Search

Time-resolved photoluminescence (PL) near 540 nm, taken from barium titanate (BaTiO3) ultrafine powders of ∼80, 90, and 110 nm in size, was measured at 11 K. Two-exponential functions were found to fit the decay curves well, and the decay lifetimes were composed of one short, about 10 ns, and one long, about 200 ns, time constants, respectively. Results also indicate that the PL peaks show a small blueshift with decreasing BaTiO3 particle size. The decay process consists of the recombination of self-trapped excitons (long lifetime decay) and of the electrons in the surface states with the holes in the valence band (short lifetime decay). The short lifetime component makes comparable contribution to the decay intensity of PL with the long lifetime one. [ABSTRACT FROM AUTHOR]

A search for the lepton-flavor-violating decays B0s → e± μ± and B0 → e± μ± is performed with a data sample, corresponding to an integrated luminosity of 1.0 fb-1 of pp collisions at √s = 7 TeV, collected by the LHCb experiment. The observed number of B0s → e± μ± and B0 → e± μ± candidates is consistent with background expectations. Upper limits on the branching fractions of both decays are determined to be B(B0s → e± μ±) < 1.1(1.4) x 10-8 and B(B0 → e± μ± ) <2.8(3.7) X 10-9 at 90% (95%) confidence level (C.L.). These limits are a factor of 20 lower than those set by previous experiments. Lower bounds on the Pati-Salam leptoquark masses are also calculated, MLQ(B0s → e± μ±)> 101 TeV/c2 and MLQ(B0s → e± μ±)> 126 TeV/c2 at 95% C.L., and are a factor of 2 higher than the previous bounds. [ABSTRACT FROM AUTHOR]

Abstract: A search for the decays and is performed with about of pp collisions at collected by the LHCb experiment at the Large Hadron Collider at CERN. The observed numbers of events are consistent with the background expectations. The resulting upper limits on the branching ratios are and at 95% confidence level. [Copyright &y& Elsevier]

Abstract: A 900-l liquid xenon (LXe) detector was constructed for the MEG experiment to look for . With proper calibration and monitoring the detector was successfully operated during the first physics data taking for three months in 2008. We evaluated the performance of the LXe detector around the energy of 52.8MeV by using 54.9-MeV photons obtained from decays. [ABSTRACT FROM AUTHOR]

Abstract: Using an improved “analytic K-matrix model”, we reconsider the extraction of the and γγ widths from scatterings data of Crystal Ball and Belle. Our main results are summarized in Tables 3 and 4. The averaged σ “direct width” to γγ is 0.16(3) keV which confirms a previous result of Mennessier et al. (2007, 2008) and which does neither favour a large four-quark/molecule nor a pure components. The “direct width” of the of 0.28(2) keV is much larger than the four-quark expectation but can be compatible with a or a gluonium component. We also found that the rescattering part of each amplitude is relatively large indicating an important contribution of the meson loops in the determinations of the σ and γγ total widths. This is mainly due to the large couplings of the σ and to ππ and/or , which can also be due to a light scalar gluonium with large OZI violating couplings but not necessary to a four-quark or molecule state. Our average results for the total (direct + rescattering) γγ widths: , are comparable with the ones from dispersion relations and PDG values. Using the parameters from QCD spectral sum rules, we complete our analysis by showing that the production rates of unmixed scalar gluonia and agree with the data from , ϕ radiative and semi-leptonic decays. [ABSTRACT FROM AUTHOR]

We update our 2006-2007 results for FCNC processes in the Littlest Higgs model with T-parity (LHT). The removal of the logarithmic UV cutoff dependence in our previous results through a new contribution to the Z0-penguin diagrams identified by Goto et al. and del Aguila et al., while making the deviations from the SM expectations in the quark sector less spectacular, still allows for sizable new physics effects in K → πνν and KL → π0l+l- decays and in the CP-asymmetry Sψφ with the latter unaffected by the new contribution. We extend our analysis by a study of the fine-tuning required to fit the data on εK and by the inclusion of the decay KL → μ+&mu-. A number of correlations can distinguish this model from the custodially protected Randall--Sundrum model analysed recently. We also reconsider lepton flavour violating decays, including now a discussion of fine-tuning. While the li → ljγ decays are unaffected by the removal of the logarithmic cutoff dependence, the branching ratios for decays with three leptons in the final state, like μ → 3e are lowered by almost an order of magnitude. In spite of this, the pattern of lepton flavour violation in the LHT model can still be distinguished from the one in supersymmetric models. [ABSTRACT FROM AUTHOR]

