arXiv subjects

F. Blanc

Publications and source records attributed to F. Blanc.

At least 91 records · Page 5Linked to original sources

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.

hep-ex↗

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.

hep-ex↗

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.

hep-ex↗

arXiv2025

Search for charge-parity violation in semileptonically tagged $D^{0} \to K^{+} π^{-}$ decays

An analysis of the flavour oscillations of the charmed neutral meson is presented. The ratio of $D^{0} \to K^{+} π^{-}$ and $D^{0} \to K^{-} π^{+}$ decay rates is measured as a function of the decay time of the $D^{0}$ meson and compared with the charge-conjugated system to search for charge-parity violation. The meson flavour at production is double-tagged by the charges of the muon and pion in the preceding $\overline{B} \to D^{*}(2010)^{+} μ^{-} X$ and ${{D^{*}(2010)^{+}} \to D^{0}π^{+}}$ decays, respectively. These decays are selected from proton-proton collision data collected by the LHCb experiment at a centre-of-mass energy of ${13\,\text{TeV}}$ and corresponding to an integrated luminosity of ${5.4\,\text{fb}^{-1}}$. The flavour oscillation parameters, relating to the differences in mass and width of the mass eigenstates, are found to be ${y^\prime=(5.8\pm1.6)\times10^{-3}}$ and ${(x^\prime)^2=(0.0\pm1.2)\times10^{-4}}$. No evidence for charge-parity violation is seen either in the flavour oscillations or in the decay, where the direct charge-parity asymmetry is measured to be ${A_{D}=(2.3\pm1.7)\,{\%}}$.

hep-ex↗

arXiv2025

Search for resonance-enhanced $CP$ and angular asymmetries in the $Λ^+_{c}\to pμ^+μ^-$ decay at LHCb

The first measurement of the $CP$ asymmetry of the decay rate ($A_{CP}$) and the $CP$ average ($ΣA_{\text{FB}}$) and $CP$ asymmetry ($ΔA_{\text{FB}}$) of the forward-backward asymmetry in the muon system of $\mathitΛ^+_c\to pμ^+μ^-$ decays is reported. The measurement is performed using a data sample of proton-proton collisions, recorded by the LHCb experiment from 2016 to 2018 at a center-of-mass energy of 13$\text{ TeV}$, which corresponds to an integrated luminosity of 5.4$\text{ fb}^{-1}$. The asymmetries are measured in two regions of dimuon mass near the $ϕ$-meson mass peak. The dimuon-mass integrated results are \begin{align*} A_{CP} &= (-1.1 \pm 4.0 \pm 0.5)\%,\\ ΣA_{\text{FB}} &= (\phantom{-}3.9 \pm 4.0 \pm 0.6)\%,\\ ΔA_{\text{FB}} &= (\phantom{-}3.1 \pm 4.0 \pm 0.4)\%, \end{align*} where the first uncertainty is statistical and the second systematic. The results are consistent with the conservation of $CP$ symmetry and the Standard Model expectations.

hep-ex↗

arXiv2025

Comprehensive analysis of local and nonlocal amplitudes in the $B^0\rightarrow K^{*0}μ^+μ^-$ decay

A comprehensive study of the local and nonlocal amplitudes contributing to the decay $B^0\rightarrow K^{*0}(\to K^+π^-) μ^+μ^-$ is performed by analysing the phase-space distribution of the decay products. The analysis is based on $pp$ collision data corresponding to an integrated luminosity of 8.4fb$^{-1}$ collected by the LHCb experiment. This measurement employs for the first time a model of both one-particle and two-particle nonlocal amplitudes, and utilises the complete dimuon mass spectrum without any veto regions around the narrow charmonium resonances. In this way it is possible to explicitly isolate the local and nonlocal contributions and capture the interference between them. The results show that interference with nonlocal contributions, although larger than predicted, only has a minor impact on the Wilson Coefficients determined from the fit to the data. For the local contributions, the Wilson Coefficient $C_9$, responsible for vector dimuon currents, exhibits a $2.1σ$ deviation from the Standard Model expectation. The Wilson Coefficients $C_{10}$, $C_{9}'$ and $C_{10}'$ are all in better agreement than $C_{9}$ with the Standard Model and the global significance is at the level of $1.5σ$. The model used also accounts for nonlocal contributions from $B^{0}\to K^{*0}\left[τ^+τ^-\to μ^+μ^-\right]$ rescattering, resulting in the first direct measurement of the $b sττ$ vector effective-coupling $C_{9τ}$.

