arXiv subjects

T. Ackernley

Publications and source records attributed to T. Ackernley.

365 records · Page 21Linked to original sources

arXiv2019

Measurement of the $B_c^-$ meson production fraction and asymmetry in 7 and 13 TeV $pp$ collisions

The production fraction of the $B_c^-$ meson with respect to the sum of $B^-$ and $\bar{B}^0$ mesons is measured in both 7 and 13 TeV center-of-mass energy $pp$ collisions produced by the Large Hadron Collider (LHC), using the LHCb detector. The rate, approximately 3.7 per mille, does not change with energy, but shows a transverse momentum dependence. The $B_c^- - B_c^+$ production asymmetry is also measured, and is consistent with zero within the determined statistical and systematic uncertainties of a few percent.

hep-ex↗

arXiv2019

Measurement of the electron reconstruction efficiency at LHCb

The single electron track-reconstruction efficiency is calibrated using a sample corresponding to $1.3~\mathrm{fb}^{-1}$of $pp$ collision data recorded with the LHCb detector in 2017. This measurement exploits $B^+\to J/ψ(e^+e^-)K^+$ decays, where one of the electrons is fully reconstructed and paired with the kaon, while the other electron is reconstructed using only the information of the vertex detector. Despite this partial reconstruction, kinematic and geometric constraints allow the $B^+$-meson mass to be reconstructed and the signal to be well separated from backgrounds. This in turn allows the electron reconstruction efficiency to be measured by matching the partial track segment found in the vertex detector to tracks found by LHCb's regular reconstruction algorithms. The agreement between data and simulation is evaluated, and corrections are derived for simulated electrons in bins of kinematics. These correction factors allow LHCb to measure branching fractions involving single electrons with a systematic uncertainty below $1\%$.

hep-ex↗

arXiv2019

Search for the doubly charmed baryon $Ξ_{cc}^{+}$

A search for the doubly charmed baryon $Ξ_{cc}^{+}$ is performed through its decay to the $Λ_c^+ K^- π^+$ final state, using proton-proton collision data collected with the LHCb detector at centre-of-mass energies of 7, 8 and 13$\mathrm{\,Te\kern -0.1em V}$. The data correspond to a total integrated luminosity of $9\,\mathrm{fb}^{-1}$. No significant signal is observed in the mass range from 3.4 to 3.8$\mathrm{\,Ge\kern -0.1em V}/c^2$. Upper limits are set at $95\%$ credibility level on the ratio of the $Ξ_{cc}^{+}$ production cross-section times the branching fraction to that of $Λ_c^+$ and $Ξ_{cc}^{++}$ baryons. The limits are determined as functions of the $Ξ_{cc}^{+}$ mass for different lifetime hypotheses, in the rapidity range from 2.0 to 4.5 and the transverse momentum range from 4 to 15$\mathrm{\,Ge\kern -0.1em V}/c$.

hep-ex↗

arXiv2019

Observation of the $Λ_b^0\rightarrow χ_{c1}(3872)pK^-$ decay

Using proton-proton collision data, collected with the LHCb detector and corresponding to 1.0, 2.0 and 1.9fb$^{-1}$ of integrated luminosity at the centre-of-mass energies of 7, 8, and 13 TeV, respectively, the decay $Λ_b^0\to χ_{c1}(3872)pK^-$ with $χ_{c1}\to J/ψπ^+π^-$ is observed for the first time. The significance of the observed signal is in excess of seven standard deviations. It is found that $(58\pm15)\%$ of the decays proceed via the two-body intermediate state $χ_{c1}(3872)Λ(1520)$. The~branching fraction with respect to that of the $Λ_b\rightarrowψ(2S)p K^{-}$ decay mode, where the $ψ(2S)$~meson is reconstructed in the $J/ψπ^+π^-$ final state, is measured to be: \begin{equation*} \frac{Λ_b^0\toχ_{c1}(3872)pK^-}{Λ_b\toψ(2S)p K^-} \times \frac{\mathcal{B}(χ_{c1} \to J/ψπ^+π^-)}{\mathcal{B}(ψ(2S)\to J/ψπ^+π^-)} = \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.

hep-ex↗

arXiv2019

Search for the lepton-flavour violating decays $B^+ \to K^+ μ^{\pm} e^{\mp}$

A search for the lepton-flavour violating decays $B^+ \to K^+ μ^{\pm} e^{\mp}$ is performed using a sample of proton-proton collision data, collected with the LHCb experiment at centre-of-mass energies of $7$ and $8~{\rm TeV}$ and corresponding to an integrated luminosity of 3$\rm~fb^{-1}$. No significant signal is observed, and upper limits on the branching fractions are set as $\mathcal{B}(B^+ \to K^+ μ^- e^+) < 7.0~(9.5) \times 10^{-9}$ and $\mathcal{B}(B^+ \to K^+ μ^+ e^-) < 6.4~(8.8) \times 10^{-9}$ at 90 (95) % confidence level. The results improve the current best limits on these decays by more than one order of magnitude.

hep-ex↗