Showing papers by "Mark Wilkinson published in 2018"

Test of lepton flavor universality by the measurement of the B0 →d∗-τ+ντ branching fraction using three-prong τ decays

Abstract: The ratio of branching fractions R(D∗-)≡B(B0→D∗-τ+ντ)/B(B0→D∗-μ+νμ) is measured using a data sample of proton-proton collisions collected with the LHCb detector at center-of-mass energies of 7 and 8 TeV, corresponding to an integrated luminosity of 3 fb-1. The τ lepton is reconstructed with three charged pions in the final state. A novel method is used that exploits the different vertex topologies of signal and backgrounds to isolate samples of semitauonic decays of b hadrons with high purity. Using the B0→D∗-π+π-π+ decay as the normalization channel, the ratio B(B0→D∗-τ+ντ)/B(B0→D∗-π+π-π+) is measured to be 1.97±0.13±0.18, where the first uncertainty is statistical and the second systematic. An average of branching fraction measurements for the normalization channel is used to derive B(B0→D∗-τ+ντ)=(1.42±0.094±0.129±0.054)%, where the third uncertainty is due to the limited knowledge of B(B0→D∗-π+π-π+). A test of lepton flavor universality is performed using the well-measured branching fraction B(B0→D∗-μ+νμ) to compute R(D∗-)=0.291±0.019±0.026±0.013, where the third uncertainty originates from the uncertainties on B(B0→D∗-π+π-π+) and B(B0→D∗-μ+νμ). This measurement is in agreement with the Standard Model prediction and with previous measurements.

Measurement of the Ratio of the B0→D*−τ+ντ and B0→D*−μ+νμ Branching Fractions Using Three-Prong τ -Lepton Decays

Abstract: The ratio of branching fractions R(D^{*-})≡B(B^{0}→D^{*-}τ^{+}ν_{τ})/B(B^{0}→D^{*-}μ^{+}ν_{μ}) is measured using a data sample of proton-proton collisions collected with the LHCb detector at center-of-mass energies of 7 and 8 TeV, corresponding to an integrated luminosity of 3 fb^{-1}. For the first time, R(D^{*-}) is determined using the τ-lepton decays with three charged pions in the final state. The B^{0}→D^{*-}τ^{+}ν_{τ} yield is normalized to that of the B^{0}→D^{*-}π^{+}π^{-}π^{+} mode, providing a measurement of B(B^{0}→D^{*-}τ^{+}ν_{τ})/B(B^{0}→D^{*-}π^{+}π^{-}π^{+})=1.97±0.13±0.18, where the first uncertainty is statistical and the second systematic. The value of B(B^{0}→D^{*-}τ^{+}ν_{τ})=(1.42±0.094±0.129±0.054)% is obtained, where the third uncertainty is due to the limited knowledge of the branching fraction of the normalization mode. Using the well-measured branching fraction of the B^{0}→D^{*-}μ^{+}ν_{μ} decay, a value of R(D^{*-})=0.291±0.019±0.026±0.013 is established, where the third uncertainty is due to the limited knowledge of the branching fractions of the normalization and B^{0}→D^{*-}μ^{+}ν_{μ} modes. This measurement is in agreement with the standard model prediction and with previous results.

Measurement of the Ratio of Branching Fractions B (Bc+ →j /ψτ+ντ)/ B (Bc+ →j /ψμ+νμ)

Abstract: A measurement is reported of the ratio of branching fractions R(J/ψ)=B(B_{c}^{+}→J/ψτ^{+}ν_{τ})/B(B_{c}^{+}→J/ψμ^{+}ν_{μ}), where the τ^{+} lepton is identified in the decay mode τ^{+}→μ^{+}ν_{μ}ν[over ¯]_{τ}. This analysis uses a sample of proton-proton collision data corresponding to 3.0 fb^{-1} of integrated luminosity recorded with the LHCb experiment at center-of-mass energies of 7 and 8 TeV. A signal is found for the decay B_{c}^{+}→J/ψτ^{+}ν_{τ} at a significance of 3 standard deviations corrected for systematic uncertainty, and the ratio of the branching fractions is measured to be R(J/ψ)=0.71±0.17(stat)±0.18(syst). This result lies within 2 standard deviations above the range of central values currently predicted by the standard model.

