arXiv subjects

J. Buytaert

Publications and source records attributed to J. Buytaert.

At least 37 records · Page 2Linked to original sources

arXiv2018

Observation of the decay $Λ_b^0 \to Λ_c^+ p \overline{p} π^-$

The decay $Λ_b^0 \to Λ_c^+ p \overline{p} π^-$ is observed using $pp$ collision data collected with the LHCb detector at centre-of-mass energies of $\sqrt{s}=$ 7 and 8 TeV, corresponding to an integrated luminosity of 3 $fb^{-1}$. The ratio of branching fractions between $Λ_b^0 \to Λ_c^+ p \overline{p} π^-$ and $Λ_b^0 \to Λ_c^+ π^-$ decays is measured to be \begin{equation*} \frac{\mathcal{B}(Λ_b^0 \to Λ_c^+ p \overline{p}π^-)}{\mathcal{B}(Λ_b^0 \to Λ_c^+ π^-)} = 0.0540 \pm 0.0023 \pm 0.0032. \end{equation*} Two resonant structures are observed in the $ Λ_c^+ π^-$ mass spectrum of the ${Λ_b^0 \to Λ_c^+ p\overline{p} π^-}$ decays, corresponding to the $Σ_c(2455)^0$ and $Σ_c^{*}(2520)^0$ states. The ratios of branching fractions with respect to the decay $Λ_b^0 \to Λ_c^+ p \overline{p} π^-$ are \begin{align*} \frac{\mathcal{B}(Λ_b^0 \to Σ_c^0 p\overline{p})\times\mathcal{B}(Σ_c^0\to Λ_c^+ π^-)}{\mathcal{B}(Λ_b^0 \to Λ_c^+ p \overline{p}π^-)} = 0.089\pm0.015\pm0.006, \frac{\mathcal{B}(Λ_b^0 \to Σ_c^{*0} p\overline{p})\times\mathcal{B}(Σ_c^{*0}\to Λ_c^+ π^-)}{\mathcal{B}(Λ_b^0 \to Λ_c^+ p \overline{p}π^-)} = 0.119\pm0.020\pm0.014. \end{align*} In all of the above results, the first uncertainty is statistical and the second is systematic. The phase space is also examined for the presence of dibaryon resonances. No evidence for such resonances is found.

hep-ex↗

arXiv2018

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

The production cross-sections of $Υ(1S)$, $Υ(2S)$ and $Υ(3S)$ 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 $Υ$ mesons are reconstructed in the decay mode $Υ\toμ^{+}μ^{-}$. The differential production cross-sections times the dimuon branching fractions are measured as a function of the $Υ$ 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.

hep-ex↗

arXiv2018

Evidence for the decay $B_{s}^0 \rightarrow \overline{K}{}^{*0}μ^+μ^-$

A search for the decay $B_{s}^0 \rightarrow \overline{K}{}^{*0}μ^+μ^-$ is presented using data sets corresponding to 1.0, 2.0 and 1.6 $\text{fb}^{-1}$ 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 $B_{s}^0 \rightarrow \overline{K}{}^{*0}μ^+μ^-$ decay is determined to be $\mathcal{B}(B_{s}^0 \rightarrow \overline{K}{}^{*0}μ^+μ^-) = [2.9 \pm 1.0~(\text{stat}) \pm 0.2~(\text{syst}) \pm 0.3~(\text{norm})] \times 10^{-8}$, 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.

hep-ex↗

arXiv2018

Measurement of the $CP$ asymmetry in $B^-\to D_s^-D^0$ and $B^-\to D^-D^0$ decays

The $CP$ asymmetry in $B^-\to D_s^-D^0$ and $B^-\to D^-D^0$ decays is measured using LHCb data corresponding to an integrated luminosity of 3.0 fb$^{-1}$, collected in $pp$ collisions at centre-of-mass energies of 7 and 8 TeV. The results are $A^{CP}(B^-\to D_s^-D^0)=(-0.4\pm 0.5\pm 0.5)\%$ and $A^{CP}(B^-\to D^-D^0)=( 2.3\pm 2.7\pm 0.4)\%$, where the first uncertainties are statistical and the second systematic. This is the first measurement of $A^{CP}(B^-\to D_s^-D^0)$ and the most precise determination of $A^{CP}(B^-\to D^-D^0)$. Neither result shows evidence of $CP$ violation.

