arXiv subjects

A. Anelli

Publications and source records attributed to A. Anelli.

At least 181 records · Page 10Linked to original sources

arXiv2024

Search for the rare decay of charmed baryon $Λ_c^+$ into $p μ^+ μ^-$ final state

A search for the nonresonant $Λ_c^+ \to p μ^+ μ^-$ decay is performed using proton-proton collision data recorded at a centre-of-mass energy of 13 TeV by the LHCb experiment, corresponding to an integrated luminosity of 5.4 fb$^{-1}$. No evidence for the decay is found in the dimuon invariant-mass regions where the expected contributions of resonances is subdominant. The upper limit on the branching fraction of the $Λ_c^+ \to p μ^+ μ^-$ decay is determined to be $2.9~(3.2) \times 10^{-8}$ at 90% (95%) confidence level. The branching fractions in the dimuon invariant-mass regions dominated by the $η$, $ρ$ and $ω$ resonances are also determined.

hep-ex↗

arXiv2024

Tracking of charged particles with nanosecond lifetimes at LHCb

A method is presented to reconstruct charged particles with lifetimes between 10 ps and 10 ns, which considers a combination of their decay products and the partial tracks created by the initial charged particle. Using the $Ξ^-$ baryon as a benchmark, the method is demonstrated with simulated events and proton-proton collision data at $\sqrt{s}=13$ TeV, corresponding to an integrated luminosity of 2.0 fb${}^{-1}$ collected with the LHCb detector in 2018. Significant improvements in the angular resolution and the signal purity are obtained. The method is implemented as part of the LHCb Run 3 event trigger in a set of requirements to select detached hyperons. This is the first demonstration of the applicability of this approach at the LHC, and the first to show its scaling with instantaneous luminosity.

hep-ex↗

arXiv2024

Amplitude analysis and branching fraction measurement of $B^{+}\to D^{*-}D^{+}_{s}π^{+}$ decays

The decays of the $B^{+}$ meson to the final state $D^{*-}D^{+}_{s}π^{+}$ are studied in proton-proton collision data collected with the LHCb detector at centre-of-mass energies of 7, 8, and 13 TeV, corresponding to a total integrated luminosity of 9 fb$^{-1}$. The ratio of branching fractions of the $B^{+}\to D^{*-}D^{+}_{s}π^{+}$ and $B^{0}\to D^{*-}D^{+}_{s}$ decays is measured to be $0.173\pm 0.006\pm 0.010$, where the first uncertainty is statistical and the second is systematic. Using partially reconstructed $D^{*+}_{s}\to D^{+}_{s}γ$ and $D^{+}_{s}π^{0}$ decays, the ratio of branching fractions between the $B^{+}\to D^{*-}D^{*+}_{s}π^{+}$ and $B^{+}\to D^{*-}D^{+}_{s}π^{+}$ decays is determined as $1.31\pm 0.07\pm 0.14$. An amplitude analysis of the $B^{+}\to D^{*-}D^{+}_{s}π^{+}$ decay is performed for the first time, revealing dominant contributions from known excited charm resonances decaying to the $D^{*-}π^{+}$ final state. No significant evidence of exotic contributions in the $D^{+}_{s}π^{+}$ or $D^{*-}D^{+}_{s}$ channels is found. The fit fraction of the scalar state $T_{c\bar{s} 0}^{\ast}(2900)^{++}$ observed in the $B^{+}\to D^{-}D^{+}_{s}π^{+}$ decay is determined to be less than 2.3% at a 90% confidence level.

hep-ex↗

arXiv2024

Search for time-dependent $CP$ violation in $D^0 \rightarrow π^+ π^- π^0$ decays

A measurement of time-dependent $CP$ violation in $D^0 \rightarrow π^+ π^- π^0$ decays using a $pp$ collision data sample collected by the LHCb experiment in 2012 and from 2015 to 2018, corresponding to an integrated luminosity of 7.7$\,\mathrm{fb}^{-1}$, is presented. The initial flavour of each $D^0$ candidate is determined from the charge of the pion produced in the $D^*(2010)^+ \rightarrow D^0 π^+$ decay. The decay $D^0 \rightarrow K^- π^+ π^0$ is used as a control channel to validate the measurement procedure. The gradient of the time-dependent $CP$ asymmetry, $ΔY$, in $D^0 \rightarrow π^+ π^- π^0$ decays is measured to be \begin{equation*} ΔY = (-1.3 \pm 6.3 \pm 2.4) \times 10^{-4}, \end{equation*} where the first uncertainty is statistical and the second is systematic, which is compatible with $CP$ conservation.