hep-ex↗

arXiv2025

Search for $D^0$ meson decays to $π^+ π^- e^+ e^-$ and $K^+ K^- e^+ e^-$ final states

A search for $D^0$ meson decays to the $π^+π^-e^+e^-$ and $K^+K^-e^+e^-$ final states is reported using a sample of proton-proton collisions collected by the LHCb experiment at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 6 fb$^{-1}$. The decay $D^0 \rightarrow π^+π^-e^+e^-$ is observed for the first time when requiring that the two electrons are consistent with coming from the decay of a $ϕ$ or $ρ^0/ω$ meson. The corresponding branching fractions are measured relative to the $D^0 \rightarrow K^-π^-[e^+e^-]_{ρ^0/ω}$ decay, where the two electrons are consistent with coming from the decay of a $ρ^0$ or $ω$ meson. No evidence is found for the $D^0 \rightarrow K^+K^-e^+e^-$ decay and world-best limits are set on its branching fraction. The results are compared to, and found to be consistent with, the branching fractions of the $D^0 \rightarrow π^+π^-μ^+μ^-$ and $D^0 \rightarrow K^+K^-μ^+μ^-$ decays recently measured by LHCb and confirm lepton universality at the current precision.

hep-ex↗

arXiv2025

Study of light-meson resonances decaying to $K^0_{\rm S} K π$ in the $B \to (K^0_{\rm S} K π) K$ channels

A study is presented of $B^+ \to K^0_{\rm S} K^- π^+ K^-$ and $B^+ \to K^0_{\rm S} K^+ π^- K^+$ decays based on the analysis of proton-proton collision data collected with the LHCb detector at centre-of-mass energies of 7, 8 and 13 TeV, corresponding to an integrated luminosity of $9 fb^{-1}$. The $K^0_{\rm S} K π$ invariant-mass distributions of both $B^+$ decay modes show, in the $m(K^0_{\rm S} K π)<1.85$ GeV mass region, large activity which is resolved using an amplitude analysis. A simple model, were $J^{PC}$ amplitudes are described by multiple Breit--Wigner functions with appropriate angular distributions provides a good description of the experimental data. In this approach a complex mixture of $J^{PC}=0^{-+}, 1^{++}$ and $1^{+-}$ amplitudes is observed that is dominated by $η(1405)$, $η(1470)$, $η(1760)$, $f_1(1285)$, $f_1(1420)$ and $h_1(1405)$ resonances. The $K^0_{\rm S} K π$ Dalitz plots are dominated by asymmetric crossing $K^* \bar{K}$ bands which are different for the two $B^+$ decay modes. This is due to a different interference pattern between the $1^{++}$ and $1^{+-}$ amplitudes in the two channels. Branching fractions are measured for each resonant contribution.

hep-ex↗

arXiv2025

Branching fraction measurement of the decay $B^+ \to ψ(2S) ϕ(1020) K^+$

The branching fraction of the decay $B^+\to ψ(2S)ϕ(1020)K^+$, relative to the topologically similar decay $B^+\to J/ψϕ(1020) K^+$, is measured using proton-proton collision data collected by the LHCb experiment at center-of-mass energies of 7, 8, and 13 TeV, corresponding to an integrated luminosity of $9\,\mathrm{fb}^{-1}$. The ratio is found to be $0.061 \pm 0.004 \pm 0.009$, where the first uncertainty is statistical and the second systematic. Using the world-average branching fraction for $B^+ \to J/ψϕ(1020) K^+$, the branching fraction for the decay $B^+\to ψ(2S) ϕ(1020) K^+$ is found to be $ (3.0 \pm 0.2 \pm 0.5 \pm 0.2) \times 10^{-6}$, where the first uncertainty is statistical, the second systematic, and the third is due to the branching fraction of the normalization channel.

