$90^{\circ}$ phase-matched parametric frequency conversion in AgGa1-xInxS2

AgGa_1-xIn_xS₂ with x=0.14±0.01 was found to be 90° phase-matchable for type-I difference-frequency generation (DFG) by mixing the dual-wavelength pulses emitted from an electronically tuned Ti:sapphire laser. Infrared radiation continuously tunable over the range of 4.80–6.98 μm was generated by independently varying the two wavelengths in the 705–932 nm spectral range, and 4.04 μm radiation by mixing a Nd:YAG laser with the Ti:sapphire laser. In addition, this material was found to be noncritically phase-matchable for the second harmonic generation (SHG) of CO₂ laser radiation at 10.591 μm at 203 °C. Sellmeier equations that reproduce well these experimental data are presented. PACS  42.65.-k; 42.65.ky     

Jet quenching parameter $\hat{q}$ in the stochastic QCD vacuum with Landau damping

We argue that the radiative energy loss of a parton traversing the quark–gluon plasma is determined by Landau damping of soft modes in the plasma. Using this idea, we calculate the jet quenching parameter of a gluon. The calculation is done in SU(3) quenched QCD within the stochastic vacuum model. At the LHC-relevant temperatures, the result depends on the gluon condensate, the vacuum correlation length, and the gluon Debye mass. Numerically, when the temperature varies from T=T_c to T = 900 MeV, the jet quenching parameter rises from to approximately 1.8 GeV²/fm. We compare our results with the predictions of perturbative QCD and other calculations.     

Shape dependence of the finite-size scaling limit in a strongly anisotropic $\mathsf{O(\infty)}$ model

We discuss the shape dependence of the finite-size scaling limit in a strongly anisotropic O(N) model in the large-N limit. We show that scaling is observed even if an incorrect value for the anisotropy exponent is considered. However, the related exponents may only be effective ones, differing from the correct critical exponents of the model. We discuss the implications of our results for numerical finite-size scaling studies of strongly anisotropic systems.Received: 9 April 2003, Published online: 4 August 2003PACS:   05.70.Jk Critical point phenomena - 64.60.-i General studies of phase transitions     

Effect of top quark spin on the unparticle couplings in $\gamma\gamma \to t\bar{t}$

We investigate the potential of γ γ collisions to probe scalar unparticle couplings via top–antitop quark pair production. We find 95% confidence level limits on the unparticle couplings with an integrated luminosity of 500 fb⁻¹ and an energy of  TeV. We investigate the effect of the top quark spin polarization on the unparticle couplings. It is shown that spin polarization of the top quark leads to a significant improvement in the sensitivity limits.     

Vision of a fully laser-driven ${\sf n\gamma}{-}{\sf m\gamma}$ collider

The use is suggested of a laser-accelerated dense electron sheet with an energy of (E=[(g)\tilde] mc²E=\tilde{\gamma} mc^2) as a relativistic mirror to reflect coherently a second laser with photon energy ħω, generating by the Doppler boost high-energy γ photons with $ \hbar \omega ' = 4\tilde \gamma ^2 \hbar \omega $ \hbar \omega ' = 4\tilde \gamma ^2 \hbar \omega and short duration [A. Einstein, Annalen der Physik 17, 891 (1905); D. Habs et al., Appl. Phys. B 93, 349 (2008)]. Two of these counter-propagating γ beams are focused by the parabolically shaped electron sheets into the interaction region with small, close to diffraction-limited, spot size. Comparing the new nγ-mγ collider with former proposed γγ collider schemes we achieve the conversion of many photon-pairs in a small space-time volume to matter-antimatter particles, while in the other discussed setups only two isolated, much more high-energetic photons will be converted, reaching in the new approach much higher energy densities and temperatures. With a γ-field strength somewhat below the Schwinger limit we can reach this complete conversion of the γ bunch energy into e⁺e^- or quark-antiquark q[`(q)]q\bar{q}-plasmas. For a Bose-Einstein condensate (BEC) [A. Einstein, Physikalisch-mathematische Klasse (Berlin) 22, 261 (1924); A. Einstein, Physikalisch-mathematische Klasse (Berlin) 22, 3 (1925); A. Griffin, D.W. Snoke, S. Stringari, Bose-Einstein Condensation (Cambridge University Press, 1995)] final state or for the Cooper pair ground state at higher densities [A.J. Leggett, Quantum Liquids, Oxford Graduate Texts (Oxford University Press, 2006)] the strong induced transition into this coherent state is of special interest for single-cycle γ pulses. Due to annihilation these cold coherent states are very short-lived. For γ beams with photon energies of 1–10 keV the rather cold e<sup>+</sup>e<sup>-</sup>-plasma or e<sup>+</sup>e<sup>-</sup>-BEC expands to a cold dense aggregate of positronium (Ps) atoms, where the production of Ps molecules is discussed. For photon energies of 1–10 MeV we discuss the production of a cold induced π<sup>0</sup>-BEC followed by the formation of molecules. For the direct population of higher q[`(q)]q\bar{q} densities we can study condensates of color-neutral mesons with enhanced population. For a γγ collider with several-cycle laser pulses the following cycles heat up the fermion-antifermion f[`(f)]f\bar{f} system to a certain temperature. Thus we can reach high energy densities and temperatures of an e⁺e^-γ plasma, where the production of hadrons in general or the quark-gluon phase transition can be observed. Within the long-term goal of very high photon energies of about 1 GeV in the nγ-mγ-collider, even the electro-weak phase transition or SUSY phase transition could be reached.     

