Photoproduction of charged hadrons at large transverse momenta

A quantitative test of QCD from high energy photoproduction of large transverse momentum charged hadrons, using incident γ energies between 50 and 150 GeV, is presented. The inclusive hadron P₁ and P_t distributions show a clear excess over the VDM contribution. This excess is found to be in good agreement with second-order QCD calculations. This agreement does not depend critically on the choice of the gluon fragmentation function, and is observed over the large kinematical domain covered by this experiment.     

Observation of Vavilov-Cherenkov radiation and EAS charged particles at large zenith angles

Extensive air showers (EASes) at zenith angles of 70–80 degrees with Vavilov-Cherenkov radiation having two and three maxima were registered at the Tian Shan Mountain Station of the Lebedev Physical Institute. In each such event, the subsequent maxima came with a time delay of 100 or more nanoseconds. Extensive air showers at a zenith angle of 70° with charged particles and Vavilov-Cherenkov radiation were also registered.     

A search for charged Higgs bosons at tristan

We searched for pair production of charged Higgs bosons via e⁺e⁻ annihilation, using data (23.3 pb⁻) collected by the TOPAZ detector in the energy range . We observed no evidence for charged Higgs pair production and extended the excluded region in the M_H^±---BR (hadron) plane. The 95% CL lower mass limit is the most stringent for BR (hadron) = 0.6, giving m_H^±<22 GeV.     

Measurement of neutral and charged current cross-sections in positron-proton collisions at large momentum transfer

The inclusive single and double differential cross-sections for neutral and charged current processes with four-momentum transfer squared between 150 and 30 000 GeV and with Bjorken x between 0.0032 and 0.65 are measured in collisions. The data were taken with the H1 detector at HERA between 1994 and 1997, and they correspond to an integrated luminosity of . The evolution of the parton densities of the proton is tested, yielding no significant deviation from the prediction of perturbative QCD. The proton structure function is determined. An extraction of the u and d quark distributions at high x is presented. At high electroweak effects of the heavy bosons and are observed and found to be consistent with Standard Model expectation. Received: 27 August 1999 / Published online: 25 February 2000     

Improving the discovery potential of charged Higgs bosons at the Tevatron and large hadron collider

We outline several improvements to the experimental analyses carried out at Tevatron (Run 2) or simulated in view of the large hadron collider (LHC) that could increase the scope of CDF/D0 and ATLAS/CMS in detecting charged Higgs bosons.     

A phenomenological bound for charged and neutral D meson life times

It is shown that recently reported branching ratios of $\text{D}\text{→}\text{K}\text{π}$ and Δ = 1 property of weak nonleptonic hamiltonian for ΔC =ΔS = ±1 processes as give a phenomenological bound for χ(D⁺)/χ((D⁰). Also, using previously calculated values of χ(D→ e^±X), the total widths of neutral and charged D mesons are guessed and their life times turn out to be rather short.     

Associated charged Higgs and $W$ boson production in the MSSM at the CERN large hadron collider

We investigate the viability of observing charged Higgs bosons () produced in association with bosons at the CERN large hadron collider, using the leptonic decay and hadronic decay, within different scenarios of the minimal supersymmetric standard model (MSSM) with both real and complex parameters. Performing a parton level study we show how the irreducible standard model background from jets can be controlled by applying appropriate cuts and find that the size of a possible signal depends on the cuts needed to suppress QCD backgrounds and misidentifications. In the standard maximal mixing scenario of the MSSM we find a viable signal for large and intermediate masses () when using softer cuts (,  50 GeV), whereas for harder cuts (, 100 GeV) we only find a viable signal for very large (). We have also investigated a special class of MSSM scenarios with large mass splittings among the heavy Higgs bosons where the cross-section can be resonantly enhanced by factors up to one hundred, with a strong dependence on the -violating phases. Even so we find that the signal after cuts remains small except for small masses () when using the softer cuts. Finally, in all the scenarios we have investigated we have only found small -asymmetries.     

