230 Matching Results

Search Results

Advanced search parameters have been applied.

Weak matrix elements on the lattice - Circa 1995

Description: Status of weak matrix elements is reviewed. In particular, e{prime}/e, B {yields} K*{gamma}, B{sub B} and B{sub B}, are discussed and the overall situation with respect to the lattice effort and some of its phenomenological implications are summarised. For e{prime}/e the need for the relevant matrix elements is stressed in view of the forthcoming improved experiments. For some of the operators, (e.g. O{sub 6}), even bound on their matrix elements would be very helpful. On B {yields} K{degrees}{gamma}, a constant behavior of T{sub 2} appears disfavored although dependence of T{sub 2} could, of course, be milder than a simple pole. Improved data is badly needed to settle this important issue firmly, especially in view of its ramification for extractions of V{sub td} from B {yields} {rho}{gamma}. On B{sub {kappa}}, the preliminary result from JLQCD appears to contradict Sharpe et al. JLQCD data seems to fit very well to linear {alpha} dependence and leads to an appreciably lower value of B{sub {kappa}}. Four studies of B{sub {kappa}} in the {open_quotes}full{close_quotes} (n{sub f} = 2) theory indicate very little quenching effects on B{sub {kappa}}; the full theory value seems to be just a little less than the quenched result. Based on expectations from HQET, analysis of B-parameter (B{sub h}{ell}) for the heavy-light mesons via B{sub h}{ell}) = constant + constants{prime}/m{sub h}{ell} is suggested. A summary of an illustrative sample of hadron matrix elements is given and constraints on CKM parameters (e.g. V{sub td}/V{sub ts}, on the unitarity triangle and on x{sub s}/x{sub d}, emerging from the lattice calculations along with experimental results are briefly discussed. In quite a few cases, for the first time, some indication of quenching errors on weak matrix elements are now becoming available.
Date: October 3, 1995
Creator: Soni, A.
Partner: UNT Libraries Government Documents Department

Radiative higgs boson decays H {yields} f{anti f}{gamma}

Description: Higgs boson radiative decays of the form H {r_arrow} f{ovr f}{gamma} are calculated in the Standard Model using the complete one-loop expressions for the decay amplitudes. Contributions to the radiative width from leptons and light quarks are given. We also present e{ovr e} invariant mass distributions for H {r_arrow} e{ovr e}{gamma}, which illustrate the importance of the photon pole contribution and the effects of the box diagrams. 4 refs., 6 figs.
Date: October 10, 1996
Creator: Abbasabadi, A.; Bowser-Chao, D.; Repko, W.W. & Dicus, D.A.
Partner: UNT Libraries Government Documents Department

Radiative width of the a {subscript 2} meson

Description: We present data on coherent production of the ({pi}{sup +}{pi}{sup -}{pi}{sup -}) system by 600 GeV/c pion beam in the reaction {pi}{sup -} + A {yields} A + ({pi}{sup +}{pi}{sup -}{pi}{sup -}) for the C, Cu and Pb targets. The Primakoff formalism was used for extracting the radiative width of the a{sub 2} meson. We obtain a preliminary value {Gamma}(a{sub 2}{sup -} {yields} {pi}{sup -}{gamma}) = 225 {+-} 25(stat) {+-} 45(syst) keV.
Date: May 3, 1999
Creator: al., V.P. Kubarovsky et
Partner: UNT Libraries Government Documents Department

Relativistic Multireference Many-body Perturbation Theory for Open-shell Ions with Multiple Valence Shell Electrons: the Transition Rates and Lifetimes of the Excited Levels in Chlorinelike Fe X

Description: A recently developed relatistic multireference many-body perturbation theory based on multireference configuration-interaction wavefunctions as zeroth order wavefunctions is outlined. The perturbation theory employs a general class of configuration-interaction wve functions as reference functions, and thus is applciable to multiple open valence shell systems with near degeneracy of a manifold of strongly interacting configurations. Multireference many-body perturbation calculations are reported for the ground and excited states of chlorine-like Fe X in which the near degeneracy of a manifold of strongly interacting configurations mandates a multireference treatment. Term energies of a total of 83 excited levels arising from the 3s{sup 2}3p{sup 5}, 3s3p{sup 6}, 3s{sup 2}3p{sup 4}3d, 3s3p{sup 5}3d, and 3s{sup 2}3p{sup 3}3d{sup 2} configurations of the ion are evaluated to high accuracy. Transition rates associated with E1/M1/E2/M2/E3 radiative decays and lifetimes of a number of excited levels are calculated and compared with laboratory measurements to critically evaluate recent experiments.
Date: September 30, 2009
Creator: Ishikawa, Y; Santana, J A & Trabert, E
Partner: UNT Libraries Government Documents Department

