Lambda Gamma Research Articles

Rare baryon decaysΛb→Λℓ+ℓ−(ℓ=e,μ,τ) andΛb→Λγ: Differential and total rates, lepton- and hadron-side forward-backward asymmetries

Using the covariant constituent quark model previously developed by us we calculate the differential rate and the forward-backward asymmetries on the lepton and hadron side for the rare baryon decays Lambda_b -> Lambda l+ l- (l=e, mu, tau) and Lambda_b -> Lambda gamma. We use helicity methods to write down a three-fold joint angular decay distribution for the cascade decay Lambda_b -> Lambda (-> p pi-) + J_eff (-> l+ l-). Through appropriate angular integrations we obtain expressions for the rates, the lepton-side forward-backward (FB) asymmetry and the polarization of the daughter baryon Lambda leading to a hadron-side forward-backward asymmetry. We present numerical results on these observables using the covariant quark model and compare our results to the results of other calculations that have appeared in the literature.

Branching ratio of the electromagnetic decay of theΣ+(1385)

The CLAS detector was used to obtain the first ever measurement of the electromagnetic decay of the ${\ensuremath{\Sigma}}^{*+}(1385)$ from the reaction $\ensuremath{\gamma}p\ensuremath{\rightarrow}{K}^{0}{\ensuremath{\Sigma}}^{*+}(1385)$. A real photon beam with a maximum energy of 3.8 GeV was incident on a liquid-hydrogen target, resulting in the photoproduction of the kaon and ${\ensuremath{\Sigma}}^{*}$ hyperon. Kinematic fitting was used to separate the reaction channel from the background processes. The fitting algorithm exploited a new method to kinematically fit neutrons in the CLAS detector, leading to the measured decay widths ratio ${\ensuremath{\Sigma}}^{+}(1385)\ensuremath{\rightarrow}{\ensuremath{\Sigma}}^{+}\ensuremath{\gamma}/{\ensuremath{\Sigma}}^{+}(1385)\ensuremath{\rightarrow}{\ensuremath{\Sigma}}^{+}{\ensuremath{\pi}}^{0}=11.95\ifmmode\pm\else\textpm\fi{}2.21(\mathrm{stat}{)}_{\ensuremath{-}1.21}^{+0.53}(\mathrm{sys})%$ and a deduced partial width of $250.0\ifmmode\pm\else\textpm\fi{}56.9(\mathrm{stat}{)}_{\ensuremath{-}41.2}^{+34.3}(\mathrm{sys})\text{ }\text{ }\mathrm{keV}$. A U-spin symmetry test using the SU(3) flavor-multiplet representation yields predictions for the ${\ensuremath{\Sigma}}^{*+}(1385)\ensuremath{\rightarrow}{\ensuremath{\Sigma}}^{+}\ensuremath{\gamma}$ and ${\ensuremath{\Sigma}}^{*0}(1385)\ensuremath{\rightarrow}\ensuremath{\Lambda}\ensuremath{\gamma}$ partial widths that agree with the experimental measurements.

Heavy-to-light baryonic form factors at large recoil

We analyze heavy-to-light baryonic form factors at large recoil and derive the scaling behavior of these form factors in the heavy quark limit. It is shown that only one universal form factor is needed to parameterize Lambda_b to p and Lambda_b to Lambda matrix elements in the large recoil limit of light baryons, while hadronic matrix elements of Lambda_b to Sigma transition vanish in the large energy limit of Sigma baryon due to the space-time parity symmetry. The scaling law of the soft form factor eta(P^{\prime} \cdot v), P^{\prime} and v being the momentum of nucleon and the velocity of Lambda_b baryon, responsible for Lambda_b to p transitions is also derived using the nucleon distribution amplitudes in leading conformal spin. In particular, we verify that this scaling behavior is in full agreement with that from light-cone sum rule approach in the heavy-quark limit. With these form factors, we further investigate the Lambda baryon polarization asymmetry alpha in Lambda_b to Lambda gamma and the forward-backward asymmetry A_{FB} in Lambda_b to Lambda l^{+} l^{-}. Both two observables (alpha and A_{FB}) are independent of hadronic form factors in leading power of 1/m_b and in leading order of alpha_s. We also extend the analysis of hadronic matrix elements for Omega_b to Omega transitions to rare Omega_b to Omega gamma and Omega_b to Omega l^{+} l^{-} decays and find that radiative Omega_b to Omega gamma decay is probably the most promising FCNC b to s radiative baryonic decay channel. In addition, it is interesting to notice that the zero-point of forward-backward asymmetry of Omega_b to Omega l^{+} l^{-} is the same as the one for Lambda_b to Lambda l^{+} l^{-} to leading order accuracy provided that the form factors \bar{\zeta}_i (i=3, 4, 5) are numerically as small as indicated from the quark model.

