584,361 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
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
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
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
Elastic Electroproduction of
No full textThe total cross sections for the elastic electroproduction of % and J=/ mesons for Q 2 ? 8 GeV 2 and hW i ' 90 GeV=c 2 are measured at HERA with the H1 detector. The measurements are for an integrated electron\Gammaproton luminosity of ' 3 pb \Gamma1 . The dependences of the total virtual photon\Gammaproton (fl p) cross sections on Q 2 , W and the momentum transfer squared to the proton (t), and, for the ae, the dependence on the polar decay angle (cos ` ), are presented. The J=/ : % cross section ratio is determined. The results are discussed in the light of theoretical models and of the interplay of hard and soft physics processes. S. Aid 14 , V. Andreev 26 , B. Andrieu 29 , R.-D. Appuhn 12 , M. Arpagaus 37 , A. Babaev 25 , J. Bahr 36 , J. B'an 18 , Y. Ban 28 , P. Baranov 26 , E. Barrelet 30 , R. Barschke 12 , W. Bartel 12 , M. Barth 5 , U. Bassler 30 , H.P. Beck 38 , H.-J. Behrend 12 , A. Belousov 26 , Ch. Berger 1 , G. Berna..
Photo-Production of
No full textQuasi-elastic (z ? 0:95) photo-production of /(2S) mesons has been observed at HERA for photon-proton centre-of-mass energies in the range 40 to 160 GeV. The /(2S) mesons were identified through their decays to ` + ` \Gamma and to J=/ ß + ß \Gamma , where the J=/ subsequently decays to ` + ` \Gamma , the lepton ` being either a muon or an electron. The cross-section for quasi-elastic photoproduction was measured to be (18:0 \Sigma 2:8(stat) \Sigma 3:0(syst)) nb at a photon-proton centre-of-mass energy of 80 GeV. The ratio of the /(2S) to J=/ quasi-elastic cross-sections is (0:150 \Sigma 0:027(stat) \Sigma 0:022(syst)). Submitted to Physics Letters B C. Adloff 35 , S. Aid 13 , M. Anderson 23 , V. Andreev 26 , B. Andrieu 29 , V. Arkadov 36 , C. Arndt 11 , I. Ayyaz 30 , A. Babaev 25 , J. Bahr 36 , J. B'an 18 , P. Baranov 26 , E. Barrelet 30 , R. Barschke 11 , W. Bartel 11 , U. Bassler 30 , M. Beck 14 , H.-J. Behrend 11 , C. Beier 16 , ..
Light scalar mesons at KLOE
No full textThe scalar mesons of mass below 1 GeV have been studied with the KLOE detector at the Frascati -factory DANE, through the radiative decays of the (1020). The f 0(980) has been studied in the decays ! 0 0 and ! +− looking also for a possible signal of the (600), while for the a0(980) the ! 0 decay has been exploited. The branching ratios of these decays have been measured, and the relevant parameters of the scalar mesons have been extracted from the fit of the invariant masses of the pseudoscalar mesons in the final states. Furthermore an upper limit for the branching ratio of !(a0/ f0)!K0 ̄K 0 has been obtained
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
Evidence for quark gluon plasma from hadron production in high energy nuclear collisions
No full textThe experimental results on the pion, strangeness and J/psi production in high energy nuclear collisions are discussed. The anomalous energy dependence of pion and strangeness production is consistent with the hypothesis that a transition to a deconfined phase takes place between the top AGS (15 AGeV) and the SPS (200 AGeV) energies. The J/psi production systematics at the SPS can be understood assuming that the J/psi mesons are created at hadronization according to the available hadronic phase space. This new interpretation of the J/psi data allows one to establish a coherent picture of high energy nuclear collisions based on the statistical approaches of the collision early stage and hadronization. Surprisingly, the statistical model of strong interactions is successful even in the region reserved up to now for pQCD based models
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