118557908
Excited states in lattice QCD with the stochastic LapH method
Progress in computing the spectrum of excited baryons and mesons in lattice QCD is described. Results in the zero-momentum bosonic I = 1/2, S = 1, T 1 u symmetry sector of QCD using a correlation matrix of 58 operators are presented. All needed Wick contractions are efficiently evaluated using a stochastic method of treating the low-lying modes of quark propagation that exploits Laplacian Heaviside quark-field smearing. Level identification using probe operators is discussed.
119276754
Can the nearly conformal sextet gauge model hide the Higgs impostor
Abstract New results are reported from large scale lattice simulations of a frequently discussed strongly interacting gauge theory with a fermion flavor doublet in the two-index symmetric (sextet) representation of the SU(3) color gauge group. We find that the chiral condensate and the mass spectrum of the sextet model are consistent with chiral symmetry breaking in the limit of vanishing fermion mass. In contrast, sextet fermion mass deformations of spectral properties are not consistent with leading conformal scaling behavior near the critical surface of a conformal theory. A recent paper could not resolve the conformal fixed point of the gauge coupling from the slowly walking scenario of a very small nearly vanishing β -function (DeGrand et al. [3] ). It is argued that overall consistency with our new results is resolved if the sextet model is close to the conformal window, staying outside with a very small non-vanishing β -function. The model would exhibit then the simplest composite Higgs mechanism leaving open the possibility of a light scalar state with quantum numbers of the Higgs impostor. It would emerge as the pseudo-Goldstone dilaton state from spontaneous symmetry breaking of scale invariance. We will argue that even without association with the dilaton, the scalar Higgs-like state can be light very close to the conformal window. A new Higgs project of sextet lattice simulations is outlined to resolve these important questions.
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.
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.
56105021
Twelve fundamental and two sextet fermion flavors
We report extended simulation results and their new analysis in two important gauge theories with twelve fermion flavors in the fundamental SU(3) color representation and two fermions in the sextet representation. We probe the $N_f=12$ model with respect to the conformal window using mass deformed finite size scaling (FSS) theory driven by the fermion mass anomalous dimension. Our results at fixed gauge coupling show problems with the conformal scenario of the $N_f=12$ model. In the sextet model with two flavors, under the conformal hypothesis, we determine large values for the anomalous fermion mass dimension with $\gamma\geq 1$. Since our sextet analysis favors the chiral symmetry breaking hypothesis without conformality, the large exponent $\gamma$ could play an important role in understanding the composite Higgs mechanism. The new results discussed here include our extended data sets and exceed what was presented at the conference.
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.
15166765
Explanation of the RHIC HBT Puzzle by a Granular Source of Quark-Gluon Plasma Droplets
We present a review on the explanation of the RHIC HBT puzzle by a granular pion-emitting source of quark-gluon plasma droplets. The evolution of the droplet is described by relativistic hydrodynamics with an equation of state suggested by lattice gauge results. The granular source evolution is obtained by superposing all of the evolutions of individual droplets. Pions are assumed to be emitted thermally from the droplets at the freeze-out configuration characterized by a freeze-out temperature $T_f$. We find that the average particle emission time scales with the initial radius of the droplet. Pions will be emitted earlier if the droplet radius is smaller. An earlier emission time will lead to a smaller extracted HBT radius $R_{\rm out}$, while the extracted HBT radius $R_{\rm side}$ is determined by the scale of the distribution of the droplet centers. However, a collective expansion of the droplets can further decrease $R_{\rm out}$. As a result, the value of $R_{\rm out}/R_{\rm side}$ can be close to, or even less than 1 for the
119206086
Feynman Amplitude Approach to study the Passage of a Jet in a Medium
In the Feynman amplitude approach for coherent collisions of a jet with medium partons, the Bose-Einstein symmetry with respect to the interchange of the exchanged bosons leads to a destructive interference of the amplitudes in most regions of the phase space but a constructive interference in some other regions. As a consequence, there is a collective longitudinal momentum transfer to the scatterers along the jet direction, each scatterer carrying a substantial fraction of the incident jet longitudinal momentum. The manifestation of the Bose-Einstein interference may have been observed in angular correlations of hadrons associated with a high-pT trigger in high-energy collisions at RHIC and LHC.
55908145
Lectures on the Near-Side Ridge, Landau Hydrodynamics, and Heavy Quarkonia in High Energy Heavy-Ion Collisions
We give an introduction to three diﬀerent topics that are of current interest in heavy-ion collisions. Particles associated with the near-side jet are found to exhibit a Δφ-Δη correlation in the form of a ridge in the Δη direction but a peak at Δφ ~ 0. The experimental data support the description that the ridge particles are medium partons kicked by the jet. The measurement of the characteristics of the ridge provides a unique tool to probe the nature of the (jet parton)-(medium parton) collision and the momentum distribution of dense matter formed in the early stage of the heavy-ion collision. We ﬁnd that the magnitude of the longitudinal momentum kick along the jet direction acquired by a medium parton in collision with the jet is about 1 GeV, and the early parton momentum distribution is in the form of a rapidity plateau with a thermal-type transverse momentum distribution. In the second lecture, we re-examine the validity of Landau hydrodynamics which provides a reasonable description of the space-time dynamics of the hot matter produced in high-energy heavy-ion collisions. We ﬁnd that the rapidity distribution of produced particles should be more appropriately modiﬁed from Landau’s result. Past successes of the Gaussian distribution in explaining experimental rapidity data can be understood, not because it is an approximation of the original Landau distribution, but because it is in fact a close representation of the modiﬁed distribution. In the ﬁnal lecture, we give an introduction to the development of the potential model for quarkonia, using thermodynamical quantities obtained in lattice gauge calculations. We ﬁnd that the potential model is consistent with the lattice gauge spectral function analysis, if the color-singlet heavy quark-antiquark potential is a linear combination of the color-singlet free energy F 1 and internal energy U 1 , with coeﬃcients that depend on the equation of state. We ﬁnd that the eﬀects of dynamical quark modiﬁes only slightly the stability of J/ψ and the quark drip line limits possible quarkonium states with light quarks to temperatures close to, and slightly greater than, the critical phase transition temperature.
119018883
Molecular states of heavy quark mesons
We explore molecular states of two open heavy-quark mesons (Q qbar)-(qbar Q) in a quark-based model in terms of a four-body non-relativistic Hamiltonian with pairwise effective interactions. Molecular states are found in the combinations of {D, D*, B, B*} with {Dbar, Dbar*, Bbar, Bbar*}, including a weakly-bound D-Dbar* state near the threshold which may be qualitatively identified as the 3872 state observed recently by the Belle Collaboration.
15478434
Explicit solution of the time evolution of the Wigner function
Previously, an explicit solution for the time evolution of the Wigner function was presented in terms of auxiliary phase space coordinates which obey simple equations that are analogous with, but not identical to, the classical equations of motion. They can be solved easily, and their solutions can be used to construct the time evolution of the Wigner function. In this paper, the usefulness of this explicit solution is demonstrated by solving a numerical example in which the Wigner function has strong spatial and temporal variations as well as regions with negative values. It is found that the explicit solution gives a correct description of the time evolution of the Wigner function. We examine next the pseudoparticle method which uses classical trajectories to evolve the Wigner function. We find that the lowest-order pseudoparticle approximation reproduces the general features of the time evolution, but there are deviations. We show how these deviations can be systematically reduced by including higher-order correction terms in powers of 2.