Showing papers on "Meson published in 2013"

Determination of the X(3872) meson quantum numbers

Abstract: The quantum numbers of the X(3872) meson are determined to be J(PC) = 1(++) based on angular correlations in B+ -> X(3872)K+ decays, where X(3872) -> pi(+) pi(-) j/psi and J/psi -> pi(+) mu(-). The data correspond to 1.0 fb(-1) of pp collisions collected by the LHCb detector. The only alternative assignment allowed by previous measurements J(PC) = 2(-+) is rejected with a confidence level equivalent to more than 8 Gaussian standard deviations using a likelihood-ratio test in the full angular phase space. This result favors exotic explanations of the X(3872) state.

Heavy-quark dynamics and hadronization in ultrarelativistic heavy-ion collisions: Collisional versus radiative energy loss

Abstract: We study the dynamics of energy loss and flow of heavy quarks produced in ultrarelativistic heavy-ion collisions within the framework of a Langevin equation coupled to a ($2+1$)-dimensional viscous hydrodynamic model that simulates the spacetime evolution of the produced hot and dense QCD matter. The classical Langevin approach is improved such that, apart from quasielastic scatterings, radiative energy loss is incorporated by treating gluon radiation as an additional force term. The hadronization of emitted heavy quarks is simulated via a hybrid fragmentation plus recombination model. Our calculation shows significant contribution from gluon radiation to heavy quark energy loss at high energies, and we find the recombination mechanism is important for heavy flavor meson production at intermediate energies. We present numerical results for the nuclear modification and elliptic flow of $D$ mesons, which are consistent with measurements at both the CERN Large Hadron Collider (LHC) and the BNL Relativistic Heavy-Ion Collider (RHIC); predictions for $B$ mesons are also provided.

Studies of nucleon resonance structure in exclusive meson electroproduction

Abstract: Studies of the structure of excited baryons are key factors to the N* program at Jefferson Lab (JLab). Within the first year of data taking with the Hall B CLAS12 detector following the 12 GeV upgrade, a dedicated experiment will aim to extract the N* electrocouplings at high photon virtualities Q2. This experiment will allow exploration of the structure of N* resonances at the highest photon virtualities ever achieved, with a kinematic reach up to Q2 = 12 GeV2. This high-Q2 reach will make it possible to probe the excited nucleon structures at distance scales ranging from where effective degrees of freedom, such as constituent quarks, are dominant through the transition to where nearly massless bare-quark degrees of freedom are relevant. In this document, we present a detailed description of the physics that can be addressed through N* structure studies in exclusive meson electroproduction. The discussion includes recent advances in reaction theory for extracting N* electrocouplings from meson electropro...

Measurement of the fragmentation fraction ratio fs/fd and its dependence on B meson kinematics

Abstract: The relative production rate of B0s and B 0 mesons is determined with the hadronic decays B0s→D−sπ+ and B 0 → D − K +. The measurement uses data corresponding to 1.0 fb−1 of pp collisions at a centre-of-mass energy of s√=7 TeV recorded in the forward region with the LHCb experiment. The ratio of production rates, f s /f d , is measured to be 0.238 ± 0.004 ± 0.015 ± 0.021, where the first uncertainty is statistical, the second systematic, and the third theoretical. This is combined with a previous LHCb measurement to obtain f s /f d = 0.256 ± 0.020. The dependence of f s /f d on the transverse momentum and pseudorapidity of the B meson is determined using the decays B0s→D−sπ+ and B 0 → D −π+. There is evidence for a decrease with increasing transverse momentum, whereas the ratio remains constant as a function of pseudorapidity. In addition, the ratio of branching fractions of the decays B 0 → D − K + and B 0 → D −π+ is measured to be 0.0822 ± 0.0011 (stat) ± 0.0025 (syst).

