Dalitz Plot Analysis of B- --> D+ pi- pi-

We present a Dalitz plot analysis of B- --> D+ pi- pi- decays, based on a sample of about 383 million Y(4S) --> BBbar decays collected by the BaBar detector at the PEP-II asymmetric-energy B Factory at SLAC. The analysis has been published previously in PRD. We measure the inclusive branching fraction of the three-body decay to be BR(B- --> D+ pi- pi-) = (1.08 \pm 0.03\stat \pm 0.05\syst) x 10^{-3}$. We observe the established D^{*0}_2 and confirm the existence of D^{*0}_0 in their decays to D+ pi-, where the D^{*0}_2 and D^{*0}_0 are the 2+ and 0+ c-ubar P-wave states, respectively. We measure the masses and widths of D^{*0}_2 and D^{*0}_0 to be: m_{D^{*}_2} = (2460.4 \pm 1.2 \pm 1.2 \pm 1.9) MeV/c^2, Gamma_{D^*_2} = (41.8 \pm 2.5 \pm 2.1 \pm 2.0) MeV, m_{D^{*}_0} = (2297 \pm 8 \pm 5 \pm 19) MeV/c^2, Gamma_{D^*_0} = (273 \pm 12 \pm 17 \pm 45) MeV. The stated errors reflect the statistical and systematic uncertainties, and the uncertainty related to the assumed composition of signal events and the theoretical model.Comment: 5 pages, 7 PDF figures, uses AIP style, conference proceedings of HADRON09, to be published in AIP Conference Proceedings, arXiv:0901.129

Quasiparticles governing the zero-temperature dynamics of the 1D spin-1/2 Heisenberg antiferromagnet in a magnetic field

The T=0 dynamical properties of the one-dimensional (1D) $s=1/2$ Heisenberg antiferromagnet in a uniform magnetic field are studied via Bethe ansatz for cyclic chains of $N$ sites. The ground state at magnetization $0<M_z<N/2$, which can be interpreted as a state with $2M_z$ spinons or as a state of $M_z$ magnons, is reconfigured here as the vacuum for a different species of quasiparticles, the {\em psinons} and {\em antipsinons}. We investigate three kinds of quantum fluctuations, namely the spin fluctuations parallel and perpendicular to the direction of the applied magnetic field and the dimer fluctuations. The dynamically dominant excitation spectra are found to be sets of collective excitations composed of two quasiparticles excited from the psinon vacuum in different configurations. The Bethe ansatz provides a framework for (i) the characterization of the new quasiparticles in relation to the more familiar spinons and magnons, (ii) the calculation of spectral boundaries and densities of states for each continuum, (iii) the calculation of transition rates between the ground state and the dynamically dominant collective excitations, (iv) the prediction of lineshapes for dynamic structure factors relevant for experiments performed on a variety of quasi-1D antiferromagnetic compounds, including KCuF$_3$, Cu(C$_4$H$_4$N$_2)(NO_3)_2$, and CuGeO$_3$.Comment: 13 pages, 12 figure

A numerical study of the formation of magnetisation plateaus in quasi one-dimensional spin-1/2 Heisenberg models

We study the magnetisation process of the one dimensional spin-1/2 antiferromagnetic Heisenberg model with modulated couplings over j=1,2,3 sites. It turns out that the evolution of magnetisation plateaus depends on j and on the wave number q of the modulation according to the rule of Oshikawa, et al. A mapping of two- and three-leg zig-zag ladders on one dimensional systems with modulated couplings yields predictions for the occurence of magnetization plateaus. The latter are tested by numerical computations with the DMRG algorithm.Comment: 7 pages, 10 figures, accepted for publication in Euro. Phys. J.

Spinon excitations in the XX chain: spectra, transition rates, observability

The exact one-to-one mapping between (spinless) Jordan-Wigner lattice fermions and (spin-1/2) spinons is established for all eigenstates of the one-dimensional s = 1=2 XX model on a lattice with an even or odd number N of lattice sites and periodic boundary conditions. Exact product formulas for the transition rates derived via Bethe ansatz are used to calculate asymptotic expressions of the 2-spinon and 4-spinon parts (for large even N) as well as of the 1-spinon and 3-spinon parts (for large odd N) of the dynamic spin structure factors. The observability of these spectral contributions is assessed for finite and infinite N.Comment: 19 pages, 10 figure

Lattice two-body problem with arbitrary finite range interactions

We study the exact solution of the two-body problem on a tight-binding one-dimensional lattice, with pairwise interaction potentials which have an arbitrary but finite range. We show how to obtain the full spectrum, the bound and scattering states and the "low-energy" solutions by very efficient and easy-to-implement numerical means. All bound states are proven to be characterized by roots of a polynomial whose degree depends linearly on the range of the potential, and we discuss the connections between the number of bound states and the scattering lengths. "Low-energy" resonances can be located with great precission with the methods we introduce. Further generalizations to include more exotic interactions are also discussed.Comment: 6 pages, 3 figure

Spectrum and transition rates of the XX chain analyzed via Bethe ansatz

As part of a study that investigates the dynamics of the s=1/2 XXZ model in the planar regime |Delta|<1, we discuss the singular nature of the Bethe ansatz equations for the case Delta=0 (XX model). We identify the general structure of the Bethe ansatz solutions for the entire XX spectrum, which include states with real and complex magnon momenta. We discuss the relation between the spinon or magnon quasiparticles (Bethe ansatz) and the lattice fermions (Jordan-Wigner representation). We present determinantal expressions for transition rates of spin fluctuation operators between Bethe wave functions and reduce them to product expressions. We apply the new formulas to two-spinon transition rates for chains with up to N=4096 sites.Comment: 11 pages, 4 figure