Observability of light charged Higgs decay to muon in top quark pair events at LHC

In this paper the charged Higgs signal through the decay to a pair of muon and neutrino (H ^±→μν) is analyzed. The analysis attempts to estimate the amount of muonic signal of the charged Higgs at LHC at a center of mass energy of 14 TeV. The signal process is the top quark pair production with one of the top quarks decaying to a charged Higgs (non SM anomalous top decay) and the other decaying to a W boson which is assumed to decay hadronically to two light jets. Due to the small branching ratio of charged Higgs decay to muon, results are quoted for data corresponding to an integrated luminosity of 300 fb⁻¹ which is expected to be collected at the LHC high luminosity regime. It is shown that a signal significance close to 5σ down to below 1σ is achievable for a charged Higgs mass in the range 80 GeV<m(H ^±)<150 GeV taking the top quark pair production with both top quarks decaying to W bosons as the main irreducible background.     

Thermal properties of the alloys Ni,Ru and Cr with Fe

The thermal expansion coefficient α of the Fe-Ni, Fe-Cr and Fe₇₀Ni_30-xRu_x alloys was studied over the temperature range from 4,2 to 300 K. The magnetic contribution to α for all investigated alloys is obtained. The stabilization of the γ-phase in Fe₇₀Ni₃₀ alloys by small additions of ruthenium is shown to lead to the appearance of Invar anomalies of the thermal expansion coefficient. The magnetic contribution to α of Fe-Ni and Fe-Cr alloys is shown to have the same character despite the difference of crystal structure of these alloys.     

Density functional theory analysis of reactivity of PtxPdy alloy clusters

We investigate the reactivity of various Pt_xPd_y combinations (with x + y = 10 and various x:y ratios) towards the adsorption of specific intermediates of the oxygen reduction, using the B3PW91 hybrid density functional theory. The reactivity is shown to be not only sensitive to the composition of the cluster, but also to the atomic distribution. The calculations indicate that two different ensembles: one ordered and one randomly mixed, with overall composition Pt₃Pd₇ are thermodynamically more favorable than pure Pt₁₀ for the oxygen reduction reaction. The reasons for this behavior are clearly explained in terms of the atomic and electronic distribution, which makes the Pd atoms to act as electron donors both to Pt atoms and to the adsorbates, thus the reactivity of the Pd atoms in such environment becomes intermediate between Pt and Pd. Moreover, it is found that in a mixed Pt₃Pd₇ state the electronic distribution makes the average atom more similar to Pt than to Pd, whereas in an ordered Pt₃Pd₇ cluster, the average atom is more similar to Pd than to Pt.     

Energy fluctuations in multichannel fission and heavy ion collisions

A simple theory for the variance σ_E² of the total kinetic energy distribution of the fission fragments is given and compared with the data. It seems to explain the observed variation of σ_E with the mass number as well as the differences of σ_E for the different fission channels due to shell effects. The physical origin of σ_E is supposed to be the permanent thermal noise along the path from the barrier to scission. The same theory is applied to deep inelastic collisions and leads to much larger σ_E in agreement with measurements.     

Microwave spectrum and structure of furfural

The microwave spectrum of furfural was investigated in the frequency range 7 GHz-21 GHz and 49 GHz-330 GHz. The ground and first torsional state of trans-furfural and ground state of cis-furfural were assigned and analyzed. A total of 1720 rotational lines with J up to 100 and K_a up to 53 were assigned to the ground state of trans-furfural, 1406 rotational lines with J up to 100 and K_a up to 48 were assigned to the first torsional state of trans-furfural and 2103 rotational lines with J up to 90 and K_a up to 48 to the ground state of cis-furfural. Accurate sets of centrifugal distortion constants for both conformations have been determined for the first time. The spectra of all ¹³C and ¹⁸O singly substituted isotopic species were observed in natural abundance in the 7 GHz-21 GHz range. Molecular structure co-ordinates, bond lengths and angles of the Kraitchman substitution type (r_s) and pseudo-Kraitchman type (r_pKr) are derived from the isotopic studies.     

