arXiv subjects

M. Becker

Publications and source records attributed to M. Becker.

At least 127 records · Page 7Linked to original sources

arXiv2025

Measurement of the Z-boson mass

The first dedicated $Z$-boson mass measurement at the LHC with $Z \to μ^+μ^-$ decays is reported. The dataset uses proton-proton collisions at a centre-of-mass energy of $13$ TeV, recorded in 2016 by the LHCb experiment, and corresponds to an integrated luminosity of $1.7$ fb$^{-1}$. A template fit to the $μ^+μ^-$ mass distribution yields the following result for the $Z$-boson mass, \begin{equation*} m_{Z} = 91185.7 \pm 8.3 \pm 3.9 \rm{MeV}, \end{equation*} where the first uncertainty is statistical and the second systematic. This result is consistent with previous measurements and predictions from global electroweak fits.

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arXiv2025

Measurements of charmed meson and antimeson production asymmetries at $\sqrt{s} =13.6$ TeV

This article presents doubly differential measurements of the asymmetries in production rates between mesons containing a charm quark and those containing an anticharm quark in proton-proton collisions at a centre-of-mass energy of $\sqrt{s}=13.6$ TeV using data recorded by the LHCb experiment. The asymmetries of $D^0$, $D^+$ and $D_s^+$ mesons are measured for two-dimensional intervals in transverse momentum and pseudorapidity, within the range $2.5<p_T<25.0$ GeV$/c$ and $2.0<η<4.5$. No significant production asymmetries are observed. Comparisons to the Pythia 8 and Herwig 7 event generators are also presented, and their agreement with the data is evaluated. These measurements constitute the first measurements of production asymmetries at this centre-of-mass energy of colliding beams, and the first measurements with the LHCb Run 3 detector.

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arXiv2025

Measurement of the $Ω_c^0$ and $Ξ_c^0$ baryon lifetimes using hadronic $b$-baryon decays

The lifetimes of the $Ω_c^0$ and $Ξ_c^0$ baryons are measured using a $pp$ collision dataset collected by the LHCb experiment, corresponding to an integrated luminosity of $9~\rm{fb^{-1}}$. The charm baryons are produced in the fully reconstructed decay chains $Ω_b^- \rightarrow Ω_c^0 (\rightarrow pK^-K^-π^+)~π^-$ and $Ξ_b^- \rightarrow Ξ_c^0 (\rightarrow pK^-K^-π^+)~π^-$. The measurement uses topologically and kinematically similar $B^- \rightarrow D^0(\rightarrow K^-K^+π^-π^+)~π^-$ decays for normalisation. The measured lifetimes are $τ_{Ω_c^0} = 276.3 \pm 19.4~\rm{(stat)} \pm 1.8~\rm{(syst)} \pm 0.7~(τ_{D^0})~\rm{fs}$, $τ_{Ξ_c^0} = 149.2 \pm ~\,2.5~\rm{(stat)} \pm 0.9~\rm{(syst)} \pm 0.4~(τ_{D^0})~\rm{fs}$, where the first uncertainty is statistical, the second systematic and the third due to the uncertainty of the $D^0$ lifetime. These results are consistent with previous measurements performed by the LHCb experiment.

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arXiv2025

First observation of the $\mathitΛ_b^{0}\!\rightarrow\mathitΛ_{c}^{+}D_{s}^{-}K^{+}K^{-}$ decay and search for pentaquarks in the $\mathitΛ_{c}^{+}D_{s}^{-}$ system

The $\mathitΛ_b^{0}\!\rightarrow\mathitΛ_{c}^{+}D_{s}^{-}K^{+}K^{-}$ decay is observed for the first time using the data sample from proton-proton collisions recorded at a center-of-mass energy of $13\,\text{TeV}$ with the LHCb detector, corresponding to an integrated luminosity of $6\,\text{fb}^{-1}$. The ratio of branching fraction to that of $\mathitΛ_b^{0} \!\rightarrow\mathitΛ_{c}^{+}D_{s}^{-}$ decays is measured as $0.0141 \pm 0.0019 \pm 0.0012$, where the first uncertainty is statistical and the second systematic. A search for hidden-charm pentaquarks with strangeness is performed in the $\mathitΛ_{c}^{+}D_{s}^{-}$ system. No evidence is found, and upper limits on the production ratio of $P_{c\bar{c}s}(4338)^0$ and $P_{c\bar{c}s}(4459)^0$ pentaquarks relative to the $\mathitΛ_{c}^{+}D_{s}^{-}$ final state are set at the $95\%$ confidence level as $0.12$ and $0.20$, respectively.

