Search for dark photons produced in 13 TeV pppp collisions

Searches are performed for both promptlike and long-lived dark photons, A 0 , produced in proton-proton collisions at a center-of-mass energy of 13 TeV, using A 0 → μ þ μ − decays and a data sample corresponding to an integrated luminosity of 1 . 6 fb − 1 collected with the LHCb detector. The promptlike A 0 search covers the mass range from near the dimuon threshold up to 70 GeV, while the long-lived A 0 search is restricted to the low-mass region 214 <m ð A 0 Þ < 350 MeV. No evidence for a signal is found, and 90% confidence level exclusion limits are placed on the γ – A 0 kinetic-mixing strength. The constraints placed on promptlike dark photons are the most stringent to date for the mass range 10 . 6 <m ð A 0 Þ < 70 GeV, and are comparable to the best existing limits for m ð A 0 Þ < 0 . 5 GeV. The search for long-lived dark photons is the first to achieve sensitivity using a displaced-vertex signature

Measurement of the CKM angle γ using B± → DK± with D → K S 0 π+π−, K S 0 K+K− decays

A binned Dalitz plot analysis of B ± → DK ± decays, with D→K0Sπ+π− and D→K0SK+K−, is performed to measure the CP-violating observables x ± and y ±, which are sensitive to the Cabibbo-Kobayashi-Maskawa angle γ. The analysis exploits a sample of proton-proton collision data corresponding to 3.0 fb−1 collected by the LHCb experiment. Measurements from CLEO-c of the variation of the strong-interaction phase of the D decay over the Dalitz plot are used as inputs. The values of the parameters are found to be x + = (−7.7 ± 2.4 ± 1.0 ± 0.4) × 10− 2, x − = (2.5 ± 2.5 ± 1.0 ± 0.5) × 10− 2, y + = (−2.2 ± 2.5 ± 0.4 ± 1.0) × 10− 2 and y − = (7.5 ± 2.9 ± 0.5 ± 1.4) × 10− 2. The first, second, and third uncertainties are the statistical, the experimental systematic, and that associated with the precision of the strong-phase parameters. These are the most precise measurements of these observables and correspond to γ = (62 − 14 + 15) ° , with a second solution at γ → γ + 180°, and r B  = 0.080 − 0.021 + 0.019, where r B is the ratio between the suppressed and favoured B decay amplitudes

Studies of the resonance structure in D0→K∓π±π±π∓ decays

Amplitude models are constructed to describe the resonance structure of D0→K−π+π+π− and D0→K+π−π−π+ decays using pp collision data collected at centre-of-mass energies of 7 and 8 TeV with the LHCb experiment, corresponding to an integrated luminosity of 3.0 fb−1 . The largest contributions to both decay amplitudes are found to come from axial resonances, with decay modes D0→a1(1260)+K− and D0→K1(1270/1400)+π− being prominent in D0→K−π+π+π− and D0→K+π−π−π+ , respectively. Precise measurements of the lineshape parameters and couplings of the a1(1260)+ , K1(1270)− and K(1460)− resonances are made, and a quasi model-independent study of the K(1460)− resonance is performed. The coherence factor of the decays is calculated from the amplitude models to be RK3π=0.459±0.010(stat)±0.012(syst)±0.020(model) , which is consistent with direct measurements. These models will be useful in future measurements of the unitary-triangle angle γ and studies of charm mixing and CP violation

Measurements of the branching fractions of Λ c + → pπ−π+, Λ c + → pK−K+, and Λ c + → pπ−K+

The ratios of the branching fractions of the decays $\Lambda_{c}^{+} \rightarrow p \pi^{-} \pi^{+}$, $\Lambda_{c}^{+} \rightarrow p K^{-} K^{+}$, and $\Lambda_{c}^{+} \rightarrow p \pi^{-} K^{+}$ with respect to the Cabibbo-favoured $\Lambda_{c}^{+} \rightarrow p K^{-} \pi^{+}$ decay are measured using proton-proton collision data collected with the LHCb experiment at a 7 TeV centre-of-mass energy and corresponding to an integrated luminosity of 1.0 fb$^{-1}$: \begin{align*} \frac{\mathcal{B}(\Lambda_{c}^{+} \rightarrow p \pi^{-} \pi^{+})}{\mathcal{B}(\Lambda_{c}^{+} \rightarrow p K^{-} \pi^{+})} &amp; = (7.44 \pm 0.08 \pm 0.18)\,\%, \\ \frac{\mathcal{B}(\Lambda_{c}^{+} \rightarrow p K^{-} K^{+})}{\mathcal{B}(\Lambda_{c}^{+} \rightarrow p K^{-} \pi^{+})} &amp;= (1.70 \pm 0.03 \pm 0.03)\,\%, \\ \frac{\mathcal{B}(\Lambda_{c}^{+} \rightarrow p \pi^{-} K^{+})}{\mathcal{B}(\Lambda_{c}^{+} \rightarrow p K^{-} \pi^{+})} &amp; = (0.165 \pm 0.015 \pm 0.005 )\,\%, \end{align*} where the uncertainties are statistical and systematic, respectively. These results are the most precise measurements of these quantities to date. When multiplied by the world-average value for $\mathcal{B}(\Lambda_{c}^{+} \rightarrow p K^{-} \pi^{+})$, the corresponding branching fractions are \begin{align*} \mathcal{B}(\Lambda_{c}^{+} \rightarrow p \pi^{-} \pi^{+}) &amp;= (4.72 \pm 0.05 \pm 0.11 \pm 0.25) \times 10^{-3}, \\ \mathcal{B}(\Lambda_{c}^{+} \rightarrow p K^{-} K^{+}) &amp;= (1.08 \pm 0.02 \pm 0.02 \pm 0.06) \times 10^{-3}, \\ \mathcal{B}(\Lambda_{c}^{+} \rightarrow p \pi^{-} K^{+}) &amp;= (1.04 \pm 0.09 \pm 0.03 \pm 0.05) \times 10^{-4}, \end{align*} where the final uncertainty is due to $\mathcal{B}(\Lambda_{c}^{+} \rightarrow p K^{-} \pi^{+})$