arXiv subjects

E. Buchanan

Publications and source records attributed to E. Buchanan.

At least 91 records · Page 5Linked to original sources

arXiv2017

Measurement of the $C\!P$ violation parameter $A_Γ$ in $D^0 \to K^+K^-$ and $D^0 \to π^+π^-$ decays

Asymmetries in the time-dependent rates of $D^0 \to K^+K^-$ and $D^0 \to π^+π^-$ decays are measured in a $pp$ collision data sample collected with the LHCb detector during LHC Run 1, corresponding to an integrated luminosity of $3\,\mathrm{fb}^{-1}$. The asymmetries in effective decay widths between $D^0$ and $\overline{D}^0$ decays, sensitive to indirect $CP$ violation, are measured to be $A_Γ(K^+ K^-) = (-0.30 \pm 0.32 \pm 0.10)\times 10^{-3}$ and $A_Γ(π^+π^-) = (0.46 \pm 0.58 \pm 0.12)\times 10^{-3}$, where the first uncertainty is statistical and the second systematic. These measurements show no evidence for $C\!P$ violation and improve on the precision of the previous best measurements by nearly a factor of two.

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arXiv2017

Evidence for the two-body charmless baryonic decay $B^+ \to p \barΛ$

A search for the rare two-body charmless baryonic decay $B^+ \to p \barΛ$ is performed with $pp$ collision data, corresponding to an integrated luminosity of $3\,\mbox{fb}^{-1}$, collected by the LHCb experiment at centre-of-mass energies of 7 and 8 TeV. An excess of $B^+ \to p \barΛ$ candidates with respect to background expectations is seen with a statistical significance of 4.1 standard deviations, and constitutes the first evidence for this decay. The branching fraction, measured using the $B^+ \to K^0_{\mathrm S} π^+$ decay for normalisation, is \begin{eqnarray} \mathcal{B}(B^+ \to p \barΛ) & = & ( 2.4 \,^{+1.0}_{-0.8} \pm 0.3 ) \times 10^{-7} \,, \nonumber \end{eqnarray} where the first uncertainty is statistical and the second systematic.

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arXiv2017

Search for the $B^{0}_{s} \to η^{\prime}ϕ$ decay

A search for the charmless $B^{0}_{s} \to η^{\prime}ϕ$ decay is performed using $pp$ collision data collected by the LHCb experiment at centre-of-mass energies of $7$ and $8$ TeV, corresponding to an integrated luminosity of 3 fb$^{-1}$. No signal is observed and upper limits on the $B^{0}_{s} \to η^{\prime}ϕ$ branching fraction are set to $0.82\times 10^{-6}$ at $90\%$ and $1.01\times 10^{-6}$ at $95\%$ confidence level.

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arXiv2017

Search for $CP$ violation in the phase space of $D^0\rightarrowπ^+π^-π^+π^-$ decays

A search for time-integrated $CP$ violation in the Cabibbo-suppressed decay $\mbox{$D^0\rightarrowπ^+π^-π^+π^-$}$ is performed using an unbinned, model-independent technique known as the energy test. This is the first application of the energy test in four-body decays. The search is performed for $P$-even $CP$ asymmetries and, for the first time, is extended to probe the $P$-odd case. Using proton-proton collision data corresponding to an integrated luminosity of 3.0 fb$^{-1}$ collected by the LHCb detector at centre-of-mass energies of $\sqrt{s}=$7 TeV and 8 TeV, the world's best sensitivity to $CP$ violation in this decay is obtained. The data are found to be consistent with the hypothesis of $CP$ symmetry with a $p$-value of $(4.6\pm0.5)\%$ in the $P$-even case, and marginally consistent with a $p$-value of $(0.6\pm0.2)\%$ in the $P$-odd case, corresponding to a significance for $CP$ non-conservation of 2.7 standard deviations.

