Enhancing the discovery prospects for SUSY-like decays with a forgotten kinematic variable

Abstract

The lack of a new physics signal thus far at the Large Hadron Collider motivates us to consider how to look for challenging final states, with large Standard Model backgrounds and subtle kinematic features, such as cascade decays with compressed spectra. Adopting a benchmark SUSY-like decay topology with a four-body final state proceeding through a sequence of two-body decays via intermediate resonances, we focus our attention on the kinematic variable ∆ 4 which previously has been used to parameterize the boundary of the allowed four-body phase space. We highlight the advantages of using ∆ 4 as a discovery variable, and present an analysis suggesting that the pairing of ∆ 4 with another invariant mass variable leads to a significant improvement over more conventional variable choices and techniques.

Singularity variables for missing energy event kinematics

“…3.3 and 6.3. 25 The main advantage of the focus point method is that it maximally utilizes the singularity structures in phase space. As a consequence, the true masses are identified as a kinematic peak instead of a kinematic endpoint -endpoints are more difficult to observe experimentally, once we include the finite widths and detector resolution effects [109].…”

“…• New physics searches. The Jacobian peaks in the distributions of the singularity variables can be used to discover new physics processes over the SM background [25]. Likewise, the peak structures in the heatmaps constructed in the focus point method can also be used for discovery of new physics, with the added advantage that background processes will not develop fake peaks 26 in the signal regions.…”

“…The singularity is then found at the two-dimensional surface boundary of the allowed region [16][17][18][19]. In order to maximize the sensitivity, the experimental analysis should target this two-dimensional surface; this can be done either directly [20][21][22] (e.g., using Voronoi tessellations of the data [23,24]) or by means of a suitable one-dimensional singularity coordinate [25].…”

“…Second, given a choice of masses {M k }, the constraint (1.1) defines the locus of points where the signal event density becomes singular (by construction), while the behavior of the background event density is typically unremarkable. Therefore, this locus of points is precisely the region of phase space which should be targeted (with suitable selection cuts) in an analysis aimed at a discovery [25]. Finally, we can turn the last argument around and instead of studying the phase space { p j } for a given choice of mass parameters {M k }, we can study the mass parameter space {M k } for given points in phase space as sampled by the events in the data.…”

“…The sharp peak at ∆ 4 = 0 can be used for discovering such new physics signal over the smooth SM background, as discussed in [25].…”