Showing papers on "Meson published in 2014"

B(s,d)→ℓ(+)ℓ(-) in the standard model with reduced theoretical uncertainty.

Abstract: We combine our new results for the O(αem) and O(αs2) corrections to Bs,d→l+l-, and present updated branching ratio predictions for these decays in the standard model. Inclusion of the new corrections removes major theoretical uncertainties of perturbative origin that have just begun to dominate over the parametric ones. For the recently observed muonic decay of the Bs meson, our calculation gives B¯(Bs→μ+μ-)=(3.65±0.23)×10-9.

Observation of the resonant character of the Z(4430)(-) state

Abstract: Resonant structures in B-0 -> psi'pi K--(+) decays are analyzed by performing a four-dimensional fit of the decay amplitude, using pp collision data corresponding to 3 fb(-1) collected with the LHCb detector. The data cannot be described with K+pi(-) resonances alone, which is confirmed with a model-independent approach. A highly significant Z(4430)(-) -> psi'pi(-) component is required, thus confirming the existence of this state. The observed evolution of the Z(4430)(-) amplitude with the psi'pi(-) mass establishes the resonant nature of this particle. The mass and width measurements are substantially improved. The spin parity is determined unambiguously to be 1(+).

Electron reconstruction and identification efficiency measurements with the atlas detector using the 2011 lhc proton-proton collision data

Abstract: Many of the interesting physics processes to be measured at the LHC have a signature involving one or more isolated electrons. The electron reconstruction and identification efficiencies of the ATLAS detector at the LHC have been evaluated using proton-proton collision data collected in 2011 at TeV and corresponding to an integrated luminosity of 4.7 fb. Tag-and-probe methods using events with leptonic decays of and bosons and mesons are employed to benchmark these performance parameters. The combination of all measurements results in identification efficiencies determined with an accuracy at the few per mil level for electron transverse energy greater than 30 GeV.

On the impact of power corrections in the prediction of B → K*μ+μ− observables

Abstract: The recent LHCb angular analysis of the exclusive decay B → K * μ + μ − has indicated significant deviations from the Standard Model expectations. Accurate predictions can be achieved at large K *-meson recoil for an optimised set of observables designed to have no sensitivity to hadronic input in the heavy-quark limit at leading order in α s . However, hadronic uncertainties reappear through non-perturbative ΛQCD /m b power corrections, which must be assessed precisely. In the framework of QCD factorisation we present a systematic method to include factorisable power corrections and point out that their impact on angular observables depends on the scheme chosen to define the soft form factors. Associated uncertainties are found to be under control, contrary to earlier claims in the literature. We also discuss the impact of possible non-factorisable power corrections, including an estimate of charm-loop effects. We provide results for angular observables at large recoil for two different sets of inputs for the form factors, spelling out the different sources of theoretical uncertainties. Finally, we comment on a recent proposal to explain the anomaly in B → K * μ + μ − observables through charm-resonance effects, and we propose strategies to test this proposal identifying observables and kinematic regions where either the charm-loop model can be disentangled from New Physics effects or the two options leave different imprints.

Observation of D0 meson nuclear modifications in Au+Au collisions at sNN =200GeV

Abstract: We report the first measurement of charmed-hadron (D-0) production via the hadronic decay channel (D-0 -> K- + pi(+)) in Au + Au collisions at root(NN)-N-s = 200 GeV with the STAR experiment. The charm production cross section per nucleon- nucleon collision at midrapidity scales with the number of binary collisions, N-bin, from p + p to central Au + Au collisions. The D-0 meson yields in central Au + Au collisions are strongly suppressed compared to those in p + p scaled by N-bin, for transverse momenta p(T) > 3 GeV/c, demonstrating significant energy loss of charm quarks in the hot and dense medium. An enhancement at intermediate p(T) is also observed. Model calculations including strong charm-medium interactions and coalescence hadronization describe our measurements.

New hyperon equations of state for supernovae and neutron stars in density-dependent hadron field theory

