20,353 research outputs found
Scalar mesons and tetraquarks by means of lattice QCD
No full textWe study the light scalar mesons a_0(980) and kappa using N_f = 2+1+1 flavor lattice QCD. In order to probe the internal structure of these scalar mesons, and in particular to identify, whether a sizeable tetraquark component is present, we use a large set of operators, including diquark-antidiquark, mesonic molecule and two-meson operators. The inclusion of disconnected diagrams, which are technically rather challenging, but which would allow us to extend our work to e.g. the f_0(980) meson, is introduced and discussed
Dilepton és ritka részecskék keltése nehézion reakciókban = Dilepton and strange particle production in heavy ion reactions
No full textDileptonkeltést számoltunk HADES energiákon különböző modellekben. Egy egyszerű, de nagyon pontosan fittelt modellben, IQMD-ben, azt találtuk, hogy le tudjuk írni a HADES adatokat vákuum tulajdonságú vektormezonokkal, s nem nagyon van lehetöség jelentős közegbeli változásokra. Megvizsgáltuk BUU-val, hogy hogyan lehet megfigyelni vektormezonok közegbeli módosulását a dilepton spektrumban. Azt találtuk, hogy a tömegspektrum nem elég, még erős módosulások megfigyelésére sem, legalább kétszer differenciális hatáskeresztmetszet kell. Spektrálfüggvényt vezettünk be a vektormezonokra transzport modellünkbe, és időbeli fejlődésüket ezek segitségével irjuk le. Megmutattuk, hogy a módszerünk kielégiti az enegia-impulzus megmaradást, és a vákuumban a részecskék visszanyerik vákuumbeli tulajdonságukat. Ez a modell is leirja a HADES adatokat. Rho és A1 mezonok keveredését vizsgáltuk. A keveredés függ a sürüségtöl. QCD-összegszabályok segitségével levezettük a keveredési paraméter sürüségfüggését. Kisérleti kimutatásra azt javasoltuk, hogy keressük a rho-mezonok 3 pionos bomlását p+C 1,5 GeV-es ütközésben. A kombinatorikus-háttér levágás segitségével úgy tünik van esély a jelenség megfigyelésére. Ultrarelativisztikus nehézion-ütközéseket tanulmányoztunk 3D numerikus hidrodinamikai modellel. Jelenleg a hadronizáció és a kifagyás jelenség leirásán dolgozunk. | We calculated dilepton production at HADES energies. In IQMD, we found that we can describe the HADES data with particles having vacuum properties, and there is not much space left for in-medium modification of vector mesons. We studied with BUU how can we observe medium modification of vector mesons in the dilepton mass spectrum. We found that the simple mass spectrum is not enough for observing even strong effects. One has to use at least twofold differential dilepton spectrum to see any. We introduced spectral functions for vector mesons, and let them propagate in our transport model. We showed that our approach is energy-momentum conserving and in vacuum particles regain their vacuum properties. This model could also describe the HADES data. Even strong modification of vector mesons will be washed out in the dilepton spectrum. We studied the mixing of the rho and A_1 mesons. The mixing depends on the density. We derived the mixing parameter as a function of density from QCD sum rules. For experimental signature we suggest to find 3 pion decay of the rho-meson in pi-C collision at 1.5 GeV. With combinatorial background subtraction there is a hope to see this effect. We study ultrarelativistic heavy ion collisions using a 3D numerical hydrodynamical model. We currently work on the description of the hadronization and freeze out processes during which the experimentally observed final state particles are created
Phenomenology of exotic hadrons - hybrid mesons and pentaquarks
No full textThis thesis is concerned with the properties of two classes of exotic hadron: hy- brid mesons, in which an excitation of the gluonic field causes distinction from the conventional mesons and can give rise to JPC quantum numbers not available to a qq̄ state; and pentaquarks, where the usual baryonic qqq structure is supplemented by a qq̄ pair, potentially giving the state an exotic flavour structure. In the hybrid meson sector, we work within the flux-tube model and extend upon an observation made by Isgur that the oscillations of the flux-tube can have dynamical effects upon the quarks living on the ends of the tube. We reverse the logic by allowing oscillations of the quarks caused by interactions with currents to excite