Matter (DM) candidate – either scalar or vector – and Standard Model (SM) up-type quarks at the Large Hadron Collider (LHC). This dynamics has been ignored so far in standard experimental searches of heavy quarks decaying to DM and we assess herein the regions of validity of current approaches, based on the assumption that the XQ has a narrow width. Further, we discuss the configurations of masses, widths and couplings where the latter breaks down.This paper explores the effects of finite width in processes of pair production of a heavy eXtra Quark (XQ) with charge 2/3 and its subsequent decay into a Dark Matter (DM) candidate -- either scalar or vector -- and Standard Model (SM) up-type quarks at the Large Hadron Collider (LHC). This dynamics has been ignored so far in standard experimental searches of heavy quarks decaying to DM and we assess herein the regions of validity of current approaches, based on the assumption that the XQ has a narrow width. Further, we discuss the configurations of masses, widths and couplings where the latter breaks down
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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