A
bstract
A measurement of the cross-section for
W
→
eν
production in
pp
collisions is presented using data corresponding to an integrated luminosity of 2 fb
−1
collected by the LHCb experiment at a ...centre-of-mass energy of
s
=
8
TeV. The electrons are required to have more than 20 GeV of transverse momentum and to lie between 2
.
00 and 4
.
25 in pseudorapidity. The inclusive
W
production cross-sections, where the
W
decays to
eν
, are measured to be
σ
W
+
→
e
+
ν
e
=
1124.4
±
2.1
±
21.5
±
11.2
±
13.0
p
b
,
σ
W
−
→
e
−
ν
¯
e
=
809.0
±
1.9
±
18.1
±
7.0
±
9.4
p
b
,
where the first uncertainties are statistical, the second are systematic, the third are due to the knowledge of the LHC beam energy and the fourth are due to the luminosity determination.
Differential cross-sections as a function of the electron pseudorapidity are measured. The
W
+
/W
−
cross-section ratio and production charge asymmetry are also reported. Results are compared with theoretical predictions at next-to-next-to-leading order in perturbative quantum chromodynamics. Finally, in a precise test of lepton universality, the ratio of
W
boson branching fractions is determined to be
ℬ
W
→
e
ν
/
ℬ
W
→
μ
ν
=
1.020
±
0.002
±
0.019
,
where the first uncertainty is statistical and the second is systematic.
A
bstract
The production of
J/ψ
mesons in proton-proton collisions at a centre-of-mass energy of
s
=
13
TeV is studied with the LHCb detector. Cross-section measurements are performed as a function ...of the transverse momentum
p
T
and the rapidity
y
of the
J/ψ
meson in the region
p
T
<
14 GeV/
c
and 2
.
0
< y <
4
.
5, for both prompt
J/ψ
mesons and
J/ψ
mesons from
b
-hadron decays. The production cross-sections integrated over the kinematic coverage are 15
.
30 ± 0
.
03 ± 0
.
86 μb for prompt
J/ψ
and 2
.
34 ± 0
.
01 ± 0
.
13 μb for
J/ψ
from
b
-hadron decays, assuming zero polarization of the
J/
ψ meson. The first uncertainties are statistical and the second systematic. The cross-section reported for
J/ψ
mesons from
b
-hadron decays is used to extrapolate to a total
b
b
¯
cross-section. The ratios of the cross-sections with respect to
s
=
8
TeV are also determined.
The LHCb measurement of the lifetime ratio of the Λb0 baryon to the B¯0 meson is updated using data corresponding to an integrated luminosity of 3.0 fb−1 collected using 7 and 8 TeV centre-of-mass ...energy pp collisions at the LHC. The decay modes used are Λb0→J/ψpK− and B¯0→J/ψπ+K−, where the π+K− mass is consistent with that of the K¯⁎0(892) meson. The lifetime ratio is determined with unprecedented precision to be 0.974±0.006±0.004, where the first uncertainty is statistical and the second systematic. This result is in agreement with original theoretical predictions based on the heavy quark expansion. Using the current world average of the B¯0 lifetime, the Λb0 lifetime is found to be 1.479±0.009±0.010 ps.
The production of tt‾, W+bb‾ and W+cc‾ is studied in the forward region of proton–proton collisions collected at a centre-of-mass energy of 8 TeV by the LHCb experiment, corresponding to an ...integrated luminosity of 1.98±0.02 fb−1. The W bosons are reconstructed in the decays W→ℓν, where ℓ denotes muon or electron, while the b and c quarks are reconstructed as jets. All measured cross-sections are in agreement with next-to-leading-order Standard Model predictions.
A
bstract
Using three- and four-body decays of
D
mesons produced in semileptonic
b
-hadron decays, precision measurements of
D
meson mass differences are made together with a measurement of the
D
0
...mass. The measurements are based on a dataset corresponding to an integrated luminosity of 1
.
0 fb
−1
collected in
pp
collisions at 7 TeV. Using the decay
D
0
→
K
+
K
−
K
−
π
+
, the
D
0
mass is measured to be
The mass differences
are measured using the
D
0
→
K
+
K
−
π
+
π
−
and
modes.
The differential branching fraction of the decay Λb0→Λμ+μ− is measured as a function of the square of the dimuon invariant mass, q2. A yield of 78±12Λb0→Λμ+μ− decays is observed using data, ...corresponding to an integrated luminosity of 1.0 fb−1, collected by the LHCb experiment at a centre-of-mass energy of 7 TeV. A significant signal is found in the q2 region above the square of the J/ψ mass, while at lower-q2 values upper limits are set on the differential branching fraction. Integrating the differential branching fraction over q2, while excluding the J/ψ and ψ(2S) regions, gives a branching fraction of B(Λb0→Λμ+μ−)=(0.96±0.16(stat)±0.13(syst)±0.21(norm))×10−6, where the uncertainties are statistical, systematic and due to the normalisation mode, Λb0→J/ψΛ, respectively.
A
bstract
The forward-backward charge asymmetry for the process
q
q
¯
→
Z
/
γ
∗
→
μ
+
μ
−
is measured as a function of the invariant mass of the dimuon system. Measurements are performed using proton ...proton collision data collected with the LHCb detector at
s
=
7
and 8 TeV, corresponding to integrated luminosities of 1 fb
−1
and 2 fb
−1
respectively. Within the Standard Model the results constrain the effective electroweak mixing angle to be
sin
2
θ
W
eff
=
0.23142
±
0.00073
±
0.00052
±
0.00056
,
where the first uncertainty is statistical, the second systematic and the third theoretical. This result is in agreement with the current world average, and is one of the most precise determinations at hadron colliders to date.
The difference in total widths between the Bc+ and B+ mesons is measured using a data sample corresponding to an integrated luminosity of 3.0 fb−1 collected by the LHCb experiment in 7 and 8 TeV ...centre-of-mass energy proton–proton collisions at the LHC. Through the study of the time evolution of Bc+→J/ψπ+ and B+→J/ψK+ decays, the width difference is measured to beΔΓ≡ΓBc+−ΓB+=4.46±0.14±0.07 mm−1c, where the first uncertainty is statistical and the second systematic. The known lifetime of the B+ meson is used to convert this to a precise measurement of the Bc+ lifetime,τBc+=513.4±11.0±5.7 fs, where the first uncertainty is statistical and the second is systematic.
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