945 research outputs found
Intermixing at the heterointerface between ZnS Zn S,O bilayer buffer and CuInS2 thin film solar cell absorber
The application of Zn compounds as buffer layers was recently extended to wide gap CuInS2 CIS based thin film solar cells. Using a new chemical deposition route for the buffer preparation aiming at the deposition of a single layer, nominal ZnS buffer without the need for any toxic reactants such as, e.g. hydrazine has helped to achieve a similar efficiency as respective CdS buffered reference devices. After identifying the deposited Zn compound, as ZnS Zn S,O bi layer buffer in former investigations [M. Bär, A. Ennaoui, J. Klaer, T. Kropp, R. S ez Araoz, N. Allsop, I. Lauermann, H. W. Schock, and M.C. Lux Steiner, Formation of a ZnS Zn S,O bilayer buffer on CuInS2 thin film solar cell absorbers by chemical bath deposition , J. Appl. Phys., accepted.], this time the focus lies on potential diffusion intermixing processes at the buffer absorber interface possibly, clarifying the effect of the heat treatment, which drastically enhances the device performance of respective final solar cells. The interface formation was investigated by x ray photoelectron and x ray excited Auger electron spectroscopy. In addition, photoelectron spectroscopy PES measurements were also conducted using tuneable monochromatized synchrotron radiation in order to gain depth resolved information. The buffer side of the buffer absorber heterointerface were investigated by means of the characterization of Zn S,O ZnS CIS structures where the ZnS Zn S,O bi layer buffer was deposited successively by different deposition times. In order to make the in terms of PES information depth deeply buried absorber side of the buffer absorber heterointerface accessible for characterization, in these cases the buffer layer was etched away by dilute HClaq. We found that while out leached Cu from the absorber layer forms together with the educts in the chemical bath a Zn 1 Z ,Cu2Z S like interlayer between buffer and absorber, Zn is incorporated in the uppermost region of the absorber. Both effects are strongly enhanced by postannealing the Zn S,O ZnS CIS samples. However, it was determined that the major fraction of the Cu and Zn can be found quite close to the heterointerface in the buffer and absorber layer, respectively. Due to this limited in the range of one monolayer spatial extent, these diffusion mechanisms were rather interpreted as a CBD induced and heat treatment promoted Cu Zn ion exchange at the buffer absorber interface. Possible impacts of this intermixing on the performance of the final solar cell devices will also be discusse
Measurement of the semileptonic charge asymmetry in B0 meson mixing with the D0 detector
We present a measurement of the semileptonic mixing asymmetry for B0 mesons,
a^d_{sl}, using two independent decay channels: B0 -> mu+D-X, with D- ->
K+pi-pi-; and B0 -> mu+D*-X, with D*- -> antiD0 pi-, antiD0 -> K+pi- (and
charge conjugate processes). We use a data sample corresponding to 10.4 fb^{-1}
of ppbar collisions at sqrt(s) = 1.96 TeV, collected with the D0 experiment at
the Fermilab Tevatron collider. We extract the charge asymmetries in these two
channels as a function of the visible proper decay length (VPDL) of the B0
meson, correct for detector-related asymmetries using data-driven methods, and
account for dilution from charge-symmetric processes using Monte Carlo
simulation. The final measurement combines four signal VPDL regions for each
channel, yielding a^d_{sl} = [0.68 \pm 0.45 \text{(stat.)} \pm 0.14
\text{(syst.)}]%. This is the single most precise measurement of this
parameter, with uncertainties smaller than the current world average of B
factory measurements.Comment: Version includes minor textual changes following peer review by
journal, most notably the updating of Ref. [21] to reflect the most recent
publicatio
Measurement of Leptonic Asymmetries and Top Quark Polarization in ttbar Production
We present measurements of lepton (l) angular distributions in ttbar -> W+ b
W- b -> l+ nu b l- nubar bbar decays produced in ppbar collisions at a
center-of-mass energy of sqrt(s)=1.96TeV, where l is an electron or muon. Using
data corresponding to an integrated luminosity of 5.4fb^-1, collected with the
D0 detector at the Fermilab Collider, we find that the angular distributions of
l- relative to anti-protons and l+ relative to protons are in agreement with
each other. Combining the two distributions and correcting for detector
acceptance we obtain the forward-backward asymmetry A^l_FB = (5.8 +- 5.1(stat)
+- 1.3(syst))%, compared to the standard model prediction of A^l_FB (predicted)
= (4.7 +- 0.1)%. This result is further combined with the measurement based on
the analysis of the l+jets final state to obtain A^l_FB = (11.8 +- 3.2)%.