End-tethered charged chains at surfaces

We present here a short review covering most of the experimental results on tethering charged chains by an end to a surface. A first class of experiments deals with solid surfaces where charged chains are either chemically grafted or adsorbed through a purposely chosen moiety. Structural studies have been carried out by scattering methods, spectroscopic techniques or microscopy. Forces between the polyelectrolyte layers covering the surfaces have also been obtained by using for instance, the surface force apparatus (SFA). A second class of experiments concerns polyelectrolytes, which are end-tethered to flexible surfaces like air–liquid or liquid–liquid interfaces. These experiments are fewer in number and mainly rely on the adsorption or spreading of charged diblock copolymers at the fluid interfaces.     

Quasinormal spectrum and the black hole membrane paradigm

The membrane paradigm approach to black hole physics introduces the notion of a stretched horizon as a fictitious time-like surface endowed with physical characteristics such as entropy, viscosity and electrical conductivity. We show that certain properties of the stretched horizons are encoded in the quasinormal spectrum of black holes. We compute analytically the lowest quasinormal frequency of a vector-type perturbation for a generic black hole with a translationally invariant horizon (black brane) in terms of the background metric components. The resulting dispersion relation is identical to the one obtained in the membrane paradigm treatment of the diffusion on stretched horizons. Combined with the Buchel–Liu universality theorem for the membrane's diffusion coefficient, our result means that in the long wavelength limit the black brane spectrum of gravitational perturbations exhibits a universal, purely imaginary quasinormal frequency. In the context of gauge–gravity duality, this provides yet another (third) proof of the universality of shear viscosity to entropy density ratio in theories with gravity duals.     

Binding of oppositely charged membranes and membrane reorganization

We consider the electrostatic interaction between two rigid membranes, with different surface charge densities of opposite sign, across an aqueous solution without added salt. Exact solutions to the nonlinear Poisson-Boltzmann equation are obtained and their physical meaning discussed. We also calculate the electrostatic contribution to the free energy and discuss the renormalization of the area per head group of the charged lipids arising from the Coulomb interaction. Received 13 October 1998     

Annealing polyelectrolytes at charged interfaces

The conformation of a weakly dissociating (annealing) polyelectrolyte chain end-tethered to a similarly or oppositely charged planar surface is analyzed in the framework of scaling arguments. For a similarly charged interface an analytical model is also utilized. We demonstrate that at low salt concentration in bulk solution there is a strong coupling between the polyelectrolyte conformation and its degree of ionization. In the case of an oppositely charged (adsorbing) surface, adsorption promotes ionization of the annealing polyelectrolyte. As a result, the adsorbed layer thickness decreases as a function of surface charge density more rapidly for an annealing polyelectrolyte than for a quenched one. In the case of a similarly charged (repulsive) surface the chain ionization is suppressed, and the annealing polyelectrolyte chain is less extended than the quenched one. Moreover, an increase in surface charge density leads to non-monotonous extension of the tethered polyelectrolyte.Received: 16 September 2003, Published online: 5 February 2004PACS: 61.25.Hq Macromolecular and polymer solutions; polymer melts; swelling - 82.35.Gh Polymers on surfaces; adhesion - 82.35.Rs Polyelectrolytes     

The charge exchange of slow highly charged ions at surfaces unraveled with freestanding 2D materials

The property of a variable charge state makes ions unique to other types of radiation a material surface can be exposed to. As a consequence of charge exchange between ions and surfaces, energy is transferred to the surface and material damage may be triggered. Furthermore, a changing charge state of the ion alters its slowing down process in solids and has important implications when back-scattered ions are to be measured for material analysis purposes. Over the last decades extensive research was devoted to the understanding of ion charge exchange with solids. Here I review recent progress in this field with special emphasize on slow ions in high charge states. This class of ions allows a detailed analysis of charge exchange in experiments, which employ also ultra-thin solid targets and therefore give experimental access to electronic processes on the femtosecond timescale. In this review I will discuss general properties of charge exchange and present typical experimental techniques. I will also discuss current developments in the modelling and simulation of ion-surface interaction. Recent findings using freestanding 2D materials are discussed as well as results from spectroscopy of emitted secondary particles. The paper concludes with a unified picture of ion charge exchange at surfaces and presents possible applications based on the understanding of the underlying physics.     

