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...
A search for scalar particles and neutralinos such as those predicted by supersymmetric models has been performed using a data sample of 4.4 million hadronic Z" decays recorded by the OPAL detector at the e+e-collider LEP. The production of such particles typically leads to event topologies consisting of an acoplanar pair of jets, or of a mono-jet, accompanied by sizeable missing energy owing to neutrinos and other undetectable neutral particles. Limits are obtained, at the 95% confidence level, on the masses and production rates of scalar particles produced in association with the p. Limits are also placed on neutralino production, for which an additional possible signature is also studied, events containing a single observed photon. Within the Minimal Supersymmetric Standard Model, the mass of the lightest neutralino is found to be larger than 12.5 GeV/c' at 95% C.L., provided that tan/3 is larger than 1.5.
Quantum mechanics predicts an exponential distribution for the decay time of massive particles. However, deviations are expected for decay times shorter than about 10 13 s in models conjecturing the existence of hidden variables. Following a recent proposal, the decay length distribution of 5843 leptons decaying into 3 charged particles was analyzed in search o f s u c h a deviation.The deviation from an exponential distribution with respect to the number of decays present within the exponential form, expressed as the relative w eight of an excess at zero decay length, was measured to be 1.1% 1.4% 3.5% . This result is consistent with zero deviation and leads to an upper limit of 8.5% and a lower limit of 6.3% at the 95% condence level.
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