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Dark-matter production through loop-induced processes at the LHC: the s-channel mediator case.

Mattelaer O, Vryonidou E - Eur Phys J C Part Fields (2015)

Bottom Line: We show how studies relevant for mono-X searches at the LHC in simplified models featuring a dark-matter candidate and an s-channel mediator can be performed within the MadGraph5_aMC@NLO framework.We focus on gluon-initiated loop-induced processes, mostly relevant to the case where the mediator couples preferentially to third generation quarks and in particular to the top quark.Our implementation allows us to study signatures at hadron colliders involving missing transverse energy plus jets or plus neutral bosons ([Formula: see text]), possibly including the effects of extra radiation by multi-parton merging and matching to the parton shower.

View Article: PubMed Central - PubMed

Affiliation: Institute for Particle Physics Phenomenology (IPPP), Durham University, Durham, DH1 3LF UK.

ABSTRACT

We show how studies relevant for mono-X searches at the LHC in simplified models featuring a dark-matter candidate and an s-channel mediator can be performed within the MadGraph5_aMC@NLO framework. We focus on gluon-initiated loop-induced processes, mostly relevant to the case where the mediator couples preferentially to third generation quarks and in particular to the top quark. Our implementation allows us to study signatures at hadron colliders involving missing transverse energy plus jets or plus neutral bosons ([Formula: see text]), possibly including the effects of extra radiation by multi-parton merging and matching to the parton shower.

No MeSH data available.


Missing transverse momentum distribution for  jets for a scalar mediator, using the exact loops (solid lines) and the top EFT (dashed lines) and the corresponding ratio
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Fig9: Missing transverse momentum distribution for jets for a scalar mediator, using the exact loops (solid lines) and the top EFT (dashed lines) and the corresponding ratio

Mentions: For the case of scalar or pseudoscalar mediators, one could also consider production cross sections in the infinite top-mass limit, i.e. employing the Lagrangian of the form [39]:3\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\begin{aligned} \mathcal {L}=\frac{\alpha _s}{12\pi v} g^S_{t} G_{\mu \nu } G^{\mu \nu } Y_0+\frac{\alpha _s}{8\pi v} g^P_{t} G_{\mu \nu } \tilde{G}^{\mu \nu } Y_0. \end{aligned}$$\end{document}L=αs12πvgtSGμνGμνY0+αs8πvgtPGμνG~μνY0.Such an approach has the clear advantage of being much simpler than computing full loop amplitudes and thanks to this simplicity, the possibility of including NLO corrections in QCD; see for instance [38]. Nevertheless, the accuracy of the infinite top approximation with respect to the exact loop computation needs to be assessed on a case-by-case basis. As an example, we show, in Fig. 9, a comparison for the missing transverse energy distribution in the case of the scalar mediator. It is clear from the plot that integrating out the top quark leads to harder distributions in the tails and the top-EFT result overshoots the loop-one for all three scenarios. We see that for the resonant case, the infinite top-mass limit provides a reliable prediction of the distribution shape up to 200 GeV. These observations are qualitatively consistent with the corresponding studies for Higgs production in the SM, where the infinite top-mass limit fails at high Higgs transverse momentum. Considering the fact that the DM searches focus on the boosted regions to overcome the large SM backgrounds, to avoid overestimating the signal and consequently setting inaccurate limits on the various DM model parameters, one needs to resort to the loop computation.Fig. 9


Dark-matter production through loop-induced processes at the LHC: the s-channel mediator case.

Mattelaer O, Vryonidou E - Eur Phys J C Part Fields (2015)

Missing transverse momentum distribution for  jets for a scalar mediator, using the exact loops (solid lines) and the top EFT (dashed lines) and the corresponding ratio
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4581402&req=5

Fig9: Missing transverse momentum distribution for jets for a scalar mediator, using the exact loops (solid lines) and the top EFT (dashed lines) and the corresponding ratio
Mentions: For the case of scalar or pseudoscalar mediators, one could also consider production cross sections in the infinite top-mass limit, i.e. employing the Lagrangian of the form [39]:3\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\begin{aligned} \mathcal {L}=\frac{\alpha _s}{12\pi v} g^S_{t} G_{\mu \nu } G^{\mu \nu } Y_0+\frac{\alpha _s}{8\pi v} g^P_{t} G_{\mu \nu } \tilde{G}^{\mu \nu } Y_0. \end{aligned}$$\end{document}L=αs12πvgtSGμνGμνY0+αs8πvgtPGμνG~μνY0.Such an approach has the clear advantage of being much simpler than computing full loop amplitudes and thanks to this simplicity, the possibility of including NLO corrections in QCD; see for instance [38]. Nevertheless, the accuracy of the infinite top approximation with respect to the exact loop computation needs to be assessed on a case-by-case basis. As an example, we show, in Fig. 9, a comparison for the missing transverse energy distribution in the case of the scalar mediator. It is clear from the plot that integrating out the top quark leads to harder distributions in the tails and the top-EFT result overshoots the loop-one for all three scenarios. We see that for the resonant case, the infinite top-mass limit provides a reliable prediction of the distribution shape up to 200 GeV. These observations are qualitatively consistent with the corresponding studies for Higgs production in the SM, where the infinite top-mass limit fails at high Higgs transverse momentum. Considering the fact that the DM searches focus on the boosted regions to overcome the large SM backgrounds, to avoid overestimating the signal and consequently setting inaccurate limits on the various DM model parameters, one needs to resort to the loop computation.Fig. 9

Bottom Line: We show how studies relevant for mono-X searches at the LHC in simplified models featuring a dark-matter candidate and an s-channel mediator can be performed within the MadGraph5_aMC@NLO framework.We focus on gluon-initiated loop-induced processes, mostly relevant to the case where the mediator couples preferentially to third generation quarks and in particular to the top quark.Our implementation allows us to study signatures at hadron colliders involving missing transverse energy plus jets or plus neutral bosons ([Formula: see text]), possibly including the effects of extra radiation by multi-parton merging and matching to the parton shower.

View Article: PubMed Central - PubMed

Affiliation: Institute for Particle Physics Phenomenology (IPPP), Durham University, Durham, DH1 3LF UK.

ABSTRACT

We show how studies relevant for mono-X searches at the LHC in simplified models featuring a dark-matter candidate and an s-channel mediator can be performed within the MadGraph5_aMC@NLO framework. We focus on gluon-initiated loop-induced processes, mostly relevant to the case where the mediator couples preferentially to third generation quarks and in particular to the top quark. Our implementation allows us to study signatures at hadron colliders involving missing transverse energy plus jets or plus neutral bosons ([Formula: see text]), possibly including the effects of extra radiation by multi-parton merging and matching to the parton shower.

No MeSH data available.