1,651 research outputs found
Stability of the In-Plane Room Temperature van der Waals Ferromagnet Chromium Ditelluride and Its Conversion to Chromium-Interleaved CrTe Compounds
Van der Waals magnetic materials are building blocks for novel kinds of
spintronic devices and playgrounds for exploring collective magnetic phenomena
down to the two-dimensional limit. Chromium-tellurium compounds are relevant in
this perspective. In particular, the 1 phase of CrTe has been argued to
have a Curie temperature above 300~K, a rare and desirable property in the
class of lamellar materials, making it a candidate for practical applications.
However, recent literature reveals a strong variability in the reported
properties, including magnetic ones. Using electron microscopy, diffraction and
spectroscopy techniques, together with local and macroscopic magnetometry
approaches, our work sheds new light on the structural, chemical and magnetic
properties of bulk 1-CrTe exfoliated in the form of flakes having a
thickness ranging from few to several tens of nanometers. We unambiguously
establish that 1-CrTe flakes are ferromagnetic above room temperature,
have an in-plane easy axis of magnetization, low coercivity, and we confirm
that their Raman spectroscopy signatures are two modes,
(103.5~cm) and (136.5~cm). We also prove that
thermal annealing causes a phase transformation to monoclinic CrTe and,
to a lesser extent, to trigonal CrTe. In sharp contrast with
1-CrTe, none of these compounds have a Curie temperature above room
temperature, and they both have perpendicular magnetic anisotropy. Our findings
reconcile the apparently conflicting reports in the literature and open
opportunities for phase-engineered magnetic properties
Observation of an Excited Bc+ State
Using pp collision data corresponding to an integrated luminosity of 8.5 fb-1 recorded by the LHCb experiment at center-of-mass energies of s=7, 8, and 13 TeV, the observation of an excited Bc+ state in the Bc+π+π- invariant-mass spectrum is reported. The observed peak has a mass of 6841.2±0.6(stat)±0.1(syst)±0.8(Bc+) MeV/c2, where the last uncertainty is due to the limited knowledge of the Bc+ mass. It is consistent with expectations of the Bc∗(2S31)+ state reconstructed without the low-energy photon from the Bc∗(1S31)+→Bc+γ decay following Bc∗(2S31)+→Bc∗(1S31)+π+π-. A second state is seen with a global (local) statistical significance of 2.2σ (3.2σ) and a mass of 6872.1±1.3(stat)±0.1(syst)±0.8(Bc+) MeV/c2, and is consistent with the Bc(2S10)+ state. These mass measurements are the most precise to date
A mesophilic anaerobic digester for treating food waste: process stability and microbial community analysis using pyrosequencing
Measurement of b hadron fractions in 13 TeV pp collisions
The production fractions of
¯
B
0
s
and
Λ
0
b
hadrons, normalized to the sum of
B
−
and
¯
B
0
fractions, are measured in 13 TeV
p
p
collisions using data collected by the LHCb experiment, corresponding to an integrated luminosity of
1.67
fb
−
1
. These ratios, averaged over the
b
hadron transverse momenta from 4 to 25 GeV and pseudorapidity from 2 to 5, are
0.122
±
0.006
for
¯
B
0
s
, and
0.259
±
0.018
for
Λ
0
b
, where the uncertainties arise from both statistical and systematic sources. The
Λ
0
b
ratio depends strongly on transverse momentum, while the
¯
B
0
s
ratio shows a mild dependence. Neither ratio shows variations with pseudorapidity. The measurements are made using semileptonic decays to minimize theoretical uncertainties. In addition, the ratio of
D
+
to
D
0
mesons produced in the sum of
¯
B
0
and
B
−
semileptonic decays is determined as
0.359
±
0.006
±
0.009
, where the uncertainties are statistical and systematic
Observation of B(s)0→J/ψpp¯ decays and precision measurements of the B(s)0 masses
The first observation of the decays
B
0
(
s
)
→
J
/
ψ
p
¯
p
is reported, using proton-proton collision data corresponding to an integrated luminosity of
5.2
fb
−
1