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arXiv2025

Precision measurement of the ${\itΞ}_b^0$ baryon lifetime

A sample of $pp$ collision data, corresponding to an integrated luminosity of 5.4 fb$^{-1}$ and collected by the LHCb experiment during LHC Run 2, is used to measure the ratio of the lifetime of the ${\itΞ}_b^0$ baryon to that of the ${\itΛ}_b^0$ baryon, $r_τ\equivτ_{{\itΞ}_b^0}/τ_{{\itΛ}_b^0}$. The value ${r_τ^{\rm Run\,2}=1.004\pm0.009\pm0.006}$ is obtained, where the first uncertainty is statistical and the second systematic. This value is averaged with the corresponding value from Run 1 to obtain ${r_τ = 1.004\pm0.008\pm0.005}$. Multiplying by the known value of the ${\itΛ}_b^0$ lifetime yields ${{τ_{{\itΞ}_b^0}} = 1.475\pm0.012\pm0.008\pm0.009~{\rm ps}}$, where the last uncertainty is due to the limited knowledge of the ${\itΛ}_b^0$ lifetime. This measurement improves the precision of the current world average of the ${\itΞ}_b^0$ lifetime by about a factor of two, and is in good agreement with the most recent theoretical predictions.

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arXiv2025

Measurements of $ψ{(2S)}$ and $χ_{c1}(3872)$ production within fully reconstructed jets

This paper presents the first measurement of $ψ{(2S)}$ and $χ_{c1}(3872)$ meson production within fully reconstructed jets. Each quarkonium state (tag) is reconstructed via its decay to the $J/ψ$($\rightarrowμ^+μ^-$)$π^+π^-$ final state in the forward region using proton-proton collision data collected by the LHCb experiment at the center-of-mass-energy of $13 \text{TeV}$ in 2016, corresponding to an integrated luminosity of $1.64 \text{fb}^{-1}$. The fragmentation function, presented as the ratio of the quarkonium-tag transverse momentum to the full jet transverse momentum ($p_{\mathrm{T}}(\text{tag})/p_{\mathrm{T}}(\text{jet})$), is measured differentially in $p_{\mathrm{T}}(\text{jet})$ and $p_{\mathrm{T}}(\text{tag})$ bins. The distributions are separated into promptly produced quarkonia from proton-proton collisions and quarkonia produced from displaced $b$-hadron decays. While the displaced quarkonia fragmentation functions are in general well described by parton-shower predictions, the prompt quarkonium distributions differ significantly from fixed-order non-relativistic QCD (NRQCD) predictions followed by a QCD parton shower.

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arXiv2025

Angular analysis of $B^0\rightarrow K^{*0}e^{+}e^{-}$ decays

An angular analysis of $B^0\rightarrow K^{*0}e^{+}e^{-}$ decays is presented using proton-proton collision data collected by the LHCb experiment at centre-of-mass energies of 7, 8 and 13 TeV, corresponding to an integrated luminosity of 9 fb$^{-1}$. The analysis is performed in the region of the dilepton invariant mass squared of 1.1-6.0 GeV$^{2}/c^{4}$. In addition, a test of lepton flavour universality is performed by comparing the obtained angular observables with those measured in $B^0\rightarrow K^{*0}μ^{+}μ^{-}$ decays. In general, the angular observables are found to be consistent with the Standard Model expectations as well as with global analyses of other $b \rightarrow s \ell^{+} \ell^{-}$ processes, where $\ell$ is either a muon or an electron. No sign of lepton-flavour-violating effects is observed.

