Production of top quark pairs in association with a hard gluon to order \alpha_s^2

The production of top quark pairs accompanied by a hard gluon in annihilation is studied including next-to-leading order corrections in the strong coupling. At leading order, the fraction r of events with respect to all events is computed analytically as a function of the minimal gluon energy. Next-to-leading order results for r are given for center-of-mass energies of 0.5 and 1 TeV. We further calculate the differential distribution of r with respect to several variables, including the top quark energy and the invariant mass. We then investigate how our results depend on the choice of the renormalization scheme for the top quark mass by comparing results expressed in terms of either the pole mass or the mass. Finally we estimate the sensitivity of the fraction r on the value of the running top quark mass at a scale of 1 TeV. Received: 7 April 1999 / Published online: 12 August 1999     

Charmonium production in deep inelastic scattering at HERA

The electroproduction of and mesons is studied in elastic, quasi-elastic and inclusive reactions for four momentum transfers and photon-proton centre of mass energies GeV. The data were taken with the H1 detector at the electron proton collider HERA in the years 1995 to 1997. The total virtual photon-proton cross section for elastic production is measured as a function of and W. The dependence of the production rates on the square of the momentum transfer from the proton (t) is extracted. Decay angular distributions are analysed and the ratio of the longitudinal and transverse cross sections is derived. The ratio of the cross sections for quasi-elastic and meson production is measured as a function of . The results are discussed in terms of theoretical models based upon perturbative QCD. Differential cross sections for inclusive and inelastic production of mesons are determined and predictions within two theoretical frameworks are compared with the data, the non-relativistic QCD factorization approach including colour octet and colour singlet contributions, and the model of Soft Colour Interactions. Received: 10 March 1999 / Published online: 8 September 1999     

Higgs production: CP studies in e^-e^- collisions

We review the production of scalar Higgs-like particles in high-energy electron–electron collisions, via the fusion of electroweak gauge bosons. The emphasis is on how to distinguish a CP-even from a CP-odd Higgs particle. Among the more significant differences, we find that in the CP-odd case, the Higgs spectrum is much harder, and the dependence of the total cross section on the product of the polarizations of the two beams much stronger, than in the CP-even case. We also briefly discuss parity violation, and the production of charged Higgs bosons. Received: 1 December 1998 / Revised version: 15 February 1999 / Published online: 18 June 1999     

On the Absorption of antibaryons in nuclei

Antiproton (ˉp) and antilambda (ˉΛ) production has been measured for minimum bias in p+A collisions and central A₁+ A₂ collisions at the CERN-SPS by the collaborations NA35/49 and NA44. The measurements are extrapolated from rapidity distributions to absolute minimum bias cross sections. It is shown that the ˉp cross sections divided by A₁· A₂ follow an exponential trend as a function of a characteristic length obtained from a Glauber type absorption model, while the ˉΛ cross sections divided by A₁· A₂ are constant. The exponential trend also holds for ˉp production at the lower energies of the Brookhaven AGS. A discussion of the physics interpretation of the established trends in terms of an effective absorption cross section is presented. Received: 15 July 1999 / Revised version: 10 November 1999     

On the ΔI= 1/2 rule in the ΛN→NN reaction

It is shown that the mass dependence of the Λ-lifetime in heavy hypernuclei is sensitive to the ratio of neutron-induced to proton-induced non-mesonic decay rates R _n/R p. A comparison of the experimental mass dependence of the lifetimes with the calculated ones for different values of R _n/R p leads to the conclusion that this ratio is larger than 2 on the confidence level of 0.75. This suggests that the phenomenological ΔI= 1/2 rule might be violated for the nonmesonic decay of the Λ-hyperon. Received: 31 March 1999     

Global QCD analysis of parton structure of the nucleon: CTEQ5 parton distributions

