arXiv subjects

N. Belloli

Publications and source records attributed to N. Belloli.

At least 19 recordsLinked to original sources

arXiv2020

Measurement of psi(2S) production cross-sections in proton-proton collisions at 7 and 13 TeV

The cross-sections of $ψ(2S)$ meson production in proton-proton collisions at $\sqrt{s}=13~\mathrm{TeV}$ are measured with a data sample collected by the LHCb detector corresponding to an integrated luminosity of $275~p\mathrm{b}^{-1}$. The production cross-sections for prompt $ψ(2S)$ mesons and those for $ψ(2S)$ mesons from $b$-hadron decays ($ψ{(2S)}\mathrm{-from-}b$) are determined as functions of the transverse momentum, $p_{\mathrm{T}}$, and the rapidity, $y$, of the $ψ(2S)$ meson in the kinematic range $2<p_{\mathrm{T}}<20~\mathrm{GeV}/c$ and $2.0<y<4.5$. The production cross-sections integrated over this kinematic region are \begin{equation*} \begin{split} σ(\mbox{prompt }ψ(2S),13~\mathrm{TeV}) &= {1.430 \pm 0.005(\mathrm{stat}) \pm 0.099 (\mathrm{syst})μ\mathrm{b}},\\ σ(ψ(2S)\mathrm{-from-}b,13~\mathrm{TeV})&={0.426 \pm 0.002(\mathrm{stat}) \pm0.030 (\mathrm{syst})μ\mathrm{b}}. \end{split} \end{equation*} A new measurement of $ψ(2S)$ production cross-sections in $pp$ collisions at $\sqrt{s}=7~\mathrm{TeV}$ is also performed using data collected in 2011, corresponding to an integrated luminosity of $614~{p\mathrm{b}^{-1}}$.The integrated production cross-sections in the kinematic range $3.5<p_{\mathrm{T}}<14~\mathrm{GeV}/c$ and $2.0<y<4.5$ are \begin{equation*} \begin{split} σ(\mbox{prompt }ψ(2S),7~\mathrm{TeV}) &={0.471 \pm0.001 (\mathrm{stat}) \pm 0.025 (\mathrm{syst})μ\mathrm{b}},\\ σ(ψ(2S)\mathrm{-from-}b,7~\mathrm{TeV}) &={0.126\pm0.001 (\mathrm{stat}) \pm0.008 (\mathrm{syst})μ\mathrm{b}}. \end{split} \end{equation*} All results show reasonable agreement with theoretical calculations.

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arXiv2020

Measurement of $CP$ violation in $B^0\to D^{*\pm} D^{\mp}$ decays

The decay-time-dependent $CP$ asymmetry in $B^0 \to D^{*\pm}D^{\mp}$ decays is measured using a data set corresponding to an integrated luminosity of $9$fb$^{-1}$ recorded by the LHCb detector in proton-proton collisions at centre-of-mass energies of 7, 8 and 13 TeV. The $CP$ parameters are measured as $ S_{D^*D} = -0.861 \pm 0.077\,\text{(stat)} \pm 0.019 \,\text{(syst)}\,, $ $ ΔS_{D^*D} = 0.019 \pm 0.075 \,\text{(stat)} \pm 0.012 \,\text{(syst)} \,, $ $ C_{D^*D} = -0.059 \pm 0.092 \,\text{(stat)} \pm 0.020 \,\text{(syst)} \,, $ $ ΔC_{D^*D} = -0.031 \pm 0.092 \,\text{(stat)} \pm 0.016 \,\text{(syst)} \,, $ $ {\cal A}_{D^*D} = 0.008 \pm 0.014 \,\text{(stat)} \pm 0.006 \,\text{(syst)}\,. $ The analysis provides the most precise single measurement of $CP$ violation in this decay channel to date. All parameters are consistent with their current world average values.

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arXiv2020

Study of $Υ$ production in $p$Pb collisions at $\sqrt{s_{NN}}=8.16$ TeV

The production of $Υ(nS)$ mesons ($n=1,2,3$) in $p$Pb and Pb$p$ collisions at a centre-of-mass energy per nucleon pair $\sqrt{s_{NN}}=8.16$ TeV is measured by the LHCb experiment, using a data sample corresponding to an integrated luminosity of 31.8 nb$^{-1}$. The $Υ(nS)$ mesons are reconstructed through their decays into two opposite-sign muons. The measurements comprise the differential production cross-sections of the $Υ(1S)$ and $Υ(2S)$ states, their forward-to-backward ratios and nuclear modification factors, performed as a function of the transverse momentum \pt and rapidity in the nucleon-nucleon centre-of-mass frame $y^*$ of the $Υ(nS)$ states, in the kinematic range $p_{\rm{T}}<25$ GeV/$c$ and $1.5<y^*<4.0$ ($-5.0<y^*<-2.5$) for $p$Pb (Pb$p$) collisions. In addition, production cross-sections for $Υ(3S)$ are measured integrated over phase space and the production ratios between all three $Υ(nS)$ states are determined. The measurements are compared to theoretical predictions and suppressions for quarkonium in $p$Pb collisions are observed.

