34 research outputs found
Search for the rare decays and
A search for the rare decay of a or meson into the final
state is performed, using data collected by the LHCb experiment
in collisions at and TeV, corresponding to an integrated
luminosity of 3 fb. The observed number of signal candidates is
consistent with a background-only hypothesis. Branching fraction values larger
than for the decay mode are
excluded at 90% confidence level. For the decay
mode, branching fraction values larger than are excluded at
90% confidence level, this is the first branching fraction limit for this
decay.Comment: All figures and tables, along with any supplementary material and
additional information, are available at
https://lhcbproject.web.cern.ch/lhcbproject/Publications/LHCbProjectPublic/LHCb-PAPER-2015-044.htm
Study of the production of and hadrons in collisions and first measurement of the branching fraction
The product of the () differential production
cross-section and the branching fraction of the decay () is
measured as a function of the beauty hadron transverse momentum, ,
and rapidity, . The kinematic region of the measurements is and . The measurements use a data sample
corresponding to an integrated luminosity of collected by the
LHCb detector in collisions at centre-of-mass energies in 2011 and in 2012. Based on previous LHCb
results of the fragmentation fraction ratio, , the
branching fraction of the decay is
measured to be \begin{equation*} \mathcal{B}(\Lambda_b^0\rightarrow J/\psi
pK^-)= (3.17\pm0.04\pm0.07\pm0.34^{+0.45}_{-0.28})\times10^{-4},
\end{equation*} where the first uncertainty is statistical, the second is
systematic, the third is due to the uncertainty on the branching fraction of
the decay , and the
fourth is due to the knowledge of . The sum of the
asymmetries in the production and decay between and
is also measured as a function of and .
The previously published branching fraction of , relative to that of , is updated.
The branching fractions of are determined.Comment: 29 pages, 19figures. All figures and tables, along with any
supplementary material and additional information, are available at
https://lhcbproject.web.cern.ch/lhcbproject/Publications/LHCbProjectPublic/LHCb-PAPER-2015-032.htm
Evidence for the strangeness-changing weak decay
Using a collision data sample corresponding to an integrated luminosity
of 3.0~fb, collected by the LHCb detector, we present the first search
for the strangeness-changing weak decay . No
hadron decay of this type has been seen before. A signal for this decay,
corresponding to a significance of 3.2 standard deviations, is reported. The
relative rate is measured to be
, where and
are the and fragmentation
fractions, and is the branching
fraction. Assuming is bounded between 0.1 and
0.3, the branching fraction would lie
in the range from to .Comment: 7 pages, 2 figures, All figures and tables, along with any
supplementary material and additional information, are available at
https://lhcbproject.web.cern.ch/lhcbproject/Publications/LHCbProjectPublic/LHCb-PAPER-2015-047.htm
Measurements of long-range near-side angular correlations in TeV proton-lead collisions in the forward region
Two-particle angular correlations are studied in proton-lead collisions at a
nucleon-nucleon centre-of-mass energy of TeV, collected
with the LHCb detector at the LHC. The analysis is based on data recorded in
two beam configurations, in which either the direction of the proton or that of
the lead ion is analysed. The correlations are measured in the laboratory
system as a function of relative pseudorapidity, , and relative
azimuthal angle, , for events in different classes of event
activity and for different bins of particle transverse momentum. In
high-activity events a long-range correlation on the near side, , is observed in the pseudorapidity range . This
measurement of long-range correlations on the near side in proton-lead
collisions extends previous observations into the forward region up to
. The correlation increases with growing event activity and is found
to be more pronounced in the direction of the lead beam. However, the
correlation in the direction of the lead and proton beams are found to be
compatible when comparing events with similar absolute activity in the
direction analysed.Comment: All figures and tables, along with any supplementary material and
additional information, are available at
https://lhcbproject.web.cern.ch/lhcbproject/Publications/LHCbProjectPublic/LHCb-PAPER-2015-040.htm
Measurements of long-range near-side angular correlations in √sNN = 5 TeV proton-lead collisions in the forward region
Two-particle angular correlations are studied in proton-lead collisions at a nucleon–nucleon centre-of-mass energy of √sNN = 5 TeV , collected with the LHCb detector at the LHC. The analysis is based on data recorded in two beam configurations, in which either the direction of the proton or that of the lead ion is analysed. The correlations are measured in the laboratory system as a function of relative pseudorapidity, Δη, and relative azimuthal angle, Δϕ, for events in different classes of event activity and for different bins of particle transverse momentum. In high-activity events a long-range correlation on the near side, Δ ϕ ≈ 0 , is observed in the pseudorapidity range 2.0 < η < 4.9 . This measurement of long-range correlations on the near side in proton-lead collisions extends previous observations into the forward region up to η = 4.9 . The correlation increases with growing event activity and is found to be more pronounced in the direction of the lead beam. However, the correlation in the direction of the lead and proton beams are found to be compatible when comparing events with similar absolute activity in the direction analysed
