Renormalization-group improved prediction for Higgs production at hadron colliders

We use renormalization-group methods in effective field theory to improve the theoretical prediction for the cross section for Higgs-boson production at hadron colliders. In addition to soft-gluon resummation at N³LL, we also resum enhanced contributions of the form (C _A π α _s ) ⁿ , which arise in the analytic continuation of the gluon form factor to time-like momentum transfer. This resummation is achieved by evaluating the matching corrections arising at the Higgs-boson mass scale at a time-like renormalization point μ ²<0, followed by renormalization-group evolution to μ ²>0. We match our resummed result to NNLO fixed-order perturbation theory and give numerical predictions for the total production cross section as a function of the Higgs-boson mass. Resummation effects are significant even at NNLO, where our improved predictions for the cross sections at the Tevatron and the LHC exceed the fixed-order predictions by about 13% and 8%, respectively, for m _H =120 GeV. We also discuss the application of our technique to other time-like processes such as Drell–Yan production, e ⁺ e ⁻→hadrons, and hadronic decays of the Higgs boson.     

The CVC prediction for the τ−→h −π0 v τ branching ratio

We present the branching ratio predictions of an isospin statistical model forτ decays to four, five and six pions. Limits on the branching ratios of the three possible six pionτ decay modes using the Conserved Vector Current (CVC) Hypothesis and thee ⁺ e ⁻→6π cross section data are also presented. We find that the isospin model prediction is in good agreement with the well-measured four pion decay modes and consistent with the five pion decay modes. However, we find that some of the recent six pionτ measurements do not agree with the isospin model and the CVC prediction.     

Interpretation of the recent Kolar events

We give plausible interpretations of the unusual events seen in the proton decay detector at Kolar Gold Fields indicating the existence of a massive (≳2GeV) long lived (10⁻⁸−10⁻⁹s) particle. We show that it is possible to accommodate the particle in the standard model as a fourth generation neutrino, or inE ₆ grand unified theory as a neutral fermion occurring in27 representation or in supersymmetric theory as a scalar neutrino. However, there is a difficulty in explaining the large production rate for the particle.     

Tau lepton production in ep collisions at HERA

The production of tau leptons in ep collisions is investigated using data recorded by the H1 detector at HERA in the period 1994–2000. Tau leptons are identified by detecting their decay products, using leptonic and hadronic decay modes. The cross section for the production of tau lepton pairs is measured for the first time at HERA. Furthermore, a search for events with an energetic isolated tau lepton and with large missing transverse momentum is performed. The results are found to be in agreement with the Standard Model predictions.     

Rare decay π<Superscript>0</Superscript> → <Emphasis Type="Italic">e</Emphasis><Superscript>+</Superscript><Emphasis Type="Italic">e</Emphasis><Superscript>−</Superscript> as a test of standard model

Experimental and theoretical progress concerning the rare decay π⁰ → e ⁺ e ⁻ is briefly reviewed. It includes the latest data from KTeV and a new model-independent estimate of the decay branching which show the deviation between experiment and theory at the level of 3.3σ. The predictions for η and η′ decays into lepton pair are presented. We also comment on the impact on the pion rare decay estimate of the data of BABAR collaboration on the pion transition form factor at large momentum transfer.     

The excitation cross section of cadmium atoms from metastable 5<Emphasis Type="Italic">s</Emphasis>5<Emphasis Type="Italic">p</Emphasis><Superscript>3</Superscript><Emphasis Type="Italic">P</Emphasis><Subscript>0, 2</Subscript> states by electron impact

By means of the optical method using the technique of crossed electron and atomic beams, we obtained the absolute values of the excitation cross sections of metastable cadmium atoms and their energy dependences. The absolute cross section values reach ∼10⁻¹⁶ cm² (at 30 eV). Sharp resonance-like maxima are observed in the energy dependences of the excitation cross section near the excitation thresholds, which are supposedly related to the formation and decay of negative-ion excited states of.     

