118639009
Multi‐hadron states in Lattice QCD spectroscopy
The ability to reliably measure the energy of an excited hadron in Lattice QCD simulations hinges on the accurate determination of all lower‐lying energies in the same symmetry channel. These include not only single‐particle energies, but also the energies of multi‐hadron states. This talk deals with the determination of multi‐hadron energies in Lattice QCD. The group‐theoretical derivation of lattice interpolating operators that couple optimally to multi‐hadron states is described. We briefly discuss recent algorithmic developments which allow for the efficient implementation of these operators in software, and present numerical results from the Hadron Spectrum Collaboration.
118432510
Conformal finite size scaling of twelve fermion flavors
Extended simulation results and their analysis are reported in a strongly coupled gauge theory with twelve fermion flavors in the fundamental SU(3) color representation. The conformality of the model is probed using mass deformed conformal finite size scaling (FSS) theory driven by the fermion mass anomalous dimension. Two independent conformal FSS fitting procedures are used in the analysis. The first one deploys physics motivated scaling functions, complemented by a second fitting procedure with spline based general B-forms for the scaling functions. The results at fixed gauge coupling show unresolved problems with the conformal hypothesis.
119102803
Pion-pion scattering phase shifts with the stochastic LapH method
Progress in calculating scattering phase shifts on $N_f=2+1$ anisotropic clover Wilson lattices is described. The stochastic LapH method facilitates computations in large volumes and for light pion masses. Results for pion masses down to 240 MeV, keeping $m_\pi L > 4$, are presented.
118446757
The ﬁnite volume spectrum of excited states from lattice QCD simulations
We present results for the spectrum of excited mesons obtained from temporal correlations of spatially-extended single-hadron and multi-hadron operators computed in lattice QCD. The stochastic LapH algorithm is implemented on anisotropic, dynamical lattices for isovectors for pions of mass 390 MeV. A large correlation matrix with single-particle and two-particle probe operators is diagonalized to identify resonances. The masses of excited states in the I = 1,S = 0,T 1u channel as well as the mixing of single and multi-particle probe operators are presented.
118848110
Baryon spectrum in the composite sextet model
The strongly coupled near-conformal gauge theory with two fermion flavors in the two-index symmetric (sextet) representation of SU(3) is potentially a minimal realization of the composite Higgs mechanism. We discuss the staggered fermion construction of baryonic states, present our first numerical results and comment on implications for dark matter.
56403927
Group-theoretical construction of finite-momentum and multi-particle operators for lattice hadron spectroscopy
Determining the spectrum of hadronic excitations from Monte Carlo simulations requires the use of interpolating operators that couple to multi-particle states. Recent algorithmic advances have made the inclusion of multi-hadron operators in spectroscopy calculations a practical reality. In this talk, a procedure for constructing a set of multi-hadron interpolators that project onto the states of interest is described. To aid in the interpretation of simulation data, operators are designed to transform irreducibly under the lattice symmetry group. The identification of a set of optimal single-hadron interpolators for states with non-zero momenta is an essential intermediate step in this analysis.
118512883
Relativistic Hard-Scattering and Tsallis Fits to p T Spectra in pp Collisions at the LHC ∗
Motivated by the good Tsallis fits to the high-p T spectra in pp collisions at the LHC, we study the relativistic hard-scattering model and obtain an approximate analytical expression for the differential hard-scattering cross section at � � 0. The power-law behavior of the transverse spectra, in the form of d�/dp 2/1/p n, gives a power index n in the range of 4.5-5.5 for jet production as predicted by pQCD, after the dependencies of the structure functions and the running coupling constant are properly taken into account. The power indices for hadron production n are slightly greater than those for jet production.
115175924
Effects of dynamical quarks on the stability of heavy quarkonia in quark-gluon plasma
To study the stability of heavy quarkonia in quark-gluon plasma, we use a color-singlet Q-Qbar potential determined previously to be a well-defined linear combination of the free energy F_1 and the internal energy U_1. Using the lattice gauge results of Kaczmarek et al., the dissociation temperatures of J/psi and chi_b in quenched QCD are found to be 1.62Tc and 1.18Tc respectively, in good agreement with spectral function analyses. The dissociation temperature of J/psi in full QCD with 2 flavors is 1.42Tc. Thus, the presence of dynamical quarks in full QCD lowers the dissociation temperature of J/psi, but J/psi remains bound up to 1.42Tc.
