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     

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     

Exclusive radiative and electroweak b\to d and b\to s penguin decays at NLO

We provide standard model expectations for the rare radiative decays , and , and the electroweak penguin decays and at the next-to-leading order (NLO), extending our previous results to transitions. We consider branching fractions, isospin asymmetries and direct CP asymmetries. For the electroweak penguin decays, the lepton-invariant mass spectrum and forward-backward asymmetry is also included. Radiative and electroweak penguin transitions in are mainly interesting in the search for new flavor-changing neutral current interactions, but in addition the decays provide constraints on the CKM parameters . The potential impact of these constraints is discussed.Received: 16 January 2005, Published online: 16 March 2005 Corresponding author: Th. Feldmann     

An analysis of the time-dependent CP asymmetryin $B \to \pi \pi$ decays in the standard model

Measurements of the time-dependent CP-asymmetry in the decay and its charge conjugate by the BELLE and BABAR collaborations currently yield and , characterizing the direct and mixing-induced CP-asymmetries, respectively. We study the implication of these measurements on the CKM phenomenology taking into account the available information in the quark mixing sector. Our analysis leads to the results that the ratio |P _c /T _c | involving the QCD-penguin and tree amplitudes and the related strong phase difference in the decays are quite substantial. Using the isospin symmetry to constrain |P _c /T _c | and , where parameterizes the penguin-induced contribution, we present a fit of the current data including the measurements of and . Our best-fits yield , , , , and . At 68% C.L., the ranges are , , , and . Currently en vogue dynamical approaches to estimate the hadronic matrix elements in decays do not provide a good fit of the current data.Received: 5 April 2004, Published online: 14 July 2004A.Ya. Parkhomenko: On leave of absence from Department of Theoretical Physics, Yaroslavl State University, Sovietskaya 14, 150000 Yaroslavl, Russia.     

The $\eta_{c}(2980)$ formation in two-photon collisions at LEP energies

production in interactions has been detected via its decays into ,K ⁺ K ^- K ⁺ K ^- and in the data taken with the DELPHI detector at LEP1 and LEP2 energies. The two-photon radiative width averaged over all observed decay channels is = 13.9 2.0 (stat.) 1.4(syst.) 2.7 (BR) keV. No direct decay channel has been observed. An upper limit < 5.5 keV at 95% confidence level has been evaluated for this decay mode.Received: 3 July 2003, Published online: 7 November 2003     

Four-fermion production at $\gamma\gamma$ colliders: 1. Lowest-order predictions and anomalous couplings

We have constructed a Monte Carlo generator (the corresponding FORTRAN code can be obtained from the authors upon request) for lowest-order predictions for the processes and in the standard model and extensions thereof by an effective coupling as well as anomalous triple and quartic gauge-boson couplings. Polarization is fully supported, and a realistic photon beam spectrum can be taken into account. For the processes all helicity amplitudes are explicitly given in a compact form. The presented numerical results contain, in particular, a survey of cross sections for representative final states and their comparison to results obtained with the program package Whizard/Madgraph. The impact of a realistic beam spectrum on cross sections and distributions is illustrated. Moreover, the size of various contributions to cross sections, such as from weak charged- or neutral-current, or from strong interactions, is analyzed. Particular attention is paid to W-pair production channels where we investigate the impact of background diagrams, possible definitions of the W-pair signal, and the issue of gauge-invariance violation caused by finite gauge-boson widths. Finally, the effects of triple and quartic anomalous gauge-boson couplings on cross sections as well as the possibility to constrain these anomalous couplings at future colliders are discussed.Received: 19 May 2004, Published online: 16 July 2004     

Factorization theorems for high energy nn, \gamma p and \gamma\gamma scattering

The robustness of the factorization theorem for total cross sections, for nn (the even portion of pp and scattering), and scattering, originally proved by Block and Kaidalov using an eikonal formalism, is demonstrated. Factorization theorems for the nuclear slope parameter B and , the ratio of the real to the imaginary portion of the forward scattering amplitude, are derived under very general conditions, using analyticity and the optical theorem.Received: 19 February 2003, Revised: 10 July 2003, Published online: 19 September 2003Work partially supported by Department of Energy contract DA-AC02-76-Er02289 Task D.     

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     

Four-fermion production at $\gamma\gamma$ colliders: 2. Radiative corrections in double-pole approximation

The electroweak radiative corrections to within the electroweak standard model are calculated in double-pole approximation (DPA). Virtual corrections are treated in DPA, leading to a classification into factorizable and non-factorizable contributions, and real-photonic corrections are based on complete lowest-order matrix elements for . Soft and collinear singularities appearing in the virtual and real corrections are combined alternatively in two different ways, namely by using the dipole subtraction method or by applying phase-space slicing. The radiative corrections are implemented in a Monte Carlo generator called Coffer - the computer code can be obtained from the authors upon request - which optionally includes anomalous triple and quartic gauge-boson couplings in addition and performs a convolution over realistic spectra of the photon beams. A detailed survey of numerical results comprises corrections to integrated cross sections as well as to angular, energy, and invariant-mass distributions. Particular attention is paid to the issue of collinear safety in the observables.Received: 3 June 2005, Published online: 5 August 2005     

