2,058 research outputs found
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Search for lepton-flavour-violating decays of Higgs-like bosons.
A search is presented for a Higgs-like boson with mass in the range 45 to 195 GeV/c2 decaying into a muon and a tau lepton. The dataset consists of proton-proton interactions at a centre-of-mass energy of 8 TeV , collected by the LHCb experiment, corresponding to an integrated luminosity of 2 fb-1 . The tau leptons are reconstructed in both leptonic and hadronic decay channels. An upper limit on the production cross-section multiplied by the branching fraction at 95% confidence level is set and ranges from 22 pb for a boson mass of 45 GeV/c2 to 4 pb for a mass of 195 GeV/c2
Observation of an Excited Bc+ State
Using pp collision data corresponding to an integrated luminosity of 8.5 fb-1 recorded by the LHCb experiment at center-of-mass energies of s=7, 8, and 13 TeV, the observation of an excited Bc+ state in the Bc+Ï+Ï- invariant-mass spectrum is reported. The observed peak has a mass of 6841.2±0.6(stat)±0.1(syst)±0.8(Bc+) MeV/c2, where the last uncertainty is due to the limited knowledge of the Bc+ mass. It is consistent with expectations of the Bcâ(2S31)+ state reconstructed without the low-energy photon from the Bcâ(1S31)+âBc+Îł decay following Bcâ(2S31)+âBcâ(1S31)+Ï+Ï-. A second state is seen with a global (local) statistical significance of 2.2Ï (3.2Ï) and a mass of 6872.1±1.3(stat)±0.1(syst)±0.8(Bc+) MeV/c2, and is consistent with the Bc(2S10)+ state. These mass measurements are the most precise to date
Evidence for an η<sub>c</sub>(1S) Ï<sup>-</sup> resonance in B<sup>0</sup>â η<sub>c</sub>(1S) K<sup>+</sup>Ï<sup>-</sup> decays
A Dalitz plot analysis of B0âηc(1S)K+Ï- decays is performed using data samples of pp collisions collected with the LHCb detector at centre-of-mass energies of âs=7, 8 and 13TeV, corresponding to a total integrated luminosity of 4.7fb-1. A satisfactory description of the data is obtained when including a contribution representing an exotic ηc(1S) Ï- resonant state. The significance of this exotic resonance is more than three standard deviations, while its mass and width are 4096±20-22+18MeV and 152±58-35+60MeV, respectively. The spin-parity assignments JP= 0+ and JP= 1- are both consistent with the data. In addition, the first measurement of the B0âηc(1S)K+Ï- branching fraction is performed and givesB(B0âηc(1S)K+Ï-)=(5.73±0.24±0.13±0.66)Ă10-4,where the first uncertainty is statistical, the second systematic, and the third is due to limited knowledge of external branching fractions
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Two-particle differential transverse momentum and number density correlations in p- Pb collisions at 5.02 TeV and Pb-Pb collisions at 2.76 TeV at the CERN Large Hadron Collider
We present measurements of two-particle differential number correlation functions R2 and transverse momentum correlation functions P2, obtained from p-Pb collisions at 5.02 TeV and Pb-Pb collisions at 2.76 TeV. The results are obtained by using charged particles in the pseudorapidity range |η|<1.0 and transverse momentum range 0.
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Measurement of CP observables in the process B <sup>0</sup> â DK <sup>*0</sup> with two- and four-body D decays
Measurements of observables in decays are presented,
where represents a superposition of and states. The
meson is reconstructed in the two-body final states , ,
and , and, for the first time, in the four-body final
states , and .
The analysis uses a sample of neutral mesons produced in proton-proton
collisions, corresponding to an integrated luminosity of 1.0, 2.0 and 1.8 collected with the LHCb detector at centre-of-mass energies of
7, 8 and 13 TeV, respectively. First observations of the decays
and are
obtained. The measured observables are interpreted in terms of the
-violating weak phase
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Updated measurement of time-dependent CP -violating observables in Bs0âJ/Ï<sup>K+</sup><sup>K-</sup> decays
The decay-time-dependent asymmetry in
decays is measured using proton-proton collision data, corresponding to an
integrated luminosity of , collected with the LHCb
detector at a centre-of-mass energy of in 2015 and 2016.
Using a sample of approximately 117\,000 signal decays with an invariant mass in the vicinity of the resonance, the -violating
phase is measured, along with the difference in decay widths of the
light and heavy mass eigenstates of the - system,
. The difference of the average and meson
decay widths, , is determined using in addition a sample of
decays. The values obtained are , and , where the first uncertainty is statistical and the
second systematic. These are the most precise single measurements of these
quantities to date and are consistent with expectations based on the Standard
Model and with a previous LHCb analysis of this decay using data recorded at
centre-of-mass energies 7 and 8 TeV. Finally, the results are combined with
recent results from decays obtained using
the same dataset as this analysis, and with previous independent LHCb results
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Observation of the Îb0âÏc1 (3872) pK<sup>â</sup> decay
Using proton-proton collision data, collected with the LHCb detector and
corresponding to 1.0, 2.0 and 1.9fb of integrated luminosity at the
centre-of-mass energies of 7, 8, and 13 TeV, respectively, the decay
with is
observed for the first time. The significance of the observed signal is in
excess of seven standard deviations. It is found that of the
decays proceed via the two-body intermediate state
. The~branching fraction with respect to that of
the decay mode, where the
~meson is reconstructed in the final state, is
measured to be: \begin{equation*}
\frac{\Lambda_b^0\to\chi_{c1}(3872)pK^-}{\Lambda_b\to\psi(2S)p K^-} \times
\frac{\mathcal{B}(\chi_{c1} \to J/\psi \pi^+\pi^-)}{\mathcal{B}(\psi(2S)\to
J/\psi \pi^+\pi^-)} = \left(5.4 \pm 1.1 \pm 0.2\right)\times 10^{-2}\,,
\end{equation*} where the first uncertainty is statistical and the second is
systematic
Particle identification in ALICE: a Bayesian approach
We present a Bayesian approach to particle identification (PID) within the ALICE experiment. The aim is to more effectively combine the particle identification capabilities of its various detectors. After a brief explanation of the adopted methodology and formalism, the performance of the Bayesian PID approach for charged pions, kaons and protons in the central barrel of ALICE is studied. PID is performed via measurements of specific energy loss () and time-of-flight. PID efficiencies and misidentification probabilities are extracted and compared with Monte Carlo simulations using high-purity samples of identified particles in the decay channels , , and in p-Pb collisions at TeV. In order to thoroughly assess the validity of the Bayesian approach, this methodology was used to obtain corrected spectra of pions, kaons, protons, and D mesons in pp collisions at TeV. In all cases, the results using Bayesian PID were found to be consistent with previous measurements performed by ALICE using a standard PID approach. For the measurement of D, it was found that a Bayesian PID approach gave a higher signal-to-background ratio and a similar or larger statistical significance when compared with standard PID selections, despite a reduced identification efficiency. Finally, we present an exploratory study of the measurement of in pp collisions at TeV, using the Bayesian approach for the identification of its decay products
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