Showing papers on "Meson published in 2010"

Prediction of narrow N* and Λ* resonances with hidden charm above 4 GeV.

Abstract: Up to now, all established baryons can be ascribed into 3-quark (qqq) configurations [1], although some of them were suggested to be meson-baryon dynamically generated states [2–8] or states with large (qqqq¯ q) components [9–11]. A difficulty to pin down the nature of these baryon resonances is that the predicted states from various models are around the same energy region and there are always some adjustable ingredients in each model to fit the experimental data. In this letter, we report a study of the interactions between various charmed mesons and charmed baryons within the framework of the coupled channel unitary approach with the local hidden gauge formalism. Several meson-baryon dynamically generated ¯ ¯ ¯

Spin determination of single-produced resonances at hadron colliders

Abstract: We study the production of a single resonance at the LHC and its decay into a pair of Z bosons. We demonstrate how full reconstruction of the final states allows us to determine the spin and parity of the resonance and restricts its coupling to vector gauge bosons. Full angular analysis is illustrated with the simulation of the production and decay chain including all spin correlations and the most general couplings of spin-zero, -one, and -two resonances to Standard Model matter and gauge fields. We note implications for analysis of a resonance decaying to other final states.

Light hadrons from lattice QCD with light (u, d), strange and charm dynamical quarks

Abstract: We present results of lattice QCD simulations with mass-degenerate up and down and mass-split strange and charm (N f = 2 + 1 + 1) dynamical quarks using Wilson twisted mass fermions at maximal twist. The tuning of the strange and charm quark masses is performed at two values of the lattice spacing a ≈ 0:078 fm and a ≈ 0:086 fm with lattice sizes ranging from L ≈ 1:9 fm to L ≈ 2:8 fm. We measure with high statistical precision the light pseudoscalar mass m PS and decay constant f PS in a range 270 ≲ m PS ≲ 510 MeV and determine the low energy parameters f 0 and $ {\bar{l}_{3,4}} $ of SU(2) chiral perturbation theory. We use the two values of the lattice spacing, several lattice sizes as well as different values of the light, strange and charm quark masses to explore the systematic effects. A first study of discretisation effects in light-quark observables and a comparison to N f = 2 results are performed.

Physics with the KLOE-2 experiment at the upgraded DA Phi NE

Abstract: Investigation at a f-factory can shed light on several debated issues in particle physics. We discuss: (i) recent theoretical development and experimental progress in kaon physics relevant for the Standard Model tests in the flavor sector, (ii) the sensitivity we can reach in probing CPT and Quantum Mechanics from time evolution of entangled-kaon states, (iii) the interest for improving on the present measurements of non-leptonic and radiative decays of kaons and eta/eta' mesons, (iv) the contribution to understand the nature of light scalar mesons, and (v) the opportunity to search for narrow di-lepton resonances suggested by recent models proposing a hidden dark-matter sector. We also report on the e(+)e(-) physics in the continuum with the measurements of (multi) hadronic cross sections and the study of gamma gamma processes.

Quasi-elastic electroproduction of charged \rho -mesons on nucleons

Abstract: The electroproduction of charged $ \rho$ -mesons on the nucleon at intermediate energy is discussed for quasi-elastic kinematics. It is shown that at these kinematics both the longitudinal $ \sigma_{{L}}^{}$ and transverse $ \sigma_{{T}}^{}$ cross-sections are dominated by the $ \rho$ -meson t -pole contribution, and thus the corresponding dσL(T)/dt data can give a valuable information on the $ \rho$ -meson component of the nucleon cloud. The differential cross-sections for the reaction p(e, e ′ $ \rho^{+}_{}$ )n at Q 2 = 2 , 3.5GeV^2 and at the invariant mass W = 3 and 4GeV are calculated on the basis of quasi-elastic knockout mechanism with form factors. Questions about the gauge invariance of the electroproduction amplitude are considered and it is noted an important difference between photo- and electroproduction amplitudes.

