178 research outputs found
Test of lepton universality in decays
The first simultaneous test of muon-electron universality using
and decays is performed, in two ranges of the dilepton
invariant-mass squared, . 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 . Each
of the four lepton universality measurements reported is either the first in
the given interval or supersedes previous LHCb measurements. The
results are compatible with the predictions of the Standard Model.Comment: All figures and tables, along with any supplementary material and
additional information, are available at
https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2022-046.html (LHCb
public pages
Precision measurement of violation in the penguin-mediated decay
A flavor-tagged time-dependent angular analysis of the decay
is performed using collision data collected
by the LHCb experiment at % at TeV, the center-of-mass energy of
13 TeV, corresponding to an integrated luminosity of 6 fb^{-1}. The
-violating phase and direct -violation parameter are measured
to be rad and
, respectively, assuming the same values
for all polarization states of the system. In these results, the
first uncertainties are statistical and the second systematic. These parameters
are also determined separately for each polarization state, showing no evidence
for polarization dependence. The results are combined with previous LHCb
measurements using collisions at center-of-mass energies of 7 and 8 TeV,
yielding rad and . This is the most precise study of time-dependent violation
in a penguin-dominated meson decay. The results are consistent with
symmetry and with the Standard Model predictions.Comment: All figures and tables, along with any supplementary material and
additional information, are available at
https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2023-001.html (LHCb
public pages
Observation of a resonant structure near the threshold in the decay
An amplitude analysis of the decay is carried out to
study for the first time its intermediate resonant contributions, using
proton-proton collision data collected with the LHCb detector at centre-of-mass
energies of 7, 8 and 13 TeV. A near-threshold peaking structure, referred to as
, is observed in the invariant-mass spectrum with
significance greater than 12 standard deviations. The mass, width and the
quantum numbers of the structure are measured to be MeV,
MeV and , respectively, where the first
uncertainties are statistical and the second systematic. The properties of the
new structure are consistent with recent theoretical predictions for a state
composed of quarks. Evidence for an additional structure is
found around 4140 MeV in the invariant mass, which might be
caused either by a new resonance with the assignment or by a coupled-channel effect.Comment: All figures and tables, along with any supplementary material and
additional information, are available at
https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2022-018.html (LHCb
public pages
Measurement of the differential branching fraction
The branching fraction of the rare decay is measured for the first time, in the squared dimuon mass
intervals, , excluding the and regions. The data
sample analyzed was collected by the LHCb experiment at center-of-mass energies
of 7, 8, and 13 TeV, corresponding to a total integrated luminosity of $9\
\mathrm{fb}^{-1}q^{2}q^{2} >15.0\
\mathrm{GeV}^2/c^4$, where theoretical predictions have the smallest model
dependence, agrees with the predictions.Comment: All figures and tables, along with any supplementary material and
additional information, are available at
https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2022-050.html (LHCb
public pages
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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Observation of a Λb0 − Λ¯b0 production asymmetry in proton-proton collisions at √s = 7 and 8 TeV
This article presents differential measurements of the asymmetry between
and baryon production rates in
proton-proton collisions at centre-of-mass energies of and
collected with the LHCb experiment, corresponding to an
integrated luminosity of . The baryons are
reconstructed through the inclusive semileptonic decay
. The production
asymmetry is measured both in intervals of rapidity in the range
and transverse momentum in . The results are found to
be incompatible with symmetric production with a significance of 5.8 standard
deviations for both and data, assuming no
violation in the decay. There is evidence for a trend as a function of rapidity
with a significance of 4 standard deviations. Comparisons to predictions from
hadronisation models in PYTHIA and heavy-quark recombination are provided. This
result constitutes the first observation of a particle-antiparticle asymmetry
in -hadron production at LHC energies
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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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Searches for low-mass dimuon resonances
Searches are performed for a low-mass dimuon resonance, , produced in
proton-proton collisions at a center-of-mass energy of 13 TeV, using a data
sample corresponding to an integrated luminosity of 5.1 fb and collected
with the LHCb detector. The bosons can either decay promptly or displaced
from the proton-proton collision, where in both cases the requirements placed
on the event and the assumptions made about the production mechanisms are kept
as minimal as possible. The searches for promptly decaying bosons explore
the mass range from near the dimuon threshold up to 60 GeV, with nonnegligible
widths considered above 20 GeV. The searches for displaced decays consider masses up to 3 GeV. None of the searches finds
evidence for a signal and 90% confidence-level exclusion limits are placed on
the cross sections, each with minimal model dependence. In
addition, these results are used to place world-leading constraints on
GeV-scale bosons in the two-Higgs-doublet and hidden-valley scenarios
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First measurement of the CP -violating phase in Bs0→J/ψ(→ e<sup>+</sup>e<sup>-</sup>) ϕ decays
A flavour-tagged time-dependent angular analysis of
decays is presented where the meson is reconstructed through its decay
to an pair. The analysis uses a sample of collision data recorded
with the LHCb experiment at centre-of-mass energies of 7 and 8 TeV,
corresponding to an integrated luminosity of 3 fb. The -violating
phase and lifetime parameters of the system are measured to be
rad,
ps and ps where the first
uncertainty is statistical and the second systematic. This is the first time
that -violating parameters are measured in the decay
with an pair in the final state. The results are consistent with
previous measurements in other channels and with the Standard Model
predictions
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