Physics / Fizik
Permanent URI for this collectionhttps://hdl.handle.net/11147/6
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Article Citation - WoS: 32Citation - Scopus: 34The Cms Barrel Calorimeter Response To Particle Beams From 2 To 350 Gev/C(Springer Verlag, 2009) CMS HCAL/ECAL Collaborations; Sönmez, NasufThe response of the CMS barrel calorimeter (electromagnetic plus hadronic) to hadrons, electrons and muons over a wide momentum range from 2 to 350 GeV/c has been measured. To our knowledge, this is the widest range of momenta in which any calorimeter system has been studied. These tests, carried out at the H2 beam-line at CERN, provide a wealth of information, especially at low energies. The analysis of the differences in calorimeter response to charged pions, kaons, protons and antiprotons and a detailed discussion of the underlying phenomena are presented. We also show techniques that apply corrections to the signals from the considerably different electromagnetic (EB) and hadronic (HB) barrel calorimeters in reconstructing the energies of hadrons. Above 5 GeV/c, these corrections improve the energy resolution of the combined system where the stochastic term equals 84.7 ± 1.6% and the constant term is 7.4 ± 0.8%. The corrected mean response remains constant within 1.3% rms. © Springer-Verlag / Società Italiana di Fisica 2009.Article Citation - WoS: 12Citation - Scopus: 15Local Oxidation Nanolithography on Hf Thin Films Using Atomic Force Microscopy (afm)(IOP Publishing Ltd., 2009) Büyükköse, Serkan; Okur, Salih; Özyüzer, Gülnur AygünWell controlled Hf oxide patterns have been grown on a flat Hf thin film surface produced by the dc magnetron sputtering method on Si and SiOx substrates. These patterns have been created by using the technique of semi-contact scanning probe lithography (SC-SPL). The thickness and width of the oxide patterns have been measured as a function of applied voltage, duration and relative humidity. There is a threshold voltage even at 87% humidity, due to insufficient energy required to start the oxide growth process for a measurable oxide protrusion. Electrical characterization was also performed via the I-V curves of Hf and HfOx structures, and the resistivity of HfO x was found to be 4.284 × 109 Ω cm. In addition to the I-V curves, electric force microscopy and spreading surface resistance images of Hf and HfOx were obtained.Article Citation - WoS: 7Citation - Scopus: 8A Way To Get Rid of Cosmological Constant and Zero-Point Energy Problems of Quantum Fields Through Metric Reversal Symmetry(IOP Publishing Ltd., 2008) Erdem, RecaiIn this paper, a framework is introduced to remove the huge discrepancy between the empirical value of the cosmological constant and the contribution to the cosmological constant predicted from the vacuum energy of quantum fields. An extra-dimensional space with metric reversal symmetry and R2 gravity (that reduces to the usual R gravity after integration over extra dimensions) is considered to this end. The resulting four-dimensional energy-momentum tensor (obtained after integration over extra dimensions) consists of terms that contain off-diagonally coupled pairs of Kaluza-Klein modes. This, in turn, generically results in the vanishing of the vacuum expectation value of the energy-momentum tensor for quantum fields, and offers a way to solve the problem of huge contribution of quantum fields to the vacuum energy density.Article Citation - WoS: 43Citation - Scopus: 45Electrical and Interface Properties of Au/Dna Organic-On Structures(Elsevier Ltd., 2009) Okur, Salih; Yakuphanoğlu, Fahrettin; Özsöz, Mehmet; Kadayıfçılar, Pınar KaraThe effect of the thickness and coverage rate of a DNA film on the electrical and interface properties of Au/DNA/n-Si organic-on-inorganic structures has been investigated. The thin film properties of the DNA deposited on n-Si wafer were characterized by atomic force microscopy. The effect of the thickness and coverage rate of the DNA layer was investigated by evaluating electrical parameters, such as the barrier height, ideality factor, series resistance, and interface state density. The thickness and coverage rate of the DNA layer significantly affects the electrical properties of the Au/DNA/n-Si organic-on-inorganic structures. The interface state density properties of the Au/DNA/n-Si diodes were determined by conductance technique. The results show that the interface state density decreases with decrease in both film thickness and coverage rate of the DNA in an acetate buffer, modifying the electronic parameters of the Au/DNA/n-Si diodes.Article Citation - WoS: 12Citation - Scopus: 12Modification of Metal/Semiconductor Junctions by Self-Assembled Monolayer Organic Films(Elsevier Ltd., 2009) Yakuphanoğlu, Fahrettin; Okur, Salih; Özgener, HüseyinTwo new metal/molecule/semiconductor contacts, Au/n-Si/TDA/Au and Au/p-Si/ODM/Au, were fabricated to understand effect of organic compounds, tridecylamine and octadecylmercaptan self-assembled monolayer (SAM) films, on electrical charge transport properties of the metal/semiconductor junctions. The morphology