Abstract
The search for light stops is of paramount importance, both in general as a promising path to the discovery of beyond the standard model physics and more specifically as a way of evaluating the success of the naturalness paradigm. While the LHC experiments have ruled out much of the relevant parameter space, there are "stop gaps", i.e., values of sparticle masses for which existing LHC analyses have relatively little sensitivity to light stops. We point out that techniques involving on-shell constrained M_2 variables can do much to enhance sensitivity in this region and hence help close the stop gaps. We demonstrate the use of these variables for several benchmark points and describe the effect of realistic complications, such as detector effects and combinatorial backgrounds, in order to provide a useful toolkit for light stop searches in particular, and new physics searches at the LHC in general.
Highlights
We demonstrate the use of these variables for several benchmark points and describe the effect of realistic complications, such as detector effects and combinatorial backgrounds, in order to provide a useful toolkit for light stop searches in particular, and new physics searches at the LHC in general
It is clear that our positive conclusions drawn for fortuitous cases of new physics like study point 1 will survive all these complications, we shall only focus on the difficult scenario discussed in section 5, i.e., the mixed events which were a hybrid between the difficult study points 4 from section 3.5 and 6 from section 4.2
Unless we are dealing with a new physics model with a widely split spectrum, a significant fraction of the signal events will lie below the background kinematic endpoints, by cutting at or near the endpoint, we will be removing a large chunk of signal events as well
Summary
Stop production has long been recognized as a viable SUSY discovery channel [12,13,14,15,16,17,18,19] and has been looked for at LEP [20,21,22,23,24] and the Tevatron [25,26,27], as well as at the LHC [7, 9, 28,29,30,31,32,33,34,35,36,37,38,39,40,41]. The beta function for a squark mass contains a positive term proportional to the corresponding Yukawa coupling. The effect of such a positive term is to suppress the mass when evolved from a high energy scale. Since the top Yukawa coupling is the largest Yukawa coupling, one generically expects the stop soft mass parameter to emerge as the lightest of the squark soft masses after RGE evolution from some high energy scale [42]. The left-right mixing is an SU(2)breaking effect, proportional to the Higgs vacuum expectation value and to the Yukawa coupling. We are especially interested in what can be done to extend sensitivity into regions of parameter space where existing LHC searches have not had sufficient sensitivity to discover or rule out the stop. Our approach is complementary to several recent analyses which have targeted difficult parameter space regions for stop discovery [48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79]
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