arXiv subjects

M. Boubdir

Publications and source records attributed to M. Boubdir.

190 records · Page 11Linked to original sources

arXiv2016

Measurement of $C\!P$ observables in $B^\pm \rightarrow D K^\pm$ and $B^\pm \rightarrow D π^\pm$ with two- and four-body $D$ decays

Measurements of $C\!P$ observables in $B^\pm \rightarrow D K^\pm$ and $B^\pm \rightarrow D π^\pm$ decays are presented where the $D$ meson is reconstructed in the final states $K^\pmπ^\mp$, $π^\pm K^\mp$, $K^+K^-$, $π^+π^-$, $K^\pmπ^\mp π^+ π^-$, $π^\pm K^\mp π^+ π^-$ and $π^+ π^- π^+ π^-$. This analysis uses a sample of charged $B$ mesons from $pp$ collisions collected by the LHCb experiment in 2011 and 2012, corresponding to an integrated luminosity of 3.0 fb$^{-1}$. Various \CP-violating effects are reported and together these measurements provide important input for the determination of the unitarity triangle angle $γ$. The analysis of the four-pion $D$ decay mode is the first of its kind.

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arXiv2016

Observation of $η_{c}(2S) \to p \bar p$ and search for $X(3872) \to p \bar p$ decays

The first observation of the decay $η_{c}(2S) \to p \bar p$ is reported using proton-proton collision data corresponding to an integrated luminosity of $3.0\rm \, fb^{-1}$ recorded by the LHCb experiment at centre-of-mass energies of 7 and 8 TeV. The $η_{c}(2S)$ resonance is produced in the decay $B^{+} \to [c\bar c] K^{+}$. The product of branching fractions normalised to that for the $J/ψ$ intermediate state, ${\cal R}_{η_{c}(2S)}$, is measured to be \begin{align*} {\cal R}_{η_{c}(2S)}\equiv\frac{{\mathcal B}(B^{+} \to η_{c}(2S) K^{+}) \times {\mathcal B}(η_{c}(2S) \to p \bar p)}{{\mathcal B}(B^{+} \to J/ψK^{+}) \times {\mathcal B}(J/ψ\to p \bar p)} =~& (1.58 \pm 0.33 \pm 0.09)\times 10^{-2}, \end{align*} where the first uncertainty is statistical and the second systematic. No signals for the decays $B^{+} \to X(3872) (\to p \bar p) K^{+}$ and $B^{+} \to ψ(3770) (\to p \bar p) K^{+}$ are seen, and the 95\% confidence level upper limits on their relative branching ratios are % found to be ${\cal R}_{X(3872)}<0.25\times10^{-2}$ and ${\cal R}_{ψ(3770))}<0.10$. In addition, the mass differences between the $η_{c}(1S)$ and the $J/ψ$ states, between the $η_{c}(2S)$ and the $ψ(2S)$ states, and the natural width of the $η_{c}(1S)$ are measured as \begin{align*} M_{J/ψ} - M_{η_{c}(1S)} =~& 110.2 \pm 0.5 \pm 0.9 \rm \, MeV, M_{ψ(2S)} -M_{η_{c}(2S)} =~ & 52.5 \pm 1.7 \pm 0.6 \rm \, MeV, Γ_{η_{c}(1S)} =~& 34.0 \pm 1.9 \pm 1.3 \rm \, MeV. \end{align*}

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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

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

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*}

hep-ex↗

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.

hep-ex↗

arXiv2016

Model-independent evidence for $J/ψp$ contributions to $Λ_b^0\to J/ψp K^-$ decays

The data sample of $Λ_b^0\to J/ψp K^-$ decays acquired with the LHCb detector from 7 and 8~TeV $pp$ collisions, corresponding to an integrated luminosity of 3 fb$^{-1}$, is inspected for the presence of $J/ψp$ or $J/ψK^-$ contributions with minimal assumptions about $K^- p$ contributions. It is demonstrated at more than 9 standard deviations that $Λ_b^0\to J/ψp K^-$ decays cannot be described with $K^- p$ contributions alone, and that $J/ψp$ contributions play a dominant role in this incompatibility. These model-independent results support the previously obtained model-dependent evidence for $P_c^+\to J/ψp$ charmonium-pentaquark states in the same data sample.

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