A design framework and exemplar metrics for FAIRness.

Abstract: The FAIR Principles provide guidelines for the publication of digital resources such as datasets, code, workflows, and research objects, in a manner that makes them Findable, Accessible, Interoperable, and Reusable (FAIR). The Principles have rapidly been adopted by publishers, funders, and pan-disciplinary infrastructure programmes and societies. The Principles are aspirational, in that they do not strictly define how to achieve a state of "FAIRness", but rather they describe a continuum of features, attributes, and behaviors that will move a digital resource closer to that goal. This ambiguity has led to a wide range of interpretations of FAIRness, with some resources even claiming to already "be FAIR"! The increasing number of such statements, the emergence of subjective and self-assessments of FAIRness2,3, and the need of data and service providers, journals, funding agencies, and regulatory bodies to qualitatively or quantitatively evaluate such claims, led us to self-assemble and establish a FAIR Metrics group to pursue the goal of defining ways to measure FAIRness.

First Observation of the Doubly Charmed Baryon Decay Ξcc + + → Ξc+ π+

Abstract: The doubly charmed baryon decay Ξcc++→Ξc+π+ is observed for the first time, with a statistical significance of 5.9σ, confirming a recent observation of the baryon in the Λc+K-π+π+ final state. The data sample used corresponds to an integrated luminosity of 1.7 fb-1, collected by the LHCb experiment in pp collisions at a center-of-mass energy of 13 TeV. The Ξcc++ mass is measured to be 3620.6±1.5(stat)±0.4(syst)±0.3(Ξc+) MeV/c2 and is consistent with the previous result. The ratio of branching fractions between the decay modes is measured to be [B(Ξcc++→Ξc+π+)×B(Ξc+→pK-π+)]/[B(Ξcc++→Λc+K-π+π+)×B(Λc+→pK-π+)]=0.035±0.009(stat)±0.003(syst).

Macroevolutionary shift in the size of amphibian genomes and the role of life history and climate

Abstract: The evolution and great diversity of genome size has been of long-standing interest to biologists, but has seldom been investigated on a broad phylogenetic scale. Here we present a comparative quantitative analysis of factors shaping genome size evolution in amphibians, the extant class of vertebrates with the largest variation in genome size. We find that amphibian genomes have undergone saltations in size, although these are rare and the evolutionary history of genome size in amphibians has otherwise been one of gradual, time-dependent variation (that is, Brownian motion). This macroevolutionary homogeneity is remarkable given the evolutionary and ecological diversity of most other aspects of the natural history of amphibians. Contrary to previous claims, we find no evidence for associations between life cycle complexity and genome size despite the high diversity of reproductive modes and the multiple events of independent evolution of divergent life cycles in the group. Climate (temperature and humidity) affects genome size indirectly, at least in frogs, as a consequence of its effect on premetamorphic developmental period, although directionality of the relationship between developmental period and genome size is not unequivocal.

Observation of the decay $\Lambda^0_b\rightarrow\psi(2S)p\pi^-$

Abstract: The Cabibbo-suppressed decay Λ$_{b}^{0}$ → ψ(2S)pπ$^{−}$ is observed for the first time using a data sample collected by the LHCb experiment in proton-proton collisions corresponding to 1.0, 2.0 and 1.9 fb$^{−1}$ of integrated luminosity at centre-of-mass energies of 7, 8 and 13 TeV, respectively. The ψ(2S) mesons are reconstructed in the μ$^{+}$μ$^{−}$ final state. The branching fraction with respect to that of the Λ$_{b}^{0}$ → ψ(2S)pK$^{−}$ decay mode is measured to be