Influence of manganese substitution and annealing temperature on the formation,microstructure and magnetic properties of Mn–Zn ferrites

The effects of annealing temperature and manganese substitution on the formation, microstructure and magnetic properties of Mn_xZn_1−xFe₂O₄ (with x varying from 0.3 to 0.9) through a solid-state method have been investigated. The correlation of the microstructure and the grain size with the magnetic properties of Mn–Zn ferrite powders was also reported. X-ray diffraction (XRD), a scanning electron microscope (SEM) and a vibrating sample magnetometer (VSM) were utilized in order to study the effect of variation of manganese substitution and its impact on crystal structure, crystalline size, microstructure and magnetic properties of the ferrite powders formed. The XRD analysis showed that pure single phases of Mn–Zn ferrites were obtained by increasing the annealing temperature to 1200–1300 °C. Increasing the annealing temperature to ?1300 °C led to abnormal grain growth with inter-granular pores and this led to a decrease in the saturation magnetization. Moreover, an increase in the Mn²⁺ ion substitution up to x=0.8 increased the lattice parameter of the formed powders due to the high ionic radii of the Mn²⁺ ion. Mn–Zn ferrites phases were formed and the positions of peaks were shifted by substituting manganese. The average crystalline size was increased by increasing the annealing temperature and decreased by increasing the substitution by manganese up to 0.8. The average crystalline size was in the range 95–137.3 nm. The saturation magnetization of the Mn–Zn-substituted ferrite powders increased continuously with an increase in the Mn concentration up to 0.8 at annealing temperatures of 1200–1300 °C. Further increase of Mn substitution up to 0.9 led to a decrease of saturation magnetization. The saturation magnetization increased from 17.3 emu/g for the Mn_0.3Zn_0.7Fe₂O₄ phase particles produced to 59.08 emu/g for Mn_0.8Mn_0.2Fe₂O₄ particles.     

High temperature NMR in vanadium: Electron paramagnetism and atomic diffusion effects

We present preliminary results on Knight shift T₁ and T₂ measurements between 300 and 1700 K. We have observed the motional narrowing due to the self diffusion as well as a strong quadrupolar contribution to T₁ due to the diffusion of interstitial gases. K varies from 0.58 to 0.63%. This temperature dependence is shown to be mainly due to an intrinsic temperature effect. The high temperature Korringa like behaviour of T₁ with T₁T = 1.05 sec. K is explained in terms of the temperature dependence of the d spin contribution.     

Renormalization-group improvement of effective actions beyond summation of leading logarithms

Invariance of the effective action under changes of the renormalization scale μ leads to relations between those (presumably calculated) terms independent of μ at a given order of perturbation theory and those higher-order terms dependent on logarithms of μ. This relationship leads to differential equations for a sequence of functions, the solutions of which give closed form expressions for the sum of all leading logs, next to leading logs, and subsequent subleading logarithmic contributions to the effective action. The renormalization group is thus shown to provide information about a model beyond the scale dependence of the model's couplings and masses. This procedure is illustrated using the φ₆³ model and Yang–Mills theory. In the latter instance, it is also shown by using a modified summation procedure that the μ dependence of the effective action resides solely in a multiplicative factor of g²(μ) (the running coupling). This approach is also shown to lead to a novel expansion for the running coupling in terms of the one-loop coupling that does not require an order-by-order redefinition of the scale factor ΛQCD. Finally, logarithmic contributions of the instanton size to the effective action of an SU(2) gauge theory are summed, allowing a determination of the asymptotic dependence on the instanton size ρ as ρ goes to infinity to all orders in the SU(2) coupling constant.     