Radiative Penguin Decays at the B Factories

Description: In this article, I review the most recent results in radiative penguin decays from the B factories Belle and BABAR. Most notably, I will talk about the recent new observations in the decays B {yields} ({rho}/{omega}) {gamma}, a new analysis technique in b {yields} s{gamma}, and first measurements of radiative penguin decays in the B{sup 0}{sub s} meson system. Finally, I will summarize the current status and future prospects of radiative penguin B physics at the B factories.
Date: November 16, 2007
Creator: Koneke, Karsten & /MIT, LNS
Partner: UNT Libraries Government Documents Department

Search for B+ to X(3872) K+, X(3872) to J/psi gamma

Description: In a study of B{sup +} {yields} J/{psi}{gamma}K{sup +} decays, they find evidence for the radiative decay X(3872) {yields} J/{psi}{gamma} with a statistical significance of 3.4{sigma}. They measure the product of branching fractions {Beta}(B{sup +} {yields} X(3872)K{sup +}) {center_dot} {Beta}(X(3872) {yields} J/{psi}{gamma}) = (3.3 {+-} 1.0 {+-} 0.3) x 10{sup -6}, where the uncertainties are statistical and systematic, respectively. They also measure the branching fraction {Beta}(B{sup +} {yields} {chi}{sub c1}K{sup +}) = (4.9 {+-} 0.20 {+-} 0.4) x 10{sup -4}. These results are obtained from (287 {+-} 3) million B{bar B} decays collected at the {Upsilon}(4S) resonance with the BABAR detector at the PEP-II B Factory at SLAC.
Date: July 31, 2006
Creator: Aubert, B.
Partner: UNT Libraries Government Documents Department

Suppression of auger recombination in ""giant"" core/shell nanocrystals

Description: Many potential applications of semiconductor nanocrystals are hindered by nonradiative Auger recombination wherein the electron-hole (exciton) recombination energy is transferred to a third charge carrier. This process severely limits the lifetime and bandwidth of optical gain, leads to large nonradiative losses in light emitting diodes and photovoltaic cells, and is believed to be responsible for intermittency ('blinking') of emission from single nanocrystals. The development of nanostructures in which Auger recombination is suppressed has been a longstanding goal in colloidal nanocrystal research. Here, we demonstrate that such suppression is possible using so-called 'giant' nanocrystals that consist of a small CdSe core and a thick CdS shell. These nanostructures exhibit a very long biexciton lifetime ({approx}10 ns) that is likely dominated by radiative decay instead of non-radiative Auger recombination. As a result of suppressed Auger recombination, even high-order multiexcitons exhibit high emission efficiencies, which allows us to demonstrate optical amplification with an extraordinarily large bandwidth (>500 me V) and record low excitation thresholds.
Date: January 1, 2009
Creator: Garcia Santamaria, Florencio; Vela, Javier; Schaller, Richard D; Hollingsworth, Jennifer A; Klimov, Victor I & Chen, Yongfen
Partner: UNT Libraries Government Documents Department

Semileptonic Form-factors from B-> K* gamma Decays in the Large Energy Limit

Description: Making use of the measurement of the $B\to K^*\gamma$ branching ratio together with the relations following from the limit of high recoil energy, we obtain stringent constraints on the values of the form-factors entering in heavy-to-light $B\to V\ell\ell'$ processes such as $B\to K^*\ell^+\ell^-$, $B\to K^*\nu \bar\nu$ and $B\to \rho\ell\nu$ decays. We show that the symmetry predictions, when combined with the experimental information on radiative decays, specify a severely restricted set of values for the vector and axial-vector form-factors evaluated at zero momentum transfer, $q^2=0$. These constraints can be used to test model calculations and to improve our understanding of the $q^2$-dependence of semileptonic form-factors. We stress that the constraints remain stringent even when corrections are taken into account.
Date: November 21, 2000
Creator: Burdman, Gustavo & Hiller, Gudrun
Partner: UNT Libraries Government Documents Department

Measurements of Branching Fractions for B+ -> rho+ gamma, B0 -> rho0 gamma, and B0 -> omega gamma

