Magnifying the ATLAS Stealth Stop Splinter: Impact of Spin Correlations and Finite Widths
arXiv:1804.00111 · doi:10.1007/JHEP07(2018)142
Abstract
In this paper, we recast a "stealth stop" search in the notoriously difficult region of the stop-neutralino Simplified Model parameter space for which . The properties of the final state are nearly identical for tops and stops, while the rate for stop pair production is of that for . Stop searches away from this stealth region have left behind a "splinter" of open parameter space when . Removing this splinter requires surgical precision: the ATLAS constraint on stop pair production reinterpreted here treats the signal as a contaminant to the measurement of the top pair production cross section using data from and in a correlated way to control for some systematic errors. ATLAS fixed and , implying that a careful recasting of these results into the full plane is warranted. We find that the parameter space with is excluded for --- although this search does cover new parameter space, it is unable to fully pull the splinter. Along the way, we review a variety of interesting physical issues in detail: (i) when the two-body width is a good approximation; (ii) what the impact on the total rate from taking the narrow width is a good approximation; (iii) how the production rate is affected when the wrong widths are used; (iv) what role the spin correlations play in the limits. In addition, we provide a guide to using MadGraph for implementing the full production including finite width and spin correlation effects, and we survey a variety of pitfalls one might encounter.
arXiv comment33 pages, 14 figures
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