The form factors of the semileptonic Bc → D0lυ transition with l = e; τ are calculated in the framework of the three point QCD sum rules. In this case, the two gluon condensate contributions as the important correction on the non-perturbative part of the correlation function, are taken into account. The heavy quark effective theory limits of the form factors are also computed. The branching fractions of these decays are also evaluated and compared with the predictions of the other non-perturbative approaches. [ABSTRACT FROM AUTHOR]

We present a numerical investigation of the fermionic two-body decays of tau sleptons τ͂1,2 and τ sneutrino in the Minimal Supersymmetric Standard Model with complex parameters. In the analysis we particularly take into account the cosmological bounds imposed by WMAP data. We plot the CP-phase dependences for each fermionic two-body channel of τ͂1,2 and τ sneutrino and speculate about the branching ratios and total (two-body) decay widths. We find that the phase dependences of the decay widths of the third family sleptons are quite significant which can provide viable probes of additional CP sources. We also draw attention to the polarization of the final-state tau in the τ͂1,2 decays. [ABSTRACT FROM AUTHOR]

Abstract: We examine the transverse momentum dependence of the helicity structure functions for massive vector bosons of mass Q in hadron reactions. We demonstrate that large logarithmic terms of the form in the helicity structure functions have the same origin as the logarithmic terms in the angular-integrated cross section and that they can be resummed to all orders in the strong coupling , in the same way as the angular-integrated cross section. As a consequence of current conservation, the resummed part of the helicity structure functions preserves the Lam–Tung relation as a function of to all orders in . [Copyright &y& Elsevier]

The rare t-quark decays t → cl l and t → cṽ j k k induced by scalar-leptoquark doublets are considered within the minimal model involving four-color quark-lepton symmetry and the Higgs mechanism of quark and lepton mass splitting. The partial widths with respect to the decays being considered and the total widths Γ( t → cl +′ l −) = Σj,k Γ( t → cl l ) and Γ( t → cl +′ l −) = Σj,kΓ( t → cṽ j v k ) with respect to, respectively, the charged leptonic and neutrino modes are calculated. It is shown that, at scalar-leptoquark masses higher than the t-quark mass ( m S > m t), the branching ratios for these modes are Br( t → cl +′ l −) ≈ (3.5−0.4) × 10−5 and Br( t → cṽ′ v) ≈ (7.1−0.8) × 10−5 at m s = 180–250 GeV and an appropriate value of the leptoquark-mixing angle (sin β ≈ 0.2) and can increase for m S < m t to Br( t → cl +′ l −) ≈ 0.03−0.002 and Br( t → cl +′ l −) ≈ 0.46−0.05 for the charged mode at m S = 150–170 GeV for sin β ≈ 1 and sin β ≈ 0.2, respectively. In the cases being considered, t-quark decays to pairs of charged leptons can be accessible to detection at LHC. In the last case, these decays could manifest themselves (for example, in dilepton events) at the Tevatron as well. [ABSTRACT FROM AUTHOR]

In this paper, the general structure of leptonic decay constants of vector mesons is evaluated in the framework of the Bethe–Salpeter equation under the Covariant Instantaneous Ansatz (CIA), which is a Lorentz-invariant generalization of Instantaneous Approximation (IA). The numerical values of fV in this CIA framework are on the low side in comparison to recent calculations of these quantities. However, the overall asymptotic behavior of fV is in conformity with QCD predictions. [ABSTRACT FROM AUTHOR]

