A
bstract
The resonant structure of the doubly Cabibbo-suppressed decay
D
+
→
K
−
K
+
K
+
is studied for the first time. The measurement is based on a sample of
pp
-collision data, collected at a ...centre-of-mass energy of 8 TeV with the LHCb detector and corresponding to an integrated luminosity of 2 fb
−1
. The amplitude analysis of this decay is performed with the isobar model and a phenomenological model based on an effective chiral Lagrangian. In both models the S-wave component in the
K
−
K
+
system is dominant, with a small contribution of the
ϕ
(1020) meson and a negligible contribution from tensor resonances. The
K
+
K
−
scattering amplitudes for the considered combinations of spin (0,1) and isospin (0,1) of the two-body system are obtained from the Dalitz plot fit with the phenomenological decay amplitude.
A
bstract
The differential branching fraction with respect to the dimuon invariant mass squared, and the
CP
asymmetry of the
B
±
→
π
±
μ
+
μ
−
decay are measured for the first time. The CKM matrix ...elements |
V
td
| and |
V
ts
|, and the ratio |
V
td
/V
ts
| are determined. The analysis is performed using proton-proton collision data corresponding to an integrated luminosity of 3.0 fb
−1
, collected by the LHCb experiment at centre-of-mass energies of 7 and 8 TeV. The total branching fraction and
CP
asymmetry of
B
±
→
π
±
μ
+
μ
−
decays are measured to be
ℬ
B
±
→
π
±
μ
+
μ
−
=
1.83
±
0.24
±
0.05
×
10
−
8
and
A
C
P
B
±
→
π
±
μ
+
μ
−
=
−
0.11
±
0.12
±
0.01
,
where the first uncertainties are statistical and the second are systematic. These are the most precise measurements of these observables to date, and they are compatible with the predictions of the Standard Model.
A
bstract
Based on data corresponding to an integrated luminosity of 0.37 fb
−1
collected by the LHCb experiment in 2011, the following ratios of branching fractions are measured:
where the first ...uncertainties are statistical and the second systematic. Using the current world average of
and the ratio of the strange to light neutral
B
meson production
f
s
/
f
d
measured by LHCb, we obtain:
The measurements of
,
and
are the most precise to date. The decay mode
is observed for the first time with a significance of more than 5
σ
.
A
bstract
The cross-section for inelastic proton-proton collisions at a centre-of-mass energy of 13 TeV is measured with the LHCb detector. The fiducial cross-section for inelastic interactions ...producing at least one prompt long-lived charged particle with momentum
p
> 2 GeV/
c
in the pseudorapidity range 2 <
η
< 5 is determined to be
σ
acc
= 62.2 ± 0.2 ± 2.5 mb. The first uncertainty is the intrinsic systematic uncertainty of the measurement, the second is due to the uncertainty on the integrated luminosity. The statistical uncertainty is negligible. Extrapolation to full phase space yields the total inelastic proton-proton cross-section
σ
inel
= 75.4 ± 3.0 ± 4.5 mb, where the first uncertainty is experimental and the second due to the extrapolation. An updated value of the inelastic cross-section at a centre-of-mass energy of 7 TeV is also reported.
A
bstract
The first observation of
Z
boson production in proton-lead collisions at a centre-of-mass energy per proton-nucleon pair of
s
N
N
= 5 TeV is presented. The data sample corresponds to an ...integrated luminosity of 1
.
6 nb
−1
collected with the LHCb detector. The
Z
candidates are reconstructed from pairs of oppositely charged muons with pseudorapidities between 2.0 and 4.5 and transverse momenta above 20 GeV
/
c. The invariant dimuon mass is restricted to the range 60 − 120 GeV
/
c. The
Z
production cross-section is measured to be
σ
Z
→
μ
+
μ
−
fwd
=
13.5
−
4.0
+
5.4
stat
.
±
1.2
syst
.
nb
in the direction of the proton beam and
σ
Z
→
μ
+
μ
−
bwd
=
10.7
−
5.1
+
8.4
stat
.
±
1.0
syst
.
nb
in the direction of the lead beam, where the first uncertainty is statistical and the second systematic.
A
bstract
The doubly Cabibbo-suppressed decay
Ξ
c
+
→
pϕ
with
ϕ
→
K
+
K
−
is observed for the first time, with a statistical significance of more than fifteen standard deviations. The data sample ...used in this analysis corresponds to an integrated luminosity of 2 fb
−1
recorded with the LHCb detector in
pp
collisions at a centre-of-mass energy of 8 TeV. The ratio of branching fractions between the decay
Ξ
c
+
→
pϕ
and the singly Cabibbo-suppressed decay
Ξ
c
+
→
pK
−
π
+
is measured to be
ℬ
Ξ
c
+
→
p
ϕ
ℬ
Ξ
c
+
→
p
K
−
π
+
=
19.8
±
0.7
±
0.9
±
0.2
×
10
−
3
,
where the first uncertainty is statistical, the second systematic and the third due to the knowledge of the
ϕ
→
K
+
K
−
branching fraction.
A
bstract
The angular distributions of the rare decays
B
+
→
K
+
μ
+
μ
−
and
are studied with data corresponding to 3fb
−1
of integrated luminosity, collected in proton-proton collisions at 7 and 8 ...TeV centre-of-mass energies with the LHCb detector. The angular distribution is described by two parameters,
F
H
and the forward-backward asymmetry of the dimuon system
A
FB
, which are determined in bins of the dimuon mass squared. The parameter
F
H
is a measure of the contribution from (pseudo)scalar and tensor amplitudes to the decay width. The measurements of
A
FB
and
F
H
reported here are the most precise to date and are compatible with predictions from the Standard Model.
Measurement of the W boson mass Ackernley, T.; Balagura, V.; Belyaev, I. ...
The journal of high energy physics,
2022, Letnik:
2022, Številka:
1
Journal Article
Recenzirano
Odprti dostop
A
bstract
The
W
boson mass is measured using proton-proton collision data at
s
= 13 TeV corresponding to an integrated luminosity of 1.7 fb
−
1
recorded during 2016 by the LHCb experiment. With a ...simultaneous fit of the muon
q/p
T
distribution of a sample of
W
→
μν
decays and the
ϕ
*
distribution of a sample of
Z
→
μμ
decays the
W
boson mass is determined to be
m
w
=
80354
±
23
stat
±
10
exp
±
17
theory
±
9
PDF
MeV
,
where uncertainties correspond to contributions from statistical, experimental systematic, theoretical and parton distribution function sources. This is an average of results based on three recent global parton distribution function sets. The measurement agrees well with the prediction of the global electroweak fit and with previous measurements.
A
bstract
A search for the doubly charmed baryon
$ \Xi_{cc}^{+} $
in the decay mode
$ \Xi_{cc}^{+}\to \Lambda_c^{+}{K^{-}}{\pi^{+}} $
is performed with a data sample, corresponding to an integrated ...luminosity of 0.65 fb
−1
, of
pp
collisions recorded at a centre-of-mass energy of 7 TeV. No significant signal is found in the mass range 3300-3800 MeV
/c
2
. Upper limits at the 95% confidence level on the ratio of the
$ \Xi_{cc}^{+} $
production cross-section times branching fraction to that of the
$ \Lambda_c^{+} $
,
R
, are given as a function of the
$ \Xi_{cc}^{+} $
mass and lifetime. The largest upper limits range from
R
< 1.5 × 10
−
2 for a lifetime of 100 fs to
R <
3
.
9 × 10
−4
for a lifetime of 400 fs.
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