Hunting a light <Emphasis Type="Italic">CP</Emphasis>-violating Higgs boson via diffraction at the LHC

We study the central diffractive production of the (three neutral) Higgs bosons, with a rapidity gap on either side, in an MSSM scenario with CP-violation. We consider the and decay for the light H₁ boson and the four b-jet final state for the heavy H₂ and H₃ bosons, and discuss the corresponding backgrounds. A direct indication of the existence of CP-violation can come from the observation of either an azimuthal asymmetry in the angular distribution of the tagged forward protons (for the exclusive process) or of a contribution in the azimuthal correlation between the transverse energy flows in the proton fragmentation regions for the process with the diffractive dissociation of both incoming protons ( ). We emphasise the advantage of reactions with the rapidity gaps (that is, production by pomeron-pomeron fusion) to probe CP-parity and to determine the quantum numbers of the produced central object.Received: 16 January 2004, Published online: 31 March 2004     

Observation of bound excited states in 15B

The structure of the A/Z = 3 nucleus ¹⁵B has been investigated using the in-beam -spectroscopy technique with a fragmentation reaction of a ³⁶S beam on a ⁹Be target at 77.5 . The fragments were identified and selected by their energy loss and time of flight using the SPEG spectrograph. -ray energies and intensities have been measured in coincidence with the projectile-like fragments. From this information as well as from the -coincidence relationships a level scheme is proposed for ¹⁵B up to the neutron separation energy. The experimental results have been interpreted using shell model calculations in the psd valence space. Effects of the weakly bound nature of the valence neutrons have been observed.Received: 4 May 2004, Revised: 2 September 2004, Published online: 19 October 2004PACS: 25.70.Mn Projectile and target fragmentation - 23.20.Lv transitions and level energies - 27.20. + n - 21.60.Cs Shell model     

Jet production in <Emphasis Type="Italic">pA</Emphasis> and <Emphasis Type="Italic">AA</Emphasis> collisions in the perturbative QCD pomeron model

Inclusive cross-sections for gluon jet production are studied numerically in the perturbative QCD pomeron model for pA and central AA collisions at high energies. Two forms for the inclusive cross-sections, with and without emission from the triple pomeron vertex, are compared. The difference was found to reduce to a numerical factor for momenta below the saturation momentum Q _s. Above Q _s no difference was found at all. For pA collisions the gluon spectrum was found to be at momenta k below Q _s and above it. For central AA collisions it was found to be at momenta k below Q _s and above it. At large k the spectrum goes like , flattening with energy. The multiplicities turned out to be proportional to A ^0.7 for pA collisions and A for central AA collisions with a good precision. In the latter case they are becoming more peaked at the center with the growth of energy. Their absolute values are high and grow rapidly with energy in accordance with the high value of the BFKL intercept.Received: 12 October 2004, Revised: 22 November 2004, Published online: 21 January 2005     

Fragmentation of Si clusters studied by a dynamical Hartree-Fock method at semi-empirical level

This study describes fragmentation of silicon clusters of size . Fragmentation is produced by the increase of the kinetic energy E_k of the nuclear system and a time-dependent Hartree-Fock method, with a semi-empirical Hamiltonian is used for the evaluation of the transient ensuing the energy input. A typical channel of fragmentation has been observed which consists on the emission of small (from 1 to 5) groups of atoms. Due to these losses, the fragmentation remnants for reach a size equal to 1/2-1/4 of the original one. These trends are in agreement with the experimental ones. Furthermore the critical energies obtained from fragmentation calculations are discussed in the light of the binding energies evaluated for the stationary state.Received: 12 August 2003, Published online: 9 April 2004PACS: 21.60.-n Nuclear structure models and methods - 31.15.Ct Semi-empirical and empirical calculations (differential overlap, Hückel, PPP methods, etc.) - 79.60.Jv Interfaces; heterostructures; nanostructures     

Uncertainties in estimating <Emphasis Type="Italic">B</Emphasis><Subscript><Emphasis Type="Italic">c</Emphasis></Subscript> hadronic productionand comparisons of the production at TEVATRON and LHC

The uncertainties in estimating the hadronic production of the B _c meson are studied in the framework of the complete approach of perturbative QCD and the gluon-gluon fusion mechanism. Quantitative comparisons of the production at TEVATRON and LHC are made. Considering the detectors at TEVATRON and LHC, we have also estimated the production with proper kinematic cuts. Based on the results, we conclude that the experimental studies of the B _c meson at the two colliders will be complementary and mutually stimulative. We find that as the CM energy is increasing from RUN-I to RUN-II at TEVATRON, the production cross section increases by about .Received: 21 July 2004, Published online: 18 November 2004PACS: 12.38.Bx, 13.85.Ni, 14.40.Nd, 14.40.Lb     

<Emphasis Type="Italic">B</Emphasis><Subscript><Emphasis Type="Italic">K</Emphasis></Subscript> from the lattice with Wilson quarks

We report our results for the bag parameter B _K obtained from the quenched simulations on the lattice with Wilson fermions for three values of the lattice spacing. We implemented the method by which no subtraction of the mixing with other four-fermion operators is needed. Our final result, in terms of the renormalization group invariant bag parameter, is .Received: 9 July 2004, Revised: 27 July 2004, Published online: 21 September 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.     

