A
bstract
The decay
$ B_c^{+}\to {J \left/ {{\psi {K^{+}}} \right.} $
is observed for the first time using a data sample, corresponding to an integrated luminosity of 1.0 fb
−1
, collected by the ...LHCb experiment in
pp
collisions at a centre-of-mass energy of 7 TeV. A yield of 46 ± 12 events is reported, with a significance of 5.0 standard deviations. The ratio of the branching fraction of
$ B_c^{+}\to {J \left/ {{\psi {K^{+}}} \right.} $
to that of
$ B_c^{+}\to {J \left/ {{\psi {\pi^{+}}} \right.} $
is measured to be 0.069 ± 0.019 ± 0.005, where the first uncertainty is statistical and the second is systematic.
A test of lepton universality, performed by measuring the ratio of the branching fractions of the $B^0 → K^{*0}μ^+μ^-$ and $B^0$ → $K^{*0}e^+e^-$ decays, $R_{K^{*0}}$, is presented. The $K^{*0}$ ...meson is reconstructed in the final state $K^+π^-$, which is required to have an invariant mass within 100 MeV/c2 of the known $K^*$ (892)0 mass. The analysis is performed using proton-proton collision data, corresponding to an integrated luminosity of about 3 fb-1, collected by the LHCb experiment at centre-of-mass energies of 7 and 8 TeV. The ratio is measured in two regions of the dilepton invariant mass squared, q2, to be R K ∗ 0 = { 0.66 − + 0.07 0.11 ( s t a t ) ± 0.03 ( s y s t ) f o r 0.045 < q 2 < 1.1 G e V 2 / c 4 , 0.69 − + 0.07 0.11 ( s t a t ) ± 0.05 ( s y s t ) f o r 1.1 < q 2 < 6.0 G e V 2 / c 4 . The corresponding 95.4% confidence level intervals are 0.52, 0.89 and 0.53, 0.94. The results, which represent the most precise measurements of $R_{K^{*0}}$ to date, are compatible with the Standard Model expectations at the level of 2.1–2.3 and 2.4–2.5 standard deviations in the two q2 regions, respectively.
A
bstract
Measurements of inclusive
W
and
Z
boson production cross-sections in
pp
collisions at
$ \sqrt {s} = 7\,{\text{TeV}} $
using final states containing muons are presented. The data sample ...corresponds to an integrated luminosity of 37 pb
−1
collected with the LHCb detector. The
W
and
Z
bosons are reconstructed from muons with a transverse momentum above 20 GeV/c and pseudorapidity between 2
.
0 and 4
.
5, and, in the case of the
Z
cross-section, a dimuon invariant mass between 60 and 120 GeV/c
2
. The cross-sections are measured to be 831 ± 9 ± 27 ± 29pb for
W
+
, 656 ± 8 ± 19 ± 23 for
W
−
and 76
.
7 ± 1
.
7 ± 3
.
3 ± 2
.
7pb for
Z
, where the first uncertainty is statistical, the second is systematic and the third is due to the luminosity. Differential cross-sections,
W
and
Z
cross-section ratios and the lepton charge asymmetry are also measured in the same kinematic region. The ratios are determined to be
$ {\sigma_{{{W^{ + }} \to {\mu^{ + }}\nu }}}/{\sigma_{{{W^{ - }} \to {\mu^{ - }}\overline \nu }}} = 1.27\pm 0.02\pm 0.01 $
and
$ \left( {{\sigma_{{{W^{ + }} \to {\mu^{ + }}\nu }}} + {\sigma_{{{W^{ - }} \to {\mu^{ - }}\overline \nu }}} \right)/{\sigma_{{Z \to \mu \mu }}} = 19.4\pm 0.5\pm 0.9 $
. The results are in general agreement with theoretical predictions, performed at next-to-next-to-leading order in QCD using recently calculated parton distribution functions.
A
bstract
The isospin asymmetries of
B
→
Kμ
+
μ
−
and
B
→
K
*
μ
+
μ
−
decays and the partial branching fractions of the
B
0
→
K
0
μ
+
μ
−
,
B
+
→
K
+
μ
+
μ
−
and
B
+
→
K
*+
μ
+
μ
−
decays are ...measured as functions of the dimuon mass squared,
q
2
. The data used correspond to an integrated luminosity of 3 fb
−1
from proton-proton collisions collected with the LHCb detector at centre-of-mass energies of 7 TeV and 8 TeV in 2011 and 2012, respectively. The isospin asymmetries are both consistent with the Standard Model expectations. The three measured branching fractions favour lower values than their respective theoretical predictions, however they are all individually consistent with the Standard Model.
A
bstract
Production cross-sections of prompt charm mesons are measured with the first data from
pp
collisions at the LHC at a centre-of-mass energy of 13 TeV. The data sample corresponds to an ...integrated luminosity of 4.98 ± 0.19 pb
−1
collected by the LHCb experiment. The production cross-sections of
D
0
,
D
+
,
D
s
+
, and
D
*+
mesons are measured in bins of charm meson transverse momentum,
p
T
, and rapidity,
y
, and cover the range 0 <
p
T
< 15GeV/c and 2.0 <
y
< 4.5. The inclusive cross-sections for the four mesons, including charge conjugation, within the range of 1 <
p
T
< 8 GeV/c are found to be
σ
pp
→
D
0
X
=
2460
±
3
±
130
μ
b
σ
pp
→
D
+
X
=
1000
±
3
±
110
μ
b
σ
pp
→
D
s
+
X
=
460
±
13
±
100
μ
b
σ
pp
→
D
∗
+
X
=
880
±
5
±
140
μ
b
where the uncertainties are due to statistical and systematic uncertainties, respectively.
In the Standard Model of particle physics, the strength of the couplings of the b quark to the u and c quarks, |Vub| and |Vcb|, are governed by the coupling of the quarks to the Higgs boson. Using ...data from the LHCb experiment at the Large Hadron Collider, the probability for the Λb0 baryon to decay into the p final state relative to the final state is measured. Combined with theoretical calculations of the strong interaction and a previously measured value of |Vcb|, the first |Vub| measurement to use a baryonic decay is performed. This measurement is consistent with previous determinations of |Vub| using B meson decays to specific final states and confirms the existing incompatibility with those using an inclusive sample of final states.
Two-particle angular correlations are studied in proton-lead collisions at a nucleon–nucleon centre-of-mass energy of sNN=5 TeV, collected with the LHCb detector at the LHC. The analysis is based on ...data recorded in two beam configurations, in which either the direction of the proton or that of the lead ion is analysed. The correlations are measured in the laboratory system as a function of relative pseudorapidity, Δη, and relative azimuthal angle, Δϕ, for events in different classes of event activity and for different bins of particle transverse momentum. In high-activity events a long-range correlation on the near side, Δϕ≈0, is observed in the pseudorapidity range 2.0<η<4.9. This measurement of long-range correlations on the near side in proton-lead collisions extends previous observations into the forward region up to η=4.9. The correlation increases with growing event activity and is found to be more pronounced in the direction of the lead beam. However, the correlation in the direction of the lead and proton beams are found to be compatible when comparing events with similar absolute activity in the direction analysed.
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