Elastic and Proton-Dissociative Photoproduction of J/psi Mesons at HERA

Abstract: Cross sections for elastic and proton-dissociative photoproduction of J/psi mesons are measured with the H1 detector in positron-proton collisions at HERA. The data were collected at $ep$ centre-of-mass energies sqrt{s} approx 318 GeV and sqrt{s} approx 225 GeV, corresponding to integrated luminosities of L = 130 pb^{-1} and L = 10.8 pb^{-1}, respectively. The cross sections are measured as a function of the photon-proton centre-of-mass energy in the range 25< Wgp < 110 GeV. Differential cross sections $\mathrm{d}\sigma / \mathrm{d}t$, where $t$ is the squared four-momentum transfer at the proton vertex, are measured in the range $|t| < 1.2 \, \gevsq$ for the elastic process and $|t| < 8 \, \gevsq$ for proton dissociation. The results are compared to other measurements. The $\Wgp$ and $t$-dependences are parametrised using phenomenological fits.

D Meson Elliptic Flow in Noncentral Pb-Pb Collisions at root(S)(NN)=2.76 TeV

Abstract: Azimuthally anisotropic distributions of D-0, D+, and D*+ mesons were studied in the central rapidity region (vertical bar y vertical bar < 0.8) in Pb-Pb collisions at a center-of-mass energy root(S)(NN) = 2.76 TeV per nucleon-nucleon collision, with the ALICE detector at the LHC. The second Fourier coefficient upsilon(2) (commonly denoted elliptic flow) was measured in the centrality class 30%-50% as a function of the D meson transverse momentum p(T), in the range 2-16 GeV/c. The measured upsilon(2) of D mesons is comparable in magnitude to that of light-flavor hadrons. It is positive in the range 2 < p(T) < 6 GeV/c with 5.7 sigma significance, based on the combination of statistical and systematic uncertainties.

D(s) meson as a quantitative probe of diffusion and hadronization in nuclear collisions.

Abstract: The modifications of ${D}_{s}$-meson spectra in ultrarelativistic heavy-ion collisions are identified as a quantitative probe of key properties of the hot nuclear medium. The unique valence-quark content of the ${D}_{s}=c\overline{s}$ couples the well-known strangeness enhancement with the collective-flow pattern of primordially produced charm quarks. This idea is illustrated utilizing a consistent strong-coupling treatment with hydrodynamic bulk evolution and nonperturbative $T$-matrix interactions for both heavy-quark diffusion and hadronization in the quark-gluon plasma (QGP). A large enhancement of the ${D}_{s}$ nuclear modification factor at Relativistic Heavy Ion Collider is predicted, with a maximum of $\ensuremath{\sim}1.5--1.8$ at transverse momenta around $2\text{ }\text{ }\mathrm{GeV}/c$. This is a direct consequence of the strong coupling of the heavy quarks to the QGP and their hadronization via coalescence with strange quarks. We furthermore introduce the effects of diffusion in the hadronic phase and suggest that an increase of the $D$-meson elliptic flow compared to the ${D}_{s}$ can disentangle the transport properties of hadronic and QGP liquids.

B → Kℓ + ℓ − decay at large hadronic recoil

Abstract: We predict the amplitude of the B → Kl + l − decay in the region of the dilepton invariant mass squared 0 < q 2 ≤ m 2 , that is, at large hadronic recoil. The B → K form factors entering the factorizable part of the decay amplitude are obtained from QCD light-cone sum rules. The nonlocal effects, generated by the four-quark and penguin operators combined with the electromagnetic interaction, are calculated at q 2 < 0, far below the hadronic thresholds. For hard-gluon contributions we employ the QCD factorization approach. The soft-gluon nonfactorizable contributions are estimated from QCD light-cone sum rules. The result of the calculation is matched to the hadronic dispersion relation in the variable q 2 , which is then continued to the kinematical region of the decay. The overall effect of nonlocal contributions in B → Kl + l − at large hadronic recoil is moderate. The main uncertainty of the predicted B → Kl + l − partial width is caused by the B → K form factors. Furthermore, the isospin asymmetry in this decay is expected to be very small. We investigate the deviation of the observables from the Standard Model predictions by introducing a generic new physics contribution to the effective Hamiltonian.

