New contributions to heavy quark sum rules

We analyze new contributions to the theoretical input in heavy quark sum rules and we show that the general theory of singularities of perturbation theory amplitudes yields the method to handle these specific features. In particular we study the inclusion of heavy quark radiation by light quarks at and of non-symmetric correlators at . Closely related with this is that we also propose a solution to the construction of moments of the spectral densities at where the presence of massless contributions invalidates the standard approach. We circumvent this problem through a new definition of the moments, providing an infrared safe and consistent procedure. Received: 11 February 2002 / Revised version: 14 March 2002 / Published online: 22 May 2002     

Upper bound on the hadronic light-by-light contribution to the muon g - 2

There are indications that hadronic loops in some electroweak observables are almost saturated by parton level effects. Taking this as the hypothesis for this work, we propose a genuine parton level estimate of the hadronic light-by-light contribution to the anomalous magnetic moment of the muon, a(LBL)/(mu)(had). Our quark mass definitions and values are motivated in detail, and the simplicity of our approach allows for a transparent error estimate. For infinitely heavy quarks our treatment is exact, while for asymptotically small quark masses a(LBL)/(mu)(had) is overestimated. Interpolating, this suggests quoting an upper bound. We obtain a(LBL)/(mu)(had)<1.59x10;{-9} (95% C.L.).     

Predictions of γ(4S)→h_b(1P,2P)π^+π^- transitions

We study the contributions of intermediate bottomonium-like Zb states and the bottom meson loops in the heavy quark spin flip transitionsγ(4 S)→hb(1 P,2 P)π+π-.Depending on the constructive or destructive interferences between the Zb-exchange and the bottom meson loops mechanisms,we predict two possible branching ratios for each process:BRγ(4 S)→hb(1 P)π+π-≈(1.20.40.8×10^-6)or(0.5-0.20.5×10^-6),and BRγ(4 S)→(2 P)π+π-≈(7.1-1.1+1.7×10^-10)or(2.4-0.10.2×10^-10)).The contribution of the bottom meson loops is found to be considerably larger than that of the Zbexchange in the T(4 S)→hb(1 P)ππtransitions,while its decay rates are not comparable to those of heavy quark spin conservedγ(4 S)→γ(1 S,2 S)ππprocesses.We also predict the contribution of the charm meson loops in the branch fractions ofΨ(3 S,4 S)→hc(1 P)ππ.     

Search for heavy toplike quarks using lepton plus jets events in 1.96 TeV pp collisions

We present the results of a search for pair production of a new heavy toplike quark t' decaying to a W boson and another quark using the Collider Detector at Fermilab II detector in run II of the Tevatron pp collider. Using a data sample corresponding to 760 pb(-1) of integrated luminosity, we fit the observed spectrum of total transverse energy and reconstructed t' quark mass to a combination of standard model processes and t' pair production. We see no evidence for t't' production, and we infer a lower limit of 256 GeV/c(2) on the mass of the t' at 95% C.L. assuming standard strong couplings for the t'.     

Heavy quark production in heavy ion colliders

We describe updated calculations of $Q\bar Q$ production in pp and π ^- p interactions. We compare these results to total cross section data and discuss how the baseline cross sections extrapolate to heavy ion collider energies. We touch upon the differences between leading and next-to-leading order heavy quark production. Finally, we discuss the implications of our calculations for quarkonium production. Our discussion here focuses on bottom quarks.     

Timelike Compton scattering: exclusive photoproduction of lepton pairs

We investigate the exclusive photoproduction of a heavy timelike photon which decays into a lepton pair, . This can be seen as the analog of deeply virtual Compton scattering, and we argue that the two processes are complementary for studying generalized parton distributions in the nucleon. In an unpolarized experiment the angular distribution of the leptons readily provides access to the real part of the Compton amplitude. We estimate the possible size of this effect in kinematics where the Compton process should be dominated by quark exchange. Received: 9 October 2001 / Published online: 5 April 2002     

Heavy and heavy to light quark expansions

We analyze the phenomenon of heavy quark condensation within the framework of the QCD sum rule approach. We discuss two alternative expansions for massive quark condensates. The first one (heavy to light quark expansion), introduced by Broadhurst and Generalis, establishes a connection between the heavy and light quark worlds. The other one (heavy quark expansion) is valid when only heavy quark systems are considered. As a byproduct we have obtained the coefficients of \(\left\langle {\bar qq} \right\rangle \) , \(\left\langle {\bar qGq} \right\rangle \) , 〈G ²〉 and 〈G ³〉 for all bilinear currents.     

Point-Form Hamiltonian Dynamics and Applications

This short review summarizes recent developments and results in connection with point-form dynamics of relativistic quantum systems. We discuss a Poincaré invariant multichannel formalism which describes particle production and annihilation via vertex interactions that are derived from field theoretical interaction densities. We sketch how this rather general formalism can be used to derive electromagnetic form factors of confined quark?Cantiquark systems. As a further application it is explained how the chiral constituent quark model leads to hadronic states that can be considered as bare hadrons dressed by meson loops. Within this approach hadron resonances acquire a finite (non-perturbative) decay width. We will also discuss the point-form dynamics of quantum fields. After recalling basic facts of the free-field case we will address some quantum field theoretical problems for which canonical quantization on a space?Ctime hyperboloid could be advantageous.     

Search for a heavy toplike quark in pp collisions at √s=1.96 TeV

We present the results of a search for pair production of a heavy toplike (t') quark decaying to Wq final states using data corresponding to an integrated luminosity of 5.6 fb(-1) collected by the CDF II detector in pp collisions at √s=1.96 TeV. We perform parallel searches for t'→Wb and t'→Wq (where q is a generic down-type quark) in events containing a lepton and four or more jets. By performing a fit to the two-dimensional distribution of total transverse energy versus reconstructed t' quark mass, we set upper limits on the t't' production cross section and exclude a standard model fourth-generation t' quark decaying to Wb (Wq) with mass below 358 (340) GeV/c(2) at 95% C.L.     