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arXiv2025

Observation of the $Λ_b^0 \to J/ψΞ^- K^+$ and $Ξ_b^0 \to J/ψΞ^- π^+$ decays

The first observation of the $Ξ_b^0 \to J/ψΞ^- π^+$ decay and the most precise measurement of the branching fraction of the $Λ_b^0 \to J/ψΞ^- K^+$ decay are reported, using proton-proton collision data from the LHCb experiment collected in 2016--2018 at a centre-of-mass energy of 13~TeV, corresponding to an integrated luminosity of 5.4~fb$^{-1}$. Using the $Λ_b^0 \to J/ψΛ$ and $Ξ_b^0 \to J/ψΞ^-$ decays as normalisation channels, the ratios of branching fractions are measured to be: \[ \frac{\mathcal{B}(Λ_b^0 \to J/ψΞ^- K^+)}{\mathcal{B}(Λ_b^0 \to J/ψΛ)} = (1.17 \pm 0.14 \pm 0.08)\times 10^{-2} \, , \] \[ \frac{\mathcal{B}(Ξ_b^0 \to J/ψΞ^- π^+)}{\mathcal{B}(Ξ_b^0 \to J/ψΞ^-)} = (11.9 \pm 1.4 \pm 0.6)\times 10^{-2}\, , \] where the first uncertainty is statistical and the second systematic.

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arXiv2025

Observation of exotic $J/ψϕ$ resonant structure in diffractive processes in proton-proton collisions

The first study of $J/ψϕ$ production in diffractive processes in proton-proton collisions is presented. The study is based on an LHCb dataset recorded at centre-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 5 fb$^{-1}$. The data disfavour a nonresonant $J/ψϕ$ production but are consistent with a resonant model including several resonant states observed previously only in $B^+ \to J/ψϕK^+$ decays. The $χ_{c0}(4500)$ state is observed with a significance over $6σ$ and the $χ_{c1}(4274)$ is confirmed with a significance of more than $4σ$.

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arXiv2025

Three-pion Bose-Einstein correlations measured in proton-proton collisions

A study on the Bose-Einstein correlations for triplets of same-sign pions is presented. The analysis is performed using proton-proton collisions at a centre-of-mass energy of $\sqrt{s}$ = 7 TeV, recorded by the LHCb experiment, corresponding to an integrated luminosity of 1.0 fb$^{-1}$. For the first time, the results are interpreted in the core-halo model. The parameters of the model are determined in regions of charged-particle multiplicity. This measurement provides insight into the nature of hadronisation in terms of coherence, showing a coherent emission of pions.

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arXiv2025

Observation of charge-parity symmetry breaking in baryon decays

The Standard Model of particle physics-the theory of particles and interactions at the smallest scale-predicts that matter and antimatter interact differently due to violation of the combined symmetry of charge conjugation ($C$) and parity ($P$). Charge conjugation transforms particles into their antimatter particles, whereas the parity transformation inverts spatial coordinates. This prediction applies to both mesons, which consist of a quark and an antiquark, and baryons, which are composed of three quarks. However, despite having been discovered in various meson decays, $CP$ violation has yet to be observed in baryons, the type of matter that makes up the observable Universe. Here we report a study of the decay of the beauty baryon $Λ^{0}_{b}$ to the $p K^{-} π^{+}π^{-}$ final state and its $CP$-conjugated process, using data collected by the Large Hadron Collider beauty experiment at the European Organization for Nuclear Research (CERN). The results reveal significant asymmetries between the decay rates of the $Λ^{0}_{b}$ baryon and its $CP$-conjugated antibaryon, providing, to our knowledge, the first observation of $CP$ violation in baryon decays and demonstrating the different behaviours of baryons and antibaryons. In the Standard Model, $CP$ violation arises from the Cabibbo-Kobayashi-Maskawa mechanism, and new forces or particles beyond the Standard Model could provide additional contributions. This discovery opens a new path in the search for physics beyond the Standard Model.

