We report the observation of a new structure in the Λb0π+π− spectrum using the full LHCb data set of pp collisions, corresponding to an integrated luminosity of 9 fb−1, collected at s=7, 8, and 13 ...TeV. A study of the structure suggests its interpretation as a superposition of two almost degenerate narrow states. The masses and widths of these states are measured to be mΛb(6146)0=6146.17±0.33±0.22±0.16 MeV,mΛb(6152)0=6152.51±0.26±0.22±0.16 MeV,ΓΛb(6146)0=2.9±1.3±0.3 MeV,ΓΛb(6152)0=2.1±0.8±0.3 MeV,with a mass splitting of Δm=6.34±0.32±0.02 MeV, where the first uncertainty is statistical, the second systematic. The third uncertainty for the mass measurements derives from the knowledge of the mass of the Λb0 baryon. The measured masses and widths of these new excited states suggest their possible interpretation as a doublet of Λb(1D)0 states.
A search for the decays Bs0 → e+e− and B0 → e+e− is performed using data collected with the LHCb experiment in proton-proton collisions at center-of-mass energies of 7, 8, and 13 TeV, corresponding ...to integrated luminosities of 1, 2, and 2 fb − 1 , respectively. No signal is observed. Assuming no contribution from B0 → e+e− decays, an upper limit on the branching fraction B (Bs0 → e+e−) < 9.4 ( 11.2 ) × 10−9 is obtained at 90(95)% confidence level. If no Bs0 → e+e− contribution is assumed, a limit of B (B0 → e+e−) < 2.5 ( 3.0 ) × 10−9 is determined at 90(95)% confidence level. These upper limits are more than one order of magnitude lower than the previous
Precision measurement of the Bc+ meson mass Alexander, M.; Alkhazov, G.; Aslanides, E. ...
The journal of high energy physics,
07/2020, Letnik:
2020, Številka:
7
Journal Article
Recenzirano
Odprti dostop
A
bstract
A precision measurement of the
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
+
mesons are reconstructed via the decays
B
c
+
→ J/ψπ
+
,
B
c
+
→ J/ψπ
+
π
−
π
+
,
B
c
+
→
J
/
ψp
p
¯
π
+
,
B
c
+
→
J
/
ψ
D
s
+
,
B
c
+
→ J/ψ D
0
K
+
and
B
c
+
→
B
s
0
π
+
. Combining the results of the individual decay channels, the
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
+
mass to date. The difference between the
B
c
+
and
B
s
0
meson masses is measured to be 907
.
75
±
0
.
37 (stat)
±
0
.
27 (syst) MeV
/c
.
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.
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
This paper presents an analysis of the
Λ
b
0
→ J/ψ
Λ angular distribution and the transverse production polarisation of
Λ
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
Λ
b
0
transverse momentum and pseudorapidity of 1
< p
T
<
20 GeV/
c
and 2
< η <
5, respectively. The data are consistent with
Λ
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.
Abstract
The first measurement of
$${{J}/\psi }$$
J
/
ψ
and
$${{D}} ^0$$
D
0
production in PbNe collisions by the LHCb experiment in its fixed-target configuration is reported. The production of
...$${{J}/\psi }$$
J
/
ψ
and
$${{D}} ^0$$
D
0
mesons is studied with a beam of lead ions with an energy of 2.5
$$\,\text {TeV}$$
TeV
per nucleon colliding on gaseous neon targets at rest, corresponding to a nucleon-nucleon centre-of-mass energy of
$$\sqrt{s_{\scriptscriptstyle \text {NN}}} =68.5\,\text {GeV} $$
s
NN
=
68.5
GeV
. The
$${{J}/\psi }$$
J
/
ψ
/
$${{D}} ^0$$
D
0
production cross-section ratio is studied as a function of rapidity, transverse momentum and collision centrality. These data are compared with measurements from
$$p\text {Ne}$$
p
Ne
collisions at the same energy and show no difference in the observed
$${{J}/\psi }$$
J
/
ψ
suppression trend when comparing
$$p\text {Ne}$$
p
Ne
and PbNe peripheral collisions with PbNe central collisions.
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