This document proposes a collection of simplified models relevant to the design of new-physics searches at the Large Hadron Collider (LHC) and the characterization of their results. Both ATLAS and CMS have already presented some results in terms of simplified models, and we encourage them to continue and expand this effort, which supplements both signature-based results and benchmark model interpretations. A simplified model is defined by an effective Lagrangian describing the interactions of a small number of new particles. Simplified models can equally well be described by a small number of masses and cross-sections. These parameters are directly related to collider physics observables, making simplified models a particularly effective framework for evaluating searches and a useful starting point for characterizing positive signals of new physics. This document serves as an official summary of the results from the 'Topologies for Early LHC Searches' workshop, held at SLAC in September

This report summarises the physics opportunities in the search and study of physics beyond the Standard Model at a 100 TeV pp collider.

Peaking consistently in June for nearly eleven years, the annual modulation signal reported by DAMA/NaI and DAMA/LIBRA offers strong evidence for the identity of dark matter. DAMA's signal strongly suggest that dark matter inelastically scatters into an excited state split by O(100 keV). We propose that DAMA is observing hyperfine transitions of a composite dark matter particle. As an example, we consider a meson of a QCD-like sector, built out of constituent fermions whose spin-spin interactions break the degeneracy of the ground state. An axially coupled U (1) gauge boson that mixes kinetically with hypercharge induces inelastic hyperfine transitions of the meson dark matter that can explain the DAMA signal.This letter proposes a new class of inelastic dark matter (iDM) models that can explain the annual modulation reported by DAMA/NaI and DAMA/LIBRA [1]. DAMA's signal peaks in early June, consistent with dark matter scattering, and has remained in phase for nearly eleven years. Moreover, the fractional modulation of the signal appears anomalously large, and the nuclear recoil spectrum has a peak near E R O(30 keV).The hypothesis that dark matter scatters inelastically off nuclei into a O(100 keV) excited state elegantly explains the salient features of the DAMA signal [2]. IDM models predict nuclear recoil spectra with a characteristic peak and an O(1) modulation fraction [3]. The large dark matter velocity threshold required by inelastic kinematics also implies that heavier nuclei targets like 127 I in DAMA provide enhanced signal sensitivity relative to lighter targets such as 74 Ge in CDMS.In composite inelastic dark matter models (CiDM), DAMA's observed signal arises from inelastic hyperfine transitions of a composite dark matter particle. (For other examples of composite dark matter, see [4].) We illustrate this mechanism with a simple model where the majority of dark matter is a meson of a strongly coupled SU (N c ) gauge sector that confines near Λ GeV. These mesons are comprised of constituent fermions whose hyperfine interactions split the ground state by O(100 keV). When one constituent quark is non-relativistic, a hierarchy between the hyperfine scale and the dark matter mass follows inevitably from an enhanced spin symmetry. The dark matter couples to a new U (1) A vector boson that kinetically mixes with the Standard Model's hypercharge [5]. Another version of iDM with kinetic mixing is given in [6]. Axial couplings of the U (1) A to the constituent fermions mediate inelastic hyperfine transitions that dominate low-energy nuclear scattering.The model considered here has two Dirac fermions, Ψ H and Ψ L , transforming in the fundamental representation of the SU (N c ) gauge group. The new U (1) A couples axially to Ψ H,L , each of which have equal and opposite unit charge. We introduce a charge-2 Higgs φ, whose vacuum expectation value generates a mass for Ψ H,L and the A . The U (1) A is non-anomalous for this particle content. The dark matter candidate is aΨ L Ψ H bound state, and its stability ca...

The QCD axion is one of the most compelling solutions of the strong CP problem. There are major current efforts into searching for an ultralight, invisible axion, which is believed to be the only phenomenologically viable realization of the QCD axion. Visible axions with decay constants at or below the electroweak scale are believed to have been long excluded by laboratory searches.Considering the significance of the axion solution to the strong CP problem, we revisit experimental constraints on QCD axions in the O(10 MeV) mass window. In particular, we find a variant axion model that remains compatible with existing constraints. This model predicts new states at the GeV scale coupled hadronically, and a variety of low-energy axion signatures, such as rare meson decays, nuclear de-excitations via axion emission, and production in e + e − annihilation and fixed target experiments. This reopens the possibility of solving the strong CP problem at the GeV scale.