Magnetic properties of titanium vanadium hydrides

Measurements have been made of the magnetic susceptibility X in ternary titanium-vanadium hydrides Ti_1?yV_yH_x in the range 0<y< 0.5 and with a hydrogen to metal ratio from 1.6 to 1.92; they cover the temperature interval from 80 to 440 K. The x^?T curves of some of the ternary hydrides possess a maximum similar to that seen in binary hydrides. Its occurrence depends upon both hydrogen and vanadium concentration. Comparison with the lattice constants shows that this dependence is related to the transition from the cubic γ-phase to the tetragonal δ-phase. The x^?T curves of those samples showing the phase transition were extrapolated from the cubic phase down to lower temperatures. Conclusions were drawn from the measured and extrapolated susceptibility values, as to the influence of both hydrogen and vanadium concentrations on the electronic structure of these hydrides. The dependence of the magnetic susceptibility on the vanadium concentration shows that, in the cubic phase, the fermi energy lies on the increasing side of a maximum in the density of states curve. The degree of occupation of the conduction band does not depend on the hydrogen concentration. The rigid band model cannot be used in the hydrides studied here to account for the effects of varying their hydrogen concentration.     

Effect of Sr content on structure and electrical properties of La1−x Sr x MnO3 from ITSOFC cathode view point

The samples belonging to La_1−x Sr _x MnO₃ series, prepared by combustion route without using fuel, exhibit crystal structural phase transition with the change in Sr content. Less than 40 mol% Sr is partially substituted in the crystal structure of LaMnO₃. The structural phase transition from rhombohedral to cubic, cubic to tetragonal, and tetragonal to orthorhombic takes place on 40, 60, and 80 mol% addition of Sr. The highest electrical conductivity in La_0.4Sr_0.6MnO₃ is understood to be due to the maximum concentration of polaron. The polarons are formed due to the conversion of Mn³⁺ to Mn⁴⁺ so as to achieve electroneutrality after substitution of Sr²⁺ for La³⁺.     

Laser-induced changes in the photoelectric properties of MnxHg1−xTe crystals

The application of pulsed laser irradiation to photoconductive n-Mn_xHg_1−xTe crystals was investigated as a possible procedure for modifying their photoelectric characteristics and increasing the photosensitivity. The photoconductivity spectra and the temperature dependences of the excess carrier lifetime of Mn_xHg_1−xTe crystals, subjected to laser irradiation with nanosecond ruby laser pulses, were studied. It was found that a range of energy density of laser pulses can be chosen to decrease the surface recombination rate and to increase the photosensitivity of the crystals. Changes in the photoelectric properties of the irradiated samples are attributed to the laser-stimulated cleaning of the surface as well as to modification of the defect structure of Mn_xHg_1−xTe crystals.     

Influence of cation substitution on the magnetic properties of the FeCr2S4 ferrimagnet

The influence of cation substitution on the magnetic properties of single and polycrystals of FeCr₂S₄ spinel has been studied. The tetrahedral A-site substitution of the Fe by Cu in Fe_1−xCu_xCr₂S₄ was found to increase significantly the value of temperature T_m of the spin-glass like magnetization anomaly, whereas the octahedral B-site substitution of the Cr by In decreases T_m. This effect is suggested to result from a structural transformation influenced by variation of internal (chemical) pressure due to lattice contraction (Cu) or expansion (In). The observed reduced values of the Curie temperature for Cu-substituted single crystals compared to that of the polycrystalline samples are attributed to presence of Cl ions in samples detected by electron-probe microanalysis. The observed reduced value of saturation magnetization in the polycrystals compared to the single crystals is ascribed to the effect of surface anisotropy. Based on the experimental data the superexchange is concluded to be the dominant exchange interaction for 0≤x≤0.5 in Fe_1−xCu_xCr₂S₄, whereas the indirect exchange through the charge carriers is considered of minor importance.     

