1,321 research outputs found
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+Ï+Ï- 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 Bcâ(2S31)+ state reconstructed without the low-energy photon from the Bcâ(1S31)+âBc+Îł decay following Bcâ(2S31)+âBcâ(1S31)+Ï+Ï-. A second state is seen with a global (local) statistical significance of 2.2Ï (3.2Ï) 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
Measurement of b hadron fractions in 13 TeV pp collisions
The production fractions of
ÂŻ
B
0
s
and
Î
0
b
hadrons, normalized to the sum of
B
â
and
ÂŻ
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
â
â
fb
â
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
ÂŻ
B
0
s
, and
0.259
±
0.018
for
Î
0
b
, where the uncertainties arise from both statistical and systematic sources. The
Î
0
b
ratio depends strongly on transverse momentum, while the
ÂŻ
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
ÂŻ
B
0
and
B
â
semileptonic decays is determined as
0.359
±
0.006
±
0.009
, where the uncertainties are statistical and systematic
Observation of B(s)0âJ/ÏppÂŻ decays and precision measurements of the B(s)0 masses
The first observation of the decays
B
0
(
s
)
â
J
/
Ï
p
ÂŻ
p
is reported, using proton-proton collision data corresponding to an integrated luminosity of
5.2
â
â
fb
â
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
â
J
/
Ï
p
ÂŻ
p
)
=
[
4.51
±
0.40
(
stat
)
±
0.44
(
syst
)
]
Ă
10
â
7
,
B
(
B
0
s
â
J
/
Ï
p
ÂŻ
p
)
=
[
3.58
±
0.19
(
stat
)
±
0.39
(
syst
)
]
Ă
10
â
6
. For the
B
0
s
meson, the result is much higher than the expected value of
O
(
10
â
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
)
â
â
MeV
and the
B
0
s
mass as
5366.85
±
0.19
(
stat
)
±
0.13
(
syst
)
â
â
MeV
Measurement of the Charm-Mixing Parameter yCP
A measurement of the charm-mixing parameter y_{CP} using D^{0}âK^{+}K^{-}, D^{0}âÏ^{+}Ï^{-}, and D^{0}âK^{-}Ï^{+} decays is reported. The D^{0} mesons are required to originate from semimuonic decays of B^{-} and B[over ÂŻ]^{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 3ââfb^{-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 â KKÏÏ 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 DÎŒX 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
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
Measurement of fs /fu Variation with Proton-Proton Collision Energy and B -Meson Kinematics
The ratio of the Bs0 and B+ fragmentation fractions fs and fu is studied with Bs0âJ/ÏÏ and B+âJ/ÏK+ decays using data collected by the LHCb experiment in proton-proton collisions at 7, 8, and 13 TeV center-of-mass energies. The analysis is performed in bins of B-meson momentum, longitudinal momentum, transverse momentum, pseudorapidity, and rapidity. The fragmentation-fraction ratio fs/fu is observed to depend on the B-meson transverse momentum with a significance of 6.0Ï. This dependency is driven by the 13 TeV sample (8.7Ï), while the results for the other collision energies are not significant when considered separately. Furthermore, the results show a 4.8Ï evidence for an increase of fs/fu as a function of collision energy
Observation of a narrow pentaquark state, P-c(4312)(+), and of the two-peak structure of the P-c(4450)(+)
A narrow pentaquark state, P-c(4312)(+), decaying to J/psi p, is discovered with a statistical significance of 7.3 sigma in a data sample of Lambda(0)(b) -> J/psi pK(-) decays, which is an order of magnitude larger than that previously analyzed by the LHCb Collaboration. The P-c(4450)(+) pentaquark structure formerly reported by LHCb is confirmed and observed to consist of two narrow overlapping peaks, P-c(4440)(+) and P-c(4457)(+), where the statistical significance of this two-peak interpretation is 5.4 sigma. The proximity of the Sigma(+)(c)(D) over bar (0) and Sigma(+)(c)(D) over bar (*0) thresholds to the observed narrow peaks suggests that they play an important role in the dynamics of these states
Study of the decay with an amplitude analysis of decays
International audienceAn amplitude analysis of B â (ÏÏ)(KÏ) decays is performed in the two-body invariant mass regions 300 < m(ÏÏ) < 1100 MeV/c, accounting for the Ï, Ï, f(500), f(980) and f(1370) resonances, and 750 < m(KÏ) < 1200 MeV/c, which is dominated by the K(892) meson. The analysis uses 3 fb of proton-proton collision data collected by the LHCb experiment at centre-of-mass energies of 7 and 8 TeV. The CP averages and asymmetries are measured for the magnitudes and phase differences of the con- tributing amplitudes. The CP-averaged longitudinal polarisation fractions of the vector-vector modes are found to be = 0.164 ± 0.015 ± 0.022 and = 0.68 ± 0.17 ± 0.16, and their CP asymmetries, = â0.62 ± 0.09 ± 0.09 and = â0.13 ± 0.27 ± 0.13, where the first uncertainty is statistical and the second systematic
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