arXiv subjects

M. -O. Bettler

Publications and source records attributed to M. -O. Bettler.

At least 19 recordsLinked to original sources

arXiv2025

Evidence for CP violation in $B^+\to p \bar p K^+$ decays

Three-body $B^+\to p \overline p K^+$ and $B^+\to p \overline p π^+$ decays are studied using a data sample corresponding to an integrated luminosity of 3.0 $fb^{-1}$ collected by the LHCb experiment in proton-proton collisions at center-of-mass energies of $7$ and $8$ TeV. Evidence of CP violation in the $B^+\to p \overline p K^+$ decay is found in regions of the phase space, representing the first measurement of this kind for a final state containing baryons. Measurements of the forward-backward asymmetry of the light meson in the $p\overline p$ rest frame yield $A_{\mathrm{FB}}(p \overline p K^+,~m_{p\overline p}<2.85\mathrm{\,Ge\kern -0.1em V\!/}c^2)=0.495\pm0.012~(\mathrm{stat})\pm0.007~(\mathrm{syst})$ and $A_{\mathrm{FB}}(p\overline p π^+,~m_{p\overline p}<2.85\mathrm{\,Ge\kern -0.1em V\!/}c^2)=-0.409\pm0.033~(\mathrm{stat})\pm0.006~(\mathrm{syst})$. In addition, the branching fraction of the decay $B^+\to\kern 0.1em\overline{\kern -0.1emΛ}(1520)p$ is measured to be $\mathcal{B}(B^+ \to \kern 0.1em\overline{\kern -0.1emΛ}(1520)p)=(3.15\pm0.48~(\mathrm{stat})\pm0.07~(\mathrm{syst})\pm0.26~(\mathrm{BF}))\times 10^{-7}$, where BF denotes the uncertainty on secondary branching fractions.

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arXiv2025

Measurements of charm mixing and $C\!P$ violation using $D^0 \to K^\pm π^\mp$ decays

Measurements of charm mixing and $C\!P$ violation parameters from the decay-time-dependent ratio of $ D^0 \to K^+ π^- $ to $ D^0 \to K^- π^+ $ decay rates and the charge-conjugate ratio are reported. The analysis uses $\overline{B}\to D^{*+} μ^- X$, and charge-conjugate decays, where $D^{*+}\to D^0 π^+$, and $D^0\to K^{\mp} π^{\pm}$. The $pp$ collision data are recorded by the LHCb experiment at center-of-mass energies $\sqrt{s}$ = 7 and 8 TeV, corresponding to an integrated luminosity of 3 fb$^{-1}$. The data are analyzed under three hypotheses: (i) mixing assuming $C\!P$ symmetry, (ii) mixing assuming no direct $C\!P$ violation in the Cabibbo-favored or doubly Cabibbo-suppressed decay amplitudes, and (iii) mixing allowing either direct $C\!P$ violation and/or $C\!P$ violation in the superpositions of flavor eigenstates defining the mass eigenstates. The data are also combined with those from a previous LHCb study of $D^0\to K π$ decays from a disjoint set of $ D^{*+} $ candidates produced directly in $pp$ collisions. In all cases, the data are consistent with the hypothesis of $C\!P$ symmetry.

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arXiv2018

Differential branching fraction and angular analysis of $Λ^{0}_{b} \rightarrow Λμ^+μ^-$ decays

The differential branching fraction of the rare decay $Λ^{0}_{b} \rightarrow Λμ^+μ^-$ is measured as a function of $q^{2}$, the square of the dimuon invariant mass. The analysis is performed using proton-proton collision data, corresponding to an integrated luminosity of $3.0 \mbox{ fb}^{-1}$, collected by the LHCb experiment. Evidence of signal is observed in the $q^2$ region below the square of the $J/ψ$ mass. Integrating over $15 < q^{2} < 20 \mbox{ GeV}^2/c^4$ the branching fraction is measured as $d\mathcal{B}(Λ^{0}_{b} \rightarrow Λμ^+μ^-)/dq^2 = (1.18 ^{+ 0.09} _{-0.08} \pm 0.03 \pm 0.27) \times 10^{-7} ( \mbox{GeV}^{2}/c^{4})^{-1}$, where the uncertainties are statistical, systematic and due to the normalisation mode, $Λ^{0}_{b} \rightarrow J/ψΛ$, respectively. In the $q^2$ intervals where the signal is observed, angular distributions are studied and the forward-backward asymmetries in the dimuon ($A^{l}_{\rm FB}$) and hadron ($A^{h}_{\rm FB}$) systems are measured for the first time. In the range $15 < q^2 < 20 \mbox{ GeV}^2/c^4$ they are found to be $A^{l}_{\rm FB} = -0.05 \pm 0.09 \mbox{ (stat)} \pm 0.03 \mbox{ (syst)}$ and $A^{h}_{\rm FB} = -0.29 \pm 0.07 \mbox{ (stat)} \pm 0.03 \mbox{ (syst)}$.

