arXiv subjects

T. Barnes

Publications and source records attributed to T. Barnes.

At least 19 recordsLinked to original sources

arXiv2026

Fast Microwave-free State Preparation and Measurement of Superconducting Qubits

Fast, high-fidelity, scalable state preparation and measurement is critical to the realization of a quantum computing system. The state-of-the-art methods for preparation and readout of superconducting qubits require finely tuned microwave signals and ~100 ns of measurement time, which are major obstacles to the scalability and performance of superconducting quantum computers. Here, we have demonstrated novel, microwave-free methods for both preparation and readout of superconducting qubits with >99% fidelity in only 10 ns for either operation while maintaining qubit coherence. This technology is compatible with scalable superconducting digital control systems, and using quantum flux parametrons for amplification, we demonstrated full quantum-to-digital conversion in only 15 ns, which is an order of magnitude faster than state-of-the-art microwave-based techniques.

quant-ph↗

arXiv2020

The SHIR Model: Realistic Fits to COVID-19 Case Numbers

We consider a global (location independent) model of pandemic growth which generalizes the SIR model to accommodate important features of the COVID-19 pandemic, notably the implementation of pandemic reduction measures. This "SHIR" model is applied to COVID-19 data, and shows promise as a simple, tractable formalism with few parameters that can be used to model pandemic case numbers. As an example we show that the average time dependence of new COVID-19 cases per day from 15 Central and Western European countries is in good agreement with the analytic, parameter-free prediction of the model

q-bio.PE↗

arXiv2018

On the interpretation of the long-term cyclic period variations in RR Lyrae stars

Many RR Lyrae stars show long-term variations of their pulsation period, some of them in a cyclic way. Such behaviour can be attributed to the light-travel time effect (LTTE) caused by an unseen companion. Solutions of the LTTE often suggest very eccentric orbits and minimal mass of the companion on the order of several solar masses, thus, in the black hole range. We discuss the possibility of the occurrence of the RR Lyr-black hole pairs and on the case of Z CVn demonstrate that the LTTE hypothesis can be false in some of the binary candidates.

astro-ph.SR↗

arXiv2014

Molecular Interpretation of the Supercharmonium State Z(4475)

Charm meson molecule (c\bar n)(n\bar c) assignments for the supercharmonium state Z(4475) are considered, both on general grounds and in the context of specific pion exchange models. Two possible charm molecule assignments for the JP = 1+, Z(4475) are considered here, involving respectively a radially and an orbitally excited charm meson. In each assignment, a lower-mass isosinglet charm molecule state is predicted. For both the Z(4475) and the Y(4260), measurement of the ratios of the branching fractions to D \bar D plus n pions is recommended as a test of the nature of these states.

hep-ph↗

arXiv2010

(A Few) Recent Developments in Hadron Spectroscopy

Recent years have seen rapid developments in our knowledge and understanding of meson spectroscopy, especially in the charm quark sectors. In my invited overview I discussed some of these recent new developments, including theoretical developments, new production mechanisms such as B decays and double charmonium production, and the discovery of several of the many new candidates for excited charmonia, charm meson molecules, and hybrid (excited glue) mesons, in both charmonium and light quark sectors. In this writeup, due to length constraints I will restrict my discussion to a few examples of these new states, some of their broader theoretical implications, and future prospects.

hep-ph↗

arXiv2010

Psi to N Nbar m

In this invited talk I discuss two recent applications of charmonium (Psi) decays to N Nbar m final states, where N is a nucleon and m is a light meson. There are several motivations for studying these decays: 1) They are useful for the study of N* spectroscopy; 2) they can be used to estimate cross sections for the associated charmonium production processes p pbar to Psi m, which PANDA plans to exploit in searches for charmonium hybrid exotics; and 3) they may allow the direct experimental measurement of NNm (meson-nucleon) strong couplings, which provide crucial input information for meson exchange models of the NN force. The latter two topics are considered in this talk, which will also compare results from a simple hadron pole model of these decays to recent experimental data.

hep-ph↗

arXiv2010

CHARM2010: Theory Summary

This invited summary gives some concluding remarks regarding theoretical aspects of the research presented at Charm2010. I will specialize to the role of theory and the relative reach of theory and experiment in three of the major areas of charm physics address at this conference, specifically 1) charm production, 2) charm weak decays, and 3) charm hadron spectroscopy. After a discussion of the status of progress on representative topics in each of these areas I will conclude with a previously unrelated Feynman story from a conference in the early days of charm.

hep-ph↗

arXiv2010

Update on Charmonium Theory

In this invited presentation I review some recent developments in the theory of charmonium that appear likely to be of importance for future experimental studies in this field. The specific areas considered are double charmonium production, LQCD studies of charmonium, recent results for hadron loops, c-cbar production cross sections at PANDA, charm molecules, and two recent developments, "charmiscelleny".

