Ricardo Granciani Diaz

A measurement of the $$ {\varXi}_{cc}^{++} $$Ξcc++ mass is performed using data collected by the LHCb experiment between 2016 and 2018 inppcollisions at a centre-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 5.6 fb⁻¹. The $$ {\varXi}_{cc}^{++} $$Ξcc++ candidates are reconstructed via the decay modes $$ {\varXi}_{cc}^{++}\to {\varLambda}_c^{+}{K}^{-}{\pi}^{+}{\pi}^{+} $$Ξcc++→Λc+K−π+π+ and $$ {\varXi}_{cc}^{++}\to {\varXi}_c^{+}{\pi}^{+} $$Ξcc++→Ξc+π+ . The result, 3621.55±0.23 (stat)±0.30 (syst) MeV/c², is the most precise measurement of the $$ {\varXi}_{cc}^{++} $$Ξcc++ mass to date.

Searches are performed for both promptlike and long-lived dark photons, $A^{\prime }$, produced in proton-proton collisions at a center-of-mass energy of 13 TeV. These searches look for $A^{\prime }\to {\mu }^{+}{\mu }^{-}$ decays using a data sample corresponding to an integrated luminosity of $5.5{\mathrm{fb}}^{-1}$ collected with the LHCb detector. Neither search finds evidence for a signal, and 90% confidence-level exclusion limits are placed on the $\gamma –A^{\prime }$ kinetic mixing strength. The promptlike $A^{\prime }$ search explores the mass region from near the dimuon threshold up to 70 GeV and places the most stringent constraints to date on dark photons with $214<m(A^{\prime })\lesssim 740\mathrm{MeV}$ and $10.6<m(A^{\prime })\lesssim 30\mathrm{GeV}$. The search for long-lived $A^{\prime }\to {\mu }^{+}{\mu }^{-}$ decays places world-leading constraints on low-mass dark photons with lifetimes $\mathcal{O}(1)\mathrm{ps}$.

The results of an amplitude analysis of the charmless three-body decay $B^{+}\to {\pi }^{+}{\pi }^{+}{\pi }^{-}$, in which $CP$-violation effects are taken into account, are reported. The analysis is based on a data sample corresponding to an integrated luminosity of $3{\mathrm{fb}}^{-1}$ of $pp$ collisions recorded with the LHCb detector. The most challenging aspect of the analysis is the description of the behavior of the ${\pi }^{+}{\pi }^{-}S$-wave contribution, which is achieved by using three complementary approaches based on the isobar model, the $K$-matrix formalism, and a quasi-model-independent procedure. Additional resonant contributions for all three methods are described using a common isobar model, and include the $\rho (770{)}^0$, $\omega (782)$ and $\rho (1450{)}^0$ resonances in the ${\pi }^{+}{\pi }^{-}$ $P$-wave, the $f_2(1270)$ resonance in the ${\pi }^{+}{\pi }^{-}$ $D$-wave, and the ${\rho }_3(1690{)}^0$ resonance in the ${\pi }^{+}{\pi }^{-}$ $F$-wave. Significant $CP$-violation effects are observed in both $S$- and $D$-waves, as well as in the interference between the $S$- and $P$-waves. The results from all three approaches agree and provide new insight into the dynamics and the origin of $CP$-violation effects in $B^{+}\to {\pi }^{+}{\pi }^{+}{\pi }^{-}$ decays.

Observations are reported of different sources of $CP$ violation from an amplitude analysis of $B^{+}\to {\pi }^{+}{\pi }^{+}{\pi }^{-}$ decays, based on a data sample corresponding to an integrated luminosity of $3{\mathrm{fb}}^{-1}$ of $pp$ collisions recorded with the LHCb detector. A large $CP$ asymmetry is observed in the decay amplitude involving the tensor $f_2(1270)$ resonance, and in addition significant $CP$ violation is found in the ${\pi }^{+}{\pi }^{-}S$ wave at low invariant mass. The presence of $CP$ violation related to interference between the ${\pi }^{+}{\pi }^{-}$S wave and the $P$ wave $B^{+}\to \rho (770{)}^0{\pi }^{+}$ amplitude is also established; this causes large local asymmetries but cancels when integrated over the phase space of the decay. The results provide both qualitative and quantitative new insights into $CP$ -violation effects in hadronic $B$ decays.

