A search for a long-lived scalar particle χ is performed, looking for the decay B+→K+χ with χ→μ+μ− in pp collision data corresponding to an integrated luminosity of 3 fb−1, collected by the LHCb ...experiment at center-of-mass energies of s=7 and 8 TeV. This new scalar particle, predicted by hidden sector models, is assumed to have a narrow width. The signal would manifest itself as an excess in the dimuon invariant mass distribution over the Standard Model background. No significant excess is observed in the accessible ranges of mass 250<m(χ)<4700 MeV/c2 and lifetime 0.1<τ(χ)<1000 ps. Upper limits on the branching fraction B(B+→K+χ(μ+μ−)) at 95% confidence level are set as a function of m(χ) and τ(χ), varying between 2×10−10 and 10−7. These are the most stringent limits to date. The limits are interpreted in the context of a model with a light inflaton particle.
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.
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^{+}.
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.
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 first amplitude analysis of the B^{±}→π^{±}K^{+}K^{-} decay is reported based on a data sample corresponding to an integrated luminosity of 3.0 fb^{-1} of pp collisions recorded in 2011 and 2012 ...with the LHCb detector. The data are found to be best described by a coherent sum of five resonant structures plus a nonresonant component and a contribution from ππ↔KK S-wave rescattering. The dominant contributions in the π^{±} K^{∓} and K^{+} K^{-} systems are the nonresonant and the B^{±}→ρ(1450)^{0}π^{±} amplitudes, respectively, with fit fractions around 30%. For the rescattering contribution, a sizable fit fraction is observed. This component has the largest CP asymmetry reported to date for a single amplitude of (-66±4±2)%, where the first uncertainty is statistical and the second systematic. No significant CP violation is observed in the other contributions.
The first measurement of heavy-flavor production by the LHCb experiment in its fixed-target mode is presented. The production of J/ψ and D^{0} mesons is studied with beams of protons of different ...energies colliding with gaseous targets of helium and argon with nucleon-nucleon center-of-mass energies of sqrts_{NN}=86.6 and 110.4 GeV, respectively. The J/ψ and D^{0} production cross sections in pHe collisions in the rapidity range 2, 4.6 are found to be σ_{J/ψ}=652±33(stat)±42(syst) nb/nucleon and σ_{D^{0}}=80.8±2.4(stat)±6.3(syst) μb/nucleon, where the first uncertainty is statistical and the second is systematic. No evidence for a substantial intrinsic charm content of the nucleon is observed in the large Bjorken-x region.
The doubly charmed baryon decay Ξ_{cc}^{++}→Ξ_{c}^{+}π^{+} is observed for the first time, with a statistical significance of 5.9σ, confirming a recent observation of the baryon in the ...Λ_{c}^{+}K^{-}π^{+}π^{+} final state. The data sample used corresponds to an integrated luminosity of 1.7 fb^{-1}, collected by the LHCb experiment in pp collisions at a center-of-mass energy of 13 TeV. The Ξ_{cc}^{++} mass is measured to be 3620.6±1.5(stat)±0.4(syst)±0.3(Ξ_{c}^{+}) MeV/c^{2} and is consistent with the previous result. The ratio of branching fractions between the decay modes is measured to be B(Ξ_{cc}^{++}→Ξ_{c}^{+}π^{+})×B(Ξ_{c}^{+}→pK^{-}π^{+})/B(Ξ_{cc}^{++}→Λ_{c}^{+}K^{-}π^{+}π^{+})×B(Λ_{c}^{+}→pK^{-}π^{+})=0.035±0.009(stat)±0.003(syst).
A
bstract
The
ϒ
(1
S
)
μ
+
μ
−
invariant-mass distribution is investigated for a possible exotic meson state composed of two
b
quarks and two
b
¯
quarks,
X
b
b
¯
b
b
¯
. The analysis is based on a ...data sample of
pp
collisions recorded with the LHCb detector at centre-of-mass energies
s
=
7
, 8 and 13 TeV, corresponding to an integrated luminosity of 6.3 fb
−1
. No significant excess is found, and upper limits are set on the product of the production cross-section and the branching fraction as functions of the mass of the
X
b
b
¯
b
b
¯
state. The limits are set in the fiducial volume where all muons have pseudorapidity in the range 2
.
0
,
5
.
0, and the
X
b
b
¯
b
b
¯
state has rapidity in the range 2
.
0
,
4
.
5 and transverse momentum less than 15 GeV/
c
.
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