Measurement of charm fragmentation ratios and fractionsin photoproduction at HERA

The production of , D⁰, D ⁺ , D_s ⁺ and charm hadrons and their antiparticles in e p scattering at HERA was measured with the ZEUS detector using an integrated luminosity of . The measurement has been performed in the photoproduction regime with the exchanged-photon virtuality and for photon-proton centre-of-mass energies in the range . The charm hadrons were reconstructed in the range of transverse momentum and pseudorapidity . The production cross sections were used to determine the ratio of neutral and charged D-meson production rates, , the strangeness-suppression factor, , and the fraction of charged D mesons produced in a vector state, . The measured and values agree with those obtained in deep inelastic scattering and in e ⁺ e^- annihilations. The measured value is smaller than, but consistent with, the previous measurements. The fractions of c quarks hadronising as a particular charm hadron, , were derived in the given kinematic range. The measured open-charm fragmentation fractions are consistent with previous results, although the measured is smaller and is larger than those obtained in e ⁺ e^- annihilations. These results generally support the hypothesis that fragmentation proceeds independently of the hard sub-process. Received: 12 August 2005, Revised: 8 September 2005, Published online: 6 October 2005     

Jordanian quantum deformations of <Emphasis Type="Italic">D</Emphasis> = 4 anti-de Sitter and Poincaré superalgebras

We consider a superextension of the extended Jordanian twist, describing the non-standard quantization of the anti-de Sitter (AdS) superalgebra in the form of a Hopf superalgebra. The super-Jordanian twisting function and corresponding basic coproduct formulae for the generators of are given in explicit form. A non-linear transformation of the classical superalgebra basis not modifying the defining algebraic relations but simplifying coproducts and antipodes is proposed. Our physical application is in the interpretation of the new super-Jordanian deformation of the superalgebra as deformed D = 4 AdS supersymmetries. Subsequently we perform a suitable contraction of the quantum Jordanian AdS superalgebra and obtain a new -deformation of the D = 4 Poincaré superalgebra, with the bosonic sector describing the light-cone -deformation of the Poincaré symmetries.Received: 19 December 2004, Revised: 13 June 2005, Published online: 19 August 2005     

Impact of four-quark shape functions on inclusive B decay spectra

It has recently been pointed out that a new class of subleading shape functions involving B-meson matrix elements of non-local four-quark operators contributes at order to decay distributions in the endpoint region. The corresponding functions and are estimated using the vacuum-insertion approximation. A numerical analysis of various decay spectra suggests that these power corrections are very small, below present theoretical uncertainties due to other subleading shape-function contributions. Received: 29 June 2005, Published online: 13 September 2005     

Can \phi mesons give an answer to the baryon puzzle at RHIC?

The PHENIX experiment at RHIC has observed a large enhancement of baryon and anti-baryon production at 2-5 GeV/c, compared to expectations from jet fragmentation. While a number of theoretical interpretations of the data are available, there is not yet a definitive answer to the "baryon puzzle". We investigate the centrality dependence of -meson production at mid-rapidity in Au + Au collisions with GeV. Comparison with the proton and anti-proton spectra reveal similar shapes, as expected for soft production described by hydrodynamics. However, the absolute yields show a different centrality dependence. The nuclear modification factors for are similar to those of pions, rather than (anti)protons that have similar mass. At intermediate , baryon/meson effects seem to be more important than the mass effects, in support of recombination models. Arrival of the final proofs: 30 June 2005 PACS: 25.75 -q     

O $$(\bar \Lambda /m_c )$$ effects in tests of factorization hypothesis for heavy-hadron nonleptonic decays

In the framework of the heavy-quark effective theory, theO ( O(_QCD)) corrections are estimated in the test of factorization hypothesis forB-meson nonleptonic decays proposed by Bjorken. Similar calculations are also carried out for _b nonleptonic decays. The effects of these corrections on the estimate of theD _s -meson decay constant are discussed.     

Mott effect and J/\psi dissociation at the quark-hadron phase transition

We investigate the in-medium modification of pseudoscalar and vector mesons in a QCD-motivated chiral quark model by solving the Dyson-Schwinger equations for quarks and mesons at finite temperature for a wide mass range of meson masses, from light ( , ) to open-charm (D, D ^*) states. At the chiral/deconfinement phase transition, the quark-antiquark bound states enter the continuum of unbound states and become broad resonances (hadronic Mott effect). We calculate the in-medium cross-sections for charmonium dissociation due to collisions with light hadrons in a chiral Lagrangian approach, and show that the D- and D ^*-meson spectral broadening lowers the threshold for charmonium dissociation by - and -mesons. This leads to a step-like enhancement in the reaction rate. We suggest that this mechanism for enhanced charmonium dissociation may be the physical mechanism underlying the anomalous suppression observed by NA50.Received: 30 September 2002, Published online: 22 October 2003PACS: 05.20.Dd Kinetic theory - 12.38.Mh Quark-gluon plasma - 14.40.-n Mesons - 25.75.Nq Quark deconfinement, quark-gluon plasma production, and phase transitions     