Description: The authors present branching fraction measurements for the radiative decays B{sup +} {yields} {rho}{sup +}{gamma}, B{sup 0} {yields} {rho}{sup 0}{gamma}, and B{sup 0} {yields} {omega}{gamma}. The analysis is based on a data sample of 465 million B{bar B} events collected with the BABAR detector at the PEP-II asymmetric-energy B Factory located at the Stanford Linear Accelerator Center (SLAC). They find {Beta}(B{sup +} {yields} {rho}{sup +}{gamma}) = (1.20{sub -0.37}{sup +0.42} {+-} 0.20) x 10{sup -6}, {Beta}(B{sup 0} {yields} {rho}{sup 0}{gamma}) = (0.97{sub -0.22}{sup +0.24} {+-} 0.06) x 10{sup -6}, and a 90% C.L. upper limit {Beta}(B{sup 0} {yields} {omega}{gamma}) < 0.9 x 10{sup -6}, where the first error is statistical and the second is systematic. They also measure the isospin-violating quantity {Lambda}(B{sup +} {yields} {rho}{sup +}{gamma})/2{Lambda}(B{sup 0} {yields} {rho}{sup 0}{gamma}) - 1 = -0.43{sub -0.22}{sup +0.25} {+-} 0.10.
Date: August 15, 2008
Creator: Aubert, B
Partner: UNT Libraries Government Documents Department

Search for a Low-mass Higgs Boson in Y(3S)--> gamma A^0, A^0--> tau^ tau^- at BABAR

Description: We search for a light Higgs boson A{sup 0} in the radiative decay Y(3S) {yields} {gamma}A{sup 0}, A{sup 0} {yields} T{sup +}T{sup -}, T{sup +} {yields} e{sup +}{nu}{sub e}{nu}{sub T}, or T{sup +} {yields} {mu}{sup +} {nu}{sub {mu}T}. The data sample contains 122 x 10{sup 6} Y(3S) events recorded with the BABAR detector. We find no evidence for a narrow structure in the studied T{sup +}T{sup -} invariant mass region of 4.03 < m{sub T{sup +}T{sup -}} < 10.10 GeV/c{sup 2}. We exclude at the 90% confidence level (C.L.) a low-mass Higgs boson decaying to T{sup +}T{sup -} with a product branching fraction B(Y(3S) {yields} {gamma}A{sup 0}) x B(A{sup 0} {yields} T{sup +}T{sup -}) > (1.5-16) x 10{sup -5} across the mT{sup +}T{sup -} range. We also set a 90% C.L. upper limit on the T{sup +}T{sup -} decay of the {eta}{sub b} at B({eta}{sub b} {yields} T{sup +}T{sup -}) < 8%.
Date: December 9, 2009
Creator: Gabareen Mokhtar, Arafat
Partner: UNT Libraries Government Documents Department

A study of the decay {mu} {yields} e{gamma} by the MEGA experiment

Description: The MEGA experiment is designed to search for the lepton-flavor number non-conserving rare decay {mu} {yields} {ital e}{gamma}. Data- taking is complete, with 450 million events on tape taken over approximately 10{sup 7} seconds. A small portion of the data sample has been processed through the complete event reconstruction codes to search for the {mu} {yields} {ital e}{gamma} process. No evidence for the {mu} {yields} {ital e}{gamma} decay is observed at a sensitivity of {approximately}7 x 10{sup -11} (90% confidence).
Date: December 31, 1996
Creator: Hogan, G.E.; Amann, J.F. & Ahmed, M.
Partner: UNT Libraries Government Documents Department

Probing supersymmetry in rare B decays

Description: We determine the ability of future experiments to observe supersymmetric contributions to the rare decays B {r_arrow} X{sub s}{gamma} and B {r_arrow} X{sub s}l{sup +}l{sup -}. A global fit to the Wilson coefficients which contribute to these decays is performed from Monte Carlo generated data. This fit is then compared to supersymmetric predictions for several different patterns of the superpartner spectrum.
Date: October 1, 1996
Creator: Hewett, J.L.
Partner: UNT Libraries Government Documents Department

