arXiv subjects

J. Buytaert

Publications and source records attributed to J. Buytaert.

At least 91 records · Page 5Linked to original sources

arXiv2016

Production of associated $Υ$ and open charm hadrons in $pp$ collisions at $\sqrt{s}=7$ and $8$TeV via double parton scattering

Associated production of bottomonia and open charm hadrons in $pp$ collisions at $\sqrt{s}=7$ and $8$TeV is observed using data corresponding to an integrated luminosity of 3$fb^{-1}$ accumulated with the LHCb detector. The observation of five combinations, $Υ(1S)D^0$, $Υ(2S)D^0$, $Υ(1S)D^+$, $Υ(2S)D^+$ and $Υ(1S)D^+_{s}$, is reported. Production cross-sections are measured for $Υ(1S)D^0$ and $Υ(1S)D^+$ pairs in the forward region. The measured cross-sections and the differential distributions indicate the dominance of double parton scattering as the main production mechanism. This allows a precise measurement of the effective cross-section for double parton scattering.

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arXiv2016

A new algorithm for identifying the flavour of $B_s^0$ mesons at LHCb

A new algorithm for the determination of the initial flavour of $B_s^0$ mesons is presented. The algorithm is based on two neural networks and exploits the $b$ hadron production mechanism at a hadron collider. The first network is trained to select charged kaons produced in association with the $B_s^0$ meson. The second network combines the kaon charges to assign the $B_s^0$ flavour and estimates the probability of a wrong assignment. The algorithm is calibrated using data corresponding to an integrated luminosity of 3 fb$^{-1}$ collected by the LHCb experiment in proton-proton collisions at 7 and 8 TeV centre-of-mass energies. The calibration is performed in two ways: by resolving the $B_s^0$-$\bar{B}_s^0$ flavour oscillations in $B_s^0 \to D_s^- π^+$ decays, and by analysing flavour-specific $B_{s 2}^{*}(5840)^0 \to B^+ K^-$ decays. The tagging power measured in $B_s^0 \to D_s^- π^+$ decays is found to be $(1.80 \pm 0.19({\rm stat}) \pm 0.18({\rm syst}))$\%, which is an improvement of about 50\% compared to a similar algorithm previously used in the LHCb experiment.

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arXiv2016

Model-independent measurement of the CKM angle $γ$ using $B^0 \to D K^{\ast 0}$ decays with $D \to K_{S}^{0} π^{+} π^{-}$ and $K_{S}^{0} K^{+} K^{-}$

A binned Dalitz plot analysis of the decays $B^0 \to D K^{\ast 0}$, with $D \to K_{S}^{0} π^{+} π^{-}$ and $K_{S}^{0} K^{+} K^{-}$, is performed to measure the observables $x_\pm$ and $y_\pm$, which are related to the CKM angle $γ$ and the hadronic parameters of the decays. The $D$ decay strong phase variation over the Dalitz plot is taken from measurements performed at the CLEO-c experiment, making the analysis independent of the $D$ decay model. With a sample of proton-proton collision data, corresponding to an integrated luminosity of $3.0\,\rm{fb}^{-1}$, collected by the LHCb experiment, the values of the $CP$ violation parameters are found to be $x_+ = 0.05 \pm 0.35 \pm 0.02$, $x_-=-0.31\pm 0.20 \pm 0.04$, $y_+=-0.81\pm 0.28\pm 0.06$ and $y_-=0.31\pm 0.21 \pm 0.05$, where the first uncertainties are statistical and the second systematic. These observables correspond to values $γ$ = $(71 \pm 20)^\circ$, $r_{B^0} = 0.56\pm 0.17$ and $δ_{B^0} = (204\,^{+21}_{-20})^\circ$. The parameters $r_{B^0}$ and $δ_{B^0}$ are the magnitude ratio and strong phase difference between the suppressed and favoured $B^0$ decay amplitudes, and have been measured in a region of $\pm 50$ MeV/$c^2$ around the $K^{\ast}(892)^{0}$ mass and with the magnitude of the cosine of the $K^{\ast}(892)^{0}$ helicity angle larger than 0.4.

