A search for B+ → Ds+K+K− decays is performed using pp collision data corresponding to an integrated luminosity of 4.8 fb−1, collected at centre-of-mass energies of 7, 8 and 13 TeV with the LHCb ...experiment. A significant signal is observed for the first time and the branching fraction is determined to beℬB+→Ds+K+K−=7.1±0.5±0.6±0.7×10−6,where the first uncertainty is statistical, the second systematic and the third due to the uncertainty on the branching fraction of the normalisation mode B+→Ds+D¯0. A search is also performed for the pure annihilation decay B+ → Ds+ϕ. No significant signal is observed and a limit ofℬB+→Ds+ϕ<4.9×10−74.2×10−7is set on the branching fraction at 95% (90%) confidence level.
A measurement of the ratio of the branching fractions of the B(+) → K(+)μ(+)μ(-) and B(+) → K(+)e(+)e(-) decays is presented using proton-proton collision data, corresponding to an integrated ...luminosity of 3.0 fb(-1), recorded with the LHCb experiment at center-of-mass energies of 7 and 8 TeV. The value of the ratio of branching fractions for the dilepton invariant mass squared range 1 < q(2) < 6 GeV(2)/c(4) is measured to be 0.745(-0.074)(+0.090)(stat) ± 0.036(syst). This value is the most precise measurement of the ratio of branching fractions to date and is compatible with the standard model prediction within 2.6 standard deviations.
The first simultaneous test of muon-electron universality using B+→K+ℓ+ℓ− and B0→K*0ℓ+ℓ− decays is performed, in two ranges of the dilepton invariant-mass squared, q2. The analysis uses beauty mesons ...produced in proton-proton collisions collected with the LHCb detector between 2011 and 2018, corresponding to an integrated luminosity of 9 fb−1. Each of the four lepton universality measurements reported is either the first in the given q2 interval or supersedes previous LHCb measurements. The results are compatible with the predictions of the Standard Model.
A highly significant structure is observed in the Λ_{c}^{+}K^{-}π^{+}π^{+} mass spectrum, where the Λ_{c}^{+} baryon is reconstructed in the decay mode pK^{-}π^{+}. The structure is consistent with ...originating from a weakly decaying particle, identified as the doubly charmed baryon Ξ_{cc}^{++}. The difference between the masses of the Ξ_{cc}^{++} and Λ_{c}^{+} states is measured to be 1334.94±0.72(stat.)±0.27(syst.) MeV/c^{2}, and the Ξ_{cc}^{++} mass is then determined to be 3621.40±0.72(stat.)±0.27(syst.)±0.14(Λ_{c}^{+}) MeV/c^{2}, where the last uncertainty is due to the limited knowledge of the Λ_{c}^{+} mass. The state is observed in a sample of proton-proton collision data collected by the LHCb experiment at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 1.7 fb^{-1}, and confirmed in an additional sample of data collected at 8 TeV.
A search is made for the highly-suppressed B meson decays B+→K+K+π− and B+→π+π+K− using a data sample corresponding to an integrated luminosity of 3.0 fb−1 collected by the LHCb experiment in ...proton–proton collisions at centre-of-mass energies of 7 and 8 TeV. No evidence is found for the decays, and upper limits at 90% confidence level are determined to be B(B+→K+K+π−)<1.1×10−8 and B(B+→π+π+K−)<4.6×10−8.
Abstract
For accurate determination of particle masses accurate
knowledge of the momentum scale of the detectors is crucial. The
procedure used to calibrate the momentum scale of the LHCb
...spectrometer is described and illustrated using the performance
obtained with an integrated luminosity of 1.6 fb
-1
collected during 2016 in
pp
running. The procedure uses large
samples of
J
/
ψ
→
μ
+
μ
-
and
B
+
→
J
/
ψ
K
+
decays and leads to a relative accuracy
of 3 × 10
-4
on the momentum scale.
Observations of exotic structures in the J/ψp channel, which we refer to as charmonium-pentaquark states, in Λ_{b}^{0}→J/ψK^{-}p decays are presented. The data sample corresponds to an integrated ...luminosity of 3 fb^{-1} acquired with the LHCb detector from 7 and 8 TeV pp collisions. An amplitude analysis of the three-body final state reproduces the two-body mass and angular distributions. To obtain a satisfactory fit of the structures seen in the J/ψp mass spectrum, it is necessary to include two Breit-Wigner amplitudes that each describe a resonant state. The significance of each of these resonances is more than 9 standard deviations. One has a mass of 4380±8±29 MeV and a width of 205±18±86 MeV, while the second is narrower, with a mass of 4449.8±1.7±2.5 MeV and a width of 39±5±19 MeV. The preferred J^{P} assignments are of opposite parity, with one state having spin 3/2 and the other 5/2.
The first full amplitude analysis of B^{+}→J/ψϕK^{+} with J/ψ→μ^{+}μ^{-}, ϕ→K^{+}K^{-} decays is performed with a data sample of 3 fb^{-1} of pp collision data collected at sqrts=7 and 8 TeV with ...the LHCb detector. The data cannot be described by a model that contains only excited kaon states decaying into ϕK^{+}, and four J/ψϕ structures are observed, each with significance over 5 standard deviations. The quantum numbers of these structures are determined with significance of at least 4 standard deviations. The lightest has mass consistent with, but width much larger than, previous measurements of the claimed X(4140) state.
Helium identification with LHCb Adinolfi, M.; Andreola, P.; Barbetti, M. ...
Journal of instrumentation,
02/2024, Letnik:
19, Številka:
2
Journal Article
Recenzirano
Odprti dostop
Abstract
The identification of helium nuclei at LHCb is achieved using a method based on
measurements of ionisation losses in the silicon sensors and timing measurements in the Outer
Tracker drift ...tubes. The background from photon conversions is reduced using the RICH detectors
and an isolation requirement. The method is developed using
pp
collision data at
√(
s
) = 13 TeV recorded by the LHCb experiment in the years 2016 to 2018, corresponding
to an integrated luminosity of 5.5 fb
-1
. A total of around 10
5
helium and antihelium
candidates are identified with negligible background contamination. The helium identification
efficiency is estimated to be approximately 50% with a corresponding background rejection
rate of up to (10
12
). These results demonstrate the feasibility of a rich
programme of measurements of QCD and astrophysics interest involving light nuclei.
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