arXiv subjects

A. Bizzeti

Publications and source records attributed to A. Bizzeti.

At least 91 records · Page 5Linked to original sources

arXiv2026

Observation of the rare baryonic decay $B^{+}\rightarrow p \bar{\itΛ}$ and measurement of its weak decay parameter

The first observation of the decay $B^{+}\rightarrow p \bar{\itΛ}$ is presented, using proton-proton collision data collected by the LHCb experiment between 2016 and 2018 at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of $5.4\,\mathrm{fb}^{-1}$. The signal significance exceeds seven standard deviations. Using the $B^{+} \rightarrow K^{\mathrm{0}}_{\mathrm{S}} π^{+}$ decay as a normalization channel, the branching fraction is measured and combined with previous LHCb results based on data collected at 7 and 8 TeV in 2011 and 2012, yielding $\mathcal{B}(B^{+}\rightarrow p \bar{\itΛ})=(1.24\pm 0.17\pm 0.05\pm 0.03)\times 10^{-7}$, where the first uncertainty is statistical, the second is systematic, and the third comes from the uncertainty on the branching fraction of the normalization channel. The $B^{+}\rightarrow p \bar{\itΛ}$ weak decay parameter is measured to be $α_B = 0.87_{-0.29}^{+0.26} \pm 0.09$, indicating the presence of comparable S-wave and P-wave decay amplitudes.

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arXiv2026

Measurement of transverse $Λ$ and $\barΛ$ hyperon polarization in $p$Pb collisions at $\sqrt{s_{NN}} = 5.02$ TeV

The transverse polarization of $Λ$ and $\barΛ$ hyperons is measured in $p$Pb collisions collected by the LHCb experiment at a nucleon-nucleon center-of-mass energy of $5.02$ TeV. The polarization is averaged over hyperon transverse momentum in the ranges $0.15 < p_{T} < 6.00 $ GeV/$c$, and Feynman-$x$ in the ranges $0.005 < x_{F} < 0.040$ (forward region) and $-0.10 < x_{F} < -0.01$ (backward region) defined relative to the proton beam direction. The transverse polarization is found to be compatible with zero for both $Λ$ and $\barΛ$ hyperons. The results are also measured as a function of $p_{T}$ and $x_{F}$ with no significant dependence on these variables observed. The results are compared with previous experimental measurements at different center-of-mass energies and collision environments.

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arXiv2025

Coherent photoproduction of $ρ^0, ω$ and excited vector mesons in ultraperipheral PbPb collisions

The invariant-mass distribution for the coherent photoproduction of dipions in ultraperipheral PbPb collisions is measured using data, corresponding to an integrated luminosity of $224.6 \pm 9.6 μ$b$^{-1}$, collected by the LHCb experiment in 2018 at a nucleon-nucleon centre-of-mass energy $\sqrt{s_{\rm NN}}=5.02$ TeV. In the mass range from 400 to 1200 MeV, the results are consistent with previous experiments, with the spectrum dominated by the $ρ^0$ meson, which interferes with a nonresonant component, together with a smaller $ω$ meson contribution. In an extended mass range up to 2300 MeV, models previously used do not fit the data and a consistent description requires the introduction of two resonances at masses of $1350\pm20$ MeV and $1790\pm20$ MeV with widths of about 300 MeV. The cross-section for each meson is measured differentially in twelve bins of rapidity from 2.05 to 4.90. The $ρ^0$ cross-section increases with rapidity from about 400 to 600 mb and is measured with a typical precision of 8\%, while the cross-section times branching fraction for the $ω,ρ^\prime$ and $ρ^{\prime\prime}$, with the statistical precision of the data, do not have a pronounced rapidity dependence and are between 0.5 and 1.5 mb, with uncertainties up to 30\%. A large nuclear suppression is observed for the $ρ^0$ meson compared to expectations based on photoproduction on the proton that use the impulse approximation. Significant suppression is also observed compared to that predicted by elastic scattering described in the Glauber approach, or with the addition of inelastic scattering in a Gribov--Glauber model.

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arXiv2025

Measurement of the $B^0\rightarrow ρ(770)^{0}γ$ branching fraction

The ratio between the branching fractions of the $B^0\rightarrow ρ(770)^{0}γ$ and $B^{0}\rightarrow K^{*}(892)^{0}γ$ decays is measured with 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 measured value is \begin{equation*} \frac{{\cal B}(B^0\rightarrow ρ(770)^{0}γ)}{{\cal B}(B^0\rightarrow K^{*}(892)^{0}γ)}=0.0189\pm 0.0007\pm 0.0005, \end{equation*} where the first uncertainty is statistical and the second systematic. The branching fraction for $B^0\rightarrow ρ(770)^{0}γ$ decays is hence obtained as \begin{equation*} {\cal{B}}(B^0\rightarrow ρ(770)^{0}γ) =(7.9\pm 0.3\pm 0.2\pm 0.2) \times 10^{-7}, \end{equation*} where the last uncertainty is due to the branching fraction of the normalisation mode. This result assumes that both the $ρ(770)^0$ and $K^{*}(892)^0$ decays saturate the dihadron mass spectra considered in the analysis. It is consistent with the current world-average value and by far the most precise measurement to date.

