[Paper Review] Testing SUSY models for the muon g-2 anomaly via Chargino-Neutralino Pair Production at the LHC

Siba Prasad Das, Monoranjan Guchait+1 more|arXiv (Cornell University)|Jun 26, 2014

Particle physics theoretical and experimental studies48 references11 citations

TL;DR

This paper proposes testing non-universal gaugino mass models that simultaneously explain the muon g-2 anomaly, dark matter relic density, and the 125 GeV Higgs boson via electroweak production of chargino-neutralino pairs at the LHC. Using trilepton and same-sign dilepton final states, it demonstrates that the 13 TeV LHC run can probe wino and left slepton masses in the 400–700 GeV range, covering the muon g-2 anomaly up to 2σ significance with 100 fb⁻¹ of data.

ABSTRACT

Non-universal gaugino mass models can naturally account for the dark matter relic density via the bulk annihilation process with relatively light bino LSP and right sleptons in the mass range of ~ 100 GeV, while accommodating the observed Higgs boson mass of ~ 125 GeV with TeV scale squark/gluino masses. A class of these models can also account for the observed muon g-2 anomaly via SUSY loops with wino and left sleptons in the mass range of 400 -- 700 GeV. These models can be tested at LHC via electroweak production of charged and neutral wino pair, leading to robust trilepton and same sign dilepton signals. We investigate these signals along with the standard model background for both 8 and 13 TeV LHC runs.

Motivation & Objective

• To test non-universal gaugino mass models that simultaneously explain the muon g-2 anomaly, dark matter relic density, and the 125 GeV Higgs boson mass.
• To investigate the discovery potential of these models at the LHC via electroweak production of chargino and neutralino pairs.
• To evaluate the sensitivity of trilepton and same-sign dilepton final states to wino and left slepton masses in the 400–700 GeV range.
• To compare the expected discovery reach at 8 TeV and 13 TeV LHC runs using realistic signal and background simulations.
• To assess the viability of the same-sign dilepton channel when left slepton masses are close to wino masses, where other channels may fail.

Proposed method

• The study employs non-universal gaugino mass models based on SU(5) GUT, with two independent gaugino mass parameters at the GUT scale derived from F-term VEVs of singlet and non-singlet superfields.
• The weak-scale spectrum is computed using renormalization group equations (RGEs), with input parameters including universal scalar mass m₀ and tri-linear coupling A₀ to achieve a 125 GeV Higgs mass.
• Chargino and neutralino pair production is simulated via Drell-Yan-like processes, followed by cascade decays: χ±₁ → ℓ± ν̃ℓ → ℓ± ℓ∓ ℓ± ν̄ν, yielding trilepton and same-sign dilepton final states.
• Signal events are extracted using optimized kinematic cuts to suppress dominant SM backgrounds, including top quark pair and Drell-Yan processes.
• Backgrounds are estimated using Monte Carlo simulations, with a jet veto applied to suppress t̄t and multijet events, though a b-jet veto is noted as more effective.
• Statistical significance is evaluated using expected signal and background rates, with discovery reach defined at 5σ and exclusion limits at 95% C.L.

Experimental results

Research questions

• RQ1 Can non-universal gaugino mass models in SU(5) GUT simultaneously explain the muon g-2 anomaly, dark matter relic density, and the 125 GeV Higgs boson mass?
• RQ2 What is the LHC discovery potential for chargino-neutralino pair production in trilepton and same-sign dilepton final states for wino and left slepton masses in the 400–700 GeV range?
• RQ3 How does the sensitivity of the same-sign dilepton channel compare to the trilepton channel when left slepton masses are nearly degenerate with wino masses?
• RQ4 To what extent can 8 TeV and 13 TeV LHC data probe the parameter space consistent with the muon g-2 anomaly?
• RQ5 How do the expected exclusion limits from this analysis compare to existing ATLAS and CMS searches using 8 TeV data?

Key findings

• The 8 TeV LHC run with 20 fb⁻¹ of data can probe wino masses up to 500 GeV in both trilepton and same-sign dilepton channels, covering the muon g-2 anomaly within 1σ of its central value.
• At 13 TeV with 100 fb⁻¹ of data, the same-sign dilepton channel can probe wino masses up to 700 GeV, covering the muon g-2 anomaly up to 2σ significance.
• The same-sign dilepton channel achieves a discovery significance of 26–66σ for benchmark point BP1 and 15–39σ for BP2, with 125–65 and 80–40 signal events respectively.
• Even with only 20 fb⁻¹ at 13 TeV, a negative search result can exclude wino masses up to 600–700 GeV at more than 5σ significance.
• The same-sign dilepton channel remains viable and background-suppressed even when the left slepton mass is very close to the wino mass, unlike other channels.
• The expected 95% C.L. exclusion limits from this analysis are consistent with and, in some cases, more conservative than the preliminary CMS results using a b-jet veto, highlighting the impact of background suppression techniques.