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arXiv2017

Measurement of $CP$ asymmetry in $D^0\rightarrow K^-K^+$ decays

A measurement of the time-integrated $CP$ asymmetry in the Cabibbo-suppressed decay $D^0\rightarrow K^-K^+$ is performed using pp collision data, corresponding to an integrated luminosity of 3fb$^{-1}$, collected with the LHCb detector at centre-of-mass energies of 7 and 8 TeV. The flavour of the charm meson at production is determined from the charge of the pion in $D^{*+}\rightarrow D^0 π^+$ and $D^{*-}\rightarrow \bar{D^0} π^-$ decays. The time-integrated $CP$ asymmetry $A_{CP}(K^-K^+)$ is obtained assuming negligible $CP$ violation in charm mixing and in Cabibbo-favoured $D^0\rightarrow K^-π^+$, $D^+\rightarrow K^-π^+π^+$ and $D^+\rightarrow \bar{K^0}π^+$ decays used as calibration channels. It is found to be $A_{CP}(K^-K^+)=(0.14\pm0.15(stat)\pm0.10(syst))\%$. A combination of this result with previous LHCb measurements yields $A_{CP}(K^-K^+)=(0.04\pm0.12(stat)\pm0.10(syst))\%$, $A_{CP}(π^-π^+)=(0.07\pm0.14(stat)\pm0.11(syst))\%$. These are the most precise measurements from a single experiment. The result for $A_{CP}(K^-K^+)$ is the most precise determination of a time-integrated $CP$ asymmetry in the charm sector to date, and neither measurement shows evidence of CP asymmetry.

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arXiv2017

Search for the decays $B_s^0\toτ^+τ^-$ and $B^0\toτ^+τ^-$

A search for the rare decays $B_s^0\toτ^+τ^-$ and $B^0\toτ^+τ^-$ is performed using proton--proton collision data collected with the LHCb detector. The data sample corresponds to an integrated luminosity of 3fb$^{-1}$ collected in 2011 and 2012. The $τ$ leptons are reconstructed through the decay $τ^-\toπ^-π^+π^-ν_τ$. Assuming no contribution from $B^0\toτ^+τ^-$ decays, an upper limit is set on the branching fraction $\mathcal{B}(B_s^0\toτ^+τ^-) < 6.8\times 10^{-3}$ at 95% confidence level. If instead no contribution from $B_s^0\toτ^+τ^-$ decays is assumed, the limit is $\mathcal{B}(B^0\toτ^+τ^-)< 2.1 \times 10^{-3}$ at 95% confidence level. These results correspond to the first direct limit on $\mathcal{B}(B_s^0\toτ^+τ^-)$ and the world's best limit on $\mathcal{B}(B^0\toτ^+τ^-)$.

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arXiv2017

Observation of the $\varXi^{-}_{b}\to J/ψ\varLambda K^{-}$ decay

The observation of the decay $\varXi^{-}_{b}\to J/ψ\varLambda K^{-}$ is reported, using a data sample corresponding to an integrated luminosity of $3~\mathrm{fb}^{-1}$, collected by the LHCb detector in $pp$ collisions at centre-of-mass energies of $7$ and $8~\mathrm{TeV}$. The production rate of $\varXi_{b}^{-}$ baryons detected in the decay $\varXi_{b}^{-}\to J/ψ\varLambda K^{-}$ is measured relative to that of $\varLambda_{b}^{0}$ baryons using the decay $\varLambda_{b}^{0}\to J/ψ\varLambda$. Integrated over the $b$-baryon transverse momentum $p_{\rm T}<25~\mathrm{GeV/}c $ and rapidity $2.0<y<4.5$, the measured ratio is \begin{equation*} \frac{f_{\varXi_{b}^{-}}}{f_{\varLambda_{b}^{0}}}\frac{\mathcal{B}(\varXi_{b}^{-}\to J/ψ\varLambda K^{-})}{\mathcal{B}(\varLambda_{b}^{0}\to J/ψ\varLambda)}=(4.19\pm 0.29~(\mathrm{stat})\pm0.15~(\mathrm{syst}))\times 10^{-2}, \end{equation*}where $f_{\varXi_{b}^{-}}$ and $f_{\varLambda_{b}^{0}}$ are the fragmentation fractions of $b\to\varXi_{b}^{-}$ and $b\to\varLambda_{b}^{0}$ transitions, and $\mathcal{B}$ represents the branching fraction of the corresponding $b$-baryon decay. The mass difference between $\varXi_{b}^{-}$ and $\varLambda_{b}^{0}$ baryons is measured to be \begin{equation*} M(\varXi_{b}^{-})-M(\varLambda_{b}^{0})=177.08\pm0.47~(\mathrm{stat})\pm0.16~(\mathrm{syst} )~\mathrm{MeV/}c^{2}. \end{equation*}

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arXiv2017

Measurement of the $B^0_s\toμ^+μ^-$ branching fraction and effective lifetime and search for $B^0\toμ^+μ^-$ decays