hep-ph↗

arXiv2010

Meson Emission Model of Psi to N Nbar m Charmonium Strong Decays

In this paper we consider a sequential "meson emission" mechanism for charmonium decays of the type Psi -> N Nbar m, where Psi is a generic charmonium state, N is a nucleon and m is a light meson. This decay mechanism, which may not be dominant in general, assumes that an NNbar pair is created during charmonium annihilation, and the light meson m is emitted from the outgoing nucleon or antinucleon line. A straightforward generalization of this model can incorporate intermediate N* resonances. We derive Dalitz plot event densities for the cases Psi = eta_c, J/psi, chi_c0, chi_c1} and psi' and m = pi0, f0 and omega (and implicitly, any 0^{-+}, 0^{++} or 1^{--} final light meson). It may be possible to separate the contribution of this decay mechanism to the full decay amplitude through characteristic event densities. For the decay subset Psi -> p pbar pi0 the two model parameters are known, so we are able to predict absolute numerical partial widths for Gamma(Psi -> p pbar pi0). In the specific case J/psi -> p pbar pi0 the predicted partial width and M_{p pi0} event distribution are intriguingly close to experiment. We also consider the possibility of scalar meson and glueball searches in Psi -> p pbar f0. If the meson emission contributions to Psi -> N Nbar m decays can be isolated and quantified, they can be used to estimate meson-nucleon strong couplings {g_NNm}, which are typically poorly known, and are a crucial input in meson exchange models of the NN interaction. The determination of g_NNpi from Jψ-> p pbar pi0 and the (poorly known) g_NNomega and the anomalous "strong magnetic" coupling kappa_{NNomega} from J/psi -> p pbar omega are considered as examples.

hep-ph↗

arXiv2009

Hadron Loops: General Theorems and Application to Charmonium

In this paper we develop a formalism for incorporating hadron loops in the quark model. We derive expressions for mass shifts, continuum components and mixing amplitudes of "quenched" quark model states due to hadron loops, as perturbation series in the valence-continuum coupling Hamiltonian. We prove three general theorems regarding the effects of hadron loops, which show that given certain constraints on the external "bare" quark model states, the valence-continuum coupling, and the hadrons summed in the loops, the following results hold: (1) The loop mass shifts are identical for all states within a given N,L multiplet. (2) These states have the same total open-flavor decay widths. (3) Loop-induced valence configuration mixing vanishes provided that $Ł_i \neq Ł_f$ or $§_i \neq §_f$. The charmonium system is used as a numerical case study, with the $^3¶_0$ decay model providing the valence-continuum coupling. We evaluate the mass shifts and continuum mixing numerically for all 1S, 1P and 2S charmonium valence states due to loops of D, D$^*$, D$_s$ and D$_s^*$ meson pairs. We find that the mass shifts are quite large, but are numerically similar for all the low-lying charmonium states, as suggested by the first theorem. Thus, loop mass shifts may have been "hidden" in the valence quark model by a change of parameters. The two-meson continuum components of the physical charmonium states are also found to be large, creating challenges for the interpretation of the constituent quark model.

hep-ph↗

arXiv2008

Physics at BES-III

This physics book provides detailed discussions on important topics in $τ$-charm physics that will be explored during the next few years at \bes3 . Both theoretical and experimental issues are covered, including extensive reviews of recent theoretical developments and experimental techniques. Among the subjects covered are: innovations in Partial Wave Analysis (PWA), theoretical and experimental techniques for Dalitz-plot analyses, analysis tools to extract absolute branching fractions and measurements of decay constants, form factors, and CP-violation and \DzDzb-oscillation parameters. Programs of QCD studies and near-threshold tau-lepton physics measurements are also discussed.

hep-ex↗

arXiv2008

Spin-lozenge thermodynamics and magnetic excitations in Na$_3$RuO$_4$

We report inelastic and elastic neutron scattering, magnetic susceptibility, and heat capacity measurements of polycrystalline sodium ruthenate (Na$_3$RuO$_4$). Previous work suggests this material consists of isolated tetramers of $S=3/2$ Ru$^{5+}$ ions in a so-called "lozenge" configuration. Using a Heisenberg antiferromagnet Hamiltonian, we analytically determine the energy eigenstates for general spin $S$. From this model, the neutron scattering cross-sections for excitations associated with spin-3/2 spin-tetramer configurations is determined. Comparison of magnetic susceptibility and inelastic neutron scattering results shows that the proposed "lozenge" model is not distinctly supported, but provides evidence that the system may be better described as a pair of non-interacting inequivalent dimers, \textit{i.e} double dimers. However, the existence of long-range magnetic order below $T_c \approx 28$ K immediately questions such a description. Although no evidence of the lozenge model is observed, future studies on single crystals may further clarify the appropriate magnetic Hamiltonian.

cond-mat.mtrl-sci↗

arXiv2008

Inelastic neutron scattering studies of Crystal Field Levels in PrOs$_4$As$_{12}$

