Search for a Supersymmetric Partner to the Top Quark in Final States with Jets and Missing Transverse Momentum ats=7  TeVwith the ATLAS Detector

Abstract

A search for direct pair production of supersymmetric top squarks (t 1 ) is presented, assuming thet 1 decays into a top quark and the lightest supersymmetric particle, 0 1 , and that both top quarks decay to purely hadronic final states. A total of 16 (4) The standard model (SM) is a successful but incomplete theory of particle interactions. Supersymmetry (SUSY) [1][2][3][4][5][6][7][8][9] provides an elegant cancellation of the quadratic mass divergences that would accompany a SM Higgs boson by introducing supersymmetric partners of all SM particles, such as a scalar partner of the top quark (t). Like t " t, directtt à is produced primarily through gluon fusion at the Large Hadron Collider (LHC). The production cross section depends mostly on the mass of the top partner and has minimal dependence on other SUSY parameters [10][11][12]. The LHC enables searches for directtt à production at higher mass scales than previous accelerators [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27]. The viability of SUSY as a scenario to stabilize the Higgs potential and to be consistent with electroweak naturalness [28,29] is tested by the search fort below the TeV scale.In this Letter, we present a search for directtt à production assumingt ! t 0 1 ! bW 0 1 , wheret 1 is the lightestt eigenstate and 0 1 represents the lightest supersymmetric particle (LSP) in R-parity conserving models [30][31][32][33][34]. We target events where both W bosons decay hadronically, yielding a final state with six high transverse momentum (p T ) jets from the all-hadronic t " t final state and large missing transverse momentum (E miss T ) from the LSPs. The kinematics of both top quarks can therefore be fully specified by the visible decay products. Additionally, SM backgrounds from all-hadronic t " t are suppressed as there is no intrinsic E miss T except from semileptonic c-and b-quark decays. The dominant background consists of t " t events that contain a W ! ' decay where the lepton ('), often of flavor, is either lost or misidentified as a jet. These events also have large E miss T from the neutrino (). The data were acquired during 2011 in LHC pp collisions at a center-of-mass energy of 7 TeV with the ATLAS detector [35], which consists of tracking detectors surrounded by a 2 T superconducting solenoid, calorimeters, and a muon spectrometer in a toroidal magnetic field. The high-granularity calorimeter system, with acceptance covering jj < 4:9 [36], is composed of liquid argon with lead, copper, or tungsten absorbers and scintillator tiles with steel absorbers. This data set, composed of events with a high-p T jet and large E miss T as selected by the trigger system, corresponds to an integrated luminosity of 4:7 fb À1 with a relative uncertainty of 3.9% [37][38][39].Jets are constructed from three-dimensional clusters of calorimeter cells using the anti-k t algorithm with a distance parameter of 0.4 [39,40]. Jet energies are corrected [41] for losses in material in front of the active calorimeter layers, detector inhomogeneit...

Third generation SUSY searches in CMS

“…This note presents results of several searches for third generation squark pair production using a dataset corresponding to an integrated luminosity of 2.3 fb −1 of proton-proton (pp) collisions collected at a center-of-mass energy of 13 TeV with the CMS detector [1] at LHC in 2015. The results of similar searches were previously reported by the ATLAS and CMS collaborations using datasets of 7 and 8 TeV pp collisions [2,3,4,5,6,7,8,9,10,11]and earlier by CDF and D0 collaborations at the Tevatron. No excess above the SM expectations was observed and the results of those searches were used to place lower limits on the mass of the squarks for different decay scenarios.…”

Search for pair-produced third-generation squarks decaying via charm quarks or in compressed supersymmetric scenarios inppcollisions ats=8 TeVAad1, Abbott2, Abdallah3 et al. 2014Phys. Rev. DSelf Cite14281740View full textAdd to dashboardCite

“…If the chargino is heavier than the stop and m W þ m b < Δm < m t , the dominant decay mode is expected to be the three-body Wbχ 0 1 decay. Several searches on 7 TeV data have been carried out in these decay channels in zero-, one-, and two-lepton final states [18][19][20][21] and have been extended using 8 TeV data [22][23][24][25].…”

Measurement of Spin Correlation in Top-Antitop Quark Events and Search for Top Squark Pair Production inppCollisions ats=8 TeVUsing the ATLAS Detect

“…In SUSY models where R parity is conserved, such as the minimal supersymmetric standard model (MSSM) [52][53][54][55][56], this could lead to ttχ 0 1χ 0 1 intermediate states, appearing like SM tt production with additional missing transverse momentum carried away by the escaping neutralinos, making traditional searches exploiting kinematic differences as presented in Refs. [57][58][59][60][61][62][63] very difficult.t 1t1 events can be distinguished from SM tt events through an increase of the measured tt cross section as analyzed in Ref. [64], and since top squarks have zero spin, through measuring angular correlations sensitive to spin correlation, as analyzed in this Letter.…”