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arXiv2025

First observation of the $Λ^0_b \to D^+ D^- Λ$ decay

The $Λ^0_b \to D^+ D^- Λ$ decay is observed for the first time using proton-proton collision data collected by the LHCb experiment at a center-of-mass energy of $13 \mathrm{TeV}$, corresponding to an integrated luminosity of $5.3 \mathrm{fb}^{-1}$. Using the $B^0 \to D^+ D^- K_{\mathrm{S}}^0$ decay as a reference channel, the product of the relative production cross-section and decay branching fractions is measured to be $$ {\cal R}=\frac{σ_{Λ^0_b}}{σ_{B^0}} \times \frac{{\cal B}(Λ^0_b \to D^+ D^- Λ)}{{\cal B}(B^0 \to D^+ D^- K_{\mathrm{S}}^0)}=0.179 \pm 0.022 \pm 0.014 $$ where the first uncertainty is statistical and the second is systematic. The known branching fraction of the reference channel, ${\cal B}(B^0 \to D^+ D^- K_{\mathrm{S}}^0)$, and the cross-section ratio, $σ_{Λ^0_b} / σ_{B^0}$, previously measured by $\mathrm{LHCb}$ are used to derive the branching fraction of the $Λ^0_b \to D^+ D^- Λ$ decay $$ {\cal B}(Λ^0_b \to D^+ D^- Λ)=(1.24 \pm 0.15 \pm 0.10 \pm 0.28 \pm 0.11) \times 10^{-4}, $$ where the third and fourth contributions are due to uncertainties of ${\cal B}(B^0 \to D^+ D^- K_{\mathrm{S}}^0)$ and $σ_{Λ^0_b} / σ_{B^0}$, respectively. Inspection of the $D^+ Λ$ and $D^+ D^-$ invariant-mass distributions suggests a rich presence of intermediate resonances in the decay. The $Λ^0_b \to D^{*+} D^- Λ$ decay is also observed for the first time as a partially reconstructed component in the $D^+ D^- Λ$ invariant mass spectrum.

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arXiv2025

Observation of the very rare $Σ^+ \to p μ^+ μ^-$ decay

The first observation of the $Σ^+ \to p μ^+ μ^-$ decay is reported with high significance using proton-proton collision data, corresponding to an integrated luminosity of $5.4\,\rm{fb}^{-1}$, collected with the LHCb detector at a centre-of-mass energy of 13~TeV. A yield of $237\pm 16$ $Σ^+ \to p μ^+ μ^-$ decays is obtained, where the uncertainty is statistical only. A branching fraction of $(1.08 \pm 0.17) \times 10^{-8}$ is measured, where the uncertainty includes statistical and systematic sources. No evidence of resonant structures is found in the dimuon invariant-mass distribution. All results are compatible with Standard Model expectations. This represents the rarest decay of a baryon ever observed.

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arXiv2025

Measurement of the branching fraction ratio $R_K$ at large dilepton invariant mass

A test of lepton universality between muons and electrons is performed using $B^+\to K^+\ell^+\ell^-$ decays (where $\ell$ = $e$, $μ$), in the dilepton invariant-mass-squared region above 14.3 GeV$^2/c^4$. The data used for the measurement consists of beauty meson decays produced in proton-proton collisions, corresponding to an integrated luminosity of 9 $\text{fb}^{-1}$, collected by the LHCb experiment between 2011 and 2018. The ratio of branching fractions for $B^+\to K^+μ^+μ^-$ and $B^+\to K^+e^+e^-$ decays is measured to be $R_K = 1.08^{+0.11}_{-0.09}\;(\text{stat})\;^{+0.04}_{-0.04}\;(\text{syst})$, which is consistent with the Standard Model prediction of unity. This constitutes the most precise test of lepton flavour universality using $B^+\to K^+\ell^+\ell^-$ decays with dilepton invariant-mass-squared above the $ψ(2S)$ mass, whilst being the first of its kind at a hadron collider.

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arXiv2025

Search for resonances decaying to photon pairs with masses between 4.9 and 19.4 GeV

A search is presented for axion-like particles (ALPs) with masses between 4.9 and 19.4 GeV decaying to a pair of photons, using proton-proton collisions collected with the LHCb detector during 2018 at a centre-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 2.1 fb$^{-1}$. The same strategy and sample is used to search for the decays of the $B^0_s$, $B^0$ and $η_b$ mesons into photon pairs. No significant excess is found. Upper limits on the photon-pair branching fraction times the cross-section of ALP production are determined as a function of the ALP mass. Limits on the branching fractions of the beauty states are determined to be $\mathcal{B}(B^0_s\toγγ)<2.7\times10^{-5}$, $\mathcal{B}(B^0\toγγ)<0.83\times10^{-5}$, and $ σ(pp\toη_b X)\times\mathcal{B}(η_b\toγγ)<765\,\text{pb}$ at 95 % confidence level.