A statistical mechanics model of isotropic turbulence well-defined within the context of the $\mathsf{\epsilon}$ expansion

A statistical mechanics model of isotropic turbulence that renormalizes the effects of turbulent stresses into a velocity-gradient-dependent random force term is introduced. The model is well-defined within the context of the renormalization group expansion, as the effective expansion parameter is . The Kolmogorov constant and N parameter of turbulence are of order unity, in accord with experimental results. Nontrivial intermittency corrections to the single-time structure functions are calculated as a controlled expansion in .Received: 20 December 2002, Published online: 23 July 2003PACS:   47.27.Ak Fundamentals - 47.27.Gs Isotropic turbulence; homogeneous turbulence - 05.10.Cc Renormalization group methods     

Electromagnetic form factors of the $\Delta(1232)$ excitation

In the resonance region we have precisely determined the electromagnetic properties of the -resonance, in particular the E2/M1 ratio . For pion electroproduction recent experimental data from Mainz, Bates, Bonn and JLab for Q² up to 4.0 (GeV/c)² have been analyzed with the isobar model MAID. The extracted E2/M1 ratio shows, starting from a small and negative value at the real photon point, a clear tendency to cross zero, and becomes positive with increasing Q². This is a possible indication of a very slow approach toward the pQCD region. The C2/M1 ratio near the photon point is found as . At high Q², the absolute value of the ratio is strongly increasing, a further indication that pQCD is not yet reached. The electromagnetic-transition form factors of the excitation are parameterized and fitted to the electroproduction data. This also shows a zero-crossing of the electric form factor G_E^* at (GeV/c)².Received: 1 November 2002, Published online: 15 July 2003PACS:   13.40.Gp Electromagnetic form factors - 13.60.Le Meson production - 14.20.Gk Baryon resonances with S=0 - 25.20.Lj Photoproduction reactions     

CMS: Hadronic calorimetry,jets, and $\rlap{\,/}E_T$ performance

The European Physical Journal C - The CMS experiment&;nbsp;[1] uses a general purpose detector designed for detecting the diverse signatures associated with Higgs production and new physics...     

Jet-Quenching of the Rotating Heavy Meson in a ${\mathcal{N}}=4$ SYM Plasma in Presence of a Constant Electric Field

In this paper, we consider a rotating heavy quark-antiquark (q[`(q)]q\bar{q}) pair in a N=4{\mathcal{N}}=4 SYM thermal plasma. We assume that q[`(q)]q\bar{q} center of mass moves at the speed v and furthermore they rotate around the center of mass. We use the AdS/CFT correspondence and consider the effect of external electromagnetic field on the motion of the rotating meson. Then we calculate the jet-quenching parameter corresponding to the rotating meson in the constant electric field.     

An ellipsometric investigation of Ag/SiO$\mathsf{_2}$ nanocomposite thin films

Dielectric properties of silver/SiO₂ nanocomposite thin films grown by high-pressure d.c. sputtering technique were studied by spectroscopic ellipsometry (300-800 nm). The dielectric behavior of the nanocomposite thin films largely depended on the particle size, its number density and the surrounding environments. The films showed semiconductor-like behavior up to a critical particle size and concentration, beyond which the films exhibited the typical surface plasmon resonance characteristics in their optical properties. The refractive index was also found to have a strong dependence on the particle size and its dispersion in the matrix. The results were found to be consistent with those obtained from UV-VIS optical absorbance data. Bruggeman effective medium theory was used to explain the experimental results.Received: 3 April 2002, Published online: 23 July 2003PACS:   78.67.-n Optical properties of nanoscale materials and structures - 78.67.Bf Nanocrystals and nanoparticles     

The role of the gluonic $gg\leftrightarrow{ggg}$ interactions in early thermalization in ultrarelativistic heavy-ion collisions

We “quantify” the role of elastic as well as inelastic pQCD processes in kinetic equilibration within a pQCD inspired parton cascade. The contributions of different processes to kinetic equilibration are manifested by the transport collision rates. We find that in a central Au+Au collision at RHIC energy pQCD bremsstrahlung processes are much more efficient for momentum isotropization compared to elastic scatterings. For the parameters chosen the ratio of their transport collision rates amounts to 5:1. PACS  05.60.-k, 25.75.-q, 24.10.Lx     

Optical manipulation of long-range interactions at the 3s + 3p asymptote of $\mathsf{Na_2}$