of the organic monolayers deposited on Si substrates was investigated by atomic force microscopy. The molecular coverage of ODM deposited on p-Si is poorer than that of TDA on n-Si substrate. The ideality factors of the p-Si/ODM and n-Si/TDA diodes were found to be 1.66 and 1.48, respectively. The electrical results show that the tridecylamine monolayer passivated junction has a lower ideality factor. The ideality factor indicates clear dependence on two different type functional groups R-SH (Thiol) and R-NH2 (Amin) groups and it increases with different functional groups of organic molecule. The barrier height φb value of the n-Si/TDA diode is smaller than that of p-Si/ODM diode, as a result of chain length of the SAM organic molecules. The interface state density Dit values of the diodes were determined using conductance technique. The n-Si/TDA diode has the smaller interface state density according to p-Si/ODM diode. We have evaluated that the organic molecules control the electronic parameters of metal/semiconductor diodes and thus, organic modification helps to get one step closer towards to new organic assisted silicon based microelectronic devices.Article Citation - WoS: 40Citation - Scopus: 45Terahertz Wave Emission From Intrinsic Josephson Junctions in High- Tc Superconductors(IOP Publishing Ltd., 2009) Özyüzer, Lütfi; Şimşek, Yılmaz; Köseoğlu, Hasan; Türkoğlu, Fulya; Kurter, Cihan; Welp, U.; Koshelev, A. E.; Gray, Kenneth E.; Kwok, W. K.; Yamamoto, T.; Kadowaki, K.; Koval, Yu I.; Wang, Huabing; Müller, Paul H.Recently, we experimentally demonstrated that rectangular mesa structures of intrinsic Josephson junctions (IJJ) in Bi2Sr2CaCu 2O8+d (Bi2212) can be used as a compact solid-state generator of continuous, coherent and polarized terahertz (THz) radiation. In the present work, we will exhibit tall mesas (over 600 junctions) which were fabricated using UV lithography, e-beam lithography with photoresist and e-beam lithography with a Ti selective etching technique. We will present measurements of the c-axis resistance as a function of temperature and of current-voltage characteristics of THz emitting mesas with lateral sizes ranging from 30 × 300 to 100 × 300νm2. Furthermore, we will discuss the dependence of the characteristics of the mesa structures on the oxygen doping level of the Bi2212 crystals. We will also experimentally show that the voltage-frequency relation of the ac Josephson effect has to match the cavity resonance for successful emission.Article Citation - WoS: 3Citation - Scopus: 2Signal Enhancement Techniques for Rf Squid Based Magnetic Imaging Systems(IOP Publishing Ltd., 2006) Akram, Rizwan; Fardmanesh, Mehdi; Schubert, Juergen; Zander, Willi; Banzet, Marko; Lomparski, Dieter; Schmidt, Miak; Krause, H. J.We have investigated the rf SQUID (radio-frequency superconducting quantum interference device) and its coupling to tank circuit configurations to achieve an optimal front-end assembly for sensitive and high spatial resolution magnetic imaging systems. The investigation of the YBCO rf SQUID coupling to the conventional LC tank circuits revealed that coupling from the back of the SQUID substrate enhances the SQUID signal while facilitating the front-end assembly configuration. The optimal thickness of the substrate material between the SQUID and the tank circuit is 0.4 mm for LaAlO3 resulting in an increase of the SQUID flux-voltage transfer function signal, Vspp, of 1.5 times, and 0.5 mm for SrTiO3 with an increase of V spp of 1.62 times compared to that for direct face to face couplings. For rf coupling with a coplanar resonator, it has been found that the best configuration, in which a resonator is sandwiched between the SQUID substrate and the resonator substrate, provides a Vspp about 3.4 times higher than that for the worse case where the resonator and the SQUID are coupled back to back. The use of a resonator leads to a limitation of the achievable spatial resolution due to its flux focusing characteristics. This resulted in a favouring of the use of the conventional tank circuits when considering the desired high spatial resolution. The effect of the YBCO flip chip magnetic shielding of the SQUIDs in the back-coupling with the LC tank circuit configuration has also been investigated, with a view to reducing the SQUID effective area to increase the spatial resolution and also for studying the effect of the coupling of various kinds of transformers to the SQUIDs. It is revealed that there is no very considerable change in the flux-voltage transfer function signal level with respect to the effective shield area, while the lowest working temperature of the SQUIDs was slightly shifted higher by a couple of degrees, depending on the shield area.Article Citation - WoS: 3Citation - Scopus: 3Reconsidering extra time-like dimensions(Springer Verlag, 2006) Erdem, Recai; Ün, Cem SalihIn this study we reconsider the phenomenological problems related to tachyonic modes in the context of extra time-like dimensions. First we reconsider a lower bound on the size of extra time-like dimensions and improve on the conclusion