hep-ex↗

arXiv2025

Test of lepton flavour universality with $B^+ \to K^+π^+π^-\ell^+\ell^-$ decays

The first test of lepton flavor universality between muons and electrons using $B^+ \to K^+π^+π^-\ell^+\ell^-$ ($\ell=e,μ$) decays is presented. The measurement is performed with data from proton-proton collisions collected by the LHCb experiment at center-of-mass energies of 7, 8, and 13 TeV, corresponding to an integrated luminosity of $9\mathrm{fb}^{-1}$. The ratio of branching fractions between $B^+ \to K^+π^+π^-e^+e^-$ and $B^+ \to K^+π^+π^-μ^+μ^-$decays is measured in the dilepton invariant-mass-squared range $1.1 < q^2 < 7.0~\mathrm{GeV}^2/c^4$ and is found to be $R_{Kππ}^{-1} = 1.31^{+0.18}_{-0.17} \;(\mathrm{stat})\;^{+0.12}_{-0.09} \;(\mathrm{syst})$, in agreement with the standard model prediction. The first observation of the $B^+ \to K^+π^+π^-e^+e^-$ decay is also reported.

hep-ex↗

arXiv2025

Measurement of $CP$ asymmetries in $Λ_b^0\to ph^{-}$ decays

A search for $CP$ violation in $Λ_b^0\rightarrow pK^-$ and $Λ_b^0\rightarrow pπ^-$ decays is presented using the full Run 1 and Run 2 data samples of $pp$ collisions collected with the LHCb detector, corresponding to an integrated luminosity of 9 $\mathrm{fb}^{-1}$ at center-of-mass energies of 7, 8, and 13 TeV. For the Run 2 data sample, the $CP$-violating asymmetries are measured to be $A_{CP}^{pK^-} = (-1.4 \pm 0.7 \pm 0.4)\%$ and $A_{CP}^{pπ^-} = (0.4 \pm 0.9 \pm 0.4)\%$, where the first uncertainty is statistical and the second is systematic. Following significant improvements in the evaluation of systematic uncertainties compared to the previous LHCb measurement, the Run 1 dataset is reanalyzed to update the corresponding results. When combining the Run 2 and updated Run 1 measurements, the final results are found to be $A_{CP}^{pK^-} = (-1.1 \pm 0.7 \pm 0.4)\%$ and $A_{CP}^{pπ^-} = (0.2 \pm 0.8 \pm 0.4)\%$, constituting the most precise measurements of these asymmetries to date.

hep-ex↗

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.

hep-ex↗

arXiv2025

Amplitude analysis of $B^+ \to ψ(2S) K^+ π^+ π^-$ decays

The first full amplitude analysis of $B^+ \to ψ(2S) K^+ π^+ π^-$ decays is performed using proton-proton collision data corresponding to an integrated luminosity of $9\,\text{fb}^{-1}$ recorded with the LHCb detector. The rich $K^+ π^+ π^-$ spectrum is studied and the branching fractions of the resonant substructure associated with the prominent $K_1(1270)^+$ contribution are measured. The data cannot be described by conventional strange and charmonium resonances only. An amplitude model with 53 components is developed comprising 11 hidden-charm exotic hadrons. New production mechanisms for charged charmonium-like states are observed. Significant resonant activity with spin-parity $J^P = 1^+$ in the $ψ(2S) π^+$ system is confirmed and a multi-pole structure is demonstrated. The spectral decomposition of the $ψ(2S) π^+ π^-$ invariant-mass structure, dominated by $X^0 \to ψ(2S) ρ(770)^0$ decays, broadly resembles the $J/ψϕ$ spectrum observed in $B^+ \to J/ψϕK^+$ decays. Exotic $ψ(2S) K^+ π^-$ resonances are observed for the first time.