A search for the rare decays $B^0_s\toμ^+μ^-$ and $B^0\toμ^+μ^-$ is performed at the LHCb experiment using data collected in $pp$ collisions corresponding to a total integrated luminosity of 4.4 fb$^{-1}$. An excess of $B^0_s\toμ^+μ^-$ decays is observed with a significance of 7.8 standard deviations, representing the first observation of this decay in a single experiment. The branching fraction is measured to be ${\cal B}(B^0_s\toμ^+μ^-)=\left(3.0\pm 0.6^{+0.3}_{-0.2}\right)\times 10^{-9}$, where the first uncertainty is statistical and the second systematic. The first measurement of the $B^0_s\toμ^+μ^-$ effective lifetime, $τ(B^0_s\toμ^+μ^-)=2.04\pm 0.44\pm 0.05$ ps, is reported. No significant excess of $B^0\toμ^+μ^-$ decays is found and a 95 % confidence level upper limit, ${\cal B}(B^0\toμ^+μ^-)<3.4\times 10^{-10}$, is determined. All results are in agreement with the Standard Model expectations.

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arXiv2017

Measurement of $CP$ asymmetries in $D^{\pm}\rightarrow η^{\prime} π^{\pm}$ and $D_s^{\pm}\rightarrow η^{\prime} π^{\pm}$ decays

A search for $CP$ violation in $D^{\pm}\rightarrow η^{\prime} π^{\pm}$ and $D^{\pm}_{s}\rightarrow η^{\prime} π^{\pm}$ decays is performed using proton-proton collision data, corresponding to an integrated luminosity of $3$ fb$^{-1}$, recorded by the LHCb experiment at centre-of-mass energies of $7$ and $8$ TeV. The measured $CP$-violating charge asymmetries are $A_{CP}(D^{\pm} \rightarrow η^{\prime} π^{\pm})=(-0.61\pm 0.72 \pm 0.53 \pm 0.12)\%$ and $A_{CP}(D^{\pm}_{s}\rightarrow η^{\prime} π^{\pm})=(-0.82\pm 0.36 \pm 0.22 \pm 0.27)\%$, where the first uncertainties are statistical, the second systematic, and the third are the uncertainties on the $A_{CP}(D^{\pm} \rightarrow K^0_S π^{\pm})$ and $A_{CP}(D^{\pm}_{s}\rightarrow ϕπ^{\pm})$ measurements used for calibration. The results represent the most precise measurements of these asymmetries to date.

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arXiv2017

Measurements of prompt charm production cross-sections in $pp$ collisions at $\sqrt{s} = 13\,\mathrm{TeV}$

Production cross-sections of prompt charm mesons are measured with the first data from $pp$ collisions at the LHC at a centre-of-mass energy of $13\,\mathrm{TeV}$. The data sample corresponds to an integrated luminosity of $4.98 \pm 0.19\,\mathrm{pb}^{-1}$ collected by the LHCb experiment. The production cross-sections of $D^{0}$, $D^{+}$, $D_{s}^{+}$, and $D^{*+}$ mesons are measured in bins of charm meson transverse momentum, $p_{\mathrm{T}}$, and rapidity, $y$, and cover the range $0 < p_{\mathrm{T}} < 15\,\mathrm{GeV}/c$ and $2.0 < y < 4.5$. The inclusive cross-sections for the four mesons, including charge conjugation, within the range of $1 < p_{\mathrm{T}} < 8\,\mathrm{GeV}/c$ are found to be \begin{equation} σ(pp \to D^{0} X) = 2072 \pm 2 \pm 124\,μ\mathrm{b}\\ σ(pp \to D^{+} X) = 834 \pm 2 \pm \phantom{1}78\,μ\mathrm{b}\\ σ(pp \to D_{s}^{+} X) = 353 \pm 9 \pm \phantom{1}76\,μ\mathrm{b}\\ σ(pp \to D^{*+} X) = 784 \pm 4 \pm \phantom{1}87\,μ\mathrm{b} \end{equation} where the uncertainties are due to statistical and systematic uncertainties, respectively.