modes in the flux-tube and hence hybrid mesons. Electromagnetic, weak and pionic currents are all applied, allowing us to make predictions about the radiative and hadronic decays of hybrid mesons and their production rates in exclusive hadronic decays of the B-meson. Such predictions are of interest to past, present and future experiments at E852, the B-factories and Jefferson Lab. In light of the possible observation of a pentaquark state, the Θ+ , we investigate some phenomenological consequences of certain models proposed to describe this state and attempt to justify one such model within a quark model framework. Jaffe and Wilczek's model for pentaquarks predicts in addition to the 10 [note: with a horizontal line above] with JP=½ , a 10 [note: with a horizontal line above] with JP=3/2+, the multiplets being initially degenerate. Within a dynamical model we are able to calculate the spin-orbit splitting between them and find it to not be large. We also consider the effect of a near degenerate 8 on the states in a pentaquark 10 [note: with a horizontal line above] , outlining a set of characteristic decay systematics that may be used in the search for non-flavour-exotic pentaquarks. In a constituent quark model with colour-spin interactions it is found to be possible to accommodate a Jaffe-Wilczek-like Θ+ with a rather low mass, while simultaneously describing the Δ-N splitting
Decays of open charmed mesons in the extended Linear Sigma Model
No full textWe enlarge the so-called extended linear Sigma model (eLSM) by including the charm quark according to the global U(4)r × U(4)l chiral symmetry. In the eLSM, besides scalar and pseudoscalar mesons, also vector and axial-vector mesons are present. Almost all the parameters of the model were fixed in a previous study of mesons below 2 GeV. In the extension to the four-flavor case, only three additional parameters (all of them related to the bare mass of the charm quark) appear.We compute the (OZI dominant) strong decays of open charmed mesons. The results are compatible with the experimental data, although the theoretical uncertainties are still large
Study of inclusive production of charmonium mesons in B decay
No full textThis is the pre-print version of the Article. The official published version can be accessed from the links below. Copyright @ 2003 APSThe inclusive production of charmonium mesons in B meson decay has been studied in a 20.3 fb-1 data set collected by the BABAR experiment operating at the Υ(4S) resonance. Branching fractions have been measured for the inclusive production of the charmonium mesons J/ψ, ψ(2S), χc1, and χc2. The branching fractions are also presented as a function of the center-of-mass momentum of the mesons and of the helicity of the J/ψ.This work was supported by DOE and NSF (USA), NSERC (Canada), IHEP (China), CEA and CNRS-IN2P3 (France), BMBF and DFG (Germany), INFN (Italy), NFR (Norway), MIST (Russia), and PPARC (United Kingdom). Individuals have received support from the A. P. Sloan Foundation, Research Corporation, and Alexander von Humboldt Foundation
Vector meson production at low x from gauge/gravity duality
No full textWe use gauge/gravity duality to study vector meson (J/?, ? 0 , ?, ?) production in electron-proton scattering, in the limit of high center of mass energy at fixed momentum transfer, corresponding to the limit of low Bjorken x, where the process is dominated by pomeron exchange. Our approach considers the pomeron at strong coupling, described by the graviton Regge trajectory in AdS space with a hard-wall to mimic confinement effects. Both the proton and vector mesons are described by simple holographic wave functions in AdS. This model agrees with HERA H1 data with a ? 2 per degree of freedom below one on total cross-sections, and below two on differential cross-sections, confirming the success of previous studies that model low x DIS and DVCS using gauge/gravity duality
H. J. Bhabha : a case study of synchronous references