Interactions of charmed mesons with light pseudoscalar mesons from lattice QCD and implications on the nature of the D s0 * (2317)

Abstract: We study the scattering of charmed mesons (D, D{sub s}) with light pseudoscalar mesons ({pi}, K) in full lattice QCD. The S-wave scattering lengths are calculated using L{umlt u}schers finite volume technique. We use the relativistic Fermilab formulation for the charm quark. For the light quark, we use domain-wall fermions in the valence sector and improved Kogut-Susskind sea quarks. We calculate the scattering lengths of isospin-3/2 D{pi}, D{sub s}{pi}, D{sub s}K, isospin-0 D{anti K} and isospin-1 D{anti K} channels on the lattice. For the chiral extrapolation, we use the chiral unitary approach to next-to-leading order, which at the same time allows us to give predictions for other channels. Furthermore, the hadronic molecular interpretation of the D{sub s0}*(2317) is consistent with our results. The isospin breaking decay width {Gamma}(D{sub s0}*(2317){yields}D{sub s}{pi}) in the hadronic molecular picture is updated to be (89{+-}22)keV.

$D_{s0}^*(2317)$ Meson and $D$-Meson-Kaon Scattering from Lattice QCD

Abstract: The scalar meson D*(s0)(2317) is found 37(17) MeV below the DK threshold in a lattice simulation of the J(P)=0(+) channel using, for the first time, both DK as well as s¯c interpolating fields. The simulation is done on N(f)=2+1 gauge configurations with m(π) is approximately equal to 156 MeV, and the resulting M(D*(s0))-1/4(M(D(s))+3M(D*(s)))=266(16) MeV is close to the experimental value 241.5(0.8) MeV. The energy level related to the scalar meson is accompanied by additional discrete levels due to DK scattering states. The levels near threshold lead to the negative DK scattering length a(0)=-1.33(20) fm that indicates the presence of a state below threshold.

Meson vacuum phenomenology in a three-flavor linear sigma model with (axial-)vector mesons

Abstract: We study scalar, pseudoscalar, vector, and axial-vector mesons with nonstrange and strange quantum numbers in the framework of a linear sigma model with global chiral U(Nf)L×U(Nf)R symmetry. We perform a global fit of meson masses, decay widths, as well as decay amplitudes. The quality of the fit is, for a hadronic model that does not consider isospin-breaking effects, surprisingly good. We also investigate the question whether the scalar q¯q states lie below or above 1 GeV and find the scalar states above 1 GeV to be preferred as q¯q states. Additionally, we also describe the axial-vector resonances as q¯q states.

Vus from pi and K decay constants in full lattice QCD with physical u, d, s and c quarks

Abstract: We determine the decay constants of the π and K mesons on gluon field configurations from the MILC Collaboration including u , d , s , and c quarks. We use three values of the lattice spacing and u/d quark masses going down to the physical value. We use the w0 parameter to fix the relative lattice spacing and fπ to fix the overall scale. This allows us to obtain a value for fK+/fπ+=1.1916(21). Comparing to the ratio of experimental leptonic decay rates gives |Vus|=0.22564(28)Br(K+)(20)EM(40)latt(5)Vud and the test of unitarity of the first row of the Cabibbo-Kobayashi-Maskawa matrix: |Vud|2+|Vus|2+|Vub|2−1=0.000 09(51).

Decay constants of heavy-light vector mesons from QCD sum rules

Abstract: We revisit QCD sum rules for the decay constants of heavy-light mesons. In the sum rules for the vector mesons B^*_(s) and D^*_(s) we improve the accuracy of OPE, taking into account the O(alpha_s^2) terms in the perturbative part and calculating the O(alpha_s) corrections to the quark-condensate contribution. With this accuracy, we obtain the ratios of decay constants: f_B^*/f_B=1.02 +0.07 -0.03, f_D^*/f_D=1.20 +0.10 -0.07. The sum rule predictions for the decay constants of pseudoscalar mesons are updated with the results f_B=(207 +17 -9) MeV, f_B_s=(242 +17 -12) MeV, f_D=(201 +12 -13) MeV, f_D_s=(238 +13 -23) MeV. In order to assess the sensitivity of our calculation to the form of the sum rule, we consider alternative versions such as the power moments and Borel sum rules with different weights of the spectral density. We also investigated the heavy quark limit of the sum rules for vector and pseudoscalar mesons, estimating the violations of the heavy-quark spin and flavour symmetry.

Phenomenology of a very light scalar (100 MeV $<m_h<$ 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 $

Tetraquark mesons in large-N quantum chromodynamics.

Abstract: It is argued that exotic mesons consisting of two quarks and two antiquarks are not ruled out in quantum chromodynamics with a large number N of colors, as generally thought. Tetraquarks of one class are typically long-lived, with decay rates proportional to 1/N.

