A search for the flavor-changing neutral-current decay Λc+→pμ+μ− is reported using a data set corresponding to an integrated luminosity of 3.0 fb−1 collected by the LHCb Collaboration. No significant ...signal is observed outside of the dimuon mass regions around the ϕ and ω resonances, and an upper limit is placed on the branching fraction of B(Λc+→pμ+μ−)<7.7(9.6)×10−8 at 90%(95%) confidence level. A significant signal is observed in the ω dimuon mass region for the first time.
The ratio of the B0s and B+ fragmentation fractions fs and fu is studied with B0s → J/ψ ϕ and B+ → J/ψK+ decays using data collected by the LHCb experiment in proton-proton collisions at 7, 8, and 13 ...TeV center-of-mass energies. The analysis is performed in bins of B -meson momentum, longitudinal momentum, transverse momentum, pseudorapidity, and rapidity. The fragmentation-fraction ratio fs/fu is observed to depend on the B -meson transverse momentum with a significance of 6.0σ . This dependency is driven by the 13 TeV sample (8.7σ), while the results for the other collision energies are not significant when considered separately. Furthermore, the results show a 4.8σ evidence for an increase of fs/fu as a function of collision energy.
A time-dependent analysis of the Bs0→ϕγ decay rate is performed to determine the CP -violating observables Sϕγ and Cϕγ and the mixing-induced observable AϕγΔ. The measurement is based on a sample of ...pp collision data recorded with the LHCb detector, corresponding to an integrated luminosity of 3 fb−1 at center-of-mass energies of 7 and 8 TeV. The measured values are Sϕγ=0.43±0.30±0.11, Cϕγ=0.11±0.29±0.11, and AϕγΔ=−0.67−0.41+0.37±0.17, where the first uncertainty is statistical and the second systematic. This is the first measurement of the observables S and C in radiative Bs0 decays. The results are consistent with the standard model predictions.
The production of charged hadrons within jets recoiling against a Z boson is measured in proton-proton collision data at √s = 8 TeV recorded by the LHCb experiment. The charged-hadron structure of ...the jet is studied longitudinally and transverse to the jet axis for jets with transverse momentum pT > 20 GeV and in the pseudorapidity range 2.5 < η < 4. These are the first measurements of jet hadronization at these forward rapidities and also the first where the jet is produced in association with a Z boson. In contrast to previous hadronization measurements at the Large Hadron Collider, which are dominated by gluon jets, these measurements probe predominantly light-quark jets which are found to be more longitudinally and transversely collimated with respect to the jet axis when compared to the previous gluon dominated measurements. Therefore, these results provide valuable information on differences between quarks and gluons regarding nonperturbative hadronization dynamics.
A
bstract
The prompt production of Λ
c
+
baryons is studied in proton-lead collisions collected with the LHCb detector at the LHC. The data sample corresponds to an integrated luminosity of 1.58 nb
...−1
recorded at a nucleon-nucleon centre-of-mass energy of
s
N
N
=
5.02
TeV. Measurements of the differential cross-section and the forwardbackward production ratio are reported for Λ
c
+
baryons with transverse momenta in the range 2 <
p
T
< 10 GeV/c and rapidities in the ranges 1.5 <
y
∗
< 4.0 and −4.5 <
y
∗
< −2.5 in the nucleon-nucleon centre-of-mass system. The ratio of cross-sections of Λ
c
+
baryons and
D
0
mesons is also reported. The results are compared with next-to-leading order calculations that use nuclear parton distribution functions.
The first observation of the rare decay Bs0→ϕπ+π− and evidence for B0→ϕπ+π− are reported, using pp collision data recorded by the LHCb detector at center-of-mass energies s=7 and 8 TeV, corresponding ...to an integrated luminosity of 3 fb−1. The branching fractions in the π+π− invariant mass range 400<m(π+π−)<1600 MeV/c2 are 3.48±0.23±0.17±0.35×10−6 and 1.82±0.25±0.41±0.14×10−7 for Bs0→ϕπ+π− and B0→ϕπ+π− respectively, where the uncertainties are statistical, systematic and from the normalization mode Bs0→ϕϕ. A combined analysis of the π+π− mass spectrum and the decay angles of the final-state particles identifies the exclusive decays Bs0→ϕf0(980), Bs0→ϕf2(1270), and Bs0→ϕρ0 with branching fractions of 1.12±0.16−0.08+0.09±0.11×10−6, 0.61±0.13−0.05+0.12±0.06×10−6 and 2.7±0.7±0.2±0.2×10−7, respectively.
