Angular analysis of D0→π+π−μ+μ−D^0 \to \pi^+\pi^-\mu^+\mu^- and D0→K+K−μ+μ−D^0 \to K^+K^-\mu^+\mu^- decays and search for CPCP violation

The first full angular analysis and an updated measurement of the decay-rate $CP$ asymmetry of the $D^0 \to \pi^+\pi^-\mu^+\mu^-$ and $D^0 \to K^+K^-\mu^+\mu^-$ decays are reported. The analysis uses proton-proton collision data collected with the LHCb detector at centre-of-mass energies of 7, 8 and 13 TeV. The data set corresponds to an integrated luminosity of 9 fb$^{-1}$. The full set of $CP$-averaged angular observables and their $CP$ asymmetries are measured as a function of the dimuon invariant mass. The results are consistent with expectations from the standard model and with $CP$ symmetry.Comment: All figures and tables, along with any supplementary material and additional information, are available at https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2021-035.html (LHCb public pages

Measurement of the photon polarization in Λb→Λγ\Lambda_b \to \Lambda \gamma decays

The photon polarization in $b \to s \gamma$ transitions is measured for the first time in radiative b-baryon decays exploiting the unique spin structure of $\Lambda_b \to \Lambda \gamma$ decays. A data sample corresponding to an integrated luminosity of $6\;fb^{-1}$ collected by the LHCb experiment in $pp$ collisions at a center-of-mass energy of $13\;TeV$ is used. The photon polarization is measured to be $\alpha_{\gamma}= 0.82^{\,+\,0.17\,+\,0.04}_{\,-\,0.26\,-\,0.13}$, where the first uncertainty is statistical and the second systematic. This result is in agreement with the Standard Model prediction and previous measurements in b-meson decays. Charge-parity breaking effects are studied for the first time in this observable and found to be consistent with $CP$ symmetry.Comment: All figures and tables, along with machine-readable versions and any supplementary material and additional information, are available at https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2021-030.html (LHCb public pages

Searches for rare Bs0 and B 0 decays into four muons

Searches for rare Bs0 and B0 decays into four muons are performed using proton-proton collision data recorded by the LHCb experiment, corresponding to an integrated luminosity of 9 fb−1. Direct decays and decays via light scalar and J/ψ resonances are considered. No evidence for the six decays searched for is found and upper limits at the 95% confidence level on their branching fractions ranging between 1.8 × 10−10 and 2.6 × 10−9 are set. [Figure not available: see fulltext.

Precision measurement of the Ξcc++Ξcc++ {\varXi}_{cc}^{++} mass

A measurement of the Ξ++cc mass is performed using data collected by the LHCb experiment between 2016 and 2018 in pp collisions at a centre-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 5.6 fb−1. The Ξ++cc candidates are reconstructed via the decay modes Ξ++cc→Λ+cK−π+π+ and Ξ++cc→Ξ+cπ+. The result, 3621.55 ± 0.23 (stat) ± 0.30 (syst) MeV/c2, is the most precise measurement of the Ξ++cc mass to date

Search for CP Violation in D-s(+) -> K-S(0)pi(+), D+ -> (KSK+)-K-0, and D+ -> phi pi(+) Decays

A search for charge-parity ($CP$) violation in Cabibbo-suppressed $D_s^+\to K_S^0 \pi^+$, $D^+\to K_S^0 K^+$ and $D^+\to \phi \pi^+$ decays is reported using proton-proton collision data, corresponding to an integrated luminosity of 3.8 fb$^{-1}$, collected at a center-of-mass energy of 13 TeV with the LHCb detector. High-yield samples of kinematically and topologically similar Cabibbo-favored $D_{(s)}^+$ decays are analyzed to subtract nuisance asymmetries due to production and detection effects, including those induced by $CP$ violation in the neutral kaon system. The results are \begin{align*} \mathcal{A}_{CP}(D_s^+\to K_S^0 \pi^+) &=\left(\phantom{-}1.3\phantom{0}\pm1.9\phantom{0}\pm0.5\phantom{0}\right)\times10^{-3},\\ \mathcal{A}_{CP}(D^+\to K_S^0 K^+) &=\left(-0.09\pm0.65\pm0.48\right)\times10^{-3},\\ \mathcal{A}_{CP}(D^+\to \phi \pi^+) &=\left(\phantom{-}0.05\pm0.42\pm0.29\right)\times10^{-3}, \end{align*} where the first uncertainties are statistical and the second systematic. They are the most precise measurements of these quantities to date, and are consistent with $CP$ symmetry.Comment: All figures and tables, along with any supplementary material and additional information, are available at https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2019-002.htm

