arXiv:1008.2483v1 [hep-ph] 14 Aug 2010 How to look for supersymmetry under the lamppost at the LHC Partha Konar, Konstantin T. Matchev, Myeonghun Park, and Gaurab K. Sarangi Physics Department, University of Florida, Gainesville, FL 32611, USA (Dated: August 14, 2010) We apply a model-independent, agnostic approach to the collider phenomenology of supersymme- try (SUSY), in which all mass parameters are taken as free inputs at the weak scale. We consider the gauginos, higgsinos, and the first two generations of sleptons and squarks, and analyze all pos- sible mass hierarchies among them (4 × 8! = 161, 280 in total) in which the lightest superpartner is neutral, leading to missing energy. In each case, we identify the full set of the dominant (i.e. least suppressed by phase space, small mixing angles or Yukawas) decay chains originating from the lightest colored superpartner. Our exhaustive search reveals several quite dramatic yet unexplored multilepton signatures with up to 8 isolated leptons (plus possibly up to 2 massive gauge or Higgs bosons) in the final state. Such events are spectacular, background-free for all practical purposes, and may lead to a discovery in the very early stage (∼ 10 pb -1 ) of LHC operations at 7 TeV. PACS numbers: 14.80.Ly,12.60.Jv,13.85.-t The ramping operations at the CERN Large Hadron Collider (LHC) have begun the long awaited and historic exploration of the TeV scale, where new physics beyond the standard model (SM) is expected to emerge. Among the multitude of new scenarios, low energy supersym- metry (SUSY) has long been the primary target of the LHC experiments, not just because it is well motivated theoretically [1], but also because its generic discovery signatures cover a much wider class of models [2]. By itself, SUSY is very predictive, as it fixes the spins and couplings of the new particles (the superpartners). Unfortunately, this is not sufficient to pin down its pre- cise collider discovery signatures, as the latter crucially depend on the SUSY mass spectrum, which is in turn determined by the mechanism of supersymmetry break- ing. Alas, almost 40 years of model building effort since the discovery of supersymmetry have failed to produce a single, universally accepted model of SUSY breaking. Given one’s utter ignorance about the expected pat- tern of SUSY masses, in this letter we adopt a most con- servative, agnostic approach, where the masses of all su- perpartners are treated as free inputs at the weak scale. We shall then consider all possible hierarchical patterns among them, and identify the set of dominant (in the sense defined below) collider signatures in each case. In our quest for interesting models, we shall be guided by ex- perimental pragmatism instead of theoretical prejudice. The purpose of this study is twofold. First, most pre- vious collider studies of SUSY have been performed for specific SUSY benchmark points, typically chosen within some minimal model such as “minimal supergravity” (MSUGRA) [3]. We will therefore be interested in un- covering new types of signatures which may have been missed in the standard benchmark approach. Secondly, we shall focus our search on signatures with a high num- ber of isolated leptons, which constitute the proverbial “smoking gun” for new physics. For example, the inclu- sive trilepton channel is already recognized as “the golden mode” for an early SUSY discovery at hadron colliders. One of our main results here will be the identification of TABLE I: The set of SUSY particles considered in this anal- ysis, shorthand notation for each multiplet, and the corre- sponding soft SUSY breaking mass parameter. ˜ uL, ˜ dL ˜ uR ˜ dR ˜ eL,˜ νL ˜ eR ˜ h ± , ˜ h 0 u , ˜ h 0 d ˜ b 0 ˜ w ± ,˜ w 0 ˜ g Q U D L E H B W G MQ MU MD ML ME MH MB MW MG a number of new SUSY mass patterns whose dominant signatures have up to eight leptons in the final state. Our setup is as follows. We take the usual superpartner content of the Minimal Supersymmetric Standard Model (MSSM) listed in Table I. For simplicity, in this letter we shall consider just two degenerate light generations of sfermions. Third generation effects can be trivially incorporated in the discussion [4], and only complicate the bookkeeping. Given the 9 input mass parameters in Table I, in general there are 9! = 362, 880 possible or- derings among them, each leading to a distinct pattern (hierarchy) of sparticle masses. We shall use the short- hand notation from Table I to label each hierarchy: for example, GQUDHLWEB is a model with M G >M Q > M U >M D >M H >M L >M W >M E >M B . Our first goal will be to identify the main collider sig- natures for each hierarchy. As in any discussion on SUSY collider phenomenology, our starting point is the fate and then the nature of the Lightest Supersymmetric Particle (LSP), which we shall generically denote by L. For our main analysis, we shall assume that R-parity is conserved (or very weakly broken), so that L is stable on the scale of the detector. (We briefly discuss the R-parity violating option at the end.) Then, the original 9! model hierar- chies can be classified into the following three categories: I. CHAMPs. In the 8! = 40, 320 cases with L = E, the LSP is an electrically charged, color-neutral parti- cle (the right-handed slepton ˜ e R ). The corresponding generic collider signature is a long-lived charged massive particle (CHAMP) [5], regardless of the particular order- ing of the heavier sparticles.