Precise predictions for Higgs production in association with a W-boson pair at ILC

Higgs-boson production in association with a W-boson pair at e ⁺ e ⁻ linear colliders is one of the important processes in probing the coupling between the Higgs boson and vector gauge bosons and discovering the signature of new physics. We describe the impact of the complete electroweak (EW) radiative corrections of to this process in the standard model (SM) at the International Linear Collider (ILC), and investigate the dependence of the lowest-order (LO) and EW next-to-leading order (NLO) corrected cross sections on the colliding energy and the Higgs-boson mass. The LO and NLO EW corrected distributions of the invariant mass of the W-boson pair and the transverse momenta of the final W-boson and Higgs boson are presented. Our numerical results show that the relative EW radiative correction (δ _ew) varies from −19.4% to 0.2% when m _H=120 GeV and grows from 300 GeV to 1.2 TeV.     

Optical nonlinearities in hyperbranched polyyne studied by?two-photon excited fluorescence and third-harmonic generation spectroscopy

The nonlinear optical properties of a hyperbranched polyyne (hb-Polyyne) have been measured at infrared wavelengths by using femtosecond and nanosecond pulsed excitation. This hyperbranched polyyne exhibited strong and intrinsic (simultaneous) two-photon absorption and upconverted blue fluorescent emission under femtosecond excitation around 800 nm. The hb-Polyyne in chloroform solution is characterized by a large two-photon absorption cross section of 9068 GM (1GM=10⁻⁵⁰ cm⁴ s) and a fluorescence quantum yield of 0.57. On the other hand, by third-harmonic generation (THG) spectroscopy with nanosecond excitation, the measured third-order nonlinear susceptibility χ ⁽³⁾ for solid films of hb-Polyyne ranged from 2.4×10⁻¹¹ to 6.1×10⁻¹¹ esu in the spectral range of 1100–1600 nm, with results comparable to the values exhibited by the well-known conjugated polymer MEH:PPV, but with a much better transparency for visible wavelengths.     

Nuclear form factor,validity of the equivalent photon approximation and Coulomb corrections to muon pair production in photon–nucleus and nucleus–nucleus collisions

We study in detail the influence of the nuclear form factor both on the Born cross section and on the Coulomb corrections to the photo-production of muon pairs off heavy nuclei (γ Z→μ ⁺ μ ⁻ Z) and in heavy-ion collisions (ZZ→ZZ μ ⁺ μ ⁻). Our findings indicate a number of issues which have not been sufficiently described as yet in the literature: (i) the use of a realistic form factor, based on the Fermi charge distribution for the nucleus, is absolutely indispensable for reliable theoretical predictions; (ii) we checked quantitatively that the equivalent photon approximation has a very good accuracy for the discussed processes; and (iii) we present a leading logarithmic calculation of the Coulomb corrections which correspond to multi-photon exchange of the produced μ ^± with the nuclei. These corrections are found to be small (on the percent level). Our result justifies using the Born approximation for numerical simulations of the discussed process at the RHIC and LHC colliders. Finally, we calculate the total cross section for muon pair production at RHIC and LHC.     

Spectroscopic properties of Nd<Superscript>3+</Superscript>:CaNb<Subscript>2</Subscript>O<Subscript>6</Subscript> crystal

The absorption spectra, fluorescence spectrum and fluorescence decay curve of Nd³⁺ ions in CaNb₂O₆ crystal were measured at room temperature. The peak absorption cross section was calculated to be 6.202×10⁻²⁰ cm² with a broad FWHM of 7 nm at 808 nm for E//a light polarization. The spectroscopic parameters of Nd³⁺ ions in CaNb₂O₆ crystal have been investigated based on Judd-Ofelt theory. The parameters of the line strengths Ω _t are Ω ₂=5.321×10⁻²⁰ cm²,Ω ₄=1.734×10⁻²⁰ cm²,Ω ₆=2.889×10⁻²⁰ cm². The radiative lifetime, the fluorescence lifetime and the quantum efficiency are 167 μs, 152 μs and 91%, respectively. The fluorescence branch ratios are calculated to be β ₁=36.03%,β ₂=52.29%,β ₃=11.15%,β ₄=0.533%. The emission cross section at 1062 nm is 9.87×10⁻²⁰ cm².     

