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Register a new userSearch for Natural SUSY with inclusive search strategies at the LHC using the CMS detector
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Sezen Sekmen
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Natural SUSY suggests the existence of light stop quarks, accessible at the LHC, which are the focus of a dedicated CMS search program. I present two inclusive CMS searches that look for TeV scale colored sparticles in final states with jets, b-tagged jets and missing transverse energy performed using up to 19.4fb-1 of 8TeV LHC proton-proton data. No deviation from the Standard Model was observed in these searches, and the implications for this was shown for several simplified model scenarios and phenomenological MSSM.
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The High-Luminosity Large Hadron Collider is expected to deliver up to 3000 fb$^{-1}$ of proton-proton collisions at 14 TeV center-of-mass energy. We present prospects for selected heavy-ion, Standard Model and Higgs sector measurements with the CMS detector at the HL-LHC, and discuss potential sensitivity to several beyond-Standard Model new physics scenarios.
Prospects for ATLAS observation of a SUSY-like signal from two gluinos are investigated within a certain region of the mSUGRA parameter space, where the cross section of the two gluinos production via gluon-gluon fusion is estimated at a rather high level of 13 pb. The event selection trigger uses a very clear signature of the process (4 jets + 4 muons + up to 4 secondary vertices topology) when final decay products of each gluino are b-anti-b and muon-anti-muon pairs and the lightest SUSY particle, the neutralino. Rather high transverse missing energy carried away by two neutralinos is an essential signature of the event and also allows the relevant Standard Model background to be reduced significantly. The generation and reconstruction processes are performed by means of the ATLAS common software framework ATHENA.
A direct search for charged lepton-flavour violation in top-quark decays is presented. The data analysed correspond to $79.8 text{fb}^{-1}$ of proton--proton collisions at a centre-of-mass energy of $sqrt{s}=13 text{TeV}$ recorded by the ATLAS experiment at the LHC. The process studied is the production of top-quark pairs, where one top quark decays into a pair of opposite-sign different-flavour charged leptons and an up-type quark, while the other decays semileptonically according to the Standard Model. The signature of the signal is thus characterised by the presence of three charged leptons, a light jet and a $b$-jet. A multivariate discriminant is deployed and its distribution used as input to extract the signal strength. In the absence of a signal, an upper limit on the branching ratio of ${cal B}(t to ell ell q) < 1.86 times 10^{-5}$ is set at the 95% confidence level.
Most limits on the fourth generation heavy top quark (the t) are based on the assumed dominance of t -> Wb, which is expected to be case in the minimal fourth generation framework with a single Higgs (the so called SM4). Here we show, within a variant of a Two Higgs Doublet Model with four generations of fermions, that, in general, a different t detection strategy is required if the physics that underlies the new heavy fermionic degrees of freedom goes beyond the naive SM4. We find that the recent CMS lower bounds: m_{t}< 450 GeV in the semi-leptonic channel pp -> tt -> l u qqbb and m_{t}< 557 GeV in the dilepton channel pp -> tt ->ll u u bb, that were obtained using the customary (SM4-driven) detection strategies, do not apply. In particular, we demonstrate that if the decay t -> ht dominates, then applying the standard CMS search tools leads to a considerably relaxed lower bound: m_{t} >~350 GeV. We, therefore, suggest an alternative search strategy that is more sensitive to beyond SM4 dynamics of the fourth generation fermions.
We report on D0 searches for leptoquarks (LQ) predicted in extended gauge theories and composite models to explain the symmetry between quarks and leptons. Data samples obtained with the D0 detector from proton-antiproton collisions at a center-of-mass energy of 1.96 TeV corresponding to intergrated luminosities of 1--4 inverse-fb were analyzed. No evidence for the production of such particles were observed and lower limits on leptoquark masses are set.
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