Precision measurement of the Ξcc++ mass Alexander, M.; Alves, A. A.; Baryshnikov, F. ...
The journal of high energy physics,
02/2020, Letnik:
2020, Številka:
2
Journal Article
Recenzirano
Odprti dostop
A
bstract
A measurement of the
Ξ
cc
+
+
mass is performed using data collected by the LHCb experiment between 2016 and 2018 in
pp
collisions at a centre-of-mass energy of 13 TeV, corresponding to an ...integrated luminosity of 5
.
6 fb
−
1
. The
Ξ
cc
+
+
candidates are reconstructed via the decay modes
Ξ
cc
+
+
→
Λ
c
+
K
−
π
+
π
+
and
Ξ
cc
+
+
→
Ξ
c
+
π
+
. The result, 3621
.
55
±
0
.
23 (stat)
±
0
.
30 (syst) MeV/
c
2
, is the most precise measurement of the
Ξ
cc
+
+
mass to date.
The production of J/ψ mesons is studied in proton-lead collisions at the centre-of-mass energy per nucleon pair sNN=8.16 TeV with the LHCb detector at the LHC. The double differential cross-sections ...of prompt and nonprompt J/ψ production are measured as a function of the J/ψ transverse momentum and rapidity in the nucleon–nucleon centre-of-mass frame. Forward-to-backward ratios and nuclear modification factors are determined. The results are compared with theoretical calculations based on collinear factorisation using nuclear parton distribution functions, on the colour glass condensate or on coherent energy loss models.
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
.
Two-particle angular correlations are studied in proton-lead collisions at a nucleon–nucleon centre-of-mass energy of sNN=5 TeV, collected with the LHCb detector at the LHC. The analysis is based on ...data recorded in two beam configurations, in which either the direction of the proton or that of the lead ion is analysed. The correlations are measured in the laboratory system as a function of relative pseudorapidity, Δη, and relative azimuthal angle, Δϕ, for events in different classes of event activity and for different bins of particle transverse momentum. In high-activity events a long-range correlation on the near side, Δϕ≈0, is observed in the pseudorapidity range 2.0<η<4.9. This measurement of long-range correlations on the near side in proton-lead collisions extends previous observations into the forward region up to η=4.9. The correlation increases with growing event activity and is found to be more pronounced in the direction of the lead beam. However, the correlation in the direction of the lead and proton beams are found to be compatible when comparing events with similar absolute activity in the direction analysed.
A
bstract
The production cross-section of
J/ψ
pairs is measured using a data sample of
pp
collisions collected by the LHCb experiment at a centre-of-mass energy of
s
=
13
TeV, corresponding to an ...integrated luminosity of 279 ±11 pb
−1
. The measurement is performed for
J/ψ
mesons with a transverse momentum of less than 10 GeV/
c
in the rapidity range 2
.
0
< y <
4
.
5. The production cross-section is measured to be 15
.
2 ± 1
.
0 ± 0
.
9 nb. The first uncertainty is statistical, and the second is systematic. The differential cross-sections as functions of several kinematic variables of the
J/ψ
pair are measured and compared to theoretical predictions.
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.
Evidence for the decay X(3872)→ψ(2S)γ Ajaltouni, Z.; An, L.; Andreotti, M. ...
Nuclear physics. B,
09/2014, Letnik:
886, Številka:
C
Journal Article
Recenzirano
Odprti dostop
Evidence for the decay mode X(3872)→ψ(2S)γ in B+→X(3872)K+ decays is found with a significance of 4.4 standard deviations. The analysis is based on a data sample of proton–proton collisions, ...corresponding to an integrated luminosity of 3 fb−1, collected with the LHCb detector, at centre-of-mass energies of 7 and 8 TeV. The ratio of the branching fraction of the X(3872)→ψ(2S)γ decay to that of the X(3872)→J/ψγ decay is measured to beB(X(3872)→ψ(2S)γ)B(X(3872)→J/ψγ)=2.46±0.64±0.29, where the first uncertainty is statistical and the second is systematic. The measured value does not support a pure DD¯⁎ molecular interpretation of the X(3872) state.
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
A combination of measurements sensitive to the CKM angle γ from LHCb is performed. The inputs are from analyses of time-integrated
B
+
→
DK
+
,
B
0
→
DK
∗0
,
B
0
→
DK
+
π
−
and
B
+
→
DK
+
π
...+
π
−
tree-level decays. In addition, results from a time-dependent analysis of
B
s
0
→
D
s
∓
K
±
decays are included. The combination yields
γ
= (72. 2
− 7.3
+ 6.8
)
°
, where the uncertainty includes systematic effects. The 95.5% confidence level interval is determined to be γ ∈ 55
.
9
,
85
.
2°. A second combination is investigated, also including measurements from
B
+
→
D
π
+
and
B
+
→
D
π
+
π
−
π
+
decays, which yields compatible results.
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