WoS İndeksli Yayınlar Koleksiyonu / WoS Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7150
Browse
42 results
Search Results
Now showing 1 - 10 of 42
Article Citation - WoS: 13Scalar Neutrinos at the Lhc(American Physical Society, 2011) Demir, Durmuş Ali; Frank, Mariana; Selbuz, Levent; Turan, IsmailWe study a softly broken supersymmetric model whose gauge symmetry is that of the standard model gauge group times an extra Abelian symmetry U(1)'. We call this gauge-extended model the U(1)' model, and we study a U(1)' model with a secluded sector such that neutrinos acquire Dirac masses via higher-dimensional terms allowed by the U(1)' invariance. In this model the mu term of the minimal supersymmetric model (MSSM) is dynamically induced by the vacuum expectation value of a singlet scalar. In addition, the model contains exotic particles necessary for anomaly cancellation, and extra singlet bosons for achieving correct Z'/Z mass hierarchy. The neutrinos are charged under U(1)', and thus, their production and decay channels differ from those in the MSSM in strength and topology. We implement the model into standard packages and perform a detailed analysis of sneutrino production and decay at the Large Hadron Collider, for various mass scenarios, concentrating on three types of signals: (1) 0l + MET, (2) 2l + MET, and (3) 4l + MET. We compare the results with those of the MSSM whenever possible, and analyze the standard model background for each signal. The sneutrino production and decays provide clear signatures enabling distinction of the U(1)' model from the MSSM at the LHC.Article Citation - WoS: 16Citation - Scopus: 16Riemann-Eddington Theory: Incorporating Matter, Degravitating the Cosmological Constant(American Physical Society, 2014) Demir, Durmuş AliHere we show that Eddington's pure affine gravity, when extended with Riemann curvature, leads to gravitational field equations that incorporate matter. This Riemanned Eddington gravity outfits a setup in which matter gravitates normally with Newton's constant but vacuum gravitates differently with an independent gravitational constant. This novel setup enables degravitation of the vacuum to observed level not by any fine-tuning but by a large hierarchy between its gravitational constant and its energy density. Remarkably, degravitation of the cosmological constant is local, causal and natural yet only empirical because the requisite degravitation condition is not predicted by the theory.Article Citation - WoS: 100Citation - Scopus: 81Search for Physics Beyond the Standard Model in Final States With a Lepton and Missing Transverse Energy in Proton-Proton Collisions at Root S = 8 Tev(American Physical Society, 2015) Demir, Durmuş Ali; Karapınar, GülerA search for new physics in proton-proton collisions having final states with an electron or muon and missing transverse energy is presented. The analysis uses data collected in 2012 with the CMS detector, at an LHC center-of-mass energy of 8 TeV, and corresponding to an integrated luminosity of 19.7 fb(-1). No significant deviation of the transverse mass distribution of the charged lepton-neutrino system from the standard model prediction is found. Mass exclusion limits of up to 3.28 TeVat 95% confidence level for a W0-boson with the same couplings as that of the standard model W-boson are determined. Results are also derived in the framework of split universal extra dimensions, and exclusion limits on Kaluza-Klein Wd(KK)((2)) states are found. The final state with large missing transverse energy also enables a search for dark matter production with a recoiling W-boson, with limits set on the mass and the production cross section of potential candidates. Finally, limits are established for a model including interference between a left-handed W'-boson and the standard model W-boson and for a compositeness model.Article Citation - WoS: 183Citation - Scopus: 184Evidence for Transverse-Momentum and Pseudorapidity-Dependent Event-Plane Fluctuations in Pbpb and Ppb Collisions(American Physical Society, 2015) Karapınar, GülerA systematic study of the factorization of long-range azimuthal two-particle correlations into a product of single-particle anisotropies is presented as a function of pT and nu of both particles and as a function of the particle multiplicity in PbPb and pPb collisions. The data were taken with the CMS detector for PbPb collisions at root sNN = 2.76 TeV and pPb collisions at root sNN = 5.02 TeV, covering a very wide range of multiplicity. Factorization is observed to be broken as a function of both particle pT and nu. When measured with particles of different pT, the magnitude of the factorization breakdown for the second Fourier harmonic reaches 20% for very central PbPb collisions but decreases rapidly as the multiplicity decreases. The data are consistent with viscous hydrodynamic predictions, which suggest that the effect of factorization breaking is