hep-ex↗

arXiv2024

First observation of $Λ_{b}^{0} \rightarrow Σ_c^{()++} D^{()-} K^{-}$ decays

The four decays, $Λ_{b}^{0} \rightarrow Σ_c^{(*)++} D^{(*)-} K^{-}$, are observed for the first time using proton-proton collision data collected with the LHCb detector at a centre-of-mass energy of $13\,\rm{TeV}$, corresponding to an integrated luminosity of $6\,\rm{fb}^{-1}$. By considering the $Λ_b^0 \rightarrow Λ_c^{+} \overline{D}^0 K^{-}$ decay as reference channel, the following branching fraction ratios are measured to be $$\frac{\cal{B} (Λ_{b}^{0} \rightarrow Σ_{c}^{++} \rm{D}^{-} {K}^{-})}{\cal{B}(Λ_{b}^{0} \rightarrow Λ_c^{+} \rm \overline{D}^0 {K}^{-})} = {0.282}\pm{0.016}\pm{0.016}\pm{0.005}, \frac{\cal{B}(Λ_{b}^{0} \rightarrow Σ_{c}^{*++} \rm {D}^{-} {K}^{-})}{\cal{B}(Λ_{b}^{0} \rightarrow Σ_c^{++} \rm {D}^{-} {K}^{-})} = {0.460}\pm{0.052}\pm{0.028}, \frac{\cal{B}(Λ_{b}^{0} \rightarrow Σ_{c}^{++} \rm {D}^{*-} {K}^{-})}{\cal{B}(Λ_{b}^{0} \rightarrow Σ_c^{++} \rm {D}^{-} {K}^{-})} = {2.261}\pm{0.202}\pm{0.129}\pm{0.046}, \frac{\cal{B}(Λ_{b}^{0} \rightarrow Σ_{c}^{*++} \rm D^{*-} K^{-})}{\cal{B}(Λ_{b}^{0} \rightarrow Σ_c^{++} \rm D^{-} K^{-})} = {0.896}\pm{0.137}\pm{0.066}\pm{0.018},$$ where the first uncertainties are statistical, the second are systematic, and the third are due to uncertainties in the branching fractions of intermediate particle decays. These initial observations mark the beginning of pentaquark searches in these modes, with more data set to become available following the LHCb upgrade.

hep-ex↗

arXiv2024

Search for the $B_s^0 \rightarrow μ^+μ^-γ$ decay

A search for the fully reconstructed $B_s^0 \rightarrow μ^+μ^-γ$ decay is performed at the LHCb experiment using proton-proton collisions at $\sqrt{s}=13$\,TeV corresponding to an integrated luminosity of $5.4\,\mathrm{fb^{-1}}$. No significant signal is found and upper limits on the branching fraction in intervals of the dimuon mass are set \begin{align} {\cal B}(B_s^0 \rightarrow μ^+μ^-γ) < 4.2\times10^{-8},~&m(μμ)\in[2m_μ,~1.70]\,\mathrm{GeV/c^2} ,\nonumber {\cal B}(B_s^0 \rightarrow μ^+μ^-γ) < 7.7\times10^{-8},~&m(μμ)\in[1.70,~2.88]\,\mathrm{GeV/c^2},\nonumber {\cal B}(B_s^0 \rightarrow μ^+μ^-γ) < 4.2\times10^{-8},~&m(μμ)\in[3.92 ,~m_{B_s^0}]\,\mathrm{GeV/c^2},\nonumber \end{align} at 95\% confidence level. Additionally, upper limits are set on the branching fraction in the $[2m_μ,~1.70]\,\mathrm{GeV/c^2}$ dimuon mass region excluding the contribution from the intermediate $ϕ(1020)$ meson, and in the region combining all dimuon-mass intervals.

hep-ex↗

arXiv2024

Amplitude analysis of the $Λ_b^0\to pK^-γ$ decay

The resonant structure of the radiative decay $Λ_b^0\to pK^-γ$ in the region of proton-kaon invariant-mass up to 2.5 GeV$/c^2$ is studied using proton-proton collision data recorded at centre-of-mass energies of 7, 8, and 13 TeV collected with the LHCb detector, corresponding to a total integrated luminosity of 9 fb$^{-1}$. Results are given in terms of fit and interference fractions between the different components contributing to this final state. Only $Λ$ resonances decaying to $pK^-$ are found to be relevant, where the largest contributions stem from the $Λ(1520)$, $Λ(1600)$, $Λ(1800)$, and $Λ(1890)$ states.