No full textQuantitative analysis of the events of synchronous references in the research papers followed throughout the publishing career of an individual scientist revealed interesting highlights on the knowledge-generating-system. In the case study of Homi Jehangir Bhabha first quinquennium and fifth quinquennium of his research career had low Self-references; third quinquennium and fourth quinquennium had moderate Self-references; whereas second quinquennium had highest Self-references. The two major clusters of Self-references occurring during the second and third quinquennium were indicators of active periods of knowledgegenerating and faster communications.(Revised version published in 2006 in International Journal of Nuclear Knowledge Management,Vol.2. No.1. pp.14-30. see PDF2
DESY 04--156 ISSN 0418--9833 August 2004 Inclusive Production of D
No full textInclusive production cross sections are measured in deep inelastic scattering at HERA for meson states composed of a charm quark and a light antiquark or the charge conjugate. The measurements cover the kinematic region of photon virtuality 2 100 GeV inelasticity 0.05 0.7, D meson transverse momenta p t (D) 2.5 GeV and pseudorapidity 1.5. The identification of the D-meson decays and the reduction of the combinatorial background profit from the reconstruction of displaced secondary vertices by means of the H1 silicon vertex detector. The production of charmed mesons containing the light quarks u, d and s is found to be compatible with a description in which the hard scattering is followed by a factorisable and universal hadronisation process. To be submitted to Eur. Phys. J. C A. Aktas , V. Andreev , T. Anthonis , A. Asmone , A. Babaev , S. Backovic , J. Bahr P. Baranov , E. Barrelet , W. Bartel , S. Baumgartner , J. Becker , M. Beckingham O. Behnke , O. Behrendt , A. Belousov , Ch. Berger , N. Berger , T. Berndt , J.C. Bizot J. Bohme , M.-O. Boenig , V. Boudry , J. Bracinik , V. Brisson , H.-B. Broker D.P. Brown , D. Bruncko , F.W. Busser , A. Bunyatyan 12,36 , G. Buschhorn L. Bystritskaya , A.J. Campbell , S. Caron , F. Cassol-Brunner , K. Cerny V. Chekelian , C. Collard , J.G. Contreras , Y.R. Coppens , J.A. Coughlan , B.E. Cox G. Cozzika , J. Cvach , J.B. Dainton , W.D. Dau , K. Daum 35,41 , B. Delcourt R. Demirchyan , A. De Roeck 10,44 , K. Desch , E.A. De Wolf , C. Diaconu , J. Dingfelder V. Dodonov , A. Dubak , C. Duprel , G. Eckerlin , V. Efremenko , S. Egli , R. Eichler F. Eisele , M. Ellerbrock , E. Elsen , M. Erdmann 10,4..
Lattice investigation of the tetraquark candidates a0(980) and kappa
No full textIt is a long discussed issue whether light scalar mesons have sizeable four-quark components. We present an exploratory study of this question using Nf = 2+1+1 twisted mass lattice QCD. A mixed action approach ignoring disconnected contributions is used to calculate correlatormatrices consisting of mesonic molecule, diquark-antidiquark and two-meson interpolating operators with quantum numbers of the scalar mesons a0(980) (1(0++)) and k (1/2(0+)). The correlation matrices are analyzed by solving the generalized eigenvalue problem. The theoretically expected free two-particle scattering states are identified, while no additional low lying states are observed. We do not observe indications for bound four-quark states in the channels investigated
Studies of Light Scalar Particles and Dressed Gauge Propagators in QCD
No full textThe equations of QCD are widely believed to describe the properties of
mesons, baryons and their hadronisation after hard interactions at particle
accelerators such as the LHC. However, the theoretical framework
linking the fundamental Lagrangian of QCD to the mesons and baryons
observed in experiment is still in development. The states observed by
experiments can be investigated using a variety of other theoretical methods.
We consider here two methods, Chiral Perturbation Theory and
carefully considering the poles in a scattering amplitude. In chapters 2
and 3 we apply these methods to determine the composition of the sigma(600) and f0(980) scalar resonances observed in scattering.
In chapter 4 we turn to make the connection between the fundamental
Lagrangian and the observed physics. The first step here is to solve the
Schwinger-Dyson equations for the gluons, ghosts and quarks which describe
how a Green’s function behaves non-perturbatively. We primarily
investigate the coupled gluon and ghost system without quarks. We find
that non–trivial vertices are required to obtain self–consistent solutions
in the simplest truncation and that a solution with a finite ghost dressing
function appears to be preferred
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