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arXiv2018

Measurement of the relative rate of prompt $χ_{c0}$, $χ_{c1}$ and $χ_{c2}$ production at $\sqrt{s}=7$TeV

Prompt production of charmonium $χ_{c0}$, $χ_{c1}$ and $χ_{c2}$ mesons is studied using proton-proton collisions at the LHC at a centre-of-mass energy of $\sqrt{s}=7$TeV. The $χ_{c}$ mesons are identified through their decay to $J/ψγ$, with $J/ψ\toμ^+μ^-$ using photons that converted in the detector. A data sample, corresponding to an integrated luminosity of $1.0\mathrm{fb}^{-1}$ collected by the LHCb detector, is used to measure the relative prompt production rate of $χ_{c1}$ and $χ_{c2}$ in the rapidity range $2.0<y<4.5$ as a function of the $J/ψ$ transverse momentum from 3 to 20 GeV$/c$. First evidence for $χ_{c0}$ meson production at a high-energy hadron collider is also presented.

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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.

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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.

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arXiv2018

Test of Lepton Flavor Universality by the measurement of the $B^0 \to D^{*-} τ^+ ν_τ$ branching fraction using three-prong $τ$ decays

The ratio of branching fractions ${\cal{R}}(D^{*-})\equiv {\cal{B}}(B^0 \to D^{*-} τ^+ ν_τ)/{\cal{B}}(B^0 \to D^{*-} μ^+ν_μ)$ 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$^{-1}$. 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 $B^0 \to D^{*-}π^+π^-π^+$ decay as the normalization channel, the ratio ${\cal{B}}(B^0 \to D^{*-} τ^+ ν_τ)/{\cal{B}}(B^0 \to D^{*-}π^+π^-π^+)$ is measured to be $1.97 \pm 0.13 \pm 0.18$, where the first uncertainty is statistical and the second systematic. An average of branching fraction measurements for the normalization channel is used to derive ${\cal{B}}(B^0 \to D^{*-} τ^+ ν_τ) = (1.42 \pm 0.094 \pm 0.129 \pm 0.054) \%$, where the third uncertainty is due to the limited knowledge of ${\cal{B}}(B^0\to D^{*-}π^+π^-π^+)$. A test of lepton flavor universality is performed using the well-measured branching fraction ${\cal{B}}(B^0 \to D^{*-} μ^+ν_μ)$ to compute ${\cal{R}}(D^{*-}) = 0.291 \pm 0.019 \pm 0.026 \pm 0.013$, where the third uncertainty originates from the uncertainties on ${\cal{B}}(B^0 \to D^{*-}π^+π^-π^+)$ and ${\cal{B}}(B^0 \to D^{*-} μ^+ν_μ)$. This measurement is in agreement with the Standard Model prediction and with previous measurements.

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arXiv2018

Measurement of the ratio of the $B^0 \to D^{-} τ^+ ν_τ$ and $B^0 \to D^{-} μ^+ ν_μ$ branching fractions using three-prong $τ$-lepton decays