mainly sensitive to the initial-state conditions rather than to the transport properties (e.g., shear viscosity) of the medium. The factorization breakdown is also computed with particles of different nu. The effect is found to be weakest for mid-central PbPb events but becomes larger for more central or peripheral PbPb collisions, and also for very-high-multiplicity pPb collisions. The nu-dependent factorization data provide new insights to the longitudinal evolution of the medium formed in heavy ion collisions.Article Citation - WoS: 26Citation - Scopus: 26Induced Affine Inflation(American Physical Society, 2018) Azri, Hemza; Demir, Durmuş AliInduced gravity, metrical gravity in which gravitational constant arises from vacuum expectation value of a heavy scalar, is known to suffer from Jordan frame vs Einstein frame ambiguity, especially in inflationary dynamics. Induced gravity in affine geometry, as we show here, leads to an emergent metric and gravity scale, with no Einstein-Jordan ambiguity. While gravity is induced by the vacuum expectation value of the scalar field, nonzero vacuum energy facilitates generation of the metric. Our analysis shows that induced gravity results in a relatively large tensor-to-scalar ratio in both metrical and affine gravity setups. However, the fact remains that the induced affine gravity provides an ambiguity-free framework.Article Citation - WoS: 47Citation - Scopus: 42Affine Inflation(American Physical Society, 2017) Azri, Hemza; Demir, Durmuş AliAffine gravity, a gravity theory based on affine connection with no notion of metric, supports scalar field dynamics only if scalar fields have nonvanishing potential. The nonvanishing vacuum energy ensures that the cosmological constant is nonvanishing. It also ensures that the energy-momentum tensor of vacuum gives the dynamically generated metric tensor. We construct this affine setup and study primordial inflation in it. We study inflationary dynamics in affine gravity and general relativity, comparatively. We show that nonminimally coupled inflaton dynamics can be transformed into minimally coupled ones with a modified potential. We also show that there is one unique frame in affine gravity, as opposed to the Einstein and Jordan frames in general relativity. Future observations with higher accuracy may be able to test affine gravity.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: 45Citation - Scopus: 47Search for Stopped Gluinos in Pp Collisions at ?s=7tev(American Physical Society, 2011) Karapınar, Güler; Demir, Durmuş AliThe results of the first search for long-lived gluinos produced in 7 TeV pp collisions at the CERN Large Hadron Collider are presented. The search looks for evidence of long-lived particles that stop in the CMS detector and decay in the quiescent periods between beam crossings. In a dataset with a peak instantaneous luminosity of 1×1032cm-2s-1, an integrated luminosity of 10pb-1, and a search interval corresponding to 62 hours of LHC operation, no significant excess above background was observed. Limits at the 95% confidence level on gluino pair production over 13 orders of magnitude of gluino lifetime are set. For a mass difference m g-mχ10>100GeV/c2, and assuming BR(g→gχ10)= 100%, mg<370GeV/c2 are excluded for lifetimes from 10μs to 1000 s. © 2010 The American Physical Society.Article Citation - WoS: 77Citation - Scopus: 86Measurement of the Isolated Prompt Photons Production Cross Section in Pp Collisions at ?s=7tev(American Physical Society, 2011) Karapınar, Güler; Demir, Durmuş AliThe differential cross section for the inclusive production of isolated prompt photons has been measured as a function of the photon transverse energy ETγ in pp collisions at √s=7TeV using data recorded by the CMS detector at the LHC. The data sample corresponds to an integrated luminosity of 2.9pb-1. Photons are required to have a pseudorapidity |ηγ|<1.45 and ETγ>21GeV, covering the kinematic region 0.006<xT<0.086. The measured cross section is found to be in agreement with next-to-leading-order perturbative QCD calculations. © 2011 American Physical Society.Article Citation - WoS: 87Citation - Scopus: 115Measurement of the B+ Production Cross Section in Pp Collisions at ?s=7tev(American Physical Society, 2011) Karapınar, Güler; Demir, Durmuş AliMeasurements of the total and differential cross sections dσ/dpTB and dσ/dyB for B+ mesons produced in pp collisions at √s=7TeV are presented. The data correspond to an integrated luminosity of 5.8pb-1 collected by the CMS experiment operating at the LHC. The exclusive decay B+→J/ψK+, with J/ψ→μ+μ-, is used to detect B+ mesons and to measure the production cross section as a function of pTB and yB. The total cross section for pTB>5GeV and |yB|<2.4 is measured to be 28.1±2.4±2.0±3.1μb, where the first uncertainty is statistical, the second is systematic, and the last is from the luminosity measurement. © 2011 American Physical Society.