Furthermore, we present a first study of the top-quark polarization.Comment: submitted versio
Search for Decay
We have searched for the charmless hadronic decay of B0 mesons into two
neutral pions. Using 9.13fb^-1 taken at the Upsilon(4S) with the CLEO detector,
we obtain an improved upper limit for the branching fraction BR(B0-->pi0pi0) <
5.7*10^-6 at the 90% confidence level.Comment: pages postscript, also available through
http://w4.lns.cornell.edu/public/CLN
Search for Zgamma events with large missing transverse energy in ppbar collisions at sqrt(s)=1.96 TeV
We present the first search for supersymmetry (SUSY) in Zgamma final states
with large missing transverse energy using data corresponding to an integrated
luminosity of 6.2 fb-1 collected with the D0 experiment in ppbar collisions at
sqrt(s)=1.96 TeV. This signature is predicted in gauge-mediated SUSY-breaking
models, where the lightest neutralino is the next-to-lightest supersymmetric
particle (NLSP) and is produced in pairs, possibly through decay from heavier
supersymmetric particles. The NLSP can decay either to a Z boson or a photon
and an associated gravitino that escapes detection. We exclude this model at
the 95% C.L. for SUSY breaking scales of Lambda < 87 TeV, corresponding to
neutralino masses of < 151 GeV.Comment: submitted to Phys. Rev. Let
Search for associated production in collisions at
This report describes a search for associated production of and Higgs
bosons based on data corresponding to an integrated luminosity of collected with the D0 detector at the Fermilab
Tevatron Collider. Events containing a
candidate (with corresponding to or ) are selected in
association with two or three reconstructed jets. One or two of the jets are
required to be consistent with having evolved from a quark. A multivariate
discriminant technique is used to improve the separation of signal and
backgrounds. Expected and observed upper limits are obtained for the product of
the production cross section and branching ratios and reported in terms of
ratios relative to the prediction of the standard model as a function of the
mass of the Higgs boson (). The observed and expected 95% C.L. upper
limits obtained for an assumed are, respectively, factors
of 4.5 and 4.8 larger than the value predicted by the standard model.Comment: 25 pages, 14 figure
Measurement of the semileptonic charge asymmetry using Bs^0 -> D_s mu X decays
We present a measurement of the time-integrated flavor-specific semileptonic
charge asymmetry in the decays of Bs mesons that have undergone flavor mixing,
a^s_ls, using B_s^0 (barB_s^0) -> D_s^-/+ mu^+/- X decays, with D_s^-/+ -> phi
pi^-/+ and phi K^+ K^-, using 10.4 fb^-1 of proton-antiproton collisions
collected by the D0 detector during Run II at the Fermilab Tevatron Collider. A
fit to the difference between the time-integrated D_s^-$ and D_s^+ mass
distributions of the B_s^0 and barB^0_s candidates yields the flavor-specific
asymmetry a^s_ls = [-1.12 pm 0.74 (stat) +/-0.17 (syst)]% which is the most
precise measurement and in agreement with the standard model prediction.Comment: 7 pages, 3 figures (updated with changes made in journal review
process
A search for charged massive long-lived particles
We report on a search for charged massive long-lived particles (CMLLPs),
based on 5.2 fb of integrated luminosity collected with the D0 detector
at the Fermilab Tevatron collider. We search for events in which one
or more particles are reconstructed as muons but have speed and ionization
energy loss inconsistent with muons produced in beam collisions.
CMLLPs are predicted in several theories of physics beyond the standard model.
We exclude pair-produced long-lived gaugino-like charginos below 267 GeV and
higgsino-like charginos below 217 GeV at 95% C.L., as well as long-lived scalar
top quarks with mass below 285 GeV.Comment: submitted to Phys. Rev. Letter
Measurements of single top quark production cross sections and |Vtb| in ppbar collisions at sqrt{s}=1.96 TeV
We present measurements of production cross sections of single top quarks in
\ppbar collisions at in a data sample corresponding
to an integrated luminosity of collected by the D0 detector
at the Fermilab Tevatron Collider. We select events with an isolated electron
or muon, an imbalance in transverse energy, and two, three, or four jets, with
one or two of them containing a bottom hadron. We obtain an inclusive cross
section of \sigma({\ppbar}{\rargap}tb+X, tqb+X) = 3.43\pm^{0.73}_{0.74}\;\rm
pb and use it to extract the CKM matrix element at
the 95% C.L. We also measure \sigma({\ppbar}{\rargap}tb+X) =
0.68\pm^{0.38}_{0.35}\;\rm pb and \sigma({\ppbar}{\rargap}tqb+X) =
2.86\pm^{0.69}_{0.63}\;\rm pb when assuming, respectively, and
production rates as predicted by the standard model.Comment: 11 pages, 8 figures, submitted to Phys. Rev.
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