First observation of excited states in the <Superscript>110</Superscript>Mo nucleus

The ground-state band in ¹¹⁰Mo has been observed for the first time. The band, comprising six levels, has been populated in the spontaneous fission of ²⁴⁸Cm and studied by means of prompt -ray spectroscopy using the EUROGAM2 array. The ratio suggests that the deformation of ¹¹⁰Mo is smaller than that in ¹⁰⁸Mo but may stabilize at higher neutron number, where an oblate shape is expected. The new data suggests that the deformation of Sr and Zr isotopes decreases above neutron number N = 64.Received: 23 February 2004, Published online: 2 June 2004PACS: 23.20.Lv transitions and level energies - 21.60.Cs Shell model - 25.85.Ca Spontaneous fission - 27.60. + j      

On the number of contacts of two polymer chains situated on fractal structures

We study the critical behavior of the number of monomer-monomer contacts for two polymers in a good solvent. Polymers are modeled by two self-avoiding walks situated on fractals that belong to the checkerboard (CB) and X family. Each member of a family is labeled by an odd integer b, . By applying the exact Renormalization Group (RG) method, we establish the relevant phase diagrams whereby we calculate the contact critical exponents (for the CB and X fractals with b = 5 and b = 7). The critical exponent is associated with power law of the number of sites at which the two polymers are touching each other.Received: 12 March 2004, Published online: 3 August 2004PACS: 64.60.Ak Renormalization-group, fractal, and percolation studies of phase transitions - 36.20.Ey Conformation (statistics and dynamics)     

Multiplicity correlations of intermediate-mass fragments with pions and fast protons in <Superscript>12</Superscript>C + <Superscript>197</Superscript>Au

Low-energy ( MeV) from ¹² C + ¹⁹⁷ Au collisions at incident energies from 300 to 1800 MeV per nucleon were detected with the Si-Si(Li)-CsI(Tl) calibration telescopes of the INDRA multidetector. The inclusive angular distributions are approximately isotropic, consistent with multiple rescattering in the target spectator. The multiplicity correlations of the low-energy pions and of energetic protons ( MeV) with intermediate-mass fragments were determined from the measured coincidence data. The deduced correlation functions for inclusive event samples reflect the strong correlations evident from the common impact parameter dependence of the considered multiplicities. For narrow impact parameter bins (based on charged-particle multiplicity), the correlation functions are close to unity and do not indicate strong additional correlations. Only for pions at high particle multiplicities (central collisions) a weak anticorrelation is observed, probably due to a limited competition between these emissions. Overall, the results are consistent with the equilibrium assumption made in statistical multifragmentation scenarios. Predictions obtained with intranuclear-cascade models coupled to the Statistical Multifragmentation Model are in good agreement with the experimental data.Received: 9 December 2003, Revised: 18 February 2004, Published online: 31 August 2004PACS: 25.70.Mn Projectile and target fragmentation - 25.70.Pq Multifragment emission and correlations - 25.75.Dw Particle and resonance production - 25.75.Gz Particle correlations     

Inclusive photoproduction of <Emphasis Type="Italic">D</Emphasis><Superscript>*</Superscript> mesons with massive charm quarks

We have calculated the next-to-leading order cross sections for the inclusive production of D ^* mesons in collisions at HERA in two approaches using massive or massless charm quarks. The usual massive theory for the direct cross section with charm quarks only in the final state was transformed into a massive theory with subtraction by subtracting the mass divergent and additional finite terms calculated earlier in connection with the process . This theory approaches the massless theory with increasing transverse momentum. The difference between the massive and the massless approach with subtraction is studied in detail in those kinematic regions relevant for comparison with experimental data. With these results and including the resolved cross section which is dominated by the part originating from the charm in the photon, we compute the fully inclusive cross section and compare it with preliminary data from the ZEUS collaboration at HERA. We find on average good agreement.Received: 5 October 2004, Published online: 26 November 2004     

Systematics of deformed states around doubly-magic <Superscript>40</Superscript>Ca

The low-lying rotational bands of A = 36-48 nuclei are consistently explained by starting from the recently discovered, superdeformed intrinsic state of ³⁶Ar as the core, filling successively the first three Nilsson orbits above the Fermi border. The critical single-particle energies were obtained from experimental data as were the residual interactions in the parametrization of Brink and Kerman. Implicit are the rearrangement energies due to configuration-dependent equilibrium deformations. The binding energies of 20 experimental bandheads were used to derive the parameters while another 38 bandheads were subsequently predicted and identified almost completely. The Racavy expression reduced by 20% reproduces or predicts the values of the deformation parameter . The empirical Nilsson model amended by -vibrational and rotation-aligned bands accounts completely for the multi-particle excitations from the N = 2 into the N = 3 major shell which are not accessible by shell-model calculations. In the case of ⁴⁰Ca a spectrum of 42 states below E _x = 8 MeV is explained.PACS: 21.60.Ev Collective models - 21.10.Dr Binding energies and masses - 27.30. + t - 27.40. + z      