First measurement of the $CP$-violating phase $\phi_s^{d\overline{d}}$ in $B_s^0\to(K^+\pi^-)(K^-\pi^+)$ decays

Abstract: A flavour-tagged decay-time-dependent amplitude analysis of B$_{s}^{0}$ → (K$^{+}$π$^{−}$)(K$^{−}$π$^{+}$) decays is presented in the K$^{±}$π$^{∓}$ mass range from 750 to 1600MeV/c$^{2}$. The analysis uses pp collision data collected with the LHCb detector at centre-of-mass energies of 7 and 8 TeV, corresponding to an integrated luminosity of 3.0 fb$^{−1}$. Several quasi-two-body decay modes are considered, corresponding to K$^{±}$π$^{∓}$ combinations with spin 0, 1 and 2, which are dominated by the K$_{0}^{*}$ (800)$^{0}$ and K$_{0}^{*}$ (1430)$^{0}$, the K$^{*}$(892)$^{0}$ and the K$_{2}^{*}$ (1430)$^{0}$ resonances, respectively. The longitudinal polarisation fraction for the $ {B}_s^0\to {K}^{\ast }(892){}^{\circ}{\overline{K}}^{\ast }{(892)}^0 $ decay is measured as f$_{L}$ = 0.208 ± 0.032 ± 0.046, where the first uncertainty is statistical and the second is systematic. The first measurement of the mixing-induced CP-violating phase, $ {\phi}_s^{d\overline{d}} $ , in $ b\to d\overline{d}s $ transitions is performed, yielding a value of $ {\phi}_s^{d\overline{d}}=-0.10\pm 0.13\left(\mathrm{stat}\right)\pm 0.14 $ (syst) rad.

Angular moments of the decay Lambda(0)(b) -> Lambda mu(+)mu(-) at low hadronic recoil

Abstract: An analysis of the angular distribution of the decay Λ$_{b}^{0}$ → Λμ$^{+}$μ$^{−}$ is presented, using data collected with the LHCb detector between 2011 and 2016 and corresponding to an integrated luminosity of approximately 5 fb$^{−1}$. Angular observables are determined using a moment analysis of the angular distribution at low hadronic recoil, corresponding to the dimuon invariant mass squared range 15 < q$^{2}$ < 20 GeV$^{2}$/c$^{4}$. The full basis of observables is measured for the first time. The lepton-side, hadron-side and combined forward-backward asymmetries of the decay are determined to be $ \begin{array}{l}{A}_{\mathrm{FB}}^{\ell }=-0.39\pm 0.04\left(\mathrm{stat}\right)\pm 0.01\left(\mathrm{syst}\right),\hfill \\ {}{A}_{\mathrm{FB}}^h=-0.30\pm 0.05\left(\mathrm{stat}\right)\pm 0.02\left(\mathrm{syst}\right),\hfill \\ {}{A}_{\mathrm{FB}}^{\ell h}=+0.25\pm 0.04\left(\mathrm{stat}\right)\pm 0.01\left(\mathrm{syst}\right).\hfill \end{array} $

Evidence for an $\eta_c(1S) \pi^-$ resonance in $B^0 \to \eta_c(1S) K^+\pi^-$ decays

Abstract: A Dalitz plot analysis of $B^0 \to \eta_c(1S) K^+\pi^-$ decays is performed using data samples of $pp$ collisions collected with the LHCb detector at centre-of-mass energies of $\sqrt{s}=7,~8$ and $13$ TeV, corresponding to a total integrated luminosity of $4.7~\text{fb}^{-1}$. A satisfactory description of the data is obtained when including a contribution representing an exotic $\eta_c(1S) \pi^-$ resonant state. The significance of this exotic resonance is more than three standard deviations, while its mass and width are $4096 \pm 20~^{+18}_{-22}$ MeV and $152 \pm 58~^{+60}_{-35}$ MeV, respectively. The spin-parity assignments $J^P=0^+$ and $J^{P}=1^-$ are both consistent with the data. In addition, the first measurement of the $B^0 \to \eta_c(1S) K^+\pi^-$ branching fraction is performed and gives $\displaystyle \mathcal{B}(B^0 \to \eta_c(1S) K^+\pi^-) = (5.73 \pm 0.24 \pm 0.13 \pm 0.66) \times 10^{-4}$, where the first uncertainty is statistical, the second systematic, and the third is due to limited knowledge of external branching fractions.