Experimental study of the reaction e + e − → K S K L in the energy range √S = 1.04−1.38 GeV

We present a measurement of the e ⁺ e ⁻ → K _S K _L cross section in the energy range √s = 1.04−1.38 GeV. For an energy of √s ≥ 1.2 GeV the cross section exceeds vector meson dominance model predictions with only ρ(770), ω(783), and ϕ(1020) mesons taken into account. The measured cross section agrees well with previous measurements. Published in Russian in Zhurnal éksperimental’noĭ i Teoreticheskoĭ Fiziki, 2006, Vol. 130, No. 5, pp. 831–839. This article was translated by the authors.     

Resonance propagation in heavy-ion scattering

The formalism developed earlier by us for the propagation of a resonance in the nuclear medium in proton-nucleus collisions has been modified to the case of vector boson production in heavy-ion collisions. The formalism includes coherently the contribution to the observed di-lepton production from the decay of a vector boson inside as well as outside the nuclear medium. The medium modification of the boson is incorporated through an energy dependent optical potential. The calculated invariant ρ mass distributions are presented for the ρ-meson production using optical potentials estimated within the VDM and the resonance model. The shift in the invariant mass distribution is found to be small. To achieve the mass shift (of about 200 MeV towards lower mass) as indicated in the high energy heavy-ion collision experiments, an unusually strong optical potential of about −120 MeV is required. We also observe that, for not so heavy nuclear systems and/or for fast moving resonances, the shape, magnitude and peak position of the invariant mass distribution is substantially different if the contributions from the resonance decay inside and outside are summed-up at the amplitude level (coherently) or at the cross section level (incoherently).     

Diffractive open charm production in deep-inelastic scattering and photoproduction at HERA

Measurements are presented of diffractive open charm production at HERA. The event topology is given by ep→eXY where the system X contains at least one charmed hadron and is well separated by a large rapidity gap from a leading low-mass proton remnant system Y. Two analysis techniques are used for the cross section measurements. In the first, the charm quark is tagged by the reconstruction of a D^*±(2010) meson. This technique is used in deep-inelastic scattering (DIS) and photoproduction (γp). In the second, a method based on the displacement of tracks from the primary vertex is used to measure the open charm contribution to the inclusive diffractive cross section in DIS. The measurements are compared with next-to-leading order QCD predictions based on diffractive parton density functions previously obtained from a QCD analysis of the inclusive diffractive cross section at H1. A good agreement is observed in the full kinematic regime, which supports the validity of QCD factorization for open charm production in diffractive DIS and γp.     

Decay rate measurements of upper laser level in He-Cd+ laser

The decay rate of² D _5/2 level of Cd II has been measured by the magnetic-field power-dip method. The decay rate at the zero-pressure limit is found to be 2.4·10⁶s⁻¹. The calculated collision cross section for excited Cd ions with He atoms equals 0.91·10⁻¹⁵ cm². This work was supported by the Institute of Quantum Electronics. WAT Warszawa, within the project 06.2.3.     

Higgs-boson pairproduction ine + e − reactions

We calculate the production cross section of Higgs-boson pairs ine ⁺ e ^? annihilation. In this reaction the lowest order contribution comes from one loop graphs. We study the behaviour of the cross section as a function of the energy, the Higgs-boson mass and the scattering angle.     

Spectroscopic properties of 1.8 μm emission of thulium ions in germanate glass

A new type host of germanate glass (GeO₂− BaO−BaF₂−Ga₂O₃−La₂O₃) codoped with Tm₂O₃ has been investigated for application as laser material. It possesses a large emission cross section with the value of 9.3×10⁻²¹ cm² at 1.8 μm. Judd-Ofelt intensity parameters and radiative transition probability are calculated and analyzed by Judd-Ofelt theory and absorption spectra. The infrared emission spectra at 1.8 μm have been obtained by using a 794 nm laser diode as excitation resource. The emission intensity ratio of 1.8 (³F₄→³H₆) to 1.47 μm (³H₄→³F₄) increases, while the experimental lifetime of the Tm³⁺:³H₄ level decreases by increasing Tm₂O₃ concentration, which is attributed to the presence of a cross relaxation process. The most intensive emission at 1.8 μm is achieved from the germanate glass with the concentration of Tm₂O₃ reaches 1.0 wt%. The extended overlap integral method is used to calculate the microparameter of the energy transfer and the critical distance, which are derived to better understand the energy transfer process of thulium ions in the germanate glass responsible for emission at 1.8 μm.     