hep-ex↗

arXiv2024

Modification of $χ_{c1}$(3872) and $ψ$(2$S$) production in $p$Pb collisions at $\sqrt{s_{NN}} = 8.16$ TeV

The LHCb collaboration measures production of the exotic hadron $χ_{c1}$(3872) in proton-nucleus collisions for the first time. Comparison with the charmonium state $ψ$(2$S$) suggests that the exotic $χ_{c1}$(3872) experiences different dynamics in the nuclear medium than conventional hadrons, and comparison with data from proton-proton collisions indicates that the presence of the nucleus may modify $χ_{c1}$(3872) production rates. This is the first measurement of the nuclear modification factor of an exotic hadron.

hep-ex↗

arXiv2024

Observation of $Λ_{b}^{0} \to Λ_{c}^{+} \bar{D}^{()0} K^{-}$ and $Λ_{b}^{0} \to Λ_{c}^{+} D_{s}^{-}$ decays

The decays $Λ_b^0 \to Λ_c^+\bar{D}^{(*)0}K^-$ and $Λ_b^0 \to Λ_c^+ D_s^{*-}$ are observed for the first time, in proton-proton collision data at $\sqrt{s}=13$TeV corresponding to an integrated luminosity of 5.4 fb${}^{-1}$ collected with the LHCb detector. Their ratios of branching fractions with respect to the $Λ_b^0\!\toΛ_c^+\mathrm{D}_s^-$ mode are measured to be \begin{align*} \begin{split} \frac{\mathcal{B}(Λ_b^0 \to Λ_c^+\bar{D}^0 K^-)}{\mathcal{B}(Λ_b^0 \to Λ_c^+ D_s^-)} & = 0.1908 {}_{-0.0034}^{+0.0036} {}_{-0.0018}^{+0.0016} \pm 0.0038 \frac{\mathcal{B}(Λ_b^0 \to Λ_c^+\bar{D}^{*0} K^-)}{\mathcal{B}(Λ_b^0 \to Λ_c^+ D_s^-)} & = 0.589 {}_{-0.017}^{+0.018} {}_{-0.018}^{+0.017} \pm 0.012 \frac{\mathcal{B}(Λ_b^0 \to Λ_c^+ D_s^{*-})}{\mathcal{B}(Λ_b^0 \to Λ_c^+ D_s^-)} & = 1.668 \pm 0.022 {}_{-0.055}^{+0.061}\ , \end{split} \end{align*} where the first uncertainties are statistical, the second systematic, and the third, for the $Λ_b^0 \to Λ_c^+ \bar{D}^{(*)0} K^-$ decays, are due to the uncertainties on the branching fractions of the $D_s^- \to K^- K^+ π^-$ and $\bar{D}^0 \to K^+π^-$ decay modes. The measured branching fractions probe factorization assumptions in effective theories and provide the normalization for future pentaquark searches in $Λ_b^0 \to Λ_c^+ \bar{D}^{(*)0}K^-$ decay channels.

hep-ex↗

arXiv2024

Multiplicity dependence of $σ_{ψ(2S)}/σ_{J/ψ}$ in $pp$ collisions at $\sqrt{s}=13$ TeV

The ratio of production cross-sections of $ψ(2S)$ over $J/ψ$ mesons as a function of charged-particle multiplicity in proton-proton collisions at a centre-of-mass energy $\sqrt{s}=13$ TeV is measured with a data sample collected by the LHCb detector, corresponding to an integrated luminosity of 658 pb$^{-1}$. The ratio is measured for both prompt and non-prompt $ψ(2S)$ and $J/ψ$ mesons. When there is an overlap between the rapidity ranges over which multiplicity and charmonia production are measured, a multiplicity-dependent modification of the ratio is observed for prompt mesons. No significant multiplicity dependence is found when the ranges do not overlap. For non-prompt production, the $ψ(2S)-to-J/ψ$ production ratio is roughly independent of multiplicity irrespective of the rapidity range over which the multiplicity is measured. The results are compared to predictions of the co-mover model and agree well except in the low multiplicity region. The ratio of production cross-sections of $ψ(2S)$ over $J/ψ$ mesons are cross-checked with other measurements in di-lepton channels and found to be compatible.

hep-ex↗

arXiv2024

Measurement of associated $J/ψ$-$ψ(2S)$ production cross-section in $pp$ collisions at $\sqrt{s}=13$ TeV

