# R. Aaij's research while affiliated with National Institute for Subatomic Physics and other places

## Publications (956)

Article
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The Large Hadron Collider beauty (LHCb) experiment at CERN is undergoing an upgrade in preparation for the Run 3 data collection period at the Large Hadron Collider (LHC). As part of this upgrade, the trigger is moving to a full software implementation operating at the LHC bunch crossing rate. We present an evaluation of a CPU-based and a GPU-based...
Article
A precision measurement of the Z boson production cross-section at s√ = 13 TeV in the forward region is presented, using pp collision data collected by the LHCb detector, corresponding to an integrated luminosity of 5.1 fb−1. The production cross-section is measured using Z → μ+μ− events within the fiducial region defined as pseudorapidity 2.0 < η...
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A bstract Coherent production of J/ψ mesons is studied in ultraperipheral lead-lead collisions at a nucleon-nucleon centre-of-mass energy of 5 TeV, using a data sample collected by the LHCb experiment corresponding to an integrated luminosity of about 10 μb ⁻¹ . The J/ψ mesons are reconstructed in the dimuon final state and are required to have tra...
Article
The centrality of heavy-ion collisions is directly related to the created medium in these interactions. A procedure to determine the centrality of collisions with the LHCb detector is implemented for lead-lead collisions at √ s NN = 5 TeV and lead-neon fixed-target collisions at √ s NN = 69 GeV. The energy deposits in the electromagnetic calorimete...
Article
A search is performed for massive long-lived particles (LLPs) decaying semileptonically into a muon and two quarks. Two kinds of LLP production processes were considered. In the first, a Higgs-like boson with mass from 30 to 200 $$\text {\,GeV\!/}c^2$$ \,GeV\!/ c 2 is produced by gluon fusion and decays into two LLPs. The analysis covers LLP mass v...
Article
Searches for rare B s 0 $${B}_s^0$$ and B0 decays into four muons are performed using proton-proton collision data recorded by the LHCb experiment, corresponding to an integrated luminosity of 9 fb−1. Direct decays and decays via light scalar and J/ψ resonances are considered. No evidence for the six decays searched for is found and upper limits...
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The first study of the angular distribution of $\mu^+ \mu^-$ pairs produced in the forward rapidity region via the Drell-Yan reaction $pp \rightarrow \gamma^{*}/Z +X \rightarrow l^+ l^- + X$ is presented, using data collected with the LHCb detector at a centre-of-mass energy of 13TeV, corresponding to an integrated luminosity of 5.1 $\rm{fb}^{-1}$....
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A measurement of the ratios of the effective decay widths of $D^0 \to \pi^-\pi^+$ and $D^0 \to K^-K^+$ decays over that of $D^0 \to K^-\pi^+$ decays is performed with the LHCb experiment using proton-proton collisions at a centre-of-mass energy of $13 \, \mathrm{TeV}$, corresponding to an integrated luminosity of $6 \, \mathrm{fb^{-1}}$. These obse...
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The $\it{\Xi_{cc}^{++}\to \Xi_{c}^{'+}\pi^{+}}$ decay is observed using proton-proton collisions collected by the LHCb experiment at a centre-of-mass energy of $13\mathrm{\,Te\kern -0.1em V}$, corresponding to an integrated luminosity of $5.4\,\mathrm{fb}^{-1}$. The $\it{\Xi_{cc}^{++}\to \Xi_{c}^{'+}\pi^{+}}$ decay is reconstructed partially, where...
Preprint
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A study of $B^+ \rightarrow J/\psi \eta K^+$ decays, followed by $J/\psi \rightarrow \mu^+ \mu^-$ and $\eta \rightarrow \gamma \gamma$, is performed using a dataset collected with the LHCb detector in proton-proton collisions at centre-of-mass energies of 7, 8 and 13 TeV, corresponding to an integrated luminosity of 9 fb$^{-1}$. The $J/psi\eta$ mas...