Search for beautiful tetraquarks in the $\Upsilon(1S)\mu\mu$ invariant-mass spectrum

Abstract: The $\Upsilon(1S)\mu^+\mu^-$ invariant-mass distribution is investigated for a possible exotic meson state composed of two $b$ quarks and two $\overline{b}$ quarks, $X_{b\overline{b}b\overline{b}}$. The analysis is based on a data sample of $pp$ collisions recorded with the LHCb detector at centre-of-mass energies $\sqrt{s} =$ 7, 8 and 13 TeV, corresponding to an integrated luminosity of 6.3 fb$^{-1}$. No significant excess is found, and upper limits are set on the product of the production cross-section and the branching fraction as functions of the mass of the $X_{b\overline{b}b\overline{b}}$ state. The limits are set in the fiducial volume where all muons have pseudorapidity in the range $[2.0,5.0]$, and the $X_{b\overline{b}b\overline{b}}$ state has rapidity in the range $[2.0,4.5]$ and transverse momentum less than 15 GeV/$c$.

Angular moments of the decay $\Lambda_b^0 \rightarrow \Lambda \mu^{+} \mu^{-}$ at low hadronic recoil.

Abstract: An analysis of the angular distribution of the decay $\Lambda_b^0 \rightarrow \Lambda \mu^{+} \mu^{-}$ is presented, using data collected with the LHCb detector between 2011 and 2016 and corresponding to an integrated luminosity of approximately $5\,fb^{-1}$. Angular observables are determined using a moment analysis of the angular distribution at low hadronic recoil, corresponding to the dimuon invariant mass squared range $15 < q^{2} < 20\, GeV^2/c^4$. The full basis of observables is measured for the first time. The lepton-side, hadron-side and combined forward-backward asymmetries of the decay are determined to be \begin{align} A_{FB}^{l} & = -0.39 \pm 0.04\,\rm{stat} \pm 0.01\, \rm{syst}, onumber\\ A_{FB}^{h} & = -0.30 \pm 0.05\,\rm{stat} \pm 0.02\, \rm{syst}, onumber\\ A_{FB}^{lh} & = +0.25 \pm 0.04\,\rm{stat} \pm 0.01\, \rm{syst}. onumber \end{align} The measurements are consistent with Standard Model predictions.

arXiv : Measurement of $\Upsilon$ production in $pp$ collisions at $\sqrt{s}$= 13 TeV

Abstract: A bstractThe production cross-sections of ϒ(1S), ϒ(2S) and ϒ(3S) mesons in proton-proton collisions at s=13$$ \\sqrt{s}=13 $$ TeV are measured with a data sample corresponding to an integrated luminosity of 277 ± 11 pb−1 recorded by the LHCb experiment in 2015. The ϒ mesons are reconstructed in the decay mode ϒ → μ+μ−. The differential production cross-sections times the dimuon branching fractions are measured as a function of the ϒ transverse momentum, pT, and rapidity, y, over the range 0 < pT< 30 GeV/c and 2.0 < y < 4.5. The ratios of the cross-sections with respect to the LHCb measurement at s=8$$ \\sqrt{s}=8 $$ TeV are also determined. The measurements are compared with theoretical predictions based on NRQCD.

