The data sample of Λ0b→J/ψpK− decays acquired with the LHCb detector from 7 and 8 TeV pp collisions, corresponding to an integrated luminosity of 3 fb−1, is inspected for the presence of J/ψp or ...J/ψK− contributions with minimal assumptions about K−p contributions. It is demonstrated at more than nine standard deviations that Λ0b→J/ψpK− decays cannot be described with K−p contributions alone, and that J/ψp contributions play a dominant role in this incompatibility. These model-independent results support the previously obtained model-dependent evidence for P+c→J/ψp charmonium-pentaquark states in the same data sample.
A
bstract
Production cross-sections of prompt charm mesons are measured with the first data from
pp
collisions at the LHC at a centre-of-mass energy of 13 TeV. The data sample corresponds to an ...integrated luminosity of 4.98 ± 0.19 pb
−1
collected by the LHCb experiment. The production cross-sections of
D
0
,
D
+
,
D
s
+
, and
D
*+
mesons are measured in bins of charm meson transverse momentum,
p
T
, and rapidity,
y
, and cover the range 0 <
p
T
< 15GeV/c and 2.0 <
y
< 4.5. The inclusive cross-sections for the four mesons, including charge conjugation, within the range of 1 <
p
T
< 8 GeV/c are found to be
σ
pp
→
D
0
X
=
2460
±
3
±
130
μ
b
σ
pp
→
D
+
X
=
1000
±
3
±
110
μ
b
σ
pp
→
D
s
+
X
=
460
±
13
±
100
μ
b
σ
pp
→
D
∗
+
X
=
880
±
5
±
140
μ
b
where the uncertainties are due to statistical and systematic uncertainties, respectively.
The first full amplitude analysis of B+→J/ψϕK+ with J/ψ→μ+μ−, ϕ→K+K− decays is performed with a data sample of 3 fb−1 of pp collision data collected at s=7 and 8 TeV with the LHCb detector. The data ...cannot be described by a model that contains only excited kaon states decaying into ϕK+, and four J/ψϕ structures are observed, each with significance over 5 standard deviations. The quantum numbers of these structures are determined with significance of at least 4 standard deviations. The lightest has mass consistent with, but width much larger than, previous measurements of the claimed X(4140) state. The model includes significant contributions from a number of expected kaon excitations, including the first observation of the K*(1680)+→ϕK+ transition.
Search for the Decays Bs0→τ+τ- and B0→τ+τ Badalov, Alexey; Calvo Gómez, Míriam; Camboni, Alessandro ...
Physical review letters,
06/2017, Letnik:
118, Številka:
25
Journal Article
Recenzirano
Odprti dostop
A search for the rare decays Bs0→τ+τ- and B0→τ+τ- is performed using proton-proton collision data collected with the LHCb detector. The data sample corresponds to an integrated luminosity of 3 fb-1 ...collected in 2011 and 2012. The τ leptons are reconstructed through the decay τ-→π-π+π-ντ. Assuming no contribution from B0→τ+τ- decays, an upper limit is set on the branching fraction B (Bs0→τ+τ- )<6.8 ×10-3 at the 95% confidence level. If instead no contribution from Bs0→τ+τ- decays is assumed, the limit is B (B0→τ+τ- )<2.1 ×10-3 at the 95% confidence level. These results correspond to the first direct limit on B (Bs0→τ+τ- ) and the world's best limit on B (B0→τ+τ- ).
Results are reported from a search for the rare decays Bs0→τ±μ∓ and B0→τ±μ∓, where the τ lepton is reconstructed in the channel τ−→π−π+π−ντ. 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 Bs0 and B0 signal regions are highly overlapping. Assuming no contribution from B0→τ±μ∓, the upper limit B(Bs0→τ±μ∓)<4.2×10−5 is obtained at 95% confidence level. If no contribution from Bs0→τ±μ∓ is assumed, a limit of B(B0→τ±μ∓)<1.4×10−5 is obtained at 95% confidence level. These results represent the first limit on B(Bs0→τ±μ∓) and the most stringent limit on B(B0→τ±μ∓).
