322 research outputs found
Bose-Einstein correlations of same-sign charged pions in the forward region in pp collisions at √s=7 TeV
Bose-Einstein correlations of same-sign charged pions, produced in protonproton collisions at a 7 TeV centre-of-mass energy, are studied using a data sample collected
by the LHCb experiment. The signature for Bose-Einstein correlations is observed in the
form of an enhancement of pairs of like-sign charged pions with small four-momentum
difference squared. The charged-particle multiplicity dependence of the Bose-Einstein correlation parameters describing the correlation strength and the size of the emitting source
is investigated, determining both the correlation radius and the chaoticity parameter. The
measured correlation radius is found to increase as a function of increasing charged-particle
multiplicity, while the chaoticity parameter is seen to decreas
Measurement of the inelastic pp cross-section at a centre-of-mass energy of 13TeV
The cross-section for inelastic proton-proton collisions at a centre-of-mass energy of 13TeV is measured with the LHCb detector. The fiducial cross-section for inelastic interactions producing at least one prompt long-lived charged particle with momentum p > 2 GeV/c in the pseudorapidity range 2 < η < 5 is determined to be ϭ acc = 62:2 ± 0:2 ± 2:5mb. The first uncertainty is the intrinsic systematic uncertainty of the measurement, the second is due to the uncertainty on the integrated luminosity. The statistical uncertainty is negligible. Extrapolation to full phase space yields the total inelastic proton-proton cross-section ϭ inel = 75:4 ± 3:0 ± 4:5mb, where the first uncertainty is experimental and the second due to the extrapolation. An updated value of the inelastic cross-section at a centre-of-mass energy of 7TeV is also reported
Measurement of branching fractions of charmless four-body Λ<sub>b</sub> <sup>0</sup> and Ξ<sub>b</sub> <sup>0</sup> decays
A search for charmless four-body decays of Λb 0 and Ξb 0 baryons with a proton and three charged mesons (either kaons or pions) in the final state is performed. The data sample used was recorded in 2011 and 2012 with the LHCb experiment and corresponds to an integrated luminosity of 3 fb−1. Six decay modes are observed, among which Λb 0 → pK−π+π−,Λb 0 → pK−K+K−,Ξb 0 → pK−π+π− and Ξb 0 → pK−π+K− are established for the first time. Their branching fractions (including the ratio of hadronisation fractions in the case of the Ξb 0 baryon) are determined relative to the Λb 0 → Λc +π− decay.[Figure not available: see fulltext.].</p
Measurement of the branching fraction and CP asymmetry in B plus . J/.. plus decays
The branching fraction and direct asymmetry of the decay
are measured using proton-proton collision
data collected with the LHCb detector at centre-of-mass energies of 7 and 8
TeV, corresponding to a total integrated luminosity of 3\mbox{fb}^{-1}. The
following results are obtained: \begin{align} \mathcal{B}(B^{+}\rightarrow
J/\psi \rho^{+}) &= (3.81 ^{+0.25}_{-0.24} \pm 0.35) \times 10^{-5}, \nonumber
\\ \mathcal{A}^{C\!P} (B^{+}\rightarrow J/\psi \rho^{+}) &=
-0.045^{+0.056}_{-0.057} \pm 0.008, \nonumber \end{align} where the first
uncertainties are statistical and the second systematic. Both measurements are
the most precise to date.Comment: All figures and tables, along with any supplementary material and
additional information, are available at
https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2018-036.htm
Prompt and nonprompt J/ψ production and nuclear modification in pPb collisions at s<sub>NN</sub>=8.16 TeV
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.</p
First observation of the rare purely baryonic decay B0 → pp¯
The first observation of the decay of a
B
0
meson to a purely baryonic final state,
B
0
→
p
¯
p
, is reported. The proton-proton collision data sample used was collected with the LHCb experiment at center-of-mass energies of 7 and 8 TeV and corresponds to an integrated luminosity of
3.0
fb
−
1
. The branching fraction is determined to be
B
(
B
0
→
p
¯
p
)
=
(
1.25
±
0.27
±
0.18
)
×
10
−
8
, where the first uncertainty is statistical and the second systematic. The decay mode
B
0
→
p
¯
p
is the rarest decay of the
B
0
meson observed to date. The decay
B
0
s
→
p
¯
p
is also investigated. No signal is seen and the upper limit
B
(
B
0
s
→
p
¯
p
)
<
1.5
×
10
−
8
at 90% confidence level is set on the branching fraction
Measurement of CP -violating and mixing-induced observables in Bs0→ϕγ decays
A time-dependent analysis of the
B
0
s
→
ϕ
γ
decay rate is performed to determine the
C
P
-violating observables
S
ϕ
γ
and
C
ϕ
γ
and the mixing-induced observable
A
Δ
ϕ
γ
. The measurement is based on a sample of
p
p
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
S
ϕ
γ
=
0.43
±
0.30
±
0.11
,
C
ϕ
γ
=
0.11
±
0.29
±
0.11
, and
A
Δ
ϕ
γ
=
−
0.67
+
0.37
−
0.41
±
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
B
0
s
decays. The results are consistent with the standard model predictions
Observation of a narrow pentaquark state, P-c(4312)(+), and of the two-peak structure of the P-c(4450)(+)
A narrow pentaquark state, P-c(4312)(+), decaying to J/psi p, is discovered with a statistical significance of 7.3 sigma in a data sample of Lambda(0)(b) -> J/psi pK(-) decays, which is an order of magnitude larger than that previously analyzed by the LHCb Collaboration. The P-c(4450)(+) pentaquark structure formerly reported by LHCb is confirmed and observed to consist of two narrow overlapping peaks, P-c(4440)(+) and P-c(4457)(+), where the statistical significance of this two-peak interpretation is 5.4 sigma. The proximity of the Sigma(+)(c)(D) over bar (0) and Sigma(+)(c)(D) over bar (*0) thresholds to the observed narrow peaks suggests that they play an important role in the dynamics of these states
- …