A
bstract
A search for the doubly heavy
$$ {\Xi}_{bc}^0 $$
Ξ
bc
0
baryon using its decay to the
D
0
pK
–
final state is performed using proton-proton collision data at a centre-of-mass energy of 13 ...TeV collected by the LHCb experiment between 2016 and 2018, corresponding to an integrated luminosity of 5.4 fb
−
1
. No significant signal is found in the invariant mass range from 6.7 to 7.2 GeV/
c
2
. Upper limits are set at 95% credibility level on the ratio of the
$$ {\Xi}_{bc}^0 $$
Ξ
bc
0
production cross-section times its branching fraction to
D
0
pK
−
relative to that of the
$$ {\Lambda}_b^0\to {D}^0{pK}^{-} $$
Λ
b
0
→
D
0
pK
−
decay. The limits are set as a function of the
$$ {\Xi}_{bc}^0 $$
Ξ
bc
0
mass and lifetime hypotheses, in the rapidity range from 2.0 to 4.5 and in the transverse momentum region from 5 to 25 GeV/
c
. Upper limits range from 1
.
7
×
10
−
2
to 3
.
0
×
10
−
1
for the considered
$$ {\Xi}_{bc}^0 $$
Ξ
bc
0
mass and lifetime hypotheses.
A
bstract
The decays B
+
→
J
/
ψπ
+
π
−
K
+
are studied using a data set corresponding to an integrated luminosity of 9 fb
−
1
collected with the LHCb detector in proton-proton collisions between ...2011 and 2018. Precise measurements of the ratios of branching fractions with the intermediate ψ
2
(3823), χ
c1
(3872) and ψ(2S) states are reported. The values are
B
B
+
→
ψ
2
3823
K
+
×
B
ψ
2
3823
→
J
/
ψπ
+
π
−
B
B
+
→
χ
c
1
3872
K
+
×
B
χ
c
1
3872
→
J
/
ψπ
+
π
−
=
3.56
±
0.67
±
0.11
×
10
−
2
,
B
B
+
→
ψ
2
3823
K
+
×
B
ψ
2
3823
→
J
/
ψπ
+
π
−
B
B
+
→
ψ
2
S
K
+
×
B
ψ
2
S
→
J
/
ψπ
+
π
−
=
1.31
±
0.25
±
0.04
×
10
−
3
,
B
B
+
→
χ
c
1
3872
K
+
×
B
χ
c
1
3872
→
J
/
ψπ
+
π
−
B
B
+
→
ψ
2
S
K
+
×
B
ψ
2
S
→
J
/
ψπ
+
π
−
=
3.69
±
0.07
±
0.06
×
10
−
2
,
where the first uncertainty is statistical and the second is systematic. The decay of B
+
→
ψ
2
(3823)K
+
with ψ
2
(3823)
→
J
/
ψπ
+
π
−
is observed for the first time with a significance of 5.1 standard deviations. The mass differences between the ψ
2
(3823), χ
c1
(3872) and ψ(2S) states are measured to be
m
χ
c
1
3872
−
m
ψ
2
3823
=
47.50
±
0.53
±
0.13
MeV
/
c
2
,
m
ψ
2
3823
−
m
ψ
2
2
S
=
137.98
±
0.53
±
0.14
MeV
/
c
2
,
m
χ
c
1
3872
−
m
ψ
2
2
S
=
185.49
±
0.06
±
0.03
MeV
/
c
2
,
resulting in the most precise determination of the χ
c1
(3872) mass. The width of the ψ
2
(3823) state is found to be below 5.2 MeV at 90% confidence level. The Breit-Wigner width of the χ
c1
(3872) state is measured to be
Γ
χ
c
1
3872
BW
=
0.96
−
0.18
+
0.19
±
0.21
MeV
which is inconsistent with zero by 5.5 standard deviations.
Results on the production of the double strange cascade hyperon Ξ^{-} are reported for collisions of p(3.5 GeV)+Nb, studied with the High Acceptance Di-Electron Spectrometer (HADES) at SIS18 at GSI ...Helmholtzzentrum for Heavy-Ion Research, Darmstadt. For the first time, subthreshold Ξ^{-} production is observed in proton-nucleus interactions. Assuming a Ξ^{-} phase-space distribution similar to that of Λ hyperons, the production probability amounts to P_{Ξ^{-}}=2.0±0.4(stat)±0.3(norm)±0.6(syst)×10^{-4} resulting in a Ξ^{-}/(Λ+Σ^{0}) ratio of P_{Ξ^{-}}/P_{Λ+Σ^{0}}=1.2±0.3(stat)±0.4(syst)×10^{-2}. Available model predictions are significantly lower than the measured Ξ^{-} yield.
A
bstract
A precision measurement of the
$$ {B}_c^{+} $$
B
c
+
meson mass is performed using proton- proton collision data collected with the LHCb experiment at centre-of-mass energies of 7
,
8 and ...13 TeV, corresponding to a total integrated luminosity of 9
.
0 fb
−
1
. The
$$ {B}_c^{+} $$
B
c
+
mesons are reconstructed via the decays
$$ {B}_c^{+} $$
B
c
+
→ J/ψπ
+
,
$$ {B}_c^{+} $$
B
c
+
→ J/ψπ
+
π
−
π
+
,
$$ {B}_c^{+}\to J/\psi p\overline{p}{\pi}^{+} $$
B
c
+
→
J
/
ψp
p
¯
π
+
,
$$ {B}_c^{+}\to J/\psi {D}_s^{+} $$
B
c
+
→
J
/
ψ
D
s
+
,
$$ {B}_c^{+} $$
B
c
+
→ J/ψ D
0
K
+
and
$$ {B}_c^{+}\to {B}_s^0{\pi}^{+} $$
B
c
+
→
B
s
0
π
+
. Combining the results of the individual decay channels, the
$$ {B}_c^{+} $$
B
c
+
mass is measured to be 6274
.
47
±
0
.
27 (stat)
±
0
.
17 (syst) MeV
/c
2
. This is the most precise measurement of the
$$ {B}_c^{+} $$
B
c
+
mass to date. The difference between the
$$ {B}_c^{+} $$
B
c
+
and
$$ {B}_s^0 $$
B
s
0
meson masses is measured to be 907
.
75
±
0
.
37 (stat)
±
0
.
27 (syst) MeV
/c
.
This paper presents an analysis of the \( {\Lambda}_b^0 \) → J/ψΛ angular distribution and the transverse production polarisation of \( {\Lambda}_b^0 \) baryons in proton-proton collisions at ...centre-of-mass energies of 7, 8 and 13 TeV. The measurements are performed using data corresponding to an integrated luminosity of 4.9 fb–1, collected with the LHCb experiment. The polarisation is determined in a fiducial region of \( {\Lambda}_b^0 \) transverse momentum and pseudorapidity of 1 < pT < 20 GeV/c and 2 < η < 5, respectively. The data are consistent with \( {\Lambda}_b^0 \) baryons being produced unpolarised in this region. The parity-violating asymmetry parameter of the Λ → pπ– decay is also determined from the data and its value is found to be consistent with a recent measurement by the BES III collaboration.
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