Associated production of a light Higgs boson and a chargino pair in the MSSM at linear colliders

In the minimal supersymmetric standard model (MSSM), we study the light Higgs boson radiation off a light-chargino pair in the process at linear colliders with GeV. We analyze cross sections in the regions of the MSSM parameter space where the process cannot proceed via on-shell production and subsequent decay of either heavier charginos or the pseudoscalar Higgs boson A. Cross sections up to a few fb are allowed, according to present experimental limits on the Higgs boson, chargino and sneutrino masses. We also show how a measurement of the production rate could provide a determination of the Higgs boson couplings to charginos.Received: 24 June 2004, Revised: 13 May 2005, Published online: 19 July 2005     

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     

Probing the CP nature of the Higgs bosons by $t\overline{t}$ productionat photon linear colliders

We study the effects of heavy Higgs bosons on the production process at photon linear colliders. The interference patterns between the resonant Higgs production amplitudes and the continuum QED amplitudes are examined. The patterns tell us not only the CP nature of the Higgs bosons but also the phase of the -Higgs vertex which gives new information about the Higgs couplings to new charged particles. We point out that it is necessary to use circularly polarized photon beams to produce efficiently heavy Higgs bosons whose masses exceed the electron beam energy, and show that the above interference patterns of the production amplitudes can be studied by observing t and decay angular distributions. Analytic expressions for the helicity amplitudes for the sequential process are presented in terms of the generic production amplitudes.Received: 2 June 2003, Published online: 24 October 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     

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 low-lying mass spectrum of the N = 1 SU(2) SUSY Yang-Mills theory with Wilson fermions

We analyze the low energy spectrum of bound states of the N = 1 SU(2) SUSY Yang-Mills Theory (SYM). This work continues the investigation of the non-perturbative properties of SYM by Monte Carlo simulations in the Wilson discretization with dynamical gluinos. The dynamics of the gluinos is included by the Two-Step Multi-Bosonic Algorithm (TSMB) for dynamical fermions. A new set of configurations has been generated on a lattice at and . The analysis also includes sets of configurations previously generated on a smaller ( ) lattice at and 0.1955. Guided by predictions from low energy Lagrangians, we consider spin-1/2, scalar and pseudoscalar particles. The spectrum of SYM is a challenging subject of investigation because of the extremely noisy correlators. In particular, meson-like correlators contain disconnected contributions. The larger time-extension of the lattice allows to observe two-state signals in the effective mass. Finite-volume effects are monitored by comparing results from the two lattice sizes.Received: 14 September 2004, Revised: 29 October 2004, Published online: 21 December 2004     

Quantum-hydrodynamical picture of the massive Higgs boson

The phenomenon of spontaneous symmetry breaking admits a physical interpretation in terms of the Bose condensation process of elementary spinless quanta. In this picture, the broken-symmetry phase emerges as a real physical medium, endowed with a hierarchical pattern of scales, supporting two types of elementary excitations for : a massive energy branch , corresponding to the usual Higgs boson field, and a collective gapless branch . This is similar to the coexistence of phonons and rotons in superfluid ⁴He that, in fact, is usually considered the condensed-matter analog of the Higgs condensate. After previous work dedicated to the properties of the gapless phonon branch, in this paper we use quantum hydrodynamics to propose a physical interpretation of the massive branch. On the base of our results, M_H coincides with the energy gap for vortex formation and a massive Higgs boson is like a roton in superfluid ⁴He. Within this interpretation of the Higgs particle, there is no naturalness problem since M_H remains a naturally intermediate, fixed energy scale, even for an ultimate ultraviolet cutoff .Received: 24 November 2003, Published online: 29 January 2004     

CP-sensitive observables in chargino production with transverse $e^{\pm}$ beam polarization

We consider the process at a linear collider with transverse beam polarization. We investigate the influence of the CP phases on azimuthal asymmetries in with subsequent two-body decays and . We show that triple product correlations involving the transverse beam polarization vanish if at least one subsequent chargino decay is not observed. We derive this result within the minimal supersymmetric standard model (MSSM) with complex parameters; however, it holds also in the general MSSM with SUSY flavor violation.Received: 29 March 2004, Published online: 30 July 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)     

Trilepton+top signal from chargino-neutralino decays of MSSM charged Higgs bosons at the LHC

We perform for the Large Hadron Collider (LHC) a detailed study of charged Higgs boson production via the top-bottom quark associated mode followed by decays into a chargino and a neutralino, with masses and couplings as given by the general minimal supersymmetric standard model (MSSM). We focus our attention on the region of parameter space with and intermediate values of , where identification of via decays into standard model (SM) particles has proven to be ineffective. Modelling the CMS detector, we find that a signature consisting of three hard leptons accompanied by a hadronically reconstructed top quark plus substantial missing transverse energy, which may result from decays, can be made viable over a large variety of initially overwhelming SM and MSSM backgrounds, provided MSSM input parameters are favourable: notably, small and light sleptons are important prerequisites. We quantify these statements by performing a fairly extensive scan of the parameter space, including realistic hadron-level simulations, and delineate some potential discovery regions.Received: 16 April 2003, Revised: 23 June 2003, Published online: 29 August 2003S. Moretti: Formerly at: Theory Division, CERN, 1211 Geneva 23, Switzerland and Institute for Particle Physics Phenomenology, University of Durham, Durham DH1 3LE, UK     