Leptonic decays of charged pseudoscalar mesons - 2012

Abstract: We review the physics of purely leptonic decays of $\pi^\pm$, $K^\pm$, $D^{\pm}$, $D_s^\pm$, and $B^\pm$ pseudoscalar mesons. The measured decay rates are related to the product of the relevant weak-interaction-based CKM matrix element of the constituent quarks and a strong interaction parameter related to the overlap of the quark and antiquark wave-functions in the meson, called the decay constant $f_P$. The interplay between theory and experiment is different for each particle. Theoretical predictions of $f_B$ that are needed in the $B$ sector can be tested by measuring $f_{D^+}$ and $f_{D_s^+}$ in the charm sector. The lighter $\pi^{\pm}$ and $K^{\pm}$ mesons provide stringent comparisons between experiment and theory due to the accuracy of both the measurements and the theoretical predictions. This review was prepared for the Particle Data Group's 2012 edition.

Interpretation of the X(3872) as a charmonium state plus an extra component due to the coupling to the meson-meson continuum

Abstract: We present a quark model calculation of the charmonium spectrum with self-energy corrections due to the coupling to the meson-meson continuum. The bare masses used in the calculation are computed within the relativized quark model by Godfrey and Isgur. The strong decay widths of $3S$, $2P$, $1D$, and $2D$ $c\overline{c}$ states are also calculated, to set the values of the ${}^{3}{P}_{0}$ pair-creation model's parameters we use to compute the vertex functions of the loop integrals. Finally, the nature of the $X(3872)$ resonance is analyzed and the main possibilities ($c\overline{c}$ state or $D{\overline{D}}^{*}$ molecule) are discussed. According to our results, the $X(3872)$ is compatible with the meson ${\ensuremath{\chi}}_{c1}(2P)$, with ${J}^{\mathrm{PC}}={1}^{++}$, and is thus interpreted as a $c\overline{c}$ core plus higher Fock components due to the coupling to the meson-meson continuum. These ${J}^{\mathrm{PC}}={1}^{++}$ quantum numbers are in agreement with the experimental results found by the LHCb collaboration. In our view, the $X(3872)$'s mass is lower than the quark model's predictions because of self-energy shifts.

Elliptic flow of identified hadrons in Au+Au collisions at s NN =7.7-62.4 GeV

Abstract: Measurements of the elliptic flow, upsilon(2), of identified hadrons (pi(+/-), K-+/-, K-s(0), p, (p) over bar, phi, Lambda, (Lambda) over bar, Xi(-), (Xi) over bar (+), Omega(-), (Omega) over bar (+)) in Au + Au collisions at root s(NN) = 7.7, 11.5, 19.6, 27, 39, and 62.4 GeV are presented. The measurements were done at midrapidity using the time-projection chamber and the time-of-flight detectors of the Solenoidal Tracker at RHIC experiment during the beam-energy scan program at Relativistic Heavy Ion Collider. A significant difference in the upsilon(2) values for particles and the corresponding antiparticles was observed at all transverse momenta for the first time. The difference increases with decreasing center-of-mass energy, root s(NN) (or increasing baryon chemical potential, mu(B)), and is larger for the baryons as compared to the mesons. This implies that particles and antiparticles are no longer consistent with the universal number-of-constituent quark (NCQ) scaling of upsilon(2) that was observed at root s(NN) = 200 GeV. However, for the selected group of particles (p(+), K+, K-s(0), p, Lambda, Xi(-), Omega(-)) NCQ scaling at (m(T) - m(0))/n(q) > 0.4 GeV/c(2) is not violated within +/- 10%. The upsilon(2) values for f mesons at 7.7 and 11.5 GeV are approximately two standard deviations from the trend defined by the other hadrons at the highest measured p(T) values.

First observation of $CP$ violation in the decays of $B^0_s$ mesons

Abstract: Using pp collision data corresponding to an integrated luminosity of 1.0 fb-1 and collected by LHCb in 2011 at a center-of-mass energy of 7 TeV, we report the measurement of direct CP violation in Bs0→K-π+ decays, ACP(Bs0→K-π+)=0.27±0.04 (stat)±0.01 (syst), with significance exceeding 5 standard deviations. This is the first observation of CP violation in the decays of Bs0 mesons. Furthermore, we provide an improved determination of direct CP violation in B0→K+π- decays, ACP(B0→K+π-)=-0.080±0.007 (stat)±0.003 (syst), which is the most precise measurement of this quantity to date.

