241 research outputs found
Schottky barrier heights and interface chemistry in Ag, In, and Al overlayers on GaP(110)
We have carried out a study of the chemical reaction of silver, indium, and aluminium layers with cleaved GaP(110) surfaces using photoemission with synchrotron radiation. Core level photoelectron spectra show that silver and indium overlayers do not cause an interface reaction with GaP(110). The deposition of Al, on the other hand, leads to an extensive exchange reaction which also proceeds at low temperature, although influenced by changes in overlayer growth morphology. Surface band bending induced by the metallic overlayers was investigated as a function of deposition for nâ and pâtype material. In contrast to earlier findings, almost identical Schottky barrier heights for In and Ag deposition are obtained, despite the large difference in work function between these two metals. Results for Al also suggest that a small range of pinning positions is responsible for the Schottky barrier heights for junctions of these metals with GaP(110). We find that large peak shifts due to a surface photovoltage induced by the photoemission light source affect the determination of the Schottky barrier heights. This and other possible reasons for the discrepancy with earlier work are discussed
Absolute Branching Fraction Measurements of Exclusive D^0 Semileptonic Decays
With the first data sample collected by the CLEO-c detector at the psi(3770)
resonance we have studied four exclusive semileptonic decays of the D0 meson.
Our results include the first observation and absolute branching fraction
measurement for D0 --> rho- e+ nu_e and improved measurements of the absolute
branching fractions for D0 decays to K- e+ nu_e, pi- e+ nu_e, and K*- e+ nu_e.Comment: 9 pages postscript,also available through
http://www.lns.cornell.edu/public/CLNS/2005/, submitted to PR
Measurement of Absolute Hadronic Branching Fractions of D Mesons and e^+e^- --> D barD Cross Sections at E_cm = 3773 MeV
Using 55.8 pb^-1 of e^+e^- collisions recorded at the psi(3770) resonance
with the CLEO-c detector at CESR, we determine absolute hadronic branching
fractions of charged and neutral D mesons using a double tag technique. Among
measurements for three D^0 and six D^+ modes, we obtain reference branching
fractions B(D^0 -> K^- pi^+)=(3.91 +- 0.08 +- 0.09)% and B(D^+ -> K^- pi^+
pi^+)=(9.5 +- 0.2 +- 0.3)%, where the uncertainties are statistical and
systematic, respectively. Final state radiation is included in these branching
fractions by allowing for additional, unobserved, photons in the final state.
Using a determination of the integrated luminosity, we also extract the cross
sections sigma(e^+e^- -> D^0 \bar D^0)=(3.60 +- 0.07 +0.07-0.05) nb and
sigma(e^+e^- -> D^+D^-)=(2.79 +- 0.07 +0.10-0.04) nb.Comment: 9 pages postscript,also available through
http://www.lns.cornell.edu/public/CLNS/2005/, submitted to PR
Measurement of the B-Meson Inclusive Semileptonic Branching Fraction and Electron-Energy Moments
We report a new measurement of the B-meson semileptonic decay momentum
spectrum that has been made with a sample of 9.4/fb of electron-positron
annihilation data collected with the CLEO II detector at the Y(4S) resonance.