Evidence for an ηc(1S)π−resonance in B0→ηc(1S)K+π−decays

Abstract: A Dalitz plot analysis of ${{B} ^0} \!\rightarrow \eta _c(1S) {{K} ^+} {{\pi } ^-} $ decays is performed using data samples of pp collisions collected with the $\text{ LHCb } $ detector at centre-of-mass energies of ${\sqrt{s}} =7,~8$ and $13{\,\mathrm {Te}\mathrm {V}} $ , corresponding to a total integrated luminosity of $4.7 \,\text{ fb }^{-1} $ . A satisfactory description of the data is obtained when including a contribution representing an exotic $\eta _c(1S) \pi ^-$ resonant state. The significance of this exotic resonance is more than three standard deviations, while its mass and width are $4096 \pm 20~^{+18-22} \,\mathrm {Me}\mathrm {V} $ and $152 \pm 58~^{+60-35} \,\mathrm {Me}\mathrm {V} $ , respectively. The spin-parity assignments $J^P=0^+$ and $J^{P}=1^-$ are both consistent with the data. In addition, the first measurement of the ${{B} ^0} \!\rightarrow \eta _c(1S) {{K} ^+} {{\pi } ^-} $ branching fraction is performed and gives $\begin{aligned} \displaystyle \mathcal {B}({{B} ^0} \!\rightarrow \eta _c(1S) {{K} ^+} {{\pi } ^-} ) = (5.73 \pm 0.24 \pm 0.13 \pm 0.66) \times 10^{-4}, \end{aligned}$ where the first uncertainty is statistical, the second systematic, and the third is due to limited knowledge of external branching fractions.

Measurement of CP asymmetries in two-body B(s)0 -meson decays to charged pions and kaons

Abstract: The time-dependent CP asymmetries in B0→π+π− and B0s→K+K− decays are measured using a data sample of p p collisions corresponding to an integrated luminosity of 3.0 fb−1, collected with the LHCb detector at center-of-mass energies of 7 and 8 TeV. The same data sample is used to measure the time-integrated CP asymmetries in B0→K+π− and B0s→π+K− decays. The results are Cπ+π−=−0.34±0.06±0.01, Sπ+π−=−0.63±0.05±0.01, CK+K−=0.20±0.06±0.02, SK+K−=0.18±0.06±0.02, AΔΓK+K−=−0.79±0.07±0.10, AB0CP=−0.084±0.004±0.003, and AB0sCP=0.213±0.015±0.007, where the first uncertainties are statistical and the second systematic. Evidence for CP violation is found in the B0s→K+K− decay for the first time.

Measurement of $\Upsilon$ production in $pp$ collisions at $\sqrt{s}$= 13 TeV

Abstract: The production cross-sections of $\Upsilon(1S)$, $\Upsilon(2S)$ and $\Upsilon(3S)$ mesons in proton-proton collisions at $\sqrt{s}$= 13 TeV are measured with a data sample corresponding to an integrated luminosity of $277 \pm 11$ $\rm pb^{-1}$ recorded by the LHCb experiment in 2015. The $\Upsilon$ mesons are reconstructed in the decay mode $\Upsilon\to\mu^{+}\mu^{-}$. The differential production cross-sections times the dimuon branching fractions are measured as a function of the $\Upsilon$ transverse momentum, $p_{\rm T}$, and rapidity, $y$, over the range $0 < p_{\rm T}< 30$ GeV/c and $2.0 < y < 4.5$. The ratios of the cross-sections with respect to the LHCb measurement at $\sqrt{s}$= 8 TeV are also determined. The measurements are compared with theoretical predictions based on NRQCD.