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     

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     

<Emphasis Type="Italic">CP</Emphasis> violation in the 3 jet and 4 jet decays of the <Emphasis Type="Italic">Z</Emphasis> boson at GigaZ

We review CP-violating effects in jet and 4 jet decays, assuming the presence of CP-violating effective and couplings. Longitudinal beam polarization is included in the studies. We propose a direct search for such CP-violating couplings by using various CP-odd observables. The data of a future linear collider running at the Z-resonance in the so-called GigaZ option should give significant information on the couplings. Finally we show that stringent bounds on the mass of excited b quarks can be derived if appropriate couplings are of a size characteristic of a strong interaction.Received: 21 August 2003, Published online: 20 November 2003     

Low mass dimuon production in proton-nucleus collisions with the NA60 apparatus

During the June 2002 run NA60 collected around 600 000 dimuon triggers in proton-nucleus collisions at 400 GeV. We show that the collected dimuon mass spectra can be understood in terms of known sources. The specific target setup, consisting of Beryllium, Indium and Lead targets, simultaneously exposed to the beam, allowed us to study the nuclear dependence of the production cross-section of the and resonances. The elementary nucleon-nucleon production cross-sections at 400 GeV for the , and mesons are also presented. By using the -Dalitz decay, dominating the mass range below 450 MeV, we, furthermore, extracted the production cross-section and its nuclear dependence. The results are discussed in the framework of previous measurements, mostly obtained in different decay channels, performed by NA27, HELIOS-1 and CERES-TAPS. Arrival of the final proofs: 1 July 2005 PACS: 25.75.Dw, 25.75.Nq     

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     

Probing the light neutral Higgs boson scenario of the <Emphasis Type="Italic">CP</Emphasis>-violating MSSM Higgs sector at the LHC

In the CP-violating minimal supersymmetric standard model (MSSM), for certain values of the CP-violating phases associated to the universal trilinear couplings (A_t, A_b) and the gluino mass , e.g., or , for GeV and -5, the lightest Higgs boson mass ( ) is GeV. This mass interval is still allowed by results of standard LEP Higgs searches because of a strongly suppressed H₁ZZ coupling. However, in the same region of parameter space in which these two conditions occur, the coupling is enhanced because the two mentioned sets of couplings satisfy a sum rule. In this paper we probe such a light Higgs scenario at the Large Hadron Collider (LHC) by studying associate production, leading to a signal. We show that the latter is readily accessible at the CERN hadron collider, upon the application of suitable selection cuts against the standard model (SM) backgrounds. Our parton level Monte Carlo (MC) analysis yields -45 signal events, completely free of SM background, for - 30 fb^-1 of accumulated luminosity, after taking into account the overall efficiency for tagging four b-jets.Received: 21 February 2005, Published online: 6 July 2005     

The $ B\to\pi K$ puzzle and its relation to rare B and K decays

The standard-model interpretation of the ratios of charged and neutral rates, R _c and R _n, respectively, points towards a puzzling picture. Since these observables are affected significantly by colour-allowed electroweak (EW) penguins, this puzzle could be a manifestation of new physics in the EW penguin sector. Performing the analysis in the R _n- R _c plane, which is very suitable for monitoring various effects, we demonstrate that we may, in fact, move straightforwardly to the experimental region in this plane through an enhancement of the relevant EW penguin parameter q. We derive analytical bounds for q in terms of a quantity L, which measures the violation of the Lipkin sum rule, and point out that strong phases around are favoured by the data, in contrast to QCD factorisation. The modes imply a correlation between q and the angle that, in the limit of negligible rescattering effects and colour-suppressed EW penguins, depends only on the value of L. Concentrating on a minimal flavour-violating new-physics scenario with enhanced Z ⁰ penguins, we find that the current experimental values on require roughly . As the data give , L has either to move to smaller values once the data improve or new sources of flavour and CP violation are needed. In turn, the enhanced values of L seen in the data could be accompanied by enhanced branching ratios for the rare decays , , and . Most interesting turns out to be the correlation between the modes and , with the latter depending approximately on a single scaling variable .Received: 8 September 2003, Published online: 12 November 2003     

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     

Flavour-independent h<Superscript>0</Superscript>A<Superscript>0</Superscript> search and two Higgs doublet model interpretation of neutral Higgs boson searches at LEP

Upper limits on the cross-section of the pair-production process , assuming 100 branching fraction to hadrons, are derived from a new search for the hadrons final state, independently of the hadronic flavour of the decay products. This study, combined with previously published searches for the neutral Higgs bosons h⁰ and A⁰, is used to constrain the Type II Two Higgs Doublet Model (2HDM(II)) with no CP violation in the Higgs sector and no additional non-Standard Model particles besides the five Higgs bosons. The analysis combines LEP1 and LEP2 data collected with the OPAL detector up to the highest available centre-of-mass energies. The searches are sensitive to the and decay modes of the Higgs bosons. A benchmark scan of the 2HDM(II) parameter space is performed. Large regions of the 2HDM(II) parameter space explored are excluded at the 95% CL in the ( and planes, using both direct neutral Higgs boson searches and indirect limits derived from Standard Model high precision measurements. The region GeV and GeV is excluded at 95 % CL, independently of and for selected values of which are representative of a complete -scan.Received: 28 July 2004, Revised: 4 January 2005, Published online: 3 March 2005