JHEP 01 (2024) 070 The production of prompt $D^+$ and $D^+_{s}$ mesons is studied in proton-lead
collisions at a centre-of-mass energy of $\sqrt {s_{\mathrm{NN}}}=5.02\,$TeV.
The data sample ...corresponding to an integrated luminosity of
$(1.58\pm0.02)\mathrm{nb}^{-1}$ is collected by the LHCb experiment at the LHC.
The differential production cross-sections are measured using $D^+$ and
$D^+_{s}$ candidates with transverse momentum in the range of $0<p_{\mathrm{T}}
<14\,\mathrm{GeV}/c$ and rapidities in the ranges of $1.5<y^*<4.0$ and
$-5.0<y^*<-2.5$ in the nucleon-nucleon centre-of-mass system. For both
particles, the nuclear modification factor and the forward-backward production
ratio are determined. These results are compared with theoretical models that
include initial-state nuclear effects. In addition, measurements of the
cross-section ratios between $D^+$, $D^+_{s}$ and $D^0$ mesons are presented,
providing a baseline for studying the charm hadronization in lead-lead
collisions at LHC energies.
Phys. Rev. C 109 (2024) 054908 Flow harmonic coefficients, $v_n$, which are the key to studying the
hydrodynamics of the quark-gluon plasma (QGP) created in heavy-ion collisions,
have been measured ...in various collision systems and kinematic regions and using
various particle species. The study of flow harmonics in a wide pseudorapidity
range is particularly valuable to understand the temperature dependence of the
shear viscosity to entropy density ratio of the QGP. This paper presents the
first LHCb results of the second- and the third-order flow harmonic
coefficients of charged hadrons as a function of transverse momentum in the
forward region, corresponding to pseudorapidities between 2.0 and 4.9, using
the data collected from PbPb collisions in 2018 at a center-of-mass energy of
$5.02$ TeV. The coefficients measured using the two-particle angular
correlation analysis method are smaller than the central-pseudorapidity
measurements at ALICE and ATLAS from the same collision system but share
similar features.
The production of prompt $D^+_{s}$ and $D^+$ mesons is measured by the LHCb
experiment in proton-lead ($p\mathrm{Pb}$) collisions in both the forward
($1.5<y^*<4.0$) and backward ($-5.0<y^*<-2.5$) ...rapidity regions at a
nucleon-nucleon center-of-mass energy of $\sqrt {s_{\mathrm{NN}}}=8.16\,$TeV.
The nuclear modification factors of both $D^+_{s}$ and $D^+$ mesons are
determined as a function of transverse momentum, $p_{\mathrm{T}}$, and
rapidity. In addition, the $D^+_{s}$ to $D^+$ cross-section ratio is measured
as a function of the charged particle multiplicity in the event. An enhanced
$D^+_{s}$ to $D^+$ production in high-multiplicity events is observed for the
whole measured $p_{\mathrm{T}}$ range, in particular at low $p_{\mathrm{T}}$
and backward rapidity, where the significance exceeds six standard deviations.
This constitutes the first observation of strangeness enhancement in charm
quark hadronization in high-multiplicity $p\mathrm{Pb}$ collisions. The results
are also qualitatively consistent with the presence of quark coalescence as an
additional charm quark hadronization mechanism in high-multiplicity proton-lead
collisions.
The longitudinal polarization fraction of the $D^{*}$ meson is measured in
$B^0\to D^{*-}\tau^{+}\nu_{\tau}$ decays, where the $\tau$ lepton decays to
three charged pions and a neutrino, using ...proton-proton collision data
collected by the LHCb experiment at center-of-mass energies of 7, 8 and 13 TeV
and corresponding to an integrated luminosity of 5 fb$^{-1}$. The $D^{*}$
polarization fraction $F_{L}^{D^{*}}$ is measured in two $q^{2}$ regions, below
and above 7 GeV$^{2}/c^{4}$, where $q^{2}$ is defined as the squared invariant
mass of the $\tau\nu_{\tau}$ system. The $F_{L}^{D^{*}}$ values are measured to
be $0.51 \pm 0.07 \pm 0.03$ and $0.35 \pm 0.08 \pm 0.02$ for the lower and
higher $q^{2}$ regions, respectively. The first uncertainties are statistical
and the second systematic. The average value over the whole $q^{2}$ range is:
$$F_{L}^{D^{*}} = 0.43 \pm 0.06 \pm 0.03.$$ These results are compatible with
the Standard Model predictions.