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arXiv2025

Search for the $B^+_c\rightarrow χ_{c1}(3872)π^+$ decay

A search for the decay $B^+_c\rightarrow χ_{c1}(3872)π^+$ is reported using proton-proton collision data collected with the LHCb detector between 2011 and 2018 at centre-of-mass energies of 7, 8, and 13 $TeV$, corresponding to an integrated luminosity of $9fb^{-1}$. No significant signal is observed. Using the decay $B^+_c\rightarrow ψ(2S)π^+$ as a normalisation channel, an upper limit for the ratio of branching fractions $$ \mathcal{R}^{χ_{c1}(3872)}_{ψ(2S)} = \frac{\mathcal{B}_{B^+_c\rightarrow χ_{c1}(3872)π^+}} {\mathcal{B}_{B^+_c\rightarrow ψ(2S)π^+}} \times \frac{\mathcal{B}_{χ_{c1}(3872)\rightarrow J/ψπ^+π^-}} {\mathcal{B}_{ψ(2S)\rightarrow J/ψπ^+π^-}} < 0.05\,(0.06)\,, $$ is set at the 90\,(95)\% confidence level.

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arXiv2025

Search for the decay $B^0 \rightarrow ϕϕ$

A search for the decay $B^0 \rightarrow ϕϕ$ is made using $pp$ 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$^{-1}$. No significant signal is observed, and an upper limit on the branching fraction of $1.3~(1.4)\times 10^{-8}$ at $90 ~(95) \%$ confidence level is set. This result supersedes the previous LHCb study and improves the upper limit by a factor of two.

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arXiv2025

Search for the lepton-flavour-violating decays $B^0 \to K^{*0} τ^\pm e^\mp$

A first search for the lepton-flavour-violating decays $B^0\to K^{*0}τ^\pm e^\mp$ is presented. The analysis is performed using a sample of proton-proton collision data, collected with the LHCb detector at a centre-of-mass energy of 13 TeV between 2016 and 2018, corresponding to an integrated luminosity of 5.4 fb$^{-1}$. No significant signal is observed, and upper limits on the branching fractions are determined to be $\cal{B}$$(B^0 \to K^{*0}τ^-e^+)< 5.9$ $(7.1)\times 10^{-6}$ and $\cal{B}$$(B^0 \to K^{*0}τ^+e^-)< 4.9$ $(5.9)\times 10^{-6}$ at the 90% (95%) confidence level.

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arXiv2025

Study of $B_{c}(1P)^{+}$ states in the $B_{c}^{+} γ$ mass spectrum

The study of a wide peaking structure in the $B_{c}^{+} γ$ mass spectrum is reported using a data sample of proton-proton collisions collected by the LHCb detector at center-of-mass energies of $7$, $8$, and $13~\text{TeV}$, corresponding to an integrated luminosity of $9~\text{fb}^{-1}$. The observed structure is consistent with the lowest excited $P$-wave $B_{c}^{+}$ states and exhibits a statistical significance exceeding seven standard deviations relative to the background-only hypothesis. A two-peak model serves as an effective description of the data, with various theory-constrained models further explored to provide physical interpretation. Based on the predictions for the $B_{c}(1P)^{+}$ spectrum, the relative production cross-section of the overall $B_{c}(1P)^{+}$ states with respect to the $B_{c}^{+}$ ground state with the transverse momentum $p_{\text{T}}$ and rapidity $y$ of $B_{c}^{+}$ mesons in the regions $p_{\text{T}}<20~\mathrm{Ge\kern -0.1em V\!/}c$ and $2.0<y<4.5$ at $\sqrt{s}=13~\text{TeV}$ is measured to be $0.20 \pm 0.03 \pm 0.02 \pm 0.03$, where the uncertainty terms represent statistical, systematic, and uncertainties related to the choice of theoretical models, respectively. The results provide a test of theoretical models and deepen our understanding of quantum chromodynamics.

