The meson BcB_c annihilation to leptons and inclusive light hadrons

The annihilation of the $B_c$ meson to leptons and inclusive light hadrons is analyzed in the framework of nonrelativistic QCD (NRQCD) factorization. We find that the decay mode, which escapes from the helicity suppression, contributes a sizable fraction width. According to the analysis, the branching ratio due to the contribution from the color-singlet component of the meson $B_c$ can be of order (10^{-2}). We also estimate the contributions from the color-octet components. With the velocity scaling rule of NRQCD, we find that the color-octet contributions are sizable too, especially, in certain phase space of the annihilation they are greater than (or comparative to) the color-singlet component. A few observables relevant to the spectrum of charged lepton are suggested, that may be used as measurements on the color-octet and color-singlet components in the future $B_c$ experiments. A typical long distance contribution in the annihilation is estimated too.Comment: 26 pages, 5 figures (6 eps-files), submitted to Phys. Rev.

Decays of the Meson BcB_c to a PP-Wave Charmonium State χc\chi_c or hch_c

The semileptonic decays, $B_{c}{\longrightarrow}{\chi_c}(h_c)+{\ell}+{{\nu}}_{\ell}$, and the two-body nonleptonic decays, $B_{c}{\longrightarrow}{\chi_c}(h_c)+h$, (here $\chi_c$ and $h_c$ denote $(c\bar c[^3P_J])$ and $(c\bar c[^1P_1])$ respectively, and $h$ indicates a meson) were computed. All of the form factors appearing in the relevant weak-current matrix elements with $B_c$ as its initial state and a $P$-wave charmonium state as its final state for the decays were precisely formulated in terms of two independent overlapping-integrations of the wave-functions of $B_c$ and the $P$-wave charmonium and with proper kinematics factors being `accompanied'. We found that the decays are quite sizable, so they may be accessible in Run-II at Tevatron and in the foreseen future at LHC, particularly, when BTeV and LHCB, the special detectors for B-physics, are borne in mind. In addition, we also pointed out that the decays $B_c\to h_c+...$ may potentially be used as a fresh window to look for the $h_c$ charmonium state, and the cascade decays, $B_c\to \chi_c[^3P_{1,2}]+l+\nu_l$ ($B_c\to \chi_c[^3P_{1,2}]+h$) with one of the radiative decays $\chi_c[^3P_{1,2}] \to J/\psi+\gamma$ being followed accordingly, may affect the observations of $B_c$ meson through the decays $B_{c}\to {J/\psi}+{l}+\nu_{l}$ ($B_c\to J/\psi+h$) substantially.Comment: 24 pages, 3 figures, the replacement for improving the presentation and adding reference

Estimate of the Hadronic Production of the Doubly Charmed Baryon Ξcc\Xi_{cc} under GM-VFN Scheme

Hadronic production of the doubly charmed baryon $\Xi_{cc}$ ($\Xi^{++}_{cc}$ and $\Xi^{+}_{cc}$) is investigated under the general-mass variable-flavor-number (GM-VFN) scheme. The gluon-gluon fusion mechanism and the intrinsic charm mechanisms, i.e. via the sub-processes $g+g\to(cc)[^3S_1]_{\bar 3}+\bar{c}+\bar{c}$, $g+g\to(cc)[^1S_0]_6+\bar{c}+\bar{c}$; $g+c\to (cc)[^3S_1]_{\bar 3}+\bar{c}$, $g+c\to (cc)[^1S_0]_6+\bar{c}$ and $c+c\to (cc)[^3S_1]_{\bar 3}+g$, $c+c\to (cc)[^1S_0]_6+g$, are taken into account in the investigation, where $(cc)[^3S_1]_{\bar 3}$ (in color {\bf $\bar 3$}) and $(cc)[^1S_0]_6$ (in color {\bf 6}) are two possible $S$-wave configurations of the doubly charmed diquark pair $(cc)$ inside the baryon $\Xi_{cc}$. Numerical results for the production at hadornic colliders LHC and TEVATRON show that both the contributions from the doubly charmed diquark pairs $(cc)[^1S_0]_6$ and $(cc)[^3S_1]_{\bar 3}$ are sizable with the assumption that the two NRQCD matrix elements are equal, and the total contributions from the `intrinsic' charm mechanisms are bigger than those of the gluon-gluon fusion mechanism. For the production in the region of small transverse-momentum $p_t$, the intrinsic mechanisms are dominant over the gluon-gluon fusion mechanism and they can raise the theoretical prediction of the $\Xi_{cc}$ by almost one order.Comment: 26 pages, 8 figure

Charge Transport in a Quantum Electromechanical System

We describe a quantum electromechanical system(QEMS) comprising a single quantum dot harmonically bound between two electrodes and facilitating a tunneling current between them. An example of such a system is a fullerene molecule between two metal electrodes [Park et al., Nature, 407, 57 (2000)]. The description is based on a quantum master equation for the density operator of the electronic and vibrational degrees of freedom and thus incorporates the dynamics of both diagonal (population) and off diagonal (coherence) terms. We derive coupled equations of motion for the electron occupation number of the dot and the vibrational degrees of freedom, including damping of the vibration and thermo-mechanical noise. This dynamical description is related to observable features of the system including the stationary current as a function of bias voltage.Comment: To appear in Phys. Rev. B., 13 pages, single colum

Gaussian approximation and single-spin measurement in OSCAR MRFM with spin noise

A promising technique for measuring single electron spins is magnetic resonance force microscopy (MRFM), in which a microcantilever with a permanent magnetic tip is resonantly driven by a single oscillating spin. If the quality factor of the cantilever is high enough, this signal will be amplified over time to the point that it can be detected by optical or other techniques. An important requirement, however, is that this measurement process occur on a time scale short compared to any noise which disturbs the orientation of the measured spin. We describe a model of spin noise for the MRFM system, and show how this noise is transformed to become time-dependent in going to the usual rotating frame. We simplify the description of the cantilever-spin system by approximating the cantilever wavefunction as a Gaussian wavepacket, and show that the resulting approximation closely matches the full quantum behavior. We then examine the problem of detecting the signal for a cantilever with thermal noise and spin with spin noise, deriving a condition for this to be a useful measurement.Comment: 12 pages, 8 figures in EPS format, RevTeX 4.

