A
bstract
A search is performed for a spin-0 boson,
ϕ
, produced in proton-proton collisions at centre-of-mass energies of 7 and 8 TeV, using prompt
ϕ
→ μ
+
μ
−
decays and a data sample corresponding ...to an integrated luminosity of approximately 3.0 fb
−1
collected with the LHCb detector. No evidence is found for a signal in the mass range from 5.5 to 15 GeV. Upper limits are placed on the product of the production cross-section and the branching fraction into the dimuon final state. The limits are comparable to the best existing over most of the mass region considered and are the first to be set near the ϒ resonances.
The LHCb simulation application, Gauss, consists of two independent phases, the generation of the primary event and the tracking of particles produced in the experimental setup. For the LHCb ...experimental program it is particularly important to model B meson decays: the EvtGen code developed in CLEO and BABAR has been chosen and customized for non-coherent B production as occuring in pp collisions at the LHC. The initial proton-proton collision is provided by a different generator engine, currently PYTHIA 6 for massive production of signal and generic pp collisions events. Beam gas events, background events originating from proton halo, cosmics and calibration events for different detectors can be generated in addition to pp collisions. Different generator packages as available in the physics community or specifically developed in LHCb are used for the different purposes. Running conditions affecting the generated events such as the size of the luminous region, the number of collisions occuring in a bunch crossing and the number of spill-over events from neighbouring bunches are modeled via dedicated algorithms appropriately configured. The design of the generator phase of Gauss will be described: a modular structure with well defined interfaces specific to the various tasks, e.g. pp collisions, particle decays, selections, etc. has been chosen. Different implementations are available for the various tasks allowing selecting and combining them as most appropriate at run time as in the case of PYTHIA 6 for pp collisions or HIJING for beam gas. The advantages of such structure, allowing for example to adopt transparently new generators packages, will be discussed.
A
bstract
A search for
CP
violation in D
0
→
π
−
π
+
π
0
decays is reported, using
pp
collision data collected by the LHCb experiment from 2015 to 2018 corresponding to an integrated luminosity of 6 ...fb
−
1
. An unbinned model-independent approach provides sensitivity to local
CP
violation within the two-dimensional phase space of the decay. The method is validated using the Cabibbo-favoured channel D
0
→ K
−
π
+
π
0
and background regions of the signal mode. The results are consistent with
CP
symmetry in this decay.
A
bstract
A measurement of the CP-violating observables from
B
±
→
D
*
K
±
and
B
±
→
D
*
π
±
decays is presented, where
D
*
(
D
) is an admixture of
D
*0
and
D
¯
∗
0
(
D
0
and
D
¯
0
) states and is ...reconstructed through the decay chains
D
*
→ Dπ
0
/γ
and
D
→
K
S
0
π
+
π
−
/
K
S
0
K
+
K
−
. The measurement is performed by analysing the signal yield variation across the
D
decay phase space and is independent of any amplitude model. The data sample used was collected by the LHCb experiment in proton-proton collisions and corresponds to a total integrated luminosity of 9 fb
−
1
at centre-of-mass energies of 7, 8 and 13 TeV. The CKM angle
γ
is determined to be
69
−
14
+
13
∘
using the measured CP-violating observables. The hadronic parameters
r
B
D
∗
K
±
,
r
B
D
∗
π
±
,
δ
B
D
∗
K
±
,
δ
B
D
∗
π
±
, which are the ratios and strong phase differences between favoured and suppressed
B
±
decays, are also reported.
Observation of the B+→ Jψη′K+ decay Alessio, F.; Aliouche, Z.; Artamonov, A. ...
The journal of high energy physics,
08/2023, Letnik:
2023, Številka:
8
Journal Article
Recenzirano
Odprti dostop
A
bstract
The
B
+
→
Jψη
′
K
+
decay is observed for the first time 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
. The branching fraction of this decay is measured relative to the known branching fraction of the
B
+
→ ψ
(2
S
)
K
+
decay and found to be
B
B
+
→
Jψη
′
K
+
B
B
+
→
ψ
2
S
K
+
=
4.91
±
0.47
±
0.29
±
0.07
×
10
−
2
,
where the first uncertainty is statistical, the second is systematic and the third is related to external branching fractions. A first look at the
J/ψη
′ mass distribution is performed and no signal of intermediate resonances is observed.