An up-to-date global QCD analysis of high energy lepton-hadron and hadron-hadron interactions is performed to better determine the gluon and quark parton distributions in the nucleon. Improved experimental data on inclusive jet production, in conjunction with precise deep inelastic scattering data, place good constraints on the gluon over a wide range of x; while new data on asymmetries in Drell-Yan processes contribute to better determine the d/u ratio. Comparisons with results of other recent global analyses are made, and the differences are described. Open issues and the general problem of determining the uncertainties of parton distributions are discussed. Received: 7 April 1999 / Published online: 21 December 1999     

Joule-Thomson expansion of charged dilatonic black holes

Based on the Einstein-Maxwell theory, the Joule-Thomson (J-T) expansion of charged dilatonic black holes (the solutions are neither flat nor AdS) in \begin{document}$ (n+1) $\end{document}-dimensional spacetime is studied herein. To this end, we analyze the effects of the dimension n and dilaton field α on J-T expansion. An explicit expression for the J-T coefficient is derived, and consequently, a negative heat capacity is found to lead to a cooling process. In contrast to its effect on the dimension, the inversion curve decreases with charge Q at low pressures, whereas the opposite effect is observed at high pressures. We can observe that with an increase in the dimension n or parameter α, both the pressure cut-off point and the minimum inversion temperature \begin{document}$T_{\rm min}$\end{document} change. Moreover, we analyze the ratio \begin{document}$T_{\rm min}/T_{\rm c}$\end{document} numerically and discover that the ratio is independent of charge; however, it depends on the dilaton field and dimension: for \begin{document}$ n=3 $\end{document} and \begin{document}$ \alpha=0 $\end{document}, the ratio is 1/2. The dilaton field is found to enhance the ratio. In addition, we identify the cooling-heating regions by investigating the inversion and isenthalpic curves, and the behavior of the minimum inversion mass \begin{document}$M_{\rm min}$\end{document} indicates that this cooling-heating transition may not occur under certain special conditions.     

Measurements of the Z partial decay width into c\bar c and multiplicity of charm quarks per b decay

The partial decay width of the Z into quark pair and the number of charm quarks per b decay are measured with the DELPHI detector at LEP 1. Particle identification provides clear , , and signatures. The charm hadron production rate is measured in each channel by a fit to the scaled energy, impact parameter information and the invariant mass spectrum. Two measurements of are presented, from the production rate and from the overall charm counting, including strange charm baryon production, in events. The multiplicity , which includes hidden and strange charm baryon production, is inferred from the charm counting in events. The final results are and . Received: 1 June 1999 / Published online: 8 December 1999     

Study of optical waveguide of barium sodium niobate films on potassium titanyl phosphate

Barium sodium niobate (BSN) optical waveguide films were grown on potassium titanyl phosphate (KTP) substrate by pulsed laser deposition (PLD). X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray pole spectroscopy, and X-ray photoelectron spectroscopy (XPS) showed that the as-grown BSN films are epitaxially smooth, fine-particled and show small constituent deviation. Both m lines of the waveguided TE and TM modes were recorded. Lattice match between the BSN(110) and both the KTP(001) and KTP(100) planes is examined with mismatch less than 3%. Effective refractive indices as a function of incident wavelength and order of the waveguided modes are studied. A phase matching relationship of k ⁽¹⁾−2k ⁽⁰⁾=0 is established between the first-order and fundamental modes in the BSN/KTP waveguided system. Effective thicknesses for TE and TM modes were obtained to be equal to 0.76 and 0.72 μm, respectively, larger than the thickness of the as-grown BSN film of 0.60 μm. A constituent ratio of Ba:Na:Nb in the BSN film measured was equal to 2:0.82:5.14, slightly deviating from the stoichiometric ratio of 2:1:5, which is attributed to higher relative asymptotic velocity for Nb species and higher evaporation pressure for Na species. Finally, the main factors affecting quality of the as-grown BSN films are also discussed. Received: 26 March 1999 / Accepted: 30 March 1999 / Published online: 19 August 1999     