Charged vector mesons in a strong magnetic field

Abstract: We show that charged vector mesons cannot be condensed by a magnetic field. Although some hadron models predict the charged vector meson condensation in a strong magnetic field, we prove, by means of the Vafa-Witten theorem, that this is not the case in QCD. We also perform the numerical analysis for the meson mass and condensation in lattice QCD. The lattice QCD data confirm no charged vector meson condensation in a magnetic field.

Open charm production at the LHC - $k_{t}$-factorization approach

Abstract: We discuss inclusive production of open charm in proton-proton scattering at LHC. The calculation is performed within the ${k}_{t}$-factorization approach. Different models of unintegrated gluon distributions (UGDFs) from the literature are used. The theoretical transverse momentum as well as (pseudo)rapidity distributions of charmed mesons are compared with recent experimental data of the ATLAS, ALICE, and LHCb Collaborations. Only the calculation with Kimber-Martin-Ryskin UGDF gives results comparable to experimental ones. All other popular models of UGDF significantly underpredict experimental data. Several sources of uncertainties of the theoretical predictions are also studied in detail. In addition, we discuss correlations between $D$ and $\overline{D}$ mesons. Good description of experimental distribution in invariant mass and in relative azimuthal angle between $D$ and $\overline{D}$ mesons is achieved for the Kimber-Martin-Ryskin UGDF. The considered correlation observables measured by the LHCb experiment were not discussed in other approaches in the literature

Measurement of the Υ(1S), Υ(2S), and Υ(3S) Polarizations in pp Collisions at s√=7 TeV

Abstract: The polarizations of the Υ(1S), Υ(2S), and Υ(3S) mesons are measured in proton-proton collisions at √s=7 TeV, using a data sample of Υ(nS)→μ^+μ^- decays collected by the CMS experiment, corresponding to an integrated luminosity of 4.9 fb^(-1). The dimuon decay angular distributions are analyzed in three different polarization frames. The polarization parameters λ_ϑ, λ_φ, and λ_(ϑφ), as well as the frame-invariant quantity λ˜, are presented as a function of the Υ(nS) transverse momentum between 10 and 50 GeV, in the rapidity ranges |y|<0.6 and 0.6<|y|<1.2. No evidence of large transverse or longitudinal polarizations is seen in the explored kinematic region.

Strangeness at high temperatures: from hadrons to quarks

Abstract: Appropriate combinations of up to fourth order cumulants of net strangeness fluctuations and their correlations with net baryon number and electric charge fluctuations, obtained from lattice QCD calculations, have been used to probe the strangeness carrying degrees of freedom at high temperatures. For temperatures up to the chiral crossover, separate contributions of strange mesons and baryons can be well described by an uncorrelated gas of hadrons. Such a description breaks down in the chiral crossover region, suggesting that the deconfinement of strangeness takes place at the chiral crossover. On the other hand, the strangeness carrying degrees of freedom inside the quark gluon plasma can be described by a weakly interacting gas of quarks only for temperatures larger than twice the chiral crossover temperature. In the intermediate temperature window, these observables show considerably richer structures, indicative of the strongly interacting nature of the quark gluon plasma.

Dense hadronic matter in holographic QCD

Abstract: We provide a method to study hadronic matter at finite density in the context of the Sakai-Sugimoto model. We introduce the baryon chemical potential through the external U(1) v gauge field in the induced (DBI plus CS) action on the D8-probe-brane, where baryons are skyrmions. Vector dominance is manifest at finite density. We derive the effect of the baryon density on the energy density, and on the dispersion relations of pions and vector mesons at large N c . The energy density asymptotes are constant at large density, suggesting that dense matter at large N c freezes, with the pion velocity dropping to zero. Holographic dense matter enforces exactly the tenets of vector dominance and efficiently screens vector mesons. At the freezing point, the ρ — ππ coupling vanishes with a finite rho mass of about 20% its vacuum value.