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A search for the decay $B^0\to\phi\mu^+\mu^-$ is performed using proton-proton collisions at centre-of-mass energies of 7, 8, and 13 TeV collected by the LHCb experiment and corresponding to an integrated luminosity of 9 fb$^{-1}$. No evidence for the $B^0\to \phi \mu^+ \mu^-$ decay is found and an upper limit on the branching fraction of $4.4 \tim... Article Using proton-proton collision data, corresponding to an integrated luminosity of 9 fb−1 collected with the LHCb detector, seven decay modes of the B c + $${\mathrm{B}}_{\mathrm{c}}^{+}$$ meson into a J/ψ or ψ(2S) meson and three charged hadrons, kaons or pions, are studied. The decays B c + $${\mathrm{B}}_{\mathrm{c}}^{+}$$ → (ψ(2S) → J/ψπ+π−)π... Preprint Full-text available The first observation of the semileptonic$b$-baryon decay$ \Lambda_b^0 \rightarrow \Lambda_c^+ \tau^-\overline{\nu}_{\tau}$, with a significance of$6.1\,\sigma$, is reported using a data sample corresponding to 3 fb$^{-1}$of integrated luminosity, collected by the LHCb experiment at centre-of-mass energies of 7 and 8~TeV at the LHC. The$\tau^-...
Article
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Mesons comprising a beauty quark and strange quark can oscillate between particle ( $${B}_{\mathrm{s}}^{0}$$ B s 0 ) and antiparticle ( $${\overline{B}}_{\mathrm{s}}^{0}$$ B ¯ s 0 ) flavour eigenstates, with a frequency given by the mass difference between heavy and light mass eigenstates, Δ m s . Here we present a measurement of Δ m s using $${B}_... Article The Large Hadron Collider beauty (LHCb) experiment at CERN is undergoing an upgrade in preparation for the Run 3 data collection period at the Large Hadron Collider (LHC). As part of this upgrade, the trigger is moving to a full software implementation operating at the LHC bunch crossing rate. We present an evaluation of a CPU-based and a GPU-based... Preprint Full-text available The first observations of B^0\rightarrow\overline{D}^{*}(2007)^{0}K^{+}\pi^{-} and B_s^0\rightarrow\overline{D}^{*}(2007)^{0}K^{-}\pi^{+} decays are presented, and their branching fractions relative to that of the B^0\rightarrow\overline{D}^{*}(2007)^{0}\pi^{+}\pi^{-} decay are reported. These modes can potentially be used to investigate the... Preprint Full-text available A data sample collected with the LHCb detector, corresponding to an integrated luminosity of 9~{\rm fb}^{-1}, is used to measure CP observables in B^\pm \to D h^\pm decays, where h^{(\prime)} is either a kaon or a pion, and the neutral D meson decay is reconstructed in the three-body final states K^\pm \pi^\mp \pi^0, \pi^\pm \pi^\mp \p... Preprint Full-text available The identification of charm jets is achieved at LHCb for data collected in 2015-2018 using a method based on the properties of displaced vertices reconstructed and matched with jets. The performance of this method is determined using a dijet calibration dataset recorded by the LHCb detector and selected such that the jets are unbiased in quantities... Preprint Full-text available A precision measurement of the Z boson production cross-section at \sqrt{s} = 13 TeV in the forward region is presented, using pp collision data collected by the LHCb detector, corresponding to an integrated luminosity of 5.1 fb^{-1}. The production cross-section is measured using Z\rightarrow\mu^+\mu^- events within the fiducial region d... Preprint Full-text available The multihadron decays \Lambda_b^0\rightarrow D^+ p \pi^-\pi^- and \Lambda_b^0\rightarrow D^{*+} p \pi^-\pi^- are observed in data corresponding to an integrated luminosity of 3fb^{-1}, collected in proton-proton collisions at centre-of-mass energies of 7 and 8TeV by the LHCb detector. Using the~decay \Lambda_b^0\rightarrow \Lambda_c^+ \pi^+... Article A flavour-tagged time-dependent angular analysis of B0s→J/ψϕ decays is presented where the J/ψ meson is reconstructed through its decay to an e+e− pair. The analysis uses a sample of pp collision data recorded with the LHCb experiment at centre-of-mass energies of 7 and 8\,Te V, corresponding to an integrated luminosity of 3\,fb−1. The CP-violating... Preprint Full-text available Searches for rare B_s^0 and B^0 decays into four muons are performed using proton-proton collision data recorded by the LHCb experiment, corresponding to an integrated luminosity of 9 \text{fb}^{-1}. Direct decays and