Massive loop amplitudes from unitarity

We show, for previously uncalculated examples containing a uniform mass in the loop, that it is possible to obtain complete massive one-loop gauge theory amplitudes solely from unitarity and known ultraviolet or infrared mass singularities. In particular, we calculate four-gluon scattering via massive quark loops in QCD. The contribution of a heavy quark to five-gluon scattering with identical helicities is also presented.     

Spin dependence of heavy quark fragmentation

We propose that the non-perturbative part of the fragmentation function describing the transition from a heavy quark to a heavy meson is proportional to the square of the produced meson wave function at the origin, taking into account hyperfine interactions. We analyze the effects of this proposal on the number of pseudoscalar mesons compared to the number of vector mesons produced and find a good agreement with experimental data. Finally, we discuss further experimental checks for our hypothesis.     

Results for all reactions e^+ e^- \rightarrow 4{\rm f}, 4{\rm f}\gamma with nonzero fermion masses

We accomplish our efforts to obtain predictions for all four–fermion final states of –annihilation and the corresponding bremsstrahlung reactions which are possible in the framework of the Standard Model. For this purpose we have developed a program ee4 . Our predictions are valid for fermions of arbitrary masses and we can obtain results for total cross sections without any collinear cut. Keeping exact fermion masses is of course required for top quark production. We give a detailed phenomenological analysis of fermion mass effects and real photon radiation for all channels of four–fermion production at LEP-II and next linear collider energies. Received: 2 October 2001 / Revised version: 2 January 2002 / Published online: 1 March 2002     

An alternative approach to heavy quark bags

We discuss a formulation of quark bags where the quark wave function depends only on the relative coordinate and the bag boundary is fixed with respect to the center of mass of the quark system. For technical reasons we have to restrict ourselves to a heavy quark-antiquark system in ans wave with spherical boundary. A phenomenological application to quarkonium states encourages further investigation of the approach.     

Extracting the light quark mass ratio m(u)/m(d) from bottomonia transitions

We propose a new method to extract the light quark mass ratio m(u)/m(d) using the Υ(4S)→h(b)π?(η) bottomonia transitions. The decay amplitudes are dominated by the light quark mass differences, and the corrections from other effects are rather small, allowing for a precise extraction. We also discuss how to reduce the theoretical uncertainty with the help of future experiments. As a by-product, we show that the decay Υ(4S)→h(b)η is expected to be a nice channel for searching for the h(b) state.     

Top quark production in e^+ e^- annihilation

We analyze the four-fermion reactions containing a single top quark and three other fermions, a possible decay product of the resonant anti-top quark, in the final state. This allows us to estimate the contribution of the nonresonant Feynman graphs and effects related to the off mass shell production and decay of the top quark. We test the sensitivity of the total cross section at center of mass energies in the threshold region and far above it to the variation of the top quark width. We perform the calculation in an arbitrary linear gauge in the framework of the standard model and discuss the important issue of gauge symmetry violation by a constant top quark width. Received: 21 February 2001 / Revised version: 27 March 2001 / Published online: 18 May 2001     

Chiral magnetism of the nucleona

We study the quark mass expansion of the magnetic moments of the nucleon in a chiral effective field theory including nucleons, pions and delta-resonances as explicit degrees of freedom. We point out that the usual power counting applied so far to this problem misses important quark mass structures generated via an intermediate isovector M1 nucleon-delta transition. We propose a modified power counting and compare the resulting chiral extrapolation function to available (quenched) lattice data. The extrapolation is found to work surprisingly well, given that the lattice data result from rather large quark masses. Our calculation raises the hope that extrapolations of lattice data utilizing chiral effective field theory might be applicable over a wider range in quark masses than previously thought, and we discuss some open questions in this context. Furthermore, we observe that within the current lattice data uncertainties the extrapolations presented here are consistent with the Padé fit ansatz introduced by the Adelaide group a few years ago. Received: 23 April 2002 / Accepted: 18 July 2002 / Published online: 17 December 2002 RID="c" ID="c"e-mail: themmert@physik.tu-muenchen.de RID="d" ID="d"e-mail: weise@ect.it Communicated by A. Sch?fer     

Single Production of Top Quark via e-γ Collision in Left-Right Twin Higgs Model

In the context of the left-right twin Higgs (LRTH) model, we fist study single production of the standard model (SM) top quark via e^-γ collisions. We find that the corrections of the LRTH model to the cross section of the process e^-γ→ν_ebt might be observed only for f≤750 GeV and the heavy top quark mass scale M≥500 GeV in future high energy linear e⁺e^- collider (LC) experiment with the center-of-mass (CM) energy s^½=500 GeV and a yearly integrated luminosity of £=100 fb^-1. We also consider single production of the heavy top quark T via e^-γ collisions. Our numerical results show that the possible signals of the heavy top quark T might be observed via the decay channel T→φ⁺b→tbb in future LC experiment with s^½=3 TeV and £=500 fb^-1.     

On the possibility of P-violation at finite baryon-number densities

We show how the introduction of a finite baryon density may trigger spontaneous parity violation in the hadronic phase of QCD. Since this involves strong interaction physics in an intermediate energy range we approximate QCD by a σ model that retains the two lowest scalar and pseudoscalar multiplets. We propose a novel mechanism based on interplay between lightest and heavy meson states which cannot be realized solely in the Goldstone boson (pion) sector and thereby is unrelated to the one advocated by Migdal some time ago. Our approach is relevant for dense matter in an intermediate regime of few nuclear densities where quark percolation does not yet play a significant role.