The ratio of branching fractions ${\cal{R}}(D^{*-})\equiv {\cal{B}}(B^0 \to D^{*-} τ^+ ν_τ)/{\cal{B}}(B^0 \to D^{*-} μ^+ν_μ)$ 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 ${\cal{R}}(D^{*-})$ is determined using the $τ$ lepton decays with three charged pions in the final state. The $B^0 \to D^{*-} τ^+ν_τ$ yield is normalized to that of the $B^0\to D^{*-} π^+π^-π^+$ mode, providing a measurement of ${\cal{B}}(B^0\to D^{*-}τ^+ν_τ)/{\cal{B}}(B^0\to D^{*-}π^+π^-π^+) = 1.97 \pm 0.13 \pm 0.18$, where the first uncertainty is statistical and the second systematic. The value of ${\cal{B}}(B^0 \to D^{*-} τ^+ ν_τ) = (1.42 \pm 0.094 \pm 0.129 \pm 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 $B^0 \to D^{*-} μ^+ν_μ$ decay, a value of ${\cal{R}}(D^{*-}) = 0.291 \pm 0.019 \pm 0.026 \pm 0.013$ is established, where the third uncertainty is due to the limited knowledge of the branching fractions of the normalization and $B^0\to D^{*-}μ^+ν_μ$ modes. This measurement is in agreement with the Standard Model prediction and with previous results.

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arXiv2018

Measurements of the branching fractions of $Λ_{c}^{+} \rightarrow p π^{-} π^{+}$, $Λ_{c}^{+} \rightarrow p K^{-} K^{+}$, and $Λ_{c}^{+} \rightarrow p π^{-} K^{+}$

The ratios of the branching fractions of the decays $Λ_{c}^{+} \rightarrow p π^{-} π^{+}$, $Λ_{c}^{+} \rightarrow p K^{-} K^{+}$, and $Λ_{c}^{+} \rightarrow p π^{-} K^{+}$ with respect to the Cabibbo-favoured $Λ_{c}^{+} \rightarrow p K^{-} π^{+}$ decay are measured using proton-proton collision data collected with the LHCb experiment at a 7 TeV centre-of-mass energy and corresponding to an integrated luminosity of 1.0 fb$^{-1}$: \begin{align*} \frac{\mathcal{B}(Λ_{c}^{+} \rightarrow p π^{-} π^{+})}{\mathcal{B}(Λ_{c}^{+} \rightarrow p K^{-} π^{+})} & = (7.44 \pm 0.08 \pm 0.18)\,\%, \frac{\mathcal{B}(Λ_{c}^{+} \rightarrow p K^{-} K^{+})}{\mathcal{B}(Λ_{c}^{+} \rightarrow p K^{-} π^{+})} &= (1.70 \pm 0.03 \pm 0.03)\,\%, \frac{\mathcal{B}(Λ_{c}^{+} \rightarrow p π^{-} K^{+})}{\mathcal{B}(Λ_{c}^{+} \rightarrow p K^{-} π^{+})} & = (0.165 \pm 0.015 \pm 0.005 )\,\%, \end{align*} where the uncertainties are statistical and systematic, respectively. These results are the most precise measurements of these quantities to date. When multiplied by the world-average value for $\mathcal{B}(Λ_{c}^{+} \rightarrow p K^{-} π^{+})$, the corresponding branching fractions are \begin{align*} \mathcal{B}(Λ_{c}^{+} \rightarrow p π^{-} π^{+}) &= (4.72 \pm 0.05 \pm 0.11 \pm 0.25) \times 10^{-3}, \mathcal{B}(Λ_{c}^{+} \rightarrow p K^{-} K^{+}) &= (1.08 \pm 0.02 \pm 0.02 \pm 0.06) \times 10^{-3}, \mathcal{B}(Λ_{c}^{+} \rightarrow p π^{-} K^{+}) &= (1.04 \pm 0.09 \pm 0.03 \pm 0.05) \times 10^{-4}, \end{align*} where the final uncertainty is due to $\mathcal{B}(Λ_{c}^{+} \rightarrow p K^{-} π^{+})$.

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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.

