Advances in High Energy Physics

Volume 2015, Article ID 982167, 24 pages

http://dx.doi.org/10.1155/2015/982167

## Searches for Prompt -Parity-Violating Supersymmetry at the LHC

Physikalisches Institut, Universität Würzburg, Emil-Hilb-Weg 22, 97074 Würzburg, Germany

Received 27 March 2015; Accepted 30 May 2015

Academic Editor: Mark D. Goodsell

Copyright © 2015 Andreas Redelbach. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The publication of this article was funded by SCOAP^{3}.

#### Abstract

Searches for supersymmetry (SUSY) at the LHC frequently assume the conservation of -parity in their design, optimization, and interpretation. In the case that -parity is not conserved, constraints on SUSY particle masses tend to be weakened with respect to -parity-conserving models. We review the current status of searches for -parity-violating (RPV) supersymmetry models at the ATLAS and CMS experiments, limited to 8 TeV search results published or submitted for publication as of the end of March 2015. All forms of renormalisable RPV terms leading to prompt signatures have been considered in the set of analyses under review. Discussing results for searches for prompt -parity-violating SUSY signatures summarizes the main constraints for various RPV models from LHC Run I and also defines the basis for promising signal regions to be optimized for Run II. In addition to identifying highly constrained regions from existing searches, also gaps in the coverage of the parameter space of RPV SUSY are outlined.

#### 1. Introduction

One of the primary objectives of the detectors at the LHC is the search for new particles and phenomena not described by the Standard Model (SM) of particle physics. Weak-scale supersymmetry (SUSY) [1–9] is a well-motivated and well-studied example of a theory beyond the SM (BSM) used to guide many of these searches. One attractive feature of SUSY is that it can solve the SM hierarchy problem [10–15] if the gluino, higgsino, and top squark masses are not much higher than the TeV scale. Closely related to this is the paradigm of naturalness, and see, for example, [16, 17].

In this document, we review constraints on SUSY models in the presence of lepton- or baryon-number violating interactions ( and , resp.) at the end of LHC Run I. These interactions are present in generic SUSY models with minimal particle content. They are renormalizable and are described by the following superpotential terms:In this notation, and indicate the lepton and quark SU(2)-doublet superfields, respectively, while , , and are the corresponding singlet superfields. The indices , , and refer to quark and lepton generations. The Higgs SU(2)-doublet superfield contains the Higgs field that couples to up-type quarks. The , , and parameters are new Yukawa couplings, referred to as* trilinear *-parity-violating couplings. The parameters have dimensions of mass and are present in models with* bilinear *-parity violation (). The terms in (1a) and (1b) are forbidden in many models of SUSY by the imposition of -parity conservation (RPC) [10, 18–21] in order to prevent rapid proton decay. However, proton decay can also be prevented by suppressing only one of or , in which case some -parity-violating interactions remain in the theory.

Introducing RPV couplings in the minimal supersymmetric Standard Model (MSSM) can significantly weaken mass and cross section limits from collider experiments and also provide a rich phenomenology; see, for example, the articles [22–24] or [25, 26]. A systematic phenomenological overview of possible signatures for specific RPV scenarios is summarized in [26] going through all possible mass orderings and determining the dominant decay signatures. Many papers have investigated signatures beyond the focus of most searches for SUSY at the LHC. Among such challenging scenarios are highly collimated LSP decay products [27, 28], same-sign dilepton signatures [29, 30], taus and -jets with reduced missing transverse energy [31], resonances of dijets [32, 33], high object multiplicities [34], or, more specifically, a charged lepton plus multiple jets [35].

In this note, we review the current constraints from various ATLAS and CMS searches for SUSY based on approximately 20 fb^{−1} of collision data with TeV collected in 2012. This review is organized as follows: After a short overview of -parity-violating parameters and previous constraints of RPV SUSY in Section 2, the main characteristics of analyses searching for RPV SUSY at ATLAS and CMS are presented in Section 3. The next sections focus on the results assuming the dominance of particular -parity-violating couplings: After the results for scenarios in Section 4, several limits for simplified models assuming , , or a combination of and relevant for resonance production are discussed in Sections 5, 6, and 7, respectively. In order to constrain models based on couplings, Section 8 summarizes several results both from ATLAS and from CMS searches. Finally, conclusions from -parity-violating searches at LHC Run I are drawn and some implications for strategies to investigate uncovered parts of the RPV SUSY parameter space for Run II are outlined.

#### 2. -Parity-Violating Parameters and Constraints

For each particle, -parity is defined as in terms of the corresponding spin, baryon, and leptons numbers. All Standard Model particles and the Higgs bosons have even -parity, while all supersymmetric particles (sparticles) have odd -parity. As described, for example, in [36], an extension of the minimal supersymmetric Standard Model (MSSM) with -parity-violating interactions, does not extend the number of the supersymmetric particles. Direct phenomenological consequences of -parity-violating interactions are as follows:(i)The lightest supersymmetric particle (LSP) is not necessarily stable.(ii)Sparticles can also be produced in odd numbers; in particular single-sparticle production is possible.

Conversely, in -parity-conserving models, only pair production of SUSY particles is possible in collision processes, with the stable LSP being a possible candidate for dark matter. An excellent review of LHC Run I searches with one focus on RPC SUSY is given by [37]. In this section a short overview of RPV parameters and also of constraints previous to LHC searches is given.

##### 2.1. Parameters for RPV SUSY

The number of -parity-violating parameters can be obtained from (1a) and (1b): Counting the possible generation indices in the terms and leads to 3 and 27 parameters, respectively. As explained, for example, in [22], antisymmetries in the summation over gauge indices, suppressed in the notation of (1a) and (1b), lead to and . Due to these antisymmetric relations, 9 independent -parity-violating parameters of type and arise, respectively. The structure of trilinear -parity-violating couplings leads to Feynman diagrams as illustrated in Figure 1 from [22].