Superconductivity of QCD vacuum in strong magnetic field

Abstract: We show that in a sufficiently strong magnetic field the QCD vacuum may undergo a transition to a new phase where charged ${\ensuremath{\rho}}^{\ifmmode\pm\else\textpm\fi{}}$ mesons are condensed. In this phase the vacuum behaves as an anisotropic inhomogeneous superconductor which supports superconductivity along the axis of the magnetic field. In the directions transverse to the magnetic field the superconductivity is absent. The magnetic-field-induced anisotropic superconductivity---which is realized in the cold vacuum, i.e. at zero temperature and density---is a consequence of a nonminimal coupling of the $\ensuremath{\rho}$ mesons to the electromagnetic field. The onset of the superconductivity of the charged ${\ensuremath{\rho}}^{\ifmmode\pm\else\textpm\fi{}}$ mesons should also induce an inhomogeneous superfluidity of the neutral ${\ensuremath{\rho}}^{0}$ mesons. We also argue that due to simple kinematical reasons a strong enough magnetic field makes the lifetime of the $\ensuremath{\rho}$ mesons longer by closing the main channels of the strong decays of the $\ensuremath{\rho}$ mesons into charged pions.

Heavy-light meson spectroscopy and Regge trajectories in the relativistic quark model

Abstract: The masses of the ground, orbitally and radially excited states of heavy-light mesons are calculated within the framework of the QCD-motivated relativistic quark model based on the quasipotential approach. Both light (q=u,d,s) and heavy (Q=c,b) quarks are treated fully relativistically without application of the heavy-quark 1/m Q expansion. The Regge trajectories in the (M 2,J) and (M 2,n r ) planes are investigated and their parameters are obtained. The results are in good agreement with available experimental data except for the masses of the anomalous $D^{*}_{s0}(2317)$ , D s1(2460) and $D_{sJ}^{*}(2860)$ states.

Soft-Gluon Resummation and the Valence Parton Distribution Function of the Pion

Abstract: Although the pion is one of the most important par- ticles in strong-interaction physics, our knowledge about its internal quark and gluon "partonic" structure is still rather poor. Most of the available information comes from Drell-Yan dimuon production by charged pions in- cident on nuclear fixed targets (1-3). These data primar- ily constrain the valence distribution v � ≡ u � + v = ¯ d � + v = √ S denote the invariant mass of the lepton pair and the overall hadronic center-of-mass (c.m.) energy, respec- tively, and x1 and x2 are the momentum fractions of the partons participating in the hard-scattering reaction. As z increases toward unity, little phase space for real-gluon radiation remains, since most of the initial partonic en- ergy is used to produce the virtual photon. The infrared cancellations between virtual and real-emission diagrams then leave behind large logarithmic higher-order correc- tions to the cross sections, the so-called threshold log- arithms. These logarithms become particularly impor- tant in the fixed-target regime, because here the ratio Q 2 /S is relatively large. It then becomes necessary to resum the large corrections to all orders in the strong coupling, a technique known as threshold resummation. QCD threshold resummation for the Drell-Yan process has been derived a long time ago (14). It turns out that the threshold logarithms lead to a strong increase of the cross section near threshold. Therefore, if threshold re- summation effects are included, it is possible that a much softer valence distribution of the pion is sufficient to de- scribe the experimental data. Indeed, as was observed in Ref. (6), the extracted valready becomes softer when going from the lowest order to NLO, where the thresh- old logarithms first appear. In this Letter, we will ad- dress the impact of resummation effects on the pion's valence distribution. We will find that indeed a falloff v � ∼ (1 − x) 2 even at a relatively low resolution scale is well consistent with the Drell-Yan data. We note that the effects of resummation on parton distributions were also examined in the context of deep-inelastic lepton scatter-

Equation of State for physical quark masses

Abstract: We calculate the QCD equation of state for temperatures corresponding to the transition region with physical mass values for two degenerate light quark flavors and a strange quark using an improved staggered fermion action (p4-action) on lattices with temporal extent ${N}_{\ensuremath{\tau}}=8$. We compare our results with previous calculations performed at twice larger values of the light quark masses as well as with results obtained from a resonance gas model calculation. We also discuss the deconfining and chiral aspects of the QCD transition in terms of renormalized Polyakov loop, strangeness fluctuations, and subtracted chiral condensate. We show that compared to the calculations performed at twice larger value of the light quark mass the transition region shifts by about 5 MeV toward smaller temperatures.