hep-ex↗

arXiv2018

Measurement of the inelastic $pp$ cross-section at a centre-of-mass energy of 13\,TeV

The cross-section for inelastic proton-proton collisions at a centre-of-mass energy of 13\,TeV is measured with the LHCb detector. The fiducial cross-section for inelastic interactions producing at least one prompt long-lived charged particle with momentum $p>2$\,GeV/$c$ in the pseudorapidity range $2<η<5$ is determined to be $σ_{\rm acc}= 62.2 \pm 0.2 \pm 2.5$\,mb. The first uncertainty is the intrinsic systematic uncertainty of the measurement, the second is due to the uncertainty on the integrated luminosity. The statistical uncertainty is negligible. Extrapolation to full phase space yields the total inelastic proton-proton cross-section $σ_{\rm inel}= 75.4 \pm 3.0 \pm 4.5$\,mb, where the first uncertainty is experimental and the second due to the extrapolation. An updated value of the inelastic cross-section at a centre-of-mass energy of 7\,TeV is also reported.

hep-ex↗

arXiv2018

Measurement of $CP$ violation in $B^{0}\rightarrow D^{\mp}π^{\pm}$ decays

A measurement of the $CP$ asymmetries $S_{f}$ and $S_{\bar{f}}$ in $B^0\to D^{\mp}π^{\pm}$ decays is reported. The decays are reconstructed in a dataset collected with the LHCb experiment in proton-proton collisions at centre-of-mass energies of 7 and 8 TeV and corresponding to an integrated luminosity of $3.0 \rm{ fb}^{-1}$. The $CP$ asymmetries are measured to be $S_{f} = 0.058 \pm 0.020 (\rm{stat}) \pm 0.011(\rm{syst})$ and $S_{\bar{f}} = 0.038\pm 0.020 (\text{stat})\pm 0.007 (\text{syst})$. These results are in agreement with, and more precise than, previous determinations. They are used to constrain $|\sin\left(2β+γ\right)|$ and $γ$ to intervals that are consistent with the current world-average values.

hep-ex↗

arXiv2018

Mapping the material in the LHCb vertex locator using secondary hadronic interactions

Precise knowledge of the location of the material in the LHCb vertex locator (VELO) is essential to reducing background in searches for long-lived exotic particles, and in identifying jets that originate from beauty and charm quarks. Secondary interactions of hadrons produced in beam-gas collisions are used to map the location of material in the VELO. Using this material map, along with properties of a reconstructed secondary vertex and its constituent tracks, a $p$-value can be assigned to the hypothesis that the secondary vertex originates from a material interaction. A validation of this procedure is presented using photon conversions to dimuons.

physics.ins-det↗

arXiv2018

Search for massive long-lived particles decaying semileptonically in the LHCb detector

A search is presented for massive long-lived particles decaying into a muon and two quarks. The dataset consists of proton-proton interactions at centre-of-mass energies of 7 and 8 TeV, corresponding to integrated luminosities of 1 and 2 1/fb, respectively. The analysis is performed assuming a set of production mechanisms with simple topologies, including the production of a Higgs-like particle decaying into two long-lived particles. The mass range from 20 to 80 GeV and lifetimes from 5 to 100 ps are explored. Results are also interpreted in terms of neutralino production in different supersymmetric models, with masses in the 23-198 GeV range. No excess above the background expectation is observed and upper limits are set on the production cross-section for various points in the parameter space of theoretical models.