Study of the psi(2)(3823) and chi(c1)(3872) states in B+->(J/psi pi(+)pi(-))K(+)decays

The decays $B^+\rightarrow J/\psi \pi^+ \pi^- K^+$ are studied using a data set corresponding to an integrated luminosity of 9fb$^{-1}$ collected with the LHCb detector in proton-proton collisions between 2011 and 2018. Precise measurements of the ratios of branching fractions with the intermediate $\psi_2(3823)$, $\chi_{c1}(3872)$ and $\psi(2S)$ states are reported. The decay of $B^+\rightarrow \psi_2(3872)K^+$ with $\psi_2(3823)\rightarrow J\psi\pi^+\pi^-$ is observed for the first time with a significance of 5.1 standard deviations. The mass differences between the $\psi_2(3823)$, $\chi_{c1}(3872)$ and $\psi(2S)$ states are measured to be $$\begin{array}{rcl} m_{\chi_{c1(3872)}} - m_{\psi_2(3823)} &= & 47.50 \pm 0.53 \pm 0.13\,\mathrm{MeV/}c^2\,, \\ m_{\psi_2(3823)} - m_{\psi(2S)} &= & 137.98 \pm 0.53 \pm 0.14\,\mathrm{MeV/}c^2\,, \\ m_{\chi_{c1}(3872)} - m_{\psi(2S)} &= & 185.49 \pm 0.06 \pm 0.03\,\mathrm{MeV/}c^2\,, \end{array}$$ resulting in the most precise determination of the $\chi_{c1}(3782)$ mass. The width of the $\psi_2(3823)$ state is found to be below 5.2MeV at 90\% confidence level. The Breit-Wigner width of the $\chi_{c1}(3872)$ state is measured to be $$\Gamma^{\mathrm{BW}}_{\chi_{c1}(3872)} = 0.96^{+0.19}_{-0.18}\pm0.21 \mathrm{MeV},$$ which is inconsistent with zero by 5.5 standard deviations.Comment: 26 pages, 3 figures. All figures and tables, along with any supplementary material and additional information, are available at https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2020-009.html (LHCb public pages

Search for the lepton-flavor-violating decays Bs0→τ±μ∓ and B0→τ±μ∓

Results are reported from a search for the rare decays B 0 s → τ ± μ ∓ and B 0 → τ ± μ ∓ , where the τ lepton is reconstructed in the channel τ − → π − π + π − ν τ . These processes are effectively forbidden in the standard model, but they can potentially occur at detectable rates in models of new physics that can induce lepton-flavor-violating decays. The search is based on a data sample corresponding to 3     fb − 1 of proton-proton collisions recorded by the LHCb experiment in 2011 and 2012. The event yields observed in the signal regions for both processes are consistent with the expected standard model backgrounds. Because of the limited mass resolution arising from the undetected τ neutrino, the B 0 s and B 0 signal regions are highly overlapping. Assuming no contribution from B 0 → τ ± μ ∓ , the upper limit B ( B 0 s → τ ± μ ∓ ) < 4.2 × 10 − 5 is obtained at 95% confidence level. If no contribution from B 0 s → τ ± μ ∓ is assumed, a limit of B ( B 0 → τ ± μ ∓ ) < 1.4 × 10 − 5 is obtained at 95% confidence level. These results represent the first limit on B ( B 0 s → τ ± μ ∓ ) and the most stringent limit on B ( B 0 → τ ± μ ∓ )