, collected with the LHCb detector. These decays are suppressed due to limited available phase space, as well as due to Okubo-Zweig-Iizuka or Cabibbo suppression. The measured branching fractions are
B
(
B
0
→
J
/
ψ
p
¯
p
)
=
[
4.51
±
0.40
(
stat
)
±
0.44
(
syst
)
]
×
10
−
7
,
B
(
B
0
s
→
J
/
ψ
p
¯
p
)
=
[
3.58
±
0.19
(
stat
)
±
0.39
(
syst
)
]
×
10
−
6
. For the
B
0
s
meson, the result is much higher than the expected value of
O
(
10
−
9
)
. The small available phase space in these decays also allows for the most precise single measurement of both the
B
0
mass as
5279.74
±
0.30
(
stat
)
±
0.10
(
syst
)
MeV
and the
B
0
s
mass as
5366.85
±
0.19
(
stat
)
±
0.13
(
syst
)
MeV
Measurement of the Charm-Mixing Parameter yCP
A measurement of the charm-mixing parameter y_{CP} using D^{0}→K^{+}K^{-}, D^{0}→π^{+}π^{-}, and D^{0}→K^{-}π^{+} decays is reported. The D^{0} mesons are required to originate from semimuonic decays of B^{-} and B[over ¯]^{0} mesons. These decays are partially reconstructed in a data set of proton-proton collisions at center-of-mass energies of 7 and 8 TeV collected with the LHCb experiment and corresponding to an integrated luminosity of 3 fb^{-1}. The y_{CP} parameter is measured to be (0.57±0.13(stat)±0.09(syst))%, in agreement with, and as precise as, the current world-average value
Search for violation through an amplitude analysis of decays
International audienceA search for CP violation in the Cabibbo-suppressed D → KKππ decay mode is performed using an amplitude analysis. The measurement uses a sample of pp collisions recorded by the LHCb experiment during 2011 and 2012, corresponding to an integrated luminosity of 3.0 fb. The D mesons are reconstructed from semileptonic b-hadron decays into DμX final states. The selected sample contains more than 160 000 signal decays, allowing the most precise amplitude modelling of this D decay to date. The obtained amplitude model is used to perform the search for CP violation. The result is compatible with CP symmetry, with a sensitivity ranging from 1% to 15% depending on the amplitude considered
Observation of the decay Λ <sub>b</sub> <sup>0</sup> → ψ(2S)pπ<sup>−</sup>
International audienceThe Cabibbo-suppressed decay Λ → ψ(2S)pπ is observed for the first time using a data sample collected by the LHCb experiment in proton-proton collisions corresponding to 1.0, 2.0 and 1.9 fb of integrated luminosity at centre-of-mass energies of 7, 8 and 13 TeV, respectively. The ψ(2S) mesons are reconstructed in the μμ final state. The branching fraction with respect to that of the Λ → ψ(2S)pK decay mode is measured to b
Search for CP Violation in D-s(+) -> K-S(0)pi(+), D+ -> (KSK+)-K-0, and D+ -> phi pi(+) Decays
A search for charge-parity () violation in Cabibbo-suppressed , and decays is reported
using proton-proton collision data, corresponding to an integrated luminosity
of 3.8 fb, collected at a center-of-mass energy of 13 TeV with the LHCb
detector. High-yield samples of kinematically and topologically similar
Cabibbo-favored decays are analyzed to subtract nuisance
asymmetries due to production and detection effects, including those induced by
violation in the neutral kaon system. The results are \begin{align*}
\mathcal{A}_{CP}(D_s^+\to K_S^0 \pi^+)
&=\left(\phantom{-}1.3\phantom{0}\pm1.9\phantom{0}\pm0.5\phantom{0}\right)\times10^{-3},\\
\mathcal{A}_{CP}(D^+\to K_S^0 K^+)
&=\left(-0.09\pm0.65\pm0.48\right)\times10^{-3},\\ \mathcal{A}_{CP}(D^+\to \phi
\pi^+) &=\left(\phantom{-}0.05\pm0.42\pm0.29\right)\times10^{-3}, \end{align*}
where the first uncertainties are statistical and the second systematic. They
are the most precise measurements of these quantities to date, and are
consistent with symmetry.Comment: All figures and tables, along with any supplementary material and
additional information, are available at
https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2019-002.htm
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