Search results for "meson"
showing 10 items of 1548 documents
Hadron correlators and the structure of the quark propagator
1994
The structure of the quark propagator of $QCD$ in a confining background is not known. We make an Ansatz for it, as hinted by a particular mechanism for confinement, and analyze its implications in the meson and baryon correlators. We connect the various terms in the K\"allen-Lehmann representation of the quark propagator with appropriate combinations of hadron correlators, which may ultimately be calculated in lattice $QCD$. Furthermore, using the positivity of the path integral measure for vector like theories, we reanalyze some mass inequalities in our formalism. A curiosity of the analysis is that, the exotic components of the propagator (axial and tensor), produce terms in the hadron c…
Prospects for dilepton rates from lattice QCD
2015
We discuss the prospects of computing thermal dilepton rates from first principles lattice QCD. The focus lies in the determination of the meson vector-vector current spectral function to estimate the electrical conductivity, heavy quark diffusion and quarkonium dissociation. We review and compare recent results from continuum-extrapolated, quenched calculations, as well as dynamical two-flavor setups.
Long-distance structure of the X(3872)
2014
We investigate heavy quark symmetries for heavy meson hadronic molecules, and explore the consequences of assuming the X(3872) and $Z_b(10610)$ as an isoscalar $D\bar D^*$ and an isovector $B\bar B^*$ hadronic molecules, respectively. The symmetry allows to predict new hadronic molecules, in particular we find an isoscalar $1^{++}$ $B\bar B^*$ bound state with a mass about 10580 MeV and the isovector charmonium partners of the $Z_b(10610)$ and the $Z_b(10650)$ states. Next, we study the $X(3872) \to D^0 \bar D^0\pi^0$ three body decay. This decay mode is more sensitive to the long-distance structure of the X(3872) resonance than its $J/\psi\pi\pi$ and $J/\psi3\pi$ decays, which are mainly c…
Top quark mass measurements in ATLAS
2014
The top quark is a fundamental constituent of the Standard Model (SM). The properties of this quark are accurately predicted by this theory, except for its mass, which remains a fundamental parameter of the SM. With the advent of the Large Hadron Collider (LHC), many million of top-antitop quark pairs are available for study. With such statistics, the physics of the top quark has entered the precision era. In this note, the most recent experimental results by ATLAS concerning the top quark mass are reported.
Elliptic Flow in Pb-Pb Collisions at
2017
We report a precise measurement of the J/ψ elliptic flow in Pb-Pb collisions at sNN=5.02 TeV with the ALICE detector at the LHC. The J/ψ mesons are reconstructed at midrapidity (|y|<0.9) in the dielectron decay channel and at forward rapidity (2.5<y<4.0) in the dimuon channel, both down to zero transverse momentum. At forward rapidity, the elliptic flow v2 of the J/ψ is studied as a function of the transverse momentum and centrality. A positive v2 is observed in the transverse momentum range 2<pT<8 GeV/c in the three centrality classes studied and confirms with higher statistics our earlier results at sNN=2.76 TeV in semicentral collisions. At midrapidity, the J/ψ v2 is investigated as …
Semi-leptonic Decays of Heavy Flavours on a Fine Grained Lattice
1994
We present the results of a numerical calculation of semi-leptonic form factors relevant for heavy flavour meson decays into light mesons, at $\beta=6.4$ on a $24^3 \times 60$ lattice, using the Wilson action in the quenched approximation. We obtain $f^+_K(0)=0.65\pm 0.18$, $V(0)=0.95\pm 0.34$, $A_1(0)=0.63\pm 0.14 $ and $A_2(0)=0.45\pm 0.33 $. We also obtain $A_1(q^2_{max})=0.62\pm 0.09$, $V(0)/A_1(0)=1.5\pm 0.28 $ and $A_2(0)/A_1(0)=0.7\pm 0.4$. The results for $f^+_K(0)$, $V(0)$ and $A_1(0)$ are consistent with the experimental data and with previous lattice determinations with larger lattice spacings. In the case of $A_2(0)$ the errors are too large to draw any firm conclusion. We have …
Two-loop gluino corrections to the inclusive decayB→Xsγin theCPviolating MSSM with largetanβ
2004
We investigate two-loop gluino corrections to the effective Lagrangian for b{yields}s+{gamma}(g) in the minimal supersymmetric extension of the standard model (MSSM) at large tan{beta}, including the contributions in which quark flavor change is mediated by charginos. Using the translation invariance of loop momenta and the Ward-Takahashi identities that are required by the SU(3){sub c}xU(1){sub em} gauge invariance, we simplify our expressions to concise forms. As an example, we discuss two-loop gluino corrections to the CP asymmetry of inclusive B{yields}X{sub s}{gamma} decay in CP violating MSSM.
Non-perturbative renormalization of the quark condensate in Ginsparg-Wilson regularizations
2001
We present a method to compute non-perturbatively the renormalization constant of the scalar density for Ginsparg-Wilson fermions. It relies on chiral symmetry and is based on a matching of renormalization group invariant masses at fixed pseudoscalar meson mass, making use of results previously obtained by the ALPHA Collaboration for O(a)-improved Wilson fermions. Our approach is quite general and enables the renormalization of scalar and pseudoscalar densities in lattice regularizations that preserve chiral symmetry and of fermion masses in any regularization. As an application we compute the non-perturbative factor which relates the renormalization group invariant quark condensate to its …
Extended van Royen-Weisskopf formalism for lepton-antilepton meson decay widths within non-relativistic quark models
2001
The classical van Royen-Weisskopf formula for the decay width of a meson into a lepton-antilepton pair is modified in order to include non-zero quark momentum contributions within the meson as well as relativistic effects. Besides, a phenomenological electromagnetic density for quarks is introduced. The meson wave functions are obtained from two different models: a chiral constituent quark model and a quark potential model including instanton effects. The modified van Royen-Weisskopf formula is found to improve systematically the results for the widths, giving an overall good description of all known decays.
Probabilities in nonorthogonal basis: Four--quark systems
2009
Four-quark states may exist as colorless meson-meson molecules or compact systems with two-body colored components. We derive an analytical procedure to expand an arbitrary four-quark wave function in terms of nonorthogonal color singlet-singlet vectors. Using this expansion we develop the necessary formalism to evaluate the probability of physical components with an arbitrary four-quark wave function. Its application to characterize bound and unbound four-quark states as meson-meson, molecular, or compact systems is discussed