A
bstract
Using proton-proton collision data, corresponding to an integrated luminosity of 9 fb
−
1
collected with the LHCb detector, seven decay modes of the
B
c
+
meson into a J
/
ψ or ψ(2S) meson ...and three charged hadrons, kaons or pions, are studied. The decays
B
c
+
→ (ψ(2S) → J
/
ψπ
+
π
−
)π
+
,
B
c
+
→ ψ(2S)π
+
π
−
π
+
,
B
c
+
→ J
/
ψK
+
π
−
π
+
and
B
c
+
→ J
/
ψK
+
K
−
K
+
are observed for the first time, and evidence for the
B
c
+
→ ψ(2S)K
+
K
−
π
+
, decay is found, where J
/
ψ and ψ(2S) mesons are reconstructed in their dimuon decay modes. The ratios of branching fractions between the different
B
c
+
decays are reported as well as the fractions of the decays proceeding via intermediate resonances. The results largely support the factorisation approach used for a theoretical description of the studied decays.
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.
A
bstract
The associated production of prompt
J/ψ
and
Υ
mesons in
pp
collisions at a centre-of-mass energy of
s
= 13 TeV is studied using LHCb data, corresponding to an integrated luminosity of 4 fb
...−
1
. The measurement is performed for
J/ψ
(
Υ
) mesons with a transverse momentum
p
T
<
10 (30) GeV/
c
in the rapidity range 2
.
0
< y <
4
.
5. In this kinematic range, the cross-section of the associated production of prompt
J/ψ
and
Υ
(1
S
) mesons is measured to be 133 ± 22 ± 7 ± 3 pb, with a significance of 7
.
9
σ
, and that of prompt
J/ψ
and
Υ
(2
S
) mesons to be 76 ± 21 ± 4 ± 7 pb, with a significance of 4
.
9
σ
. The first uncertainty is statistical, the second systematic, and the third due to uncertainties on the used branching fractions. This is the first observation of the associated production of
J/ψ
and
Υ
(1
S
) in proton-proton collisions. Differential cross-sections are measured as functions of variables that are sensitive to kinematic correlations between the
J/ψ
and
Υ
(1
S
) mesons. The effective cross-sections of the associated production of prompt
J/ψ
and
Υ
mesons are obtained and found to be compatible with measurements using other particle productions.
A
bstract
A search is performed for rare and forbidden charm decays of the form
D
s
+
→
h
±
ℓ
+
ℓ
′
∓
, where
h
±
is a pion or kaon and
ℓ
(′)±
is an electron or muon. The measurements are performed ...using proton-proton collision data, corresponding to an integrated luminosity of 1
.
6 fb
−
1
, collected by the LHCb experiment in 2016. No evidence is observed for the 25 decay modes that are investigated and 90 % confidence level limits on the branching fractions are set between 1
.
4
×
10
−
8
and 6
.
4
×
10
−
6
. In most cases, these results represent an improvement on existing limits by one to two orders of magnitude.
A measurement of
D
0
meson production by the LHCb experiment in its fixed-target configuration is presented. The production of
D
0
mesons is studied with a beam of 2.5
Te
V
protons colliding on a ...gaseous neon target at rest, corresponding to a nucleon–nucleon centre-of-mass energy of
s
NN
=
68.5
Ge
V
. The sum of the
D
0
and
D
¯
0
production cross-section in
p
Ne
collisions in the centre-of-mass rapidity range
y
⋆
∈
-
2.29
,
0
is found to be
σ
D
0
y
⋆
∈
-
2.29
,
0
=
48.2
±
0.3
±
4.5
μ
b
/
nucleon
where the first uncertainty is statistical and the second is systematic. The
D
0
-
D
¯
0
production asymmetry is also evaluated and suggests a trend towards negative values at large negative
y
⋆
. The considered models do not account precisely for all the features observed in the LHCb data, but theoretical predictions including 1
%
intrinsic charm and 10
%
recombination contributions better describe the data than the other models considered.
Observation of new excited Bs0 states Alexander, M.; Baryshnikov, F.; Belov, I. ...
The European physical journal. C, Particles and fields,
07/2021, Letnik:
81, Številka:
7
Journal Article
Recenzirano
Odprti dostop
A structure is observed in the
B
±
K
∓
mass spectrum in 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 structure is interpreted as the result of overlapping excited
B
s
0
states. With high significance, a two-peak hypothesis provides a better description of the data than a single resonance. Under this hypothesis the masses and widths of the two states, assuming they decay directly to
B
±
K
∓
, are determined to be
m
1
=
6063.5
±
1.2
(stat)
±
0.8
(syst)
Me
,
Γ
1
=
26
±
4
(stat)
±
4
(syst)
Me
,
m
2
=
6114
±
3
(stat)
±
5
(syst)
Me
,
Γ
2
=
66
±
18
(stat)
±
21
(syst)
Me
.
Alternative values assuming a decay through
B
∗
±
K
∓
, with a missing photon from the
B
∗
±
→
B
±
γ
decay, which are shifted by approximately 45
Me
V, are also determined. The possibility of a single state decaying in both channels is also considered. The ratio of the total production cross-section times branching fraction of the new states relative to the previously observed
B
s
2
∗
0
state is determined to be
0.87
±
0.15
(stat)
±
0.19
(syst)
.
A measurement of the CP-violating observables from B -> (DK +/-)-K-* and B-+/- -> D-*pi(+/-) decays is presented, where D-*(D) is an admixture of D-*0 and D-0 (D-0 and (0)) states and is ...reconstructed through the decay chains D-*-> D pi(0)/gamma and D -> KS0 pi+pi-/KS0K+K-. The measurement is performed by analysing the signal yield variation across the D decay phase space and is independent of any amplitude model. The data sample used was collected by the LHCb experiment in proton-proton collisions and corresponds to a total integrated luminosity of 9 fb(-1) at centre-of-mass energies of 7, 8 and 13 TeV. The CKM angle gamma is determined to be (69(-14)(+13))degrees using the measured CP-violating observables. The hadronic parameters r(B)(D)*(K +/-),r(B)(D)*(pi +/-),delta(D)(B)*(K +/-),delta(D)(B)*(pi +/-), which are the ratios and strong phase differences between favoured and suppressed B-+/- decays, are also reported.
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