Showing papers on "Meson published in 2012"

Suppression of non-prompt J/ψ, prompt J/ψ, and Y(1S) in PbPb collisions at √s NN = 2.76 TeV

Abstract: Yields of prompt and non-prompt J/psi, as well as Y(1S) mesons, are measured by the CMS experiment via their dimuon decays in PbPb and pp collisions at sqrt(sNN) = 2.76 TeV for quarkonium rapidity |y|<2.4. Differential cross sections and nuclear modification factors are reported as functions of y and transverse momentum pt, as well as collision centrality. For prompt J/psi with relatively high pt (6.5

Suppression of high transverse momentum D mesons in central Pb-Pb collisions at root s(NN)=2.76 TeV

Abstract: The production of the prompt charm mesons $D^0$, $D^+$, $D^{*+}$, and their antiparticles, was measured with the ALICE detector in Pb-Pb collisions at the LHC, at a centre-of-mass energy $\sqrt{s_{NN}}=2.76$ TeV per nucleon--nucleon collision. The $\pt$-differential production yields in the range $2

Excited and exotic charmonium spectroscopy from lattice QCD

Abstract: We present a spectrum of highly excited charmonium mesons up to around 4.5 GeV calculated using dynamical lattice QCD. Employing novel computational techniques and the variational method with a large basis of carefully constructed operators, we extract and reliably identify the continuum spin of an extensive set of excited states, states with exotic quantum numbers (0+−, 1−+, 2+−) and states with high spin. Calculations are performed on two lattice volumes with pion mass ≈ 400 MeV and the mass determinations have high statistical precision even for excited states. We discuss the results in light of experimental observations, identify the lightest ‘supermultiplet’ of hybrid mesons and comment on the phenomenological implications of the spectrum of exotic mesons.

$B$- and $D$-meson decay constants from three-flavor lattice QCD

Abstract: We calculate the leptonic decay constants of B_{(s)} and D_{(s)} mesons in lattice QCD using staggered light quarks and Fermilab bottom and charm quarks. We compute the heavy-light meson correlation functions on the MILC asqtad-improved staggered gauge configurations which include the effects of three light dynamical sea quarks. We simulate with several values of the light valence- and sea-quark masses (down to ~m_s/10) and at three lattice spacings (a ~ 0.15, 0.12, and 0.09 fm) and extrapolate to the physical up and down quark masses and the continuum using expressions derived in heavy-light meson staggered chiral perturbation theory. We renormalize the heavy-light axial current using a mostly nonperturbative method such that only a small correction to unity must be computed in lattice perturbation theory and higher-order terms are expected to be small. We obtain f_{B^+} = 196.9(8.9) MeV, f_{B_s} = 242.0(9.5) MeV, f_{D^+} = 218.9(11.3) MeV, f_{D_s} = 260.1(10.8) MeV, and the SU(3) flavor-breaking ratios f_{B_s}/f_{B} = 1.229(26) and f_{D_s}/f_{D} = 1.188(25), where the numbers in parentheses are the total statistical and systematic uncertainties added in quadrature.

Measurement of charm production at central rapidity in proton-proton collisions at root s=7 TeV

Abstract: The p(t)-differential inclusive production cross sections of the prompt charmed mesons D-0, D+, and D*(+) in the rapidity range vertical bar y vertical bar K-pi(+), D+ -> K-pi(+)pi(+), D*(+) -> D-0 pi(+), and their charge conjugates, about 8,400 D-0, 2,900 D+, and 2,600 D*(+) mesons with 1 < p(t) < 24 GeV/c were counted, after selection cuts, in a data sample of 3.14 x 10(8) events collected with a minimum-bias trigger (integrated luminosity L-int = 5 nb(-1)). The results are described within uncertainties by predictions based on perturbative QCD.

Possible hidden-charm molecular baryons composed of an anti-charmed meson and a charmed baryon

Abstract: Using the one-boson-exchange model, we studied the possible existence of very loosely bound hidden-charm molecular baryons composed of an anti-charmed meson and a charmed baryon. Our numerical results indicate that the Σc* and Σc states exist, but that the Λc and Λc* molecular states do not.

