Search for anomalous weak dipole moments of the $\tau$ lepton

The anomalous weak dipole moments of the lepton are measured in a data sample collected by ALEPH from 1990 to 1995 corresponding to an integrated luminosity of 155 pb^-1. Tau leptons produced in the reaction at energies close to the mass are studied using their semileptonic decays to , , or . The real and imaginary components of both the anomalous weak magnetic dipole moment and the CP-violating anomalous weak electric dipole moment, , , and , are measured simultaneously by means of a likelihood fit built from the full differential cross section. No evidence of new physics is found. The following bounds are obtained (95% CL): , , , and .Received: 25 September 2002, Published online: 29 August 2003     

Effects of the scalar FCNC in $b\rightarrow sl^ + l^-$ transitions and supersymmetry

We investigate the potential effects of the scalar flavor changing neutral currents that are generated e.g. in supersymmetry with in the transitions. Using the experimental upper limit on we place stringent model independent constraints on the impact these currents may have on the rates and . We find that in the first case, contrary to the claim made recently in the literature, the maximal potential effects are always smaller than the uncertainty of the standard model NNLO prediction, that is of order 5-15%. In the second case, the effects can be large, but the experimental errors combined with the unsettled problems associated with the relevant form factors do not allow for any firm conclusion about the detectability of a new physics signal in this process. In supersymmetry the effects of the scalar flavor changing neutral currents are further constrained by the experimental lower limit on the B⁰_s- mass difference, so that most likely no detectable signal of the supersymmetry generated scalar flavor changing neutral currents in the processes and is possible.Received: 9 September 2003, Revised: 8 October 2003, Published online: 15 January 2004     

Strange particle production at RHIC in the dual parton model

We compute the mid-rapidity densities of pions, kaons, baryons and antibaryons in Au-Au collisions at GeV in the dual parton model supplemented with final state interaction (comovers interaction). The ratios ( ) increase between peripheral ( ) and central ( collisions by a factor 2.4 (2.0) for the , 4.8 (4.1) for the and 16.5 (13.5) for the . The ratio increases by a factor 1.3 in the same centrality range. A comparison with the available data is presented.Received: 28 April 2003, Published online: 11 July 2003     

The $\beta$-function in duality-covariant non-commutative $\phi^4$-theory

We compute the one-loop -functions describing the renormalisation of the coupling constant and the frequency parameter for the real four-dimensional duality-covariant non-commutative -model, which is renormalisable to all orders. The contribution from the one-loop four-point function is reduced by the one-loop wavefunction renormalisation, but the -function remains non-negative. Both and vanish at the one-loop level for the duality-invariant model characterised by . Moreover, also vanishes in the limit , which defines the standard non-commutative -quantum field theory. Thus, the limit exists at least at the one-loop level.Received: 19 March 2004, Published online: 5 May 2004     

Measurement of inclusive jet cross sections in photoproduction at HERA

Inclusive jet cross sections are measured in photoproduction at HERA using the H1 detector. The data sample of events in the kinematic range of photon virtualities and photon-proton centre-of-mass energies represents an integrated luminosity of . Jets are defined using the inclusive algorithm. Single- and multi-differential cross sections are measured as functions of jet transverse energy E_T ^jet and pseudorapidity in the domain and . The cross sections are found to be in good agreement with next-to-leading order perturbative QCD calculations corrected for fragmentation and underlying event effects. The cross section differential in E_T ^jet, which varies by six orders of magnitude over the measured range, is compared with similar distributions from colliders at equal and higher energies.Received: 24 February 2003, Revised: 26 May 2003, Published online: 11 July 2003     

Dynamical selection rules from $p \bar p$ annihilation at restin three meson final states

The hadronic annihilation branching-ratios in quasi-two-body final states have been obtained from the observation of the reactions , at rest in hydrogen targets at different densities. The enhancement or suppression of specific hadronic channels connected to dynamical selection rules is observed in the production of different resonances both in protonium S and P-waves, systematically investigated for the first time. Besides the well known and enhancement from ³S₁ and ¹S₀ partial waves, the dominance of one isospin source in production, well established from S-waves, is confirmed also in P-waves (¹S₀, I = 0; ³S₁, I = 1; ¹P₁, I = 0; ³P₁, I = 0; ³P₂, I = 1). In addition, the experimental data clearly show a strong suppression of and final states from P-wave which has a remarkable coincidence with pattern production.Received: 4 February 2004, Published online: 5 May 2004     