Generalized parton distributions and deeply virtual Compton scattering in color glass condensate model

Within the framework of the color glass condensate model, we evaluate quark and gluon generalized parton distributions (GPDs) and the cross section of deeply virtual Compton scattering (DVCS) in the small-x_B region. We demonstrate that the DVCS cross section becomes independent of energy in the limit of very small x_B, which clearly indicates saturation of the DVCS cross section. Our predictions for the GPDs and the DVCS cross section at high energies can be tested at the future Electron–Ion Collider and in ultra-peripheral nucleus–nucleus collisions at the LHC. PACS  12.38.Mh; 13.60.Fz; 13.85.Fb; 24.85.+p; 25.20.Dc     

Dispersion and spectral characteristics of crossfield instability in collisional magnetoplasma

Results on dispersion and spectral characteristics of crossfield instability in a collisional magnetoplasma are presented for different values of externally applied radial electric field. The dispersion relation obtained experimentally differs significantly from predictions of linear theory for strong electric fields.K-spectra for density and potential fluctuations follow power law with indices (−3·7 ± 0·5) and (−5·6 ± 0·6) respectively. At large values of applied electric fields, the main crossfield modes appear to give rise to a number of other modes possibly through non-linear wave-wave interactions. Large amplitudem = 2 mode displays strong sidebands indicating particle trapping by the non-linear waves. Non-linear wave-wave and wave particle interactions, thus, appear to play at important role in the saturation of the cross field instability.     

Helicity analysis of semileptonic hyperon decays including lepton-mass effects

Using the helicity method we derive complete formulas for the joint angular decay distributions occurring in semileptonic hyperon decays including lepton-mass and polarization effects. Compared to the traditional covariant calculation, the helicity method allows one to organize the calculation of the angular decay distributions in a very compact and efficient way. In the helicity method the angular analysis is of cascade type, i.e. each decay in the decay chain is analyzed in the respective rest system of that particle. Such an approach is ideally suited as input for a Monte Carlo event generation program. As a specific example we take the decay  (l ⁻=e ⁻,μ ⁻) followed by the nonleptonic decay Σ ⁺→p+π ⁰ for which we show a few examples of decay distributions which are generated from a Monte Carlo program based on the formulas presented in this paper. All the results of this paper are also applicable to the semileptonic and nonleptonic decays of ground-state charm and bottom baryons, and to the decays of the top quark.     

Optical spectra and excited state relaxation dynamics of Sm<Superscript>3+</Superscript> in Gd<Subscript>2</Subscript>SiO<Subscript>5</Subscript> single crystal

Single crystals of gadolinium orthosilicate Gd₂SiO₅ containing 0.5 at% and 5 at% of Sm³⁺ were grown by the Czochralski method. Optical absorption spectra, luminescence spectra and luminescence decay curves were recorded for these systems at 10 K and at room temperature. Comparison of optical spectra recorded in polarized light revealed that the anisotropy of this optically biaxial host affects the intensity distribution within absorption and emission bands related to transitions between multiplets rather than the overall band intensity. It has been found that among four bands of luminescence related to the ⁴G_5/2→⁶H_J (J=5/2–11/2) transitions of Sm³⁺ in the visible and near infrared region the ⁴G_5/2 →⁶H_7/2 one has the highest intensity with a peak emission cross section of 3.54×10⁻²¹ cm² at 601 nm for light polarized parallel to the crystallographic axis c of the crystal. The luminescence decay curve recorded for Gd₂SiO₅:0.5 at% Sm³⁺ follows a single exponential time dependence with a lifetime 1.74 ms, in good agreement with the ⁴G_5/2 radiative lifetime τ _rad=1.78 ms calculated in the framework of Judd-Ofelt theory. Considerably faster and non-exponential luminescence decay recorded for Gd₂SiO₅:5 at% Sm³⁺ sample was fitted to that predicted by the Inokuti-Hirayama theory yielding the microparameter of Sm³⁺–Sm³⁺ energy transfer C _da=1.264×10⁻⁵² cm⁶×s⁻¹.