Hyperons in neutron-star cores and a 2 M⊙ pulsar

Abstract: Context. A recent measurement of the mass of PSR J1614-2230 rules out most existing models of the equation of state (EOS) of dense matter that is subjected to the high-density softening caused by either hyperonization or a phase transition to either quark matter or a boson condensate. Aims. We attempt to resolve the apparent differences between the predictions derived from up-to-date hypernuclear data, which include the appearance of hyperons at about three nuclear densities and the existence of a M = 2.0 M ⊙ neutron star.Methods. We consider a non-linear relativistic mean field (RMF) model involving the baryon octet coupled to meson fields. An effective Lagrangian includes quartic terms in the meson fields. The values of the model parameters are obtained by fitting the semi-empirical parameters of nuclear matter at the saturation point, as well as potential wells for hyperons in nuclear matter and the strength of the Λ − Λ attraction in double-Λ hypernuclei.Results. We propose a non-linear RMF model that is consistent with up-to-date semi-empirical nuclear and hypernuclear data and allows for neutron stars with hyperon cores and M > 2 M ⊙ . The model involves hidden-strangeness scalar and vector mesons, coupled only to hyperons, and quartic terms involving vector meson fields.Conclusions. Our EOS involving hyperons is stiffer than the corresponding nucleonic EOS (in which hyperons are artificially suppressed) above five nuclear densities. The required stiffening is generated by the quartic terms involving the hidden-strangeness vector meson.

Suppression of high transverse momentum D mesons in central Pb--Pb collisions at $\sqrt{s_{NN}}=2.76$ TeV

Abstract: The production of the prompt charm mesons $D^0$, $D^+$, $D^{*+}$, and their antiparticles, was measured with the ALICE detector in Pb-Pb collisions at the LHC, at a centre-of-mass energy $\sqrt{s_{NN}}=2.76$ TeV per nucleon--nucleon collision. The $\pt$-differential production yields in the range $2

Heavy-Quark Diffusion and Hadronization in Quark-Gluon Plasma

Abstract: We calculate diffusion and hadronization of heavy quarks in high-energy heavy-ion collisions, implementing the notion of a strongly coupled quark-gluon plasma in both micro- and macroscopic components. The diffusion process is simulated using relativistic Fokker-Planck dynamics for elastic scattering in a hydrodynamic background. The heavy-quark transport coefficients in the medium are obtained from nonperturbative $T$-matrix interactions which build up resonant correlations close to the transition temperature. The latter also form the basis for hadronization of heavy quarks into heavy-flavor mesons via recombination with light quarks from the medium. The pertinent resonance recombination satisfies energy conservation and provides an equilibrium mapping between quark and meson distributions. The recombination probability is derived from the resonant heavy-quark scattering rate. Recombination is found to dominate at low transverse momentum (${p}_{T}$) and to yield to fragmentation at high ${p}_{T}$. Our approach emphasizes the role of resonance correlations in the diffusion and hadronization processes. Calculations of the nuclear modification factor and elliptic flow of $D$ and $B$ mesons and their decay electrons in Au-Au collisions at the Relativistic Heavy Ion Collider indicate the importance of a realistic medium flow in a quantitative interpretation of heavy-flavor data.

Inclusive charmed-meson production at the CERN LHC

Abstract: We present predictions for the inclusive production of D mesons at the CERN LHC in the general-mass variable-flavor-number scheme at next-to-leading order. Detailed numerical results are compared to data where available, or presented in a way to ease future comparisons with experimental results. We also point out that measurements at large rapidity have the potential to pin down models of intrinsic charm.

Scattering phases for meson and baryon resonances on general moving-frame lattices

Abstract: A proposal by L\"uscher enables one to compute the scattering phases of elastic two-body systems from the energy levels of the lattice Hamiltonian in a finite volume. In this work, we generalize the formalism to $S$-, $P$- and $D$-wave meson and baryon resonances, and general total momenta. Employing nonvanishing momenta has several advantages, among them making a wider range of energy levels accessible on a single lattice volume and shifting the level crossing to smaller values of ${m}_{\ensuremath{\pi}}L$.

Dilaton in a soft-wall holographic approach to mesons and baryons

Abstract: We discuss a holographic soft-wall model developed for the description of mesons and baryons with adjustable quantum numbers n, J, L, S. This approach is based on an action which describes hadrons with broken conformal invariance and which incorporates confinement through the presence of a background dilaton field. We show that in the case of the bound-state problem (hadronic mass spectrum) two versions of the model with a positive and negative dilaton profile are equivalent to each other by a special transformation of the bulk field. We also comment on recent works which discuss the dilaton sign in the context of soft-wall approaches.

Observation of double charm production involving open charm in pp collisions at √s = 7 TeV

Abstract: The production of J/psi mesons accompanied by open charm, and of pairs of open charm hadrons are observed in pp collisions at a centre-of-mass energy of 7 TeV using an integrated luminosity of 355 pb(-1) collected with the LHCb detector. Model independent measurements of absolute cross-sections are given together with ratios to the measured J/psi and open charm cross-sections. The properties of these events are studied and compared to theoretical predictions.