A full amplitude analysis of Λ0b→J/ψpπ− decays is performed with a data sample acquired with the LHCb detector from 7 and 8 TeV pp collisions, corresponding to an integrated luminosity of 3 fb−1. A ...significantly better description of the data is achieved when, in addition to the previously observed nucleon excitations N→pπ−, either the Pc(4380)+ and Pc(4450)+→J/ψp states, previously observed in Λ0b→J/ψpK− decays, or the Zc(4200)−→J/ψπ− state, previously reported in B0→J/ψK+π− decays, or all three, are included in the amplitude models. The data support a model containing all three exotic states, with a significance of more than three standard deviations. Within uncertainties, the data are consistent with the Pc(4380)+ and Pc(4450)+ production rates expected from their previous observation taking account of Cabibbo suppression.
Resonant structures in B^{0}→ψ^{'}π^{-}K^{+} decays are analyzed by performing a four-dimensional fit of the decay amplitude, using pp collision data corresponding to 3 fb^{-1} collected with the ...LHCb detector. The data cannot be described with K^{+}π^{-} resonances alone, which is confirmed with a model-independent approach. A highly significant Z(4430)^{-}→ψ^{'}π^{-} component is required, thus confirming the existence of this state. The observed evolution of the Z(4430)^{-} amplitude with the ψ^{'}π^{-} mass establishes the resonant nature of this particle. The mass and width measurements are substantially improved. The spin parity is determined unambiguously to be 1^{+}.
Using pp collision data corresponding to an integrated luminosity of 8.5 fb−1 recorded by the LHCb experiment at center-of-mass energies of s=7, 8, and 13 TeV, the observation of an excited Bc+ ...state in the Bc+π+π− invariant-mass spectrum is reported. The observed peak has a mass of 6841.2±0.6(stat)±0.1(syst)±0.8(Bc+) MeV/c2, where the last uncertainty is due to the limited knowledge of the Bc+ mass. It is consistent with expectations of the Bc*(2S31)+ state reconstructed without the low-energy photon from the Bc*(1S31)+→Bc+γ decay following Bc*(2S31)+→Bc*(1S31)+π+π−. A second state is seen with a global (local) statistical significance of 2.2σ (3.2σ) and a mass of 6872.1±1.3(stat)±0.1(syst)±0.8(Bc+) MeV/c2, and is consistent with the Bc(2S10)+ state. These mass measurements are the most precise to date.
The Ξ_{c}^{+}K^{-} mass spectrum is studied with a sample of pp collision data corresponding to an integrated luminosity of 3.3 fb^{-1}, collected by the LHCb experiment. The Ξ_{c}^{+} is ...reconstructed in the decay mode pK^{-}π^{+}. Five new, narrow excited Ω_{c}^{0} states are observed: the Ω_{c}(3000)^{0}, Ω_{c}(3050)^{0}, Ω_{c}(3066)^{0}, Ω_{c}(3090)^{0}, and Ω_{c}(3119)^{0}. Measurements of their masses and widths are reported.
We report four narrow peaks in the Ξb0K− mass spectrum obtained using pp collisions at center-of-mass energies of 7, 8, and 13 TeV, corresponding to a total integrated luminosity of 9 fb−1 recorded ...by the LHCb experiment. Referring to these states by their mass, the mass values are mΩb(6316)−=6315.64±0.31±0.07±0.50 MeV, mΩb(6330)−=6330.30±0.28±0.07±0.50 MeV, mΩb(6340)−=6339.71±0.26±0.05±0.50 MeV, mΩb(6350)−=6349.88±0.35±0.05±0.50 MeV, where the uncertainties are statistical, systematic, and the last is due to the knowledge of the Ξb0 mass. The natural widths of the three lower mass states are consistent with zero, and the 90% confidence-level upper limits are determined to be ΓΩb(6316)−<2.8 MeV, ΓΩb(6330)−<3.1 MeV and ΓΩb(6340)−<1.5 MeV. The natural width of the Ωb(6350)− peak is 1.4−0.8+1.0±0.1 MeV, which is 2.5σ from zero and corresponds to an upper limit of 2.8 MeV. The peaks have local significances ranging from 3.6σ to 7.2σ. After accounting for the look-elsewhere effect, the significances of the Ωb(6316)− and Ωb(6330)− peaks are reduced to 2.1σ and 2.6σ, respectively, while the two higher mass peaks exceed 5σ. The observed peaks are consistent with expectations for excited Ωb− resonances.
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