We investigate the influence of a laser field, which is near-resonant to the atomic sodium 3²P_1/2 3²D_3/2 transition, on the last bound levels of the A state in Na₂. In a molecular beam experiment level shifts up to 100 MHz and light induced line broadenings were observed using an optical double resonance excitation scheme. Moreover, the coupling laser can reduce the number of bound levels of the A state by one or more units, which effectively means that in the picture of a collision of a 3²S_1/2 and a 3²P_1/2-atom the scattering phase is altered by more than . The observed effects are interpreted as light induced couplings of the A state, which correlates to the 3s _1/2 + 3p _1/2 asymptote, to the and states at the 3s _1/2 + 3d _3/2 asymptote. We performed multi-channel calculations, applying the mapped Fourier grid method, which reproduce our experimentally observed level shifts well.Received: 7 October 2003, Published online: 21 November 2003PACS:   34.50.Rk Laser-modified scattering and reactions - 33.80.-b Photon interactions with molecules - 42.62.Fi Laser spectroscopy     

Nanoscale modification of Ni/Al interfaces by low-energy $\mathrm{O}_{2}^{+}$ reactive ion beam mixing

The kinetics of growth, composition and electronic structure of thin oxide films formed by reactive ion beam mixing (IBM) of Ni/Al interfaces bombarded with low-energy (3-keV) O₂⁺\mathrm{O}_{2}^{+} ions have been studied at room temperature using X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy and factor analysis. Initially, NiO species are formed but, later, with increasing ion dose, Ni–Al mixed oxide species appear due to Al incorporation in the near-surface region. These changes are accompanied by a slight increase of the oxygen concentration and a decrease of the Ni/Al ratio in the thin oxide films formed. Angle-resolved X-ray photoelectron spectroscopy shows that Ni–Al mixed oxide species are located nearer the surface than NiO species. Experimental results have been compared with Monte Carlo TRIDYN simulations, suggesting that processes driven by residual defects or the reaction with oxygen predominate over pure ballistic mechanisms during reactive IBM of Ni/Al interfaces.     

Measurement of photons via conversion pairs in $\sqrt{s_{NN}}$ =200 GeV Au+Au collisions with the PHENIX experiment at RHIC

Thermal photons can provide information on the temperature of the new state of matter created at RHIC. In the p_T region of 1–3 GeV/c thermal photons are expected to be the dominant direct photon source. Therefore, a possible excess compared to a pure decay photon signal due to a thermal photon contribution should be seen in the double ratio (γ/γ(π⁰))_Measured/(γ/γ(π⁰))_Simulated, if sufficient accuracy can be reached. We present a method to reconstruct direct photons by measuring e⁺e^--pairs from external photon conversions.     

The small x gluon and $b\bar{b}$ production at the LHC

We study open b[`(b)]b\bar{b} production at large rapidity at the LHC in an attempt to pin down the gluon distribution at very low x. For the LHC energy of 7 TeV, at next-to-leading order (NLO), there is a large factorization scale uncertainty. We show that the uncertainty can be greatly reduced if events are selected in which the transverse momenta of the two B-mesons balance each other to some accuracy, that is |p _1T +p _2T |<k ₀. This will fix the scale μ _F ≃k ₀, and will allow the LHCb experiment, in particular, to study the x-behaviour of gluon distribution down to x∼10⁻⁵, at rather low scales, μ∼2 GeV. We evaluate the expected cross sections using, for illustrative purposes, various recent sets of Parton Distribution Functions.     

First direct measurement of jets in $\sqrt{s_{\mathit {NN}}}=200~\mbox{GeV}$ heavy ion collisions by STAR

We present the first measurement of reconstructed jets in ultra-relativistic heavy ion collisions. Utilizing the large coverage of the STAR Time Projection Chamber and Electromagnetic Calorimeter, we apply several modern jet reconstruction algorithms and background subtraction techniques and explore their systematic uncertainties in heavy ion events. The differential energy spectrum for inclusive jet production in central Au+Au collisions at is presented. In order to assess the jet reconstruction biases, this spectrum is compared with the jet cross section measured in  GeV p+p collisions scaled by the number of binary N–N collisions to account for nuclear geometric effects.     

$\mathcal{CPT}$-Symmetric Discrete Square Well

In an addendum to the recent systematic Hermitization of certain N by N matrix Hamiltonians H ^(N)(λ) (Znojil in J. Math. Phys. 50:122105, 2009) we propose an amendment H ^(N)(λ,λ) of the model. The gain is threefold. Firstly, the updated model acquires a natural mathematical meaning of Runge-Kutta approximant to a differential PT\mathcal{PT}-symmetric square well in which P\mathcal{P} is parity. Secondly, the appeal of the model in physics is enhanced since the related operator C\mathcal{C} of the so called “charge” (the requirement of observability of which defines the most popular Bender’s metric Q = PC\Theta=\mathcal{PC}) becomes also obtainable (and is constructed here) in an elementary antidiagonal matrix form at all N. Last but not least, the original phenomenological energy spectrum is not changed so that the domain of its reality (i.e., the interval of admissible couplings λ∈(−1,1)) remains the same.