Search for heavy Majorana neutrinos at future lepton colliders

A nonzero neutrino mass may be a sign of new physics beyond the standard model (SM). To explain the small neutrino mass, we can extend the SM using right-handed Majorana neutrinos in a low-scale seesaw mechanism, and the CP violation effect can be induced due to the CP phase in the interference of heavy Majorana neutrinos. The existence of heavy Majorana neutrinos may lead to lepton number violation processes, which can be used to search for the signals of heavy Majorana neutrinos. In this paper, we focus on the CP violation effect related to two generations of heavy Majorana neutrinos at \begin{document}$ 15 $\end{document} GeV \begin{document}$ <m_{N_1}< 70 $\end{document} GeV in the pair production of W bosons and rare decays. It is valuable to investigate Majorana neutrino production signals and the related CP violation effects in rare W boson decays at future lepton colliders.     

Effects of an odd particle on shape phase transitions in odd-even systems

A scheme to solve the Hamiltonian in the interacting boson-fermion model in terms of the SU(3) coupling basis is introduced,through which the effects of an odd particle on shape phase transitions(SPTs) in odd-A nuclei are examined by comparing the critical behaviors of some selected quantities in odd-even and even-even systems.The results indicate that the spherical to prolate(U(5)-SU(3)) SPT and spherical to γ-soft(U(5)-O(6)) SPT may clearly occur in the odd-even system with the SPT signatures revealed by various quantities including the excitation energies,energy ratio,B(E2) ratio,quadrupole moments,and one-particle-transfer spectroscopic intensities.In particular,the results indicate that the spherical to prolate SPT in the odd-even system can even be strengthened by the effects of the odd particle with the large fluctuations of the quadrupole deformations appearing near the critical point.     

Mass splitting of vector mesons and spontaneous spin polarization under rotation

In this study, we investigate the effect of rotation on the masses of scalar and vector mesons in the framework of the 2-flavor Nambu-Jona-Lasinio model. The existence of rotation produces a tedious quark propagator and a corresponding polarization function. By applying the random phase approximation, the meson mass is numerically calculated. It is found that the behavior of scalar and pseudoscalar meson masses under angular velocity ω is similar to that at a finite chemical potential; both rely on the behavior of the constituent quark mass and reflect the property related to chiral symmetry. However, vector meson ρ masses have a more profound relation to rotation. After analytical and numerical calculations, it turns out that at low temperature and small chemical potential, the mass for spin component \begin{document}$ s_z = 0,\pm 1 $\end{document} of a vector meson under rotation exhibits a very simple mass splitting relation \begin{document}$ m_{\rho}^{s_z}(\omega) = m_\rho(\omega = 0)-\omega s_z $\end{document}, similar to the Zeeman splitting of a charged meson under magnetic fields. Furthermore, the mass of the spin component \begin{document}$ s_z = 1 $\end{document} of vector meson ρ decreases linearly with ω and reaches zero at \begin{document}$ \omega_c = m_\rho(\omega = 0) $\end{document}, which indicates that the system will develop \begin{document}$ s_z = 1 $\end{document} vector meson condensation and the system will be spontaneously spin-polarized under rotation.     

Mono-γ production of a dark vector at future e+e? colliders

The associated production of a dark particle and photon, represented as a mono-γ event, is a promising channel to probe particle content and dynamics in the dark sector. In this study, we investigate the properties of the mono-γ production of vector dark matter at future \begin{document}$ e^+e^- $\end{document} colliders. Photon-like and Pauli operators as well as triple gauge boson interactions involving dark matter are considered in the framework of effective field theory. We show that, in comparison with the Pauli operator, the triple gauge boson couplings are significantly more interesting in high energy colliders. Beam polarization effects are also analyzed, and we show that the experimental sensitivities cannot be significantly enhanced because of the smaller luminosity.     