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arXiv2025

Angular analysis of the decay $B_{s}^{0}\toϕe^+e^-$

An angular analysis of the decay $B^0_s\toϕe^+e^-$ is presented, using proton-proton collision data collected with the LHCb detector between 2011 and 2018 at centre-of-mass energies of 7, 8 and 13$\,\mathrm{Te\kern -0.1em V}$. The combined dataset corresponds to an integrated luminosity of $9\,\mathrm{fb}^{-1}$. Observables are determined by fitting time-integrated projections of the angular distribution in three bins of dielectron mass squared, $q^2$, corresponding to $[0.1,1.1]$, $[1.1,6.0]$ and $[15.0,19.0]\,\mathrm{Ge\kern -0.1em V}^2\!/c^4$. The results are compatible with predictions based on the Standard Model of particle physics.

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arXiv2025

Observation of the decay $B^0_{s}\to K^0 p \bar{p}$ and measurement of the $B^0_{(s)} \to K^0 p \bar{p}$ branching fractions

A study of the charmless baryonic decays $B^0_{(s)} \to K^0 p \bar{p}$ is presented, where $B^0_{(s)}$ denotes either a $B^0$ or a $B^0_s$ meson. The analysis is based on proton-proton collision data collected by the LHCb experiment at centre-of-mass energies of 7, 8, and $13~\mathrm{Tev}$, corresponding to an integrated luminosity of $9~\mathrm{fb}^{-1}$. The decay $B^0_s \to K^0 p \bar{p}$ is observed for the first time, with a measured branching fraction of $(9.14 \pm 1.69 \pm 0.90 \pm 0.33 \pm 0.20) \times 10^{-7}$ and a significance of $5.6σ$. The uncertainties respectively account for statistical and systematic contributions, the precision of the branching fraction of the normalisation channel $B^0 \to K^0 π^{+} π^{-}$ and the fragmentation fraction ratio ${f_s}/{f_d}$. The branching fraction determined for $B^0 \to K^0 p \bar{p}$ is $(2.82 \pm 0.08 \pm 0.12 \pm 0.10) \times 10^{-6}$, which is the most precise measurement to date.

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arXiv2025

Evidence for $B^-\rightarrow D^{**0}τ^-\overline{ν_τ}$ decays

The first evidence for the decay $B^-\rightarrow D^{**0}τ^-\overline{ν_τ}$ is obtained using proton-proton collision data collected by the LHCb experiment, corresponding to an integrated luminosity of 9 fb$^{-1}$ , at centre-of-mass energies of 7, 8 and 13 Tev. Here, the $D^{**0}$ meson represents any of the three excited charm mesons $D_{1}(2420)^{0}$, $D_{2}^{*}(2460)^{0}$, and $D_{1}^{'}(2400)^{0}$. The $B^-\rightarrow D^{**0}τ^-\overline{ν_τ}$ signal is measured with a significance of 3.5 $σ$, including systematic uncertainties. The combined branching fraction $BR(B^-\rightarrow D^{**0}_{1,2}τ^-\overline{ν_τ})\times BR(D^{**0}_{1,2}\rightarrow D^{*+}π^-)$, where $D^{**0}_{1,2}$ denotes both $D_{1}(2420)^{0}$ and $D_{2}^{*}(2460)^{0}$ contributions, is measured to be $(0.051\pm0.013(stat)\pm 0.006(syst)\pm 0.009(\rm{ext}) )\%$, where the last uncertainty reflects that of the branching fraction of the normalisation channel $B^-\rightarrow D^{**0}_{1,2}D_s^{(*)-}$. The ratio between the tauonic and muonic semileptonic $B$ decays, with the latter taken from world average values, is also determined and found to be ${\cal R}(D^{**0}_{1,2})=0.13\pm0.03(stat)\pm0.01(syst)\pm0.02\,(\rm{ext})$.

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