Update: Precision D_s decay constant from full lattice QCD using very fine lattices

Abstract: We update our previous determination of both the decay constant and the mass of the D s meson using the highly improved staggered quark formalism. We include additional results at two finer values of the lattice spacing along with improved determinations of the lattice spacing and improved tuning of the charm and strange quark masses. We obtain m Ds = 1.9691(32) GeV, in good agreement with experiment, and f Ds = 0.2480(25) GeV. Our result for f Ds is 1.6σ lower than the most recent experimental average determined from the D s leptonic decay rate and using V cs from Cabibbo-Kobayashi-Maskawa unitarity. Combining our f Ds with the experimental rate we obtain a direct determination of V cs = 1.010(22), or alternatively 0.990 +0.013 -0.016 using a probability distribution for statistical errors for this quantity which vanishes above 1. We also include an accurate prediction of the decay constant of the η c , f ηc = 0.3947(24) GeV, as a calibration point for other lattice calculations.

Light and heavy mesons in a soft-wall holographic approach

Abstract: We study the mass spectrum and decay constants of light and heavy mesons in a soft-wall holographic approach, using the correspondence of string theory in Anti-de Sitter space and conformal field theory in physical space-time.

Nucleon mass from a covariant three-quark Faddeev equation.

Abstract: We report the first study of the nucleon where the full Poincare-covariant structure of the three-quark amplitude is implemented in the Faddeev equation. We employ an interaction kernel which is consistent with contemporary studies of meson properties and aspects of chiral symmetry and its dynamical breaking, thus yielding a comprehensive approach to hadron physics. The resulting current-mass evolution of the nucleon mass compares well with lattice data and deviates only by ∼5% from the quark-diquark result obtained in previous studies.

Light meson physics from maximally twisted mass lattice QCD

Abstract: We present a comprehensive investigation of light meson physics using maximally twisted mass fermions for N f = 2 mass-degenerate quark flavours. By employing four values of the lattice spacing, spatial lattice extents ranging from 2.0 fm to 2.5 fm and pseudo scalar masses in the range 280 ≲ m PS ≲ 650MeV we control the major systematic effects of our calculation. This enables us to confront our N f = 2 data with SU(2) chiral perturbation theory and extract low energy constants of the effective chiral Lagrangian and derived quantities, such as the light quark mass.

Dynamically generated resonances from the vector octet-baryon octet interaction

Abstract: We study the interaction of the octet of vector mesons with the decuplet of baryons using Lagrangians of the hidden gauge theory for vector interactions. The unitary amplitudes in coupled channels develop poles that can be associated with some known baryonic resonances, while there are predictions for new ones at the energy frontier of the experimental research. The work offers guidelines on how to search for these resonances.

Charmonium in medium: From correlators to experiment

Abstract: We set up a framework in which in-medium charmonium properties are constrained by thermal lattice quantum chromodynamics and subsequently implemented into a thermal rate equation enabling the comparison with experimental data in heavy-ion collisions. Specifically, we evaluate phenomenological consequences for charmonium production originating from two different scenarios in which either the free or the internal energy are identified with the in-medium two-body potential between charm and anticharm quarks. These two scenarios represent $J/\ensuremath{\psi}$ ``melting temperatures'' of approximately $1.25{T}_{c}$ (``weak binding'') and $2{T}_{c}$ (``strong binding''), respectively. Within current uncertainties in dissociation rates and charm-quark momentum spectra, both scenarios can reproduce the centrality dependence of inclusive $J/\ensuremath{\psi}$ yields in nuclear collisions at the Super Proton Synchrotron (SPS) and the Relativistic Heavy-Ion Collider (RHIC) reasonably well. However, the ``strong-binding'' scenario associated with the internal energy as the potential tends to better reproduce current data on transverse momentum spectra at both SPS and RHIC.

Essence of the vacuum quark condensate

Abstract: We show that the chiral-limit vacuum quark condensate is qualitatively equivalent to the pseudoscalar meson leptonic decay constant in the sense that they are both obtained as the chiral-limit value of well-defined gauge-invariant hadron-to-vacuum transition amplitudes that possess a spectral representation in terms of the current-quark mass. Thus, whereas it might sometimes be convenient to imagine otherwise, neither is essentially a constant mass-scale that fills all spacetime. This means, in particular, that the quark condensate can be understood as a property of hadrons themselves, which is expressed, for example, in their Bethe-Salpeter or light-front wave functions.