Conformal couplings and “azimuthal matching” of QCD pomerons

Using the asymptotic conformal invariance of perturbative QCD we derive the expression of the coupling of external states to all conformal spin p components of the forward elastic amplitude. Using the wave function formalism for structure functions at small x, we derive the perturbative coupling of the virtual photon for , which is maximal for linear transverse polarization. The non-perturbative coupling to the proton is discussed in terms of “azimuthal matching” between the proton color dipoles and the configurations of the photon. As an application, the recent conjecture of a second QCD pomeron related to the conformal spin-1 component is shown to rely upon a strong azimuthal matching of the component in –proton scattering. Received: 25 October 1999 / Revised version: 19 January 2000 / Published online: 14 April 2000     

Analysis of the interaction between the ? meson and nucleus

In this study, we systematically investigate the ? meson and nucleus interaction by analyzing and fitting the cross sections of \begin{document}$ \gamma N $\end{document}\begin{document}$ \rightarrow \phi $\end{document}N reactions near the threshold, where N represents the nucleus. Using the vector meson dominant model, the distribution of the ?-N scattering length is presented as a function of energy, and the results show that there is a slight increase in scattering length with increasing energy. Based on this, the average scattering length of a ?-proton is obtained as\begin{document}$ 0.10\pm0.01 $\end{document} fm by combining experimental data and theoretical models. Moreover, the average scattering length of the ?-deuteron interaction is derived to be \begin{document}$ 0.014\pm0.002 $\end{document} fm for the first time. Furthermore, the effect of the momentum transfer \begin{document}$|t_{{\rm min}}|$\end{document} on the ?-N scattering length at the threshold is discussed. The obtained results not only provide important theoretical information for a more comprehensive and accurate study of the ?-N scattering length, but also a basis for future experimental measurements of ? meson production.     

Axial contributions at the top threshold

We calculate the contributions of the axial current to top quark pair production in annihilation at threshold. The QCD dynamics is taken into account by solving the Lippmann-Schwinger equation for the P wave production using the QCD potential up to two loops. We demonstrate that the dependence of the total and differential cross section on the polarization of the and beams allows for an independent extraction of the axial current induced cross section. Received: 11 March 1999 / Published online: 20 May 1999     

Measurement of beauty production at HERA using events with muons and jets

A measurement of the beauty production cross section in ep collisions at a centre-of-mass energy of 319 GeV is presented. The data were collected with the H1 detector at the HERA collider in the years 1999-2000. Events are selected by requiring the presence of jets and muons in the final state. Both the long lifetime and the large mass of b-flavoured hadrons are exploited to identify events containing beauty quarks. Differential cross sections are measured in photoproduction, with photon virtualities Q² < 1 GeV², and in deep inelastic scattering, where 2 < Q² < 100 GeV². The results are compared with perturbative QCD calculations to leading and next-to-leading order. The predictions are found to be somewhat lower than the data.Received: 7 February 2005, Revised: 26 April 2005, Published online: 31 May 2005     

Forward and midrapidity charmonium production at RHIC

J/ψ production at forward and midrapidity at the Relativistic Heavy-Ion Collider (RHIC) is calculated within a previously constructed rate-equation approach accounting for both direct production and regeneration from c and . The results are compared to the experimental data. The observed stronger suppression at forward rapidity can be qualitatively explained by a smaller statistical regeneration component together with stronger cold nuclear matter induced suppression compared to midrapidity. The χ _c over J/ψ ratio and ψ′ over J/ψ ratio are also calculated.     

e+e?γ production at photon-photon colliders at complete electroweak NLO accuracy

We present the NLO electroweak radiative corrections to the \begin{document}$ e^+e^-\gamma $\end{document} production in γγ collision, which is an ideal channel for calibrating the beam luminosity of a Photon Linear Collider. We analyze the dependence of the total cross section on the beam colliding energy, and then investigate the kinematic distributions of final particles at various initial photon beam polarizations at EW NLO accuracy. The numerical results indicate that the EW relative corrections to the total cross section are non-negligible and become increasingly significant as the increase of the beam colliding energy, even can exceed –10% in the \begin{document}${{J}} = 2$\end{document} γγ collision at \begin{document}$ \sqrt{\hat{s}} = 1\; {\rm{TeV}} $\end{document}. Such EW corrections are very important and should be taken into consideration in precision theoretical and experimental studies at high-energy γγ colliders.