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arXiv2018

Observation of the decay $Λ^0_b \to p K^- μ^+ μ^-$ and a search for $C\!P$ violation

A search for $C\!P$ violation in the decay $Λ^0_b \to p K^- μ^+ μ^-$ is presented. This decay is mediated by flavour-changing neutral-current transitions in the Standard Model and is potentially sensitive to new sources of $C\!P$ violation. The study is based on a data sample of proton-proton collisions recorded with the LHCb experiment, corresponding to an integrated luminosity of $3$ $\mathrm{fb}^{-1}$. The $Λ^0_b \to p K^- μ^+ μ^-$ decay is observed for the first time, and two observables that are sensitive to different manifestations of $C\!P$ violation are measured, $Δ\mathcal{A}_{C\!P} \equiv \mathcal{A}_{C\!P}(Λ^0_b \to p K^- μ^+ μ^-)-\mathcal{A}_{C\!P}(Λ^0_b\to pK^- J/ψ)$ and $a_{C\!P}^{\widehat{T}-odd}$, where the latter is based on asymmetries in the angle between the $μ^+μ^-$ and $p K^-$ decay planes. These are measured to be $Δ\mathcal{A}_{C\!P} = (-3.5 \pm 5.0(stat) \pm 0.2(syst))\times 10^{-2}$, $a_{C\!P}^{\widehat{T}-odd} = (1.2 \pm 5.0(stat) \pm 0.7(syst))\times 10^{-2}$, and no evidence for $C\!P$ violation is found.

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arXiv2018

Measurement of $CP$ observables in $B^{\pm} \rightarrow D K^{*\pm}$ decays using two- and four-body $D$ final states

Measurements of $CP$ observables in $B^{\pm} \rightarrow D K^{*\pm}$ decays are presented, where $D$ denotes a superposition of $D^0$ and $\overline{D^0}$ meson states. Decays of the $D$ meson to $K^{-}π^{+}$, $K^{-}K^{+}$, $π^{-}π^{+}$, $K^{-}π^{+}π^{-}π^{+}$ and $π^{-}π^{+}π^{-}π^{+}$ are used and the $K^{*\pm}$ meson is reconstructed in the $K^{0}_{\mathrm{S}}π^{\pm}$ final state. This analysis uses a data sample of $pp$ collisions collected with the LHCb experiment, corresponding to integrated luminosities of 1 $\mathrm{fb}^{-1}$, 2 $\mathrm{fb}^{-1}$ and 1.8 $\mathrm{fb}^{-1}$ at centre-of-mass energies $\sqrt{s} = $ 7 TeV, 8 TeV and 13 TeV, respectively. The sensitivity of the results to the CKM angle $γ$ is discussed.

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arXiv2018

Search for the lepton-flavour violating decays $B^0_{(s)} \rightarrow e^\pm μ^\mp$

A search for the lepton-flavour violating decays $B^0_s \rightarrow e^\pm μ^\mp$ and $B^0 \rightarrow e^\pm μ^\mp$ 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 fractions are determined to be $\mathcal{B}(B^0_s \rightarrow e^\pm μ^\mp) < 5.4\,(6.3) \times 10^{-9}$ and $\mathcal{B}(B^0 \rightarrow e^\pm μ^\mp) < 1.0\,(1.3) \times 10^{-9}$ at $90\%\,(95\%)$ confidence level, which are the strongest limits on these decays to date.

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arXiv2018

Measurement of the ratio of branching fractions $\mathcal{B}(B_c^+\,\to\,J/ψτ^+ν_τ)$/$\mathcal{B}(B_c^+\,\to\,J/ψμ^+ν_μ)$

A measurement is reported of the ratio of branching fractions $\mathcal{R}(J/ψ)=\mathcal{B}(B_c^+\,\to\,J/ψτ^+ν_τ)/\mathcal{B}(B_c^+\,\to\,J/ψμ^+ν_μ)$, where the $τ^+$ lepton is identified in the decay mode $τ^+\,\to\,μ^+ν_μ\overlineν_τ$. This analysis uses a sample of proton-proton collision data corresponding to 3.0$\mathrm{\,fb}^{-1}$ of integrated luminosity recorded with the LHCb experiment at center-of-mass energies $7\,\mathrm{TeV}$ and $8\,\mathrm{TeV}$. A signal is found for the decay $B_c^+\,\to\,J/ψτ^+ν_τ$ at a significance of 3 standard deviations, corrected for systematic uncertainty, and the ratio of the branching fractions is measured to be $\mathcal{R}(J/ψ) = 0.71 \pm 0.17 \mathrm{\,(stat)} \pm 0.18\mathrm{\,(syst)}$. This result lies within 2 standard deviations above the range of existing predictions in the Standard Model.