Resonance parameters of the rho-meson from asymmetrical lattices

Abstract: We present a lattice QCD calculation of the parameters of the $\rho$ meson decay. The study is carried out on spatially asymmetric boxes using nHYP-smeared clover fermions with two mass-degenerate quark flavors. Our calculations are carried out at a pion mass $m_\pi=304(2)$ MeV on the set of lattices $V=24^2\times \eta 24\times48$ with $\eta=1.0,1.25$, and 2.0 with lattice spacing $a=0.1255(7)$ fm. The resonance mass $m_\rho=827(3)(5)$ MeV and coupling constant $g_{\rho\pi\pi}=6.67(42)$ are calculate using the P-wave scattering phase shifts. We construct a 2$\times$2 correlation matrix to extract the energy of the scattering states and compute the phase shifts using the finite volume formula. By varying the degree of asymmetry, we are able to compute a set of phase shifts that are evenly distributed throughout the spectral region where the $\rho$ decays.

Measurement of B meson production cross-sections in proton-proton collisions at \sqrt{s}=7 TeV

Abstract: The production cross-sections of B mesons are measured using data, corresponding to a integrated luminosity of 0.36 fb-1, collected with the LHCb detector at a centre-of-mass energy of 7 TeV. The B+, B0 and Bs0 mesons are reconstructed in the exclusive decays B+ -> J/psi K+, B0 -> J/psi K*0 and Bs0 -> J/psi phi, with J/psi -> mu+ mu-, K*0 -> K+ pi- and phi -> K+ K-. The differential cross-sections as functions of B meson transverse momentum pT and rapidity y, in the range 0 B+ + X) = 38.9 +- 0.3 (stat.) +- 2.5 (syst.) +- 1.3 (norm.) mub, sigma(pp -> B0 + X) = 38.1 +- 0.6 (stat.) +- 3.7 (syst.) +- 4.7 (norm.) mub, sigma(pp -> Bs0 + X) = 10.5 +- 0.2 (stat.) +- 0.8 (syst.) +- 1.0 (norm.) mub, where the third uncertainty arises from the pre-existing branching fraction measurements.

Excited spectroscopy of charmed mesons from lattice QCD

Abstract: We present spectra of highly excited D and Ds mesons up to around 3:8 GeV determined using dynamical lattice QCD. We employ novel computational techniques and the variational method with a large basis of carefully constructed operators in order to extract and reliably identify the continuum spin of an extensive set of excited states. These include states with high spin and states identied as having an explicit gluonic contribution. Calculations were performed on two volumes, both with a pion mass of approximately 400 MeV, achieving a high statistical precision for both ground and excited states. We discuss our results in light of experimental observations, comment on the phenomenological implications and identify the lightest 'supermultiplet' of hybrid mesons in each sector.

Measurement of upsilon production in 7 TeV pp collisions at ATLAS

Abstract: Using 1.8 fb(-1) of pp collisions at a center- of- mass energy of 7 TeV recorded by the ATLAS detector at the Large Hadron Collider, we present measurements of the production cross sections of Upsilon(1S,2S,3S) mesons. Upsilon mesons are reconstructed using the dimuon decay mode. Total production cross sections for p(T) < 70 GeV and in the rapidity interval vertical bar y(Upsilon)vertical bar < 2. 25 are measured to be, 8.01 +/- 0.02 +/- 0.36 +/- 0.31 nb, 2.05 +/- 0.01 +/- 0.12 +/- 0.08 nb, and 0.92 +/- 0.01 +/- 0.07 +/- 0.04 nb, respectively, with uncertainties separated into statistical, systematic, and luminosity measurement effects. In addition, differential cross section times dimuon branching fractions for Upsilon(1S), Upsilon(2S), and Upsilon(3S) as a function of Upsilon transverse momentum pT and rapidity are presented. These cross sections are obtained assuming unpolarized production. If the production polarization is fully transverse or longitudinal with no azimuthal dependence in the helicity frame, the cross section may vary by approximately +/- 20%. If a nontrivial azimuthal dependence is considered, integrated cross sections may be significantly enhanced by a factor of 2 or more. We compare our results to several theoretical models of Upsilon meson production, finding that none provide an accurate description of our data over the full range of Upsilon transverse momenta accessible with this data set.