The decays Formula: see text and Formula: see text are observed for the first time using a data sample corresponding to an integrated luminosity of 3.0 fbFormula: see text, collected by the LHCb ...experiment in proton-proton collisions at the centre-of-mass energies of 7 and 8Formula: see text. The branching fractions relative to that of Formula: see text are measured to be Formula: see textwhere the first uncertainties are statistical and the second are systematic.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
A search for the decay K_{S}^{0}→μ^{+}μ^{-} is performed using proton-proton collision data, corresponding to an integrated luminosity of 5.6 fb^{-1} and collected with the LHCb experiment during ...2016, 2017, and 2018 at a center-of-mass energy of 13 TeV. The observed signal yield is consistent with zero, yielding an upper limit of B(K_{S}^{0}→μ^{+}μ^{-})<2.2×10^{-10} at 90% C.L.. The limit reduces to B(K_{S}^{0}→μ^{+}μ^{-})<2.1×10^{-10} at 90% C.L. once combined with the result from data taken in 2011 and 2012.
(ProQuest: ... denotes formulae and/or non-USASCII text omitted; see image) Abstract A measurement of the inclusive W arrow right muν production cross-section using data from pp collisions at a ...centre-of-mass energy of ... TeV is presented. The analysis is based on an integrated luminosity of about 1.0 fb-1 recorded with the LHCb detector. Results are reported for muons with a transverse momentum greater than 20 GeV/c and pseudorapidity between 2.0 and 4.5. The W + and W - production cross-sections are measured to be ... ... where the first uncertainty is statistical, the second is systematic and the third is due to the luminosity determination. Cross-section ratios and differential distributions as functions of the muon pseudorapidity are also presented. The ratio of W + to W - cross-sections in the same fiducial kinematic region is determined to be ... where the uncertainties are statistical and systematic, respectively. Results are in good agreement with theoretical predictions at next-to-next-to-leading order in perturbative quantum chromodynamics. Figure not available: see fulltext.
A
bstract
A new baryon state is observed in the
Λ
b
0
π
+
π
−
mass spectrum with high significance using a data sample of pp collisions, collected with the LHCb detector at centre-of-mass energies
s
...= 7
,
8 and 13 TeV, corresponding to an integrated luminosity of 9 fb
−
1
. The mass and natural width of the new state are measured to be
m
=
6072.3
±
2.9
±
0.6
±
0.2
MeV
,
Γ
=
72
±
11
±
2
MeV
,
where the first uncertainty is statistical and the second systematic. The third uncertainty for the mass is due to imprecise knowledge of the
Λ
b
0
baryon mass. The new state is consistent with the first radial excitation of the
Λ
b
0
baryon, the Λ
b
(2S)
0
resonance. Updated measurements of the masses and the upper limits on the natural widths of the previously observed Λ
b
(5912)
0
and Λ
b
(5920)
0
states are also reported.
Results are reported from a search for the rare decays B_{s}^{0}→τ^{±}μ^{∓} and B^{0}→τ^{±}μ^{∓}, where the τ lepton is reconstructed in the channel τ^{-}→π^{-}π^{+}π^{-}ν_{τ}. These processes are ...effectively forbidden in the standard model, but they can potentially occur at detectable rates in models of new physics that can induce lepton-flavor-violating decays. The search is based on a data sample corresponding to 3 fb^{-1} of proton-proton collisions recorded by the LHCb experiment in 2011 and 2012. The event yields observed in the signal regions for both processes are consistent with the expected standard model backgrounds. Because of the limited mass resolution arising from the undetected τ neutrino, the B_{s}^{0} and B^{0} signal regions are highly overlapping. Assuming no contribution from B^{0}→τ^{±}μ^{∓}, the upper limit B(B_{s}^{0}→τ^{±}μ^{∓})<4.2×10^{-5} is obtained at 95% confidence level. If no contribution from B_{s}^{0}→τ^{±}μ^{∓} is assumed, a limit of B(B^{0}→τ^{±}μ^{∓})<1.4×10^{-5} is obtained at 95% confidence level. These results represent the first limit on B(B_{s}^{0}→τ^{±}μ^{∓}) and the most stringent limit on B(B^{0}→τ^{±}μ^{∓}).
A
bstract
The ratio of branching fractions of the decays
Λ
b
0
→
pK
−
e
+
e
−
and
Λ
b
0
→
pK
−
μ
+
μ
−
,
R
pK
−
1
, is measured for the first time using proton-proton collision data corresponding to ...an integrated luminosity of 4
.
7 fb
−
1
recorded with the LHCb experiment at center-of-mass energies of 7, 8 and 13 TeV. In the dilepton mass-squared range 0
.
