Gluino meets flavored naturalness

Published for SISSA by Springer Received: January 7, 2016 Accepted: March 23, 2016 Published: April 7, 2016 Gluino meets flavored naturalness a Institut fur Theoretische Teilchenphysik, Karlsruhe Institute of Technology, Engesserstraße 7, D-76128 Karlsruhe, Germany b Institut fur Kernphysik, Karlsruhe Institute of Technology, Hermann-von-Helmholtz-Platz 1, D-76344 Eggenstein-Leopoldshafen, Germany c Sorbonne Universités, UPMC Univ. Paris 06, UMR 7589, LPTHE, F-75005, Paris, France d CNRS, UMR 7589, LPTHE, F-75005, Paris, France e Department of Physics and Astronomy, University of California, Irvine, CA 92697, U.S.A. f Department of Particle Physics and Astrophysics, Weizmann Institute of Science, Rehovot 76100, Israel E-mail: , , , Abstract: We study constraints from LHC run I on squark and gluino masses in the presence of squark flavor violation. Inspired by the concept of ‘flavored naturalness’, we focus on the impact of a non-zero stop-scharm mixing and mass splitting in the right-handed sector. To this end, we recast four searches of the ATLAS and CMS collaborations, dedicated either to third generation squarks, to gluino and squarks of the first two generations, or to charm-squarks. In the absence of extra structure, the mass of the gluino provides an additional source of fine tuning and is therefore important to consider within models of flavored naturalness that allow for relatively light squark states. When combining the searches, the resulting constraints in the plane of the lightest squark and gluino masses are rather stable with respect to the presence of flavor-violation, and do not allow for gluino masses of less than 1.2 TeV and squarks lighter than about 550 GeV. While these constraints are stringent, interesting models with sizable stop-scharm mixing and a relatively light squark state are still viable and could be observed in the near future. Keywords: Beyond Standard Model, Supersymmetric Standard Model ArXiv ePrint: 1512.03813 Open Access, c The Authors. Article funded by SCOAP3 . doi:10.1007/JHEP04(2016)044 JHEP04(2016)044 Monika Blanke,a,b Benjamin Fuks,c,d Iftah Galone and Gilad Perezf Contents 1 Introduction 1 2 Theoretical framework: a simplified model for studying gluino flavor violation 3 5 5 6 7 8 8 4 Results / T + lepton veto 4.1 ATLAS: multijets + E /T 4.2 CMS: single lepton + at least four jets (including at least one b-jet) + E / 4.3 CMS: at least 3 jets + E T + lepton veto 4.4 ATLAS: scharm pair-production using charm-tagging + lepton veto 4.5 Combined reach 9 10 13 13 14 18 5 Conclusions 22 A Implementation and validation of ATLAS-SUSY-2013-04 in MadAnalysis 5 23 1 Introduction While the Large Hadron Collider (LHC) has just begun its second period of data taking, its first run has been an experimental success with many new measurements at an energy regime unexplored beforehand. In particular, the search for new phenomena has been given a boost with the discovery of a new particle, the celebrated Higgs boson [1, 2]. Theoretically, however, we are still in the dark, as most searches performed at the LHC seem to be consistent with the Standard Model (SM) predictions. This includes the measurements of the Higgs couplings [3], the searches for new physics at the energy frontier with the ATLAS and CMS experiments and at the luminosity frontier with the LHCb experiment. 1 In the absence of new physics signals, the naturalness argument that motivates the possible observation of new dynamics at the TeV scale seems slightly less appealing as a guiding 1 Although the recent discovery of pentaquark-like states [4] is explained within the SM, the recent LHCb flavor anomalies might imply new physics [5–7]. –1– JHEP04(2016)044 3 Monte Carlo simulations and LHC analysis reinterpretation details 3.1 Technical setup and general considerations / T + lepton veto 3.2 ATLAS: multijets + E /T 3.3 CMS: single lepton + at least four jets (including at least one b-jet) + E / T + lepton veto 3.4 CMS: at least 3 jets + E 3.5 ATLAS: scharm pair-production using charm-tagging + lepton veto mg̃ . 2mq̃ . –2– (1.1) JHEP04(2016)044 principle (see ref. [8] for a general status review and ref. [9] for a focus on supersymmetry). One of the main tasks of the next high-energy LHC runs at 13 TeV and 14 TeV will hence be to shed more light on the electroweak symmetry breaking mechanism and to estimate to what extent the Higgs-boson mass is fine-tuned. One of the robust features of all natural extensions of the SM is the presence of top partners. These act to screen away the quadratic sensitivity of the Higgs-boson mass to the ultraviolet (UV) scales due mostly to the large top Yukawa coupling. Naively, one might expect that flavor physics and naturalness are two decoupled concepts. However, even within a minimal top partner sector, the definition of the flavor structure of the model could be non-trivial. The mass-eigenstates of the theory could be non-pure top partners and still yield a sufficient cancellation of the UV-sensitive quantum contributions to the Higgsboson mass. In this way, even a model exhibiting a single top-partner might incorporate large flavor- and CP-violating effects. This possibility, however, is typically ignored, due to prejudices and a possibly too simplistic interpretation of the bounds stemming from lowenergy flavor-changing neutral current processes. Indeed, most studies on naturalness have assumed either flavor universality among the partners or an approximate U(2) symmetry which acts on the partners of the first two generations. Nonetheless, a thorough analysis of the constraints arising from D − D̄ and K − K̄ mixing has shown that the degeneracy of the partners is not required for models of down alignment [10], and such frameworks in which new physics couplings are non-diagonal in flavor-space have been considered both in the context of supersymmetry [11, 12] and Higgs compositeness [13, 14]. Taking supersymmetry as an illustrative example, the non-degeneracy of the partners is even more appealing as the direct experimental bounds on second generation squarks are rather weak, their masses being only constrained to be larger than 500 GeV. This is a consequence of the underlying ingredients of all supersymmetry searches which are mainly sensitive either to ‘valence’ squarks or to third generation squarks [15]. If the supersymmetric top-partners are not flavor-eigenstates but rather admixtures of stops and scharms, then the signatures of supersymmetric events could change dramatically. In particular, the /T) typically sought signatures such as top-quark pairs and missing transverse energy ( E / could be exchanged for charm-jet pairs and top-charm pairs plus E T . This has led to the concept of supersymmetric ‘flavored naturalness’. Despite the non-trivial flavor structure of the top sector, the level of fine tuning of these setups is similar to more conventional supersymmetric scenarios with pure-stop mass eigensta (...truncated)