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arXiv2016

Measurement of the $B_{s}^{0} \rightarrow D_{s}^{()+}D_{s}^{()-}$ branching fractions

The branching fraction of the decay $B_{s}^{0} \rightarrow D_{s}^{(*)+}D_{s}^{(*)-}$ is measured using $pp$ collision data corresponding to an integrated luminosity of $1.0fb^{-1}$, collected using the LHCb detector at a centre-of-mass energy of $7$TeV. It is found to be \begin{align*} {\mathcal{B}}(B_{s}^{0}\rightarrow~D_{s}^{(*)+}D_{s}^{(*)-}) = (3.05 \pm 0.10 \pm 0.20 \pm 0.34)\%, \end{align*} where the uncertainties are statistical, systematic, and due to the normalisation channel, respectively. The branching fractions of the individual decays corresponding to the presence of one or two $D^{*\pm}_{s}$ are also measured. The individual branching fractions are found to be \begin{align*} {\mathcal{B}}(B_{s}^{0}\rightarrow~D_{s}^{*\pm}D_{s}^{\mp}) = (1.35 \pm 0.06 \pm 0.09 \pm 0.15)\%, \newline{\mathcal{B}}(B_{s}^{0}\rightarrow~D_{s}^{*+}D_{s}^{*-}) = (1.27 \pm 0.08 \pm 0.10 \pm 0.14)\%. \end{align*} All three results are the most precise determinations to date.

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arXiv2016

First observation and amplitude analysis of the $B^{-}\to D^{+}K^{-}π^{-}$ decay

The $B^{-}\to D^{+}K^{-}π^{-}$ decay is observed in a data sample corresponding to $3.0~\rm{fb}^{-1}$ of $pp$ collision data recorded by the LHCb experiment during 2011 and 2012. Its branching fraction is measured to be ${\cal B}(B^{-}\to D^{+}K^{-}π^{-}) = (7.31 \pm 0.19 \pm 0.22 \pm 0.39) \times 10^{-5}$ where the uncertainties are statistical, systematic and from the branching fraction of the normalisation channel $B^{-}\to D^{+}π^{-}π^{-}$, respectively. An amplitude analysis of the resonant structure of the $B^{-}\to D^{+}K^{-}π^{-}$ decay is used to measure the contributions from quasi-two-body $B^{-}\to D_{0}^{*}(2400)^{0}K^{-}$, $B^{-}\to D_{2}^{*}(2460)^{0}K^{-}$, and $B^{-}\to D_{J}^{*}(2760)^{0}K^{-}$ decays, as well as from nonresonant sources. The $D_{J}^{*}(2760)^{0}$ resonance is determined to have spin~1.

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arXiv2016

First observation of the rare $B^{+}\to D^{+} K^{+} π^{-}$ decay

The $B^{+}\to D^{+} K^{+} π^{-}$ decay is observed in a data sample corresponding to $3.0\,{\rm fb}^{-1}$ of $pp$ collision data recorded by the LHCb experiment during 2011 and 2012. The signal significance is $8\,σ$ and the branching fraction is measured to be ${\cal B}\left(B^{+}\to D^{+} K^{+} π^{-}\right) = (5.31 \pm 0.90 \pm 0.48 \pm 0.35)\times 10^{-6}$, where the uncertainties are statistical, systematic and due to the normalisation mode $B^{+}\to D^{-} K^{+} π^{+}$, respectively. The Dalitz plot appears to be dominated by broad structures. Angular distributions are exploited to search for quasi-two-body contributions from $B^{+}\to D^{*}_{2}(2460)^{0}K^{+}$ and $B^{+}\to D^{+} K^{*}(892)^{0}$ decays. No significant signals are observed and upper limits are set on their branching fractions.

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arXiv2016

First observation of $D^0-\bar D^0$ oscillations in $D^0\to K^+π^-π^+π^-$ decays and measurement of the associated coherence parameters

Charm meson oscillations are observed in a time-dependent analysis of the ratio of $D^0\to K^+π^-π^+π^-$ to $D^0\to K^-π^+π^-π^+$ decay rates, using data corresponding to an integrated luminosity of $3.0\,{\rm fb}^{-1}$ recorded by the LHCb experiment. The measurements presented are sensitive to the phase-space averaged ratio of doubly Cabibbo-suppressed to Cabibbo-favoured amplitudes $r_{D}^{K3π}$ and the product of the coherence factor $R_{D}^{K3π}$ and a charm mixing parameter $y^{'}_{K3π}$. The constraints measured are $r_{D}^{K3π}=(5.67 \pm 0.12)\times10^{-2}$, which is the most precise determination to date, and $R_{D}^{K3π} \cdot y^{'}_{K3π} = (0.3 \pm 1.8)\times 10^{-3}$, which provides useful input for determinations of the CP-violating phase $γ$ in $B^\pm \to D K^\pm, D \to K^\mpπ^\pmπ^\mpπ^\pm$ decays. The analysis also gives the most precise measurement of the $D^0\to K^+π^-π^+π^-$ branching fraction, and the first observation of $D^0-\bar D^0$ oscillations in this decay mode, with a significance of 8.2 standard deviations.

