232 research outputs found
flavour tagging using charm decays at the LHCb experiment
An algorithm is described for tagging the flavour content at production of
neutral mesons in the LHCb experiment. The algorithm exploits the
correlation of the flavour of a meson with the charge of a reconstructed
secondary charm hadron from the decay of the other hadron produced in the
proton-proton collision. Charm hadron candidates are identified in a number of
fully or partially reconstructed Cabibbo-favoured decay modes. The algorithm is
calibrated on the self-tagged decay modes and using of data collected by the LHCb
experiment at centre-of-mass energies of and
. Its tagging power on these samples of
decays is .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-2015-027.htm
Identification of beauty and charm quark jets at LHCb
Identification of jets originating from beauty and charm quarks is important
for measuring Standard Model processes and for searching for new physics. The
performance of algorithms developed to select - and -quark jets is
measured using data recorded by LHCb from proton-proton collisions at
TeV in 2011 and at TeV in 2012. The efficiency for
identifying a jet is about 65%(25%) with a probability for
misidentifying a light-parton jet of 0.3% for jets with transverse momentum
GeV and pseudorapidity . The dependence of
the performance on the and of the jet is also measured
Search for Bâșc decays to the ppâŸÏâș final state
A search for the decays of the B + c meson to pp-Ï + is performed for the first time using a data sample corresponding to an integrated luminosity of 3.0 fb -1 collected by the LHCb experiment in pp collisions at centre-of-mass energies of 7 and 8 TeV. No signal is found and an upper limit, at 95% confidence level, is set, fcfuĂB(B + c âppÏ + ) < 3.6Ă10-8 in the kinematic region m(pp) < 2.85 GeV/c2, p T (B) < 20 GeV/c and 2.0 < y(B) < 4.5, where B is the branching fraction and f c (f u ) is the fragmentation fraction of the b quark into a B c + (B + ) meson
Measurement of CP observables in B± â D(â)K± and B± â D(â)ϱ decays
Measurements of CP observables in B ± âD (â) K ± and B ± âD (â) Ï Â± decays are presented, where D (â) indicates a neutral D or D â meson that is an admixture of D (â)0 and DÂŻ (â)0 states. Decays of the D â meson to the DÏ 0 and DÎł final states are partially reconstructed without inclusion of the neutral pion or photon, resulting in distinctive shapes in the B candidate invariant mass distribution. Decays of the D meson are fully reconstructed in the K ± Ï â , K + K â and Ï + Ï â final states. The analysis uses a sample of charged B mesons produced in pp collisions collected by the LHCb experiment, corresponding to an integrated luminosity of 2.0, 1.0 and 2.0 fb â1 taken at centre-of-mass energies of s=7, 8 and 13 TeV, respectively. The study of B ± âD â K ± and B ± âD â Ï Â± decays using a partial reconstruction method is the first of its kind, while the measurement of B ± âDK ± and B ± âDÏ Â± decays is an update of previous LHCb measurements. The B ± âDK ± results are the most precise to date
Observation of the decay B0s â Ï(2S)K +Ïâ
The decay B0
s â Ï(2S)K +Ïâ is observed using a data set corresponding to an integrated luminosity of
3.0 fbâ1 collected by the LHCb experiment in pp collisions at centre-of-mass energies of 7 and 8 TeV.
The branching fraction relative to the B0 â Ï(2S)K +Ïâ decay mode is measured to be
B(B0
s â Ï(2S)K +Ïâ)
B(B0 â Ï(2S)K +Ïâ) = 5.38 ± 0.36 (stat) ± 0.22 (syst) ± 0.31 (f s/ fd)%,
where f s/ fd indicates the uncertainty due to the ratio of probabilities for a b quark to hadronise into
a B0
s or B0 meson. Using an amplitude analysis, the fraction of decays proceeding via an intermediate
Kâ(892)0 meson is measured to be 0.645 ± 0.049 (stat) ± 0.049 (syst) and its longitudinal polarisation
fraction is 0.524 ± 0.056 (stat) ± 0.029 (syst). The relative branching fraction for this component is
determined to be
B(B0
s â Ï(2S)Kâ(892)0)
B(B0 â Ï(2S)Kâ(892)0) = 5.58 ± 0.57 (stat) ± 0.40 (syst) ± 0.32 (f s/ fd)%.
In addition, the mass splitting between the B0
s and B0 mesons is measured as
M(B0
s ) â M(B0) = 87.45 ± 0.44 (stat) ± 0.09 (syst) MeV/c2
Observation of the B0 â Ï0Ï0 decay from an amplitude analysis of B0 â (Ï+Ïâ)(Ï+Ïâ) decays
Protonâproton collision data recorded in 2011 and 2012 by the LHCb experiment, corresponding to
an integrated luminosity of 3.0 fbâ1, are analysed to search for the charmless B0 â Ï0Ï0 decay.