We measure the mass of the top quark using 162 pb-1 of data collected by the CDF experiment at the Fermilab Tevatron in Run II. The decay chain $t{\bar t} \to bq{\bar q}{\bar b}l\nu$ is studied using a novel technique called the Multivariate Template Method (MTM). Using this technique we obtain a result of $M_{top} = 179.6^{+6.4}_{-6.3}({\rm stat.}) \pm 6.8({\rm syst.})\ {\rm GeV}/c^2$ for the top quark. [ABSTRACT FROM AUTHOR]

We measure the ratio R = B(t→Wb)/B(t→Wq) in top-quark decays at CDF. R is determined from the relative rates of identified b jets in $t{\bar t}$ decays reconstructed both in the lepton-plus-jets and dilepton final states. We obtain R>0.62 at the 95% CL, consistent with Standard Model expectations. [ABSTRACT FROM AUTHOR]

Polarized forward-backward asymmetries in thedecay are calculated using the most general, model independent form of the effective Hamiltonian, including all possible forms of interactions. The dependencies of the asymmetries on new Wilson coefficients are investigated. The detectability of the asymmetries at LHC is discussed. [ABSTRACT FROM AUTHOR]

We study the Lorentz andCPTviolating effects on the branching ratio, theCPTviolating asymmetry and the ratio of the decay width, including only the Lorentz violating effects, to the one obtained in the standard model, for the flavor dependent part of the lepton flavor conserving() decay. The inclusion of the Lorentz andCPTviolating effects in the standard model contribution are too small to be detected, since the corresponding coefficients are highly suppressed at the low energy scale. [ABSTRACT FROM AUTHOR]

Objective: The aim of this study was to develop a MCNP4c2-code and to further refine the small-scale anatomy intestinal dosimetry model based on a EGS4-code developed by Jnsson et al.1,2Method: The small intestine was modeled as a hexagonal tube system and includes cross-dose contribution from activity in nearby intestine loops. The model includes villi (height, 500 m), radiosensitive crypt cells (height, 150 m), and an overlying mucus layer of thicknesses (5200 m). The developed intestinal model used in either of the two Monte Carlo codes make it possible to calculate S-values and subsequent mean absorbed dose to the radiation-sensitive crypt cells in the small intestinal wall by considering contributions from the self-dose and from the cross-dose from nearby intestinal loops. Results are given for monoenergetic electrons and photons and for full decay schemes of 99mTc, 111In, 131I, 67Ga, 90Y, and 211At. Results: Results show that the cross-dose from nearby intestinal loops is significant, and that the fraction of cumulated activity in the intestinal wall contents is important for accurate absorbed-dose estimation. Conclusion: It is evident from our study that previous Medical Internal Radiation Dose (MIRD) and International Conference on Radiological Protection (ICRP) models tend to overestimate the absorbed dose to the wall. Our work on the gastrointestinal tract model includes several noticeable refinements, as compared to the MIRD- and ICRP model, and the "onion shell" geometry can easily be transferred to similar geometrical dosimetry applications. [ABSTRACT FROM AUTHOR]

We derive simple analytical formulae for the renormalization group running of neutrino masses, leptonic mixing angles and CP phases, which allow an easy understanding of the running. Particularly for a small angle θ13 the expressions become very compact, even when non-vanishing CP phases are present. Using these equations we investigate: (i) the influence of Dirac and Majorana phases on the evolution of all parameters, (ii) the implications of running neutrino parameters for leptogenesis, (iii) changes of the mass bounds from WMAP and neutrinoless double β decay experiments, relevant for high-energy mass models, (iv) the size of radiative corrections to θ13 and θ23 and implications for future precision measurements. [Copyright &y& Elsevier]

In this Letter we investigate the subleading twist corrections to the photon energy spectrum in the decay Λb→Xsγ and to the lepton energy spectrum in Λb→Xuℓν¯ℓ. As a first step we rederive the matching coefficients of the subleading twist using a much simpler method. Parametrizing the matrix elements for Λb and using reparametrization invariance, we show that the energy spectra close to the endpoints are given in terms of only a single universal function. [Copyright &y& Elsevier]

