Large Hadron Collider reach for supersymmetric models with compressed mass spectra

TL;DR

The paper investigates the LHC reach for supersymmetric models with compressed mass spectra by introducing a gaugino compression parameter $c$ that tunes the TeV-scale gaugino masses relative to the gluino mass $M_{ ilde g}$. Using ATLAS-like multijet and lepton search channels with $m_{ m eff}$ and $E_T^{ m miss}$ cuts, the authors compute acceptances and cross-section×acceptance across several model lines (light squarks with winos, heavy winos, heavy squarks, and light stops motivated by dark matter). They find that moderate compression can preserve or even enhance the reach compared with mSUGRA, while very compressed spectra drastically reduce signal acceptance, and the most stringent $m_{ m eff}$ cuts can be especially suppressive. The study highlights that intermediate $m_{ m eff}$ thresholds and signals sensitive to higher jet multiplicities or bottom tagging could extend sensitivity in compressed scenarios, and emphasizes the need for dedicated background studies and higher luminosity to fully probe these models. Overall, the work provides a quantitative framework for understanding LHC sensitivity to a broad class of compressed SUSY spectra and guides future search strategies at higher energies and luminosities.

Abstract

Many theoretical and experimental results on the reach of the Large Hadron Collider are based on the mSUGRA-inspired scenario with universal soft supersymmetry breaking parameters at the apparent gauge coupling unification scale. We study signals for supersymmetric models in which the sparticle mass range is compressed compared to mSUGRA, using cuts like those employed by ATLAS for 2010 data. The acceptance and the cross-section times acceptance are found for several model lines that employ a compression parameter to smoothly interpolate between the mSUGRA case and the extreme case of degenerate gaugino masses at the weak scale. For models with moderate compression, the reach is not much worse, and can even be substantially better, than the mSUGRA case. For very compressed mass spectra, the acceptances are drastically reduced, especially when a more stringent effective mass cut is chosen.

Figures (10)

• Figure 1: The masses of the most relevant superpartners for the class of models defined in subsection \ref{['subsec:cmodel']}, as a function of the compression parameter $c$, for fixed $M_{\tilde{g}} = 700$ GeV. The case $c=0$ corresponds to an mSUGRA-like model.
• Figure 2: The distributions before cuts of $E_T^{\rm miss}$ (left panel) and $m_{\rm eff}$ with 3 jets included (right panel) for models described in subsection \ref{['subsec:cmodel']} with $M_{\tilde{g}} = 700$ GeV and $c = 0.0$, 0.3, 0.6, and 0.9, from right to left. The cuts for signals C and D are also shown. The $m_{\rm eff}$ distribution decreases more quickly than $E_T^{\rm miss}$ does as $c$ increases.
• Figure 3: The acceptances for model lines defined in section \ref{['subsec:cmodel']} as a function of $M_{\tilde{g}} - M_{{\tilde{N}_1}}$, obtained by varying the gaugino mass compression factor $c$. The lines from bottom to top correspond to $M_{\tilde{g}} = 300, 400, \ldots, 1000$ GeV. The dots on each line correspond to, from right to left, $c = -0.1, 0, 0.1, \ldots 0.9$, with $c=0$ corresponding to the mSUGRA-like case and $c=1$ to a completely compressed gaugino spectrum. The four panels are for the four sets of cuts A, C, D, and L.
• Figure 4: Contours of cross-section times acceptance for the models defined in section \ref{['subsec:cmodel']}, in the $M_{\tilde{g}} - M_{{\tilde{N}_1}}$ vs. $M_{\tilde{g}}$ plane, obtained by varying the gaugino mass compression parameter $c$ between $-0.1$ and $0.9$. The dashed line corresponds to the mSUGRA-like case $c=0$, with increased compression lower in the plane. The four panels correspond to cuts A, C, D, and L.
• Figure 5: The acceptances for heavy-wino model lines defined in section \ref{['subsec:HWmodel']} with $M_{\tilde{g}} = 300, 400, \ldots, 1000$ GeV, as a function of $M_{\tilde{g}} - M_{{\tilde{N}_1}}$, obtained by varying the compression factor $c$. The dots on each line correspond to, from right to left, $c = -0.1, 0, 0.1, \ldots 0.9$, with $c=0$ corresponding to the mSUGRA-like case and $c=1$ to a degenerate gluino and bino. The three panels are for the cuts A, C, and D.