Brent Nelson

Supersymmetric discovery potential and benchmarks for early runs at √s=7 TeV at the LHC

Baris Altunkaynak et al. — Fri, 04 May 2012 19:47:32 PDT

We carry out an analysis of the potential of the Large Hadron Collider (LHC) to discover supersymmetry in runs at √s=7 TeV with an accumulated luminosity of (0.1–2) fb⁻¹ of data. The analysis is done with both minimal supergravity and supergravity models with nonuniversal soft breaking. Benchmarks for early discovery with (0.1–2) fb⁻¹ of data are given. We provide an update of b-tagging efficiencies in PGS 4 appropriate for LHC analyses. A large number of signature channels are analyzed, and it is shown that each of the models exhibited are discoverable at the 5σ level or more above the standard model background in several signature channels which would provide cross checks for a discovery of supersymmetry. It is shown that some of the benchmarks are discoverable with 0.1 fb⁻¹ of data again with detectable signals in several channels.

Predictive signatures of supersymmetry: Measuring the dark matter mass and gluino mass with early LHC data

Daniel Feldman et al. — Fri, 04 May 2012 19:47:31 PDT

We present a focused study of a predictive unified model whose measurable consequences are immediately relevant to early discovery prospects of supersymmetry at the LHC. ATLAS and CMS have released their analysis with 35 pb^-1 of data and the model class we discuss is consistent with this data. It is shown that with an increase in luminosity, the LSP dark matter mass and the gluino mass can be inferred from simple observables such as kinematic edges in leptonic channels and peak values in effective mass distributions. Specifically, we consider cases in which the neutralino is of low mass and where the relic density consistent with WMAP observations arises via the exchange of Higgs bosons in unified supergravity models. The magnitudes of the gaugino masses are sharply limited to focused regions of the parameter space, and, in particular, the dark matter mass lies in the range ∼(50–65) GeV with an upper bound on the gluino mass of 575 GeV, with a typical mass of 450 GeV. We find that all model points in this paradigm are discoverable at the LHC at √s=7 TeV. We determine lower bounds on the entire sparticle spectrum in this model based on existing experimental constraints. In addition, we find the spin-independent cross section for neutralino scattering on nucleons to be generally in the range of σ_χ˜10_p^SI=10^-46±1 cm² with much higher cross sections also possible. Thus, direct detection experiments such as CDMS and XENON already constrain some of the allowed parameter space of the low mass gaugino models and further data will provide important cross-checks of the model assumptions in the near future.

Explaining PAMELA and WMAP data through coannihilations in extended SUGRA with collider implications

Daniel Feldman et al. — Fri, 04 May 2012 19:47:30 PDT

The PAMELA positron excess is analyzed within the framework of nonuniversal supergravity (SUGRA) models with an extended U(1)ⁿ gauge symmetry in the hidden sector leading to neutralino dark matter with either a mixed Higgsino-wino lightest R-parity odd supersymmetric particle (LSP) or an essentially pure wino-dominated LSP. The Higgsino-wino LSP can produce the observed PAMELA positron excess and satisfy relic density constraints in the extended class of models due to a near degeneracy of the mass spectrum of the extended neutralino sector with the LSP mass. The simultaneous satisfaction of the WMAP relic density data and the PAMELA data is accomplished through a coannihilation mechanism (B_Co-mechanism), and leads to predictions of a neutralino and a chargino in the mass range (180–200) GeV as well as low-lying sparticles accessible at colliders. We show that the models are consistent with the antiproton constraints from PAMELA as well as the photon flux data from EGRET and FERMI-LAT. Predictions for the scalar neutralino-proton cross section relevant for the direct detection of dark matter are also discussed and signatures at the LHC for these PAMELA inspired models are analyzed. It is shown that the mixed Higgsino-wino LSP model will be discoverable with as little as 1 fb⁻¹ of data and is thus a prime candidate for discovery in the low luminosity runs at the LHC.

Dark matter as a guide toward a light gluino at the LHC

Daniel Feldman et al. — Mon, 31 Jan 2011 09:33:02 PST

Motivated by specific connections to dark matter signatures, we study the prospects of observing the presence of a relatively light gluino whose mass is in the range ~ (500 − 900) GeV with a wino-like lightest supersymmetric particle with mass in the range of ~ (170 − 210) GeV. The light gaugino spectra studied here is generally different from other models, and in particular those with a wino dominated LSP, in that here the gluinos can be significantly lighter. The positron excess reported by the PAMELA satellite data is accounted for by annihilations of the wino LSP and their relic abundance can generally be brought near the WMAP constraints due to the late decay of a modulus field re-populating the density of relic dark matter. We also mention the recent FERMI photon constraints on annihilating dark matter in this class of models and implications for direct detection experiments including CDMS and XENON. We study these signatures in models of supersymmetry with non-minimal soft breaking terms derived from both string compactifications and related supergravity models which generally lead to non-universal gaugino masses. At the LHC, large event rates from the three-body decays of the gluino in certain parts of the parameter space are found to give rise to early discovery prospects for the gaugino sector. Excess events at the 5 sigma level can arise with luminosity as low as O(100) pb⁻¹ at a center of mass energy of 10 TeV and ≲ O(1) fb⁻¹ at √s = 7 TeV.

Dark matter prospects in deflected mirage mediation

Michael Holmes et al. — Mon, 31 Jan 2011 09:33:01 PST

The recently introduced detected mirage mediation (DMM) model is a string-motivated paradigm in which all three of the major supersymmetry-breaking transmission mechanisms are operative. We begin a systematic exploration of the parameter space of this rich model context, paying special attention to the pattern of gaugino masses which arise. In this work we focus on the dark matter phenomenology of the DMM model as such signals are the least influenced by the model-dependent scalar masses. We find that a large portion of the parameter space in which the three mediation mechanisms have a similar effective mass scale of 1 TeV or less will be probed by future direct and indirect detection experiments. Distinguishing detected mirage mediation from the mirage model without gauge mediation will prove difficult without collider input, though we indicate how gamma ray signals may provide an opportunity for distinguishing between the two paradigms.