Multi-mode absorption spectroscopy of oxygen for measurement of concentration, temperature and pressure

The use of multi-mode absorption spectroscopy (MUMAS) to detect multiple transitions in the A-band b¹Σ_g ⁺-X³Σ_g ^- of molecular oxygen is reported. The modelling of MUMAS signatures and the procedure for fitting such model signatures to experimental data obtained using a multi-mode diode laser is described. The technique is shown to allow accurate and precise measurement of concentration, temperature over the range 300 to 500 K and of pressure over the range 0.2 to 1 bar. Extension of the technique to other ranges of temperature and pressure and to other species is discussed. PACS 42.62.Fi; 33.20.Kf     

Optical properties of methane to 288 GPa at 300 K

Optical properties of solid methane (CH₄) were studied at high pressure and room temperature using a diamond anvil cell. Reflectivity and transmission measurements were used to measure the refractive index to 288 GPa. Fabry-Perot interferometery was used to measure the sample thickness to 172 GPa. This data was fitted to the derived expression of thickness vs. pressure that was then used to calculate the thickness to 288 GPa. This in turn was combined with optical absorption experiments to obtain the absorption coefficient and hence the extinction coefficient k^*. From combined reflection and absorption experiments the refractive index n=n_s+ik^* was obtained. The index of refraction and the ratio of molar refraction to molar volume showed a large increase between 208 and 288 GPa. This behavior indicated that a phase transformation of insulator-semiconductor might have occurred in solid CH₄ by 288 GPa.     

Local variation of the dielectric properties of poly(vinylidene fluoride) during the α- to β-phase transformation

The phase transformation from the non-polar α-phase to the polar electroactive β-phase of polyvinylidene fluoride (PVDF) has been investigated using the fluorescence from Nile red. Films of α-PVDF doped with Nile red were stretched at controlled rates at a temperature of 80 °C to produce the α- to β-phase transition. The thermo/mechanical dependent changes in the crystalline structure are related to the physical rotation of the polar (CH₂-CF₂) group, which can be monitored by steady state fluorescence techniques. The degree of phase transformation is related to variation in the fluorescence, which in turn is linked to local dielectric constant of the polymer. The variation of the refractive index is more associated to the alignment of the polymeric chains than to the phase transformation. Thus, fluorescence is a suitable technique to monitor phase transitions coupled to a variation in the polarity of the dielectric medium.     

Evidence of formation of tetravacancies in uniformly oxygen irradiated n-type silicon

High purity n-type silicon single crystal with resistivity in the order of 4000 Ω cm has been irradiated with high-energy oxygen ions at room temperature up to a fluence of 5E15 ions/cm². The energy of the beam was varied from 3 to 140 MeV using a rotating degrader to achieve a depthwise near-uniform implantation profile. Radiation induced defects and their dynamics have been studied using positron annihilation spectroscopy along with isochronal annealing up to 700 °C in steps of 50 °C for 30 min. After annealing the sample at 200 °C for 30 min, formation of silicon tetravacancies has been noticed. The formation of the tetravacancies was found to be due to agglomeration of divacancies present in the irradiated sample. An experimentally obtained positron lifetime value of 338±10 ps has been reported for silicon tetravacancies, which has a very close agreement with the value obtained from recent theoretical calculations. The tetravacancies were found to dissociate into trivacancy clusters upon further annealing. The trivacancies thus obtained were observed to agglomerate beyond 400 °C to form larger defect clusters. Finally, all the defects were found to anneal out after annealing the sample at 650 °C.     

Regularization in the J-matrix method of scattering revisited

We present an alternative, but equivalent, approach to the regularization of the reference problem in the J-matrix method of scattering. After identifying the regular solution of the reference wave equation with the “sine-like” solution in the J-matrix approach we proceed by direct integration   to find the expansion coefficients in an L²$L^2$ basis set that ensures a tridiagonal representation of the reference Hamiltonian. A differential equation in the energy is then deduced for these coefficients. The second independent solution of this equation, called the “cosine-like” solution, is derived by requiring it to pertain to the L²$L^2$ space. These requirements lead to solutions that are exactly identical to those obtained in the classical J-matrix approach. We find the present approach to be more direct and transparent than the classical differential approach of the J-matrix method.     