The non-factorizable terms in the operator product expansion have been recognized as one of the theoretical obstacles for precision determination of the mixing parameter V[sub ub] from semileptonic B decays. It is pointed out here that the recent CLEO data on the parameters of the heavy quark expansion λ[sub 1] and &Λmacr;, combined with a theoretical bound on λ[sub 1] strongly favor the existence of a sizeable contribution of non-factorizable terms in semileptonic decays of D mesons. Thus these terms are likely to solve the long-standing problem of the deficit of semileptonic decay rate of the D mesons, and with better data their magnitude can be determined and used in studies of the parameter V[sub ub]. [ABSTRACT FROM AUTHOR]

The ten nonleptonic weak decays K→2π, K→ 3π, K[sub L]→2γ, K[sub S]→2γ, K[sub L]→π[sup 0]2γ, are predicted for a chiral pole model based on the linear sigma model theory which automatically satisfies the partial conservation of axial current (PCAC) hypothesis. These predictions, agreeing with data to the 5% level and containing no or at most one free parameter, are compared with the results of chiral perturbation theory (ChPT). The latter ChPT approach to one-loop level is known to contain at least four free parameters and then predicts a K[sub L]→π[sup 0]γγ rate which is 60% shy of the experimental value. [ABSTRACT FROM AUTHOR]

A measurement of the ratio of branching fractions, R = B(t→Wb)/B(t→Wq), with q being any quark with I3 = -1/2 and Q = -1/3, is presented. This analysis considers samples of single- and double-tagged lepton+jets events obtained with the DØ detector, corresponding to integrated luminosities of 169 pb-1 and 158 pb-1, respectively in the e+jets and μ+jets channels. Two different lifetime taggers, CSIP and SVT, are used. [ABSTRACT FROM AUTHOR]

We present the results of a search for charged Higgs in the decay products of ${\rm t{\bar t}}$ at the CDF II detector at the Tevatron. The search is based on the cross section measurements of ${\rm t{\bar t}}$ production in three exclusive decay channels: dilepton, lepton + jets and lepton + hadronic tau. Assuming the charged Higgs decays only via $H^+ \to {\rm c}{\rm \bar {s}}$, and $H^+ \to \tau {\bar \nu}$, and $H^+ \to {\rm t}^\ast {\rm b} \to {\rm Wb}{\rm \bar {b}}$, limits in the MSSM (mHiggs, tan(β)) plane are obtained at tree level. A model-independent analysis is introduced in which the results are independent of Higgs branching ratios. This analysis results in BR(t→Hb)<0.7 at 95%CL for 80 GeV

Most past work on weak nonleptonic decays has mixed dimensional regularization in the weak operator product expansion with some form of a cutoff regularization in the evaluation of the matrix elements. Even with the usual technique of matching the two schemes, this combination misses physics at short distance which can be described by dimension eight (and higher dimension) operators. I describe some recent work with V. Cirigliano and E. Golowich which clarifies these effects and provides a numerical estimate suggesting that they are important. [ABSTRACT FROM AUTHOR]

The hadronic current of the matrix element for the transition γ[sub c] → γ e[sup +] ν within the framework of HQET is parameterized in terms of two form factors. By studying the decay rate distribution in the space of the decay kinematic variables one can extract the ratio R = f[sub 2]/f[sub 1] of the form factors. The first measurement of R was made by the CLEO collaboration in 1995. In this note we describe the study of the statistical and systematic errors for a 4.5 times larger data sample. The central value for R will be presented shortly. [ABSTRACT FROM AUTHOR]

The decay τ[sup -] → μ[sup -]γ has been searched for using the CLEO detector at the Cornell Electron Storage Ring (CESR). Using 13.8fb[sup -1] of data collected with the CLEO II and CLEO II.V detector an upper limit of B(τ[sup -] → μ[sup -]γ)≤ 1.1 × 10[sup -6] @ 90% CL is obtained. [ABSTRACT FROM AUTHOR]