Abstract: We develop new hyperon equation of state (EoS) tables for core-collapse supernova simulations and neutron stars. These EoS tables are based on a density-dependent relativistic hadron field theory where baryon-baryon interaction is mediated by mesons, using the parameter set DD2 for nucleons. Furthermore, light and heavy nuclei along with interacting nucleons are treated in the nuclear statistical equilibrium model of Hempel and Schaffner-Bielich which includes excluded volume effects. Of all possible hyperons, we consider only the contribution of Λs. We have developed two variants of hyperonic EoS tables: in the npΛφ case the repulsive hyperon-hyperon interaction mediated by the strange φ meson is taken into account, and in the npΛ case it is not. The EoS tables for the two cases encompass a wide range of densities (10{sup –12} to ∼1 fm{sup –3}), temperatures (0.1 to 158.48 MeV), and proton fractions (0.01 to 0.60). The effects of Λ hyperons on thermodynamic quantities such as free energy per baryon, pressure, or entropy per baryon are investigated and found to be significant at higher densities. The cold, β-equilibrated EoS (with the crust included self-consistently) results in a 2.1 M {sub ☉} maximum mass neutron star for the npΛφ case, whereas that formore » the npΛ case is 1.95 M {sub ☉}. The npΛφ EoS represents the first supernova EoS table involving hyperons that is directly compatible with the recently measured 2 M {sub ☉} neutron stars.« less

Neutron skin of (208)pb from coherent pion photoproduction.

Abstract: Information on the size and shape of the neutron skin on (208)Pb is extracted from coherent pion photoproduction cross sections measured using the Crystal Ball detector together with the Glasgow tagger at the MAMI electron beam facility. On exploitation of an interpolated fit of a theoretical model to the measured cross sections, the half-height radius and diffuseness of the neutron distribution are found to be c(n)=6.70±0.03(stat.) fm and a(n)=0.55±0.01(stat.)(-0.03)(+0.02)(sys.) fm, respectively, corresponding to a neutron skin thickness Δr(np)=0.15±0.03(stat.)(-0.03)(+0.01)(sys.) fm. The results give the first successful extraction of a neutron skin thickness with an electromagnetic probe and indicate that the skin of (208)Pb has a halo character. The measurement provides valuable new constraints on both the structure of nuclei and the equation of state for neutron-rich matter.

Phenomenology of a very light scalar (100 MeV < mh < 10 GeV) mixing with the SM Higgs

Abstract: In this paper we investigate the phenomenology of a very light scalar, h, with mass 100 MeV < m h < 10 GeV, mixing with the SM Higgs. As a benchmark model we take the real singlet scalar extension of the SM. We point out apparently unresolved uncertainties in the branching ratios and lifetime of h in a crucial region of parameter space for LHC phenomenology. Bounds from LEP, meson decays and fixed target experiments are reviewed. We also examine prospects at the LHC. For m h ≲ m B the dominant production mechanism is via meson decay; our main result is the calculation of the differential p T spectrum of h scalars originating from B mesons and the subsequent prediction of up to thousands of moderate (triggerable) p T displaced dimuons possibly hiding in the existing dataset at ATLAS/CMS or at LHCb. We also demonstrate that the subdominant V h production channel has the best sensitivity for m h ≳ m B and that future bounds in this region could conceivably compete with those of LEP.

Present and Future K and B Meson Mixing Constraints on TeV Scale Left-Right Symmetry

Abstract: We revisit the Δ F = 2 transitions in the K and B d , s neutral meson systems in the context of the minimal left-right symmetric model. We take into account, in addition to up-to-date phenomenological data, the contributions related to the renormalization of the flavor-changing neutral Higgs tree-level amplitude. These contributions were neglected in recent discussions, albeit formally needed in order to obtain a gauge-independent result. Their impact on the minimal LR model is crucial and twofold. First, the effects are relevant in B meson oscillations, for both CP conserving and CP violating observables, so that for the first time these imply constraints on the LR scenario which compete with those of the K sector (plagued by long-distance uncertainties). Second, they sizably contribute to the indirect kaon CP violation parameter ϵ . We discuss the bounds from B and K mesons in both cases of LR symmetry: generalized parity ( P ) and charge conjugation ( C ). In the case of P , the interplay between the CP-violation parameters ϵ and ϵ ′ leads us to rule out the regime of very hierarchical bidoublet vacuum expectation values v 2 / v 1 m b / m t ≃ 0.02 . In general, by minimizing the scalar field contribution up to the limit of the perturbative regime and by definite values of the relevant CP phases in the charged right-handed currents, we find that a right-handed gauge boson W R as light as 3 TeV is allowed at the 95% C. L. This is well within the reach of direct detection at the next LHC run. If not discovered, within a decade the upgraded LHCb and Super B factories may reach an indirect sensitivity to a left-right scale of 8 TeV.

Single meson contributions to the muon’s anomalous magnetic moment

Abstract: We develop the formalism to provide an improved estimate for the hadronic light-by-light correction to the muon’s anomalous magnetic moment $$a_\mu $$ , by considering single meson contributions beyond the leading pseudoscalar mesons. We incorporate available experimental input as well as constraints from light-by-light scattering sum rules to estimate the effects of axial-vector, scalar, and tensor mesons. We give numerical evaluations for the hadronic light-by-light contribution of these states to $$a_\mu $$ . The presented formalism allows one to further improve on these estimates, once new data for such meson states will become available.