A
bstract
Correlations of same-sign charged pions are analysed using proton-lead collision data collected by the LHCb experiment at a nucleon-nucleon centre-of-mass energy of 5.02 TeV, corresponding ...to an integrated luminosity of 1.06 nb
−
1
. Bose-Einstein correlations are observed in the form of an enhancement of pair production for same-sign charged pions with a small four-momentum difference. The dependence of the correlation radius and the intercept parameter on the reconstructed charged-particle multiplicity is investigated. The measured correlation radii scale linearly with the cube root of the reconstructed charged-particle multiplicity, being compatible with predictions of hydrodynamic models on the collision system evolution.
A
bstract
A study of
D
+
π
−
,
D
0
π
+
and
D
∗+
π
−
final states is performed using
pp
collision data, corresponding to an integrated luminosity of 1.0 fb
−1
, collected at a centre-of-mass energy of ...7 TeV with the LHCb detector. The
D
1
(2420)
0
resonance is observed in the
D
∗+
π
−
final state and the
$ D_2^{*}\left( {2460} \right) $
resonance is observed in the
D
+
π
−
,
D
0
π
+
and
D
∗+
π
−
final states. For both resonances, their properties and spin-parity assignments are obtained. In addition, two natural parity and two unnatural parity resonances are observed in the mass region between 2500 and 2800 MeV. Further structures in the region around 3000 MeV are observed in all the
D
∗+
π
−
,
D
+
π
−
and
D
0
π
+
final states.
The calibration and performance of the opposite-side flavour tagging algorithms used for the measurements of time-dependent asymmetries at the LHCb experiment are described. The algorithms have been ...developed using simulated events and optimized and calibrated with
B
+
→
J
/
ψK
+
,
B
0
→
J
/
ψK
∗0
and
B
0
→
D
∗−
μ
+
ν
μ
decay modes with 0.37 fb
−1
of data collected in
pp
collisions at
during the 2011 physics run. The opposite-side tagging power is determined in the
B
+
→
J
/
ψK
+
channel to be (2.10±0.08±0.24) %, where the first uncertainty is statistical and the second is systematic.
A
bstract
The angular distribution and differential branching fraction of the decay
B
+
→
K
+
μ
+
μ
−
are studied with a dataset corresponding to 1.0fb
−1
of integrated luminosity, collected by the ...LHCb experiment. The angular distribution is measured in bins of dimuon invariant mass squared and found to be consistent with Standard Model expectations. Integrating the differential branching fraction over the full dimuon invariant mass range yields a total branching fraction of
(
B
+
→
K
+
μ
+
μ
−
) = (4
.
36
±
0
.
15
±
0
.
18)
×
10
−7
. These measurements are the most precise to date of the
B
+
→
K
+
μ
+
μ
−
decay.
Measurements of CP observables in B±→D(⁎)K± and B±→D(⁎)π± decays are presented, where D(⁎) indicates a neutral D or D⁎ meson that is an admixture of D(⁎)0 and D¯(⁎)0 states. Decays of the D⁎ meson to ...the Dπ0 and Dγ final states are partially reconstructed without inclusion of the neutral pion or photon, resulting in distinctive shapes in the B candidate invariant mass distribution. Decays of the D meson are fully reconstructed in the K±π∓, K+K− and π+π− final states. The analysis uses a sample of charged B mesons produced in pp collisions collected by the LHCb experiment, corresponding to an integrated luminosity of 2.0, 1.0 and 2.0 fb−1 taken at centre-of-mass energies of s=7, 8 and 13 TeV, respectively. The study of B±→D⁎K± and B±→D⁎π± decays using a partial reconstruction method is the first of its kind, while the measurement of B±→DK± and B±→Dπ± decays is an update of previous LHCb measurements. The B±→DK± results are the most precise to date.
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