Exclusive semileptonic rare decays $B \to K^{(*)} l^ + l^-$ in a SUSY SO(10) GUT

In the SUSY SO(10) GUT context, we study the exclusive processes . Using the Wilson coefficients of the relevant operators including the new operators which are induced by neutral Higgs boson (NHB) penguins, we evaluate some possible observables associated with these processes like the invariant mass spectrum (IMS), lepton pair forward-backward asymmetry (FBA), lepton polarization asymmetries etc. In this model the contributions from Wilson coefficients , among new contributions, are dominant. Our results show that the NHB effects are sensitive to the FBA, , and of decay, which are expected to be measured in B factories, the deviation of in can reach 0.1 from SM, which could be seen in B factories, and the average of the normal polarization can reach several percent for and it is 0.05 or so for , which could be measured in the future super B factories and provide useful information to probe new physics and discriminate different models.Received: 30 October 2004, Published online: 9 March 2005     

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     

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     

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     

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     

An analysis of $B \to \eta' K$ decays using a global fit in QCD factorization

In the framework of QCD factorization, we study decays. In order to more reliably determine the phenomenological parameters X _H and X _A arising from end-point divergences in the hard spectator scattering and weak annihilation contributions, we use the global analysis for twelve and VP decay modes, such as , , , , et cetera, but excluding the modes whose (dominant) internal quark-level process is . Based on the global analysis, we critically investigate possible magnitudes of X _H,A and find that both large and small X _H,A terms are allowed by the global fit. In the case of the large X _H,A effects, the standard model (SM) prediction of the branching ratios (BRs) for is large and well consistent with the experimental results. In contrast, in the case of the small X _H,A effects, the SM prediction for these BRs is smaller than the experimental data. Motivated by the recent Belle measurement of through , if we take into account possible new physics effects on the quark-level process , we can explicitly show that these large BRs can be understood even in the small X _H,A case. Specifically, we present two new physics scenarios: R-parity violating SUSY and R-parity conserving SUSY.Received: 28 April 2004, Revised: 12 July 2004, Published online: 7 September 2004     

Quasi-degenerate neutrinos and lepton flavor violationin supersymmetric models

In supersymmetric models the misalignment between fermion and sfermion families introduces unsuppressed flavor-changing processes. Even if the mass parameters are chosen to give no flavor violation, family dependent radiative corrections make this adjustment not stable. We analyze the rate of in SUSY-GUT models with three quasi-degenerate neutrinos and universal scalar masses at the Planck scale. We pay special attention to a recently proposed scenario where the low-energy neutrino mixings are generated from identical quark and lepton mixings at large scales. We show the following. (i) To take universal slepton masses at the GUT scale is a very poor approximation, even in no-scale models. (ii) For large neutrino Yukawa couplings the decay would be observed in the planned experiment at PSI. (iii) For large values of the tau coupling gives important corrections, pushing and to accessible rates. In particular, the non-observation of these processes in the near future would exclude the scenario with unification of quark and lepton mixing angles. (iv) The absence of lepton flavor violating decays in upcoming experiments would imply a low value of , small neutrino couplings, and large ( GeV) SUSY-breaking masses.     

M easur em ent of th e $\mathit{H Z\gamma}$ coupling at th e futur e lin ear e+ e- collid er

We examine the prospects for measuring the coupling of a standard model-like Higgs boson with a mass between 120 and 160 GeV at the future TESLA linear e ⁺ e ^- collider, assuming an integrated luminosity of 1 ab^-1 and a center-of-mass energy of 500 GeV. We consider the Higgs boson produced in association with via the W W fusion reaction , followed by the rare decay into a Z boson and a photon, . Accounting for all main background contributions, a precision of 27% can be achieved in unpolarized e ⁺ e ^- collisions for M _H = 140 GeV. With appropriate initial state polarisations BF( )/BF( ), or the precisions on the partial width, can be improved to 17% and provide valuable information on the coupling. For M _H = 120 and 160 GeV, the small significance of the signals in unpolarized collisions sets upper limits of 79% respectively 72% at 90% confidence level on the branching fraction.Received: 5 March 2003, Revised: 14 July 2003, Published online: 5 September 2003     

Complete description of polarization effects in emission of a photon by an electron in the field of a strong laser wave

We consider the emission of a photon by an electron in the field of a strong laser wave. Polarization effects in this process are important for a number of physical problems. The probability of this process for circularly or linearly polarized laser photons and for arbitrary polarization of all other particles is calculated. We obtain the complete set of functions which describe such a probability in a compact invariant form. Besides this, we discuss in some detail the polarization effects in the kinematics relevant to the problem of conversion at and colliders.Received: 13 February 2004, Published online: 23 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     

The $Z \rightarrow \gamma \gamma,\;gg$ decays in the non-commutative standard model

On non-commutative spacetime, the standard model (SM) allows new, usually SM forbidden, triple gauge boson interactions to occur. In this letter we propose the SM strictly forbidden and decay modes coming from the gauge sector of the non-commutative standard model (NCSM) as a place where non-commutativity could be experimentally discovered. Received: 2 July 2002, Revised: 28 February 2003, Published online: 18 June 2003