1,071 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+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
Measurement of the branching fraction and CP asymmetry in B plus . J/.. plus decays
The branching fraction and direct asymmetry of the decay
are measured using proton-proton collision
data collected with the LHCb detector at centre-of-mass energies of 7 and 8
TeV, corresponding to a total integrated luminosity of 3\mbox{fb}^{-1}. The
following results are obtained: \begin{align} \mathcal{B}(B^{+}\rightarrow
J/\psi \rho^{+}) &= (3.81 ^{+0.25}_{-0.24} \pm 0.35) \times 10^{-5}, \nonumber
\\ \mathcal{A}^{C\!P} (B^{+}\rightarrow J/\psi \rho^{+}) &=
-0.045^{+0.056}_{-0.057} \pm 0.008, \nonumber \end{align} where the first
uncertainties are statistical and the second systematic. Both measurements are
the most precise to date.Comment: All figures and tables, along with any supplementary material and
additional information, are available at
https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2018-036.htm
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 CP Violation in Charm Decays
A search for charge-parity (CP) violation in D-0 -> K-K+ and D-0 -> pi(-)pi(+) decays is reported, using pp collision data corresponding to an integrated luminosity of 5.9 fb(-1) collected at a center-of-mass energy of 13 TeV with the LHCb detector. The flavor of the charm meson is inferred from the charge of the pion in D* (2010)(+) -> D-0 pi(+) decays or from the charge of the muon in (B) over bar -> D-0 mu(-)(nu) over bar X-mu decays. The difference between the CP asymmetries in D-0 -> K-K+ and D-0 -> pi(-)pi(+) decays is measured to be Delta A(CP) = [-18.2 +/- 3.2(stat) +/- 0.9(syst)] x 10(-4) for pi-tagged and Delta A(CP) = [-9 +/- 8(stat) +/- 5(syst)] x 10(-4) for mu-tagged D-0 mesons. Combining these with previous LHCb results leads to Delta A(CP) = (-15.4 +/- 2.9) x 10(-4), where the uncertainty includes both statistical and systematic contributions. The measured value differs from zero by more than 5 standard deviations. This is the first observation of CP violation in the decay of charm hadrons
Measurement of B+, B0 and Λb0 production in pPb collisions at √sNN=8.16 TeV
The production of
B
+
,
B
0
and
Λ
0
b
hadrons is studied in proton-lead collisions at a center-of-mass energy per nucleon pair of
√
s
NN
=
8.16
TeV
recorded with the LHCb detector at the LHC. The measurement uses a dataset corresponding to an integrated luminosity of
12.2
±
0.3
nb
−
1
for the case where the proton beam is projected into the LHCb detector (corresponding to measuring hadron production at positive rapidity) and
18.6
±
0.5
nb
−
1
for the lead beam projected into the LHCb detector (corresponding to measuring hadron production at negative rapidity). Double-differential cross sections are measured and used to determine forward-backward ratios and nuclear modification factors, which directly probe nuclear effects in the production of beauty hadrons. The double-differential cross sections are measured as a function of the beauty-hadron transverse momentum and rapidity in the nucleon-nucleon center-of-mass frame. Forward-to-backward cross section ratios and nuclear modification factors indicate a significant nuclear suppression at positive rapidity. The ratio of
Λ
0
b
over
B
0
production cross sections is reported and is consistent with the corresponding measurement in
p
p
collisions
Observation of the Decay Λ0b→Λ+cτ−¯ν
The first observation of the semileptonic b-baryon decay Λb0→Λc+τ-ν¯τ, with a significance of 6.1σ, is reported using a data sample corresponding to 3 fb-1 of integrated luminosity, collected by the LHCb experiment at center-of-mass energies of 7 and 8 TeV at the LHC. The τ- lepton is reconstructed in the hadronic decay to three charged pions. The ratio K=B(Λb0→Λc+τ-ν¯τ)/B(Λb0→Λc+π-π+π-) is measured to be 2.46±0.27±0.40, where the first uncertainty is statistical and the second systematic. The branching fraction B(Λb0→Λc+τ-ν¯τ)=(1.50±0.16±0.25±0.23)% is obtained, where the third uncertainty is from the external branching fraction of the normalization channel Λb0→Λc+π-π+π-. The ratio of semileptonic branching fractions R(Λc+)B(Λb0→Λc+τ-ν¯τ)/B(Λb0→Λc+μ-ν¯μ) is derived to be 0.242±0.026±0.040±0.059, where the external branching fraction uncertainty from the channel Λb0→Λc+μ-ν¯μ contributes to the last term. This result is in agreement with the standard model prediction
Measurement of CP -violating and mixing-induced observables in Bs0→ϕγ decays
A time-dependent analysis of the
B
0
s
→
ϕ
γ
decay rate is performed to determine the
C
P
-violating observables
S
ϕ
γ
and
C
ϕ
γ
and the mixing-induced observable
A
Δ
ϕ
γ
. The measurement is based on a sample of
p
p
collision data recorded with the LHCb detector, corresponding to an integrated luminosity of
3
fb
−
1
at center-of-mass energies of 7 and 8 TeV. The measured values are
S
ϕ
γ
=
0.43
±
0.30
±
0.11
,
C
ϕ
γ
=
0.11
±
0.29
±
0.11
, and
A
Δ
ϕ
γ
=
−
0.67
+
0.37
−
0.41
±
0.17
, where the first uncertainty is statistical and the second systematic. This is the first measurement of the observables
S
and
C
in radiative
B
0
s
decays. The results are consistent with the standard model predictions
Measurement of the mass and production rate of Ξb− baryons
The first measurement of the production rate of
Ξ
−
b
baryons in
p
p
collisions relative to that of
Λ
0
b
baryons is reported, using data samples collected by the LHCb experiment, and corresponding to integrated luminosities of 1, 2 and
1.6
fb
−
1
at
√
s
=
7
, 8 and 13 TeV, respectively. In the kinematic region
2
<
η
<
6
and
p
T
<
20
GeV
/
c
, we measure
f
Ξ
−
b
f
Λ
0
b
B
(
Ξ
−
b
→
J
/
ψ
Ξ
−
)
B
(
Λ
0
b
→
J
/
ψ
Λ
)
=
(
10.8
±
0.9
±
0.8
)
×
10
−
2
[
√
s
=
7
,
8
TeV
],
f
Ξ
−
b
f
Λ
0
b
B
(
Ξ
−
b
→
J
/
ψ
Ξ
−
)
B
(
Λ
0
b
→
J
/
ψ
Λ
)
=
(
13.1
±
1.1
±
1.0
)
×
10
−
2
[
√
s
=
13
TeV
], where
f
Ξ
−
b
and
f
Λ
0
b
are the fragmentation fractions of
b
quarks into
Ξ
−
b
and
Λ
0
b
baryons, respectively;
B
represents branching fractions; and the uncertainties are due to statistical and experimental systematic sources. The values of
f
Ξ
−
b
/
f
Λ
0
b
are obtained by invoking SU(3) symmetry in the
Ξ
−
b
→
J
/
ψ
Ξ
−
and
Λ
0
b
→
J
/
ψ
Λ
decays. Production asymmetries between
Ξ
−
b
and
¯
Ξ
+
b
baryons are also reported. The mass of the
Ξ
−
b
baryon is also measured relative to that of the
Λ
0
b
baryon, from which it is found that
m
(
Ξ
−
b
)
=
5796.70
±
0.39
±
0.15
±
0.17
MeV
/
c
2
, where the last uncertainty is due to the precision on the known
Λ
0
b
mass. This result represents the most precise determination of the
Ξ
−
b
mass
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