Azimuthal anisotropy of D-meson production in Pb-Pb collisions at √sNN=2.76 TeV

Abstract: The production of the prompt charmed mesons D0, D+, and D*+ relative to the reaction plane was measured in Pb-Pb collisions at a center-of-mass energy per nucleon-nucleon collision of √sNN=2.76TeV with the ALICE detector at the CERN Large Hadron Collider. D mesons were reconstructed via their hadronic decays at central rapidity in the transverse-momentum (p_T) interval 2–16 GeV/c. The azimuthal anisotropy is quantified in terms of the second coefficient v2 in a Fourier expansion of the D-meson azimuthal distribution and in terms of the nuclear modification factor R_AA, measured in the direction of the reaction plane and orthogonal to it. The v2 coefficient was measured with three different methods and in three centrality classes in the interval 0%–50%. A positive v2 is observed in midcentral collisions (30%–50% centrality class), with a mean value of 0.204+0.099−0.036 (tot. unc.) in the interval 2

Born-Oppenheimer Approximation for the XYZ Mesons

Abstract: Many of theXY Z mesons discovered in the last decade can be identied as bound states in BornOppenheimer (B-O) potentials for a heavy quark and antiquark. They include quarkonium hybrids, which are bound states in excited avor-singlet B-O potentials, and quarkonium tetraquarks, which are bound states in avor-nonsinglet B-O potentials. We present simple parameterizations of the deepest avor-singlet B-O potentials. We infer the deepest avor-nonsinglet B-O potentials from lattice QCD calculations of static adjoint mesons. Selection rules for hadronic transitions are used to identifyXY Z mesons that are candidates for ground-state energy levels in the B-O potentials for charmonium hybrids and tetraquarks. The energies of the lowest-energy charmonium hybrids are predicted by using the results of lattice QCD calculations to calculate the energy splittings between the ground states of dierent B-O potentials and using the Schroedinger equation to determine the

Measurement of prompt D -meson production in p-Pb collisions at sNN =5.02TeV

Abstract: The p_{T}-differential production cross sections of the prompt charmed mesons D^{0}, D^{+}, D^{*+}, and D_{s}^{+} and their charge conjugate in the rapidity interval -0.96

Study of J/psi production and cold nuclear matter effects in pPb collisions at root S-NN=5 TeV

Abstract: The production of J/ψ mesons with rapidity 1.5 < y < 4.0 or −5.0 < y < −2.5 and transverse momentum p T < 14 GeV/c is studied with the LHCb detector in proton-lead collisions at a nucleon-nucleon centre-of-mass energy √sNN = 5TeV. The J/ψ mesons are reconstructed using the dimuon decay mode. The analysis is based on a data sample corresponding to an integrated luminosity of about 1.6 nb−1. For the first time the nuclear modification factor and forward-backward production ratio are determined separately for prompt J/ψ mesons and J/ψ from b-hadron decays. Clear suppression of prompt J/ψ production with respect to proton-proton collisions at large rapidity is observed, while the production of J/ψ from b-hadron decays is less suppressed. These results show good agreement with available theoretical predictions. The measurement shows that cold nuclear matter effects are important for interpretations of the related quark-gluon plasma signatures in heavy-ion collisions.

Scattering lengths of Nambu-Goldstone bosons off $D$ mesons and dynamically generated heavy-light mesons

Abstract: Recent lattice QCD simulations of the scattering lengths of Nambu-Goldstone bosons off the $D$ mesons are studied using unitary chiral perturbation theory. We show that the lattice QCD data are better described in the covariant formulation than in the heavy-meson formulation. The ${D}_{s0}^{*}(2317)$ can be dynamically generated from the coupled-channels $DK$ interaction without a priori assumption of its existence. A new renormalization scheme is proposed which manifestly satisfies chiral power counting rules and has well-defined behavior in the infinite heavy-quark mass limit. Using this scheme we predict the heavy-quark spin and flavor symmetry counterparts of the ${D}_{s0}^{*}(2317)$.