The cross-section of associated $J/ψ$-$ψ(2S)$ production in proton-proton collisions at a centre-of-mass energy of $\sqrt{s}=13$ TeV is measured using a data sample corresponding to an integrated luminosity of 4.2 fb$^{-1}$, collected by the LHCb experiment. The measurement is performed for both $J/ψ$ and $ψ(2S)$ mesons having transverse momentum $p_{\text{T}}<14$ GeV/$c$ and rapidity $2.0<y<4.5$, assuming negligible polarisation of the $J/ψ$ and $ψ(2S)$ mesons. The production cross-section is measured to be $4.5\pm0.7\pm0.3$ nb, where the first uncertainty is statistical and the second systematic. The differential cross-sections are measured as functions of several kinematic variables of the $J/ψ$-$ψ(2S)$ candidates. The results are combined with a measurement of $J/ψ$-$J/ψ$ production, giving a cross-section ratio between $J/ψ$-$ψ(2S)$ and $J/ψ$-$J/ψ$ production of $0.274\pm0.044\pm0.008$, where the first uncertainty is statistical and the second systematic.

hep-ex↗

arXiv2024

Measurement of the Branching Fraction of $B^{0} \rightarrow J/ψπ^{0}$ Decays

The ratio of branching fractions between $B^{0} \rightarrow J/ψπ^{0}$ and $B^{+} \rightarrow J/ψK^{*+}$ decays is measured with proton-proton collision data collected by the LHCb experiment, corresponding to an integrated luminosity of 9 fb$^{-1}$. The measured value is $\frac{\mathcal{B}_{B^{0} \rightarrow J/ψπ^{0}}}{\mathcal{B}_{B^{+} \rightarrow J/ψK^{*+}}} = (1.153 \pm 0.053 \pm 0.048 ) \times 10^{-2}$, where the first uncertainty is statistical and the second is systematic. The branching fraction for $B^{0} \rightarrow J/ψπ^{0}$ decays is determined using the branching fraction of the normalisation channel, resulting in $\mathcal{B}_{B^{0} \rightarrow J/ψπ^{0}} = (1.670 \pm 0.077 \pm 0.069 \pm 0.095) \times 10^{-5}$, where the last uncertainty corresponds to that of the external input. This result is consistent with the current world average value and competitive with the most precise single measurement to date.

hep-ex↗

arXiv2024

Search for $B_c^+\toπ^+μ^+μ^-$ decays and measurement of the branching fraction ratio ${\cal B}(B_c^+\toψ(2S)π^+)/{\cal B}(B_c^+\to J/ψπ^+)$

The first search for nonresonant $B_c^+\toπ^+μ^+μ^-$ decays is reported. The analysis uses proton-proton collision data collected with the LHCb detector between 2011 and 2018, corresponding to an integrated luminosity of 9 fb$^{-1}$. No evidence for an excess of signal events over background is observed and an upper limit is set on the branching fraction ratio ${\cal B}(B_c^+\toπ^+μ^+μ^-)/{\cal B}(B_c^+\to J/ψπ^+) < 2.1\times 10^{-4}$ at $90\%$ confidence level. Additionally, an updated measurement of the ratio of the $B_c^+\toψ(2S)π^+$ and $B_c^+\to J/ψπ^+$ branching fractions is reported. The ratio ${\cal B}(B_c^+\toψ(2S)π^+)/{\cal B}(B_c^+\to J/ψπ^+)$ is measured to be $0.254\pm 0.018 \pm 0.003 \pm 0.005$, where the first uncertainty is statistical, the second systematic, and the third is due to the uncertainties on the branching fractions of the leptonic $J/ψ$ and $ψ(2S)$ decays. This measurement is the most precise to date and is consistent with previous LHCb results.

hep-ex↗

arXiv2024

Measurement of forward charged hadron flow harmonics in peripheral PbPb collisions at $\sqrt{s_{NN}}=5.02$ TeV with the LHCb detector

Flow harmonic coefficients, $v_n$, which are the key to studying the hydrodynamics of the quark-gluon plasma (QGP) created in heavy-ion collisions, have been measured in various collision systems and kinematic regions and using various particle species. The study of flow harmonics in a wide pseudorapidity range is particularly valuable to understand the temperature dependence of the shear viscosity to entropy density ratio of the QGP. This paper presents the first LHCb results of the second- and the third-order flow harmonic coefficients of charged hadrons as a function of transverse momentum in the forward region, corresponding to pseudorapidities between 2.0 and 4.9, using the data collected from PbPb collisions in 2018 at a center-of-mass energy of $5.02$ TeV. The coefficients measured using the two-particle angular correlation analysis method are smaller than the central-pseudorapidity measurements at ALICE and ATLAS from the same collision system but share similar features.