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arXiv2016

Search for violations of Lorentz invariance and $ CPT$ symmetry in $ B^0_{(s)}$ mixing

Violations of $ CPT$ symmetry and Lorentz invariance are searched for by studying interference effects in $ B^0$ mixing and in $ B^0_s$ mixing. Samples of $ B^0\to J/ψK^0_{\mathrm{S}}$ and $ B^0_s\to J/ψK^+ K^-$ decays are recorded by the LHCb detector in proton--proton collisions at centre-of-mass energies of 7 and 8 TeV, corresponding to an integrated luminosity of 3 fb$^{-1}$. No periodic variations of the particle-antiparticle mass differences are found, consistent with Lorentz invariance and $ CPT$ symmetry. Results are expressed in terms of the Standard Model Extension parameter $Δa_μ$ with precisions of $ \mathcal{O}(10^{-15})$ and $ \mathcal{O}(10^{-14})$ GeV for the $ B^0$ and $ B^0_s$ systems, respectively. With no assumption on Lorentz (non-)invariance, the $ CPT$-violating parameter $z$ in the $ B^0_s$ system is measured for the first time and found to be $ \mathcal{R}e(z) = -0.022 \pm 0.033 \pm 0.005$ and $ \mathcal{I}m(z) = 0.004 \pm 0.011\pm 0.002$, where the first uncertainties are statistical and the second systematic.

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arXiv2016

Search for $B_c^+$ decays to the $p\bar pπ^+$ final state

A search for the decays of the $B_c^+$ meson to $p\bar pπ^+$ is performed for the first time using a data sample corresponding to an integrated luminosity of 3.0 $\mathrm{fb}^{-1}$ collected by the LHCb experiment in $pp$ collisions at centre-of-mass energies of $7$ and $8$ TeV. No signal is found and an upper limit, at 95\% confidence level, is set, $\frac{f_c}{f_u}\times\mathcal{B}(B_c^+\to p\bar pπ^+)<3.6\times10^{-8}$ in the kinematic region $m(p\bar p)<2.85\mathrm{\,Ge\kern -0.1em V\!/}c^2$, $p_{\rm T}(B)<20\mathrm{\,Ge\kern -0.1em V\!/}c$ and $2.0<y(B)<4.5$, where $\mathcal{B}$ is the branching fraction and $f_c$ ($f_u$) is the fragmentation fraction of the $b$ quark into a $B_c^+$ ($B^+$) meson.

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arXiv2016

Observation of $ Λ_b^0 \to ψ(2S)pK^-$ and $ Λ_b^0 \to J/ψπ^+ π^- pK^-$ decays and a measurement of the $Λ_b^0$ baryon mass

The decays $ Λ_b^0 \to ψ(2S)pK^-$ and $ Λ_b^0 \to J/ψπ^+ π^- pK^-$ are observed in a data sample corresponding to an integrated luminosity of 3fb$^{-1}$, collected in proton-proton collisions at 7 and 8TeV centre-of-mass energies by the LHCb detector. The $ψ(2S)$ mesons are reconstructed through the decay modes $ψ(2S)\toμ^+μ^-$ and $ψ(2S)\to J/ψπ^+π^-$. The branching fractions relative to that of $ Λ_b^0 \to J/ψpK^-$ are measured to be \begin{eqnarray*} \frac{\mathcal{B}(Λ_b^0 \to ψ(2S) pK^-)} {\mathcal{B}(Λ_b^0 \to J/ψpK^-)} & = & (20.70\pm 0.76\pm 0.46\pm 0.37)\times10^{-2} \,, \frac{\mathcal{B}(Λ_b^0 \to J/ψπ^+ π^- pK^-)} {\mathcal{B}(Λ_b^0 \to J/ψpK^-)} & = & (20.86\pm 0.96\pm 1.34)\times10^{-2} \,, \end{eqnarray*} where the first uncertainties are statistical, the second are systematic and the third is related to the knowledge of $J/ψ$ and $ψ(2S)$ branching fractions. The mass of the $Λ_b^0$ baryon is measured to be $$ M(Λ_b^0) = 5619.65 \pm 0.17 \pm 0.17\mathrm{MeV}/c^2,$$ where the uncertainties are statistical and systematic.

