Opening Up the Compressed Region of Top Squark Searches at 13 TeV LHC

Abstract

Light top superpartners play a key role in stabilizing the electroweak scale in supersymmetric theories. For R-parity conserved supersymmetric models, traditional searches are not sensitive to the compressed regions. In this Letter, we propose a new method targeting this region, with top squark and neutralino mass splitting ranging from m~t − m χ ≳ m t to about 20 GeV. In particular, we focus on the signal process in which a pair of top squarks are produced in association with a hard jet, and we define a new observable R M whose distribution has a peak in this compressed region. The position of the peak is closely correlated with m~t. We show that for the 13 TeV LHC with a luminosity of 3000 fb −1 , this analysis can extend the reach of the top squark in the compressed region to m~t around 800 GeV. DOI: 10.1103/PhysRevLett.115.181602 PACS numbers: 11.30.Pb, 14.80.Ly, 12.15.-y Introduction.-With the discovery of the Higgs boson [1,2], particle physics reached an important milestone. However, the mechanism of stabilizing the electroweak scale from large quantum corrections is one of the outstanding mysteries. In most of the models addressing this problem, a key ingredient is a light top partner. As the most prominent example, in supersymmetry, the top squarkt should be less than about a TeV to be an effective solution to the fine-tuning problem [3]. Traditional searches for top squarks focus on pair production of top squarks where each of them decays into t and the lightest supersymmetric particle (LSP), χ. If m~t ≫ m χ þ m t , the top quark can be quite energetic. In the top pair production, a main background of this search, most of the top quarks are produced near the threshold. Based on this observation, various kinematical variables (e.g., m T2 [4][5][6][7][8], H T [9], the razor variables [10][11][12], and the variables invented in Ref. [13]) have been defined to distinguish top squark pair production from top pair production. For recent global studies of the minimal version of the supersymmetric standard model, see Ref. [14] and the references therein. However, in the compressed region where m~t ≈ m t þ m χ , the kinematics of the top quarks from top squark decay are similar to those in the top pair production, and such observables are less sensitive. In the region that m χ ≪ m~t ≈ m t , spin correlations of the top quarks can help to distinguish the signal from the background [15][16][17]. Such analysis has been done by the CDF, D0, ATLAS, and CMS collaborations [18][19][20][21][22][23][24][25]. However, with larger m~t this method does not work well due to a smaller production rate. In other extreme regions of the parameter space m~t ≈ m χ ,t decays into four-body final states or a light quark plus the LSP through flavor-changing processes. In cases where the flavor-changing processes are important, charm tagging can be useful [26][27][28]. However, the jets from the decay are usually soft and cannot be

Revealing compressed stops using high-momentum recoils

“…While this paper was nearing completion, [42] appeared, which has significant overlap with our results. Their proposed R M variable (a very close variant of what was originally proposed in [33]) is highly correlated with the E T / H T variable that we use here, and in general with any variable proportional to E T in the presence of a hard ISR-jet p T cut.…”

“…There are a number of other differences in our analysis strategy, which lead to a higher S/B with comparable formal statistical significance, and somewhat different sensitivity contours. (E.g., near the specific mass point mt = m χ + m t 350 GeV, we find S/B 2, versus the S/B 1 found in [42].) We also pay additional attention to the approach to the stealth region and the possible role of E T resolution.…”

A light stop with a heavy gluino: enlarging the stop gap

“…There is also no fine-tuning required to get the correct electroweak scale and Higgs. Thus, in general, it is still interesting to develop experimental search techniques [26][27][28][29][30] to probe stop masses in the 200-800 GeV range that would allow a natural SUSY theory.…”

Probing compressed mass spectra in electroweak supersymmetry with Recursive Jigsaw Reconstruction

“…This is the case for supersymmetric spectra in which the difference in mass between the pair-produced parent superparticles,P , and the LSPs is low. Scenarios with a small mass-splitting are referred to herein as compressed [9].…”