in the literature. Next we discuss the issues of spontaneous decay of stable fermions through tachyonic decays and disappearance of fermions due to tachyonic contributions to their self-energies. We find that the tachyonic modes due to extra time-like dimensions are less problematic than the tachyonic modes in the usual 4-dimensional setting because the most troublesome Feynman diagrams are forbidden once the conservation of momentum in the extra time-like dimensions is imposed.Article Citation - WoS: 6Citation - Scopus: 11Electrical and Mechanical Properties of Superconducting Mgb2/Mg Metal Matrix Composites(IOP Publishing Ltd., 2006) Eğilmez, Mehmet; Özyüzer, Lütfi; Tanoğlu, Metin; Okur, Salih; Kamer, Orhan; Öner, YıldırhanMgB2/Mg composites were prepared using a metal matrix composite fabrication method that offers the potential to produce superconducting wires as an alternative approach to the powder in tube process. To obtain composites, MgB2 and Mg powders were mixed at different weight fractions and uniaxially pressed in a cylindrical die under the pressure of 0.5 and 1.0GPa for two hours at various temperatures. The x-ray diffraction technique was used for phase identification. Temperature dependence of resistivity and magnetization measurements were carried out to determine superconducting properties. The effects of composite fabrication temperature and the addition of the Mg on the mechanical properties of MgB2/Mg composites were investigated. For this purpose, the compressive mechanical testing was performed to measure the elastic modulus and fracture strength values of the composites. It was found that the relative weight fraction of the Mg and the fabrication conditions of the composites have considerable effect on the superconducting and mechanical properties of the composites.Article Citation - WoS: 775Citation - Scopus: 759CMS physics technical design report, volume II: Physics performance(IOP Publishing Ltd., 2007) Demir, Durmuş Ali; Karapınar, GülerCMS is a general purpose experiment, designed to study the physics of pp collisions at 14 TeV at the Large Hadron Collider (LHC). It currently involves more than 2000 physicists from more than 150 institutes and 37 countries. The LHC will provide extraordinary opportunities for particle physics based on its unprecedented collision energy and luminosity when it begins operation in 2007. The principal aim of this report is to present the strategy of CMS to explore the rich physics programme offered by the LHC. This volume demonstrates the physics capability of the CMS experiment. The prime goals of CMS are to explore physics at the TeV scale and to study the mechanism of electroweak symmetry breaking - through the discovery of the Higgs particle or otherwise. To carry out this task, CMS must be prepared to search for new particles, such as the Higgs boson or supersymmetric partners of the Standard Model particles, from the start-up of the LHC since new physics at the TeV scale may manifest itself with modest data samples of the order of a few fb-1 or less. The analysis tools that have been developed are applied to study in great detail and with all the methodology of performing an analysis on CMS data specific benchmark processes upon which to gauge the performance of CMS. These processes cover several Higgs boson decay channels, the production and decay of new particles such as Z′ and supersymmetric particles, Bs production and processes in heavy ion collisions. The simulation of these benchmark processes includes subtle effects such as possible detector miscalibration and misalignment. Besides these benchmark processes, the physics reach of CMS is studied for a large number of signatures arising in the Standard Model and also in theories beyond the Standard Model for integrated luminosities ranging from 1 fb-1 to 30 fb-1. The Standard Model processes include QCD, B-physics, diffraction, detailed studies of the top quark properties, and electroweak physics topics such as the W and Z0 boson properties. The production and decay of the Higgs particle is studied for many observable decays, and the precision with which the Higgs boson properties can be derived is determined. About ten different supersymmetry benchmark points are analysed using full simulation. The CMS discovery reach is evaluated in the SUSY parameter space covering a large variety of decay signatures. Furthermore, the discovery reach for a plethora of alternative models for new physics is explored, notably extra dimensions, new vector boson high mass states, little Higgs models, technicolour and others. Methods to discriminate between models have been investigated. This report is organized as follows. Chapter 1, the Introduction, describes the context of this document. Chapters 2-6 describe examples of full analyses, with photons, electrons, muons, jets, missing E T, B-mesons and τ's, and for quarkonia in heavy ion collisions. Chapters 7-15 describe the physics reach for Standard Model processes, Higgs discovery and searches for new physics beyond the Standard Model.
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