Search for CP violation using triple product asymmetries in Lambda(0)(b) -> pK(-) pi(+) pi(-), Lambda(0)(b) -> pK(-) K+ K- and Xi(0)(b) -> pK(-) K- pi(+) decays

Abstract: A search for CP and P violation using triple-product asymmetries is performed with Λ$_{b}^{0}$ → pK$^{−}$π$^{+}$π$^{−}$, Λ$_{b}^{0}$ → pK$^{−}$K$^{+}$K$^{−}$ and Ξ$_{b}^{0}$ → pK$^{−}$K$^{−}$π$^{+}$ decays. The data sample corresponds to integrated luminosities of 1.0 fb$^{−1}$ and 2.0 fb$^{−1}$, recorded with the LHCb detector at centre-of-mass energies of 7 TeV and 8 TeV, respectively. The CP - and P - violating asymmetries are measured both integrating over all phase space and in specific phase-space regions. No significant deviation from CP or P symmetry is found. The first observation of Λ$_{b}^{0}$ → pK$^{−}$χ$_{c0}$(1P)(→π$^{+}$π$^{−}$, K$^{+}$K$^{−}$) decay is also reported.

Search for the lepton-flavour violating decays B ( s) 0 → e±μ∓

Abstract: A search for the lepton-flavour violating decays Bs0 → e±μ∓ and B0 → e±μ∓ is performed based on a sample of proton-proton collision data corresponding to an integrated luminosity of 3 fb−1, collected with the LHCb experiment at centre-of-mass energies of 7 and 8 TeV. The observed yields are consistent with the background-only hypothesis. Upper limits on the branching fraction of the Bs0 → e±μ∓ decays are evaluated both in the hypotheses of an amplitude completely dominated by the heavy eigenstate and by the light eigenstate. The results are @@ℬ(Bs0→e)<6.3(5.4)×10−9 and @@ℬ(Bs0→e)<7.2(6.0)×10−9 at 95% (90%) confidence level, respectively. The upper limit on the branching fraction of the B0 → e±μ∓ decay is also evaluated, obtaining @@ℬ(B0→e)<1.3(1.0)×10−9 at 95% (90%) confidence level. These are the strongest limits on these decays to date.[Figure not available: see fulltext.].

Search for the rare decay Λc+ →pμ+μ-

Abstract: A search for the flavor-changing neutral-current decay Λc+→pμ+μ- is reported using a data set corresponding to an integrated luminosity of 3.0 fb-1 collected by the LHCb Collaboration. No significant signal is observed outside of the dimuon mass regions around the φ and ω resonances, and an upper limit is placed on the branching fraction of B(Λc+→pμ+μ-)<7.7(9.6)×10-8 at 90%(95%) confidence level. A significant signal is observed in the ω dimuon mass region for the first time.

Evidence for the decay $ {B}_S^0\to {\overline{K}}^{\ast 0}{\mu}^{+}{\mu}^{-}

Abstract: A search for the decay $$ {B}_S^0\to {\overline{K}}^{\ast 0}{\mu}^{+}{\mu}^{-} $$ is presented using data sets corresponding to 1.0, 2.0 and 1.6 fb−1 of integrated luminosity collected during pp collisions with the LHCb experiment at centre-of-mass energies of 7, 8 and 13 TeV, respectively. An excess is found over the background-only hypothesis with a significance of 3.4 standard deviations. The branching fraction of the $$ {B}_S^0\to {\overline{K}}^{\ast 0}{\mu}^{+}{\mu}^{-} $$ decay is determined to be $$ \mathrm{\mathcal{B}}\left({B}_s^0\to {\overline{K}}^{\ast 0}{\mu}^{+}{\mu}^{-}\right)=\left[2.9\pm 1.0\left(\mathrm{stat}\right)\pm 0.2\left(\mathrm{syst}\right)\pm 0.3\left(\mathrm{norm}\right)\right]\times {10}^{-8} $$ , where the first and second uncertainties are statistical and systematic, respectively. The third uncertainty is due to limited knowledge of external parameters used to normalise the branching fraction measurement.