A search for decay-time-dependent charge-parity ($CP$) asymmetry in $D^0\to K^{+}{K}^{-}$ and $D^0\to {\pi }^{+}{\pi }^{-}$ decays is performed at the LHCb experiment using proton-proton collision data recorded at a center-of-mass energy of 13 TeV, and corresponding to an integrated luminosity of $5.4{\text{fb}}^{-1}$. The $D^0$ mesons are required to originate from semileptonic decays of $b$ hadrons, such that the charge of the muon identifies the flavor of the neutral $D$ meson at production. The asymmetries in the effective decay widths of $D^0$ and ${\overline{D}}^0$ mesons are determined to be $A_{\mathrm{\Gamma }}(K^{+}{K}^{-})=(-4.3\pm 3.6\pm 0.5)\times 10^{-4}$ and $A_{\mathrm{\Gamma }}({\pi }^{+}{\pi }^{-})=(2.2\pm 7.0\pm 0.8)\times 10^{-4}$, where the uncertainties are statistical and systematic, respectively. The results are consistent with $CP$ symmetry and, when combined with previous LHCb results, yield $A_{\mathrm{\Gamma }}(K^{+}{K}^{-})=(-4.4\pm 2.3\pm 0.6)\times 10^{-4}$ and $A_{\mathrm{\Gamma }}({\pi }^{+}{\pi }^{-})=(2.5\pm 4.3\pm 0.7)\times 10^{-4}$.

A measurement of the time-dependent CP-violating asymmetry in $$ {B}_s^0\to \phi \phi $$ B s 0 → ϕϕ decays is presented. Using a sample of proton-proton collision data corresponding to an integrated luminosity of 5.0 fb ⁻¹ collected by the LHCb experiment at centre-of-mass energies $$ \sqrt{s} $$ s = 7 TeV in 2011, 8 TeV in 2012 and 13 TeV in 2015 and 2016, a signal yield of around 9000 $$ {B}_s^0\to \phi \phi $$ B s 0 → ϕϕ decays is obtained. The CP-violating phase $$ {\phi}_s^{s\overline{s}s} $$ ϕ s s s ¯ s is measured to be −0.073 ± 0.115(stat) ± 0.027(syst) rad, under the assumption it is independent of the helicity of the ϕϕ decay. In addition, the CP-violating phases of the transverse polarisations under the assumption of CP conservation of the longitudinal phase are measured. The helicity-independent direct CP-violation parameter is also measured, and is found to be |λ| = 0.99 ± 0.05(stat) ± 0.01(syst). In addition, T-odd triple-product asymmetries are measured. The results obtained are consistent with the hypothesis of CP conservation in $$ \overline{b}\to \overline{s}s\overline{s}s $$ b ¯ → s ¯ s s ¯ s transitions. Finally, a limit on the branching fraction of the B ⁰ → ϕϕ decay is determined to be $$ \mathcal{B}\left({B}^0\to \phi \phi \right)<2.7\times {10}^{-8} $$ B B 0 → ϕϕ < 2.7 × 10 − 8 at 90 % confidence level.

The production fraction of the $B_c^{-}$ meson with respect to the sum of $B^{-}$ and ${\overline{B}}^0$ mesons is measured in both 7 and 13 TeV center-of-mass (c.m.) 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.

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

The first amplitude analysis of the $B^{\pm }\to {\pi }^{\pm }{K}^{+}{K}^{-}$ decay is reported based on a data sample corresponding to an integrated luminosity of $3.0{\mathrm{fb}}^{-1}$ of $pp$ collisions recorded in 2011 and 2012 with the LHCb detector. The data are found to be best described by a coherent sum of five resonant structures plus a nonresonant component and a contribution from $\pi \pi \leftrightarrow KK$ $S$-wave rescattering. The dominant contributions in the ${\pi }^{\pm }$ $K^{\mp }$ and $K^{+}$ $K^{-}$ systems are the nonresonant and the $B^{\pm }\to \rho (1450{)}^0{\pi }^{\pm }$ amplitudes, respectively, with fit fractions around 30%. For the rescattering contribution, a sizable fit fraction is observed. This component has the largest $CP$ asymmetry reported to date for a single amplitude of $(-66\pm 4\pm 2)\%$, where the first uncertainty is statistical and the second systematic. No significant $CP$ violation is observed in the other contributions.