Phys. Rev. Lett. 124, 222001 (2020) The $\Lambda_c^+K^-$ mass spectrum is studied with a data sample of $pp$
collisions at a centre-of-mass energy of 13 TeV corresponding to an integrated
luminosity ...of 5.6 fb$^{-1}$ collected by the LHCb experiment. Three $\Xi_c^0$
states are observed with a large significance and their masses and natural
widths are measured to be \begin{eqnarray*} m(\Xi_c(2923)^0)&=& 2923.04 \pm
0.25 \pm 0.20 \pm 0.14 ~\mathrm{MeV}, \Gamma(\Xi_c(2923)^0) &=& 7.1 \pm 0.8 \pm
1.8 ~\mathrm{MeV}, \end{eqnarray*} \begin{eqnarray*} m(\Xi_c(2939)^0) &=&
2938.55 \pm 0.21 \pm 0.17 \pm 0.14 ~\mathrm{ MeV}, \Gamma(\Xi_c(2939)^0) &=&
10.2 \pm 0.8 \pm 1.1 ~\mathrm{ MeV}, \end{eqnarray*} \begin{eqnarray*}
m(\Xi_c(2965)^0) &=& 2964.88 \pm 0.26 \pm 0.14 \pm 0.14~\mathrm{ MeV},
\Gamma(\Xi_c(2965)^0) &=& 14.1 \pm 0.9 \pm 1.3~\mathrm{ MeV}, \end{eqnarray*}
where the uncertainties are statistical, systematic, and due to the limited
knowledge of the $\Lambda_c^+$ mass. The $\Xi_c(2923)^0$ and $\Xi_c(2939)^0$
baryons are new states. The $\Xi_c(2965)^0$ state is in the vicinity of the
known $\Xi_c(2970)^0$ baryon; however, their masses and natural widths differ
significantly.
Phys. Rev. Lett. 125, 011802 (2020) An angular analysis of the $B^{0}\rightarrow K^{*0}(\to
K^{+}\pi^{-})\mu^{+}\mu^{-}$ decay is presented using a data set corresponding
to an integrated luminosity ...of 4.7 fb$^{-1}$ of $pp$ collision data collected
with the LHCb experiment. The full set of $C\!P$-averaged observables are
determined in bins of the invariant mass squared of the dimuon system.
Contamination from decays with the $K^{+}\pi^{-}$ system in an S-wave
configuration is taken into account. The tension seen between the previous LHCb
results and the Standard Model predictions persists with the new data. The
precise value of the significance of this tension depends on the choice of
theory nuisance parameters.
Phys. Rev. Lett. 124 (2020) 211802 A search for the decays $B^0_s\to e^+e^-$ and $B^0\to e^+e^-$ is performed
using data collected with the LHCb experiment in proton-proton collisions at
...center-of-mass energies of $7$, $8$ and $13\,\text{TeV}$, corresponding to
integrated luminosities of $1$, $2$ and $2\,\text{fb}^{-1}$, respectively. No
signal is observed. Assuming no contribution from $B^0\to e^+e^-$ decays, an
upper limit of $\mathcal{B}(B^0_s\to e^+e^-)<9.4\,(11.2)\times10^{-9}$ is
obtained at $90\,(95)\,\%$ confidence level. If no $B^0_s\to e^+e^-$
contribution is assumed, a limit of $\mathcal{B}(B^0\to
e^+e^-)<2.5\,(3.0)\times10^{-9}$ is determined at $90\,(95)\,\%$ confidence
level. These upper limits are more than one order of magnitude lower than the
previous values.
JHEP 12 (2020) 144 The shape of the $B_s^0\rightarrow D_s^{*-}\mu^+\nu_{\mu}$ differential decay
rate is obtained as a function of the hadron recoil using proton-proton
collision data at a ...centre-of-mass energy of 13 TeV, corresponding to an
integrated luminosity of 1.7 fb$^{-1}$ collected by the LHCb detector. The
$B_s^0\rightarrow D_s^{*-}\mu^+\nu_{\mu}$ decay is reconstructed through the
decays $D_s^{*-}\rightarrow D_s^{-}\gamma$ and $D_s^{-}\rightarrow
K^-K^+\pi^-$. The differential decay rate is fitted with the
Caprini-Lellouch-Neubert (CLN) and Boyd-Grinstein-Lebed (BGL) parametrisations
of the form factors, and the relevant quantities for both are extracted.
