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.
Observations are reported of different sources of CP violation from an amplitude analysis of B^{+}→π^{+}π^{+}π^{-} decays, based on a data sample corresponding to an integrated luminosity of 3 ...fb^{-1} of pp collisions recorded with the LHCb detector. A large CP asymmetry is observed in the decay amplitude involving the tensor f_{2}(1270) resonance, and in addition significant CP violation is found in the π^{+}π^{-}S wave at low invariant mass. The presence of CP violation related to interference between the π^{+}π^{-}S wave and the P wave B^{+}→ρ(770)^{0}π^{+} amplitude is also established; this causes large local asymmetries but cancels when integrated over the phase space of the decay. The results provide both qualitative and quantitative new insights into CP -violation effects in hadronic B decays.
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 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 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
Production cross-sections of prompt charm mesons are measured using data from
pp
collisions at the LHC at a centre-of-mass energy of 5 TeV. The data sample corresponds to an integrated ...luminosity of 8
.
60 ± 0
.
33 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
. They cover the rapidity range 2
.
0
< y <
4
.
5 and transverse momentum ranges 0
< p
T
<
10 GeV
/c
for
D
0
and
D
+
and 1
< p
T
<
10 GeV
/c
for
D
s
+
and
D
∗+
mesons. The inclusive cross-sections for the four mesons, including charge-conjugate states, within the range of 1
< p
T
<
8 GeV
/c
are determined to be
σ
pp
→
D
0
X
=
1004
±
3
±
54
μ
b
,
σ
pp
→
D
+
X
=
402
±
2
±
30
μ
b
,
σ
pp
→
D
s
+
X
=
170
±
4
±
16
μ
b
,
σ
pp
→
D
∗
+
X
=
421
±
5
±
36
μ
b
,
where the uncertainties are statistical and systematic, respectively.
A
bstract
Measurements are reported of the central exclusive production of
J/ψ
and
ψ
(2
S
) mesons in
pp
collisions at a centre-of-mass energy of 13 TeV. Backgrounds are significantly reduced ...compared to previous measurements made at lower energies through the use of new forward shower counters. The products of the cross-sections and the branching fractions for the decays to dimuons, where both muons are within the pseudorapidity range 2
.
0
< η <
4
.
5, are measured to be
σ
J
/
ψ
→
μ
+
μ
−
=
435
±
18
±
11
±
17
p
b
σ
ψ
2
S
→
μ
+
μ
−
=
11.1
±
1.1
±
0.3
±
0.4
p
b
.
The first uncertainties are statistical, the second are systematic, and the third are due to the luminosity determination. The cross-sections are also measured differentially for meson rapidities between 2.0 and 4.5. Good agreement is observed with theoretical predictions. Photoproduction cross-sections are derived and compared to previous experiments, and a deviation from a pure power-law extrapolation of lower energy data is observed.
Study of J/ψ Production in Jets Andrews, J E; Appleby, R B; Artamonov, A ...
Physical review letters,
05/2017, Letnik:
118, Številka:
19
Journal Article
Recenzirano
Odprti dostop
The production of J/ψ mesons in jets is studied in the forward region of proton-proton collisions using data collected with the LHCb detector at a center-of-mass energy of 13 TeV. The fraction of the ...jet transverse momentum carried by the J/ψ meson, z(J/ψ)≡p_{T}(J/ψ)/p_{T}(jet), is measured using jets with p_{T}(jet)>20 GeV in the pseudorapidity range 2.5<η(jet)<4.0. The observed z(J/ψ) distribution for J/ψ mesons produced in b-hadron decays is consistent with expectations. However, the results for prompt J/ψ production do not agree with predictions based on fixed-order nonrelativistic QCD. This is the first measurement of the p_{T} fraction carried by prompt J/ψ mesons in jets at any experiment.
A measurement of the phase difference between the short- and long-distance contributions to the Formula: see text decay is performed by analysing the dimuon mass distribution. The analysis is based ...on
collision data corresponding to an integrated luminosity of 3Formula: see text collected by the LHCb experiment in 2011 and 2012. The long-distance contribution to the Formula: see text decay is modelled as a sum of relativistic Breit-Wigner amplitudes representing different vector meson resonances decaying to muon pairs, each with their own magnitude and phase. The measured phases of the Formula: see text and Formula: see text resonances are such that the interference with the short-distance component in dimuon mass regions far from their pole masses is small. In addition, constraints are placed on the Wilson coefficients, Formula: see text and Formula: see text, and the branching fraction of the short-distance component is measured.
The data sample of Λ_{b}^{0}→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 Λ_{b}^{0}→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.
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