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arXiv2019

Amplitude analysis of $B^\pm \to π^\pm K^+ K^-$ decays

The first amplitude analysis of the $B^\pm \to π^\pm K^+ K^-$ decay is reported based on a data sample corresponding to an integrated luminosity of 3.0 fb$^{-1}$ of $pp$ collisions recorded in 2011 and 2012 with the LHCb detector. The data is found to be best described by a coherent sum of five resonant structures plus a nonresonant component and a contribution from $ππ\leftrightarrow KK$ $S$-wave rescattering. The dominant contributions in the $π^\pm K^\mp$ and $K^{+}K^{-}$ systems are the nonresonant and the $B^\pm \to ρ(1450)^{0}π^{\pm}$ amplitudes, respectively, with fit fractions around $30\%$. For the rescattering contribution, a sizeable fit fraction is observed. This component has the largest $CP$ asymmetry reported to date for a single amplitude of $(-66 \pm 4 \pm 2)\%$, where the first uncertainty is statistical and the second systematic. No significant $CP$ violation is observed in the other contributions.

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arXiv2019

Measurement of charged hadron production in $Z$-tagged jets in proton-proton collisions at $\sqrt{s}=8$ TeV

The production of charged hadrons within jets recoiling against a $Z$ boson is measured in proton-proton collision data at $\sqrt{s}=8$ TeV recorded by the LHCb experiment. The charged-hadron structure of the jet is studied longitudinally and transverse to the jet axis for jets with transverse momentum $p_{\mathrm{T}}>20$ GeV and in the pseudorapidity range $2.5<η<4$. These are the first measurements of jet hadronization at these forward rapidities and also the first where the jet is produced in association with a $Z$ boson. In contrast to previous hadronization measurements at the Large Hadron Collider, which are dominated by gluon jets, these measurements probe predominantly light-quark jets which are found to be more longitudinally and transversely collimated with respect to the jet axis when compared to the previous gluon dominated measurements. Therefore, these results provide valuable information on differences between quarks and gluons regarding nonperturbative hadronization dynamics.

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arXiv2019

First measurement of charm production in fixed-target configuration at the LHC

The first measurement of heavy-flavour production by the LHCb experiment in its fixed-target mode is presented. The production of $J/ψ$ and $D^0$ mesons is studied with beams of protons of different energies colliding with gaseous targets of helium and argon with nucleon-nucleon centre-of-mass energies of $\sqrt{s_{NN}} = 86.6 $ and $ 110.4$ ${\rm GeV}$, respectively. The $J/ψ$ and $D^0$ (including charge conjugate) production cross sections in $p{\rm He}$ collisions in the rapidity range $[2,4.6]$ are found to be $σ_{J/ψ} = 652 \pm 33$ (stat) $\pm 42$ (syst) nb$/$nucleon and $σ_{D^0} = 80.8 \pm 2.4$ (stat) $\pm 6.3$ (syst) $μ$b$/$nucleon, where the first uncertainty is statistical and the second is systematic. No evidence for a substantial intrinsic charm content of the nucleon is observed in the large Bjorken-$x$ region.

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arXiv2019

A search for $\itΞ^{++}_{cc} \rightarrow D^{+} p K^{-} π^{+}$ decays

A search for the $\itΞ^{++}_{cc}$ baryon through the $\itΞ^{++}_{cc} \rightarrow D^{+} p K^{-} π^{+}$ decay is performed with a data sample corresponding to an integrated luminosity of 1.7 $\mathrm{fb}^{-1}$ recorded by the LHCb experiment in $pp$ collisions at a centre-of-mass energy of 13 TeV. No significant signal is observed in the mass range from the kinematic threshold of the decay to 3800 $\mathrm{MeV}/c^{2}$. An upper limit is set on the ratio of branching fractions $\mathcal{R} = \frac{\mathcal{B}(\itΞ^{++}_{cc} \rightarrow D^{+} p K^{-} π^{+})}{\mathcal{B}(\itΞ^{++}_{cc} \rightarrow Λ^{+}_{c} K^{-} π^{+}π^{+})}$ with $\mathcal{R} < 1.7 \hspace{2pt} (2.1) \times 10^{-2}$ at the 90% (95%) confidence level at the known mass of the $\itΞ^{++}_{cc}$ state.