A search is presented for the lepton flavour violating decay $B^+ \rightarrow
K^+ \mu^- \tau^+$ using a sample of proton--proton collisions at centre-of-mass
energies of 7, 8, and 13 TeV, collected ...with the LHCb detector and
corresponding to a total integrated luminosity of 9 fb^{-1}$. The $\tau$
leptons are selected inclusively, primarily via decays with a single charged
particle. The four-momentum of the $\tau$ lepton is determined by using $B^+$
mesons from $B_{s2}^{*0} \rightarrow B^+ K^-$ decays. No significant excess is
observed, and an upper limit is set on the branching fraction $B(B^+
\rightarrow K^+ \mu^- \tau^+) < 3.9 \times 10^{-5}$ at 90% confidence level.
The obtained limit is comparable to the world-best limit.
J. High Energ. Phys. 06, 40 (2020) Measurements of $CP$ observables in $B^\pm \to D K^\pm$ and $B^\pm \to D
\pi^\pm$ decays are presented, where $D$ represents a superposition of $D^0$
and ...$\bar{D}^0$ states. The $D$ meson is reconstructed in the three-body final
state $K_{\rm{S}}^0K^\pm \pi^\mp$. The analysis uses samples of $B$ mesons
produced in proton-proton collisions, corresponding to an integrated luminosity
of 1.0, 2.0, and 6.0 fb$^{-1}$ collected with the LHCb detector at
centre-of-mass energies of $\sqrt{s} = $ 7, 8, and 13 TeV, respectively. These
measurements are the most precise to date, and provide important input for the
determination of the CKM angle $\gamma$.
JHEP 06 (2020) 136 A new baryon state is observed in the $\Lambda_b^0\pi^+\pi^-$ mass spectrum
with high significance using a data sample of $pp$ collisions, collected with
the LHCb detector at ...centre-of-mass energies $\sqrt{s}=7, 8$ and 13TeV,
corresponding to an integrated luminosity of 9fb$^{-1}$. The mass and natural
width of the new state are measured to be \begin{eqnarray*} m & = & 6072.3 \pm
2.9 \pm 0.6 \pm 0.2 MeV\,, \Gamma & = & 72 \pm 11 \pm 2 MeV\,, \end{eqnarray*}
where the first uncertainty is statistical and the second systematic. The third
uncertainty for the mass is due to imprecise knowledge of the $\Lambda_b^0$
baryon mass. The new state is consistent with the first radial excitation of
the $\Lambda_b^0$ baryon, the $\Lambda_b(2S)^0$ resonance. Updated measurements
of the masses and the upper limits on the natural widths of the previously
observed $\Lambda_b(5912)^0$ and $\Lambda_b(5920)^0$ states are also reported.
Phys. Rev. D 102, 012011 (2020) A measurement of the branching fraction of the decay $B_s^0 \to K_S^0 K_S^0$
is performed using proton-proton collision data corresponding to an integrated
luminosity ...of 5 $fb^{-1}$ collected by the LHCb experiment between 2011 and
2016. The branching fraction is determined to be BR($B_s^0 \to K_S^0 K_S^0$) =
8.3 $\pm$ 1.6 (stat) $\pm$ 0.9 (syst) $\pm$ 0.8 (norm) $\pm$ 0.3 ($f_s/f_d$)
$\times 10^{-6}$ , where the first uncertainty is statistical, the second is
systematic, and the third and fourth are due to uncertainties on the branching
fraction of the normalization mode $B^0 \to \phi K_S^0$ and the ratio of
hadronization fractions $f_s/f_d$. This is the most precise measurement of this
branching fraction to date.
Furthermore, a measurement of the branching fraction of the decay $B^0 \to
K_S^0 K_S^0$ is performed relative to that of the $B_s^0 \to K_S^0 K_S^0$
channel, and is found to be $\frac{BR(B^0 \to K_S^0 K_S^0)}{BR(B_s^0 \to K_S^0
K_S^0)}$ = 7.5 $\pm$ 3.1 (stat) $\pm$ 0.5 (syst) $\pm$ 0.3 ($f_s/f_d$)
$\times 10^{-2}$.
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 \(B^+\to J/\psi (e^+e^-)K^+\) 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 \(1\%\).
Phys. Rev. Lett. 125, 231801 (2020) A search for the decay $K^0_{\mathrm{S}}\rightarrow\mu^{+}\mu^{-}$ is
performed using proton-proton collision data, corresponding to an integrated
luminosity of ...$5.6\,\text{fb}^{-1}$ and collected with the LHCb experiment
during 2016, 2017 and 2018 at a center-of-mass energy of $13\,\mathrm{TeV}$.
The observed signal yield is consistent with zero, yielding an upper limit of
${\cal B}(K^0_{\mathrm{S}}\rightarrow\mu^{+}\mu^{-}) < 2.2 \times 10^{-10}$ at
90% CL. The limit reduces to ${\cal
B}(K^0_{\mathrm{S}}\rightarrow\mu^{+}\mu^{-}) < 2.1 \times 10^{-10}$ at 90% CL
once combined with the result from data taken in 2011 and 2012.
