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

Search for CP violation in the Bs/Bs-bar system

We present studies from the LHCb experiment leading to the measurement of the weak phase {\phi}s. At first, flavor tagging is established by measuring the B0s oscillation frequency \Deltams. Then, flavor tagging is used to perform a measurement of the well known CKM angle sin 2{\beta} in B0 \rightarrow J/{\psi} KS0, before we constrain {\phi}s through an amplitude analysis of B0s \rightarrow J/{\psi} {\phi} decays. These studies use about 35 inverse pb of data taken in 2010. In addition, we present the measurement of B(B+\rightarrowJ/{\psi}{\pi}+)/B(B+\rightarrowJ/{\psi}K+) and the first observation of B0s \rightarrowJ/{\psi}f2'(1525).Comment: 3 pages, 6 figures, The 19th Particles & Nuclei International Conference (PANIC11), MIT, Boston, July 24th-29th, 201

Introduction to the Bethe ansatz I

The Bethe ansatz for the one-dimensional s=1/2 Heisenberg ferromagnet is introduced at an elementary level. The presentation follows Bethe's original work very closely. A detailed description and a complete classification of all two-magnon scattering states and two-magnon bound states are given for finite and infinite chains. The paper is designed as a tutorial for beginning graduate students. It includes 10 problems for further study.Comment: 8 pages, 4 figure

Computational probes of collective excitations in low-dimensional magnetism

The investigation of the dynamics of quantum many-body systems is a concerted effort involving computational studies of mathematical models and experimental studies of material samples. Some commonalities of the two tracks of investigation are discussed in the context of the quantum spin dynamics of low-dimensional magnetic systems, in particular spin chains. The study of quantum fluctuations in such systems at equilibrium amounts to exploring the spectrum of collective excitations and the rate at which they are excited from the ground state by dynamical variables of interest. The exact results obtained via Bethe ansatz or algebraic analysis (quantum groups) for a select class of completely integrable models can be used as benchmarks for numerical studies of nonintegrable models, for which computational access to the spectrum of collective excitations is limited.Comment: 22 pages. Talk given at the 7th Summer School on Neutron Scattering, Zuoz Switzerland, August 199

Using a new multivariate technique in high energy physics

This project focuses on testing and developing algorithms for multivariate data analysis, that separate signal processes from abundant backgrounds and on helping with organizing and filtering colossal amounts of raw data, gathered from the Large Hadron Collider beauty (LHCb) experiment, to find extremely rare events of interest. Moreover, working on this project also meant trying to apply new, faster method to take the place of systems that are now used at CERN to pare down the relevant data, but require relatively extensive processing and analysis to determine relevance and usefulness

Quasiparticles in the XXZ model

The coordinate Bethe ansatz solutions of the XXZ model for a one-dimensional spin-1/2 chain are analyzed with focus on the statistical properties of the constituent quasiparticles. Emphasis is given to the special cases known as XX, XXX, and Ising models, where considerable simplifications occur. The XXZ spectrum can be generated from separate pseudovacua as configurations of sets of quasiparticles with different exclusion statistics. These sets are complementary in the sense that the pseudovacuum of one set contains the maximum number of particles from the other set. The Bethe ansatz string solutions of the XXX model evolve differently in the planar and axial regimes. In the Ising limit they become ferromagnetic domains with integer-valued exclusion statistics. In the XX limit they brake apart into hard-core bosons with (effectively) fermionic statistics. Two sets of quasiparticles with spin 1/2 and fractional statistics are distinguished, where one set (spinons) generates the XXZ spectrum from the unique, critical ground state realized in the planar regime, and the other set (solitons) generates the same spectrum from the twofold, antiferromagnetically ordered ground state realized in the axial regime. In the Ising limit, the solitons become antiferromagnetic domain walls.Comment: 6 figure

Introduction to the Bethe Ansatz III

Having introduced the magnon in part I and the spinon in part II as the relevant quasi-particles for the interpretation of the spectrum of low-lying excitations in the one-dimensional (1D) s=1/2 Heisenberg ferromagnet and antiferromagnet, respectively, we now study the low-lying excitations of the Heisenberg antiferromagnet in a magnetic field and interpret these collective states as composites of quasi-particles from a different species. We employ the Bethe ansatz to calculate matrix elements and show how the results of such a calculation can be used to predict lineshapes for neutron scattering experiments on quasi-1D antiferromagnetic compounds. The paper is designed as a tutorial for beginning graduate students. It includes 11 problems for further study.Comment: 11 page

Transition rates via Bethe ansatz for the spin-1/2 Heisenberg chain

We use the exact determinantal representation derived by Kitanine, Maillet, and Terras for matrix elements of local spin operators between Bethe wave functions of the one-dimensional s=1/2 Heisenberg model to calculate and numerically evaluate transition rates pertaining to dynamic spin structure factors. For real solutions z_1,...,z_r of the Bethe ansatz equations, the size of the determinants is of order r x r. We present applications to the zero-temperature spin fluctuations parallel and perpendicular to an external magnetic field.Comment: 4 pages, 4 figures and LaTeX-svjour clas