Canonical local algorithms for spin systems: heat bath and Hasting’s methods

We introduce new fast canonical local algorithms for discrete and continuous spin systems. We show that for a broad selection of spin systems they compare favorably to the known ones except for the Ising 1 spins. The new procedures use discretization scheme and the necessary information have to be stored in computer memory before the simulation. The models for testing discrete spins are the Ising 1, the general Ising S or Blume-Capel model, the Potts and the clock models. The continuous spins we examine are the O(N) models, including the continuous Ising model (N = 1), the Ising model (N = 1), the XY model (N = 2), the Heisenberg model (N = 3), the Heisenberg model (N = 3), the O(4) model with applications to the SU(2) lattice gauge theory, and the general O(N) vector spins with .Received: 16 August 2004, Published online: 21 October 2004PACS: 05.70.Fh Phase transitions: general studies - 64.60.Cn Order-disorder transformations; statistical mechanics of model systems - 75.10.Hk Classical spin models - 75.10.Nr Spin-glass and other random models     

Isospin mixing in the 4<Superscript> + </Superscript> doublet of <Superscript>54</Superscript><Emphasis Type="Italic">Co</Emphasis>

The T = 1 admixture into the T = 0 member of a recently discovered isospin-doublet in ⁵⁴Co is obtained from the measured electromagnetic E2/M1 multipole mixing ratio, of the transition. Combining these data with shell model calculations for strong isovector M1 and isoscalar E2 electromagnetic matrix elements one obtains a value for the T = 1 admixture into the T = 0, 4 ⁺ state of . The corresponding mixing matrix element in the 4 ⁺ doublet is keV.Received: 31 October 2002, Published online: 9 March 2004PACS: 21.10.Hw Spin, parity, and isobaric spin - 21.60.Cs Shell model - 23.20.Gq Multipole mixing ratios     

Flavor changing neutral currents from lepton and <Emphasis Type="Italic">B</Emphasis> decays in the two Higgs doublet model

Constraints on the whole spectrum of lepton flavor violating vertices are shown in the context of the standard two Higgs doublet model. The vertex involving the e- mixing is much more constrained than the others, and the decays proportional to such a vertex are usually very suppressed. On the other hand, bounds on the quark sector are obtained from leptonic decays of the B_d,s⁰ mesons and from . We emphasize that although the B_d⁰- mixing restricts severely the d-b mixing vertex, the upper bound for this vertex could still give a sizable contribution to the decay with respect to the standard model contribution, from which we see that such a vertex could still play a role in the phenomenology.Received: 16 September 2004, Published online: 26 April 2005PACS: 12.60.Fr, 12.15.Mm, 12.15.Ff, 11.30.Hv     

Study of <Emphasis Type="Italic">N</Emphasis> = <Emphasis Type="Italic">Z</Emphasis> nuclei in variation-after-projection framework

Variation-after-projection (VAP) calculations in conjunction with the Hartree- Bogoliubov (HB) ansatz have been carried out for A = 68-88, N = Z nuclei. In this framework, the yrast spectra with , B(E2) transition probabilities and deformation parameter ( ) have been obtained. A pairing interaction for like particles as well as protons and neutrons has been included in the model for a two-body interaction.Received: 28 April 2003, Revised: 20 March 2004, Published online: 14 September 2004PACS: 21.10.-k Properties of nuclei; nuclear energy levels - 21.60.-n Nuclear structure models and methods - 27.50. + e      

<Emphasis Type="Italic">B</Emphasis> decays into light scalar particles and glueball

The recent observations of f ₀(980) in charmless B decays motivate further studies of scalar particle and glueball production in these processes. Amplitudes for charmless two-body B decays involving the members of the scalar nonet are presented based on the symmetries of the dominant penguin contribution. Different scenarios for the lightest scalar nonet are investigated in view of the presently available data. We describe the evidence from B decays for f ₀(1500) with a flavor octet like mixing and the hints towards the members of the nonet of lowest mass. There is further support for the hypothesis of a broad 0 ^{+ +} glueball acting as coherent background especially in . The estimated B decay rates into gluonic mesons represent a sizable fraction of the theoretically derived decay rate for .Received: 23 April 2004, Revised: 27 October 2004, Published online: 21 December 2004Work supported in part by the Schweizerischer Nationalfonds.     

<Emphasis Type="Italic">K</Emphasis><Subscript><Emphasis Type="Italic">e</Emphasis>3</Subscript> decays and CKM unitarity

We present a detailed numerical study of the K_e3 decays to in chiral perturbation theory with virtual photons and leptons. We describe the extraction of the CKM matrix element |V_us| from the experimental K_e3 decay parameters. We propose a consistency check of the K ⁺ _e3 and K⁰_e3 data that is largely insensitive to the dominating theoretical uncertainties, in particular the contributions of . Our analysis is highly relevant in view of the recent high statistics measurement of the K ⁺ _e3 branching ratio by E865 at Brookhaven which does not indicate any significant deviation from CKM unitarity but rather a discrepancy with the present K⁰_e3 data.Received: 22 January 2004, Published online: 30 April 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)