The first observation and study of two new baryonic structures in the final
state $\Xi_b^0\pi^+\pi^-$ and the confirmation of the $\Xi_b(6100)^-$ state in
the $\Xi_b^-\pi^+\pi^-$ decay mode are ...reported using proton-proton collision
data collected by the LHCb experiment, corresponding to an integrated
luminosity of 9$\mathrm{fb}^{-1}$. In addition, the properties of the known
$\Xi_b^{*0}$, $\Xi_b^{'-}$ and $\Xi_b^{*-}$ resonances are measured with
improved precision. The new decay mode of the $\Xi_b^0$ baryon to the
$\Xi_c^+\pi^-\pi^+\pi^-$ final state is observed and exploited for the first
time in these measurements.
Phys. Rev. Lett. 132 (2024) 102302 The fraction of $\chi_{c1}$ and $\chi_{c2}$ decays in the prompt $J/\psi$
yield, $F_{\chi c}=\sigma_{\chi_c \to J/\psi}/\sigma_{J/\psi}$, is measured by
the LHCb ...detector in pPb collisions at $\sqrt{s_{NN}}=8.16$ TeV. The study
covers the forward ($1.5<y^*<4.0$) and backward ($-5.0<y^*<-2.5$) rapidity
regions, where $y^*$ is the $J/\psi$ rapidity in the nucleon-nucleon
center-of-mass system. Forward and backward rapidity samples correspond to
integrated luminosities of 13.6 $\pm$ 0.3 nb$^{-1}$ and 20.8 $\pm$ 0.5
nb$^{-1}$, respectively. The result is presented as a function of the $J/\psi$
transverse momentum $p_{T,J/\psi}$ in the range 1$<p_{T, J/\psi}<20$ GeV/$c$.
The $F_{\chi c}$ fraction at forward rapidity is compatible with the LHCb
measurement performed in $pp$ collisions at $\sqrt{s}=7$ TeV, whereas the
result at backward rapidity is 2.4 $\sigma$ larger than in the forward region
for $1<p_{T, J/\psi}<3$ GeV/$c$. The increase of $F_{\chi c}$ at low $p_{T,
J/\psi}$ at backward rapidity is compatible with the suppression of the
$\psi$(2S) contribution to the prompt $J/\psi$ yield. The lack of in-medium
dissociation of $\chi_c$ states observed in this study sets an upper limit of
180 MeV on the free energy available in these pPb collisions to dissociate or
inhibit charmonium state formation.
JHEP 03 (2024) 107 A search for $\textit{CP}$ violation in $D^{0} \rightarrow K_{S}^{0} K^{+}
\pi^{-} $ and $D^{0} \rightarrow K_{S}^{0} K^{-} \pi^{+} $ decays is reported.
The search is performed ...using an unbinned model-independent method known as the
energy test that probes local $\textit{CP}$ violation in the phase space of the
decays. The data analysed correspond to an integrated luminosity of
$5.4~$fb$^{-1}$ collected in proton-proton collisions by the LHCb experiment at
a centre-of-mass energy of $\sqrt{s}=13$~TeV, amounting to approximately 950
thousand and 620 thousand signal candidates for the $D^{0} \rightarrow
K_{S}^{0} K^{-} \pi^{+} $ and $D^{0} \rightarrow K_{S}^{0} K^{+} \pi^{-} $
modes, respectively. The method is validated using $D^{0} \rightarrow K^{-}
\pi^{+} \pi^{-} \pi^{+} $ and $D^{0} \rightarrow K_{S}^{0} \pi^{+} \pi^{-} $
decays, where $\textit{CP}$-violating effects are expected to be negligible,
and using background-enhanced regions of the signal decays. The results are
consistent with $\textit{CP}$ symmetry in both the $D^{0} \rightarrow K_{S}^{0}
K^{-} \pi^{+} $ and the $D^{0} \rightarrow K_{S}^{0} K^{+} \pi^{-} $ decays,
with $p$-values for the hypothesis of no $\textit{CP}$ violation of 70% and
66%, respectively.