Power correctionsto the space-like transition form factor {{F_{\eta^{\prime}g^{*}g^{*}}(Q^2,\omega )}}

Employing the standard hard-scattering approach (HSA) in conjunction with the running coupling (RC) method, the latter joined with the infrared renormalon calculus, we compute power-suppressed corrections to the massless -meson-virtual-gluon transition form factor (FF) . Contributions to the form factor from the quark and gluon components of the meson are taken into account. Analytic expressions for the FFs and are also presented, as well as Borel transforms and resummed expressions. It is shown that except for , the Borel transform contains an infinite number of infrared renormalon poles. It is demonstrated that in the explored range of the total gluon virtuality , power corrections found with the RC method considerably enhance the FF relative to results obtained only in the context of the standard HSA with a frozen coupling.Received: 19 May 2003, Revised: 24 October 2003, Published online: 8 December 2003Permanent address: S.S. Agaev: High Energy Physics Lab., Baku State University, Z. Khalilov St. 23, 370148 Baku, Azerbaijan     

Search for lepton-flavor violation at HERA

A search for lepton-flavor-violating interactions and has been performed with the ZEUS detector using the entire HERA I data sample, corresponding to an integrated luminosity of . The data were taken at center-of-mass energies, , of 300 and . No evidence of lepton-flavor violation was found, and constraints were derived on leptoquarks (LQs) that could mediate such interactions. For LQ masses below , limits were set on , where is the coupling of the LQ to an electron and a first-generation quark q₁, and is the branching ratio of the LQ to the final-state lepton (μ or ) and a quark q. For LQ masses much larger than , limits were set on the four-fermion interaction term for LQs that couple to an electron and a quark and to a lepton and a quark , where and are quark generation indices. Some of the limits are also applicable to lepton-flavor-violating processes mediated by squarks in R-Parity-violating supersymmetric models. In some cases, especially when a higher-generation quark is involved and for the process , the ZEUS limits are the most stringent to date. Received: 1 April 2005, Revised: 13 July 2005, Published online: 18 October 2005     

Di-jet production in photon-photon collisionsat $\sqrt{s_{\protect\bf\mathrm{ee}}}$ from 189 to 209 GeV

Di-jet production is studied in collisions of quasi-real photons at e ⁺ e^- centre-of-mass energies from 189 to 209 GeV at LEP. The data were collected with the OPAL detector. Jets are reconstructed using an inclusive -clustering algorithm for all cross-section measurements presented. A cone jet algorithm is used in addition to study the different structure of the jets resulting from either of the algorithms. The inclusive di-jet cross-section is measured as a function of the mean transverse energy of the two leading jets, and as a function of the estimated fraction of the photon momentum carried by the parton entering the hard sub-process, , for different regions of . Angular distributions in di-jet events are measured and used to demonstrate the dominance of quark and gluon initiated processes in different regions of phase space. Furthermore the inclusive di-jet cross-section as a function of and is presented, where is the jet pseudo-rapidity. Different regions of the - -space are explored to study and control the influence of an underlying event. The results are compared to next-to-leading order perturbative QCD calculations and to the predictions of the leading order Monte Carlo generator PYTHIA.Received: 20 December 2002, Published online: 17 October 2003     

The pion form factor within the hidden local symmetry model

We analyze a pion form factor formulation which fulfills the Analyticity requirement within the Hidden Local Symmetry (HLS) Model. This implies an s-dependent dressing of the VMD coupling and an account of several coupled channels. The corresponding function provides nice fits of the pion form factor data from s=-0.25 to s=1 GeV². It is shown that the coupling to has little effect, while improves significantly the fit probability below the mass. No need for additional states like shows up in this invariant-mass range. All parameters, except for the subtraction polynomial coefficients, are fixed from the rest of the HLS phenomenology. The fits show consistency with the expected behaviour of at s=0 up to and with the phase shift data on from threshold to somewhat above the mass. The sector is also examined in relation with recent data from CMD-2. Received: 13 January 2003, Revised: 12 March 2003, Published online: 2 June 2003     