Large $N$ approach to kaon decays and mixing 28 years later: $\Delta I = 1/2$ rule, $\hat B_K$ and $\Delta M_K$

Abstract: We review and update our results for K-> pipi decays and K^0-ar K^0 mixing obtained by us in the 1980s within an approach based on the dual representation of QCD as a theory of weakly interacting mesons for large N colours. In our analytic approach the dynamics behind the enhancement of ReA_0 and suppression of ReA_2, the so-called Delta I = 1/2 rule for K-> pi pi decays, has a simple structure: the usual octet enhancement through quark-gluon renormalization group evolution down to the scales O(1 GeV) is continued as a meson evolution down to zero momentum scales at which the factorization of hadronic matrix elements is at work. The inclusion of lowest-lying vector meson contributions in addition to the pseudoscalar ones and of Wilson coefficients in a momentum scheme improves significantly the matching between quark-gluon and meson evolutions. In particular, the anomalous dimension matrix governing the meson evolution exhibits the structure of the known anomalous dimension matrix in the quark-gluon evolution. The recent results on ReA_2 and ReA_0 from the RBC-UKQC collaboration give support for our approach. In particular, the signs of the two main contractions found numerically by these authors follow uniquely from our analytic approach. At NLO in 1/N we obtain ReA_0/ReA_2= 16.0pm 1.5 which amounts to an order of magnitude enhancement over the strict large N limit value sqrt{2}. QCD penguins contribute at 15% level to this result. We also find hat B_K=0.73pm 0.02, with the smallness of 1/N corrections to the large N value hat B_K=3/4 resulting within our approach from an approximate cancellation between pseudoscalar and vector meson one-loop contributions. We summarize the status of Delta M_K in this approach.

Anomalous magnetic moment of the muon in a dispersive approach

Abstract: PRISMA Cluster of Excellence, Johannes Gutenberg-Universitat, Mainz, Germany(Dated: September 4, 2014)We present a new general dispersive formalism for evaluating the hadronic light-by-light scatteringcontribution to the anomalous magnetic moment of the muon. In the suggested approach, thiscorrection is related to the imaginary part of the muon’s electromagnetic vertex function. The lattermay be directly related to measurable hadronic processes by means of unitarity and analyticity. Asa test we apply the introduced formalism to the case of meson pole exchanges and nd agreementwith the direct two-loop calculation.

Observation of an Excited B±c Meson State with the ATLAS Detector

Abstract: A search for excited states of the B-c(+/-) meson is performed using 49 fb(-1) of 7 TeV and 192 fb(-1) of 8 TeV pp collision data collected by the ATLAS experiment at the LHC A new state is obse

Spectral Functions for the Quark-Meson Model Phase Diagram from the Functional Renormalization Group

Abstract: We present a method to obtain spectral functions at finite temperature and density from the functional renormalization group. Our method is based on a thermodynamically consistent truncation of the flow equations for 2-point functions with analytically continued frequency components in the originally Euclidean external momenta. For the uniqueness of this continuation at finite temperature we furthermore implement the physical Baym-Mermin boundary conditions. We demonstrate the feasibility of the method by calculating the mesonic spectral functions in the quark-meson model along the temperature axis of the phase diagram, and at finite quark chemical potential along the fixed-temperature line that crosses the critical end point of the model.

Exclusive vector meson production at high energies and gluon saturation

Abstract: We systematically study exclusiv2 diffractive (photo)production of vector mesons (J/ψ, ψ(2s), φ, and ρ) off protons in high-energy collisions and investigate whether the production is a sensitive probe of gluon saturation. We confront saturation-based results for diffractive ψ(2s) and ρ production at HERA and J/ψ photoproduction with all available data, including recent work from HERA, ALICE, and LHCb, finding good agreement. In particular, we show that the t distribution of differential cross sections of photoproduction of vector mesons offers a unique opportunity to discriminate among saturation and nonsaturation models. This is due to the emergence of a pronounced dip (or multiple dips) in the t distribution of diffractive photoproduction of vector mesons at relatively large, but potentially accessible |t| that can be traced back to the unitarity features of color dipole amplitude in the saturation regime. We show that in saturation models the dips in t distribution recede towards lower |t| with decreasing mass of the vector meson, increasing energy or decreasing Bjorken-x, and decreasing virtuality Q. We provide various predictions for exclusive (photo)production of different vector mesons including the ratio of ψ(2s)/J/ψ at HERA, the LHC, and future colliders.

Observation and studies of double J/psi production at the Tevatron

Abstract: We present the observation of doubly-produced $J/\psi$ mesons with the D0 detector at Fermilab in $p\bar{p}$ collisions at $\sqrt{s}=1.96$ TeV. The production cross section for both singly and doubly-produced $J/\psi$ mesons is measured using a sample with an integrated luminosity of 8.1~fb$^{-1}$. For the first time, the double $J/\psi$ production cross section is separated into contributions due to single and double parton scatterings. Using these measurements, we determine the effective cross section \sigteff, a parameter characterizing an effective spatial area of the parton-parton interactions and related to the parton spatial density inside the nucleon.