Observation of Time-Reversal Violation in the B-0 Meson System

Abstract: Although CP violation in the B meson system has been well established by the B factories, there has been no direct observation of time-reversal violation. The decays of entangled neutral B mesons into definite flavor states (B^0 or B^0), and J/ψK_L^0 or cc K_S^0 final states (referred to as B_+ or B_-), allow comparisons between the probabilities of four pairs of T-conjugated transitions, for example, B^0→B_- and B_-→B^0, as a function of the time difference between the two B decays. Using 468×10^6 BB pairs produced in Υ(4S) decays collected by the BABAR detector at SLAC, we measure T-violating parameters in the time evolution of neutral B mesons, yielding ΔS_T^+=-1.37±0.14(stat)±0.06(syst) and ΔS_T^-=1.17±0.18(stat)±0.11(syst). These nonzero results represent the first direct observation of T violation through the exchange of initial and final states in transitions that can only be connected by a T-symmetry transformation.

Investigation of rainbow-ladder truncation for excited and exotic mesons

Abstract: Ground-state, radially excited, and exotic scalar, vector, and flavored-pseudoscalar mesons are studied in rainbow-ladder truncation using an interaction kernel that is consonant with modern Dyson-Schwinger equation and lattice-QCD results. The inability of this truncation to provide realistic predictions for the masses of excited and exotic states is confirmed and explained. However, its application does provide information that is potentially useful when working beyond this leading-order truncation, e.g.: assisting with the development of projection techniques that ease the computation of excited-state properties; placing qualitative constraints on the long-range behavior of the interaction kernel; and highlighting and illustrating some features of hadron observables that do not depend on details of the dynamics.

The $B$ and $B_s$ Meson Decay Constants from Lattice QCD

Abstract: We present a new determination of the B and Bs meson decay constants using nonrelativistic quantum chromodynamics (NRQCD) b-quarks, highly improved staggered quark (HISQ) light and strange valence quarks and the MILC collaboration Nf=2+1 lattices. The new calculations improve on HPQCD’s earlier work with NRQCD b-quarks by replacing AsqTad with HISQ valence quarks, by including a more chiral MILC fine ensemble in the analysis, and by employing better tuned quark masses and overall scale. We find fB=0.191(9) GeV, fBs=0.228(10) GeV and fBs/fB=1.188(18). Combining the new value for fBs/fB with a recent very precise determination of the Bs meson decay constant based on HISQ b-quarks, fBs=0.225(4) GeV, leads to fB=0.189(4) GeV. With errors of just 2.1% this represents the most precise fB available today.

Branching ratios and direct CP asymmetries in D -> PV decays

Abstract: We study the two-body hadronic D -> PV decays, where P (V) denotes a pseudoscalar (vector) meson, in the factorization- assisted topological- amplitude approach proposed in our previous work. This approach is based on the factorization of short- distance and long- distance dynamics into Wilson coefficients and hadronic matrix elements of four-fermion operators, respectively, with the latter being parametrized in terms of several nonperturbative quantities. We further take into account the rho-omega mixing effect, which improves the global fit to the branching ratios involving the rho(0) and omega mesons. Combining short- distance dynamics associated with penguin operators and the hadronic parameters determined from the global fit to branching ratios, we predict direct CP asymmetries. In particular, the direct CP asymmetries in the D-0 -> K-0(K) over bar*(0), K-0(K) over bar*(0) -> pi(+) rho(0), and D-s(+) -> K+omega, K+phi decays are found to be of O(10(-3)), which can be observed at the LHCb and future Belle II experiment. We also predict the CP asymmetry observables of some neutral D meson decays.

New meson spectroscopy with open charm and beauty

Abstract: All the available experimental information on open charm and beauty mesons is used to classify the observed states in heavy quark doublets. The masses of some of the still unobserved states are predicted, in particular in the beauty sector. Adopting an effective Lagrangian approach based on the heavy quark and chiral symmetry, individual decay rates and ratios of branching fractions are computed, with results useful to assign the quantum numbers to recently observed charmed states which still need to be properly classified. Implications and predictions for the corresponding beauty mesons are provided. The experimental results are already copious, and are expected to grow up thanks to the experiments at the LHC and to the future high-luminosity flavor and $p\ensuremath{-}\overline{p}$ facilities.

Dispersive analysis of omega --> 3pi and phi --> 3pi decays

Abstract: We study the three-pion decays of the lightest isoscalar vector mesons, omega and phi, in a dispersive framework that allows for a consistent description of final-state interactions between all three pions. Our results are solely dependent on the phenomenological input for the pion-pion P-wave scattering phase shift. We predict the Dalitz plot distributions for both decays and compare our findings to recent measurements of the phi --> 3pi Dalitz plot by the KLOE and CMD-2 collaborations. Dalitz plot parameters for future precision measurements of omega --> 3pi are predicted. We also calculate the pi-pi P-wave inelasticity contribution from omega-pi intermediate states.