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arXiv2017

Measurement of the ratio of branching fractions $\mathcal{B}(B_{c}^{+} \to J/ψK^{+})/\mathcal{B}(B_{c}^{+} \to J/ψπ^{+})$

The ratio of branching fractions $R_{K/π} \equiv \mathcal{B}(B_{c}^{+} \to J/ψK^{+})/\mathcal{B}(B_{c}^{+} \to J/ψπ^{+})$ is measured with $pp$ collision data collected by the LHCb experiment at centre-of-mass energies of 7 TeV and 8 TeV, corresponding to an integrated luminosity of 3${\mbox{fb}^{-1}}$. It is found to be $ R_{K/π} = 0.079\pm0.007\pm0.003$, where the first uncertainty is statistical and the second is systematic. This measurement is consistent with the previous LHCb result, while the uncertainties are significantly reduced.

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arXiv2017

Study of the $D^0 p$ amplitude in $Λ_b^0\to D^0 p π^-$ decays

An amplitude analysis of the decay $Λ_b^0\to D^0 p π^-$ is performed in the part of the phase space containing resonances in the $D^0 p$ channel. The study is based on a data sample corresponding to an integrated luminosity of 3.0 fb$^{-1}$ of $pp$ collisions recorded by the LHCb experiment. The spectrum of excited $Λ_c^+$ states that decay into $D^0 p$ is studied. The masses, widths and quantum numbers of the $Λ_c(2880)^+$ and $Λ_c(2940)^+$ resonances are measured. The constraints on the spin and parity for the $Λ_c(2940)^+$ state are obtained for the first time. A near-threshold enhancement in the $D^0 p$ amplitude is investigated and found to be consistent with a new resonance, denoted the $Λ_c(2860)^+$, of spin $3/2$ and positive parity.

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arXiv2017

Measurements of prompt charm production cross-sections in $pp$ collisions at $\sqrt{s} = 5\,$TeV

Production cross-sections of prompt charm mesons are measured using data from $pp$ collisions at the LHC at a centre-of-mass energy of $5\,$TeV. The data sample corresponds to an integrated luminosity of $8.60\pm0.33\,$pb$^{-1}$ collected by the LHCb experiment. The production cross-sections of $D^0$, $D^+$, $D_s^+$, and $D^{*+}$ mesons are measured in bins of charm meson transverse momentum, $p_{\text{T}}$, and rapidity, $y$. They cover the rapidity range $2.0<y<4.5$ and transverse momentum ranges $0 < p_{\text{T}} < 10\, \text{GeV}/c$ for $D^0$ and $D^+$ and $1 < p_{\text{T}} < 10\, \text{GeV}/c$ for $D_s^+$ and $D^{*+}$ mesons. The inclusive cross-sections for the four mesons, including charge-conjugate states, within the range of $1 < p_{\text{T}} < 8\, \text{GeV}/c$ are determined to be σ(pp\rightarrow D^0 X) = 1004 \pm 3 \pm 54\,μ\text{b} σ(pp\rightarrow D^+ X) = 402 \pm 2 \pm 30\,μ\text{b} σ(pp\rightarrow D_s^+ X) = 170 \pm 4 \pm 16\,μ\text{b} σ(pp\rightarrow D^{*+} X)= 421 \pm 5 \pm 36\,μ\text{b} where the uncertainties are statistical and systematic, respectively.

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arXiv2017

Measurement of forward $J/ψ$ production cross-sections in $pp$ collisions at $\sqrt{s}=13$ TeV

The production of $J/ψ$ mesons in proton-proton collisions at a centre-of-mass energy of $\sqrt{s}=13$ TeV is studied with the \lhcb detector. Cross-section measurements are performed as a function of the transverse momentum $p_\mathrm{T}$ and the rapidity $y$ of the $J/ψ$ meson in the region $p_\mathrm{T}<14\mathrm{GeV}/c$ and $2.0<y<4.5$, for both prompt $J/ψ$ mesons and $J/ψ$ mesons from $b$-hadron decays. The production cross-sections integrated over the kinematic coverage are $15.03\pm 0.03\pm 0.94$ $μ$b for prompt $J/ψ$ and $2.25\pm 0.01\pm 0.14$ $μ$b for $J/ψ$ from $b$-hadron decays, assuming zero polarization of the $J/ψ$ meson. The first uncertainties are statistical and the second systematic. The cross-section reported for $J/ψ$ mesons from $b$-hadron decays is used to extrapolate to a total $b\bar{b}$ cross-section. The ratios of the cross-sections with respect to $\sqrt{s}=8$ TeV are also determined.