hep-ex↗

arXiv2025

Measurement of exclusive $J/ψ$ and $ψ(2S)$ production at $\sqrt{s}=13$ TeV

Measurements are presented of the cross-section for the central exclusive production of $J/ψ\toμ^+μ^-$ and $ψ(2S)\toμ^+μ^-$ processes in proton-proton collisions at $\sqrt{s} = 13 $ TeV with 2016-2018 data. They are performed by requiring both muons to be in the LHCb acceptance (with pseudorapidity $2<η_{μ^\pm} < 4.5$) and mesons in the rapidity range $2.0 < y < 4.5$. The integrated cross-section results are \begin{equation*} σ_{J/ψ\toμ^+μ^-}(2.0<y_{J/ψ}<4.5,2.0<η_{μ^\pm} < 4.5) = 400 \pm 2 \pm 5 \pm 12 \,{\rm pb}\,, \end{equation*} \begin{equation*} σ_{ψ(2S)\toμ^+μ^-}(2.0<y_{ψ(2S)}<4.5,2.0<η_{μ^\pm} < 4.5) = 9.40 \pm 0.15 \pm 0.13 \pm 0.27 \,{\rm pb}\,, \end{equation*} where the uncertainties are statistical, systematic and due to the luminosity determination. In addition, a measurement of the ratio of $ψ(2S)$ and $J/ψ$ cross-sections, at an average photon-proton centre-of-mass energy of 1 TeV, is performed, giving \begin{equation*} \frac{σ_{ψ(2S)}}{σ_{J/ψ}} = 0.1763 \pm 0.0029 \pm 0.0008 \pm 0.0039 \,, \end{equation*} where the first uncertainty is statistical, the second systematic and the third due to the knowledge of the involved branching fractions. For the first time, the dependence of the $J/ψ$ and $ψ(2S)$ cross-sections on the total transverse momentum transfer is determined in $pp$ collisions and is found consistent with the behaviour observed in electron-proton collisions.

hep-ex↗

arXiv2025

Measurement of the branching fraction ratios $R(D^{+})$ and $R(D^{*+})$ using muonic $τ$ decays

The branching fraction ratios of $\overline{B}^0\to D^+τ^-\overlineν_τ$ and $\overline{B}^0\to D^{*+}τ^-\overlineν_τ$ decays are measured with respect to their muonic counterparts, using a data sample corresponding to an integrated luminosity of 2.0 fb$^{-1}$ collected by the LHCb experiment in proton-proton collisions at $\sqrt{s} = 13$ TeV. The reconstructed final states are formed by combining $D^+$ mesons with $τ^-\toμ^-\overlineν_μν_τ$ candidates, where the $D^+$ is reconstructed via the $D^+\to K^-π^+π^+$ decay. The results are \begin{align*} R(D^{+}) &= 0.249 \pm 0.043 \pm 0.047, R(D^{*+}) &= 0.402 \pm 0.081\pm 0.085, \end{align*} where the first uncertainties are statistical and the second systematic. The two measurements have a correlation coefficient of $-0.39$ and are compatible with the Standard Model.

hep-ex↗

arXiv2025

Production of $η$ and $η'$ mesons in $pp$ and $p$Pb collisions

The production of $η$ and $η'$ mesons is studied in proton-proton and proton-lead collisions collected with the LHCb detector. Proton-proton collisions are studied at center-of-mass energies of $5.02$ and $13~{\rm TeV}$, and proton-lead collisions are studied at a center-of-mass energy per nucleon of $8.16~{\rm TeV}$. The studies are performed in center-of-mass rapidity regions $2.5<y_{\rm c.m.}<3.5$ (forward rapidity) and $-4.0<y_{\rm c.m.}<-3.0$ (backward rapidity) defined relative to the proton beam direction. The $η$ and $η'$ production cross sections are measured differentially as a function of transverse momentum for $1.5<p_{\rm T}<10~{\rm GeV}$ and $3<p_{\rm T}<10~{\rm GeV}$, respectively. The differential cross sections are used to calculate nuclear modification factors. The nuclear modification factors for $η$ and $η'$ mesons agree at both forward and backward rapidity, showing no significant evidence of mass dependence. The differential cross sections of $η$ mesons are also used to calculate $η/π^0$ cross section ratios, which show evidence of a deviation from the world average. These studies offer new constraints on mass-dependent nuclear effects in heavy-ion collisions, as well as $η$ and $η'$ meson fragmentation.

nucl-ex↗

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.

hep-ex↗

arXiv2025

A measurement of $ΔΓ_{s}$

Using a dataset corresponding to $9~\mathrm{fb}^{-1}$ of integrated luminosity collected with the LHCb detector between 2011 and 2018 in proton-proton collisions, the decay-time distributions of the decay modes $B_s^0 \rightarrow J/ψη'$ and $B_s^0 \rightarrow J/ψπ^{+} π^{-}$ are studied. The decay-width difference between the light and heavy mass eigenstates of the $B_s^0$ meson is measured to be $ΔΓ_s = 0.087 \pm 0.012 \pm 0.009 \, \mathrm{ps}^{-1}$, where the first uncertainty is statistical and the second systematic.

hep-ex↗