More than 600 B0 â (Ï+Ïâ)(Ï+Ïâ) signal decays are selected and used to perform an amplitude
analysis, under the assumption of no CP violation in the decay, from which the B0 â Ï0Ï0 decay is
observed for the first time with 7.1 standard deviations significance. The fraction of B0 â Ï0Ï0 decays
yielding a longitudinally polarised final state is measured to be fL = 0.745+0.048
â0.058(stat) ± 0.034(syst).
The B0 â Ï0Ï0 branching fraction, using the B0 â ÏKâ(892)0 decay as reference, is also reported as
B(B0 â Ï0Ï0) = (0.94 ± 0.17(stat) ± 0.09(syst) ± 0.06(BF)) Ă 10â6
Measurement of the CP-violating phase ÎČ in B0 â J/ÏÏ+Ïâ decays and limits on penguin effects
Time-dependent CP violation is measured in the (â)
B 0 â J/ÏÏ+Ïâ channel for each Ï+Ïâ resonant
final state using data collected with an integrated luminosity of 3.0 fbâ1 in pp collisions using the LHCb
detector. The final state with the largest rate, J/ÏÏ0(770), is used to measure the CP-violating angle
2ÎČeff to be (41.7 ± 9.6+2.8
â6.3)âŠ. This result can be used to limit the size of penguin amplitude contributions
to CP violation measurements in, for example, (â)
B 0
s â J/ÏÏ decays. Assuming approximate SU(3) flavour
symmetry and neglecting higher order diagrams, the shift in the CP-violating phase Ïs is limited to be
within the interval [â1.05âŠ,+1.18âŠ] at 95% confidence level. Changes to the limit due to SU(3) symmetry
breaking effects are also discussed
LHCb detector performance
The LHCb detector is a forward spectrometer at the Large Hadron Collider (LHC) at CERN. The experiment is designed for precision measurements of CP violation and rare decays of beauty and charm hadrons. In this paper the performance of the various LHCb sub-detectors and the trigger system are described, using data taken from 2010 to 2012. It is shown that the design criteria of the experiment have been met. The excellent performance of the detector has allowed the LHCb collaboration to publish a wide range of physics results, demonstrating LHCb's unique role, both as a heavy flavour experiment and as a general purpose detector in the forward region
Search for CP violation in D-0 -> pi(-)pi(+)pi(0) decays with the energy test
A search for time-integrated CP violation in the Cabibbo-suppressed decay
is performed using for the first time an unbinned
model-independent technique known as the energy test. Using proton-proton
collision data, corresponding to an integrated luminosity of 2.0 fb
collected by the LHCb detector at a centre-of-mass energy of = 8
TeV, the world's best sensitivity to CP violation in this decay is obtained.
The data are found to be consistent with the hypothesis of CP symmetry with a
p-value of (2.6 +/- 0.5)%
Observation of the decay B0sâÏ(2S)K+Ïâ
The decay is observed 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 branching fraction relative to the
decay mode is measured to be \begin{equation} \frac{{\cal B}(\overline{B}^0_s
\rightarrow \psi(2S) K^+ \pi^-)}{{\cal B}(B^0
\rightarrow \psi(2S) K^+ \pi^-)} = 5.38 \pm 0.36 (stat) \pm 0.22 (syst) \pm
0.31 \, (f_s/f_d) \, \%,\nonumber \end{equation} where indicates the
uncertainty due to the ratio of probabilities for a quark to hadronise into
a or meson. Using an amplitude analysis, the fraction of decays
proceeding via an intermediate meson is measured to be and its longitudinal polarisation fraction is
. The relative branching fraction for
this component is determined to be \begin{equation} \frac{{\cal
B}(\overline{B}^0_s \rightarrow \psi(2S) K^*(892)^0)}{{\cal B}(B^0
\rightarrow \psi(2S) K^*(892)^0)} = 5.58 \pm 0.57 (stat) \pm 0.40 (syst) \pm
0.32 \, (f_s/f_d) \, \%. \nonumber \end{equation} In addition, the mass
splitting between the and mesons is measured as \begin{equation}
M(B^0_s) - M(B^0) = 87.45 \pm 0.44 (stat) \pm 0.07 (syst) MeV/c^2. \nonumber
\end{equation}Comment: 15 pages, 7 figures. v2 updated with published version. 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-2015-010.htm
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