Exclusive $B \to (K^*, \rho) \gamma$ decays in general two-Higgs-doublet models

By employing the QCD factorization approach, we calculated the next-to-leading order new physics contributions to the branching ratios, CP asymmetries, isospin and U-spin symmetry breaking of the exclusive decays ( ), induced by the charged Higgs penguins in general two-Higgs-doublet models. Within the considered parameter space, we found that (a) the new physics corrections to the observables are generally small in model I and model III-A, moderate in model II, but large in model III-B; (b) from the well measured branching ratios and upper limits, a lower bound of M_H > 200 GeV in model II was obtained, while the allowed range of M_H in model III-B is GeV; these bounds are comparable with those from the inclusive decay; (c) the NLO Wilson coefficient C₇(m_b) in model III-B is positive and disfavored by the measured value of isospin symmetry breaking , but it still cannot be excluded if we take the large errors into account; (d) the CP asymmetry in model III-B has an opposite sign to the one in the standard model (SM), which may be used as a good observable to distinguish the SM from model III-B; (e) the isospin symmetry breaking is less than in the region of preferred by the global fit result, but it can be as large as 20 to in the regions of and . The SM and model III-B predictions for are opposite in sign for small or large values of the CKM angles; (f) the U-spin symmetry breaking in the SM and the general two-Higgs-doublet models is generally small in size: .Received: 9 October 2003, Revised: 11 November 2003, Published online: 18 February 2004     

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     

Renormalization-group improved calculation of the $B\to X_s\gamma$ branching ratio

Using results on soft-collinear factorization for inclusive B-meson decay distributions, a systematic study of the partial decay rate with a cut on photon energy is performed. For values of E ₀ below about 1.9 GeV, the rate can be calculated without reference to shape functions using a multi-scale operator product expansion (MSOPE). The transition from the shape-function region to the MSOPE region is studied analytically. The resulting prediction for the branching ratio depends on three large scales: m _b , , and . Logarithms associated with these scales are resummed at next-to-next-to-leading logarithmic order. While power corrections in turn out to be small, the sensitivity to the scale GeV (for GeV) introduces significant perturbative uncertainties, which so far have been ignored. The new theoretical prediction for the branching ratio with GeV is , where the first error is an estimate of perturbative uncertainties and the second one reflects uncertainties in input parameters. With this cut of all events are contained. When this fraction is combined with the previously best prediction for the total decay rate, one obtains , with a somewhat less conservative estimate of parametric uncertainties. The implications of larger theory uncertainties for new physics searches are briefly explored with the example of the type-II two-Higgs-doublet model, for which the lower bound on the charged-Higgs mass is reduced compared with previous estimates to approximately 200 GeV at 95% confidence level.Received: 18 September 2004, Revised: 18 January 2005, Published online: 21 February 2005     

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     

Spectra and decays of $\pi \pi$ and $\pi K$ atoms

We describe the spectra and decays of and atoms within a non-relativistic effective field theory. The evaluations of the energy shifts and widths are performed at next-to-leading order in isospin symmetry breaking. We provide general formulae for all S-states, and discuss the states with angular momentum one in some detail. The prediction for the lifetime of the atom in its ground state yields s.Received: 9 May 2004, Published online: 23 July 2004     

CP asymmetry in $B \rightarrow \phi K_{S}$ in a general two-Higgs-doublet model with fourth-generation quarks

We discuss the time-dependent CP asymmetry of the decay in an extension of the standard model with both a two Higgs doublet and additional fourth-generation quarks. We show that, although the standard model with a two Higgs doublet and the standard model with fourth-generation quarks alone are not likely to largely change the effective from the decay , the model with both an additional Higgs doublet and fourth-generation quarks can easily account for the possible large negative value of without conflicting with other experimental constraints. In this model, additional large CP violating effects may arise from the flavor-changing Yukawa interactions between neutral Higgs bosons and the heavy fourth-generation down type quark, which can modify the QCD penguin contributions. With the constraints obtained from processes such as and , this model can lead to an effective as large as - 0.4 in the CP asymmetry of .Received: 25 March 2004, Revised: 20 April 2004, Published online: 18 June 2004     

Search for a narrow charmed baryonic state decaying to $D^{\ast \pm} p^\mp$in ep collisions at HERA

A resonance search has been made in the invariant-mass spectrum with the ZEUS detector at HERA using an integrated luminosity of . The decay channels and (and the corresponding antiparticle decays) were used to identify mesons. No resonance structure was observed in the mass spectrum from more than 60 000 reconstructed mesons. The results are not compatible with a report of the H1 Collaboration of a charmed pentaquark, .Received: 14 September 2004, Revised: 29 September 2004, Published online: 9 November 2004     

Search for chargino and neutralino productionat $\sqrt{s} = 192$-209 GeV at LEP

Approximately 438 pb^-1 of e ⁺ e^- data from the OPAL detector, taken with the LEP collider running at centre-of-mass energies of 192-209 GeV, are analyzed to search for evidence of chargino pair production, , or neutralino associated production, . Limits are set at the 95% confidence level on the product of the cross-section for the process and its branching ratios to topologies containing jets and missing energy, or jets with a lepton and missing energy, and on the product of the cross-section for and its branching ratio to jets. R-parity conservation is assumed throughout this paper. When these results are interpreted in the context of the Constrained Minimal Supersymmetric Standard Model, limits are also set on the masses of the and , and regions of the parameter space of the model are ruled out. Nearly model-independent limits are also set at the 95% confidence level on with the assumption that each chargino decays via a W boson, and on with the assumed to decay via a Z⁰.Received: 15 December 2003, Revised: 16 February 2004, Published online: 23 April 2004     

Masses and couplings of vector mesonsfrom the pion electromagnetic,weak, and $\pi\gamma$ transition form factors

