Measurements of Masses in SUGRA Models at LHC

TL;DR

This work demonstrates that supersymmetric masses in minimal SUGRA can be reconstructed at the LHC from four-body decay kinematics in a multi-step cascade, using end-point and lower-edge observables to extract $M_{{\tilde{\chi}}_1^0}$, $M_{{\tilde{\ell}}_R}$, $M_{{\tilde{\chi}}_2^0}$, and $M_{{\tilde{q}}_L}$ with model-independence. By combining $M_{\ell\ell}^{\max}$, $M_{\ell\ell q}^{\max}$, $M_{\ell q}^{\max}$, and $M_{\ell\ell q}^{\min}$, the study achieves mass determinations with percent-level precision and demonstrates the potential to test $e/\mu$ universality at the ~0.1% level with high luminosity, while addressing detector systematics. The analysis further explores non-minimal SUGRA by varying SU(5) representations and the third generation, showing how new signals emerge and how global fits can constrain additional high-scale parameters such as $m_{h{\rm -GUT}}$, $m_{10}$, $m_5$, and $m_{3^{\rm rd}}$, albeit with varying sensitivity. Overall, the paper highlights the power of endpoint techniques for SUSY mass reconstruction at the LHC, while also outlining practical challenges related to detector resolution, jet energy scale, tau channels, and the viability of full event reconstruction in realistic data sets.

Abstract

This paper presents new measurements in a case study of the minimal SUGRA model with m_0=100 GeV, mhalf=300 GeV, A_0=0, tan(beta)=2.1, and mu=+1 based on four-body distributions from three-step decays and on minimum masses in such decays. These measurements allow masses of supersymmetric particles to be determined without relying on a model. The feasibility of testing slepton universality at the ~0.1% level at high luminosity is discussed. In addition, the effect of enlarging the parameter space of the minimal SUGRA model is discussed. The direct production of left handed sleptons and the non-observation of additional structure in the dilepton invariant mass distributions is shown to provide additional constraints.

Figures (22)

• Figure 1: Mass distribution for the smaller of the two $\ell^+\ell^-q$ masses showing a linear fit near the four-body end point.
• Figure 2: Distribution of the larger of the two $\ell^\pm q$ masses for $\ell^+\ell^-q$ events in which $M_{\ell\ell q}<600\,{\rm GeV}$ and a fit described in the text.
• Figure 3: Distribution for the smaller of the two $\ell^+\ell^-q$ masses from Figure \ref{['c5_mllq0']}; a Gaussian-smeared fit plus a linear background described in the text is also shown.
• Figure 4: Distribution of the larger of the two $\ell\ell q$ masses after cuts described in the text, showing the lower edge.
• Figure 5: Larger of the two $b \bar{b} q$ jet masses, showing the $hq$ mass threshold.