Simplified models for photohadronic interactions in cosmic accelerators

Abstract: We discuss simplified models for photo-meson production in cosmic accelerators, such as active galactic nuclei (AGNs) and gamma-ray bursts (GRBs). Our self-consistent models are directly based on the underlying physics used in the SOPHIA software and can be easily adapted if new data are included. They allow for the efficient computation of neutrino and photon spectra (from π0 decays) as a major requirement of modern time-dependent simulations of the astrophysical sources and parameter studies. In addition, the secondaries (pions and muons) are explicitly generated, a necessity if cooling processes are to be included. For the neutrino production, we include the helicity dependence of the muon decays which in fact leads to larger corrections than the details of the interaction model. The separate computation of the π0, π+, and π– fluxes allows, for instance, for flavor ratio predictions of the neutrinos at the source, which are a requirement of many tests of neutrino properties using astrophysical sources. We confirm that for charged pion generation, the often used production by the Δ(1232)-resonance is typically not the dominant process in AGNs and GRBs, and we show, for arbitrary input spectra, that the number of neutrinos are underestimated by at least a factor of two if they are obtained from the neutral-to-charged pion ratio. We compare our results for several levels of simplification using isotropic synchrotron and thermal spectra and demonstrate that they are sufficiently close to the SOPHIA software.

Constraints on two-lepton two-quark operators

Abstract: Physics from beyond the Standard Model, such as leptoquarks, can induce four fermion operators involving a quark, an anti-quark, a lepton and an anti-lepton. We update the (flavour-dependent) constraints on the coefficients of such interactions, arising from collider searches for contact interactions, meson decays and other rare processes. We then make naive estimates for the magnitude of the coefficients, as could arise in texture models or from inverse hierarchies in the kinetic term coefficients. These “expectations” suggest that rare kaon decays could be a good place to look for such operators.

Scaling studies of QCD with the dynamical highly improved staggered quark action

Abstract: We study the lattice spacing dependence, or scaling, of physical quantities using the highly improved staggered quark (HISQ) action introduced by the HPQCD/UKQCD Collaboration, comparing our results to similar simulations with the asqtad fermion action. Results are based on calculations with lattice spacings approximately 0.15, 0.12, and 0.09 fm, using four flavors of dynamical HISQ quarks. The strange and charm quark masses are near their physical values, and the light-quark mass is set to 0.2 times the strange-quark mass. We look at the lattice spacing dependence of hadron masses, pseudoscalar meson decay constants, and the topological susceptibility. In addition to the commonly used determination of the lattice spacing through the static quark potential, we examine a determination proposed by the HPQCD Collaboration that uses the decay constant of a fictitious ''unmixed ss'' pseudoscalar meson. We find that the lattice artifacts in the HISQ simulations are much smaller than those in the asqtad simulations at the same lattice spacings and quark masses.

Hadrons in strongly interacting matter

Abstract: We review the current status of theories and experiments aiming at an understanding and a determination of the properties of light vector and scalar mesons inside strongly interacting hadronic matter. Starting from a discussion of the relevant symmetries of QCD and their connection with the hadronic description through QCD sum rules we then discuss hadronic models used to calculate the in-medium self-energies of hadrons and their spectral functions. The difficulties to link these calculated properties to actual observables are emphasized. Finally, we review in detail all the running experiments searching for in-medium changes of vector and scalar mesons, both with relativistic heavy-ion reactions as well as with elementary reactions on (cold) nuclei. Inconsistencies among experimental results are discussed. While almost all experiments observe a considerable broadening of vector mesons inside the nuclear medium, no evidence for mass changes is observed in the majority of the experiments.

Meson fluctuations and thermodynamics of the Polyakov-loop-extended quark-meson model

Abstract: Thermodynamics of the Polyakov-loop-extended two-flavor chiral quark-meson model (PQM) is explored. The analysis of the PQM model is based on the functional renormalization group method. An appropriate truncation of the effective action with quarks coupled to background gluonic fields is introduced. Within this scheme, we derive the renormalization group flow equation for the scale-dependent thermodynamic potential at finite temperature and density in the presence of a symmetry breaking external field. The influence of fluctuations and of the background gluon field on the properties of net-quark number density fluctuations and their higher moments is explored. We study the dependence of the kurtosis of quark-number fluctuations on the pion mass and show that, in the presence of a symmetry-breaking term, the fluctuations lead to a smoothing of observables near the crossover transition.

