Scopus İndeksli Yayınlar Koleksiyonu / Scopus Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7148
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Article Citation - WoS: 16Citation - Scopus: 16Stop on Top: Susy Parameter Regions and Fine-Tuning Constraints(American Physical Society, 2014) Demir, Durmuş Ali; Ün, Cem SalihWe analyze minimal supersymmetric models in order to determine in what parameter regions with what amount of fine-tuning they are capable of accommodating the LHC-allowed top-stop degeneracy window. The stops must be light enough to enable Higgs naturalness yet heavy enough to induce a 125 GeV Higgs boson mass. These two constraints imply a large mass splitting. By an elaborate scan of the parameter space, we show that the stop-on-top scenario requires at least ΔCMSSM≃O(104) fine-tuning in the constrained minimal supersymmetric Standard Model (CMSSM). By relaxing the CMSSM parameter space with nonuniversal Higgs masses, we find that ΔNUHM1≃O(104). The CMSSM with a gravitino lightest supersymmetric particle works slightly better than the nonuniversal Higgs mass model. Compared to all these, the CMSSM with μ<0 and nonuniversal gauginos yields a much smaller fine-tuning Δμ,g≃O(100). Our results show that the gaugino sector can pave the road toward a more natural stop-on-top scenario.Article Citation - WoS: 22Citation - Scopus: 38Combined Search for the Quarks of a Sequential Fourth Generation(American Physical Society, 2012) CMS Collaboration; Karapınar, GülerResults are presented from a search for a fourth generation of quarks produced singly or in pairs in a data set corresponding to an integrated luminosity of 5fb-1 recorded by the CMS experiment at the LHC in 2011. A novel strategy has been developed for a combined search for quarks of the up and down type in decay channels with at least one isolated muon or electron. Limits on the mass of the fourth-generation quarks and the relevant Cabibbo-Kobayashi-Maskawa matrix elements are derived in the context of a simple extension of the standard model with a sequential fourth generation of fermions. The existence of mass-degenerate fourth-generation quarks with masses below 685GeV is excluded at 95% confidence level for minimal off-diagonal mixing between the third- and the fourth-generation quarks. With a mass difference of 25GeV between the quark masses, the obtained limit on the masses of the fourth-generation quarks shifts by about ±20GeV. These results significantly reduce the allowed parameter space for a fourth generation of fermions. © 2012 CERN.Article Citation - WoS: 20Citation - Scopus: 45Search for Pair Production of First- and Second-Generation Scalar Leptoquarks in Pp Collisions at ?s=7tev(American Physical Society, 2012) CMS Collaboration; Karapınar, GülerResults are presented from a search for the pair production of first- and second-generation scalar leptoquarks in proton-proton collisions at √s=7TeV. The data sample corresponds to an integrated luminosity of 5.0fb -1, collected by the CMS detector at the LHC. The search signatures involve either two charged leptons of the same flavor (electrons or muons) and at least two jets or a single charged lepton (electron or muon), missing transverse energy, and at least two jets. If the branching fraction of the leptoquark decay into a charged lepton and a quark is assumed to be β=1, leptoquark pair production is excluded at the 95% confidence level for masses below 830 GeV and 840 GeV for the first and second generations, respectively. For β=0.5, masses below 640 GeV and 650 GeV are excluded. These limits are the most stringent to date. © 2012 CERN.