decays via light scalar and J/\psi resonances are considered. No evidence for the six decays searched for is found and upper... Preprint Full-text available The photon polarization in b \to s \gamma transitions is measured for the first time in radiative b-baryon decays exploiting the unique spin structure of \Lambda_b \to \Lambda \gamma decays. A data sample corresponding to an integrated luminosity of 6\;fb^{-1} collected by the LHCb experiment in pp collisions at a center-of-mass energy of ... Preprint Full-text available The first full angular analysis and an updated measurement of the decay-rate CP asymmetry of the D^0 \to \pi^+\pi^-\mu^+\mu^- and D^0 \to K^+K^-\mu^+\mu^- decays are reported. The analysis uses proton-proton collision data collected with the LHCb detector at centre-of-mass energies of 7, 8 and 13 TeV. The data set corresponds to an integrated... Preprint Full-text available Using proton-proton collision data, corresponding to an integrated luminosity of 9fb^{-1} collected with the LHCb detector, seven decay modes of the B_c^+ meson into a J/\psi or \psi(2S) meson and three charged hadrons, kaons or pions, are studied. The decays B_c^+\rightarrow ( \psi(2S) \rightarrow J/\psi \pi^+ \pi^-)\pi^+ , B_c^+\righta... Preprint Full-text available The centrality of heavy-ion collisions is directly related to the medium created therein. A procedure to determine the centrality of collisions with the LHCb detector is implemented for lead-lead collisions at \sqrt{s_{\scriptscriptstyle\text{NN}}}=5\, \mathrm{TeV} and lead-neon fixed-target collisions at \sqrt{s_{\scriptscriptstyle\text{NN}}}=6... Preprint Full-text available Tests of lepton universality in B^0\to K^0_S l^+ l^- and B^+\to K^{*+}\ell^+\ell^- decays where l is either an electron or a muon are presented. The differential branching fractions of B^0\to K^0_S l^+ l^- and B^+\to K^{*+}\ell^+\ell^- decays are measured in intervals of the dilepton invariant mass squared. The measurements are performed... Preprint Full-text available A search is performed for massive long-lived particles (LLP) decaying semileptonically into a muon and two quarks. Two kinds of LLP production processes were considered. In the first a Higgs-like boson with mass from 30 to 200 GeV is produced by gluon fusion and decays into two LLPs. The analysis covers LLP mass values from 10 GeV up to about one h... Preprint Full-text available Two narrow resonant states are observed in the {\it\Lambda}_b^0 K^-\pi^+ mass spectrum using a data sample of proton-proton collisions at a center-of-mass energy of 13~\rm TeV, collected by the LHCb experiment and corresponding to an integrated luminosity of 6~{\rm fb}^{-1}. The minimal quark content of the {\it\Lambda}_b^0 K^-\pi^+ system... Preprint Full-text available A combination of measurements sensitive to the CP violation angle \gamma of the Cabibbo-Kobayashi-Maskawa unitarity triangle and to the charm mixing parameters that describe oscillations between D^0 and \bar{D}^0 mesons is performed. Results from the charm and beauty sectors, based on data collected with the LHCb detector at CERN's Large Ha... Article Full-text available A search for the doubly charmed baryon Ω +cc with the decay mode Ω +cc → Ξ +c K−π+ is performed using proton-proton collision data at a centre-of-mass energy of 13 TeV collected by the LHCb experiment from 2016 to 2018, corresponding to an integrated luminosity of 5.4 fb−1. No significant signal is observed within the invariant mass range of 3.6 to... Article Full-text available A bstract This article presents differential measurements of the asymmetry between$$ {\varLambda}_b^0 $$Λ b 0 and$$ {\overline{\varLambda}}_b^0 $$Λ ¯ b 0 baryon production rates in proton-proton collisions at centre-of-mass energies of$$ \sqrt{s} $$s = 7 and 8 TeV collected with the LHCb experiment, corresponding to an integrated luminosity o... Preprint Full-text available The fraction of Z+jet events that contain a charm jet is measured for the first time in the forward region of proton-proton collisions. The data sample used corresponds to an integrated luminosity of 6 fb^{-1} collected at a center-of-mass energy of 13 TeV with the LHCb detector. The ratio of production cross sections {\sigma(Zc)/\sigma(Zj)}... Preprint Full-text available The production cross-section of the \chi_{c1}(3872) state relative to the \psi(2S) meson is measured using