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arXiv2016

First observation of the decay $D^{0}\rightarrow K^{-}π^{+}μ^{+}μ^{-}$ in the $ρ^{0}$-$ω$ region of the dimuon mass spectrum

A study of the decay $D^{0}\rightarrow K^{-}π^{+}μ^{+}μ^{-}$ is performed using data collected by the LHCb detector in proton-proton collisions at a centre-of-mass energy of 8 TeV, corresponding to an integrated luminosity of 2.0 fb$^{-1}$. Decay candidates with muon pairs that have an invariant mass in the range 675--875 MeV$/c^2$ are considered. This region is dominated by the $ρ^{0}$ and $ω$ resonances. The branching fraction in this range is measured to be ${\cal B}$($D^{0}\rightarrow K^{-}π^{+}μ^{+}μ^{-}$) = $(4.17 \pm 0.12(stat) \pm 0.40(syst))\times10^{-6}$. This is the first observation of the decay $D^{0}\rightarrow K^{-}π^{+}μ^{+}μ^{-}$. Its branching fraction is consistent with the value expected in the Standard Model.

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arXiv2016

Measurement of the properties of the $Ξ_b^{*0}$ baryon

We perform a search for near-threshold $Ξ_b^0$ resonances decaying to $Ξ_b^- π^+$ in a sample of proton-proton collision data corresponding to an integrated luminosity of 3 fb$^{-1}$ collected by the LHCb experiment. We observe one resonant state, with the following properties: \begin{eqnarray*} m(Ξ_b^{*0}) - m(Ξ_b^-) - m(π^+) &=& 15.727 \pm 0.068 \, (\mathrm{stat}) \pm 0.023 \, (\mathrm{syst}) \, \mathrm{MeV}/c^2, Γ(Ξ_b^{*0}) &=& 0.90 \pm 0.16 \, (\mathrm{stat}) \pm 0.08 \, (\mathrm{syst}) \, \mathrm{MeV} . \end{eqnarray*} This confirms the previous observation by the CMS collaboration. The state is consistent with the $J^P=3/2^+$ $Ξ_b^{*0}$ resonance expected in the quark model. This is the most precise determination of the mass and the first measurement of the natural width of this state. We have also measured the ratio \begin{align*} \frac{σ(pp \to Ξ_b^{*0} X){\cal{B}}(Ξ_b^{*0} \to Ξ_b^- π^+)}{σ(pp \to Ξ_b^- X)} = 0.28 \pm 0.03 \, (\mathrm{stat}) \pm 0.01 \, (\mathrm{syst}) . \end{align*}

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arXiv2016

Measurement of forward $W$ and $Z$ boson production in association with jets in proton-proton collisions at $\sqrt{s}=8$ TeV

The production of $W$ and $Z$ bosons in association with jets is studied in the forward region of proton-proton collisions collected at a centre-of-mass energy of 8 TeV by the LHCb experiment, corresponding to an integrated luminosity of 1.98 $\pm$ 0.02 fb$^{-1}$. The $W$ boson is identified using its decay to a muon and a neutrino, while the $Z$ boson is identified through its decay to a muon pair. Total cross-sections are measured and combined into charge ratios, asymmetries, and ratios of $W+$jet and $Z$+jet production cross-sections. Differential measurements are also performed as a function of both boson and jet kinematic variables. All results are in agreement with Standard Model predictions.

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arXiv2016

Observations of $Λ_b^0 \to ΛK^+π^-$ and $Λ_b^0 \to ΛK^+K^-$ decays and searches for other $Λ_b^0$ and $Ξ_b^0$ decays to $Λh^+h^{\prime -}$ final states

A search is performed for the charmless three-body decays of the $Λ_b^0$ and $Ξ_b^0$ baryons to the final states $Λh^+h^{\prime -}$, where $h^{(\prime)} = π$ or $K$. The analysis is based on a data sample, corresponding to an integrated luminosity of $3 \rm fb^{-1}$ of $pp$ collisions, collected by the LHCb experiment. The $Λ_b^0 \to ΛK^+π^-$ and $Λ_b^0 \to ΛK^+K^-$ decays are observed for the first time and their branching fractions and $CP$ asymmetry parameters are measured. Evidence is seen for the $Λ_b^0 \to Λπ^+π^-$ decay and limits are set on the branching fractions of $Ξ_b^0$ baryon decays to the $Λh^+h^{\prime -}$ final states.