1
< q
2
<
6
.
0 GeV
2
/c
4
and the
pK
−
mass range
m
(
pK
−
)
<
2600 MeV
/c
2
, the ratio of branching fractions is measured to be
R
pK
−
1
=
1.17
−
0.16
+
0.18
±
0.07
, where the first uncertainty is statistical and the second systematic. This is the first test of lepton universality with
b
baryons and the first observation of the decay
Λ
b
0
→
pK
−
e
+
e
−
.
The ratio of the B_{s}^{0} and B^{+} fragmentation fractions f_{s} and f_{u} is studied with B_{s}^{0}→J/ψϕ and B^{+}→J/ψK^{+} decays using data collected by the LHCb experiment in proton-proton ...collisions at 7, 8, and 13 TeV center-of-mass energies. The analysis is performed in bins of B-meson momentum, longitudinal momentum, transverse momentum, pseudorapidity, and rapidity. The fragmentation-fraction ratio f_{s}/f_{u} is observed to depend on the B-meson transverse momentum with a significance of 6.0σ. This dependency is driven by the 13 TeV sample (8.7σ), while the results for the other collision energies are not significant when considered separately. Furthermore, the results show a 4.8σ evidence for an increase of f_{s}/f_{u} as a function of collision energy.
Ratios of isospin amplitudes in hadron decays are a useful probe of the interplay between weak and strong interactions and allow searches for physics beyond the standard model. We present the first ...results on isospin amplitudes in b-baryon decays, using data corresponding to an integrated luminosity of 8.5 fb^{-1}, collected with the LHCb detector in pp collisions at center of mass energies of 7, 8, and 13 TeV. The isospin amplitude ratio |A_{1}(Λ_{b}^{0}→J/ψΣ^{0})/A_{0}(Λ_{b}^{0}→J/ψΛ)|, where the subscript on A indicates the final-state isospin, is measured to be less than 1/21.8 at 95% confidence level. The Cabibbo suppressed Ξ_{b}^{0}→J/ψΛ decay is observed for the first time, allowing for the measurement |A_{0}(Ξ_{b}^{0}→J/ψΛ)/A_{1/2}(Ξ_{b}^{0}→J/ψΞ^{0})|=0.37±0.06±0.02, where the uncertainties are statistical and systematic, respectively.
A
bstract
The Cabibbo-suppressed semileptonic decay
B
+
→
p
p
¯
μ
+
ν
μ
is observed for the first time using a sample of
pp
collisions corresponding to an integrated luminosity of 1.0, 2.0 and 1.7 fb
...−
1
at centre-of-mass energies of 7, 8 and 13 TeV, respectively. The differential branching fraction is measured as a function of the
p
p
¯
invariant mass using the decay mode
B
+
→ J/ψK
+
for normalisation. The total branching fraction is measured to be
ℬ
B
+
→
p
p
¯
μ
+
ν
μ
=
5.27
−
0.24
+
0.23
±
0.21
±
0.15
×
10
−
6
,
where the first uncertainty is statistical, the second systematic and the third is from the uncertainty on the branching fraction of the normalisation channel.
A measurement of the time-dependent CP-violating asymmetry in Bs0→ϕϕ\ {B}_s^0\to \phi \phi \ decays is presented. Using a sample of proton-proton collision data corresponding to an integrated ...luminosity of 5.0 fb−1 collected by the LHCb experiment at centre-of-mass energies s\ \sqrt{s} \ = 7 TeV in 2011, 8 TeV in 2012 and 13 TeV in 2015 and 2016, a signal yield of around 9000 Bs0→ϕϕ\ {B}_s^0\to \phi \phi \ decays is obtained. The CP-violating phase ϕsss¯s\ {\phi}_s^{s\overline{s}s} \ is measured to be −0.073 ± 0.115(stat) ± 0.027(syst) rad, under the assumption it is independent of the helicity of the ϕϕ decay. In addition, the CP-violating phases of the transverse polarisations under the assumption of CP conservation of the longitudinal phase are measured. The helicity-independent direct CP-violation parameter is also measured, and is found to be |λ| = 0.99 ± 0.05(stat) ± 0.01(syst). In addition, T-odd triple-product asymmetries are measured. The results obtained are consistent with the hypothesis of CP conservation in b¯→s¯ss¯s\ \overline{b}\to \overline{s}s\overline{s}s \ transitions. Finally, a limit on the branching fraction of the B0 → ϕϕ decay is determined to be BB0→ϕϕ<2.7×10−8\ \mathcal{B}\left({B}^0\to \phi \phi \right)<2.7\times {10}^{-8} \ at 90 % confidence level.
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