Response of fcc metals and L12 and D022 type trialuminides to uniaxial loading along [100] and [001]: ab initio DFT calculations

Ab initio density-functional calculations have been used to investigate the response of the face-centred cubic (fcc) metals Al and Cu, and of the L1₂- and D0₂₂-type trialuminides Al₃(Sc,Ti,V) to uniaxial loading along the [100] and [001] directions. The results obtained under uniaxial strains are compared to the response to biaxial (epitaxial) strains. The ideal tensile and compressive strengths and their limitation by shear instabilities along these deformation paths have been calculated. Although the response of both pure fcc metals could be expected to be very similar, our results show a fundamental difference: whereas for Cu a special invariant state with C ₂₂?=?C ₂₃, leading to a bifurcation from the tetragonal to an orthorhombic deformation path, is reached at a strain of 10%, for Al this state is reached only at a strain of 33% close to the critical strain defining the ideal tensile strength. The reaction of the L1₂-type trialuminides is comparable to the response of Al; no bifurcation to an orthorhombic deformation path is predicted. The response of the D0₂₂-type trialuminides is different from that of the L1₂-type phases because of the difference in the stacking of the atomic planes along the [001] direction. For D0₂₂-type trialuminides, the uniaxial compression along this direction or epitaxial tension in the (001) plane leads to the formation of a stress-free D0₃ structure, in complete analogy to the fcc???bcc transformations observed for the pure metals. Under uniaxial [100] loading the guiding symmetry along the deformation path is orthorhombic and leads to the formation of special structures under both tension and compression parts, which are related to the D0₃ structure in the same way as the parent D0₂₂-lattice is related to the L1₂ structure.     

The spin-isospin decomposition of the nuclear symmetry energy from low to high density

The energy per particle BA in nuclear matter is calculated up to high baryon density in the whole isospin asymmetry range from symmetric matter to pure neutron matter.The results,obtained in the framework of the Brueckner-Hartree-Fock approximation with two-and three-body forces,confirm the well-known parabolic dependence on the asymmetry parameterβ=(N?Z)/A(β^2 law)that is valid in a wide density range.To investigate the extent to which this behavior can be traced back to the properties of the underlying interaction,aside from the mean field approximation,the spin-isospin decomposition of BA is performed.Theoretical indications suggest that theβ^2 law could be violated at higher densities as a consequence of the three-body forces.This raises the problem that the symmetry energy,calculated according to theβ^2 law as a difference between BA in pure neutron matter and symmetric nuclear matter,cannot be applied to neutron stars.One should return to the proper definition of the nuclear symmetry energy as a response of the nuclear system to small isospin imbalance from the Z=N nuclei and pure neutron matter.     

Study of in-medium <Emphasis Type="Italic">ω</Emphasis>-meson properties in <Emphasis Type="Italic">Ap</Emphasis> and <Emphasis Type="Italic">pA</Emphasis> collisions

The possibility to investigate the in-medium properties of the vector ω mesons at normal nuclear density is considered. The folding model and simulations with the RQMD generator have been used for studying of the ω-resonance production in Ap and pA reactions and its ω → π ⁰ γ → 3γ decay. We show that measurements in the inverse Ap kinematics is an effective way to get information about the ω-meson mass modification especially in not yet explored range of small meson momenta relative to the projectile nuclei where the strength of the effect is expected to be most strong. The traditional pA kinematics appears to be more preferable for the investigation of the in-medium ω-meson width. Using of compact electromagnetic calorimeter provides the possibility to collect large statistics and study the momentum dependencies of both the ω-meson mass and width at the density of normal nuclei.