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arXiv2016

Measurement of the mass and lifetime of the $Ω_b^-$ baryon

A proton-proton collision data sample, corresponding to an integrated luminosity of 3 fb$^{-1}$ collected by LHCb at $\sqrt{s}=7$ and 8 TeV, is used to reconstruct $63\pm9$ $Ω_b^-\toΩ_c^0π^-$, $Ω_c^0\to pK^-K^-π^+$ decays. Using the $Ξ_b^-\toΞ_c^0π^-$, $Ξ_c^0\to pK^-K^-π^+$ decay mode for calibration, the lifetime ratio and absolute lifetime of the $Ω_b^-$ baryon are measured to be \begin{align*} \frac{τ_{Ω_b^-}}{τ_{Ξ_b^-}} &= 1.11\pm0.16\pm0.03, \\ τ_{Ω_b^-} &= 1.78\pm0.26\pm0.05\pm0.06~{\rm ps}, \end{align*} where the uncertainties are statistical, systematic and from the calibration mode (for $τ_{Ω_b^-}$ only). A measurement is also made of the mass difference, $m_{Ω_b^-}-m_{Ξ_b^-}$, and the corresponding $Ω_b^-$ mass, which yields \begin{align*} m_{Ω_b^-}-m_{Ξ_b^-} &= 247.4\pm3.2\pm0.5~{\rm MeV}/c^2, \\ m_{Ω_b^-} &= 6045.1\pm3.2\pm 0.5\pm0.6~{\rm MeV}/c^2. \end{align*} These results are consistent with previous measurements.

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arXiv2016

Measurement of the difference of time-integrated CP asymmetries in $D^0 \rightarrow K^{-} K^{+} $ and $D^0 \rightarrow π^{-} π^{+} $ decays

A search for CP violation in $D^0 \rightarrow K^{-} K^{+} $ and $D^0 \rightarrow π^{-} π^{+} $ decays is performed using $pp$ collision data, corresponding to an integrated luminosity of $3~fb^{-1}$, collected using the LHCb detector at centre-of-mass energies of 7 and $8~$TeV. The flavour of the charm meson is inferred from the charge of the pion in $D^{*+}\rightarrow D^0π^+$ and $D^{*-}\rightarrow \bar{D^0}π^{-}$ decays. The difference between the CP asymmetries in $D^0 \rightarrow K^{-} K^{+} $ and $D^0 \rightarrow π^{-} π^{+} $ decays, $ΔA_{CP} \equiv A_{CP}(K^{-} K^{+}) - A_{CP}(π^{-} π^{+})$, is measured to be $\left( -0.10 \pm 0.08(stat) \pm 0.03(syst) \right) \%$. This is the most precise measurement of a time-integrated CP asymmetry in the charm sector from a single experiment.

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arXiv2016

Observation of $B^0_s\to\bar{D}^0 K^0_S$ and evidence for $B^0_s\to\bar{D}^{*0} K^0_S$ decays

The first observation of the $B^0_s\to\bar{D}^0 K^0_S$ decay mode and evidence for the $B^0_s\to\bar{D}^{*0} K^0_S$ decay mode are reported. The data sample corresponds to an integrated luminosity of 3.0 $\text{fb}^{-1}$ collected in $pp$ collisions by LHCb at center-of-mass energies of 7 and 8 TeV. The branching fractions are measured to be \begin{align*} \mathcal{B}(B^0_s\to\bar{D}^0 \bar{K}^0) &= (4.3\pm0.5(\text{stat})\pm0.3(\text{syst})\pm0.3(\text{frag})\pm0.6(\text{norm}))\times10^{-4},\\ \mathcal{B}(B^0_s\to\bar{D}^{*0} \bar{K}^0) &= (2.8\pm1.0(\text{stat})\pm0.3(\text{syst})\pm0.2(\text{frag})\pm0.4(\text{norm}))\times10^{-4}, \end{align*} where the uncertainties are due to contributions coming from statistical precision, systematic effects, and the precision of two external inputs, the ratio $f_s/f_d$ and the branching fraction of $B^0\to\bar{D}^0 K^0_S$, which is used as a calibration channel.

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arXiv2016

Observation of the $B_s^0 \rightarrow J/ψϕϕ$ decay

The $B_s^0 \rightarrow J/ψϕϕ$ decay is observed in $pp$ collision data corresponding to an integrated luminosity of 3 fb$^{-1}$ recorded by the LHCb detector at centre-of-mass energies of 7 TeV and 8 TeV. This is the first observation of this decay channel, with a statistical significance of 15 standard deviations. The mass of the $B_s^0$ meson is measured to be $5367.08\,\pm \,0.38\,\pm\, 0.15$ MeV/c$^2$. The branching fraction ratio $\mathcal{B}(B_s^0 \rightarrow J/ψϕϕ)/\mathcal{B}(B_s^0 \rightarrow J/ψϕ)$ is measured to be $0.0115\,\pm\, 0.0012\, ^{+0.0005}_{-0.0009}$. In both cases, the first uncertainty is statistical and the second is systematic. No evidence for non-resonant $B_s^0 \rightarrow J/ψϕK^+ K^-$ or $B_s^0 \rightarrow J/ψK^+ K^- K^+ K^-$ decays is found.

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