Monolithic tin oxide aerogels synthesized using the epoxide technique were characterized with X-ray diffraction, diffusive reflectance spectroscopy, infrared spectroscopy, particle induced X-ray ...emission and photoluminescence. Our results indicate that the resulting aerogel is an electrical semi-insulator. This happens due to an incomplete chemical reaction that leaves chloride and hydroxide ions unreacted. These ions form complexes with oxygen vacancy sites producing electron trapping. Furthermore, ions of Cu, Zn and Fe were identified as naturally occurring impurities in the gel matrix, substituting Sn+4 ions.
•High surface area tin oxide aerogel was grown using the epoxide technique.•We study the electronic structure of the material using spectroscopy and photoluminescence.•The absence of electrical conductivity is a consequence of high electron trapping.•Ions of Cu, Fe and Zn were identified by PIXE as naturally occurring impurities.
The prompt production of the charm baryon Λ+c and the Λ+c/D0 production ratios were measured at midrapidity with the ALICE detector in pp and p-Pb collisions at √sNN=5.02 TeV. These new measurements ...show a clear decrease of the Λ+c/D0 ratio with increasing transverse momentum (pT) in both collision systems in the range 2<pT<12 GeV/c, exhibiting similarities with the light-flavor baryon-to-meson ratios p/π and Λ/K0S. At low pT, predictions that include additional color-reconnection mechanisms beyond the leading-color approximation, assume the existence of additional higher-mass charm-baryon states, or include hadronization via coalescence can describe the data, while predictions driven by charm-quark fragmentation processes measured in e+e− and e−p collisions significantly underestimate the data. The results presented in this Letter provide significant evidence that the established assumption of universality (colliding-system independence) of parton-to-hadron fragmentation is not sufficient to describe charm-baryon production in hadronic collisions at LHC energies.
Invariant differential yields of deuterons and antideuterons in pp collisions at s = 0.9, 2.76 and 7 TeV and the yields of tritons, He3 nuclei, and their antinuclei at s = 7 TeV have been measured ...with the ALICE detector at the CERN Large Hadron Collider. The measurements cover a wide transverse momentum (pT) range in the rapidity interval |y|
The azimuthal anisotropy coefficient v2 of prompt D0, D+, D∗+, and Ds+ mesons was measured in midcentral (30%-50% centrality class) Pb-Pb collisions at a center-of-mass energy per nucleon pair ...sNN=5.02 TeV, with the ALICE detector at the LHC. The D mesons were reconstructed via their hadronic decays at midrapidity, |y|
The production of K*(892)0 and φ(1020) mesons in proton-proton (pp) and lead-lead (Pb-Pb) collisions at sNN=2.76TeV has been analyzed using a high luminosity data sample accumulated in 2011 with the ...ALICE detector at the Large Hadron Collider (LHC). The transverse momentum (pT) spectra have been measured for K*(892)0 and φ(1020) mesons via their hadronic decay channels for pT up to 20 GeV/c. The measurements in pp collisions have been compared to model calculations and used to determine the nuclear modification factor and particle ratios. The K*(892)0/K ratio exhibits significant reduction from pp to central Pb-Pb collisions, consistent with the suppression of the K*(892)0 yield at low pT due to rescattering of its decay products in the hadronic phase. In central Pb-Pb collisions the pT dependent φ(1020)/π and K*(892)0/π ratios show an enhancement over pp collisions for pT ≈ 3 GeV/c, consistent with previous observations of strong radial flow. At high pT, particle ratios in Pb-Pb collisions are similar to those measured in pp collisions. In central Pb-Pb collisions, the production of K*(892)0 and φ(1020) mesons is suppressed for pT > 8 GeV/c. This suppression is similar to that of charged pions, kaons, and protons, indicating that the suppression does not depend on particle mass or flavor in the light quark sector.
The production cross section of prompt Λc+ charm baryons was measured with the ALICE detector at the LHC at midrapidity in proton-proton (pp) and proton-lead (p-Pb) collisions at a center-of-mass ...energy per nucleon pair of sNN=5.02TeV. The Λc+ and Λ¯c- baryons were reconstructed in the hadronic decay channels Λc+→pK-π+ and Λc+→pKS0 and respective charge conjugates. The measured differential cross sections as a function of transverse momentum (pT) and the pT-integrated Λc+ production cross section in pp and in p-Pb collisions are presented. The Λc+ nuclear modification factor (RpPb), calculated from the cross sections in pp and in p-Pb collisions, is presented and compared with the RpPb of D mesons. The Λc+/D0 ratio is also presented and compared with the light-flavor baryon-to-meson ratios p/π and Λ/KS0, and measurements from other LHC experiments. The results are compared to predictions from model calculations and Monte Carlo event generators.
The ALICE Collaboration has measured the energy dependence of exclusive photoproduction of
J
/
ψ
vector mesons off proton targets in ultra–peripheral p–Pb collisions at a centre-of-mass energy per ...nucleon pair
s
NN
=
5.02
TeV. The e
+
e
-
and
μ
+
μ
-
decay channels are used to measure the cross section as a function of the rapidity of the
J
/
ψ
in the range
-
2.5
<
y
<
2.7
, corresponding to an energy in the
γ
p centre-of-mass in the interval
40
<
W
γ
p
<
550
GeV. The measurements, which are consistent with a power law dependence of the exclusive
J
/
ψ
photoproduction cross section, are compared to previous results from HERA and the LHC and to several theoretical models. They are found to be compatible with previous measurements.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
In principle, the depth distribution of the different chemical elements near the surface of solids can be determined quantitatively and absolutely with subnanometric depth resolution using medium ...energy ion scattering (MEIS), which is a refined version of Rutherford backscattering spectrometry (RBS). The energy resolution of current MEIS analyzers reveals spectral features that cannot be resolved using conventional RBS detectors. Thus, the usual data analysis framework based on a standard Gaussian approximation for the ion energy distribution in the target is applicable to regular RBS, but not generally to MEIS, in particular if one aims at subnanometric depth resolution. The observed asymmetry in the ion energy loss distributions is a direct consequence of the asymmetric character of inelastic energy transfers during individual atomic collisions and of the stochastic character of the resulting energy losses. We propose a model that accounts for the proper statistics of the small energy loss events and for an approximate electronic energy loss distribution during the backscattering event. The validity of this model is discussed and applied to the determination of HfO
2 and TiO
2 film thicknesses as well as to detect Al
2O
3 and HfO
2 intermixing. This final application case also illustrates the potentialities as well as some inherent limitations of MEIS. The model developed here has been made available to the public in the form of a software for MEIS data analysis.
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