New weakly-coupled forces hidden in low-energy QCD

Abstract: Is it possible to detect a new weakly coupled force at the QCD scale that interacts primarily with quarks? This work investigates experimental signatures of a new MeV–GeV gauge boson that couples to the baryon number, with attention to the 100 MeV–GeV mass range that is the regime of nonperturbative QCD Such a state can be searched for in rare radiative decays of light mesons ( η , η ′ , ϕ , ω ) as a π 0 γ resonance, which is its leading decay mode from 140 to 620 MeV This is a new discovery window for forces beyond the Standard Model that is not covered by existing dark photon searches

Light-front quark model consistent with Drell-Yan-West duality and quark counting rules

Abstract: We propose a phenomenological light-front wave function for hadrons with arbitrary twist-dimension (mesons, baryons and multiquark states), which gives the correct scaling behavior of structure functions (parton distributions) and form factors for pions and nucleons. For other hadronic states the proposed wave function produces form factors consistent with quark counting rules, and gives predictions for structure functions (parton distributions). As an application we build a light-front quark model for nucleons based on the proposed wave function.

Comprehensive amplitude analysis of γγ→π+π-,π0π0 and K¯K below 1.5 GeV

Abstract: In this paper we perform an amplitude analysis of essentially all published pion and kaon pair production data from two photon collisions below 1.5 GeV. This includes all the high statistics results from Belle, as well as older data from Mark II at SLAC, CELLO at DESY, Crystal Ball at SLAC. The purpose of this analysis is to provide as close to a model-independent determination of the γγ to meson pair amplitudes as possible. Having data with limited angular coverage, typically |cosθ| more » by the recent precision Dalitz plot analysis from BaBar. With these hadronic amplitudes built into unitarity, we can constrain the overall description of γγ → ππ and K⁻K datasets, both integrated and differential cross-sections, including the high statistics charged and neutral pion data from Belle. A region of solutions is found for the γγ → ππ partial waves with both isospin 0 and 2. Since this analysis invokes coupled hadronic channels, even the relatively poor integrated cross-section data on γγ → K⁻K narrows the patch of solutions to essentially a single form. For this we present the complete partial wave amplitudes, show how well they fit all the available data, and give the two photon couplings of scalar and tensor resonances that appear. « less

Spectra and elliptic flow for identified hadrons in 2.76 A TeV Pb + Pb collisions

Abstract: Using the vishnu hybrid model that couples (2+1)-dimensional viscous hydrodynamics to a microscopic hadronic transport model, we calculate the multiplicity, ${p}_{T}$ spectra, and elliptic flow for pions, kaons, and protons in 2.76$A$ TeV Pb+Pb collisions, using mc-kln initializations with smoothed initial conditions, obtained by averaging over a large number of events. The results from our calculations are compared to data from the ALICE Collaboration, showing nice agreement over several centrality bins. Using the same inputs, we predict the ${p}_{T}$ spectra and elliptic flow for $\ensuremath{\phi}$ mesons and explore their flow development in the strong and weak coupling limits through hydrodynamic calculations with different decoupling temperatures. In addition we study the influence of baryon and antibaryon annihilation processes on common observables and demonstrate that, by including annihilation processes below a switching temperature of 165 MeV, vishnu provides a good description of the multiplicity and ${p}_{T}$ spectra for pions, kaons, and protons measured by PHENIX and ALICE at both the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC).

Proton decay matrix elements on the lattice

Abstract: Hadronic matrix elements of proton decay are essential ingredients to bridge the grand unification theory to low energy observables like proton lifetime. In this paper we non-perturbatively calculate the matrix elements, relevant for the process of a nucleon decaying into a pseudoscalar meson and an anti-lepton through generic baryon number violating four-fermi operators. Lattice QCD with 2+1 flavor dynamical domain-wall fermions with the direct method, which is direct measurement of matrix element from three-point function without using chiral perturbation theory, are used for this study to have good control over the error due to lattice discretization effects, operator renormalization, and chiral extrapolation. The relevant form factors for possible transition process from an initial proton or neutron to a final pion or kaon induced by all types of three quark operators are obtained through three-point functions of (nucleon)-(three-quark operator)-(meson) with physical kinematics. In this study all the relevant systematic uncertainties of the form factors are taken into account for the first time, and the total error is found to be the range 30%–40% for π and 20%–40% for K final states.