proton-proton collision data collected with the LHCb experiment at centre-of-mass energies of \sqrt{s}=8 and 13 TeV, corresponding to integrated luminosities of 2.0 and 5.4 fb^{-1}, respectively. The two mesons are reconstructed in the... Preprint Full-text available A search for the doubly charmed baryon \it{\Xi}_{cc}^{+} is performed in the \it{\Xi}_{cc}^{+} \rightarrow \it{\Xi}_{c}^{+} \pi^{-} \pi^{+} decay mode, where the \it{\Xi}_{c}^{+} baryon is reconstructed in the p K^{-} \pi^{+} final state. The study uses proton-proton collision data collected with the LHCb detector at a centre-of-mass energy... Preprint Full-text available A study of \Lambda_b^0 baryon decays to the DpK^- final state is presented based on a proton-proton collision data sample corresponding to an integrated luminosity of 9 fb^{-1} collected with the LHCb detector. Two \Lambda_b^0 decays are considered, \Lambda_b^0\to DpK^- with D\to K^-\pi^+ and D\to K^+\pi^-, where D represents a supe... Preprint Full-text available A measurement of the lifetimes of the \Omega^{0}_{c} and \Xi^{0}_{c} baryons is reported using proton-proton collision data at a centre-of-mass energy of 13\text{ TeV}, corresponding to an integrated luminosity of 5.4\text{ fb}^{-1} collected by the LHCb experiment. The \Omega^{0}_{c} and \Xi^{0}_{c} baryons are produced directly from p... Preprint Full-text available The W boson mass is measured using proton-proton collision data at \sqrt{s}=13 TeV corresponding to an integrated luminosity of 1.7 fb^{-1} recorded during 2016 by the LHCb experiment. With a simultaneous fit of the muon q/p_T distribution of a sample of W \to \mu\nu decays and the \phi^* distribution of a sample of Z\to\mu\mu decays... Preprint Full-text available An exotic narrow state in the D^0D^0\pi^+ mass spectrum just below the D^{*+}D^0 mass threshold is studied using a data set corresponding to an integrated luminosity of 9 fb^{-1} acquired with the LHCb detector in proton-proton collisions at centre-of-mass energies of 7, 8 and 13 TeV. The state is consistent with the ground isoscalar T^+_{cc... Preprint Full-text available Conventional hadronic matter consists of baryons and mesons made of three quarks and quark-antiquark pairs, respectively. The observation of a new type of hadronic state, a doubly charmed tetraquark containing two charm quarks, an anti-u and an anti-d quark, is reported using data collected by the LHCb experiment at the Large Hadron Collider. T... Preprint Full-text available A data set corresponding to an integrated luminosity of 9 \text{fb}^{-1} of proton-proton collisions collected by the LHCb experiment has been analysed to search for B_c^+ \to D^{(*)+}_{(s)} \overset{\scriptstyle (-)}{D}{}^{(*)0} decays. The decays are fully or partially reconstructed, where one or two missing neutral pions or photons from the... Preprint Full-text available The production cross-sections of J/\psi mesons in proton-proton collisions at a centre-of-mass energy of \sqrt{s}=5 TeV are measured using a data sample corresponding to an integrated luminosity of 9.13\pm0.18~\text{pb}^{-1}, collected by the LHCb experiment. The cross-sections are measured differentially as a function of transverse momentum,... Preprint Full-text available The production of prompt charged particles in proton-lead collisions and in proton-proton collisions at the nucleon-nucleon centre-of-mass energy {\sqrt{s_{\scriptscriptstyle\mathrm{NN}}}=5\,\mathrm{TeV}} is studied at LHCb as a function of pseudorapidity (\eta) and transverse momentum (p_{\mathrm{T}}) with respect to the proton beam directio... Preprint Full-text available Branching fraction and effective lifetime measurements of the rare decay B^0_s\to\mu^+\mu^- and searches for the decays B^0\to\mu^+\mu^- and B^0_s\to\mu^+\mu^-\gamma are reported using proton-proton collision data collected with the LHCb detector at centre-of-mass energies of 7 TeV, 8 TeV and 13 TeV, corresponding to a luminosity of~9~f... Preprint Full-text available An improved measurement of the decay B^0_s\to\mu^+\mu^- and searches for the decays B^0\to\mu^+\mu^- and B^0_s\to\mu^+\mu^-\gamma are performed at the LHCb experiment using data collected in proton-proton collisions at \sqrt{s} = 7,~8 and 13 TeV, corresponding to integrated luminosities of 1, 2 and 6 fb^{-1}, respectively. The B^0_s\to... Preprint Full-text available The first search for the rare