A
bstract
The suppressed decay Λ
b
0
→
pπ
−
μ
+
μ
−
, excluding the J/
ψ
and
ψ
(2
S
) →
μ
+
μ
−
resonances, is observed for the first time with a significance of 5.5 standard deviations. The ...analysis is performed with proton-proton collision data corresponding to an integrated luminosity of 3 fb
−1
collected with the LHCb experiment. The Λ
b
0
→
pπ
−
μ
+
μ
−
branching fraction is measured relative to the Λ
b
0
→ J/
ψ
(→
μ
+
μ
−
)
pπ
−
branching fraction giving
ℬ
Λ
b
0
→
p
π
−
μ
+
μ
−
ℬ
Λ
b
0
→
J
/
ψ
→
μ
+
μ
−
p
π
−
=
0.044
±
0.012
±
0.007
,
where the first uncertainty is statistical and the second is systematic. This is the first observation of a
b
→
d
transition in a baryonic decay.
The calibration and performance of the LHCb Calorimeter system in Run 1 and 2 at the LHC are described. After a brief description of the sub-detectors and of their role in the trigger, the ...calibration methods used for each part of the system are reviewed. The changes which occurred with the increase of beam energy in Run 2 are explained. The performances of the calorimetry for \(\gamma\) and \(\pi^0\) are detailed. A few results from collisions recorded at \(\sqrt {s}\) = 7, 8 and 13 TeV are shown.
The first observation of the decays Λb0→χc 1p K- and Λb0→χc 2p K- is reported using a data sample corresponding to an integrated luminosity of 3.0 fb-1, collected by the LHCb experiment in p p ...collisions at center-of-mass energies of 7 and 8 TeV. The following ratios of branching fractions are measured: B/(Λb0→χc 1p K-) B (Λb0→J /ψ p K-) =0.242 ±0.014 ±0.013 ±0.009 ,B/(Λb0→χc 2p K-) B (Λb0→J /ψ p K-) =0.248 ±0.020 ±0.014 ±0.009 ,B/(Λb0→χc 2p K-) B (Λb0→χc 1p K-) =1.02 ±0.10 ±0.02 ±0.05 , where the first uncertainty is statistical, the second systematic, and the third due to the uncertainty on the branching fractions of the χc 1→J /ψ γ and χc 2→J /ψ γ decays. Using both decay modes, the mass of the Λb0 baryon is also measured to be mΛb0=5619.44 ±0.28 ±0.26 MeV /c2 , where the first and second uncertainties are statistical and systematic, respectively.
A search for the rare decays Bs0→μ+μ- and B0→μ+μ- is performed at the LHCb experiment using data collected in p p collisions corresponding to a total integrated luminosity of 4.4 fb-1. An excess of ...Bs0→μ+μ- decays is observed with a significance of 7.8 standard deviations, representing the first observation of this decay in a single experiment. The branching fraction is measured to be B (Bs0→μ+μ- )=(3.0 ±0. 6-0.2+0.3) ×10-9 , where the first uncertainty is statistical and the second systematic. The first measurement of the Bs0→μ+μ- effective lifetime, τ (Bs0→μ+μ- )=2.04 ±0.44 ±0.05 ps , is reported. No significant excess of B0→μ+μ- decays is found, and a 95% confidence level upper limit, B (B0 →μ+μ-) <3.4 ×10-10 , is determined. All results are in agreement with the standard model expectations.
The Ξc+K- mass spectrum is studied with a sample of p p collision data corresponding to an integrated luminosity of 3.3 fb-1, collected by the LHCb experiment. The Ξc+ is reconstructed in the decay ...mode p K-π+. Five new, narrow excited Ωc0 states are observed: the Ωc(3000 )0, Ωc(3050 )0, Ωc(3066 )0, Ωc(3090 )0, and Ωc(3119 )0. Measurements of their masses and widths are reported.
Using proton-proton collision data corresponding to an integrated luminosity of 3.0 fb-1, recorded by the LHCb detector at center-of-mass energies of 7 and 8 TeV, the Bc+→D0K+ decay is observed with ...a statistical significance of 5.1 standard deviations. By normalizing to B+→D¯ 0 π+ decays, a measurement of the branching fraction multiplied by the production rates for Bc+ relative to B+ mesons in the LHCb acceptance is obtained, RD0K=(fc/fu)×B (Bc+→D0K+)=(9. 3-2.5+2.8±0.6 )×10-7 , where the first uncertainty is statistical and the second is systematic. This decay is expected to proceed predominantly through weak annihilation and penguin amplitudes, and is the first Bc+ decay of this nature to be observed.
The polarization of photons produced in radiative B-s(0) decays is studied for the first time. The data are recorded by the LHCb experiment in pp collisions corresponding to an integrated luminosity ...of 3 fb(-1) at center-of-mass energies of 7 and 8 TeV. A time-dependent analysis of the B-s(0) ->phi gamma decay rate is conducted to determine the parameter A(Delta), which is related to the ratio of right-over left-handed photon polarization amplitudes in b -> s gamma transitions. A value of A(Delta) = -0.98(-0.52)(-0.20)(+0.46)(+0.23) is measured. This result is consistent with the standard model prediction within 2 standard deviations.
The first observation of the B 0 s → η ′ η ′ decay is reported. The study is based on a sample of proton-proton collisions corresponding to 3.0 fb − 1 of integrated luminosity collected with the ...LHCb detector. The significance of the signal is 6.4 standard deviations. The branching fraction is measured to be 3.31 ± 0.64 ( stat ) ± 0.28 ( syst ) ± 0.12 ( norm ) × 10 − 5 , where the third uncertainty comes from the B ± → η ′ K ± branching fraction that is used as a normalization. In addition, the charge asymmetries of B ± → η ′ K ± and B ± → ϕ K ± , which are control channels, are measured to be ( − 0.2 ± 1.3 ) % and ( + 1.7 ± 1.3 ) % , respectively. All results are consistent with theoretical expectations.
Measurements are presented of the C P violation observables S and C in the decays of B 0 and ¯ B 0 mesons to the J / ψ K 0 S final state. The data sample corresponds to an integrated luminosity of ...3.0 fb − 1 collected with the LHCb experiment in proton-proton collisions at center-of-mass energies of 7 and 8 TeV, and contains a total of 41 560 selected B 0 and ¯ B 0 decays. The analysis of the time evolution of these decays yields S = 0.731 ± 0.035 ( stat ) ± 0.020 ( syst ) and C = − 0.038 ± 0.032 ( stat ) ± 0.005 ( syst ) . In the standard model, S equals sin ( 2 β ) to a good level of precision. The values are consistent with the current world averages and with the standard model expectations.
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