nucl-ex↗

arXiv2024

Observation of the $B_c^+ \to J/ψπ^+ π^0$ decay

The first observation of the $B_c^+ \to J/ψπ^+ π^0$ decay is reported with high significance using proton-proton collision data, corresponding to an integrated luminosity of 9fb$^{-1}$, collected with the LHCb detector at centre-of-mass energies of 7, 8, and 13 TeV. The ratio of its branching fraction relative to the $B_c^+ \to J/ψπ^+$ channel is measured to be $$ \frac{ {\cal{B}}( B_c^+ \to J/ψπ^+π^0 ) } { {\cal{B}}( B_c^+ \to J/ψπ^+ ) } = 2.80 \pm 0.15 \pm 0.11 \pm 0.16 \,, $$ where the first uncertainty is statistical, the second systematic and the third related to imprecise knowledge of the branching fractions for $B^+ \to J/ψK^{*+}$ and $B^+ \to J/ψK^+$ decays, which are used to determine the $π^0$ detection efficiency. The $π^+π^0$ mass spectrum is found to be consistent with the dominance of an intermediate $ρ^+$ contribution in accordance with a model based on QCD factorisation.

hep-ex↗

arXiv2024

Study of $CP$ violation in $B^0_{(s)} \to D K^{*}(892)^0$ decays with $D \to K π( ππ)$, $ ππ( ππ)$, and $KK$ final states

A measurement of $CP$-violating observables associated with the interference of $B^0\to D^0 K^{*}(892)^0$ and $B^0\to \bar{D}^0 K^*(892)^0$ decay amplitudes is performed in the $D^0 \to K^{\mp}π^{\pm}(π^+π^-),$ $D^0 \to π^+π^-(π^+π^-)$, and $D^0\to K^+K^-$ final states using data collected by the LHCb experiment corresponding to an integrated luminosity of $9$ $\text{fb}^{-1}$. $CP$-violating observables related to the interference of $B^0_s\to D^0 \bar{K}^*(892)^0$ and $B_s^0\to \bar{D}^0 \bar{K}^*(892)^0$ are also measured, but no evidence for interference is found. The $B^0$ observables are used to constrain the parameter space of the CKM angle $γ$ and the hadronic parameters $r_{B^0}^{DK^*}$ and $δ_{B^0}^{DK^*}$ with inputs from other measurements. In a combined analysis, these measurements allow for four solutions in the parameter space, only one of which is consistent with the world average.

hep-ex↗

arXiv2024

Prompt and nonprompt $ψ(2S)$ production in $p$Pb collisions at $\sqrt{s_{NN}}=8.16$ TeV

The production of $ψ(2S)$ mesons in proton-lead collisions at a centre-of-mass energy per nucleon pair of $\sqrt{s_{NN}}=8.16$ TeV is studied with the LHCb detector using data corresponding to an integrated luminosity of 34 nb$^{-1}$. The prompt and nonprompt $ψ(2S)$ production cross-sections and the ratio of the $ψ(2S)$ to $J/ψ$ cross-section are measured as a function of the meson transverse momentum and rapidity in the nucleon-nucleon centre-of-mass frame, together with forward-to-backward ratios and nuclear modification factors. The production of prompt $ψ(2S)$ is observed to be more suppressed compared to $pp$ collisions than the prompt $J/ψ$ production, while the nonprompt productions have similar suppression factors.

hep-ex↗

arXiv2024

Curvature-bias corrections using a pseudomass method

Momentum measurements for very high momentum charged particles, such as muons from electroweak vector boson decays, are particularly susceptible to charge-dependent curvature biases that arise from misalignments of tracking detectors. Low momentum charged particles used in alignment procedures have limited sensitivity to coherent displacements of such detectors, and therefore are unable to fully constrain these misalignments to the precision necessary for studies of electroweak physics. Additional approaches are therefore required to understand and correct for these effects. In this paper the curvature biases present at the LHCb detector are studied using the pseudomass method in proton-proton collision data recorded at centre of mass energy $\sqrt{s}=13$ TeV during 2016, 2017 and 2018. The biases are determined using $Z\toμ^+μ^-$ decays in intervals defined by the data-taking period, magnet polarity and muon direction. Correcting for these biases, which are typically at the $10^{-4}$ GeV$^{-1}$ level, improves the $Z\toμ^+μ^-$ mass resolution by roughly 18% and eliminates several pathological trends in the kinematic-dependence of the mean dimuon invariant mass.

hep-ex↗