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
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.
A
bstract
The production cross-section of
J/ψ
pairs is measured using a data sample of
pp
collisions collected by the LHCb experiment at a centre-of-mass energy of
s
=
13
TeV, corresponding to an ...integrated luminosity of 279 ±11 pb
−1
. The measurement is performed for
J/ψ
mesons with a transverse momentum of less than 10 GeV/
c
in the rapidity range 2
.
0
< y <
4
.
5. The production cross-section is measured to be 15
.
2 ± 1
.
0 ± 0
.
9 nb. The first uncertainty is statistical, and the second is systematic. The differential cross-sections as functions of several kinematic variables of the
J/ψ
pair are measured and compared to theoretical predictions.
A
bstract
A measurement of the production cross-section of Z bosons in pp collisions at
s
=
13
TeV is presented using dimuon and dielectron final states in LHCb data. The cross-section is measured ...for leptons with pseudorapidities in the range 2
.
0
< η <
4
.
5, transverse momenta
p
T
>
20 GeV and dilepton invariant mass in the range 60
< m
(
ℓℓ
)
<
120 GeV. The integrated cross-section from averaging the two final states is
σ
Z
ℓℓ
= 194.3 ± 0.9 ± 3.3 ± 7.6 pb
,
where the first uncertainty is statistical, the second is due to systematic effects, and the third is due to the luminosity determination. In addition, differential cross-sections are measured as functions of the Z boson rapidity, transverse momentum and the angular variable
ϕ
η
*
.
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.
The production of J/ψ mesons accompanied by open charm, and of pairs of open charm hadrons are observed in pp collisions at a centre-of-mass energy of 7 TeV using an integrated luminosity of 355 pb−1 ...collected with the LHCb detector. Model independent measurements of absolute cross-sections are given together with ratios to the measured J/ψ and open charm cross-sections. The properties of these events are studied and compared to theoretical predictions.
Production cross-sections of prompt charm mesons are measured using data from pp collisions at the LHC at a centre-of-mass energy of 5TeV. The data sample corresponds to an integrated luminosity of ...8.60±0.33pb−1 collected by the LHCb experiment. The production cross-sections of D0, D+, D+s, and D∗+ mesons are measured in bins of charm meson transverse momentum, pT, and rapidity, y. They cover the rapidity range 2.0<y<4.5 and transverse momentum ranges 0<pT<10GeV/c for D0 and D+ and 1<pT<10GeV/c for D+s and D∗+ mesons. The inclusive cross-sections for the four mesons, including charge-conjugate states, within the range of 1<pT<8GeV/c are determined to beσ(pp→D0X)=1190±3±64μbσ(pp→D+X)=456±3±34μbσ(pp→D+sX)=195±4±19μbσ(pp→D∗+X)=467±6±40μbwhere the uncertainties are statistical and systematic, 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 production of Upsilon(1S), Upsilon(2S) and Upsilon(3S) mesons in proton-proton collisions at the centre-of-mass energy of sqrt(s)=7 TeV is studied with the LHCb detector. The analysis is based on ...a data sample of 25 pb-1 collected at the Large Hadron Collider. The Upsilon mesons are reconstructed in the decay mode Upsilon -> mu+ mu- and the signal yields are extracted from a fit to the mu+ mu- invariant mass distributions. The differential production cross-sections times dimuon branching fractions are measured as a function of the Upsilon transverse momentum pT and rapidity y, over the range pT < 15 GeV/c and 2.0 < y < 4.5. The cross-sections times branching fractions, integrated over these kinematic ranges, are measured to be sigma(pp -> Upsilon(1S) X) x B(Upsilon(1S)->mu+ mu-) = 2.29 {\pm} 0.01 {\pm} 0.10 -0.37 +0.19 nb, sigma(pp -> Upsilon(2S) X) x B(Upsilon(2S)->mu+ mu-) = 0.562 {\pm} 0.007 {\pm} 0.023 -0.092 +0.048 nb, sigma(pp -> Upsilon(3S) X) x B(Upsilon(3S)->mu+ mu-) = 0.283 {\pm} 0.005 {\pm} 0.012 -0.048 +0.025 nb, where the first uncertainty is statistical, the second systematic and the third is due to the unknown polarisation of the three Upsilon states.
The differential cross-section for the inclusive production of ψ(2S) mesons in pp collisions at s√=7 TeVs=7 TeV has been measured with the LHCb detector. The data sample corresponds to an integrated ...luminosity of 36 pb−1. The ψ(2S) mesons are reconstructed in the decay channels ψ(2S)→μ + μ − and ψ(2S)→J/ψπ + π −, with the J/ψ meson decaying into two muons. Results are presented both for promptly produced ψ(2S) mesons and for those originating from b-hadron decays. In the kinematic range p T(ψ(2S))≤16 GeV/c and 2<y(ψ(2S))≤4.5 we measure
https://static-content.springer.com/image/art%3A10.1140%2Fepjc%2Fs10052-012-2100-4/MediaObjects/10052_2012_2100_Equa_HTML.gif
where the last uncertainty on the prompt cross-section is due to the unknown ψ(2S) polarization. Recent QCD calculations are found to be in good agreement with our measurements. Combining the present result with the LHCb J/ψ measurements we determine the inclusive branching fraction
https://static-content.springer.com/image/art%3A10.1140%2Fepjc%2Fs10052-012-2100-4/MediaObjects/10052_2012_2100_Equb_HTML.gif
where the last uncertainty is due to the (b→J/ψX)B(b→J/ψX) , (J/ψ→μ+μ−)B(J/ψ→μ+μ−) and (ψ(2S)→e+e−)B(ψ(2S)→e+e−) branching fraction uncertainties.
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