991 research outputs found
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
Differential branching fraction and angular analysis of the decay B0âKâ0ÎŒ+ÎŒâ
The angular distribution and differential branching fraction of the decay B 0â K â0 ÎŒ + ÎŒ â are studied using a data sample, collected by the LHCb experiment in pp collisions at sâ=7 TeV, corresponding to an integrated luminosity of 1.0 fbâ1. Several angular observables are measured in bins of the dimuon invariant mass squared, q 2. A first measurement of the zero-crossing point of the forward-backward asymmetry of the dimuon system is also presented. The zero-crossing point is measured to be q20=4.9±0.9GeV2/c4 , where the uncertainty is the sum of statistical and systematic uncertainties. The results are consistent with the Standard Model predictions
Observation of associated production of a boson with a meson in the~forward region
A search for associated production of a boson with an open charm meson is
presented using a data sample, corresponding to an integrated luminosity of
of proton--proton collisions at a centre-of-mass energy
of 7\,TeV, collected by the LHCb experiment. %% Seven candidate events for
associated production of a boson with a meson and four candidate
events for a boson with a meson are observed with a combined
significance of 5.1standard deviations. The production cross-sections in the
forward region are measured to be where the first uncertainty is statistical and the
second systematic.Comment: 18 pages, 2 figure
Search for hidden-sector bosons in decays
A search is presented for hidden-sector bosons, , produced in the decay
, with and
. The search is performed using -collision data
corresponding to 3.0 fb collected with the LHCb detector. No significant
signal is observed in the accessible mass range
MeV, and upper limits are placed on the branching fraction product
as
a function of the mass and lifetime of the boson. These limits are of
the order of for lifetimes less than 100 ps over most of the
range, and place the most stringent constraints to date on many
theories that predict the existence of additional low-mass bosons.Comment: All figures and tables, along with supplementary material, are
available at
https://lhcbproject.web.cern.ch/lhcbproject/Publications/LHCbProjectPublic/LHCb-PAPER-2015-036.htm
Measurements of the , , meson and baryon lifetimes
Measurements of -hadron lifetimes are reported using collision data,
corresponding to an integrated luminosity of 1.0fb, collected by the
LHCb detector at a centre-of-mass energy of Tev. Using the exclusive decays
, , ,
and the average decay
times in these modes are measured to be = 0.004 0.003 ps, =
0.006 0.004 ps, = 0.013
0.005 ps, = 0.027
0.006 ps and = 0.011
0.005 ps, where the first uncertainty is statistical and the second is
systematic. These represent the most precise lifetime measurements in these
decay modes. In addition, ratios of these lifetimes, and the ratio of the
decay-width difference, , to the average width, , in
the system, , are
reported. All quantities are found to be consistent with Standard Model
expectations.Comment: 28 pages, 4 figures. Updated reference
Search for the decay Bs0âD*âϱ
A search for the decay Bs0âD*âϱ is presented using a data sample corresponding to an integrated luminosity of 1.0ââfb-1 of pp collisions collected by LHCb. This decay is expected to be mediated by a W-exchange diagram, with little contribution from rescattering processes, and therefore a measurement of the branching fraction will help us to understand the mechanism behind related decays such as Bs0âÏ+Ï- and Bs0âDD- . Systematic uncertainties are minimized by using B0âD*âϱ as a normalization channel. We find no evidence for a signal, and set an upper limit on the branching fraction of B(Bs0âD*âϱ)<6.1(7.8)Ă10-6 at 90% (95%) confidence level
Constraints on the unitarity triangle angle from Dalitz plot analysis of decays
The first study is presented of CP violation with an amplitude analysis of
the Dalitz plot of decays, with , and . The analysis is based on a data sample corresponding to
of collisions collected with the LHCb detector. No
significant CP violation effect is seen, and constraints are placed on the
angle of the unitarity triangle formed from elements of the
Cabibbo-Kobayashi-Maskawa quark mixing matrix. Hadronic parameters associated
with the decay are determined for the first time. These
measurements can be used to improve the sensitivity to of existing and
future studies of the 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-2015-059.html;
updated to correct figure 9 (numerical results unchanged
A new algorithm for identifying the flavour of mesons at LHCb
A new algorithm for the determination of the initial flavour of
mesons is presented. The algorithm is based on two neural networks and exploits
the hadron production mechanism at a hadron collider. The first network is
trained to select charged kaons produced in association with the meson.
The second network combines the kaon charges to assign the flavour and
estimates the probability of a wrong assignment. The algorithm is calibrated
using data corresponding to an integrated luminosity of 3 fb collected
by the LHCb experiment in proton-proton collisions at 7 and 8 TeV
centre-of-mass energies. The calibration is performed in two ways: by resolving
the - flavour oscillations in
decays, and by analysing flavour-specific
decays. The tagging power measured in decays is found
to be \%, which is an
improvement of about 50\% compared to a similar algorithm previously used in
the LHCb experiment.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-2015-056.htm
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
Measurements of the branching fractions of B+âppK+ decays
The branching fractions of the decay B+ â ppÌK+ for different intermediate states are measured using data, corresponding to an integrated luminosity of 1.0 fb-1, collected by the LHCb experiment. The total branching fraction, its charmless component MppÌ < 2.85 GeV/c2 and the branching fractions via the resonant ccÌ states η c(1S) and Ï(2S) relative to the decay via a J/Ï intermediate state are [Equation not available: see fulltext.] Upper limits on the B + branching fractions into the η c(2S) meson and into the charmonium-like states X(3872) and X(3915) are also obtained
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