Isospin constraints from/on $B \to \pi\pi$

The Standard Model constraints on which can be derived from the decays are revisited in some depth. As experimental inputs, the , decays complemented by the decays, the CP parameters and , and/or the value of as determined by the global CKM fit are used. The constraints discussed here are model independent in the sense that they rely only on Isospin symmetry, following the Gronau-London proposal. A new bound on and the function are introduced. While another bound applied to BABAR results is shown to imply that is negative. The Grossman-Quinn bound is rediscussed. A close form expression is given for as a function of the measurements. Various scenarios for the future of the isospin analysis are explored. To probe the Standard Model the plane is introduced.Received: 17 December 2004, Published online: 25 January 2005     

Lepton flavor violating <Emphasis Type="Italic">Z</Emphasis>-decays in supersymmetric seesaw model

In the supersymmetric seesaw model, large flavor mixings of sleptons induce the lepton flavor violating (LFV) interactions ( ), which give rise to various LFV processes. In this work we examine the LFV decays . Subject to the constraints from the existing neutrino oscillation data and the experimental bounds on the decays , these LFV Z-decays are found to be sizable, and among them the largest-rate channel can occur with a branching ratio of 10^-8 and may be accessible at the LHC or GigaZ experiment.Received: 1 September 2003, Published online: 20 November 2003     

Double-diffractive $\chi$ meson production at the hadron colliders

The double-diffractive production of and mesons, with a rapidity gap on either side, is studied, using both the Regge formalism and the perturbative QCD approach. Due to the rather low scale, the exclusive double-diffractive process is predicted to dominate, whereas the probability that the incoming protons dissociate is expected to be relatively small. We evaluate the corresponding production cross sections at the Tevatron and LHC energies. For the double-diffractive process with proton dissociation, it is possible to select events with large transverse momenta transferred through the rapidity gaps, by measuring the transverse energy, , flows in the proton fragmentation regions. Then the large provides a scale to justify the use of perturbative QCD, and to allow a spin-parity analysis of the centrally produced system to be performed, by studying the azimuthal angular correlations between the directions of the forward and backward flows. The central production of the new X(3872) charmonium state is considered.Received: 24 March 2004, Published online: 11 May 2004     

CP violation in $B \to \phi K$ decay with anomalous right-handed top quark couplings

We explore CP violation in decay processes in the presence of the anomalous right-handed and couplings. The complex anomalous top coupling can be a source of new CP violation and may lead to a deviation of the observed weak phase in decays, which accounts for the present disagreement of the observed between and decays. Direct CP violation is also predicted. Received: 27 November 2002, Revised: 28 March 2003, Published online: 2 June 2003     

Jet production in charged current deep inelastic <Emphasis Type="Italic">e</Emphasis><Superscript> + </Superscript><Emphasis Type="Italic">p</Emphasis> scatteringat HERA

The production rates and substructure of jets have been studied in charged current deep inelastic e ⁺ p scattering for Q ² > 200 GeV² with the ZEUS detector at HERA using an integrated luminosity of 110.5 pb^-1. Inclusive jet cross sections are presented for jets with transverse energies GeV and pseudorapidities in the range . Dijet cross sections are presented for events with a jet having GeV and a second jet having GeV. Measurements of the mean subjet multiplicity, , of the inclusive jet sample are presented. Predictions based on parton-shower Monte Carlo models and next-to-leading-order QCD calculations are compared to the measurements. The value of , determined from at for jets with GeV, is . The mean subjet multiplicity as a function of Q ² is found to be consistent with that measured in NC DIS.Received: 5 June 2003, Published online: 10 October 2003     