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arXiv2019

Measurements of $CP$ asymmetries in charmless four-body $Λ_b$ and $Ξ_b^0$ decays

A search for $CP$ violation in charmless four-body decays of $Λ_b$ and $Ξ_b^0$ baryons with a proton and three charged mesons in the final state is performed. To cancel out production and detection charge-asymmetry effects, the search is carried out by measuring the difference between the $CP$ asymmetries in a charmless decay and in a decay with an intermediate charmed baryon with the same particles in the final state. The data sample used was recorded in 2011 and 2012 with the LHCb detector and corresponds to an integrated luminosity of $3 {\rm fb}^{-1}$. A total of 18 $CP$ asymmetries are considered, either accounting for the full phase space of the decays or exploring specific regions of the decay kinematics. No significant $CP$-violation effect is observed in any of the measurements.

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arXiv2019

Observation of $B^0_{(s)} \to J/ψp \overline{p}$ decays and precision measurements of the $B^0_{(s)}$ masses

The first observation of the decays $B^0_{(s)} \to J/ψp \overline{p}$ is reported, using proton-proton collision data corresponding to an integrated luminosity of $5.2{\text{\,fb}}^{-1}$, collected with the \mbox{LHCb}\xspace detector. These decays are suppressed due to limited available phase space, as well as due to Okubo-Zweig-Iizuka or Cabibbo suppression. The measured branching fractions are \begin{align*} \mathcal{B}(B^0 \to J/ψp \overline{p}) &= (4.51\pm 0.40\; \text{(stat)} \pm 0.44\; \text{(syst)}) \times 10^{-7}, \\ \mathcal{B}(B^0_s \to J/ψp \overline{p}) &= (3.58\pm 0.19\; \text{(stat)} \pm 0.39\; \text{(syst)}) \times 10^{-6}. \end{align*} For the $B^0_s$ meson, the result is much higher than the expected value of $ {\cal O} (10^{-9})$. The small available phase space in these decays also allows for the most precise single measurement of both the $B^0$ mass as ${5279.74 \pm 0.30\; ({\rm stat})\pm 0.10\; ({\rm syst})}$ MeV, and the $B^0_s$ mass as ${5366.85 \pm 0.19\; ({\rm stat})\pm 0.13\; ({\rm syst})}$ MeV.

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arXiv2019

Measurement of $CP$-violating and mixing-induced observables in $B_s^0 \to ϕγ$ decays

A time-dependent analysis of the $B_s^0 \to ϕγ$ decay rate is performed to determine the $CP$-violating observables $S_{ϕγ}$ and $C_{ϕγ}$, and the mixing-induced observable $\mathcal{A}^Δ_{ϕγ}$. The measurement is based on a sample of $pp$ collision data recorded with the LHCb detector, corresponding to an integrated luminosity of 3 fb$^{-1}$ at center-of-mass energies of 7 and 8 TeV. The measured values are \begin{align*} S_{ϕγ} &= 0.43 \pm 0.30 \pm 0.11, \\ C_{ϕγ} &= 0.11 \pm 0.29 \pm 0.11, \\ \mathcal{A}^Δ_{ϕγ} &= -0.67 \, ^{+0.37}_{-0.41} \pm 0.17, \end{align*} where the first uncertainty is statistical and the second systematic. This is the first measurement of the observables $S$ and $C$ in radiative $B_s^0$ decays. The results are consistent with the Standard Model predictions.

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arXiv2019

Search for the rare decay $B^{+} \rightarrow μ^{+}μ^{-}μ^{+}ν_{μ}$

A search for the rare leptonic decay $B^{+} \rightarrow μ^{+}μ^{-}μ^{+}ν_{μ}$ is performed using proton-proton collision data corresponding to an integrated luminosity of $4.7$ fb$^{-1}$ collected by the LHCb experiment. The search is carried out in the region where the lowest of the two $μ^{+}μ^{-}$ mass combinations is below $980$MeV/c$^{2}$. The data are consistent with the background-only hypothesis and an upper limit of $1.6 \times 10^{-8}$ at 95% confidence level is set on the branching fraction in the stated kinematic region.