118706711
Magnetic States at Short Distances
3 P ++ 0 states admit two types of eigenstates with drastically different behaviors for the radial wave function u = rψ. One type of states, with u growing as r �+1 at small r, will be called usual states. The other type of states with u growing as rwill be called peculiar states. Both of the usual and peculiar eigenstates have admissible behaviors at short distances. Remarkably, the solutions for both sets of 1 S0 states can be written out analytically. The usual bound 1 S0 states possess attributes the same as those one usually encounters in QED and QCD, with bound state energies explicitly agreeing with the standard perturbative results through order α 4 . In contrast, the peculiar bound 1 S0 states, yet to be observed, not only have different behaviors at the origin, but also distinctly different bound state properties (and scattering phase shifts). For the peculiar 1 S0 ground state of fermion-antifermion pair with fermion rest mass m, the root-mean-square radius is approximately 1/m, binding energy is approximately (2 p 2)m, and rest mass approximately p 2m. On the other hand, the (n+1) 1 S0 peculiar state with principal quantum number (n + 1) is nearly degenerate in energy and approximately equal in size with the n 1 S0 usual states. For the 3 P0 states, the usual solutions lead to the standard bound state energies and no resonance, but resonances have been found for the peculiar states whose energies depend on the description of the internal structure of the charges, the mass of the constituent, and the coupling constant. The existence of both usual and peculiar eigenstates in the same system leads to the non- self-adjoint property of the mass operator and two non-orthogonal complete sets. As both sets of states are physically admissible, the mass operator can be made self-adjoint with a single complete set of admissible states by introducing a new peculiarity quantum number and an enlarged Hilbert space that contains both the usual and peculiar states in different peculiarity sectors. Whether or not these newly-uncovered quantum-mechanically acceptable peculiar 1 S0 bound states and 3 P0 resonances for point fermion-antifermion systems correspond to physical states remains to be further investigated.
119074511
Tests of two-body Dirac equation wave functions in the decays of quarkonium and positronium into two photons
Two-body Dirac equations of constraint dynamics provide a covariant framework to investigate the problem of highly relativistic quarks in meson bound states. This formalism eliminates automatically the problems of relative time and energy, leading to a covariant three dimensional formalism with the same number of degrees of freedom as appears in the corresponding nonrelativistic problem. It provides bound state wave equations with the simplicity of the nonrelativistic Schr\"odinger equation. Here we begin important tests of the relativistic 16 component wave function solutions obtained in a recent work on meson spectroscopy, extending a method developed previously for positronium decay into two photons. Preliminary to this we examine the positronium decay in the $^{3}P_{0,2}$ states as well as the $^{1}S_{0}$. The two-gamma quarkonium decays that we investigate are for the ${\ensuremath{\eta}}_{c}$, ${\ensuremath{\eta}}_{c}^{\ensuremath{'}}$, ${\ensuremath{\chi}}_{c0}$, ${\ensuremath{\chi}}_{c2}$, ${\ensuremath{\pi}}^{0}$, ${\ensuremath{\pi}}_{2}$, ${a}_{2}$, and ${f}_{2}^{\ensuremath{'}}$ mesons. Our results for the four charmonium states compare well with those from other quark models and show the particular importance of including all components of the wave function as well as strong and c.m. energy dependent potential effects on the norm and amplitude. The results for the ${\ensuremath{\pi}}^{0}$, although off the experimental rate by 13%, are much closer than the usual expectations from a potential model. We conclude that the two-body Dirac equations lead to wave functions which provide good descriptions of the two-gamma decay amplitude and can be used with some confidence for other purposes.
36760880
Potential Models and Lattice Gauge Current-Current Correlators
We compare current-current correlators in lattice gauge calculations with correlators in different potential models for a pseudoscalar charmonium in the quark-gluon plasma. An important ingredient in the evaluation of the current-current correlator in the potential model is the basic principle that, out of the set of continuum states, only resonance states and Gamow states with lifetimes of sufficient magnitudes can propagate as composite objects and can contribute to the current-current correlator. When the contributions from the bound states and continuum states are properly treated, the potential model current-current correlators obtained with the potential proposed by Wong [Phys. Rev. C 72, 034906 (2005)] are consistent with the lattice gauge correlators. The proposed potential model thus gains support to be a useful tool to complement lattice gauge calculations for the study of QQ{bar} states at high temperatures.