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     

Dilaton field induces a commutative D<Emphasis Type="Italic">p</Emphasis>-brane coordinate

It is well known that the space-time coordinates and the corresponding Dp-brane world-volume become non-commutative when the ends of the open string are attached to a Dp-brane with the Neveu-Schwarz background field . In this paper, we extend these considerations by including an additional dilaton field , linear in . In that case, the conformal part of the world-sheet metric becomes a new non-commutative variable, while the coordinate in the direction orthogonal to the hyper plane becomes commutative. Received: 15 November 2004, Revised: 11 May 2005, Published online: 6 October 2005 PACS: . Work supported in part by the Serbian Ministry of Science and Environmental Protection, under contract No. 1486.     

Five-Body Calculation of Resonance and Scattering States of the uudd\bar{s} System

The scattering problem of the system, in the standard non-relativistic quark model of Isgur-Karl, is solved for the first time, by treating the large five-body model space, including the NK scattering channel, accurately with the Gaussian expansion method and the Kohn-type coupled-channel variational method. The calculated NK scattering phase shift shows no resonance in the energy region of the reported pentaquark Θ⁺(1540) that is, at 0–500 MeV above the NK threshold (1.4–1.9 GeV in mass). The phase shift does show two resonances just above 500 MeV: a broad ⁺ resonance with a width of Γ ∼ 110 MeV located at ∼ 520 MeV (∼ 2.0 GeV in mass) and a sharp ⁻ resonance with Γ = 0.12 MeV at 540 MeV.     

Leading/nonleading charm-production asymmetry in Σ− p interactions

The asymmetry between the spectra of leading and nonleading charmed mesons that was measured in Σ^? A interactions at p _L=340 GeV/c in the WA89 experiment is described within the Model of Quark-Gluon Strings (QGS model also known as QGSM) under the assumption that there is a fraction of charmed sea quark-antiquark pairs (intrinsic charm) in an interacting hyperon. It is shown that the asymmetries between D ^?-and D ⁺-meson spectra and between D _s ^? -and D _s ⁺ -meson spectra can be approximated by QGSM curves obtained with the same string-fragmentation parameter, a ₁=10, and the same intrinsic-charm fraction, $\delta _{c,\bar c} = 0.01$ , as those that were used in describing D _s ^? /D _s ⁺ -meson asymmetry of π^? A experiments in previous studies. The asymmetry between the spectra of Λ_c and $\bar \Lambda _c $ that was measured in Σ^? A collisions at p _L=600 GeV/c in the E781 experiment is also described within this scheme. The QGSM results are compared with the results of the calculations in the next-to-leading approximation of perturbative QCD that were performed by other authors.     

Properties of theρ-meson in dense nuclear matter

The properties of-mesons in dense nuclear matter are studied in a model which satisfies unitarity and current conservation. The important coupling of the-meson to two pions as well as the strong mixing of pions and delta-nucleon-hole states in nuclear matter are included. The-meson self energy in nuclear matter is evaluated with in-medium pion propagators and the corresponding vertex corrections required by current conservation. We find that the-meson width grows drastically with increasing density while its mass remains almost unchanged.     

The experimental status of Higgs Sector of the Standard Electroweak Model at the end of the LEP-SLC era

A method is proposed to calculate the confidence level for agreement of data with the Higgs sector of the Standard Model (SM). This is done by combining information from direct and indirect Higgs Boson searches. Good agreement with the SM is found for GeV using the observables most sensitive to m_H: A_l and m_W. In particular, quantum corrections, as predicted by the SM, are observed with a statistical significance of forty-four standard deviations. However, apparent deviations from the SM of 3.7 and 2.8 are found for the Z and right-handed Zb couplings respectively. The maximum confidence level for agreement with the SM of the entire data set considered is for GeV. The reason why confidence levels about an order of magnitude higher than this have been claimed for global fits to similar data sets is explained.Received: 8 September 2004, Revised: 22 March 2005, Published online: 18 May 2005     

