149 research outputs found
Study of decays to the final state and evidence for the decay
A study of decays is performed for the first time
using data corresponding to an integrated luminosity of 3.0
collected by the LHCb experiment in collisions at centre-of-mass energies
of and TeV. Evidence for the decay
is reported with a significance of 4.0 standard deviations, resulting in the
measurement of
to
be .
Here denotes a branching fraction while and
are the production cross-sections for and mesons.
An indication of weak annihilation is found for the region
, with a significance of
2.4 standard deviations.Comment: All figures and tables, along with any supplementary material and
additional information, are available at
https://lhcbproject.web.cern.ch/lhcbproject/Publications/LHCbProjectPublic/LHCb-PAPER-2016-022.html,
link to supplemental material inserted in the reference
Amplitude analysis of decays
The first full amplitude analysis of with
, decays is performed with a data sample
of 3 fb of collision data collected at and TeV
with the LHCb detector. The data cannot be described by a model that contains
only excited kaon states decaying into , and four
structures are observed, each with significance over standard deviations.
The quantum numbers of these structures are determined with significance of at
least standard deviations. The lightest has mass consistent with, but width
much larger than, previous measurements of the claimed state. The
model includes significant contributions from a number of expected kaon
excitations, including the first observation of the
transition.Comment: 62 pages 26 figure
Measurement of the Z+b-jet cross-section in pp collisions at √s = 7 TeV in the forward region
The associated production of a Z boson or an off-shell photon γ
∗ with a bottom
quark in the forward region is studied using proton-proton collisions at a centre-of-mass energy
of 7 TeV. The Z bosons are reconstructed in the Z/γ∗ → µ
+µ
− final state from muons
with a transverse momentum larger than 20 GeV, while two transverse momentum thresholds
are considered for jets (10 GeV and 20 GeV). Both muons and jets are reconstructed
in the pseudorapidity range 2.0 < η < 4.5. The results are based on data corresponding
to 1.0 fb−1
recorded in 2011 with the LHCb detector. The measurement of the Z+b-jet
cross-section is normalized to the Z+jet cross-section. The measured cross-sections are
σ(Z/γ∗
(µ
+µ
−) + b-jet) = 295 ± 60 (stat) ± 51 (syst) ± 10 (lumi) fb (0.1)
for pT(jet) > 10 GeV, and
σ(Z/γ∗
(µ
+µ
−) + b-jet) = 128 ± 36 (stat) ± 22 (syst) ± 5 (lumi) fb (0.2)
for pT(jet) > 20 GeV
Measurement of the B0s →J/ψη lifetime
Using a data set corresponding to an integrated luminosity of 3 fb−1, collected by the LHCb experiment in pp collisions at centre-of-mass energies of 7 and 8 TeV, the effective lifetime in the Bs0→J/ψη decay mode, τeff, is measured to be
τeff=1.479±0.034 (stat)±0.011 (syst) ps. Assuming CP conservation, τeff corresponds to the lifetime of the light Bs0 mass eigenstate. This is the first measurement of the effective lifetime in this decay mode
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
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
Search for CP violation in Λb0→pK− and Λb0→pπ− decays
A search for CP violation in Λb0→pK− and Λb0→pπ− decays is presented using a sample of pp collisions collected with the LHCb detector and corresponding to an integrated luminosity of 3.0fb−1. The CP -violating asymmetries are measured to be ACPpK−=−0.020±0.013±0.019 and ACPpπ−=−0.035±0.017±0.020, and their difference ACPpK−−ACPpπ−=0.014±0.022±0.010, where the first uncertainties are statistical and the second systematic. These are the most precise measurements of such asymmetries to date
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
Highlights from the LHCb experiment
We report recent results by the LHCb collaboration in heavy-ion collisions in collider and fixed-target mode at the LHC. A large variety of measurements show the potential of LHCb in nuclear collisions
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
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