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arXiv2025

Observation of orbitally excited $B_{c}^{+}$ states

The observation of a wide peaking structure in the $B_{c}^{+} γ$ mass spectrum is reported using proton-proton collision data collected by the LHCb detector at center-of-mass energies of $7$, $8$, and $13~\text{TeV}$, corresponding to a total integrated luminosity of $9~\text{fb}^{-1}$. The statistical significance over the background-only hypothesis exceeds seven standard deviations. The width of the observed structure is larger than the expectation from a single-peak hypothesis, and is well described by an effective minimal model consisting of two narrow peaks located at $6704.8 \pm 5.5 \pm 2.8 \pm 0.3~\mathrm{Me\kern -0.1em V\!/}c^2$ and $6752.4 \pm 9.5 \pm 3.1 \pm 0.3~\mathrm{Me\kern -0.1em V\!/}c^2$. The uncertainty terms are statistical, systematic, and associated to the knowledge of the $B_{c}^{+}$ mass, respectively. The measured peak locations are in line with theoretical predictions for lowest excited $P$-wave $B_{c}^{+}$ states, marking the first observation of orbitally excited beauty-charm mesons and providing important insights into the internal dynamics of hadrons containing two heavy quarks.

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arXiv2025

Deuteron identification via time of flight with LHCb

It is shown that the timing capabilities of the LHCb detector operated during the LHC Run 2 can be used to identify light ion particles with momenta of a few GeV/$c$. This is achieved by estimating the particle time of flight through a newly developed technique. A dedicated reconstruction procedure and a neural-network-based estimator of the particle speed have been developed to enable deuteron identification by suppressing the abundant background from lighter particles. The performance of the identification procedure is demonstrated in a sample of proton-helium collisions at $\sqrt{s_{\text{NN}}}=110$ GeV, where the production of deuteron and triton particles is observed. This novel approach opens the way to study deuteron and antideuteron production for different collision systems at different energy scales, exploiting the rich dataset collected by the LHCb experiment.

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arXiv2025

Inclusive $B$-meson flavour-tagging algorithm at LHCb

A new algorithm is developed to identify the flavour of neutral $B$ mesons at production in $pp$ collisions by utilising all tracks from the hadronisation process. The algorithm is calibrated separately for $B^0$ and $B^{0}_{s}$ mesons using $B^{0}\to J/ψK^{+}π^-$ and $B^{0}_{s}\to D_{s}^{-}π^+$ decays from $pp$ collision data collected by the LHCb experiment at a centre-of-mass energy of 13\,TeV. This new algorithm improves the tagging power by 35\% for $B^{0}$ mesons and 20\% for $B^{0}_{s}$ mesons when compared to the combined performance of the existing LHCb flavour-tagging algorithms.

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arXiv2025

Measurement of the $ψ(2S)$ to $J/ψ$ cross-section ratio as a function of centrality in PbPb collisions at $\sqrt{s_{\text{NN}}}$ = 5.02 TeV

The dissociation of quarkonium states with different binding energies produced in heavy-ion collisions is a powerful probe for investigating the formation and properties of the quark-gluon plasma. The ratio of production cross-sections of $ψ(2S)$ and $J/ψ$ mesons times the ratio of their branching fractions into the dimuon final state is measured as a function of centrality using data collected by the LHCb detector in PbPb collisions at $\sqrt{s_{\text{NN}}}$ = 5.02 TeV. The measured ratio shows no dependence on the collision centrality, and is compared to the latest theory predictions and to the recent measurements in literature.

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arXiv2025

Analysis of $\itΛ^\mathrm{0}_b \rightarrow pK^-μ^+μ^-$ decays

The differential branching fraction and angular coefficients of $\itΛ^\mathrm{0}_b \rightarrow pK^-μ^+μ^-$ decays are measured in bins of the dimuon mass squared and dihadron mass. The analysis is performed using a data set corresponding to 9$\text{fb}^{-1}$ of integrated luminosity collected with the $\mbox{LHCb}$ detector between 2011 and 2018. The data are consistent with receiving contributions from a mixture of $\itΛ$ resonances with different spin-parity quantum numbers. The angular coefficients show a pattern of vector-axial vector interference that is a characteristic of the type of flavour-changing neutral-current transition relevant for these decays.

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arXiv2025

Amplitude analysis of the $Ξ^+_c\to pK^-π^+$ decay and $Ξ^+_c$ baryon polarization measurement in semileptonic beauty-hadron decays

An amplitude analysis of the $Ξ^+_c\to pK^-π^+$ decay together with a measurement of the $Ξ^+_c$ polarization vector in semileptonic beauty-hadron decays is presented. The analysis is performed using proton-proton collision data collected by the LHCb experiment, corresponding to an integrated luminosity of 9 ${\rm fb}^{-1}$. An amplitude model is developed and the resonance fractions as well as two- and three-body decay parameters are reported. A sizeable $Ξ^+_c$ polarization is found. A large sensitivity of the $Ξ^+_c\to pK^-π^+$ decay to the polarization is seen, making the amplitude model suitable for $Ξ^+_c$ polarization measurements in other systems.