Nonperturbative Approach to Circuit Quantum Electrodynamics

We outline a rigorous method which can be used to solve the many-body Schroedinger equation for a Coulomb interacting electronic system in an external classical magnetic field as well as a quantized electromagnetic field. Effects of the geometry of the electronic system as well as the polarization of the quantized electromagnetic field are explicitly taken into account. We accomplish this by performing repeated truncations of many-body spaces in order to keep the size of the many particle basis on a manageable level. The electron-electron and electron-photon interactions are treated in a nonperturbative manner using "exact numerical diagonalization". Our results demonstrate that including the diamagnetic term in the photon-electron interaction Hamiltonian drastically improves numerical convergence. Additionally, convergence with respect to the number of photon states in the joint photon-electron Fock space basis is fast. However, the convergence with respect to the number of electronic states is slow and is the main bottleneck in calculations.Comment: Revtex, pdflatex, 8 pages, with 5 included pdf figure

Time-dependent transport of electrons through a photon cavity

We use a non-Markovian master equation to describe the transport of Coulomb interacting electrons through an electromagnetic cavity with one quantized photon mode. The central system is a finite parabolic quantum wire that is coupled weakly to external parabolic quasi-one-dimensional leads at $t=0$. With a stepwise introduction of complexity to the description of the system and a corresponding stepwise truncation of the ensuing many-body spaces we are able to describe the time-dependent transport of Coulomb-interacting electrons through a geometrically complex central system. We take into account the full electromagnetic interaction of electrons and cavity photons without resorting to the rotating wave approximation or reduction of the electron states to two levels. We observe that the number of initial cavity photons and their polarization can have important effects on the transport properties of the system. The quasiparticles formed in the central system have a lifetime limited by the coupling to the leads and radiation processes active on a much longer timescale.Comment: RevTeX (pdf-LaTeX) 11 pages with 12 jpg-figures include

Stochastic Interactions of Two Brownian Hard Spheres in the Presence of Depletants

A quantitative analysis is presented for the stochastic interactions of a pair of Brownian hard spheres in non-adsorbing polymer solutions. The hard spheres are hypothetically trapped by optical tweezers and allowed for random motion near the trapped positions. The investigation focuses on the long-time correlated Brownian motion. The mobility tensor altered by the polymer depletion effect is computed by the boundary integral method, and the corresponding random displacement is determined by the fluctuation-dissipation theorem. From our computations it follows that the presence of depletion layers around the hard spheres has a significant effect on the hydrodynamic interactions and particle dynamics as compared to pure solvent and pure polymer solution (no depletion) cases. The probability distribution functions of random walks of the two interacting hard spheres that are trapped clearly shifts due to the polymer depletion effect. The results show that the reduction of the viscosity in the depletion layers around the spheres and the entropic force due to the overlapping of depletion zones have a significant influence on the correlated Brownian interactions.Comment: 30 pages, 9 figures, 1 appendix, 40 formulas inside the text, 5 formulas in appendi

Wind study of Kaiser Center office building

CER69-70GH-JEC-WZS-13.September 1969.For Metronics Associates, Inc.Includes bibliographical references.Mean and fluctuating wind loading on a 1:192 scale model of Kaiser Center Office Building 403 ft high was studied in a uniform flow. Pressure measurements were carried out for four different wind directions (N, NE, E, and S). The wind loading was influenced strongly by a tall building immediately to the southeast when the wind was from the south, Generally, the mean pressure was higher at the center portion of an upwind face than near its edges. On the leewind surface relatively uniform negative pressure (suction) was obtained. Its absolute value was about one-third of that along an upwind face. On the other hand, the fluctuating pressure was highest near the building base, in the flow separation region and in the wake of the adjacent building in a southly wind. A model of the upstream topography to the northeast was constructed using a 1:600 scale. This model terrain was 24 ft long (2.7 miles of the prototype terrain) with the Kaiser building site near its trailing edge. Mean velocity and turbulence intensity profiles were measured along the terrain

Fast tuning of superconducting microwave cavities

Photons are fundamental excitations of the electromagnetic field and can be captured in cavities. For a given cavity with a certain size, the fundamental mode has a fixed frequency {\it f} which gives the photons a specific "color". The cavity also has a typical lifetime $\tau$, which results in a finite linewidth $\delta${\it f}. If the size of the cavity is changed fast compared to $\tau$, and so that the frequency change $\Delta${\it f} $\gg \delta${\it f}, then it is possible to change the "color" of the captured photons. Here we demonstrate superconducting microwave cavities, with tunable effective lengths. The tuning is obtained by varying a Josephson inductance at one end of the cavity. We show data on four different samples and demonstrate tuning by several hundred linewidths in a time $\Delta t \ll \tau$. Working in the few photon limit, we show that photons stored in the cavity at one frequency will leak out from the cavity with the new frequency after the detuning. The characteristics of the measured devices make them suitable for different applications such as dynamic coupling of qubits and parametric amplification.Comment: 2nd International Workshop on Solid-State Quantum Computing, June 2008, Taipei, Taiwa