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.
We report the observation of a new structure in the Λb0π+π− spectrum using the full LHCb data set of pp collisions, corresponding to an integrated luminosity of 9 fb−1, collected at s=7, 8, and 13 ...TeV. A study of the structure suggests its interpretation as a superposition of two almost degenerate narrow states. The masses and widths of these states are measured to be mΛb(6146)0=6146.17±0.33±0.22±0.16 MeV,mΛb(6152)0=6152.51±0.26±0.22±0.16 MeV,ΓΛb(6146)0=2.9±1.3±0.3 MeV,ΓΛb(6152)0=2.1±0.8±0.3 MeV,with a mass splitting of Δm=6.34±0.32±0.02 MeV, where the first uncertainty is statistical, the second systematic. The third uncertainty for the mass measurements derives from the knowledge of the mass of the Λb0 baryon. The measured masses and widths of these new excited states suggest their possible interpretation as a doublet of Λb(1D)0 states.
A combined amplitude analysis is performed for the decays B^{0}→Dover ¯^{0}D_{s}^{+}π^{-} and B^{+}→D^{-}D_{s}^{+}π^{+}, which are related by isospin symmetry. The analysis is based on data collected ...by the LHCb detector in proton-proton collisions at center-of-mass energies of 7, 8, and 13 TeV. The full data sample corresponds to an integrated luminosity of 9 fb^{-1}. Two new resonant states with masses of 2.908±0.011±0.020 GeV and widths of 0.136±0.023±0.013 GeV are observed, which decay to D_{s}^{+}π^{+} and D_{s}^{+}π^{-} respectively. The former state indicates the first observation of a doubly charged open-charm tetraquark state with minimal quark content csover ¯udover ¯, and the latter state is a neutral tetraquark composed of csover ¯uover ¯d quarks. Both states are found to have spin-parity of 0^{+}, and their resonant parameters are consistent with each other, which suggests that they belong to an isospin triplet.
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.
To maximize the light yield of the liquid scintillator (LS) for the Jiangmen Underground Neutrino Observatory (JUNO), a 20 t LS sample was produced in a pilot plant at Daya Bay. The optical ...properties of the new LS in various compositions were studied by replacing the gadolinium-loaded LS in one antineutrino detector. The concentrations of the fluor, PPO, and the wavelength shifter, bis-MSB, were increased in 12 steps from 0.5 g/L and <0.01 mg/L to 4 g/L and 13 mg/L, respectively. The numbers of total detected photoelectrons suggest that, with the optically purified solvent, the bis-MSB concentration does not need to be more than 4 mg/L. To bridge the one order of magnitude in the detector size difference between Daya Bay and JUNO, the Daya Bay data were used to tune the parameters of a newly developed optical model. Then, the model and tuned parameters were used in the JUNO simulation. This enabled to determine the optimal composition for the JUNO LS: purified solvent LAB with 2.5 g/L PPO, and 1 to 4 mg/L bis-MSB.
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.
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- ).
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.
Measurements of the cross section for producing b quarks in the reaction pp→bbover ¯X are reported in 7 and 13 TeV collisions at the LHC as a function of the pseudorapidity η in the range 2<η<5 ...covered by the acceptance of the LHCb experiment. The measurements are done using semileptonic decays of b-flavored hadrons decaying into a ground-state charmed hadron in association with a muon. The cross sections in the covered η range are 72.0±0.3±6.8 and 154.3±1.5±14.3 μb for 7 and 13 TeV. The ratio is 2.14±0.02±0.13, where the quoted uncertainties are statistical and systematic, respectively. The agreement with theoretical expectation is good at 7 TeV, but differs somewhat at 13 TeV. The measured ratio of cross sections is larger at lower η than the model prediction.
The quantum numbers of the X(3872) meson are determined to be J(PC)=1(++) based on angular correlations in B(+)→X(3872)K(+) decays, where X(3872)→π(+)π(-)J/ψ and J/ψ→μ(+)μ(-). The data correspond to ...1.0 fb(-1) of pp collisions collected by the LHCb detector. The only alternative assignment allowed by previous measurements J(PC)=2(-+) is rejected with a confidence level equivalent to more than 8 Gaussian standard deviations using a likelihood-ratio test in the full angular phase space. This result favors exotic explanations of the X(3872) state.
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