radiative decay Xib2XiGamma is performed using data collected by the LHCb experiment in proton-proton collisions at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 5.4 fb^{-1}. The Xib2XiJpsi channel is used as normalization. No Xib2XiGamma signal is found and an upper limit of B(Xib2XiG... Preprint Full-text available An amplitude analysis of flavour-untagged B_s^0 \to J/\psi p \bar{p} decays is performed using a sample of 797\pm31 decays reconstructed with the LHCb detector. The data, collected in proton-proton collisions between 2011 and 2018, correspond to an integrated luminosity of 9 \text{fb}^{-1}. Evidence for a new structure in the J/\psi p and ... Preprint Full-text available The photo-production of J/\psi mesons at low transverse momentum is studied in peripheral lead-lead collisions collected by the LHCb experiment at a centre-of-mass energy per nucleon pair of 5 TeV, corresponding to an integrated luminosity of 210 \rm{\mu b}^{-1}. The J/\psi candidates are reconstructed through the prompt decay into two muons... Preprint Full-text available An angular analysis of the rare decay B^0_s\rightarrow\phi\mu^+\mu^- is presented, using proton-proton collision data collected by the LHCb experiment at centre-of-mass energies of 7, 8 and 13~\rm{TeV}, corresponding to an integrated luminosity of 8.4~\rm{fb}^{-1}. The observables describing the angular distributions of the decay B^0_s\r... Preprint Full-text available The differential cross-section of prompt inclusive production of long-lived charged particles in proton-proton collisions is measured using a data sample recorded by the LHCb experiment at a centre-of-mass energy of {\sqrt{s} = 13\,\mathrm{TeV}}. The data sample, collected with an unbiased trigger, corresponds to an integrated luminosity of {5.4... Preprint Full-text available This article presents differential measurements of the asymmetry between \Lambda_b^0 and \overline{\Lambda}_b^0 baryon production rates in proton-proton collisions at centre-of-mass energies of \sqrt{s}=7 and 8\,\textrm{TeV} collected with the LHCb experiment, corresponding to an integrated luminosity of 3\,\textrm{fb}^{-1}. The \Lambda_... Article A structure is observed in the$${B} ^{\pm }{K} ^{\mp }$$B ± K ∓ mass spectrum in a sample of proton–proton collisions at centre-of-mass energies of 7, 8, and 13 TeV, collected with the LHCb detector and corresponding to a total integrated luminosity of 9$$\,\text {fb} ^{-1}$$fb - 1 . The structure is interpreted as the result of overlapping exc... Preprint Full-text available The first observation of the \Omega_b^-\to\Xi_c^+ K^- \pi^- decay is reported using proton-proton collision data at centre-of-mass energies of 7, 8 and 13\,\mathrm{TeV} collected by the LHCb experiment, corresponding to an integrated luminosity of 9\,\mathrm{fb}^{-1}. Four excited \Omega_c^0 baryons are observed in the \Xi_c^+ K^- mas... Preprint Full-text available Coherent production of J/\psi mesons is studied in ultraperipheral lead-lead collisions at a nucleon-nucleon centre-of-mass energy of 5 TeV, using a data sample collected by the LHCb experiment corresponding to an integrated luminosity of about 10 \mu b^{-1}. The J/\psi mesons are reconstructed in the dimuon final state and are required to ha... Preprint Full-text available The upgraded LHCb detector, due to start datataking in 2022, will have to process an average data rate of 4~TB/s in real time. Because LHCb's physics objectives require that the full detector information for every LHC bunch crossing is read out and made available for real-time processing, this bandwidth challenge is equivalent to that of the ATLAS... Preprint Full-text available A measurement of mixing and C\!P violation in neutral charm mesons is performed using data reconstructed in proton-proton collisions collected by the LHCb experiment from 2016 to 2018, corresponding to an integrated luminosity of 5.4\textrm{fb}^{-1}. A total of 30.6 million D^{0}\rightarrow K^{0}_{\mathrm{S}}\pi^{+}\pi^{-} decays are analyz... Article Full-text available A bstract The first full angular analysis of the$$ {B}^0\to {D}^{\ast -}{D}_s^{\ast +} $$B 0 → D ∗ − D s ∗ + decay is performed using 6 fb − 1 of pp collision data collected with the LHCb experiment at a centre-of-mass energy of 13 TeV. The$$ {D}_s^{\ast +}\to {D}_s^{+}\gamma $$D s ∗ + → D s + γ and D * − →$$ {\overline{D}}^0{\pi}^{-}  D ¯ 0...