Scaling and the Smoluchowski equations

The Smoluchowski equations, which describe coalescence growth, take into account combination reactions between a j-mer and a k-mer to form a (j+k)-mer, but not breakup of larger clusters to smaller ones. All combination reactions are assumed to be second order, with rate constants K(jk). The K(jk) are said to scale if K(lambda j,gamma k) = lambda(mu)gamma(nu)K(jk) for j < or = k. It can then be shown that, for large k, the number density or population of k-mers is given by Ak(a)e(-bk), where A is a normalization constant (a function of a, b, and time), a = -(mu+nu), and b(mu+nu-1) depends linearly on time. We prove this in a simple, transparent manner. We also discuss the origin of odd-even population oscillations for small k. A common scaling arises from the ballistic model, which assumes that the velocity of a k-mer is proportional to 1/square root of m(k) (Maxwell distribution), i.e., thermal equilibrium. This does not hold for the nascent distribution of clusters produced from monomers by reactive collisions. By direct calculation, invoking conservation of momentum in collisions, we show that, for this distribution, velocities are proportional to m(k)(-0.577). This leads to mu+nu = 0.090, intermediate between the ballistic (0.167) and diffusive (0.000) results. These results are discussed in light of the existence of systems in the experimental literature which apparently correspond to very negative values of mu+nu.

Erratum: Radiative decays of theΣ0(1385)andΛ(1520)hyperons [Phys. Rev. C71, 054609 (2005)

The electromagnetic decays of the Sig0(1385) and Lambda(1520) hyperons were studied in photon-induced reactions gamma p -> K+ Lambda(1116)gamma in the CLAS detector at the Thomas Jefferson National Accelerator Facility. We report the first observation of the radiative decay of the Sig0(1385) and a measurement of the Lambda(1520) radiative decay width. For the Sig0(1385) -> Lambda(1116)gamma transition, we measured a partial width of 479+/-120(stat)+81-100(sys) keV, larger than all of the existing model predictions. For the Lambda(1520) -> Lambda(1116)gamma transition, we obtained a partial width of 167+/-43(stat)+26-12(sys) keV.

Radiative decays of theΣ0(1385)andΛ(1520)hyperons

The electromagnetic decays of the Sig0(1385) and Lambda(1520) hyperons were studied in photon-induced reactions gamma p -> K+ Lambda(1116)gamma in the CLAS detector at the Thomas Jefferson National Accelerator Facility. We report the first observation of the radiative decay of the Sig0(1385) and a measurement of the Lambda(1520) radiative decay width. For the Sig0(1385) -> Lambda(1116)gamma transition, we measured a partial width of 479+/-120(stat)+81-100(sys) keV, larger than all of the existing model predictions. For the Lambda(1520) -> Lambda(1116)gamma transition, we obtained a partial width of 167+/-43(stat)+26-12(sys) keV.

Hyperon radiative decays in the1/Ncexpansion

Using a recent calculation of transition magnetic moments in the 1/N_c expansion and a calculation showing the suppression of E2/M1 by powers of N_c, we compute the widths for the radiative decays Sigma^* --> Sigma gamma, Sigma^* --> Lambda gamma, and Xi^* --> Xi gamma.

Towards Covariant Quantization of the Supermembrane

By replacing ten-dimensional pure spinors with eleven-dimensional pure spinors, the formalism recently developed for covariantly quantizing the d=10 superparticle and superstring is extended to the d=11 superparticle and supermembrane. In this formalism, kappa symmetry is replaced by a BRST-like invariance using the nilpotent operator Q=int (lambda^alpha d_alpha) where d_alpha is the worldvolume variable corresponding to the d=11 spacetime supersymmetric derivative and lambda^alpha is an SO(10,1) pure spinor variable satisfying (lambda Gamma^c lambda)=0 for c=1 to 11. Super-Poincare covariant unintegrated and integrated supermembrane vertex operators are explicitly constructed which are in the cohomology of Q. After double-dimensional reduction of the eleventh dimension, these vertex operators are related to Type IIA superstring vertex operators where Q=Q_L+Q_R is the sum of the left and right-moving Type IIA BRST operators and the eleventh component of the pure spinor constraint, (lambda Gamma^{11} lambda)=0, replaces the (b_L^0 - b_R^0) constraint of the closed superstring. A conjecture is made for the computation of M-theory scattering amplitudes using these supermembrane vertex operators.