Simulations of counterions at charged plates

Using Monte Carlo simulations, we study the counterion distribution close to planar charged walls in two geometries: i) when only one charged wall is present and the counterions are confined to one half-space, and ii) when the counterions are confined between two equally charged walls. In both cases the surface charge is smeared out and the dielectric constant is the same everywhere. We obtain the counterion density profile and compare it with both the Poisson-Boltzmann theory (asymptotically exact in the limit of weak coupling, i.e. low surface charge, high temperature and low counterion valence) and the strong-coupling theory (valid in the opposite limit of high surface charge, low temperature and high counterion valence) and with previously calculated correction terms to both theories for different values of the coupling parameter, thereby establishing the domain of validity of the asymptotic limits. Gaussian corrections to the leading Poisson-Boltzmann behavior (obtained via a systematic loop expansion) in general perform quite poorly: At coupling strengths low enough so that the Gaussian (or one-loop) correction does describe the numerical deviations from the Poisson-Boltzmann result correctly, the leading Poisson-Boltzmann term by itself matches the data within high accuracy. This reflects the slow convergence of the loop expansion. For a single charged plane, the counterion pair correlation function indicates a behavioral change from a three-dimensional, weakly correlated counterion distribution (at low coupling) to a two-dimensional, strongly correlated counterion distribution (at high coupling), which is paralleled by the specific-heat capacity which displays a rounded hump at intermediate coupling strengths. For the case of counterions confined between two equally charged walls, we analyze the inter-wall pressure and establish the complete phase diagram, featuring attraction between the walls for large enough coupling strength and at intermediate wall separation. Depending on the thermodynamic ensemble, the phase diagram exhibits a discontinuous transition where the inter-wall distance jumps to infinity (in the absence of a chemical potential coupling to the inter-wall distance, as for charged lamellae in excess solvent) or a critical point where two coexisting states with different inter-wall distance become indistinguishable (in the presence of a chemical potential, as for charged lamellae with a finite fixed solvent fraction). The attractive pressure decays with the inter-wall distance as an inverse cube, similar to analytic predictions, although the amplitude differs by an order of magnitude from previous theoretical results. Finally, we discuss in detail our simulation methods and compare the finite-size scaling behavior of different boundary conditions (periodic, minimal image and open). Received 6 November 2001     

A large volume flat coil probe for oriented membrane proteins

15N detection of mechanically aligned membrane proteins benefits from large sample volumes that compensate for the low sensitivity of the observe nuclei, dilute sample preparation, and for the poor filling factor arising from the presence of alignment plates. Use of larger multi-tuned solenoids, however, is limited by wavelength effects that lead to inhomogeneous RF fields across the sample, complicating cross-polarization experiments. We describe a 600 MHz 15N-1H solid-state NMR probe with large (580 mm3) RF solenoid for high-power, multi-pulse sequence experiments, such as polarization inversion spin exchange at the magic angle (PISEMA). In order to provide efficient detection for 15N, a 4-turn solenoidal sample coil is used that exceeds 0.27 lambda at the 600 MHz 1H resonance. A balanced tuning-matching circuit is employed to preserve RF homogeneity across the sample for adequate magnetization transfer from 1H to 15N. We describe a procedure for optimization of the shorted 1/4 lambda coaxial trap that allows for the sufficiently strong RF fields in both 1H and 15N channels to be achieved within the power limits of 300 W 1H and 1 kW 15N amplifiers. The 8 x 6 x 12 mm solenoid sustains simultaneous B1 irradiation of 100 kHz at 1H frequency and 51 kHz at 15N frequency for at least 5 ms with 265 and 700 W of input power in the respective channels. The probe functionality is demonstrated by 2D 15N-1H PISEMA spectroscopy for two applications at 600 MHz.