Anomalous $\eta/\eta^\prime$ decays: the triangle and box anomalies

We examine the decay modes within the context of the hidden local symmetry (HLS) model. Using numerical information derived in previous fits to the and Ve ⁺ e ^- decay modes in isolation and the lineshape determined in a previous fit to the pion form factor, we show that all aspects of these decays can be predicted with fair accuracy. Freeing some parameters does not improve the picture. This is interpreted as strong evidence in favor of the box anomaly in the decays, which occurs at precisely the level expected. We also construct the set of equations defining the amplitudes for and at the chiral limit, as predicted from the anomalous HLS Lagrangian appropriately broken. This provides a set of four equations depending on only one parameter, instead of three for the traditional set. This is also shown to match the (two-angle, two-decay-constant) - mixing scheme recently proposed and is also fairly well fulfilled by the data. The information returned from the fits also matches expectations from previously published fits to the decay modes in isolation.Received: 29 June 2003, Revised: 17 September 2003, Published online: 4 November 2003     

Strongest gravitational waves from neutrino oscillationsat supernova core bounce

Resonant active-to-active ( ), as well as active-to-sterile ( ) neutrino ( ) oscillations can take place during the core bounce of a supernova collapse. Besides, over this phase, weak magnetism increases the antineutrino ( ) mean free path, and thus its luminosity. Because the oscillation feeds mass-energy into the target species, the large mass-squared difference between the species ( ) implies a huge amount of energy to be given off as gravitational waves ( erg s^-1), due to anisotropic but coherent flow over the oscillation length. This asymmetric -flux is driven by both the spin-magnetic and the universal spin-rotation coupling. The novel contribution of this paper stems from (1) the new computation of the anisotropy parameter -0.01, and (2) the use of the tight constraints from neutrino experiments as SNO and KamLAND, and the cosmic probe WMAP, to compute the gravitational-wave emission during neutrino oscillations in supernovae core collapse and bounce. We show that the mass of the sterile neutrino that can be resonantly produced during the flavor conversions makes it a good candidate for dark matter as suggested by Fuller et al. , Phys. Rev. D 68, 103002 (2003). The new spacetime strain thus estimated is still several orders of magnitude larger than those from diffusion (convection and cooling) or quadrupole moments of neutron star matter. This new feature turns these bursts into the more promising supernova gravitational-wave signals that may be detected by observatories as LIGO, VIRGO, etc., for distances far out to the VIRGO cluster of galaxies.Received: 26 November 2003, Revised: 26 February 2004, Published online: 3 June 2004     

Isospin breaking in $K \rightarrow \pi\pi$ decays

We perform a complete analysis of isospin breaking in amplitudes in chiral perturbation theory, including both strong isospin violation ( ) and electromagnetic corrections to next-to-leading order in the low-energy expansion. The unknown chiral couplings are estimated at leading order in the 1/N_c expansion. We study the impact of isospin breaking on CP conserving amplitudes and rescattering phases. In particular, we extract the effective couplings g₈ and g₂₇ from a fit to branching ratios, finding small deviations from the isospin-limit case. The ratio measuring the enhancement is found to decrease from in the isospin limit to in the presence of isospin breaking. We also analyze the effect of isospin violation on the CP violation parameter , finding a destructive interference between three different sources of isospin violation. Within the uncertainties of large-N_c estimates for the low-energy constants, the isospin violating correction for is below 15%.Received: 21 November 2003, Published online: 4 February 2004Work supported in part by IHP-RTN, Contract No. HPRN-CT2002-00311 (EURIDICE) and by Acciones Integradas, Project No. 19/2003 (Austria), HU2002-0044 (MCYT, Spain)     

Charmonium production and nuclear absorption in p-A interactions at 450 GeV

The production of and charmonium states in proton-nucleus interactions has been investigated by the NA50 experiment, at the CERN SPS. High statistics data sets were collected with collisions induced by 450 GeV protons incident on Be, Al, Cu, Ag and W targets. The and production cross-sections have been determined for each p-A system and their dependences on the nucleus size have been studied, leading to the so-called normal nuclear absorption. Comparing the two patterns we see that the nuclear absorption is stronger for the than for the . Given the high statistics of the data samples, the (or rapidity) differential cross-sections of the and states have also been studied, for each of the target nuclei.Received: 23 September 2003, Revised: 29 November 2003, Published online: 29 January 2004