Abstract:The energy dependence of the electroweak gauge couplings has not been measured above the weak scale. We propose that percent-level measurements of the energy dependence of α 1,2 can be performed now at the LHC and at future higher energy hadron colliders. These measurements can be used to set limits on new particles with electroweak quantum numbers without relying on any assumptions about their decay properties. The shape of the high invariant mass spectrum of Drell-Yan, pp → Z * /γ * → + − , constrains α 1,2 (Q), and the shape of the high transverse mass distribution of pp → W * → ν constrains α 2 (Q). We use existing data to perform the first fits to α 1,2 above the weak scale. Percent-level measurements are possible because of high precision in theoretical predictions and existing experimental measurements. We show that the LHC already has the reach to improve upon electroweak precision tests for new particles that dominantly couple through their electroweak charges. The 14 TeV LHC is sensitive to the predicted Standard Model (SM) running of α 2 , and can show that α 2 decreases with energy at 2-3σ significance. A future 100 TeV proton-proton collider will have significant reach to measure running weak couplings, with sensitivity to the SM running of α 2 at 4-5σ and sensitivity to winos with masses up to ∼ 1.3 TeV at 2σ.

This work explores the potential reach of the 7 TeV LHC to new colored states in the context of simplified models and addresses the issue of which search regions are necessary to cover an extensive set of event topologies and kinematic regimes. This article demonstrates that if searches are designed to focus on specific regions of phase space, then new physics may be missed if it lies in unexpected corners. Simple multiregion search strategies can be designed to cover all of kinematic possibilities. A set of benchmark models are created that cover the qualitatively different signatures and a benchmark multiregion search strategy is presented that covers these models.

LHC experiments have placed strong bounds on the production of supersymmetric colored particles (squarks and gluinos), under the assumption that all flavors of squarks are nearly degenerate. However, the current experimental constraints on stop squarks are much weaker, due to the smaller production cross section and difficult backgrounds. While light stops are motivated by naturalness arguments, it has been suggested that such particles become nearly impossible to detect near the limit where their mass is degenerate with the sum of the masses of their decay products. We show that this is not the case, and that searches based on missing transverse energy ( / E T ) have significant reach for stop masses above 175 GeV, even in the degenerate limit. We consider direct pair production of stops, decaying to invisible LSPs and tops with either hadronic or semi-leptonic final states. Modest intrinsic differences in / E T are magnified by boosted kinematics and by shape analyses of / E T or suitably-chosen observables related to / E T . For these observables we show that the distributions of the relevant backgrounds and signals are well-described by simple analytic functions, in the kinematic regime where signal is enhanced. Shape analyses of / E T -related distributions will allow the LHC experiments to place significantly improved bounds on stop squarks, even in scenarios where the stop-LSP mass difference is degenerate with the top mass. Assuming 20 fb −1 of luminosity at √ s = 8 TeV, we conservatively estimate that experiments can exclude or discover degenerate stops with mass as large as ∼ 360 GeV and 560 GeV for massless LSPs.

Composite dark matter is a natural setting for implementing inelastic dark matter -the O(100 keV) mass splitting arises from spin-spin interactions of constituent fermions. In models where the constituents are charged under an axial U(1) gauge symmetry that also couples to the Standard Model quarks, dark matter scatters inelastically off Standard Model nuclei and can explain the DAMA/LIBRA annual modulation signal. This article describes the early Universe cosmology of a minimal implementation of a composite inelastic dark matter model where the dark matter is a meson composed of a light and a heavy quark. The synthesis of the constituent quarks into dark hadrons results in several qualitatively different configurations of the resulting dark matter composition depending on the relative mass scales in the system.