Study of ϒ production in pPb collisions at√ sNN = 8.16 TeV

Abstract: The production of ϒ(nS) mesons (n = 1, 2, 3) in pPb and Pbp collisions at a centre-of-mass energy per nucleon pair $$ \sqrt{s_{\mathrm{NN}}}=8.16 $$ TeV is measured by the LHCb experiment, using a data sample corresponding to an integrated luminosity of 31.8 nb−1. The ϒ(nS) mesons are reconstructed through their decays into two opposite-sign muons. The measurements comprise the differential production cross-sections of the ϒ(1S) and ϒ(2S) states, their forward-to-backward ratios and nuclear modification factors. The measurements are performed as a function of the transverse momentum pT and rapidity in the nucleon-nucleon centre-of-mass frame y* of the ϒ(nS) states, in the kinematic range pT < 25 GeV/c and 1.5 < y* < 4.0 (−5.0 < y* < −2.5) for pPb (Pbp) collisions. In addition, production cross-sections for ϒ(3S) are measured integrated over phase space and the production ratios between all three ϒ(nS) states are determined. Suppression for bottomonium in proton-lead collisions is observed, which is particularly visible in the ratios. The results are compared to theoretical models.

Erratum to: Differential branching fraction and angular analysis of Λ b 0 → Λμ + μ − decays

Abstract: The angular distribution of the dimuon system of the decays.

Central exclusive production of $J/\psi$ and $\psi(2S)$ mesons in $pp$ collisions at $\sqrt{s}=13~$TeV

Abstract: Measurements are reported of the central exclusive production of \jpsi and \psitwos mesons in $pp$ collisions at a centre-of-mass energy of 13 TeV. Backgrounds are significantly reduced compared to previous measurements made at lower energies through the use of new forward shower counters. The products of the cross-sections and the branching fractions for the decays to dimuons, where both muons are within the pseudorapidity range $2.0<\eta<4.5$, are measured to be $$ \begin{array}{rcl} \sigma_{J/\psi\rightarrow\mu^+\mu^-}&=&435 \pm 18 \pm 17 \pm 16 {\rm \ pb},\\ \sigma_{\psi(2S)\rightarrow\mu^+\mu^-}&=&11.1 \pm 1.1 \pm 0.3 \pm 0.4 {\rm \ pb}.\\ \end{array} $$ The first uncertainties are statistical, the second are systematic, and the third are due to the luminosity determination. The cross-sections are also measured differentially for meson rapidities between 2.0 and 4.5. Good agreement is observed with theoretical predictions. Photoproduction cross-sections are derived and compared to previous experiments, and a deviation from a pure power-law extrapolation of lower energy data is observed.

Updated determination of D-0-(D)over-bar(0) mixing and CP violation parameters with D-0 -> K+ pi(-) decays

Abstract: We report measurements of charm-mixing parameters based on the decay-time-dependent ratio of D0→K+π- to D0→K-π+ rates. The analysis uses a data sample of proton-proton collisions corresponding to an integrated luminosity of 5.0 fb-1 recorded by the LHCb experiment from 2011 through 2016. Assuming charge-parity (CP) symmetry, the mixing parameters are determined to be x′2=(3.9±2.7)×10-5, y′=(5.28±0.52)×10-3, and RD=(3.454±0.031)×10-3. Without this assumption, the measurement is performed separately for D0 and D¯0 mesons, yielding a direct CP-violating asymmetry AD=(-0.1±9.1)×10-3, and magnitude of the ratio of mixing parameters 1.00<|q/p|<1.35 at the 68.3% confidence level. All results include statistical and systematic uncertainties and improve significantly upon previous single-measurement determinations. No evidence for CP violation in charm mixing is observed.

Measurement of the Omega(0)(c) Baryon Lifetime

Abstract: We report a measurement of the lifetime of the Ω_{c}^{0} baryon using proton-proton collision data at center-of-mass energies of 7 and 8 TeV, corresponding to an integrated luminosity of 3.0 fb^{-1} collected by the LHCb experiment. The sample consists of about 1000 Ω_{b}^{-}→Ω_{c}^{0}μ^{-}ν[over ¯]_{μ}X signal decays, where the Ω_{c}^{0} baryon is detected in the pK^{-}K^{-}π^{+} final state and X represents possible additional undetected particles in the decay. The Ω_{c}^{0} lifetime is measured to be τ_{Ω_{c}^{0}}=268±24±10±2 fs, where the uncertainties are statistical, systematic, and from the uncertainty in the D^{+} lifetime, respectively. This value is nearly four times larger than, and inconsistent with, the current world-average value.

