ATLAS Z excess in minimal supersymmetric standard model

Abstract

Recently the ATLAS collaboration reported a 3σ excess in the search for the events containing a dilepton pair from a Z boson and large missing transverse energy. Although the excess is not sufficiently significant yet, it is quite tempting to explain this excess by a well-motivated model beyond the standard model. In this paper we study a possibility of the minimal supersymmetric standard model (MSSM) for this excess. Especially, we focus on the MSSM spectrum where the sfermions are heavier than the gauginos and Higgsinos. We show that the excess can be explained by the reasonable MSSM mass spectrum.

ATLAS on-Z excess via gluino-Higgsino-singlino decay chains in the NMSSM

“…It should be noted that the two-body gluino decay modesg → gχ 0 2,3 at one-loop level are the dominant ones when the mass differences between the gluino and the Higgsinos are moderate and the squark masses are in the several TeV range [15,21,22]. Besides, as we will show, the radiative decay of the gluino reproduces the distribution of the jet multiplicity observed in the ATLAS results well.…”

“…After the report, many scenarios in the MSSM as well as in the NMSSM have been proposed to explain the ATLAS on-Z excess without conflicting with constraints from various SUSY searches including the CMS on-Z result [6,[8][9][10][11][12][13][14][15][16][17][18][19][20]. To have on-shell Z bosons in final states while escaping other SUSY search constraints, scenarios with a gravitino as the lightest SUSY particle (LSP) seems to be one of the simplest possibilities.…”

“…Finally, to suppress the decay of the gluino into bb + Higgsino, we take the squark masses to be of order of 10 TeV. Note that the loopinduced gluino two-body decay into the gluon + Higgsino is relatively enhanced by a factor (ln(mt/m t )) 2 [15,21,22].…”

Explanation of the ATLAS Z-peaked excess by squark pair production in the NMSSM

“…As we mentioned at the end of section 2, a more complex scenario with higher dimensional SUSY parameters may improve this situation, but it needs tremendous calculation to search for the relevant parameter space [11]. Third, we note that so far there have appeared other simple SUSY scenarios to explain the excess, and the studies of these scenarios indicated that they can explain the excess at 1σ level in certain narrow SUSY parameter spaces [12,13]. This conclusion is slightly better than ours, where the best explanation is about 1.2σ away from the central value of the excess.…”

“…So far there have been several attempts to explain the excess by the production of new physics particles, which are needed to decay with a sizeable rate into jets as well as at least one Z boson and one invisible particle [4][5][6][7][8][9][10][11][12][13]. In the context of supersymmetric theories (SUSY), in order to provide enough events after the rather tight cuts employed in [3], the production of a pair of moderately light gluinos was usually utilized for the explanation [4, 6-9, 12, 13].…”