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arXiv2017

Observation of five new narrow $Ω_c^0$ states decaying to $Ξ_c^+ K^-$

The $Ξ_c^+ K^-$ mass spectrum is studied with a sample of $pp$ collision data corresponding to an integrated luminosity of 3.3 fb$^{-1}$, collected by the LHCb experiment. The $Ξ_c^+$ is reconstructed in the decay mode $p K^- π^+$. Five new, narrow excited $Ω_c^0$ states are observed: the $Ω_c(3000)^0$, $Ω_c(3050)^0$, $Ω_c(3066)^0$, $Ω_c(3090)^0$, and $Ω_c(3119)^0$. Measurements of their masses and widths are reported.

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arXiv2017

New algorithms for identifying the flavour of $B^0$ mesons using pions and protons

Two new algorithms for use in the analysis of $pp$ collision are developed to identify the flavour of $B^0$ mesons at production using pions and protons from the hadronization process. The algorithms are optimized and calibrated on data, using $B^0 \rightarrow D^- π^+$ decays from $pp$ collision data collected by LHCb at centre-of-mass energies of 7 and 8 TeV. The tagging power of the new pion algorithm is 60 % greater than the previously available one; the algorithm using protons to identify the flavour of a $B^0$ meson is the first of its kind.

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arXiv2017

Measurements of the S-wave fraction in $B^{0}\rightarrow K^{+}π^{-}μ^{+}μ^{-}$ decays and the $B^{0}\rightarrow K^{\ast}(892)^{0}μ^{+}μ^{-}$ differential branching fraction

A measurement of the differential branching fraction of the decay ${B^{0}\rightarrow K^{\ast}(892)^{0}μ^{+}μ^{-}}$ is presented together with a determination of the S-wave fraction of the $K^+π^-$ system in the decay $B^{0}\rightarrow K^{+}π^{-}μ^{+}μ^{-}$. The analysis is based on $pp$-collision data corresponding to an integrated luminosity of 3\,fb$^{-1}$ collected with the LHCb experiment. The measurements are made in bins of the invariant mass squared of the dimuon system, $q^2$. Precise theoretical predictions for the differential branching fraction of $B^{0}\rightarrow K^{\ast}(892)^{0}μ^{+}μ^{-}$ decays are available for the $q^2$ region $1.1<q^2<6.0\,{\rm GeV}^2/c^4$. In this $q^2$ region, for the $K^+π^-$ invariant mass range $796 < m_{Kπ} < 996\,{\rm MeV}/c^2$, the S-wave fraction of the $K^+π^-$ system in $B^{0}\rightarrow K^{+}π^{-}μ^{+}μ^{-}$ decays is found to be \begin{equation*} F_{\rm S} = 0.101\pm0.017({\rm stat})\pm0.009 ({\rm syst}), \end{equation*} and the differential branching fraction of $B^{0}\rightarrow K^{\ast}(892)^{0}μ^{+}μ^{-}$ decays is determined to be \begin{equation*} {\rm d}\mathcal{B}/{\rm d} q^2 = (0.342_{\,-0.017}^{\,+0.017}({\rm stat})\pm{0.009}({\rm syst})\pm0.023({\rm norm}))\times 10^{-7}c^{4}/{\rm GeV}^{2}. \end{equation*} The differential branching fraction measurements presented are the most precise to date and are found to be in agreement with Standard Model predictions.

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arXiv2017

Measurement of the phase difference between short- and long-distance amplitudes in the $B^{+}\to K^{+}μ^{+}μ^{-}$ decay

A measurement of the phase difference between the short- and long-distance contributions to the $B^{+}\to K^{+}μ^{+}μ^{-}$ decay is performed by analysing the dimuon mass distribution. The analysis is based on $pp$ collision data corresponding to an integrated luminosity of 3 $\rm fb^{-1}$ collected by the LHCb experiment in 2011 and 2012. The long-distance contribution to the $B^{+}\to K^{+}μ^{+}μ^{-}$ decay is modelled as a sum of relativistic Breit--Wigner amplitudes representing different vector meson resonances decaying to muon pairs, each with their own magnitude and phase. The measured phases of the $J/ψ$ and $ψ(2S)$ resonances are such that the interference with the short-distance component in dimuon mass regions far from their pole masses is small. In addition, constraints are placed on the Wilson coefficients, $\mathcal{C}_{9}$ and $\mathcal{C}_{10}$, and the branching fraction of the short-distance component is measured.

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