{mu}{sup +} {yields} e{sup +}{gamma} and related rare decays

Description: The connection of rare decays to supersymmetric grand unification is highlighted, and a brief review of the status of rare decay experiments is given. The status of the MEGA experiment, a search for {mu}{sup +} {yields} e{sup +}{gamma}, is reported. Some ideas for a new experimental arrangement that has the potential to reach a sensitivity of 10{sup {minus}14} are presented.
Date: February 1, 1997
Creator: Cooper, M.D.
Partner: UNT Libraries Government Documents Department

MEGA -- A search for {mu} {r_arrow} e{gamma}

Description: The MEGA experiment is a search for the decay {mu} {r_arrow} e{gamma}. Even though there is no fundamental reason to expect lepton number to be a conserved quantity, processes such as {mu} {r_arrow} e{gamma} have not been observed. (The present upper limit for the branching ratio for {mu} {r_arrow} e{gamma} is 4.9 x 10{sup {minus}11}.) The minimal standard model of electroweak interactions, which is enormously successful, builds in lepton number conservation. However, the decay {mu} {r_arrow} e{gamma} is expected in many extensions to the standard model, in particular in supersymmetry models. The experimental signature for {mu} {r_arrow} e{gamma} from decays at rest is the observation of a positron and photon, each of 52.8 MeV , that are back-to-back, in time coincidence, and originate from a common spatial point. The MEGA detector consists of two spectrometers designed to measure the kinematic characteristics of positrons and photons to search for events with this signature. The primary difficulty in the analysis of these data has been the development of reconstruction algorithms that balance efficiency and resolution. Also, many calibrations and corrections are needed to get optimum resolutions. Most surviving candidate events are accidentals. Results of analysis are given.
Date: December 1, 1998
Creator: Mischke, R. E.
Partner: UNT Libraries Government Documents Department


Description: This paper reviews the current status of experimental results on radiative kaon decays. Several experiments at BNL, CERN and FNAL have recently or will soon complete data collection; as a result, there are several new results.
Date: November 19, 1999
Creator: KETTELL,S.
Partner: UNT Libraries Government Documents Department

Radiative Decays, Nonet Symmetry and SU(3) Breaking

Description: We re-examine the problem of simultaneously describing in a consistent way all radiative and leptonic decays of light mesons (V {yields} P{gamma}, P {yields} V{gamma}, P {yields} {gamma}{gamma}, V {yields} e{sup +}e{sup -}). For this purpose, we rely on the Hidden Local Symmetry model in both its anomalous and non-anomalous sectors. We show that the SU(3) symmetry breaking scheme proposed by Bando, Kugo and Yamawaki, supplemented with nonet symmetry breaking in the pseudoscalar sector, allows one to reach a nice agreement with all data, except for the K*{sup {+-}} radiative decay. An extension of this breaking pattern allows one to account for this particular decay mode too. Considered together, the whole set of radiative decays provides a pseudoscalar mixing angle {theta}{sub P} {approx_equal} and a value for {theta}{sub V} which is {approx_equal} 3{sup o} from that of ideal mixing. We also show that it is impossible, in a practical sense, to disentangle the effects of nonet symmetry breaking and those of glue inside the {eta}{prime}, using only light meson decays.
Date: June 30, 1999
Creator: O'Connell, Heath B
Partner: UNT Libraries Government Documents Department

Hyperon particle physics at JHF

Description: This paper discusses the possibility of a program in hyperon decay physics at the Japan Hadron Facility. The study of hyperon decays has a history of over 40 years of experimental results. However, many of the earliest results are still the best available and there are many gaps in the data. The static properties of hyperons (masses, magnetic moments) are in relatively good shape. Much work remains to be done on the decays of hyperons and hyperon resonances. There are current experiments at the major accelerator facilities that address various hyperon decays, but no comprehensive program. This presents an excellent opportunity for such a program to be considered at JHF. The high-intensity beams of {pi}, K, and p beams will allow experiments to be designed that optimize the properties of the hyperons being studied. It is possible to envision experiments with samples of 10{sup 9} hyperon decays in 10{sup 7} sec runs.
Date: December 1, 1998
Creator: Mischke, R.E.
Partner: UNT Libraries Government Documents Department

Branching Fractions and CP-Violating Asymmetries in Radiative B Decays to eta K gamma