Observations and Parameterizations of Particle Size Distributions in Deep Tropical Cirrus and Stratiform Precipitating Clouds: Results from In Situ Observations in TRMM Field Campaigns

In this study, we report on the evolution of particle size distributions (PSDs) and habits as measured during slow, Lagrangian-type spiral descents through deep subtropical and tropical cloud layers in Florida, Brazil, and Kwajalein, Marshall Islands, most of which were precipitating. The objective of the flight patterns was to learn more about how the PSDs evolved in the vertical and to obtain information of the vertical structure of microphysical properties. New instrumentation yielding better information on the concentrations of particles in the size (D) range between 0.2 and 2 cm, as well as improved particle imagery, produced more comprehensive observations for tropical stratiform precipitation regions and anvils than have been available previously. Collocated radar observations provided additional information on the vertical structure of the cloud layers sampled. Most of the spirals began at cloud top, with temperatures (T) as low as -50 C, and ended at cloud base or below the melting layer (ML). The PSDs broadened from cloud top towards cloud base, with the largest particles increasing in size from several millimeters at cloud top to one centimeter or larger towards cloud base. Some continued growth was noted in the upper part of the ML. Concentrations of particles less than 1 mm in size decreased with decreasing height. The result was a consistent change in the PSDs in the vertical. Similarly, systematic changes in the size dependence of the particle cross-sectional area was noted with decreasing height. Aggregation-as ascertained from both the changes in the PSDs and evolution of particle habits as observed in high detail with the cloud particle imager (CPI) probe-was responsible for these trends. The PSDs were generally well-represented by gamma distributions of the form N = N0 gamma D microns e- lambda gamma D that were fitted to the PSDs over 1-km horizontal intervals throughout the spirals. The intercept (N0 gamma), slope (lambda gamma), and dispersion (microns) values were derived for each PSD. Exponential curves (N = N0e- lambdaD; micron = 0) were also fitted to the distributions. The lambda gamma values for given spirals varied systematically with temperature as did the values of lambda (exponential), and the data generally conformed to values found in previous studies involving exponential fits to size distributions in mid-latitude frontal and cirrus layers. Considerable variability often noted in the PSD properties during the loops of individual spirals was manifested primarily in large changes in N0 gamma and N0, but micron, lambda gamma and lambda remained fairly stable. Temperature is not found to be the sole factor controlling lambda gamma or lambda but is a primary one. Direct relationships were found between lambda gamma and N0 gamma or lambda gamma and micron for the gamma distributions and lambda and N0 for the exponential. The latter relationship was not found as distinctly in earlier studies; observed PSDs in this study had better fidelity with less scatter. The micron values changed monotonically with T over the range of temperatures and were directly related to N0 gamma or lambda gamma, thereby reducing the number of variables in the PSD functional equation to two. In the upper part of the ML, N0 and lambda continued to decrease, and in the lower part these values began to increase as the largest particles melted. We developed general expressions relating various bulk microphysical, radar, and radiative transfer-related variables to N0 gamma and lambda gamma, useful for both tropical and mid-latitude clouds. These relationships facilitate the specification of a number of bulk properties in cloud and climate models. The results presented in this paper apply best to temperatures between 0 and -40 C, for which the measured radar reflectivities fall in the range of 0 to 25 dBZe.

Some new neural network architectures with improved learning schemes

Here, we present two new neuron model architectures and one modified form of existing standard feedforward architecture (MSTD). Both the new models use self-scaling scaled conjugate gradient algorithm (SSCGA) and lambda–gamma (L–G) algorithm and entail the properties of basic as well as higher order neurons (i.e., multiplication and the aggregation functions). Of these two, compensatory neural network architecture (CNNA) requires relatively smaller number of inter-neuronal connections, cuts down on the computational budget by almost 50% and speeds up convergence, besides, gives better training and prediction accuracy. The second model sigma–pi–sigma (SPS) ensures faster convergence, better training and prediction accuracy. The third model (MSTD) performs much better than the standard feedforward architecture (STD). The effect of normalizing the outputs for training also studied here shows virtually no improvement, at low iteration level, say ∼500, with increasing range of scaling. Increasing the number of neurons beyond a point also shows to have little effect in the case of higher order neuron.The numerous simulation runs for the problem of satellite orbit determination and the complex XOR problems establishes the robustness of the proposed neuron models architectures.