Studies of the resonance structure in $D^{0} \to K^\mp \pi^\pm \pi^\pm \pi^\mp$ decays

Abstract: Amplitude models are constructed to describe the resonance structure of ${D^{0}\to K^{-}\pi^{+}\pi^{+}\pi^{-}}$ and ${D^{0} \to K^{+}\pi^{-}\pi^{-}\pi^{+}}$ 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 $3.0\mathrm{fb}^{-1}$. The largest contributions to both decay amplitudes are found to come from axial resonances, with decay modes $D^{0} \to a_1(1260)^{+} K^{-}$ and $D^{0} \to K_1(1270/1400)^{+} \pi^{-}$ being prominent in ${D^{0}\to K^{-}\pi^{+}\pi^{+}\pi^{-}}$ and $D^{0}\to K^{+}\pi^{-}\pi^{-}\pi^{+}$, respectively. Precise measurements of the lineshape parameters and couplings of the $a_1(1260)^{+}$, $K_1(1270)^{-}$ 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 $R_{K3\pi} = 0.459\pm 0.010\,(\mathrm{stat}) \pm 0.012\,(\mathrm{syst}) \pm 0.020\,(\mathrm{model})$, which is consistent with direct measurements. These models will be useful in future measurements of the unitary-triangle angle $\gamma$ and studies of charm mixing and $C\!P$ violation.

Prompt $\Lambda^+_c$ production in $p\mathrm{Pb}$ collisions at $\sqrt{s_{NN}} = 5.02$ TeV.

Abstract: The production of $\Lambda^+_c$ baryons produced directly at the interacting point is studied in proton-lead collisions collected with the LHCb detector at the LHC. The data sample corresponds to an integrated luminosity of $1.58\mathrm{nb}^{-1}$ recorded at a nucleon-nucleon centre-of-mass energy of $\sqrt{s_{NN}}=5.02$ TeV. Measurements of the differential cross-section and the forward-backward production ratio are reported for $\Lambda^+_c$ baryons with transverse momenta in the range $2

Central exclusive production of J/ψ and ψ(2S) mesons in pp collisions at s√=13 TeV

Abstract: Measurements are reported of the central exclusive production of J/ψ and ψ(2S) mesons in pp collisions at a centre-of-mass energy of 13 TeV. Backgrounds are significantly reduced compared to previous measurements made at lower energies through the use of new forward shower counters. The products of the cross-sections and the branching fractions for the decays to dimuons, where both muons are within the pseudorapidity range 2.0 < η < 4.5, are measured to be σJ/ψ→μ+μ−=435±18±11±17pbσψ(2S)→μ+μ−=11.1±1.1±0.3±0.4pb. The first uncertainties are statistical, the second are systematic, and the third are due to the luminosity determination. The cross-sections are also measured differentially for meson rapidities between 2.0 and 4.5. Good agreement is observed with theoretical predictions. Photoproduction cross-sections are derived and compared to previous experiments, and a deviation from a pure power-law extrapolation of lower energy data is observed.[Figure not available: see fulltext.]

Evidence for the Rare Decay Σ⁺→pμ⁺μ⁻

Abstract: A search for the rare decay Σ+→pμ+μ− is performed using pp collision data recorded by the LHCb experiment at center-of-mass energies √s=7 and 8 TeV, corresponding to an integrated luminosity of 3 fb−1. An excess of events is observed with respect to the background expectation, with a signal significance of 4.1 standard deviations. No significant structure is observed in the dimuon invariant mass distribution, in contrast with a previous result from the HyperCP experiment. The measured Σ+→pμ+μ− branching fraction is (2.2+1.8−1.3)×10−8, where statistical and systematic uncertainties are included, which is consistent with the standard model prediction.