2,798 research outputs found
First determination of the content of and updated determination of the contents of and
Quantum-correlated decays collected by the CLEO-c
experiment are used to perform a first measurement of , the
fractional -even content of the self-conjugate decay , obtaining a value of . An important
input to the measurement comes from the use of
and decays to tag the signal mode. This same
technique is applied to the channels and , yielding and
, where the first uncertainty is
statistical and the second systematic. These measurements are consistent with
those of an earlier analysis, based on -eigenstate tags, and can be
combined to give values of and
. The results will enable the three modes to
be included in a model-independent manner in measurements of the unitarity
triangle angle using decays, and in time-dependent
studies of violation and mixing in the system.Comment: Minor revisions following journal acceptanc
Measurement of the CKM angle γ from a combination of B±→Dh± analyses
A combination of three LHCb measurements of the CKM angle γ is presented. The decays B±→D K± and
B±→Dπ± are used, where D denotes an admixture of D0 and D0 mesons, decaying into K+K−, π+π−, K±π∓, K±π∓π±π∓, K0Sπ+π−, or K0S K+K− final states. All measurements use a dataset corresponding to 1.0 fb−1 of integrated luminosity. Combining results from B±→D K± decays alone a best-fit value of
γ =72.0◦ is found, and confidence intervals are set
γ ∈ [56.4,86.7]◦ at 68% CL,
γ ∈ [42.6,99.6]◦ at 95% CL.
The best-fit value of γ found from a combination of results from B±→Dπ± decays alone, is γ =18.9◦,
and the confidence intervals
γ ∈ [7.4,99.2]◦ ∪ [167.9,176.4]◦ at 68% CL
are set, without constraint at 95% CL. The combination of results from B± → D K± and B± → Dπ±
decays gives a best-fit value of γ =72.6◦ and the confidence intervals
γ ∈ [55.4,82.3]◦ at 68% CL,
γ ∈ [40.2,92.7]◦ at 95% CL
are set. All values are expressed modulo 180◦, and are obtained taking into account the effect of D0–D0
mixing
Observation of two new baryon resonances
Two structures are observed close to the kinematic threshold in the mass spectrum in a sample of proton-proton collision data, corresponding
to an integrated luminosity of 3.0 fb recorded by the LHCb experiment.
In the quark model, two baryonic resonances with quark content are
expected in this mass region: the spin-parity and
states, denoted and .
Interpreting the structures as these resonances, we measure the mass
differences and the width of the heavier state to be
MeV,
MeV,
MeV, where the first and second
uncertainties are statistical and systematic, respectively. The width of the
lighter state is consistent with zero, and we place an upper limit of
MeV at 95% confidence level. Relative
production rates of these states are also reported.Comment: 17 pages, 2 figure
Searches for B0(s)→J/ψppˉ and B+→J/ψppˉπ+ decays
The results of searches for B0(s)→J/ψ pp¯ and B + → J/ψ p p¯ π+ decays are reported. The analysis is based on a data sample, corresponding to an integrated luminosity of 1.0 fb−1 of pp collisions, collected with the LHCb detector. An excess with 2.8 σ significance is seen for the decay B0s→J/ψ pp¯ and an upper limit on the branching fraction is set at the 90 % confidence level: B(B0s→J/ψ pp¯) < 4.8 × 10−6, which is the first such limit. No significant signals are seen for B0 → J/ψ pp¯ and B+ → J/ψ pp¯ π + decays, for which the corresponding limits are set: B(B0→J/ψ pp¯) < 5.2 × 10−7, which significantly improves the existing limit; and B(B+→J/ψ pp¯π+) < 5.0 × 10−7, which is the first limit on this branching fraction
Measurement of the relative rate of prompt χc0, χc1 and χc2 production at √s=7TeV