Weak Radiative Decay b -&gt; and Quark-Confined Effects in the Covariant Oscillator Quark Model

Motivated by the observation of the decay B to K* gamma by the CLEO collaboration, we have systematically analyzed the weak radiative decay Lambda_b to Lambda gamma, evaluating the confined effects of quarks in the covariant oscillator quark model. This decay process receives both short distance (electromagnetic penguins at the one loop level) the long distance contributions in the quark level. The long distance contributions are analyzed using the vector meson dominance (VMD) method. The estimated branching ratio is found to be 0.23 times 10^-5.

A count probability cookbok: Spurious effects and the scaling model

We study the errors brought by finite volume effects and dilution effects on the practical determination of the count probability distribution function P(sub N)(n,l), which is the probability of having N objects in a cell of volume l cubed for a set of average number density n. Dilution effects are particularly revelant to the so-called sparse sampling strategy. This work is mainly done in the framework of the Bailan & Schaeffer scaling model, which assumes that the Q-body correlation functions obey the scaling relation Xi(sub Q)(lambda r(sub l),....lambda r(sub Q) = lambda(exp -(Q-1)gamma) Xi(sub Q)(r(sub 1),....r(sub Q)). We use three synthetic samples as references to perform our analysis: a fractal generated by a Rayleigh-Levy random walk with approximately 3 x 10(exp 4) objects, a sample dominated by a spherical power-law cluster with approximately 3 x 10(exp 4) objects and a cold dark matter (CDM) universe involving approximately 3 x 10(exp 5) matter particles.

Radiative decays of theK−p atom

We use an extension of the cloudy bag model to SU(3) x SU(3) to calculate the radiative decay of the K/sup -/p atom. Our result differs from earlier work in a fundamental way because of the inclusion of coupling to the open ..sigma pi.. channel. The branching ratio into ..sigma../sup 0/..gamma.. is predicted to be of order 10--20 % bigger than that into ..lambda gamma.., which should make it accessible to a current experiment.

Radiative capture of stopped kaons: K-p--> Lambda gamma and K-p--> Sigma 0 gamma.

The radiative-capture reactions K/sup -/p..--> lambda gamma.. and K/sup -/p..--> sigma../sup 0/..gamma.. are investigated within a pole-model calculation. Both pseudoscalar and pseudovector coupling schemes are used and both give branching ratios comparable to current experimental bounds. The sensitivity to the ..lambda..(1405) is investigated and improved constraints are determined for its contribution. Our methods and results are compared with those of other recent calculations of these reactions.

Re-analysis of dysprosium magnetostriction

A re-analysis for earlier magnetostriction measurements on dysprosium is presented. Domain effects have been corrected for using the phase theory. The re-analysed results for the temperature dependence of the magnetostriction constants and of the magnetocrystalline anisotropy energy are in reasonable agreement with theoretical predictions and the results of other experimental workers. For T to 0K it is found that lambda gamma ,2=(10.6+or-0.2)*10-3 and K66=(-1.4+or-0.2)*106 Jm-3.

The investigation of cryoglobulins

In recent years the discovery of cryoglobulins has become increasingly frequent in a wide variety of disease states including multiple myeloma, acute and chronic infections, and immune complex diseases. However, proper collection of specimens is essential for their detection. In our laboratory, 10 ml clotted blood and 10 ml oxalated blood are taken and kept at 37 C for at least 1 h before centrifugation and separation. This procedure is followed by incubation at 4 C for a minimum period of 3 days. Depending on the circumstances, identification and quantitation of the cryoprecipitate are carried out in the following order: (a) total protein and albumin estimation; (b) electrophoresis and quantitation of globulin fractions; (c) specific quantitations by radial immunodiffusion; (d) Immunoelectrophoresis; (e) serological investigations, particularly the estimation of rheumatoid factor. For an initial patient sample of 108, there were 11 occurrences of cryofibrinogen and 5 of cryoglobulins. Two cases of cryoglobulin of special interest have been found: (1) monoclonal cryoglobulin of lambda gamma type with massive crystalglobulinaemia and peripheral gangrene; and (2) mixed monoclonal/polyclonal cryoglobulin with a kappa mu paraprotein having strong rheumatoid factor activity which was undetected in serum unless cryoglobulin collection was done.