hep-ex↗

arXiv2018

Observation of the $Λ_b^0\toΛϕ$ decay

The $Λ_b^0\toΛϕ$ decay is observed using data corresponding to an integrated luminosity of 3.0fb$^{-1}$ recorded by the LHCb experiment. The decay proceeds at leading order via a $b\to s\bar{s}s$ loop transition and is therefore sensitive to the possible presence of particles beyond the Standard Model. A first observation is reported with a significance of $5.9$ standard deviations. The value of the branching fraction is measured to be $(5.18\pm1.04\pm0.35\,^{+0.67}_{-0.62})\times10^{-6}$, where the first uncertainty is statistical, the second is systematic, and the third is related to external inputs. Triple-product asymmetries are measured to be consistent with zero.

hep-ex↗

arXiv2018

Measurement of the $b$-quark production cross-section in 7 and 13 TeV $pp$ collisions

Measurements of the cross-section for producing \bquark quarks in the reaction $pp\to b\bar{b} X$ are reported in 7 and 13 TeV collisions at the LHC as a function of the pseudorapidity $η$ in the range $2<η<5$ covered by the acceptance of the LHCb experiment. The measurements are done using semileptonic decays of $b$-flavored hadrons decaying into a ground-state charmed hadron in association with a muon. The cross-sections in the covered $η$ range are $72.0\pm 0.3\pm6.8~μ$b and $144\pm 1\pm 21~μ$b for 7 and 13 TeV. The ratio is $2.00\pm0.02\pm0.26$, where the quoted uncertainties are statistical and systematic, respectively. The agreement with theoretical expectation is good at 7 TeV, but differs somewhat at 13 TeV. The measured ratio of cross-sections is larger at lower $η$ than the model prediction.

hep-ex↗

arXiv2017

Measurement of matter-antimatter differences in beauty baryon decays

Differences in the behaviour of matter and antimatter have been observed in $K$ and $B$ meson decays, but not yet in any baryon decay. Such differences are associated with the non-invariance of fundamental interactions under the combined charge-conjugation and parity transformations, known as $C\!P$ violation. Using data from the LHCb experiment at the Large Hadron Collider, a search is made for $C\!P$-violating asymmetries in the decay angle distributions of $Λ^0_b$ baryons decaying to $pπ^-π^+π^-$ and $pπ^-K^+K^-$ final states. These four-body hadronic decays are a promising place to search for sources of $C\!P$ violation both within and beyond the Standard Model of particle physics. We find evidence for $C\!P$ violation in $Λ^0_b$ to $pπ^-π^+π^-$ decays with a statistical significance corresponding to 3.3 standard deviations including systematic uncertainties. This represents the first evidence for $C\!P$ violation in the baryon sector.

hep-ex↗

arXiv2017

Observation of the suppressed decay $Λ^{0}_{b}\rightarrow pπ^{-}μ^{+}μ^{-}$

The suppressed decay $Λ^{0}_{b}\rightarrow pπ^{-}μ^{+}μ^{-}$, excluding the $J/ψ$ and $ψ(2S)\rightarrow μ^{+}μ^{-}$ resonances, is observed for the first time with a significance of 5.5 standard deviations. The analysis is performed with proton-proton collision data corresponding to an integrated luminosity of $3\mathrm{fb}^{-1}$ collected with the LHCb experiment. The $Λ^{0}_{b}\rightarrow pπ^{-}μ^{+}μ^{-}$ branching fraction is measured relative to the $Λ^{0}_{b}\rightarrow J/ψ(\rightarrow μ^{+}μ^{-})pπ^{-}$ branching fraction giving \begin{align} \nonumber \frac{\mathcal{B}(Λ^{0}_{b}\rightarrow pπ^{-}μ^{+}μ^{-})}{\mathcal{B}({Λ^{0}_{b}\rightarrow J/ψ(\rightarrow μ^{+}μ^{-})pπ^{-}})} &= 0.044\pm0.012\pm0.007, \end{align} where the first uncertainty is statistical and the second is systematic. This is the first observation of a $b\rightarrow d$ transition in a baryonic decay.

hep-ex↗

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.

hep-ex↗

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.

hep-ex↗

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.

hep-ex↗

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.

hep-ex↗

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.

hep-ex↗

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.

hep-ex↗