Exotic colored scalars at the LHC

Journal of High Energy Physics, Feb 2017

We study the phenomenology of exotic color-triplet scalar particles X with charge |Q| = 2/3, 4/3, 5/3, 7/3, 8/3 and 10/3. If X is an SU(2) W -non-singlet, mass splitting within the multiplet allows for cascade decays of the members into the lightest state. We study examples where the lightest state, in turn, decays into a three-body W ± jj final state, and show that in such case the entire multiplet is compatible with indirect precision tests and with direct collider searches for continuum pair production of X down to m X ∼ 250 GeV. However, bound states S, made of XX † pairs at m S ≈ 2m X , form under rather generic conditions and their decay to diphoton can be the first discovery channel of the model. Furthermore, for SU(2) W -non-singlets, the mode S → W + W − may be observable and the width of S → γγ and S → jj may appear large as a consequence of mass splittings within the X-multiplet. As an example we study in detail the case of an SU(2) W -quartet, finding that m X ≃ 450 GeV is allowed by all current searches.

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Exotic colored scalars at the LHC

Received: November Exotic colored scalars at the LHC to mX 0 1 Open Access 0 1 c The Authors. 0 1 0 Department of Particle Physics and Astrophysics, Weizmann Institute of Science 1 K r Blum , Aielet Efrati, Claudia Frugiuele and Yosef Nir charge jQj = 2=3; 4=3; 5=3; 7=3; 8=3 and 10=3. If X is an SU(2)W -non-singlet, mass splitting within the multiplet allows for cascade decays of the members into the lightest state. We study examples where the lightest state, in turn, decays into a three-body W nal state, and show that in such case the entire multiplet is compatible with indirect precision tests and with direct collider searches for continuum pair production of X down 250 GeV. However, bound states S, made of XXy pairs at mS under rather generic conditions and their decay to diphoton can be the rst discovery channel of the model. Furthermore, for SU(2)W -non-singlets, the mode S ! W +W be observable and the width of S ! and S ! jj may appear large as a consequence of mass splittings within the X-multiplet. As an example we study in detail the case of an SU(2)W -quartet, nding that mX ' 450 GeV is allowed by all current searches. Exotics; Hadron-Hadron scattering (experiments); Particle and resonance 1 Introduction 2 Theoretical framework 3 Direct searches for continuum pair production 4 Mass splitting and cascade decays 5 A model example: X(3; 4)+ 16 Degenerate SU(2)W -quartet Non-degenerate SU(2)W -quartet 6 SU(2)W phenomenology Electroweak precision measurements (EWPM) Gauge coupling running Additional constraints 7 QCD bound state Diphoton signature 7.3 Back to our model examples 7.3.1 7.3.2 Degenerate SU(2)W -quartet Non-degenerate SU(2)W -quartet 8 Summary and conclusions A (W +jj)(W jj) nal state B (W +W +jj)(W W jj) nal state C (` t)(` t) nal state D Running of gauge coupling constants E E ective operators F Oblique parameters G Higgs couplings H Quartic coupling running Distinct features of a bound state composed of SU(2)W -non-singlet conThe large hadron collider (LHC) search for new physics at or below the TeV scale is far from complete, even for strongly interacting particles. As concerns the commonly studied Standard Model (SM) extensions [1{3], the dedicated searches by CMS and ATLAS for new strongly interacting light degrees of freedom are covering a large part of the parameter space. However, new colored particles beyond these standard scenarios could still have unexpected phenomenology and, in this case, traditional LHC searches often lose much of their power. In this work we consider colored scalar states with exotic EM charges, with a focus on SU(2)W -non-singlets. Such particles, while being copiously produced at the LHC, could still be hiding undiscovered amidst the large QCD background. Three di erent paths can be pursued in the experimental search for these particles: 1. Direct collider searches for QCD continuum pair production of XQ, a colored particle with EM charge Q. Such searches are potentially e ective, but depend on the decay modes of XQ and hence are model dependent. search for XQ. 2. Precision measurements of electroweak (EW) processes, constituting an indirect 3. Direct collider searches for SQ, the bound state formed out of XQXQy through Coulomb gluon exchange, with mass mSQ ' 2mXQ . SQ decays into diboson states, with branching ratios that are determined to a large extent by the quantum numbers of XQ. For exotic states the consequent constraints are often less model dependent than continuum pair production searches (see e.g. [4, 5]). We pursue all three avenues in this work. Color-triplet elds with exotic charges and/or in high SU(2)W representations are a rather generic outcome of uni ed models (see, e.g., ref. [6]). Within SU(5) models, SU(2)triplets are parts of the 35, 45 and 70 representations, and an SU(2)W -quartet is contained in the 700 representation [7]. Some of these representations are embedded in, for example, the 126 and 320 representations of the SO(10) group. These large representations are often invoked in GUT scenarios that address the issues of neutrino masses and of doublettriplet splitting. Of course, the masses of these multiplets are not necessarily light. On a more phenomenological level, color-triplets of exotic charges have been introduced to explain various anomalies, such as the B ! D( ) anomaly [8], and the forward-backward asymmetry in tt events [9]. In these cases, these new degrees of freedom must be at the electroweak scale. Finally, we believe that, given the current status of experimental search for new physics, it is appropriate and timely to consider scenarios which are not necessarily related to the ne-tuning problem. In particular, special attention should be drawn to particles which can be produced abundantly at the LHC but would evade detection due to their distinct signature. Looking for novel signatures which were not the main focus of the experimental searches in recent years might encode new and interestin (...truncated)


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Kfir Blum, Aielet Efrati, Claudia Frugiuele, Yosef Nir. Exotic colored scalars at the LHC, Journal of High Energy Physics, 2017, pp. 104, Volume 2017, Issue 2, DOI: 10.1007/JHEP02(2017)104