arXiv subjects

Irene Niessen

Publications and source records attributed to Irene Niessen.

7 recordsLinked to original sources

arXiv2012

Higgs and non-universal gaugino masses: no SUSY signal expected yet?

So far, no supersymmetric particles have been detected at the Large Hadron Collider (LHC). However, the recent Higgs results have interesting implications for the SUSY parameter space. In this paper, we study the consequences of an LHC Higgs signal for a model with non-universal gaugino masses in the context of SU(5) unification. The gaugino mass ratios associated with the higher representations produce viable spectra that are largely inaccessible to the current LHC and direct dark matter detection experiments. Thus, in light of the Higgs results, the non-observation of SUSY is no surprise.

hep-ph↗

arXiv2011

NNLL resummation for squark-antisquark production

We report on the resummation of soft-gluon emissions for squark-antisquark production at next-to-next-to-leading-logarithmic (NNLL) accuracy. We will put particular emphasis on the one loop hard matching coefficients required to perform the resummation. Furthermore we will discuss the numerical effect of the different ingredients in the corrections. We find a significant reduction in the scale uncertainty and a considerable increase in the prediction of the total cross section at the central scale. Compared to the next-to-leading order prediction, the corrections increase the cross section by up to 30% for 1.5 TeV squarks at a centre-of-mass energy of 7 TeV at the LHC.

hep-ph↗

arXiv2011

Top polarisation studies in $H^-t$ and $Wt$ production

The polarisation of top quarks produced in high energy processes can be a very sensitive probe of physics beyond the Standard Model. The kinematical distributions of the decay products of the top quark can provide clean information on the polarisation of the produced top and thus can probe new physics effects in the top quark sector. We study some of the recently proposed polarisation observables involving the decay products of the top quark in the context of $H^-t$ and $Wt$ production. We show that the effect of the top polarisation on the decay lepton azimuthal angle distribution, studied recently for these processes at leading order in QCD, is robust with respect to the inclusion of next-to-leading order and parton shower corrections. We also consider the leptonic polar angle, as well as recently proposed energy-related distributions of the top decay products. We construct asymmetry parameters from these observables, which can be used to distinguish the new physics signal from the $Wt$ background and discriminate between different values of $\tanβ$ and $m_{H^-}$ in a general type II two-Higgs doublet model. Finally, we show that similar observables may be useful in separating a Standard Model $Wt$ signal from the much larger QCD induced top pair production background.

hep-ph↗

arXiv2011

Improved squark and gluino mass limits from searches for supersymmetry at hadron colliders

Squarks and gluinos have been searched for at hadron colliders in events with multiple jets and missing transverse energy. No excess has been observed to date, and from a comparison of experimental cross section limits and theoretical cross section predictions one can deduce lower bounds on the squark and gluino masses. We present an improved analysis of squark and gluino mass bounds which is based on state-of-the-art cross section calculations including the summation of large threshold corrections. For illustration, we consider experimental data obtained by the CDF collaboration at the Fermilab Tevatron and discuss the impact of the improved cross section predictions on the squark and gluino mass limits.

hep-ph↗

arXiv2010

Supersymmetric top and bottom squark production at hadron colliders

The scalar partners of top and bottom quarks are expected to be the lightest squarks in supersymmetric theories, with potentially large cross sections at hadron colliders. We present predictions for the production of top and bottom squarks at the Tevatron and the LHC, including next-to-leading order corrections in supersymmetric QCD and the resummation of soft gluon emission at next-to-leading-logarithmic accuracy. We discuss the impact of the higher-order corrections on total cross sections and transverse-momentum distributions, and provide an estimate of the theoretical uncertainty due to scale variation and the parton distribution functions.

hep-ph↗

arXiv2009

Soft-gluon resummation for squark and gluino hadroproduction

We consider the resummation of soft gluon emission for squark and gluino hadroproduction at next-to-leading-logarithmic (NLL) accuracy in the framework of the minimal supersymmetric standard model. We present analytical results for squark-squark and squark-gluino production and provide numerical predictions for all squark and gluino pair-production processes at the Tevatron and at the LHC. The size of the soft-gluon corrections and the reduction in the scale uncertainty are most significant for processes involving gluino production. At the LHC, where the sensitivity to squark and gluino masses ranges up to 3 TeV, the corrections due to NLL resummation over and above the NLO predictions can be as high as 35% in the case of gluino-pair production, whereas at the Tevatron, the NLL corrections are close to 40% for squark-gluino final states with sparticle masses around 500 GeV.

hep-ph↗

arXiv2008

Supersymmetric Phenomenology in the mSUGRA Parameter Space

In this master thesis the possible supersymmetric phenomenologies associated with low-mass mSUGRA are investigated. The main characteristics of the supersymmetric mass spectrum are explained and a systematic method is presented to predict phenomenology directly from the mass spectrum. The resulting phenomenologies are compared to the current ATLAS benchmark points. It is found that some phenomenological scenarios are not covered by these benchmark points.

hep-ph↗