Observation of double charm production involving open charm in pp collisions at $\sqrt{s}$=7 TeV

Abstract: The production of $J/\psi$ mesons accompanied by open charm, and of pairs of open charm hadrons are observed in pp collisions at a centre-of-mass energy of 7 TeV using an integrated luminosity of $355pb^{-1}$ collected with the LHCb detector. Model independent measurements of absolute cross-sections are given together with ratios to the measured $J/\psi$ and open charm cross-sections. The properties of these events are studied and compared to theoretical predictions.

Tracing masses of ground-state light-quark mesons

Abstract: We describe a symmetry-preserving calculation of the light-quark meson spectrum, which combines a description of pion properties with reasonable estimates of the masses of heavier mesons, including axial-vector states. The kernels used in formulating the problem are essentially nonperturbative, incorporating effects of dynamical chiral symmetry breaking (DCSB) that were not previously possible to express. Our analysis clarifies a causal connection between DCSB and the splitting between vector and axial-vector mesons and exposes a key role played by the anomalous chromomagnetic moment of dressed quarks in forming the spectrum.

AdS/QCD holographic wave function for the ρ meson and diffractive ρ meson electroproduction.

Abstract: We show that anti-de Sitter/quantum chromodynamics generates predictions for the rate of diffractive ρ-meson electroproduction that are in agreement with data collected at the Hadron Electron Ring Accelerator electron-proton collider.

Hybrid Baryons in QCD

Abstract: In this study, we present the first comprehensive study of hybrid baryons using lattice QCD methods. Using a large basis of composite QCD interpolating fields we extract an extensive spectrum of baryon states and isolate those of hybrid character using their relatively large overlap onto operators which sample gluonic excitations. We consider the spectrum of Nucleon and Delta states at several quark masses finding a set of positive parity hybrid baryons with quantum numbers $$N_{1/2^+},\,N_{1/2^+},\,N_{3/2^+},\, N_{3/2^+},\,N_{5/2^+},\,$$ and $$\Delta_{1/2^+},\, \Delta_{3/2^+}$$ at an energy scale above the first band of `conventional' excited positive parity baryons. This pattern of states is compatible with a color octet gluonic excitation having $$J^{P}=1^{+}$$ as previously reported in the hybrid meson sector and with a comparable energy scale for the excitation, suggesting a common bound-state construction for hybrid mesons and baryons.

QCD with two light dynamical chirally improved quarks: Mesons

Abstract: We present results for the spectrum of light and strange mesons on configurations with two flavors of mass-degenerate Chirally Improved sea quarks. The calculations are performed on seven ensembles of lattice size ${16}^{3}\ifmmode\times\else\texttimes\fi{}32$ at three different gauge couplings and with pion masses ranging from 250 to 600 MeV. To reliably extract excited states, we use the variational method with an interpolator basis containing both Gaussian and derivative quark sources. Both conventional and exotic channels up to spin 2 are considered. Strange quarks are treated within the partially quenched approximation. For kaons we investigate the mixing of interpolating fields corresponding to definite $C$-parity in the SU(3) limit. This enlarged basis allows for an improved determination of the low-lying kaon spectrum. In addition to masses we also extract the ratio of the pseudoscalar decay constants of the kaon and pion and obtain ${F}_{K}/{F}_{\ensuremath{\pi}}=1.215(41)$. The results presented here include some ensembles from previous publications and the corresponding results supersede the previously published values.

Dispersive analysis of ω→3π and ϕ→3π decays

Abstract: We study the three-pion decays of the lightest isoscalar vector mesons, ω and ϕ, in a dispersive framework that allows for a consistent description of final-state interactions between all three pions. Our results are solely dependent on the phenomenological input for the pion–pion P-wave scattering phase shift. We predict the Dalitz plot distributions for both decays and compare our findings to recent measurements of the ϕ→3π Dalitz plot by the KLOE and CMD-2 collaborations. Dalitz plot parameters for future precision measurements of ω→3π are predicted. We also calculate the ππ P-wave inelasticity contribution from ωπ intermediate states.

Power Counting and Perturbative One Pion Exchange in Heavy Meson Molecules

Abstract: We discuss the possible power counting schemes that can be applied in the effective field theory description of heavy meson molecules, such as the $X(3872)$ or the recently discovered ${Z}_{b}(10\text{ }610)$ and ${Z}_{b}(10\text{ }650)$ states. We argue that the effect of coupled channels is suppressed by at least two orders in the effective field theory expansion, meaning that they can be safely ignored at lowest order. The role of the one pion exchange potential between the heavy mesons, and, in particular, the tensor force, is also analyzed. By using techniques developed in atomic physics for handling power-law singular potentials, which have been also successfully employed in nuclear physics, we determine the range of center-of-mass momenta for which the tensor piece of the one pion exchange potential is perturbative. In this momentum range, the one pion exchange potential can be considered a subleading order correction, leaving at lowest order a very simple effective field theory consisting only of contact-range interactions.