41 research outputs found
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Updated measurement of time-dependent CP -violating observables in Bs0→J/ψ<sup>K+</sup><sup>K-</sup> decays
The decay-time-dependent asymmetry in
decays is measured using proton-proton collision data, corresponding to an
integrated luminosity of , collected with the LHCb
detector at a centre-of-mass energy of in 2015 and 2016.
Using a sample of approximately 117\,000 signal decays with an invariant mass in the vicinity of the resonance, the -violating
phase is measured, along with the difference in decay widths of the
light and heavy mass eigenstates of the - system,
. The difference of the average and meson
decay widths, , is determined using in addition a sample of
decays. The values obtained are , and , where the first uncertainty is statistical and the
second systematic. These are the most precise single measurements of these
quantities to date and are consistent with expectations based on the Standard
Model and with a previous LHCb analysis of this decay using data recorded at
centre-of-mass energies 7 and 8 TeV. Finally, the results are combined with
recent results from decays obtained using
the same dataset as this analysis, and with previous independent LHCb results
Observation of Two New Excited Ξb0 States Decaying to Λb0 K-π+
Two narrow resonant states are observed in the Λb0K-π+ mass spectrum using a data sample of proton-proton collisions at a center-of-mass energy of 13 TeV, collected by the LHCb experiment and corresponding to an integrated luminosity of 6 fb-1. The minimal quark content of the Λb0K-π+ system indicates that these are excited Ξb0 baryons. The masses of the Ξb(6327)0 and Ξb(6333)0 states are m[Ξb(6327)0]=6327.28-0.21+0.23±0.12±0.24 and m[Ξb(6333)0]=6332.69-0.18+0.17±0.03±0.22 MeV, respectively, with a mass splitting of Δm=5.41-0.27+0.26±0.12 MeV, where the uncertainties are statistical, systematic, and due to the Λb0 mass measurement. The measured natural widths of these states are consistent with zero, with upper limits of Γ[Ξb(6327)0]<2.20(2.56) and Γ[Ξb(6333)0]<1.60(1.92) MeV at a 90% (95%) credibility level. The significance of the two-peak hypothesis is larger than nine (five) Gaussian standard deviations compared to the no-peak (one-peak) hypothesis. The masses, widths, and resonant structure of the new states are in good agreement with the expectations for a doublet of 1D Ξb0 resonances
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Measurement of the η<inf>c</inf>(1 S) production cross-section in p p collisions at √s=13TeV
Using a data sample corresponding to an integrated luminosity of
, collected by the LHCb experiment, the production of the
state in proton-proton collisions at a centre-of-mass energy of
is studied in the rapidity range
and in the transverse momentum range . The
cross-section for prompt production of mesons relative to that of
the meson is measured using the decay mode and is found
to be . The quoted uncertainties are, in order, statistical, systematic and due
to uncertainties on the branching fractions of the and
decays. The prompt production
cross-section is determined to be , where the last uncertainty includes that on the
meson cross-section. The ratio of the branching fractions of -hadron decays
to the and states is measured to be
, where the last uncertainty is due to those on the branching
fractions of the and decays.
The difference between the and masses is also
determined to be , which is the most
precise single measurement of this quantity to date
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Test of lepton universality in beauty-quark decays
Funder: We express our gratitude to our colleagues in the CERN accelerator departments for the excellent performance of the LHC. We thank the technical and administrative staff at the LHCb institutes. We acknowledge support from CERN and from the national agencies: CAPES, CNPq, FAPERJ and FINEP (Brazil); MOST and NSFC (China); CNRS/IN2P3 (France); BMBF, DFG and MPG (Germany); INFN (Italy); NWO (Netherlands); MNiSW and NCN (Poland); MEN/IFA (Romania); MSHE (Russia); MICINN (Spain); SNSF and SER (Switzerland); NASU (Ukraine); STFC (United Kingdom); DOE NP and NSF (USA). We acknowledge the computing resources that are provided by CERN, IN2P3 (France), KIT and DESY (Germany), INFN (Italy), SURF (Netherlands), PIC (Spain), GridPP (United Kingdom), RRCKI and Yandex LLC (Russia), CSCS (Switzerland), IFIN-HH (Romania), CBPF (Brazil), PL-GRID (Poland) and NERSC (USA). We are indebted to the communities behind the multiple open-source software packages on which we depend. Individual groups or members have received support from ARC and ARDC (Australia); AvH Foundation (Germany); EPLANET, Marie Sk\l{}odowska-Curie Actions and ERC (European Union); A*MIDEX, ANR, Labex P2IO and OCEVU, and R\'{e}gion Auvergne-Rh\^{o}ne-Alpes (France); Key Research Program of Frontier Sciences of CAS, CAS PIFI, CAS CCEPP, Fundamental Research Funds for the Central Universities, and Sci. \& Tech. Program of Guangzhou (China); RFBR, RSF and Yandex LLC (Russia); GVA, XuntaGal and GENCAT (Spain); the Leverhulme Trust, the Royal Society and UKRI (United Kingdom).The Standard Model of particle physics currently provides our best
description of fundamental particles and their interactions. The theory