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arXiv2025

First measurement of $b$-jet mass with and without grooming

The LHCb collaboration presents a novel suite of heavy-flavour jet substructure measurements at forward rapidity in proton-proton collisions at a centre-of-mass energy of $\sqrt{s} = 13$ TeV. The jet mass is a perturbatively calculable probe of the virtuality of hard-scattered quarks and gluons, connecting small-distance quantum chromodynamics (QCD) with long-distance experimental measurement. It becomes dominated by nonperturbative corrections at small values, presenting an excellent test of QCD across a broad range of energies. Measuring heavy-flavour jet mass with a theoretically unambiguous flavour definition for the first time probes the gluon splitting mechanism for heavy-flavour production and pushes tests of perturbative QCD to unprecedented theoretical precision. Utilising the soft drop jet-grooming technique to access the perturbative jet core further enhances constraints on first-principles theory. Measurements of the jet mass for jets containing fully reconstructed $B^\pm$ hadrons are reported with and without grooming. These results offer unparalleled tests of quark flavour and mass dependence in QCD and provide a baseline for future studies of heavy-flavour jet quenching in heavy-ion collisions.

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arXiv2025

Measurement of the Lund plane for light- and beauty-quark jets

The substructure of jets in quantum chromodynamics (QCD) has garnered significant attention with the advent of infrared- and collinear-safe clustering algorithms and observables. A key question emerging from these studies is how in-jet emissions at soft and hard energy scales, across collinear and wide angles relative to the emitter, differ with the mass of the emitting parton. The Lund jet plane (LJP) is a perturbatively well-defined substructure observable that maps the radiation pattern of jets onto a plane, visually distinguishing emissions with different kinematic properties. Comparing LJP for jets containing hadrons of low versus high mass enables the testing of QCD splitting functions from first-principles calculations across both soft and hard regimes and at different radiation angles. This article presents the first measurement of the LJP for light-quark-enriched and beauty-initiated jets at center-of-mass energy of 13\tev at LHCb. This marks the first direct observation of the dead-cone effect in beauty-quark jets, measured in the collinear region of the LJP.

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arXiv2025

Rapidity and multiplicity dependence of charged-particle flow in $p$Pb collisions at $\sqrt{s_{NN}} = 8.16$ TeV

The elliptic and triangular flow of charged particles are measured using two-particle angular correlations in $p$Pb collisions in the pseudorapidity range \cal{2.0 $< |η| <$ 4.8}. The data sample was collected by the LHCb experiment in 2016 at a centre-of-mass energy per nucleon pair of $\sqrt{s_{NN}} = 8.16$ TeV, containing in total approximately 1.5 billion collision events. Non-flow contributions are obtained in low-multiplicity collisions and subtracted to extract the flow harmonics. The results are presented as a function of event multiplicity and hadron transverse momentum. Comparisons with a full (3+1)D dynamic model indicate that it overestimates the measured elliptic flow. A comparison between the forward and backward regions reveals no significant differences in flow parameters, suggesting that final-state effects may dominate over initial-state effects in the origin of flow in small systems.

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arXiv2025

Observation of the doubly-charmed-baryon decay ${\it Ξ}_{cc}^{++}\to{\it Ξ}_{c}^{0}π^{+}π^{+}$

A search for the doubly-charmed-baryon decay ${\it Ξ}_{cc}^{++}\to{\it Ξ}_{c}^{0}π^{+}π^{+}$ is performed using 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 $5.4\text{fb}^{-1}$. A significant structure consistent with the ${\it Ξ}_{cc}^{++}$ baryon is observed in the ${\it Ξ}_{c}^{0} π^{+}π^{+}$ invariant-mass spectrum. Using the ${\it Ξ}_{cc}^{++}\to{\it Λ}_{c}^{+}K^{-}π^{+}π^{+}$ decay as the normalisation channel, the branching fraction ratio, $\frac{{\cal B}({\it Ξ}_{cc}^{++} \to {\it Ξ}_{c}^{0}π^{+}π^{+})} {{\cal B}({\it Ξ}_{cc}^{++}\to{\it Λ}_{c}^{+} K^{-}π^{+}π^{+})}$, is measured to be $1.37\pm 0.18\text{(stat)} \pm 0.09\text{(syst)} \pm 0.35\text{(ext)}$. This measurement provides critical input for testing QCD factorisation methods in the weak decays of doubly-heavy baryons, particularly in quantifying nonperturbative effects such as final-state interactions and resonance contributions to the hadronisation process.

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