A
bstract
A measurement of the cross-section for
W
→
eν
production in
pp
collisions is presented using data corresponding to an integrated luminosity of 2 fb
−1
collected by the LHCb experiment at a ...centre-of-mass energy of
s
=
8
TeV. The electrons are required to have more than 20 GeV of transverse momentum and to lie between 2
.
00 and 4
.
25 in pseudorapidity. The inclusive
W
production cross-sections, where the
W
decays to
eν
, are measured to be
σ
W
+
→
e
+
ν
e
=
1124.4
±
2.1
±
21.5
±
11.2
±
13.0
p
b
,
σ
W
−
→
e
−
ν
¯
e
=
809.0
±
1.9
±
18.1
±
7.0
±
9.4
p
b
,
where the first uncertainties are statistical, the second are systematic, the third are due to the knowledge of the LHC beam energy and the fourth are due to the luminosity determination.
Differential cross-sections as a function of the electron pseudorapidity are measured. The
W
+
/W
−
cross-section ratio and production charge asymmetry are also reported. Results are compared with theoretical predictions at next-to-next-to-leading order in perturbative quantum chromodynamics. Finally, in a precise test of lepton universality, the ratio of
W
boson branching fractions is determined to be
ℬ
W
→
e
ν
/
ℬ
W
→
μ
ν
=
1.020
±
0.002
±
0.019
,
where the first uncertainty is statistical and the second is systematic.
The first observation of the D0→π+π-μ+μ- and D0→K+K-μ+μ- decays is reported using a sample of proton-proton collisions collected by LHCb at a center-of-mass energy of 8 TeV, and corresponding to 2 ...fb-1 of integrated luminosity. The corresponding branching fractions are measured using as normalization the decay D0→K-π+μ+μ-ρ0/ω, where the two muons are consistent with coming from the decay of a ρ0 or ω meson. The results are B (D0→π+π-μ+μ- )=(9.64 ±0.48 ±0.51 ±0.97 )×10-7 and B (D0→K+K-μ+μ- )=(1.54 ±0.27 ±0.09 ±0.16 )×10-7 , where the uncertainties are statistical, systematic, and due to the limited knowledge of the normalization branching fraction. The dependence of the branching fraction on the dimuon mass is also investigated.
Observation of Bc+ → D0K+ Decays Adinolfi, M.; Alessio, F.; Aslanides, E. ...
Physical review letters,
03/2017, Letnik:
118, Številka:
11
Journal Article
Recenzirano
Odprti dostop
Using proton-proton collision data corresponding to an integrated luminosity of 3.0 fb-1, recorded by the LHCb detector at center-of-mass energies of 7 and 8 TeV, the $B_c^+$ → $D^0K^+$ decay is ...observed with a statistical significance of 5.1 standard deviations. By normalizing to $B^+$ → $\bar{D}^0π^+$ decays, a measurement of the branching fraction multiplied by the production rates for $B_c^+$ relative to B+ mesons in the LHCb acceptance is obtained, $R_{D^0K}$ = ($f_c / f_u$) x $B$($B^+_c$ → $D^0K^+$) = ($9.3_{-2.5}^{+2.8}$ ± 0.6) × 10-7, where the first uncertainty is statistical and the second is systematic. This decay is expected to proceed predominantly through weak annihilation and penguin amplitudes, and is the first $B^+_c$ decay of this nature to be observed.
A
bstract
Using proton-proton collision data, corresponding to an integrated luminosity of 9 fb
−1
, collected with the LHCb detector between 2011 and 2018, a new narrow charmonium state, the X(3842) ...resonance, is observed in the decay modes
X
3842
→
D
0
D
¯
0
and X(3842) →
D
+
D
−
. The mass and the natural width of this state are measured to be
m
X
3842
=
3842.71
±
0.16
±
0.12
M
e
V
/
c
2
,
Γ
X
3842
=
2.79
±
0.51
±
0.35
M
e
V
,
where the first uncertainty is statistical and the second is systematic. The observed mass and narrow natural width suggest the interpretation of the new state as the unobserved (spin-3
ψ
3
1
3
D
3
) charmonium state.
In addition, prompt hadroproduction of the
ψ
(3770) and
χ
2
(3930) states is observed for the first time, and the parameters of these states are measured to be
m
ψ
3770
=
3778.1
±
0.7
±
0.6
M
e
V
/
c
2
,
m
χ
2
3930
=
3921.9
±
0.6
±
0.2
M
e
V
/
c
2
,
Γ
χ
2
3930
=
36.6
±
1.9
±
0.9
M
e
V
,
where the first uncertainty is statistical and the second is systematic.
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