Description: The authors present measurements of the CP-violation parameters S and C for the radiative decay B{sup 0} {yields} {eta}K{sub S}{sup 0}{gamma}; for B {yields} {eta}K{gamma} they also measure the branching fractions and for B{sup +} {yields} {eta}K{sup +}{gamma} the time-integrated charge asymmetry {Alpha}{sub ch}. The data, collected with the BABAR detector at the Stanford Linear Accelerator Center, represent 465 x 10{sup 6} B{bar B} pairs produced in e{sup +}e{sup -} annihilation. The results are S = -0.18{sub -0.46}{sup +0.49} {+-} 0.12, C = -0.32{sub -0.39}{sup +0.40} {+-} 0.07, {Beta}(B{sup 0} {yields} {eta}K{sup 0}{gamma}) = (7.1{sub -2.0}{sup +2.1} {+-} 0.4) x 10{sup -6}, {Beta}(B{sup +} {yields} {eta}K{sup +}{gamma}) = (7.7 {+-} 1.0 {+-} 0.4) x 10{sup -6}, and {Alpha}{sub ch} = (-9.0{sub -9.8}{sup +10.4} {+-} 1.4) x 10{sup -2}. The first error quoted is statistical and the second systematic.
Date: May 14, 2008
Creator: Aubert, B.
Partner: UNT Libraries Government Documents Department

A Study of Radiative Bottomonium Transitions using Converted Photons

Description: The authors use (111 {+-} 1) million {Upsilon}(3S) and (89 {+-} 1) million {Upsilon}(2S) events recorded by the BABAR detector at the PEP-II B-factory at SLAC to perform a study of radiative transitions betwen bottomonium states using photons that have been converted to e{sup +}e{sup -} pairs by the detector material. They observe {Upsilon}(3S) {yields} {gamma}{chi}{sub b0,2}(1P) decay, make precise measurements of the branching fractions for {chi}{sub b1,2}(1P, 2P) {yields} {gamma}{Upsilon}(1S) and {chi}{sub b1,2}(2P) {yields} {gamma}{Upsilon}(2S) decays, and search for radiative decay to the {eta}{sub b}(1S) and {eta}{sub b}(2S) states.
Date: August 15, 2011
Creator: Lees, J.P.; Poireau, V.; Prencipe, E.; Tisserand, V.; /Annecy, LAPP; Garra Tico, J. et al.
Partner: UNT Libraries Government Documents Department

Radiative Penguin Decays at the B Factories

Description: Recent results from the B-Factories on radiative decays such as b {yields} s(d){gamma}, b {yields} s{ell}{ell} and leptonic decay B{sup 0} {yields} {tau}{sup +}{tau}{sup -} are reviewed.
Date: March 5, 2007
Creator: Cuhadar-Donszelmann, T. & U., /British Columbia
Partner: UNT Libraries Government Documents Department

Recent BaBar Results on $B$ Decays

Description: Several recent key results from the BABAR experiment are presented, most using 383.6 fb{sup -1} of data. In particular, the search for B{sup +} {yields} {tau}{sup +}{nu}, inclusive and exclusive measurements of |V{sub ub}|, measurements of b {yields} d{gamma} decays and new observations of rare charmless hadronic decays. The new results provide important experimental constraints on the Standard Model and new physics models. Keywords: B decays; flavor; leptonic; semi-leptonic, radiative, hadronic.
Date: November 15, 2011
Creator: Clark, P.J. & U., /Edinburgh
Partner: UNT Libraries Government Documents Department

Searches for Exotic Decays of the Upsilon(3S) at BaBar

Description: In this paper we present two searches for new physics in {Upsilon}(3S) decays collected by the BABAR detector. We search for charged lepton-flavour violating decays of the {Upsilon}(3S), which are unobservable in the Standard Model but are predicted to occur in several beyond-the-Standard Model scenarios. We also search for production of a light Higgs or Higgs-like state produced in radiative decays of the {Upsilon}(3S) and decaying to muon pairs.
Date: December 1, 2011
Creator: Hooberman, Benjamin & /LBL, Berkeley /Heidelberg U.
Partner: UNT Libraries Government Documents Department

Efficient multi-exciton emission from quantum dots.

Description: The fundamental spontaneous emission rate an emitter can be modified by its photonic environment. By enhancing the spontaneous emission rate, there is a possibility of extracting multi-exciton energies through radiative decay. In this report, we explore using high Q and small volume cavities to enhance the spontaneous emission rate. We observed greater than 50 folds enhancement in the spontaneous emission from photonic crystal waveguide or microcavity using close-packed monolayer of PbS quantum dot emitters.
Date: September 1, 2010
Creator: Luk, Ting Shan
Partner: UNT Libraries Government Documents Department