We analyze the pion electromagnetic, charged-current, and transition form factors at timelike momentum transfers q, GeV², using a dispersion approach. We discuss in detail the propagator matrix of the photon-vector meson system and define certain reduced amplitudes, or vertex functions, describing the coupling of this system to final states. We then apply the derived analytic expressions to the analysis of the recent , , and data. We find the reduced amplitudes for the coupling of the photon and vector mesons to two pseudoscalars to be constant, independent of s, in the range considered, indicating a freezing of the amplitudes for GeV. The fit to the form factor data leads to the following values of the Breit-Wigner resonance masses MeV, MeV and MeV, where the errors are only statistical.Received: 8 December 2003, Published online: 23 March 2004T. Paulus: Now at Philips     

Measurement of the strange spectral function in hadronic \tau decays

Tau lepton decays with open strangeness in the final state are measured with the OPAL detector at LEP to determine the strange hadronic spectral function of the lepton. The decays , and with final states consisting of neutral and charged kaons and pions have been studied. The invariant mass distributions of of these final states have been experimentally determined. Monte Carlo simulations have been used for the remaining and for the strange final states including mesons. The reconstructed strange final states, corrected for resolution effects and detection efficiencies, yield the strange spectral function of the lepton. The moments of the spectral function and the ratio of strange to non-strange moments, which are important input parameters for theoretical analyses, are determined. Furthermore, the branching fractions and have been measured.Received: 18 February 2004, Revised: 30 April 2004, Published online: 15 June 2004     

The rare annihilation decays $\bar{B}^0_{s,d} \to J/\psi\gamma$

We investigate the physics potential of the annihilation decays in the standard model and beyond. In a naive factorization approach, the branching ratios are estimated to be and . In the framework of QCD factorization, we compute the non-factorizable corrections and get , . Future measurements of these decays would be useful for testing the factorization frameworks. The smallness of these decays in the SM makes them sensitive probes of new physics. As an example, we will consider the possible admixture of the (V + A) charge current to the standard (V-A) current. This admixture will give a significant contribution to the decays.Received: 29 August 2003, Revised: 17 January 2004, Published online: 19 March 2004Corresponding author: Y.D. Yang     

$\overline pp$ annihilation into four charged pions at rest and in flight

The spin-parity analysis of the data on the annihilation reaction at rest in liquid and in gaseous hydrogen at 3 bar pressure and in flight at momentum of MeV/c, collected by the Obelix spectrometer at the LEAR complex of CERN, is presented. The relative branching ratios and are obtained. It is also shown that the inclusion of the exotic meson , J^PC = 1^{- +} , mass and width , GeV/c², in its decay to , improves the fit and some implications of these results are briefly discussed. The relative S and P-wave annihilation percentages in four charged pions at two target densities are obtained.Received: 2 December 2003, Published online: 23 April 2004     

Search for the \phi1860 Pentaquark at COMPASS

Narrow and resonances produced by quasi-real photons have been searched for by the COMPASS experiment at CERN. The study was stimulated by the recent observation of an exotic baryonic state decaying into , at a mass of 1862 MeV, interpreted as a pentaquark. While the ordinary hyperon states and are clearly seen, no exotic baryon is observed in the data taken in 2002 and 2003.Received: 15 March 2005, Published online: 31 May 2005PACS: 13.60.Hb, 13.60.Rj, 14.20.Jn, 14.80.-j     

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     

Waiting for the discovery of $B^0_d\to K^0\bar K^0$

The CP asymmetries of the decay , which originates from flavor-changing neutral-current processes, and its CP-averaged branching ratio BR offer interesting avenues to explore flavor physics. We show that we may characterize this channel, within the standard model, in a theoretically clean manner through a surface in observable space. In order to extract the relevant information from BR , further information is required, which is provided by the system and the SU(3) flavor symmetry, where we include the leading factorizable SU(3)-breaking corrections and discuss how experimental insights into non-factorizable effects can be obtained. We point out that the standard model implies a lower bound for BR , which is very close to its current experimental upper bound, thereby suggesting that this decay should soon be observed. Moreover, we explore the implications for color suppression in the system, and convert the data for these modes in a peculiar standard-model pattern for the CP-violating observables.Received: 3 August 2004, Published online: 15 November 2004     

CP-sensitive observables in e^ + e^-\to\tilde\chi^0_i \tilde\chi^0_j and neutralino decay into the Z boson

We study CP-sensitive observables in the neutralino production and the subsequent two-body decays of the neutralino and of the Z boson . We identify the CP-odd elements of the Z boson density matrix and propose CP-sensitive triple-product asymmetries. We calculate these observables and the cross sections in the minimal supersymmetric standard model with complex parameters and M ₁ for an e ⁺ e ^- linear collider with GeV and longitudinally polarized beams. We show that the asymmetries can reach for and for and discuss the feasibility of measuring these asymmetries.Received: 4 February 2004, Revised: 17 May 2004, Published online: 2 July 2004     

Forward $\pi^\circ$ production and associated transverse energy flow in deep-inelastic scattering at HERA

Deep-inelastic positron-proton interactions at low values of Bjorken-x down to which give rise to high transverse momentum -mesons are studied with the H1 experiment at HERA. The inclusive cross section for -mesons produced at small angles with respect to the proton remnant (the forward region) is presented as a function of the transverse momentum and energy of the and of the four-momentum transfer Q ² and Bjorken-x. Measurements are also presented of the transverse energy flow in events containing a forward -meson. Hadronic final state calculations based on QCD models implementing different parton evolution schemes are confronted with the data.Received: 8 April 2004, Revised: 7 July 2004, Published online: 30 July 2004Dedicated to the memory of Krzysztof Rybicki     

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     

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