447 research outputs found
Penguin decays of B mesons
Penguin, or loop, decays of B mesons induce effective flavor-changing neutral
currents, which are forbidden at tree level in the Standard Model. These decays
give special insight into the CKM matrix and are sensitive to non-standard
model effects. In this review, we give a historical and theoretical
introduction to penguins and a description of the various types of penguin
processes: electromagnetic, electroweak, and gluonic. We review the
experimental searches for penguin decays, including the measurements of the
electromagnetic penguins b -> s gamma and B -> K* gamma and gluonic penguins B
-> K pi, B+ -> omega K+ and B -> eta' K, and their implications for the
Standard Model and New Physics. We conclude by exploring the future prospects
for penguin physics.Comment: 49 pages, LATEX, 30 embedded figures, submitted to Annual Reviews of
Nuclear and Particle Scienc
Der Einfluss des metakognitiven Wissens auf die Entwicklung der Mathematikleistung am Beginn der Sekundarstufe I
Metakognitives Wissen, also das Wissen über kognitive Prozesse und ihre Steuerung, ist in der Gedächtnis- und Leseverstehensforschung in einem breiten Altersbereich vom Kindergartenalter bis zum Ende der Sekundarstufe I als wichtiger Prädiktor kognitiver Leistungen etabliert.
Im Inhaltsbereich Mathematik deuten punktuelle Befunde zu korrelativen Zusammenhängen sowie die Wirknachweise metakognitiver Trainingsprogramme auf leistungsrelevante Effekte des metakognitiven Wissens hin. Jedoch fehlt nach wie vor systematische Forschung zum Zusammenhang zwischen metakognitivem Wissen über Planung, Überwachung und Regulation mathematischer Lösungsprozesse und der Entwicklung in curricularen mathematischen Kompetenzen.
Diese Fragestellung wurde anhand von drei Forschungsfragen in der Sekundarstufe I untersucht: (a) Unterscheiden sich die Schüler der drei Schularten zu Beginn der fünften Jahrgangsstufe im metakognitiven Wissen? (b) Kann das metakognitive Wissen die Mathematikleistung zu einem späteren Zeitpunkt vorhersagen? (c) Trägt das metakognitive Wissen einen eigenen Anteil zur Vorhersage der Mathematikleistung bei, der über den Einfluss anderer allgemeiner und mathematikspezifischer Leistungsdeterminanten hinaus geht?
Die Analysen basieren auf der längsschnittlichen Untersuchung einer Stichprobe von 763 nordbayerischen Schülerinnen und Schülern aus Gymnasien, Realschulen und Hauptschulen. Neben der Mathematikleistung am Beginn und am Ende der fünften Jahrgangsstufe und dem metakognitiven Wissen wurden als Prädiktoren mathematischer Leistungen allgemeine (Intelligenz und soziale Herkunft) sowie mathematikspezifische Schülermerkmale (Rechenfertigkeiten, mathematisches Selbstkonzept und mathematisches Interesse) erhoben.
Die Auswertungen erbrachten bedeutsame Schulartunterschiede im metakognitiven Wissen. Das metakognitive Wissen leistet darüber hinaus auch unter Kontrolle der Vorwissensunterschiede und weiterer allgemeiner und spezifischer Leistungsdeterminanten einen bedeutsamen Beitrag in der Vorhersage der Mathematikleistung am Ende der fünften Jahrgangsstufe.
Diese Befunde werden als Nachweis für die substanzielle Bedeutung des metakognitiven Wissens für Ausprägung und Entwicklung mathematischer Kompetenzen am Beginn der Sekundarstufe I interpretiert.Metacognitive knowledge, that is the knowledge about cognitive processes and their regulation is established in memory and reading comprehension research as an important predictor of cognitive achievement. ln mathematics some correlational findings and the effects of metacognitive trainings point to the predictive account of metacognitive knowledge in the prediction of achievement. However, there is no systematic research on the relations between metacognitive knowledge on planning, monitoring and regulation processes in the solution of mathematical problems and the development of curricular mathematical achievement.
To explore the relation between metacognitive knowledge and achievement in secondary school three research questions were examined: (a) Are there differences in metacognitive knowledge between the students allocated to the three tracks of German educational system? (b) Does metacognitive knowledge predict mathematics achievement? (c) Does metacognitive knowledge show a unique predictive influence even when other general and specific predictors of mathematics achievement are controlled?
Two measurement points at the beginning and at the end of Grade 5 were analyzed. The sample consisted of N=763 students from northern Bavaria on three tracks (academic track, intermediate track and vocational track). Mathematics achievement was assessed at both measurement points. Metacognitive knowledge as well as general (intelligence, socio-economic status) and specific (computation skills, mathematical self-concept and mathematical interest) predictors of achievement were assessed at the first measurement point.
Students attending the three tracks differed in metacognitive knowledge. Additionally, metacognitive knowledge predicted mathematics achievement at T2. This predictive influence remained significant even under control for prior knowledge as well as general and the specific determinants of mathematics achievement.