Diffractive electroproduction of \rho and \phi mesons at HERA

Abstract: Diffractive electroproduction of rho and phi mesons is measured at HERA with the H1 detector in the elastic and proton dissociative channels. The data correspond to an integrated luminosity of 51 pb^-1. About 10500 rho and 2000 phi events are analysed in the kinematic range of squared photon virtuality 2.5 < Q^2 < 60 GeV^2, photon-proton centre of mass energy 35 < W < 180 GeV and squared four-momentum transfer to the proton |t| < 3 GeV^2. The total, longitudinal and transverse cross sections are measured as a function of Q^2, W and |t|. The measurements show a transition to a dominantly "hard" behaviour, typical of high gluon densities and small q\bar{q} dipoles, for Q^2 larger than 10 to 20 GeV^2. They support flavour independence of the diffractive exchange, expressed in terms of the scaling variable (Q^2 + M_V^2)/4, and proton vertex factorisation. The spin density matrix elements are measured as a function of kinematic variables. The ratio of the longitudinal to transverse cross sections, the ratio of the helicity amplitudes and their relative phases are extracted. Several of these measurements have not been performed before and bring new information on the dynamics of diffraction in a QCD framework. The measurements are discussed in the context of models using generalised parton distributions or universal dipole cross sections.

Vacuum Properties of Mesons in a Linear Sigma Model with Vector Mesons and Global Chiral Invariance

Abstract: We present a two-flavor linear sigma model with global chiral symmetry and vector and axial-vector mesons. We calculate {pi}{pi} scattering lengths and the decay widths of scalar, vector, and axial-vector mesons. It is demonstrated that vector and axial-vector meson degrees of freedom play an important role in these low-energy processes and that a reasonable theoretical description requires globally chirally invariant terms other than the vector-meson mass term. An important question for meson vacuum phenomenology is the quark content of the physical scalar f{sub 0}(600) and a{sub 0}(980) mesons. We investigate this question by assigning the quark-antiquark {sigma} and a{sub 0} states of our model with these physical mesons. We show via a detailed comparison with experimental data that this scenario can describe all vacuum properties studied here except for the decay width of the {sigma}, which turns out to be too small. We also study the alternative assignment f{sub 0}(1370) and a{sub 0}(1450) for the scalar mesons. In this case the decay width agrees with the experimental value, but the {pi}{pi} scattering length a{sub 0}{sup 0} is too small. This indicates the necessity to extend our model by additional scalar degrees of freedom.

Baryon Asymmetry of the Universe in the NuMSM

Abstract: We perform a detailed analysis of baryon asymmetry generation in the NuMSM (an extension of the Standard Model by three singlet Majorana fermions with masses below the Fermi scale). Fixing a number of parameters of the NuMSM by the neutrino oscillation data, we determine the remaining domain of the parameter space from the requirement of successful baryogenesis. We derive, in particular, the constraints on the mass splitting of a pair of singlet fermions, and on the strength of their coupling to ordinary leptons, essential for searches of these particles in rare decays of mesons and in beam-dump experiments with intensive proton beams.

Average up/down, strange and charm quark masses with Nf=2 twisted mass lattice QCD

Abstract: We present a high precision lattice calculation of the average up/down, strange and charm quark masses performed with Nf=2 twisted mass Wilson fermions. The analysis includes data at four values of the lattice spacing and pion masses as low as ~270 MeV, allowing for accurate continuum limit and chiral extrapolation. The strange and charm masses are extracted by using several methods, based on different observables: the kaon and the eta_s meson for the strange quark and the D, D_s and eta_c mesons for the charm. The quark mass renormalization is carried out non-perturbatively using the RI-MOM method. The results for the quark masses in the MSbar scheme read: m_ud(2 GeV)= 3.6(2) MeV, m_s(2 GeV)=95(6) MeV and m_c(m_c)=1.28(4) GeV. We also obtain the ratios m_s/m_ud=27.3(9) and m_c/m_s=12.0(3).

Prediction for the mass spectra of resonance mesons in the soft-wall AdS/QCD model with a modified 5D metric

Abstract: A soft-wall anti-de Sitter/QCD model with a modified five-dimensional metric at the infrared region is constructed to obtain a nontrivial dilaton solution, which incorporates the chiral symmetry breaking and linear confinement. By taking the pion mass and decay constant as two input mass scales, the resulting predictions for the resonance states of pseudoscalar, scalar, vector, and axial-vector mesons agree remarkably with the experimentally confirmed resonance states. The effects of the quartic interaction term are investigated by taking an appropriate sign and magnitude for maintaining the stability of the bulk scalar potential. It is shown that such a simply modified soft-wall anti-de Sitter/QCD model can lead to a consistent prediction for the mass spectra of resonance states in the pseudoscalar, scalar, vector, and axial-vector mesons; the agreement with the experimental data is found to be better than 10% for the excited meson states. The resulting pion form factor also agrees well with the experimental data.