ATLAS sensitivity to top quark and W boson polarizationin $t\bar{t}$ events

The inelastic production of mesons in ep collisions has been studied with the ZEUS detector at HERA using an integrated luminosity of . The mesons were identified using the decay channel . The measurements were performed in the kinematic range , , 0.2 < z < 0.9 and , where Q² is the virtuality of the exchanged photon, W is the photon-proton centre-of-mass energy, z is the fraction of the photon energy carried by the meson in the proton rest frame and is the rapidity of the in the laboratory frame. The measured cross sections are compared to theoretical predictions within the non-relativistic QCD framework including colour-singlet and colour-octet contributions, as well as to predictions based on the k_T-factorisation approach. Calculations of the colour-singlet process generally agree with the data, whereas inclusion of colour-octet terms spoils this agreement.Received: 18 May 2005, Revised: 24 June 2005, Published online: 27 July 2005     

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     

Parity non-conservation in proton-proton elastic scattering

The parity-non-conserving longitudinal asymmetry in proton-proton (p p) elastic scattering is calculated in the lab energy range 0-350 MeV using contemporary, realistic strong-interaction potentials combined with a weak-interaction potential comprised of - and -meson exchanges as exemplified by the DDH model. Values for the - and -meson coupling constants, and , are determined from comparison with the measured asymmetries at 13.6 MeV, 45 MeV, and 221 MeV.Received: 30 September 2002, Published online: 22 October 2003PACS: 21.30.-x Nuclear forces - 24.80. + y Nuclear tests of fundamental interactions and symmetries - 25.40.Cm Elastic proton scattering     

Total and differential cross-sections for the pp\rightarrow pp\eta^\prime reaction near threshold

The -meson production in the reaction has been studied at excess energies of Q = 26.5, 32.5 and 46.6 MeV using the internal beam facility COSY-11 at the cooler synchrotron COSY. The total cross-sections as well as one angular distribution for the highest Q-value are presented. The excitation function of the near-threshold data can be described by a pure s-wave phase space distribution with the inclusion of the proton-proton final-state interaction and Coulomb effects. The obtained angular distribution of the -mesons is also consistent with pure s-wave production.Received: 11 August 2003, Revised: 14 November 2003, Published online: 6 April 2004PACS: 13.60.Le Meson production - 13.75.-n Hadron-induced low- and intermediate-energy reactions and scattering (energy GeV) - 13.85.Lg Total cross-sections - 25.40.-h Nucleon-induced reactions     

Pair-produced heavy particle topologies: MSSM neutralino properties at the LHC from gluino/squark cascade decays

Processes of the form pp → anything → X_iX_j → + + notE are studied via a technique that may be viewed as an adaptation of time-honoured Dalitz plot analyses. X_i and X_j are new heavy states (with i, j =1, . . .,n), which may be identical or distinct; and and are necessarily distinct standard model (SM) fermion pairs whose invariant masses can be measured. A Dalitz-like plot of said invariant masses, versus , exhibits a topology connected to the masses and specific decay chains of X_i and X_j. Aside from relatively minor details, observed patterns consist of a collection of box and wedge shapes. This collection is model-dependent: comparison of the observed pattern to the possibilities for a specific model yields information on which new particle pair combinations are actually being produced, information beyond that extractable from conventional one-dimensional invariant mass distributions. The technique is illustrated via application to the minimal supersymmetric standard model (MSSM) process pp → → e⁺e^- + μ⁺μ^- notE. Here the heavy states are neutralinos (i = 2,3,4) - note that is excluded - which are produced in gluino/squark ( / ) cascade decay chains. Even with fairly modest expectations for the LHC performance during the first few years, this method still provides substantial insight into the neutralino mass spectrum and couplings if gluino/squark masses are relatively low (≃ 400 GeV). Arrival of the final proofs: 29 November 2005     

Charm photo-and electroproduction at high energies

The differential and total cross sections for the photoproduction of vector D* mesons and for their production in deep-inelastic interactions at the HERA collider are estimated on the basis of a model motivated by perturbative calculations within QCD. The proposed model makes it possible to take into account higher twists in the meson transverse momentum at pT～m _c and to reproduce correctly the dominance of c-quark fragmentation for p _T m _c . The possibility of the hadronization of an octet c $\bar q$ state into a meson is considered, whereby good agreement with experimental data is obtained both for the case of D*-meson photoproduction and for the case of D*-meson formation in a deep-inelastic process.     

Low-mass dielectrons from the PHENIX experiment at RHIC

The production of the low-mass dielectrons is considered to be a powerful tool to study the properties of the hot and dense matter created in the ultra-relativistic heavy-ion collisions. We present the preliminary results on the first measurements of the low-mass dielectron continuum in Au + Au collisions and the φ-meson production measured in Au + Au and d + Au collisions at = 200GeV performed by the PHENIX experiment.