Prompt production of charmonium χc0, χc1 and χc2 mesons is studied using proton-proton collisions at the LHC at a centre-of-mass energy of √s=7TeV. The χc mesons are identified through their decay to J/ψγ, with J/ψ→μ+mu− using photons that converted in the detector. A data sample, corresponding to an integrated luminosity of 1.0fb−1 collected by the LHCb detector, is used to measure the relative prompt production rate of χc1 and χc2 in the rapidity range 2.0<y<4.5 as a function of the J/ψ transverse momentum from 3 to 20 GeV/c. First evidence for χc0 meson production at a hadron collider is also presented
Measurement of the mass and lifetime of the baryon
A proton-proton collision data sample, corresponding to an integrated
luminosity of 3 fb collected by LHCb at and 8 TeV, is used
to reconstruct , decays. Using the , decay mode for calibration, the lifetime ratio and absolute
lifetime of the baryon are measured to be \begin{align*}
\frac{\tau_{\Omega_b^-}}{\tau_{\Xi_b^-}} &= 1.11\pm0.16\pm0.03, \\
\tau_{\Omega_b^-} &= 1.78\pm0.26\pm0.05\pm0.06~{\rm ps}, \end{align*} where the
uncertainties are statistical, systematic and from the calibration mode (for
only). A measurement is also made of the mass difference,
, and the corresponding mass, which
yields \begin{align*} m_{\Omega_b^-}-m_{\Xi_b^-} &= 247.4\pm3.2\pm0.5~{\rm
MeV}/c^2, \\ m_{\Omega_b^-} &= 6045.1\pm3.2\pm 0.5\pm0.6~{\rm MeV}/c^2.
\end{align*} These results are consistent with previous measurements.Comment: 11 pages, 5 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-2016-008.htm
Differential branching fraction and angular analysis of decays
The differential branching fraction of the rare decay is measured as a function of , the
square of the dimuon invariant mass. The analysis is performed using
proton-proton collision data, corresponding to an integrated luminosity of 3.0
\mbox{ fb}^{-1}, collected by the LHCb experiment. Evidence of signal is
observed in the region below the square of the mass. Integrating
over 15 < q^{2} < 20 \mbox{ GeV}^2/c^4 the branching fraction is measured as
d\mathcal{B}(\Lambda^{0}_{b} \rightarrow \Lambda \mu^+\mu^-)/dq^2 = (1.18 ^{+
0.09} _{-0.08} \pm 0.03 \pm 0.27) \times 10^{-7} ( \mbox{GeV}^{2}/c^{4})^{-1},
where the uncertainties are statistical, systematic and due to the
normalisation mode, , respectively.
In the intervals where the signal is observed, angular distributions are
studied and the forward-backward asymmetries in the dimuon ()
and hadron () systems are measured for the first time. In the
range 15 < q^2 < 20 \mbox{ GeV}^2/c^4 they are found to be A^{l}_{\rm FB} =
-0.05 \pm 0.09 \mbox{ (stat)} \pm 0.03 \mbox{ (syst)} and A^{h}_{\rm FB} =
-0.29 \pm 0.07 \mbox{ (stat)} \pm 0.03 \mbox{ (syst)}.Comment: 27 pages, 10 figures, Erratum adde
Measurement of the lifetime
Using a data set corresponding to an integrated luminosity of ,
collected by the LHCb experiment in collisions at centre-of-mass energies
of 7 and 8 TeV, the effective lifetime in the
decay mode, , is measured to be ps. Assuming
conservation, corresponds to the lifetime of the light
mass eigenstate. This is the first measurement of the effective
lifetime in this decay mode.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-2016-017.htm
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
Precision measurement of violation in decays
The time-dependent asymmetry in decays is
measured using collision data, corresponding to an integrated luminosity
of fb, collected with the LHCb detector at centre-of-mass energies
of and TeV. In a sample of 96 000 decays, the
-violating phase is measured, as well as the decay widths
and of the light and heavy mass eigenstates of the
system. The values obtained are rad, ps, andps, where the first uncertainty is
statistical and the second systematic. These are the most precise single
measurements of those quantities to date. A combined analysis with decays gives rad. All
measurements are in agreement with the Standard Model predictions. For the
first time the phase is measured independently for each polarisation
state of the system and shows no evidence for polarisation
dependence.Comment: 6 figure
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