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arXiv2019

Measurement of b-hadron fractions in 13 TeV pp collisions

The production fractions of $\overline{B}_s^0$ and $Λ_b^0$ hadrons, normalized to the sum of $B^-$ and $\overline{B}^0$ fractions, are measured in 13 TeV pp collisions using data collected by the LHCb experiment, corresponding to an integrated luminosity of 1.67/fb. These ratios, averaged over the $b$-hadron transverse momenta from 4 to 25 GeV and pseudorapidity from 2 to 5, are $0.122 \pm 0.006$ for $\overline{B}_s^0$, and $0.259 \pm 0.018$ for $Λ_b^0$, where the uncertainties arise from both statistical and systematic sources. The $Λ_b^0$ ratio depends strongly on transverse momentum, while the $\overline{B}_s^0$ ratio shows a mild dependence. Neither ratio shows variations with pseudorapidity. The measurements are made using semileptonic decays to minimize theoretical uncertainties. In addition, the ratio of $D^+$ to $D^0$ mesons produced in the sum of $\overline{B}^0$ and $B^-$ semileptonic decays is determined as $0.359\pm0.006\pm 0.009$, where the uncertainties are statistical and systematic.

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arXiv2019

Measurement of the $CP$-violating phase $ϕ_s$ from $B_{s}^{0}\to J/ψπ^+π^-$ decays in 13 TeV $pp$ collisions

Decays of $B_{s}^{0}$ and $\overline{B}{}_{s}^{0}$ mesons into $J/ψπ^+π^-$ final states are studied in a data sample corresponding to 1.9 fb$^{-1}$ of integrated luminosity collected with the LHCb detector in 13 TeV $pp$ collisions. A time-dependent amplitude analysis is used to determine the final-state resonance contributions, the $CP$-violating phase $ϕ_s=-0.057\pm 0.060\pm 0.011$ rad, the decay-width difference between the heavier mass $B_{s}^{0}$ eigenstate and the $B^{0}$ meson of $-0.050\pm 0.004\pm 0.004$ ps$^{-1}$, and the $CP$-violating parameter $|λ|=1.01_{-0.06}^{+0.08}\pm0.03$, where the first uncertainty is statistical and the second systematic. These results are combined with previous LHCb measurements in the same decay channel using 7 TeV and 8 TeV $pp$ collisions obtaining $ϕ_s =0.002\pm0.044\pm0.012$ rad, and $|λ| =0.949\pm0.036\pm0.019$.

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arXiv2019

Precision measurement of the $Λ_c^+$, $Ξ_c^+$ and $Ξ_c^0$ baryon lifetimes

We report measurements of the lifetimes of the $Λ_c^+$, $Ξ_c^+$ and $Ξ_c^0$ charm baryons using proton-proton collision data at center-of-mass energies of 7 and 8\tev, corresponding to an integrated luminosity of 3.0 fb$^{-1}$, collected by the LHCb experiment. The charm baryons are reconstructed through the decays $Λ_c^+\to pK^-π^+$, $Ξ_c^+\to pK^-π^+$ and $Ξ_c^0\to pK^-K^-π^+$, and originate from semimuonic decays of beauty baryons. The lifetimes are measured relative to that of the $D^+$ meson, and are determined to be \begin{align*} τ_{Λ_c^+} &= 203.5\pm1.0\pm1.3\pm1.4~{\rm fs}, \newline τ_{Ξ_c^+} &= 456.8\pm3.5\pm2.9\pm3.1~{\rm fs}, \newline τ_{Ξ_c^0} &= 154.5\pm1.7\pm1.6\pm1.0~{\rm fs}, \end{align*} where the uncertainties are statistical, systematic, and due to the uncertainty in the $D^+$ lifetime. The measurements are approximately 3--4 times more precise than the current world average values. The $Λ_c^+$ and $Ξ_c^+$ lifetimes are in agreement with previous measurements; however, the $Ξ_c^0$ baryon lifetime is approximately 3.3 standard deviations larger than the world average value.