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arXiv2018

Measurement of the shape of the $Λ_b^0\toΛ_c^+ μ^- \overlineν$ differential decay rate

A measurement of the shape of the differential decay rate and the associated Isgur-Wise function for the decay $Λ_b^0\toΛ_c^+μ^-\overlineν$ is reported, using data corresponding to $3 fb^{-1}$ collected with the LHCb detector in proton-proton collisions. The $Λ_c^+μ^-\overlineν$(+ anything) final states are reconstructed through the detection of a muon and a $Λ_c^+$ baryon decaying into $pK^-π^+$, and the decays $Λ_b^0\toΛ_c^+π^+π^-μ^-\overlineν$ are used to determine contributions from $Λ_b^0\to Λ_c^{\star+}μ^-\barν$ decays. The measured dependence of the differential decay rate upon the squared four-momentum transfer between the heavy baryons, $q^2$, is compared with expectations from heavy-quark effective theory and from unquenched lattice QCD predictions.

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arXiv2018

Measurement of branching fractions of charmless four-body $Λ_b^0$ and $Ξ_b^0$ decays

A search for charmless four-body decays of $Λ_{b}^{0}$ and $Ξ_{b}^{0}$ baryons with a proton and three charged mesons (either kaons or pions) in the final state is performed. The data sample used was recorded in 2011 and 2012 with the LHCb experiment and corresponds to an integrated luminosity of 3 fb$^{-1}$. Six decay modes are observed, among which $Λ_{b}^{0} \to pK^{-}π^{+}π^{-}$, $Λ_{b}^{0} \to pK^{-}K^{+}K^{-}$, $Ξ_{b}^{0} \to pK^{-}π^{+}π^{-}$ and $Ξ_{b}^{0} \to pK^{-} π^{+}K^{-}$ are established for the first time. Their branching fractions (including the ratio of hadronisation fractions in the case of the $Ξ_{b}^{0}$ baryon) are determined relative to the $Λ_{b}^{0} \to Λ_{c}^{+}π^{-}$ decay.

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arXiv2018

Search for dark photons produced in 13 TeV $pp$ collisions

Searches are performed for both prompt-like and long-lived dark photons, $A^{\prime}$, produced in proton-proton collisions at a center-of-mass energy of 13 TeV, using $A^{\prime}\toμ^+μ^-$ decays and a data sample corresponding to an integrated luminosity of 1.6 fb$^{-1}$ collected with the LHCb detector. The prompt-like $A^{\prime}$ search covers the mass range from near the dimuon threshold up to 70 GeV, while the long-lived $A^{\prime}$ search is restricted to the low-mass region $214<m(A^{\prime})<350$ MeV. No evidence for a signal is found, and 90% confidence level exclusion limits are placed on the $γ$-$A^{\prime}$ kinetic-mixing strength. The constraints placed on prompt-like dark photons are the most stringent to date for the mass range $10.6 < m(A^{\prime}) < 70$ GeV, and are comparable to the best existing limits for $m(A^{\prime}) < 0.5$ GeV. The search for long-lived dark photons is the first to achieve sensitivity using a displaced-vertex signature.

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arXiv2018

First observation of forward $Z \rightarrow b \bar{b}$ production in $pp$ collisions at $\sqrt{s}=8$ TeV

The decay $Z \rightarrow b \bar{b}$ is reconstructed in $pp$ collision data, corresponding to 2 fb$^{-1}$ of integrated luminosity, collected by the LHCb experiment at a centre-of-mass energy of $\sqrt{s}=8$ TeV. The product of the $Z$ production cross-section and the $Z \rightarrow b \bar{b}$ branching fraction is measured for candidates in the fiducial region defined by two particle-level $b$-quark jets with pseudorapidities in the range $2.2 < η< 4.2$, with transverse momenta $p_{T}>20$ GeV and dijet invariant mass in the range $45 < m_{jj} < 165$ GeV. From a signal yield of $5462 \pm 763$ $Z \rightarrow b \bar{b}$ events, where the uncertainty is statistical, a production cross-section times branching fraction of $332 \pm 46 \pm 59$ pb is obtained, where the first uncertainty is statistical and the second systematic. The measured significance of the signal yield is 6.0 standard deviations. This measurement represents the first observation of the $Z \rightarrow b \bar{b}$ production in the forward region of $pp$ collisions.

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