A measurement of the ratio of branching fractions of the decays B^{+}→K^{+}μ^{+}μ^{-} and B^{+}→K^{+}e^{+}e^{-} is presented. The proton-proton collision data used correspond to an integrated ...luminosity of 5.0 fb^{-1} recorded with the LHCb experiment at center-of-mass energies of 7, 8, and 13 TeV. For the dilepton mass-squared range 1.1<q^{2}<6.0 GeV^{2}/c^{4} the ratio of branching fractions is measured to be R_{K}=0.846_{-0.054}^{+0.060}_{-0.014}^{+0.016}, where the first uncertainty is statistical and the second systematic. This is the most precise measurement of R_{K} to date and is compatible with the standard model at the level of 2.5 standard deviations.
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
The cross-sections of exclusive (coherent) photoproduction
J/ψ
and
ψ
(2S) mesons in ultra-peripheral PbPb collisions at a nucleon-nucleon centre-of-mass energy of 5
.
02 TeV are measured ...using a data sample corresponding to an integrated luminosity of 228 ± 10 μb
−
1
, collected by the LHCb experiment in 2018. The differential cross-sections are measured separately as a function of transverse momentum and rapidity in the nucleus-nucleus centre-of-mass frame for
J/ψ
and
ψ
(2S) mesons. The integrated cross-sections are measured to be
σ
J
/
ψ
coh
= 5
.
965
±
0
.
059
±
0
.
232
±
0
.
262 mb and
σ
ψ
2
S
coh
= 0
.
923
±
0
.
086
±
0
.
028
±
0
.
040 mb, where the first listed uncertainty is statistical, the second systematic and the third due to the luminosity determination. The cross-section ratio is measured to be
σ
ψ
2
S
coh
/
σ
J
/
ψ
coh
= 0
.
155
±
0
.
014
±
0
.
003, where the first uncertainty is statistical and the second is systematic. These results are compatible with theoretical predictions.
A
bstract
The CKM angle
γ
is determined from
CP
-violating observables measured in
B
±
→
D
K
∓
π
±
π
±
π
∓
h
±
, (
h
=
K, π
) decays, where the measurements are performed in bins of the decay ...phase-space of the
D
meson. Using proton-proton collision data collected by the LHCb experiment at centre-of-mass energies of 7
,
8 and 13 TeV, corresponding to a total integrated luminosity of 9 fb
−
1
,
γ
is determined to be
γ
=
54.8
+
6.0
−
5.8
+
0.6
−
0.6
+
6.7
−
4.3
∘
,
where the first uncertainty is statistical, the second systematic and the third from the external inputs on the coherence factors and strong phases of the
D
-meson decays.
A
bstract
A first search for the lepton-flavour violating decays
B
0
→
K
*0
τ
±
μ
∓
is presented. The analysis is performed using a sample of proton-proton collision data, collected with the LHCb ...detector at centre-of-mass energies of 7, 8 and 13 TeV between 2011 and 2018, corresponding to an integrated luminosity of 9 fb
−
1
. No significant signal is observed, and upper limits on the branching fractions are determined to be
B
B
0
→
K
∗
0
τ
+
μ
−
<
1.0
1.2
×
10
−
5
and
B
B
0
→
K
∗
0
τ
−
μ
+
<
8.2
9.8
×
10
−
6
at the 90% (95%) confidence level.
The LHCb simulation application, Gauss, is based on the Gaudi framework and on experiment basic components such as the Event Model and Detector Description. Gauss also depends on external libraries ...for the generation of the primary events (PYTHIA 6, EvtGen, etc.) and on GEANT4 for particle transport in the experimental setup. The application supports the production of different types of events from minimum bias to B physics signals and particle guns. It is used for purely generator-level studies as well as full simulations. Gauss is used both directly by users and in massive central productions on the grid. The design and implementation of the application and its evolution due to evolving requirements will be described as in the case of the recently adopted Python-based configuration or the possibility of taking into account detectors conditions via a Simulation Conditions database. The challenge of supporting at the same time the flexibililty needed for the different tasks for which it is used, from evaluation of physics reach to background modeling, together with the stability and reliabilty of the code will also be described.
A
bstract
The
CP
asymmetries of seven
B
−
decays to two charm mesons are measured using data corresponding to an integrated luminosity of 9 fb
−
1
of proton-proton collisions collected by the LHCb ...experiment. Decays involving a
D
*0
or
D
s
∗
−
meson are analysed by reconstructing only the
D
0
or
D
s
−
decay products. This paper presents the first measurement of
A
CP
(
B
−
→
D
s
∗
−
D
0
) and
A
CP
(
B
−
→
D
s
−
D
∗
0
), and the most precise measurement of the other five
CP
asymmetries. There is no evidence of
CP
violation in any of the analysed decays. Additionally, two ratios between branching fractions of selected decays are measured.
A search for rare B → Dμ+μ− decays Alessio, F.; Aliouche, Z.; Artamonov, A. ...
The journal of high energy physics,
02/2024, Letnik:
2024, Številka:
2
Journal Article
Recenzirano
Odprti dostop
A
bstract
A search for rare
B → Dμ
+
μ
−
decays is performed using proton-proton collision data collected by the LHCb experiment, corresponding to an integrated luminosity of 9 fb
−
1
. No ...significant signals are observed in the non-resonant
μ
+
μ
−
modes, and upper limits of
B
B
0
→
D
¯
0
μ
+
μ
−
<
5.1
×
10
−
8
,
B
B
+
→
D
s
+
μ
+
μ
−
<
3.2
×
10
−
8
,
B
B
s
0
→
D
¯
0
μ
+
μ
−
<
1.6
×
10
−
7
and
f
c
/
f
u
·
B
B
c
+
→
D
s
+
μ
+
μ
−
<
9.6
×
10
−
8
are set at the 95 % confidence level, where
f
c
and
f
u
are the fragmentation fractions of a
B
meson with a
c
and
u
quark respectively in proton-proton collisions. Each result is either the first such measurement or an improvement by three orders of magnitude on an existing limit. Separate upper limits are calculated when the muon pair originates from a
J/ψ → μ
+
μ
−
decay. The branching fraction of
B
c
+
→
D
s
+
J
/
ψ
multiplied by the fragmentation-fraction ratio is measured to be
f
c
f
u
·
B
B
c
+
→
D
s
+
J
/
ψ
=
1.63
±
0.15
±
0.13
×
10
−
5
,
where the first uncertainty is statistical and the second systematic.
A
bstract
An amplitude analysis of the
D
+
→ π
−
π
+
π
+
decay is performed with a sample corresponding to 1.5 fb
−
1
of integrated luminosity of
pp
collisions at a centre-of-mass energy
s
= 8 TeV ...collected by the LHCb detector in 2012. The sample contains approximately six hundred thousand candidates with a signal purity of 95%. The resonant structure is studied through a fit to the Dalitz plot where the
π
−
π
+
S-wave amplitude is extracted as a function of
π
−
π
+
mass, and spin-1 and spin-2 resonances are included coherently through an isobar model. The S-wave component is found to be dominant, followed by the
ρ
(770)
0
π
+
and
f
2
(1270)
π
+
components. A small contribution from the
ω
(782)
→ π
−
π
+
decay is seen for the first time in the
D
+
→ π
−
π
+
π
+
decay.
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