We use neutron scattering to study the Pr$^{3+}$ crystalline electric field (CEF) excitations in the filled skutterudite PrOs$_4$As$_{12}$. By comparing the observed levels and their strengths under neutron excitation with the theoretical spectrum and neutron excitation intensities, we identify the Pr$^{3+}$ CEF levels, and show that the ground state is a magnetic $Γ_4^{(2)}$ triplet, and the excited states $Γ_1$, $Γ_4^{(1)}$ and $Γ_{23}$ are at 0.4, 13 and 23 meV, respectively. A comparison of the observed CEF levels in PrOs$_4$As$_{12}$ with the heavy fermion superconductor PrOs$_4$Sb$_{12}$ reveals the microscopic origin of the differences in the ground states of these two filled skutterudites.

cond-mat.str-el↗

arXiv2008

Evidence for a J/psi-ppbar Pauli Strong Coupling ?

The couplings of charmonia and charmonium hybrids (generically Psi) to ppbar are of great interest in view of future plans to study these states using an antiproton storage ring at GSI. These low to moderate energy Psi-ppbar couplings are not well understood theoretically, and currently must be determined from experiment. In this letter we note that the two independent Dirac (gamma_mu) and Pauli (sigma_munu) ppbar couplings of the J/psi and psi' can be constrained by the angular distribution of e+e- -> (J/psi, psi') -> ppbar on resonance. A comparison of our theoretical results to recent unpolarized data allows estimates of the ppbar couplings; in the better determined J/psi case the data is inconsistent with a pure Dirac (gamma_mu) coupling, and can be explained by the presence of a sigma_munu term. This Pauli coupling may significantly affect the cross section of the PANDA process p pbar -> pi0 J/psi near threshold. There is a phase ambiguity that makes it impossible to uniquely determine the magnitudes and relative phase of the Dirac and Pauli couplings from the unpolarized angular distributions alone; we show in detail how this can be resolved through a study of the polarized reactions.

hep-ph↗

arXiv2007

Magnetism in the high-Tc analogue Cs2AgF4 studied with muon-spin relaxation

We present the results of a muon-spin relaxation study of the high-Tc analogue material Cs2AgF4. We find unambiguous evidence for magnetic order, intrinsic to the material, below T_C=13.95(3) K. The ratio of inter- to intraplane coupling is estimated to be |J'/J|=1.9 x 10^-2, while fits of the temperature dependence of the order parameter reveal a critical exponent beta=0.292(3), implying an intermediate character between pure two- and three- dimensional magnetism in the critical regime. Above T_C we observe a signal characteristic of dipolar interactions due to linear F-mu-F bonds, allowing the muon stopping sites in this compound to be characterized.

cond-mat.str-el↗

arXiv2007

Associated Charmonium Production in p-pbar Annihilation

In this paper we summarize our recent results for low energy associated charmonium production cross sections, using 1) crossing symmetry, and 2) an explicit hadronic model. These predictions are of relevance to the planned charmonium and charmonium hybrid production experiment PANDA at GSI.

hep-ph↗

arXiv2007

Charmonium-Nucleon Dissociation Cross Sections in the Quark Model

Charmonium dissociation cross sections due to flavor-exchange charmonium-baryon scattering are computed in the constituent quark model. We present results for inelastic $J/ψN$ and $η_c N$ scattering amplitudes and cross sections into 46 final channels, including final states composed of various combinations of $D$, $D^*$, $Σ_c$, and $Λ_c$. These results are relevant to experimental searches for the deconfined phase of quark matter, and may be useful in identifying the contribution of initial $c\bar c$ production to the open-charm final states observed at RHIC through the characteristic flavor ratios of certain channels. These results are also of interest to possible charmonium-nucleon bound states.

nucl-th↗

arXiv2006

Associated Charmonium Production in Low Energy p-pbar Annihilation

The QCD mechanisms underlying the exclusive strong decays and hadronic production amplitudes of charmonium remain poorly understood, despite decades of study and an increasingly detaled body of experimental information. One set of hadronic channels of special interest are those that include baryon-antibaryon states. These are being investigated experimentally at BES and CLEO-c in terms of their baryon resonance content, and are also of interest for the future PANDA experiment, in which charmonium and charmonium hybrids will be produced in p-pbar annihilation in association with light mesons. In this paper we develop a simple initial-state light meson emission model of the near-threshold associated charmonium production processes p pbar -> pi0 ccbar, and evaluate the differential and total cross sections for these reactions in this model. (Here we consider the ccbar states eta_c, J/psi, psi', chi_0 and chi_1.) The predicted near-threshold cross section for p pbar -> pi0 J/psi is found to be numerically similar to two previous theoretical estimates, and is roughly comparable to the (sparse) existing data for this process. The theoretical charmonium angular distributions predicted by this model are far from isotropic, which may be of interest for PANDA detector design studies.

hep-ph↗