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arXiv2019

Near-threshold $D\bar{D}$ spectroscopy and observation of a new charmonium state

Using proton-proton collision data, corresponding to an integrated luminosity of 9$fb^{-1}$, collected with the~LHCb detector between 2011 and 2018, a new narrow charmonium state, the $X(3842)$ resonance, is observed in the decay modes $X(3842)\rightarrow D^0\bar{D}^0$ and $X(3842)\rightarrow D^+D^-$. The mass and the natural width of this state are measured to be \begin{eqnarray*} m_{X(3842)} & = & 3842.71 \pm 0.16 \pm 0.12 MeV/c^2\,, Γ_{X(3842)} & = & 2.79 \pm 0.51 \pm 0.35 MeV\,, \end{eqnarray*} where the first uncertainty is statistical and the~second is systematic. The observed mass and narrow natural width suggest the~interpretation of the new state as the~unobserved spin\nobreakdash-3 $ψ_3\mathrm{\left(1^3D_3\right)}$ charmonium state. In addition, prompt hadroproduction of the $ψ(3770)$~and $χ_{c2}(3930)$ states is observed for the first time, and the parameters of these~states are measured to be \begin{eqnarray*} m_{ψ(3770)} & = & 3778.1 \pm 0.7 \pm 0.6 MeV/c^2\,, m_{χ_{c2}(3930)} & = & 3921.9 \pm 0.6 \pm 0.2 MeV/c^2\,, Γ_{χ_{c2}(3930)} & = &36.6 \pm 1.9 \pm 0.9 MeV\,, \end{eqnarray*} where the first uncertainty is statistical and the~second is systematic.

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arXiv2019

First observation of the radiative decay $Λ_{b}^{0} \to Λγ$

The radiative decay $Λ_{b}^{0} \to Λγ$ is observed for the first time using a data sample of proton-proton collisions corresponding to an integrated luminosity of $1.7\,fb^{-1}$ collected by the LHCb experiment at a center-of-mass energy of $13\,TeV$. Its branching fraction is measured exploiting the $B^{0} \to K^{*0} γ$ decay as a normalization mode and is found to be $\mathcal{B}(Λ_{b}^{0} \to Λγ)= (7.1 \pm 1.5 \pm 0.6 \pm 0.7) \times 10^{-6}$, where the quoted uncertainties are statistical, systematic and systematic from external inputs, respectively. This is the first observation of a radiative decay of a beauty baryon.

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arXiv2019

Amplitude analysis of the $B_{(s)} \to K^{0} \overline{K}^{0}$ decays and measurement of the branching fraction of the $B \to K^{0} \overline{K}^{0}$ decay

The $B^0 \to K^{*0} \overline{K}^{*0}$ and $B^0_s \to K^{*0} \overline{K}^{*0}$ decays are studied using proton-proton collision data corresponding to an integrated luminosity of 3fb$^{-1}$. An untagged and time-integrated amplitude analysis of $B^0_{(s)} \to (K^+π^-)(K^-π^+) $ decays in two-body invariant mass regions of 150 MeV$/c^2$ around the $K^{*0}$ mass is performed. A stronger longitudinal polarisation fraction in the ${B^0 \to K^{*0} \overline{K}^{*0}}$ decay, ${f_L = 0.724 \pm 0.051 \,({\rm stat}) \pm 0.016 \,({\rm syst})}$, is observed as compared to ${f_L = 0.240 \pm 0.031 \,({\rm stat}) \pm 0.025 \,({\rm syst})}$ in the ${B^0_s\to K^{*0} \overline{K}^{*0}}$ decay. The ratio of branching fractions of the two decays is measured and used to determine $\mathcal{B}(B^0 \to K^{*0} \overline{K}^{*0}) = (8.0 \pm 0.9 \,({\rm stat}) \pm 0.4 \,({\rm syst})) \times 10^{-7}$.

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arXiv2019

Amplitude analysis of $B^{0}_{s} \rightarrow K^{0}_{\textrm{S}} K^{\pm}π^{\mp}$ decays

The first untagged decay-time-integrated amplitude analysis of $B^{0}_{s} \rightarrow K^{0}_{\textrm{S}} K^{\pm}π^{\mp}$ decays is performed using a sample corresponding to $3.0\,$fb$^{-1}$ of $pp$ collision data recorded with the LHCb detector during 2011 and 2012. The data are described with an amplitude model that contains contributions from the intermediate resonances $K^{*}(892)^{0,+}$, $K^*_2(1430)^{0,+}$ and $K^*_0(1430)^{0,+}$, and their charge conjugates. Measurements of the branching fractions of the decay modes $B^{0}_{s} \rightarrow K^{*}(892)^{\pm}K^{\mp}$ and $B^{0}_{s} \rightarrow K^{*}(892)^{0}\kern 0.2em\overline{\kern -0.2em K}{}^{0}, \kern 0.2em\overline{\kern -0.2em K}{}^{*}(892)^{0}K^{0}$ are in agreement with, and more precise than, previous results. The decays $B^{0}_{s} \rightarrow K^*_0(1430)^{\pm} K^{\mp}$ and $B^{0}_{s} \rightarrow K^{*}_{0}(1430)^{0}\kern 0.2em\overline{\kern -0.2em K}{}^{0}, \kern 0.2em\overline{\kern -0.2em K}{}^{*}_{0}(1430)^{0}K^{0}$ are observed for the first time, each with significance over 10 standard deviations.

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