Hunt for new phenomena using large jet multiplicities and missing transverse momentum with ATLAS in 4.7 fb−1 of $ \sqrt {s} = 7\;TeV $ proton-proton collisions

Abstract

Hunt for new phenomena using large jet multiplicities and missing transverse momentum with ATLAS in 4.7 fb −1 of √ s = 7 TeV proton-proton collisionsThe ATLAS collaboration Abstract: Results are presented of a search for new particles decaying to large numbers of jets in association with missing transverse momentum, using 4.7 fb −1 of pp collision data at √ s = 7 TeV collected by the ATLAS experiment at the Large Hadron Collider in 2011. The event selection requires missing transverse momentum, no isolated electrons or muons, and from ≥6 to ≥9 jets. No evidence is found for physics beyond the Standard Model. The results are interpreted in the context of a MSUGRA/CMSSM supersymmetric model, where, for large universal scalar mass m 0 , gluino masses smaller than 840 GeV are excluded at the 95% confidence level, extending previously published limits. Within a simplified model containing only a gluino octet and a neutralino, gluino masses smaller than 870 GeV are similarly excluded for neutralino masses below 100 GeV. Keywords: Hadron-Hadron ScatteringOpen Access, Copyright CERN, for the benefit of the ATLAS collaboration doi:10.1007/JHEP07(2012)167 The ATLAS collaboration 24 JHEP07(2012)167 IntroductionMany extensions of the Standard Model of particle physics predict the presence of TeVscale strongly interacting particles that decay to lighter, weakly interacting descendants. Any such weakly interacting particles that are massive and stable can contribute to the dark matter content of the universe. The strongly interacting parents would be produced in the proton-proton interactions at the Large Hadron Collider (LHC), and such events would be characterized by significant missing transverse momentum E miss T from the unobserved weakly interacting daughters, and jets from emissions of quarks and/or gluons.In the context of R-parity conserving [1-5] supersymmetry [5][6][7][8][9][10], the strongly interacting parent particles are the squarksq and gluinosg, they are produced in pairs, and the lightest supersymmetric particles can provide the stable dark matter candidates [11,12]. Jets are produced from a variety of sources: from quark emission in supersymmetric cascade decays, production of heavy Standard Model particles (W , Z or t) which then decay hadronically, or from QCD radiation. Examples of particular phenomenological interest -1 - JHEP07(2012)167include models where squarks are significantly heavier than gluinos. In such models the gluino pair production and decay process g +g → t +t +χ 0 1 + t +t +χ 0 1 can dominate, producing large jet multiplicities when the resulting top quarks decay hadronically. In the context of MSUGRA/CMSSM models, a variety of different cascade decays, including thegg initiated process above, can lead to large jet multiplicities. A previous ATLAS search in high jet multiplicity final states [13] examined data taken during the first half of 2011, corresponding to an integrated luminosity of 1.34 fb −1 . This paper extends the analysis to the complete ATLAS 2011 pp data set, corresponding...

Inclusive searches for squarks and gluinos with the ATLAS detector

“…The search for SUSY in events with 6-9 jets and missing transverse energy [4] covers supersymmetric scenarios with high jet multiplicities, which may arise from quark emission in supersymmetric cascade decays, production of W or Z bosons decaying to hadrons, or from QCD radiation. Examples of particular phenomenological interest include models where squarks are significantly heavier than gluinos.…”

“…The lines on either side of the observed limit represent the ±1σ uncertainty on the expected signal cross-section. 4. Searches in final states with 1 lepton, 2-4 jets, and missing transverse energy Supersymmetry searches with leptons in addition to jets and E miss T in the final state are complementary to the fully hadronic searches.…”

“…36th International Conference on High Energy Physics, July [4][5][6][7][8][9][10][11]2012 Melbourne, Australia…”

Interpretation of searches for supersymmetry with simplified models

“…The simplified model framework was also applied by CMS to a limited number of analyses in 2010 [27]. The ATLAS Collaboration has published similar interpretations [28][29][30][31][32][33][34].…”

Quark jet rates and quark-gluon discrimination in multijet final states

“…Many new physics models form multi-jet final states. For example, heavy colored resonances in each model, like gluino or squarks in SUSY, could emit many partons via their cascade decays, and there are several studies for these at the LHC [73][74][75][76][77][78][79]. Another example is searches of low-scale gravity which deals with the hierarchy problem concerned with the difference between the electroweak and Plack scale.…”