Reconstructing Sparticle Mass Spectra using Hadronic Decays

TL;DR

This paper addresses the challenge of reconstructing the supersymmetric (SUSY) mass spectrum from fully hadronic cascade decays at the LHC. It introduces a hadronic-analysis framework based on the kT jet algorithm, jet substructure, and a sub-jet scale cut to tag boosted W/Z/h decays and suppress backgrounds, starting from missing energy signals. Applying the method to benchmark SUSY points, it demonstrates that invariant-moss endpoints in qW, qZ, and qh channels can constrain squark, chargino, and neutralino masses, with percent-level precision for lighter scenarios and around 10% for heavier ones. The results indicate that hadronic final states provide valuable SUSY spectroscopy complementary to leptonic channels and suggest broad applicability of the approach to other heavy-particle decays, though detector-level studies are needed for full validation.

Abstract

Most sparticle decay cascades envisaged at the Large Hadron Collider (LHC) involve hadronic decays of intermediate particles. We use state-of-the art techniques based on the \kt jet algorithm to reconstruct the resulting hadronic final states for simulated LHC events in a number of benchmark supersymmetric scenarios. In particular, we show that a general method of selecting preferentially boosted massive particles such as W, Z or Higgs bosons decaying to jets, using sub-jets found by the \kt algorithm, suppresses QCD backgrounds and thereby enhances the observability of signals that would otherwise be indistinct. Consequently, measurements of the supersymmetric mass spectrum at the per-cent level can be obtained from cascades including the hadronic decays of such massive intermediate bosons.

Figures (12)

• Figure 1: Scatter plot of the jet mass against the jet splitting scale $yp_T^2$ for (a) jets from $W^\pm$ decays (determined by a match better than 0.1 units in $\eta-\phi$) and (b) QCD jets in $W^\pm$+jet and SUSY events. The distributions of the splitting scale are shown in (c) and the $y$ distributions in (d), for the same types of jets, after a cut on the jet mass at $75 < M < 90$ GeV. In all these plots, the requirement $p_T > 250$ GeV is applied to all jets. The histograms in the lower two plots are normalised to unity.
• Figure 2: The SUSY decay chain of Eq. (\ref{['eq:chargino']}).
• Figure 3: The invariant mass distributions of $qW^\pm$, $qZ$ and $qh$ combinations for the chosen SUSY benchmark points.
• Figure 4: Invariant mass distributions for SUSY benchmark scenario $\alpha$: combinations of jets and $W^\pm$ candidates (a) with and (b) without the cut on the separation scale, (c) the $\ell q$ invariant mass distribution resulting from $W^\pm \to \ell^\pm \nu$ decays, combinations of jets and $Z^0$ bosons decaying (d) hadronically and (e) leptonically, and (f) combinations of jets and $h$ bosons. Signal - blue, solid lines; SUSY background - red, dashed lines; SM background - green, dotted lines.
• Figure 5: Various invariant mass distributions obtained in a simulation of events for SUSY benchmark scenario $\beta$. See Fig. \ref{['fig:m_alpha']} and text for details.