Study of ψ(2S) production and cold nuclear matter effects in pPb collisions at √ sNN = 5 TeV
The production of ψ(2S) mesons is studied in dimuon final states using proton-lead (pPb) collision data collected by the LHCb detector. The data sample corresponds to an integrated luminosity of 1.6 nb−1. The nucleon-nucleon centre-of-mass energy of the pPb collisions is (Formula presented.) TeV. The measurement is performed using ψ(2S) mesons with transverse momentum less than 14 GeV/c and rapidity y in the ranges 1.5 < y < 4.0 and −5.0 < y < −2.5 in the nucleon-nucleon centre-of-mass system. The forward-backward production ratio and the nuclear modification factor are determined for ψ(2S) mesons. Using the production cross-section results of ψ(2S) and J/ψ mesons from b-hadron decays, the (Formula presented.) cross-section in pPb collisions at (Formula presented.) TeV is obtained
Measurements of long-range near-side angular correlations in √SNN = 5TeV proton-lead collisions in the forward region
Two-particle angular correlations are studied in proton-lead collisions at a nucleon–nucleon centre-ofmass
energy of √sN N = 5 TeV, collected with the LHCb detector at the LHC. The analysis is based on
data recorded in two beam configurations, in which either the direction of the proton or that of the
lead ion is analysed. The correlations are measured in the laboratory system as a function of relative
pseudorapidity, η, and relative azimuthal angle, φ, for events in different classes of event activity
and for different bins of particle transverse momentum. In high-activity events a long-range correlation
on the near side, φ ≈ 0, is observed in the pseudorapidity range 2.0 < η < 4.9. This measurement of
long-range correlations on the near side in proton-lead collisions extends previous observations into the
forward region up to η = 4.9. The correlation increases with growing event activity and is found to be
more pronounced in the direction of the lead beam. However, the correlation in the direction of the lead
and proton beams are found to be compatible when comparing events with similar absolute activity in
the direction analysed
Measurement of asymmetries and polarisation fractions in decays
An angular analysis of the decay is
performed using collisions corresponding to an integrated luminosity of
collected by the LHCb experiment at a centre-of-mass energy
TeV. A combined angular and mass analysis separates six helicity
amplitudes and allows the measurement of the longitudinal polarisation fraction
for the decay. A large scalar contribution from the
and resonances is found, allowing the
determination of additional asymmetries. Triple product and direct
asymmetries are determined to be compatible with the Standard Model
expectations. The branching fraction is measured to be
Measurement of the Difference of Time-Integrated CPAsymmetries in D0→K−K+ and D0→π−π+ Decays
A search for CP violation in and decays is performed using collision data,
corresponding to an integrated luminosity of , collected using the
LHCb detector at centre-of-mass energies of 7 and TeV. The flavour of the
charm meson is inferred from the charge of the pion in and decays. The difference
between the CP asymmetries in and decays, , is measured to be . This is the most precise measurement of a
time-integrated CP asymmetry in the charm sector from a single experiment.Comment: All figures and tables, along with any supplementary material and
additional information, are available at
http://lhcbproject.web.cern.ch/lhcbproject/Publications/LHCbProjectPublic/LHCb-PAPER-2015-055.htm
Measurement of forward W and Z boson production in collisions at TeV
Measurements are presented of electroweak boson production using data from
collisions at a centre-of-mass energy of . The analysis is based on an integrated luminosity of
recorded with the LHCb detector. The bosons are
identified in the and decay
channels. The cross-sections are measured for muons in the pseudorapidity range
and, in the case of the boson, a dimuon mass within . The results are
\begin{align*} \sigma_{W^{+}\rightarrow\mu^{+}\nu} &= 1093.6 \pm 2.1 \pm 7.2
\pm 10.9 \pm 12.7{\rm \,pb} \, , \sigma_{W^{-}\rightarrow\mu^{-}\bar{\nu}} &=
\phantom{0}818.4 \pm 1.9 \pm 5.0 \pm \phantom{0}7.0 \pm \phantom{0}9.5{\rm
\,pb} \, , \sigma_{Z\rightarrow\mu^{+}\mu^{-}} &= \phantom{00}95.0 \pm 0.3 \pm
0.7 \pm \phantom{0}1.1 \pm \phantom{0}1.1{\rm \,pb} \, , \end{align*} 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. The evolution of the and boson cross-sections
with centre-of-mass energy is studied using previously reported measurements
with of data at .
Differential distributions are also presented. Results are in good agreement
with theoretical predictions at next-to-next-to-leading order in perturbative
quantum chromodynamics.Comment: All figures and tables, along with any supplementary material and
additional information, are available at
https://lhcbproject.web.cern.ch/lhcbproject/Publications/LHCbProjectPublic/LHCb-PAPER-2015-049.htm