Model-Independent Jets plus Missing Energy Searches

TL;DR

This work proposes a model-independent framework for jets plus missing-energy searches by constraining the differential cross section as a function of $H_T$ and $E_T^{miss}$, enabling constraints on arbitrary new-physics models using Standard Model backgrounds. It demonstrates the approach with Tevatron-like gluino pair production, analyzing both direct decays and single-step cascades, and shows how sensitivity shifts with mass spectra and initial-state radiation. The study provides a method to translate model-independent limits into model-specific exclusions and discusses potential extensions to the LHC, including complementary channels such as monophoton and leptonic final states. Overall, the paper shows that differential cross-section grids can significantly broaden the reach beyond CMSSM-focused searches and offer flexible, cross-model constraints for new strong-sector particles.

Abstract

We present a proposal for performing model-independent jets plus missing energy searches. Currently, these searches are optimized for mSUGRA and are consequently not sensitive to all kinematically-accessible regions of parameter space. We show that the reach of these searches can be broadened by setting limits on the differential cross section as a function of the total visible energy and the missing energy. These measurements only require knowledge of the relevant Standard Model backgrounds and can be subsequently used to limit any theoretical model of new physics. We apply this approach to an example where gluinos are pair-produced and decay to the LSP through a single-step cascade, and show how sensitivity to different gluino masses is altered by the presence of the decay chain. The analysis is closely based upon the current searches done at the Tevatron and our proposal requires only small modifications to the existing techniques. We find that within the MSSM, the gluino can be as light as 125 GeV. The same techniques are applicable to jets and missing energy searches at the Large Hadron Collider.

Figures (6)

• Figure 1: Comparison of DO $\not$ cuts and optimized cuts for a sample dijet signal for $m_{\tilde{g}} = 210 \text{ GeV}$ and $m_{\widetilde{B}} = 100 \text{ GeV}$. Background distribution is shown in gray and signal distribution in white. (Left) Using the DO $\not$ cuts $H_T \geq 300 \text{ GeV}$ and $\hbox{$E_T\space\not\space$} \geq 225 \text{ GeV}$ (Right) Using the more optimal cuts $H_T \geq 150 \text{ GeV}$ and $\hbox{$E_T\space\not\space$} \geq 100 \text{ GeV}$. The optimized cuts allow us to probe regions with larger $S/B$.
• Figure 2: Differential $0\to1$ jet rate for a matched sample of light gluino production. The full black curve shows the matched distribution, and the broken curves show the contributions from different matrix element parton multiplicity samples. The matching scale $Q_{\text{min}}^{\text{PS}}$ is marked by the dashed line. The full red curve shows the result using Pythia only.
• Figure 3: Comparison of matched and unmatched events for a dijet sample of 150$\text{ GeV}$ gluinos directly decaying into 40$\text{ GeV}$ (top) and 130$\text{ GeV}$ (bottom) binos. The $p_T$ of the hardest jet is plotted in the histograms (1 fb$^{-1}$ luminosity). Matching is very important in the degenerate case when the contribution from initial state radiation is critical. The different colors indicate the contributions from 0j (orange), 1j (blue), and 2j (cyan).
• Figure 4: The 95% exclusion region for ${\hbox{DO $\not$}}$ at 4 fb$^{-1}$ assuming 50% systematic error on background. The exclusion region for a directly decaying gluino is shown in light blue; the worst case scenario for the cascade decay is shown in dark blue. The dashed line represents the CMSSM points and the "X" is the current ${\hbox{DO $\not$}}$ exclusion limit at 2 fb$^{-1}$.
• Figure 5: 95% exclusion region (purple) for a 240 $\text{ GeV}$ gluino decaying into a bino through a wino. The dashed line is $m_{\widetilde{W}} = m_{\widetilde{B}} + \mathcal{O}(m_{Z^0})$. The black dot at $(m_{\widetilde{B}},m_{\widetilde{W}})$ = $(60,160)$, is the minimum bino mass for which a 240 GeV gluino is excluded for all wino masses. The inset shows the one-step cascade considered in the paper.