The first measurement of the lifetime of the doubly charmed baryon Ξ_{cc}^{++} is presented, with the signal reconstructed in the final state Λ_{c}^{+}K^{-}π^{+}π^{+}. The data sample used ...corresponds to an integrated luminosity of 1.7 fb^{-1}, collected by the LHCb experiment in proton-proton collisions at a center-of-mass energy of 13 TeV. The Ξ_{cc}^{++} lifetime is measured to be 0.256_{-0.022}^{+0.024}(stat)±0.014(syst) ps.
A
bstract
A search is presented for the lepton flavour violating decay
B
+
→
K
+
μ
−
τ
+
using a sample of proton-proton collisions at centre-of-mass energies of 7, 8, and 13 TeV, collected with the ...LHCb detector and corresponding to a total integrated luminosity of 9 fb
−
1
. The
τ
leptons are selected inclusively, primarily via decays with a single charged particle. The four-momentum of the
τ
lepton is determined by using
B
+
mesons from
B
s
2
∗
0
→
B
+
K
−
decays. No significant excess is observed, and an upper limit is set on the branching fraction
ℬ(
B
+
→
K
+
μ
−
τ
+
) < 3.9 × 10
−5
at 90 % confidence level.
The obtained limit is comparable to the world-best limit.
We report four narrow peaks in the Ξ_{b}^{0}K^{-} 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 mΩ_{b}(6316)^{-}=6315.64±0.31±0.07±0.50 MeV, mΩ_{b}(6330)^{-}=6330.30±0.28±0.07±0.50 MeV, mΩ_{b}(6340)^{-}=6339.71±0.26±0.05±0.50 MeV, mΩ_{b}(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 Ξ_{b}^{0} 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 ΓΩ_{b}(6316)^{-}<2.8 MeV, ΓΩ_{b}(6330)^{-}<3.1 MeV and ΓΩ_{b}(6340)^{-}<1.5 MeV. The natural width of the Ω_{b}(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 Ω_{b}(6316)^{-} and Ω_{b}(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 Ω_{b}^{-} resonances.
A
bstract
The production of
B
±
mesons is studied in pp collisions at centre-of-mass energies of 7 and 13 TeV, using
B
±
→
J
/
ψ K
±
decays and data samples corresponding to 1.0 fb
−1
and 0.3 fb
−1
, ...respectively. The production cross-sections summed over both charges and integrated over the transverse momentum range 0 <
p
T
< 40 GeV/
c
and the rapidity range 2.0 <
y
< 4.5 are measured to be
σ
pp
→
B
±
X
,
s
=
7
T
e
V
=
43.0
±
0.2
±
2.5
±
1.7
μ
b
,
σ
pp
→
B
±
X
,
s
=
13
T
e
V
=
86.6
±
0.5
±
5.4
±
3.4
μ
b
,
where the first uncertainties are statistical, the second are systematic, and the third are due to the limited knowledge of the
B
±
→
J
/
ψ K
±
branching fraction. The ratio of the cross-section at 13 TeV to that at 7 TeV is determined to be 2.02 ± 0.02 (stat) ± 0.12 (syst). Differential cross-sections are also reported as functions of
p
T
and
y
. All results are in agreement with theoretical calculations based on the state-of-art fixed next-to-leading order quantum chromodynamics.
The first observation of two structures consistent with resonances in the final states Λ_{b}^{0}π^{-} and Λ_{b}^{0}π^{+} is reported using samples of pp collision data collected by the LHCb ...experiment at sqrts=7 and 8 TeV, corresponding to an integrated luminosity of 3 fb^{-1}. The ground states Σ_{b}^{±} and Σ_{b}^{*±} are also confirmed and their masses and widths are precisely measured.
Search for the doubly charmed baryon Ξcc Alexander, M.; Alves, A. A.; Baryshnikov, F. ...
Science China. Physics, mechanics & astronomy,
02/2020, Letnik:
63, Številka:
2
Journal Article
Recenzirano
Odprti dostop
A search for the doubly charmed baryon
Ξ
c
c
+
is performed through its decay to the
Λ
c
+
K
−
π
+
final state, using proton-proton collision data collected with the LHCb detector at centre-of-mass ...energies of 7, 8 and 13 TeV. The data correspond to a total integrated luminosity of 9 fb
−1
. No significant signal is observed in the mass range from 3.4 to 3.8 GeV/
c
2
. Upper limits are set at 95% credibility level on the ratio of the
Ξ
c
c
+
production cross-section times the branching fraction to that of
Λ
c
+
and
Ξ
c
c
+
+
baryons. The limits are determined as functions of the
Ξ
c
c
+
mass for different lifetime hypotheses, in the rapidity range from 2.0 to 4.5 and the transverse momentum range from 4 to 15 GeV/
c
.
A
bstract
The production cross-sections of
ϒ
(1
S
),
ϒ
(2
S
) and
ϒ
(3
S
) mesons in proton-proton collisions at
s
=
13
TeV are measured with a data sample corresponding to an integrated luminosity ...of 277 ± 11 pb
−1
recorded by the LHCb experiment in 2015. The
ϒ
mesons are reconstructed in the decay mode
ϒ
→
μ
+
μ
−
. The differential production cross-sections times the dimuon branching fractions are measured as a function of the
ϒ
transverse momentum,
p
T
, and rapidity,
y
, over the range 0
< p
T
<
30 GeV
/c
and 2
.
0
< y <
4
.
5. The ratios of the cross-sections with respect to the LHCb measurement at
s
=
8
TeV are also determined. The measurements are compared with theoretical predictions based on NRQCD.
A
bstract
Forward top quark pair production is studied in
pp
collisions in the
μeb
final state using a data sample corresponding to an integrated luminosity of 1.93 fb
−1
collected with the LHCb ...experiment at a centre-of-mass energy of 13 TeV. The cross-section is measured in a fiducial region where both leptons have a transverse momentum greater than 20 GeV and a pseudorapidity between 2.0 and 4.5. The quadrature sum of the azimuthal separation and the difference in pseudorapidities, denoted Δ
R
, between the two leptons must be larger than 0.1. The
b
-jet axis is required to be separated from both leptons by a Δ
R
of 0.5, and to have a transverse momentum in excess of 20 GeV and a pseudorapidity between 2.2 and 4.2. The cross-section is measured to be
σ
t
t
¯
=
126
±
19
stat
±
16
syst
±
5
lumi
f
b
where the first uncertainty is statistical, the second is systematic, and the third is due to the luminosity determination. The measurement is compatible with the Standard Model prediction.
We report a measurement of the lifetime of the Ω_{c}^{0} baryon using proton-proton collision data at center-of-mass energies of 7 and 8 TeV, corresponding to an integrated luminosity of 3.0 fb^{-1} ...collected by the LHCb experiment. The sample consists of about 1000 Ω_{b}^{-}→Ω_{c}^{0}μ^{-}νover ¯_{μ}X signal decays, where the Ω_{c}^{0} baryon is detected in the pK^{-}K^{-}π^{+} final state and X represents possible additional undetected particles in the decay. The Ω_{c}^{0} lifetime is measured to be τ_{Ω_{c}^{0}}=268±24±10±2 fs, where the uncertainties are statistical, systematic, and from the uncertainty in the D^{+} lifetime, respectively. This value is nearly four times larger than, and inconsistent with, the current world-average value.
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