The production of $\eta$ and $\eta'$ mesons is studied in proton-proton and
proton-lead collisions collected with the LHCb detector. Proton-proton
collisions are studied at center-of-mass energies of ...$5.02$ and $13~{\rm TeV}$,
and proton-lead collisions are studied at a center-of-mass energy per nucleon
of $8.16~{\rm TeV}$. The studies are performed in center-of-mass rapidity
regions $2.5<y_{\rm c.m.}<3.5$ (forward rapidity) and $-4.0<y_{\rm c.m.}<-3.0$
(backward rapidity) defined relative to the proton beam direction. The $\eta$
and $\eta'$ production cross sections are measured differentially as a function
of transverse momentum for $1.5<p_{\rm T}<10~{\rm GeV}$ and $3<p_{\rm
T}<10~{\rm GeV}$, respectively. The differential cross sections are used to
calculate nuclear modification factors. The nuclear modification factors for
$\eta$ and $\eta'$ mesons agree at both forward and backward rapidity, showing
no significant evidence of mass dependence. The differential cross sections of
$\eta$ mesons are also used to calculate $\eta/\pi^0$ cross section ratios,
which show evidence of a deviation from the world average. These studies offer
new constraints on mass-dependent nuclear effects in heavy-ion collisions, as
well as $\eta$ and $\eta'$ meson fragmentation.
The $\Xi_b^0 \rightarrow \Xi_c^+ D_s^-$ and $\Xi_b^- \rightarrow \Xi_c^0
D_s^-$ decays are observed for the first time using proton-proton collision
data collected by the LHCb experiment at a ...centre-of-mass energy of
$\sqrt{s}=13\mathrm{TeV}$, corresponding to an integrated luminosity of
$5.1\mathrm{fb}^{-1}$. The relative branching fractions times the beauty-baryon
production cross-sections are measured to be
\begin{align*}
\mathcal{R}\left(\frac{\Xi_b^0}{\Lambda_b^0}\right) \equiv
\frac{\sigma\left(\Xi_b^0\right)}{\sigma\left(\Lambda_b^0\right)}
\times
\frac{\mathcal{B}\left(\Xi_b^0 \rightarrow \Xi_c^+
D_s^-\right)}{\mathcal{B}\left(\Lambda_b^0 \rightarrow \Lambda_c^0
D_s^-\right)}
=(15.8\pm1.1\pm0.6\pm7.7)\%,
\mathcal{R}\left(\frac{\Xi_b^-}{\Lambda_b^0}\right) \equiv
\frac{\sigma\left(\Xi_b^-\right)}{\sigma\left(\Lambda_b^0\right)}
\times
\frac{\mathcal{B}\left(\Xi_b^- \rightarrow \Xi_c^0
D_s^-\right)}{\mathcal{B}\left(\Lambda_b^0 \rightarrow \Lambda_c^0
D_s^-\right)}
=(16.9\pm1.3\pm0.9\pm4.3)\%,
\end{align*} where the first uncertainties are statistical, the second
systematic, and the third due to the uncertainties on the branching fractions
of relevant charm-baryon decays. The masses of $\Xi_b^0$ and $\Xi_b^-$ baryons
are measured to be $m_{\Xi_b^0}=5791.12\pm0.60\pm0.45\pm0.24\mathrm{MeV}/c^2$
and $m_{\Xi_b^-}=5797.02\pm0.63\pm0.49\pm0.29\mathrm{MeV}/c^2$, where the
uncertainties are statistical, systematic, and those due to charm-hadron
masses, respectively.
Using a dataset corresponding to $9~\mathrm{fb}^{-1}$ of integrated
luminosity collected with the LHCb detector between 2011 and 2018 in
proton-proton collisions, the decay-time distributions of the ...decay modes
$B_s^0 \rightarrow J/\psi \eta'$ and $B_s^0 \rightarrow J/\psi \pi^{+} \pi^{-}$
are studied. The decay-width difference between the light and heavy mass
eigenstates of the $B_s^0$ meson is measured to be $\Delta \Gamma_s = 0.087 \pm
0.012 \pm 0.009 \, \mathrm{ps}^{-1}$, where the first uncertainty is
statistical and the second systematic.