The findings show the substantial importance of metacognitive knowledge on mathematics achievement and on development of mathematics achievement at the beginning of secondary school
Rare radiative B decays to orbitally excited K mesons
The exclusive rare radiative B meson decays to orbitally excited axial-vector
mesons K_1^*(1270), K_1(1400) and to the tensor meson K_2^*(1430) are
investigated in the framework of the relativistic quark model based on the
quasipotential approach in quantum field theory. These decays are considered
without employing the heavy quark expansion for the s quark. Instead the s
quark is treated to be light and the expansion in inverse powers of the large
recoil momentum of the final K^{**} meson is used to simplify calculations. It
is found that the ratio of the branching fractions of rare radiative B decays
to axial vector K^*_1(1270) and K_1(1400) mesons is significantly influenced by
relativistic effects. The obtained results for B decays to the tensor meson
K_2^*(1430) agree with recent experimental data from CLEO.Comment: 17 pages, revte
The sensitivity of the zero position of the forward--backward asymmetry to new physics effects in the B -> K^\ast \mu^+ \mu^- decay
Starting with the most general effective Hamiltonian comprising scalar and
vector operators beyond the standard model, we discuss the impact of various
operators on the zero of the forward--backward asymmetry in the dileptonic B
decay B -> K^\ast \mu^+ \mu^-. We find that, zero of the asymmetry is highly
sensitive to the sign and size of the vector--vector operators and opposite
chirality counterparts of the usual operators. The scalar--scalar four--fermion
operators, on the other hand, have mild effect on the zero of the asymmetry.
Our results are expected to be checked in the near future experiments.Comment: 16 pp, 6 ps fig
Observation of the Dynamic Beta Effect at CESR with CLEO
Using the silicon strip detector of the CLEO experiment operating at the
Cornell Electron-positron Storage Ring (CESR), we have observed that the
horizontal size of the luminous region decreases in the presence of the
beam-beam interaction from what is expected without the beam-beam interaction.
The dependence on the bunch current agrees with the prediction of the dynamic
beta effect. This is the first direct observation of the effect.Comment: 9 page uuencoded postscript file, postscritp file also available
through http://w4.lns.cornell.edu/public/CLNS, submitted to Phys. Rev.
Hadronic B decays: Supersymmetric enhancement and a simple spectator model
Two aspects of hadronic B decays are investigated. Firstly, the
supersymmetric enhancement of hadronic b decays by gluino penguin processes is
studied through their effect on the Wilson coefficients of the effective
Hamiltonian. Secondly, hadronization of the final state quarks is studied
through a simple phase space spectator model.Comment: 24 pages, REVTEX, minor additional text and some references adde
Measurement of the Inclusive Semi-electronic Branching Fraction
Using the angular correlation between the emitted in a decay and the emitted in the subsequent decay, we have measured the branching fraction for the
inclusive semi-electronic decay of the meson to be: {\cal B}(D^0
\rightarrow X e^+ \nu) = [6.64 \pm 0.18 (stat.) \pm 0.29 (syst.)] \%. The
result is based on 1.7 fb of collisions recorded by the CLEO II
detector located at the Cornell Electron Storage Ring (CESR). Combining the
analysis presented in this paper with previous CLEO results we find,
\frac{{\cal B} (D^0 \rightarrow X e^+ \nu)}
{{\cal B} (D^0 \rightarrow K^- \pi^+)}
= 1.684 \pm 0.056 (stat.) \pm 0.093(syst.) and
\frac{{\cal B}(D\rightarrow K^-e^+\nu)}
{{\cal B}(D\rightarrow Xe^+\nu)}
= 0.581 \pm 0.023 (stat.) \pm 0.028(syst.).
The difference between the inclusive rate and the sum of the measured
exclusive branching fractions (measured at CLEO and other experiments) is of the inclusive rate.Comment: Latex file, 33pages, 4 figures Submitted to PR
Precision Measurement of the Mass Difference
We have measured the vector-pseudoscalar mass splitting , significantly more precise than the previous
world average. We minimize the systematic errors by also measuring the
vector-pseudoscalar mass difference using the radiative
decay , obtaining
. This is
then combined with our previous high-precision measurement of
, which used the decay . We also
measure the mass difference MeV, using the
decay modes of the and mesons.Comment: 18 pages uuencoded compressed postscript (process with uudecode then
gunzip). hardcopies with figures can be obtained by sending mail to:
[email protected]
Further Search for the Two-Photon Production of the Glueball Candidate
The CLEOII detector at the Cornell e+ e- storage ring CESR has been used to
search for the two-photon production of the decaying into pi+ pi-.
No evidence for a signal is found in data corresponding to an integrated
luminosity of 4.77/fb and a 95% CL upper limit on of 2.5 eV is set. If this result is combined with the BES Collaboration's
measurement of in radiative decay, a 95% CL
lower limit on the stickiness of the of 73 is obtained. If the
recent CLEO result for \Gamma_{two-photon} * BR{\K_S K_S} is combined with
the present result, the stickiness of the is found to be larger
than 102 at the 95% CL. These results for the stickiness (the ratio of the
probabilities for two-gluon coupling and two-photon coupling) provide further
support for a substantial neutral parton content in the .Comment: 8 pages, postscript file also available through
http://w4.lns.cornell.edu/public/CLN
Measurements of the Ratios and
Using the CLEO~II detector we measure , and .
We find the vector to pseudoscalar ratio, , which is similar to the
ratio found in non strange decays.Comment: 11 page uuencoded postscript file, postscript file also available
through http://w4.lns.cornell.edu/public/CLN
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