New ATLAS results in inclusive searches for supersymmetric squarks and gluinos

Abstract. Despite the absence of experimental evidence, weak-scale supersymmetry remains one of the best motivated and most studied Standard Model extensions. These proceedings summarise recent results from the ATLAS experiment at the LHC on inclusive searches for supersymmetric squarks and gluinos in events containing jets, missing transverse momentum, and possibly isolated leptons in R-parity conserving scenarios.


SUSY in strong production
If present at TeV scale, squarks and gluinos may be copiously produced at the LHC.
Gluinos and squarks decay either directly or via a cascade into: jets, coming from gluinos and squarks decays the LSP (the lightest supersymmetric particle), escaping the detector and resulting in E miss T (assuming R-parity conservation in this talk) and: possibly lepton(s), coming from chargino, neutralino or slepton decays   0-lepton + multi-jets: signal regions arXiv:1308.1841, submitted to JHEP Dedicated analysis to look for longer SUSY decay chains -up to 10 jets in the final state The usage multi-jet triggers without E miss T requirements allows to have low cuts on E miss T Three sets of signal regions: Veto events with isolated electrons or muons in order to suppress W +jets or tt background 8, 9 or at least 10 jets with p T > 50 GeV and zero, one or at least two b-tagged jets 7 or at least 8 jets with p T > 80 GeV and zero, one or at least two b-tagged jets Signal regions with "mega-jets": At least 8, 9 or 10 jets with p T > 50 GeV and M J > 340 or 420 GeV All signal regions also impose E miss T / H T > 4 √ GeV (H T = p jet T using jets with p T > 40 GeV and |η| < 2.8)

Mega-jets:
Re-clustering anti-k T jets with cone radius of 0.4 into 'mega'-jets: anti-k T jets with cone radius of 1.0 Discriminating variable M J = m R=1.0 jet constructed by using mega-jets with p T > 100 GeV and |η| < 1.5 (SUSY) (BG) 0-lepton + multi-jets Backgrounds: Multi-jet production: strong production, fully hadronic decays of tt, W and Z bosons  At least one isolated lepton + 2-6 jets ATLAS-CONF-2013-062 Reduction of the large QCD multi-jet background by requiring at least one lepton (electron or muon) Powerful discriminant between background and signal: Decays of gluinos or squarks via one, two or more steps into the LSP at least one soft lepton (6 (µ)/10 (e) < p T < 25 GeV )  80, 30 > 80, 50, 40, 40, 40 > 80, 50, 40, 40, 40, 40 pT add. jets  Events / 20 GeV Also exploit the longitudinal information of an event. Idea: • Both sparticles are pair-produced, the initial heavy sparticles are assumed here to have the same masses or to be at the same mass scale → Both decay chains are symmetric if going into the frame where the initial heavy sparticle is at rest → Can group all visible particles of one decay chain into a mega-jet; both mega-jets should have the same energy Variables to benefit from this configuration: • Characteristic mass of the event: M R = (j 1.E + j 2,E ) 2 − (j 1,L + j 2,L ) 2 (E: energy, L: longitudinal component, j 1 and j 2 : four-vectors of the two mega-jets) • Transverse information of the event: Background events tend to have lower R, SUSY like signal events tend to be uniformly distributed between 0 and 1 in R Good agreement between background estimation and observed data. Tightest limit on the visible cross section in the 1-lepton + 6 jets SRs: 0.15 fb Production of same-sign lepton pairs (focus here on ee, eµ and µµ) rare in the SM Several production possibilities in SUSY decay chains, e.g. ing → tt → ttχ 0 1 Due to rareness of same-sign events in SM processes low background expectation: prompt same-sign lepton pairs with two real same-sign leptons: tt+ vector boson, dibosons; estimated by using the MC prediction and validated in validation regions fake lepton background -at least one of the selected leptons is misidentified: mostly semi-leptonic tt events; estimated by a matrix method charge mis-identification: emission of hard bremsstrahlung followed by an asymmetric conversion (e ± → e ± γ → e ± e ± e ∓ ) only for events with electrons; mostly di-leptonic tt events; estimated by determining the ratio between same-sign and opposite-sign electron pairs in Drell-Yan events and applying this ratio to regions similar to the SRs, but containing opposite-sign events

Interpretation summary
The various analyses are interpreted in multiple models:

2-lepton Razor
Limits are placed on the gluino mass (up to ∼ 1.3 TeV, depending on model) and on the squark masses (up to ∼ 700 GeV, depending on model).
Model independent upper limits on the visible cross section have been derived and can be as low as 0.15 fb (depending on the analysis).
All results can be found on this webpage, summarising all public ATLAS SUSY results.

Mass limit Reference
Inclusive Searches 3 rd gen. g med.