predicts that the different charged leptons, the electron, muon and tau, have
identical electroweak interaction strengths. Previous measurements have shown a
wide range of particle decays are consistent with this principle of lepton
universality. This article presents evidence for the breaking of lepton
universality in beauty-quark decays, with a significance of 3.1 standard
deviations, based on proton-proton collision data collected with the LHCb
detector at CERN's Large Hadron Collider. The measurements are of processes in
which a beauty meson transforms into a strange meson with the emission of
either an electron and a positron, or a muon and an antimuon. If confirmed by
future measurements, this violation of lepton universality would imply physics
beyond the Standard Model, such as a new fundamental interaction between quarks
and leptons
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Search for long-lived particles decaying to e<sup>±</sup> μ<sup>∓</sup> ν
Long-lived particles decaying to , with masses between 7
and GeV/c and lifetimes between 2 and ps, are searched for by
looking at displaced vertices containing electrons and muons of opposite
charges. The search is performed using fb of collisions
collected with the LHCb detector at a centre-of-mass energy of
TeV. Three mechanisms of production of long-lived particles are considered: the
direct pair production from quark interactions, the pair production from the
decay of a Standard-Model-like Higgs boson with a mass of GeV/c, and
the charged current production from an on-shell boson with an additional
lepton. No evidence of these long-lived states is obtained and upper limits on
the production cross-section times branching fraction are set on the different
production modes
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Measurement of the branching fraction of the <sup>B0</sup>→Ds+<sup>π-</sup> decay
A branching fraction measurement of the
decay is presented using proton-proton collision data collected with the LHCb
experiment, corresponding to an integrated luminosity of fb. The
branching fraction is found to be , where the
first uncertainty is statistical, the second systematic and the third is due to
the uncertainty on the , and branching
fractions. This is the most precise single measurement of this quantity to
date. As this decay proceeds through a single amplitude involving a
charged-current transition, the result provides information on non-factorisable
strong interaction effects and the magnitude of the Cabibbo-Kobayashi-Maskawa
matrix element . Additionally, the collision energy dependence of the
hadronisation-fraction ratio is measured through
and
decays
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Observation of new excited Bs0 states
A structure is observed in the 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. The structure is interpreted as the result of
overlapping excited 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 , are determined to be
Alternative values assuming a decay through , with a missing
photon from the decay, which are shifted by
approximately 45 MeV 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 state is determined to be
Evidence for an η<inf>c</inf>(1 S) π<sup>-</sup> resonance in B<sup>0</sup>→ η<inf>c</inf>(1 S) K<sup>+</sup>π<sup>-</sup> decays
© 2018, CERN for the benefit of the LHCb collaboration. A Dalitz plot analysis of B0→ηc(1S)K+π- decays is performed using data samples of pp collisions collected with the LHCb detector at centre-of-mass energies of s=7,8 and 13TeV, corresponding to a total integrated luminosity of 4.7fb-1. A satisfactory description of the data is obtained when including a contribution representing an exotic ηc(1 S) π- resonant state. The significance of this exotic resonance is more than three standard deviations, while its mass and width are 4096±20-22+18MeV and 152±58-35+60MeV, respectively. The spin-parity assignments JP= 0 + and JP= 1 - are both consistent with the data. In addition, the first measurement of the B0→ηc(1S)K+π- branching fraction is performed and gives B(B0→ηc(1S)K+π-)=(5.73±0.24±0.13±0.66)×10-4,where the first uncertainty is statistical, the second systematic, and the third is due to limited knowledge of external branching fractions
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Erratum to: Updated measurement of time-dependent C P -violating observables in B s 0 → J / ψ K + K - decays (The European Physical Journal C, (2019), 79, 8, (706), 10.1140/epjc/s10052-019-7159-8)
In the Introduction section of the original article [1].</jats:p
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Centrality determination in heavy-ion collisions with the LHCb detector
The centrality of heavy-ion collisions is directly related to the medium
created therein. A procedure to determine the centrality of collisions with the
LHCb detector is implemented for lead-lead collisions at
and lead-neon
fixed-target collisions at . The energy deposits in the electromagnetic calorimeter are used
to determine and define the centrality classes. The correspondence between the
number of participants and the centrality for the lead-lead collisions is in
good agreement with the correspondence found in other experiments, and the
centrality measurements for the lead-neon collisions presented here are the
first performed in fixed-target collisions at the LHC