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     

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     

Longitudinal $\bar{\Lambda}_0$ polarization in heavy-ion collisions as a probe for QGP formation

We present an analysis of the longitudinal polarization in ultrarelativistic heavy-ion collisions. The polarization of s coming from the decay chain exhibits a very well differentiated behavior depending on the production region of the primordial s. This effect reflects the different values of the ratio in the QGP region, where nucleon-nucleon interactions take place in a hot and dense environment, and the peripherical region, in which ordinary nucleon-nucleon interactions occur. An increase in the longitudinal polarization signals a strangeness enhancement which is thought of as a property of the QGP phase.Received: 21 September 2004, Revised: 25 October 2004, Published online: 17 December 2004     

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     

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     

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     

New gauge bosons from the littlest Higgs modeland the process $e^{ + }e^{-}\rightarrow t\bar{t}$

In the context of the littlest Higgs (LH) model, we study the process . We find that the new gauge bosons Z _H and B _H can produce significant correction effects on this process, which can be further enhanced by suitably polarized beams. In most of the parameter space preferred by the electroweak precision data, the absolute value of the relative correction parameter is larger than 5 %. As long as and the absolute value of the relative correction parameter is larger than . With reasonable values of the parameters of the LH model, the possible signals of the new gauge bosons B _H and Z _H can be detected via the process in the future LC experiments with the CM energy . B _H exchange and Z _H exchange can generate significantly corrections to the forward-backward asymmetry only in a small part of the parameter space.Received: 29 October 2004, Revised: 29 November 2004, Published online: 15 February 2005     

Diffractive $\gamma \gamma$ production at hadron colliders

We compute the cross section for exclusive double-diffractive production at the Tevatron, , and the LHC. We evaluate both the gg and -channel exchange contributions to the process. The observation of exclusive production at the Tevatron will provide a check on the model predictions and offer an opportunity to confirm the expectations for exclusive double-diffractive Higgs production at the LHC.Received: 10 September 2004, Revised: 8 October 2004, Published online: 1 December 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     

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.     

Structures of the f 0(980), a 0(980) mesons and the strong coupling constants g_{f_0 K^+ K^-} , g_{a_0 K^+ K^-} with light-cone QCD sum rules

Making the assumption of explicit isospin violation arising from f ₀(980)-a ₀(980) mixing, we take the point of view that the scalar mesons f ₀(980) and a ₀(980) have both strange and non-strange quark-antiquark components and evaluate the strong coupling constants within the framework of the light-cone QCD sum rules approach. The large strong scalar-KK couplings through both the and components , , and will support the hadronic dressing mechanism; furthermore, in spite of the constituent structure differences between the f ₀(980) and a ₀(980) mesons, the strange components have larger strong coupling constants with the K ⁺ K ^- state than the corresponding non-strange ones, and . From the existing controversial values, we cannot reach a general consensus on the strong coupling constants and the mixing angles.Received: 9 January 2004, Revised: 23 July 2004, Published online: 2 September 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)     

Leptoproduction of $\varrho$ mesons within Regge approach

A model describing the leptoproduction of mesons is considered. For the amplitude of the photon dissociation into a pair, the light-cone wave function is used. Scattering of the colorless pair off the nucleon is computed within reggeon exchange phenomenology. The transition of the scattered quark and antiquark into the final meson is treated with the aid of the parton-hadron duality concept. Numerical calculations of and r⁰⁴₀₀ describe the world data at Q² < 4 GeV² rather reasonably. The calculations of the meson spin density matrix show that the computed matrix elements except r⁰⁴₀₀ are in good agreement with the available experimental data at Q² up to 8 GeV² and the total mass of the system greater than 4 GeV. The Regge phenomenology predictions at the highest experimentally available energies agree with both the HERA data and calculations performed within the perturbative QCD approach even for very high Q² ( -20 GeV²). The predicted scale of the S-channel helicity non-conservation is in reasonable agreement with the experimental data.Received: 18 September 2003, Revised: 17 December 2003, Published online: 13 February 2004     

<Emphasis Type="Italic">T</Emphasis>-dependent Dyson-Schwinger equation in IR regime of QCD: the critical point

The quark mass function in QCD is revisited, using a gluon propagator in the form 1/(k ² + m _g ²) plus , where the second (IR) term gives linear confinement for m _g = 0 in the instantaneous limit, being another scale. To find we propose a new (differential) form of the Dyson-Schwinger equation (DSE) for , based on an infinitesimal subtractive renormalization via a differential operator which lowers the degree of divergence in integration on the RHS, by two units. This warrants in the integrand since its k-dependence is no longer sensitive to the principal term (p-k)² in the quark propagator. The simplified DSE (which incorporates the Ward-Takahashi (WT) identity in the Landau gauge) is satisfied for large p ² by = , except for Log factors. The limit p ² = 0 determines . A third limit, p ² = -m ₀ ², defines the dynamical mass m ₀ via . After two checks ( MeV and = ), for with MeV, the T-dependent DSE is used in the real time formalism to determine the critical index analytically, with the IR term partly serving as the H-field. We find MeV and check the vanishing of and at T _c.Received: 31 August 2004, Published online: 11 January 2005PACS: 24.85. + p, 12.38.Lg, 12.38.AwA.N. Mitra: Permanent address: 244 Tagore Park, Delhi-110009, India.     

Polarisation in sfermion decays: determining $\tan\beta$ and trilinear couplings

The basic parameters of supersymmetric theories can be determined at future e ⁺ e ^- linear colliders with high precision. We investigate in this report how polarisation measurements in and or decays to leptons and t quarks plus neutralinos or charginos can be used to measure (in particular for large values) and to determine the trilinear couplings , A _t and A _b in sfermion pair production.Received: 17 April 2003, Revised: 3 July 2003, Published online: 29 August 2003     

Resumming QCD vacuum fluctuations in three-flavor Chiral Perturbation Theory

Due to its light mass, of order , the strange quark can play a special role in chiral symmetry breaking ( SB): differences in the pattern of SB in the limits N_f = 2 ( , m_s physical) and N_f = 3 ( ) may arise due to vacuum fluctuations of pairs, related to the violation of the Zweig rule in the scalar sector and encoded in particular in the O(p⁴) low-energy constants L₄ and L₆. In case of large fluctuations, we show that the customary treatment of SU(3) x SU(3) chiral expansions generates instabilities upsetting their convergence. We develop a systematic program to cure these instabilities by resumming non-perturbatively vacuum fluctuations of pairs, in order to extract information about SB from experimental observations even in the presence of large fluctuations. We advocate a Bayesian framework for treating the uncertainties due to the higher orders. As an application, we present a three-flavor analysis of the low-energy scattering and show that the recent experimental data imply a lower bound on the quark mass ratio at 95% confidence level. We outline how additional information may be incorporated to further constrain the pattern of SB in the N_f = 3 chiral limit.Received: 2 December 2003, Published online: 3 March 2004J. Stern: stern@ipno.in2p3.fr     

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     

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