Electrons from primary semileptonic decays and secondary charm decays were
separated by using charge and angular correlations in Y(4S) events with a
high-momentum lepton and an additional electron. We determined the semileptonic
branching fraction to be (10.91 +- 0.09 +- 0.24)% from the normalization of the
electron-energy spectrum. We also measured the moments of the electron energy
spectrum with minimum energies from 0.6 GeV to 1.5 GeV.Comment: 36 pages postscript, als available through
http://w4.lns.cornell.edu/public/CLNS/, Submitted to PRD (back-to-back with
preceding preprint hep-ex/0403052
Measurement of \cal{B}(D^+ --> mu^+ nu) and the Pseudoscalar Decay Constant
In 60 pb-1 of data taken on the psi(3770) resonance with the CLEO-c detector,
we find 8 D+ to mu+ nu event candidates that are mostly signal, containing only
1 estimated background. Using this statistically compelling sample, we measure
preliminary values of B(D+ to mu+ nu) = (3.5 +- 1.4 +- 0.6)*10^{-4}, and
determine f_{D+} =(201+- 41+- 17) MeV.Comment: 17 pages postscript, also available through
http://www.lns.cornell.edu/public/CONF/2004/, Presented at ICHEP Aug
16-22,2004, Beijing, Chin
New Measurements of Upsilon(1S) Decays to Charmonium Final States
Using substantially larger data samples collected by the CLEO III detector,
we report on new measurements of the decays of Upsilon(1S) to charmonium final
states, including J/Psi, psi(2S), and chi_cJ. The latter two are first
observations of these decays. We measure the branching fractions as follows:
B(Y(1S)--> J/Psi+X)=(6.4+-0.4+-0.6)x10^-4, B(Y(1S)--> psi(2S)+X)/B(Y(1S)-->
J/Psi+X)=0.41+-0.11+-0.08, B(Y(1S)--> chi_c1+X)/B(Y(1S)-->
J/Psi+X)=0.35+-0.08+-0.06, B(Y(1S)--> chi_c2+X)/B(Y(1S)-->
J/Psi+X)=0.52+-0.12+-0.09, and B(Y(1S)--> chi_c0+X)/B(Y(1S)--> J/Psi+X)<7.4% at
90% confidence level. We also report on the momentum and angular spectra of
J/Psi's in Upsilon(1S) decay. The results are compared to predictions of the
color octet and color singlet models.Comment: 27 pages postscript,also available through
http://w4.lns.cornell.edu/public/CLNS/, submitted to PR
Search for X(3872) in gamma gamma Fusion and ISR at CLEO
We report on a search for the recently reported X(3872) state using 15.1
fb^{-1} e+ e- data taken in the \sqrt{s} = 9.46-11.30 GeV region. Separate
searches for the production of X(3872) in untagged gamma-gamma fusion and e+ e-
annihilation following initial state radiation (ISR) are made by taking
advantage of the unique correlation of J/psi -> l+ l- in X(3872) decay to pi+
pi- J/psi. No signals are observed in either case, and 90% confidence upper
limits are established as (2J+1)\Gamma_{\gamma\gamma}B(X -> pi+ pi- J/psi) <
12.9 eV and \Gamma_{ee}B(X -> pi+ pi- J/psi) < 8.3 eV.Comment: 8 pages postscript,also available through
http://www.lns.cornell.edu/public/CLNS/2004/, submitted to PR
The Search for eta(1440) --> K^0_S K^pm \pi^mp in Two-Photon Fusion at CLEO
We analyze 13.8 \rm fb^{-1} of the integrated e^+e^- luminosity collected at
10.6 GeV center-of-mass energy with the CLEO II and CLEO II.V detectors to
study exclusive two-photon production of hadrons with masses below 1.7{\rm \
GeV/c^2} decaying into the K^0_S K^\pm \pi^\mp final state. We observe two
statistically significant enhancements in the \eta(1440) mass region. These
enhancements have large transverse momentum which rules them out as being due
to pseudoscalar resonances but is consistent with the production of
axial-vector mesons. We use tagged two-photon events to study the properties of
the observed enhancements and associate them with the production of f_1(1285)
and f_1(1420). Our non-observation of \eta(1440) is inconsistent by more than
two standard deviations with the first observation of this resonance in
two-photon collisions by the L3 experiment. We present our estimates for 90%
confidence level upper limits on the products of two-photon partial widths of
pseudoscalar hadrons and their branching fractions into
K^0_S(\pi^+\pi^-)K^\pm\pi^\mp.Comment: 24 pages postscript,also available through
http://www.lns.cornell.edu/public/CLNS/2004/, submitted to PR
Study of tau Decays to Four-Hadron Final States with Kaons
The tau decays to four hadrons have been studied with the CLEO III detector
at the Cornell Electron Storage Ring (CESR) using (7.56 +- 0.15) fb^{-1} of
data collected near the Y(4S) resonance. We present the first statistically
significant measurements of B(tau- -> K- pi+pi- pi0 nu, excluding K^0) = (7.4
+- 0.8 +- 1.1) x 10^{-4} and B(tau--> K- K+ pi- pi0 nu) = (5.5 +- 1.4 +- 1.2) x
10^{-5}, including the first observation of the decay, tau- -> K- omega nu,
with branching fraction (4.1 +- 0.6 +- 0.7) x 10^{-4}. We also publish the
first upper limit for B(tau- -> K- K+ K- pi0 nu) < 4.8 (6.1) x 10^{-6} at 90%
(95%) confidence level (C.L.).Comment: 9 pages postscript, also available from
http://www.lns.cornell.edu/public/CLNS/2004/, submitted to PR
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