arXiv subjects

W. Bonivento

Publications and source records attributed to W. Bonivento.

At least 55 records · Page 3Linked to original sources

arXiv2018

Observation of the decay $Λ^0_b \to p K^- μ^+ μ^-$ and a search for $C\!P$ violation

A search for $C\!P$ violation in the decay $Λ^0_b \to p K^- μ^+ μ^-$ is presented. This decay is mediated by flavour-changing neutral-current transitions in the Standard Model and is potentially sensitive to new sources of $C\!P$ violation. The study is based on a data sample of proton-proton collisions recorded with the LHCb experiment, corresponding to an integrated luminosity of $3$ $\mathrm{fb}^{-1}$. The $Λ^0_b \to p K^- μ^+ μ^-$ decay is observed for the first time, and two observables that are sensitive to different manifestations of $C\!P$ violation are measured, $Δ\mathcal{A}_{C\!P} \equiv \mathcal{A}_{C\!P}(Λ^0_b \to p K^- μ^+ μ^-)-\mathcal{A}_{C\!P}(Λ^0_b\to pK^- J/ψ)$ and $a_{C\!P}^{\widehat{T}-odd}$, where the latter is based on asymmetries in the angle between the $μ^+μ^-$ and $p K^-$ decay planes. These are measured to be $Δ\mathcal{A}_{C\!P} = (-3.5 \pm 5.0(stat) \pm 0.2(syst))\times 10^{-2}$, $a_{C\!P}^{\widehat{T}-odd} = (1.2 \pm 5.0(stat) \pm 0.7(syst))\times 10^{-2}$, and no evidence for $C\!P$ violation is found.

hep-ex↗

arXiv2018

Measurement of the shape of the $Λ_b^0\toΛ_c^+ μ^- \overlineν$ differential decay rate

A measurement of the shape of the differential decay rate and the associated Isgur-Wise function for the decay $Λ_b^0\toΛ_c^+μ^-\overlineν$ is reported, using data corresponding to $3 fb^{-1}$ collected with the LHCb detector in proton-proton collisions. The $Λ_c^+μ^-\overlineν$(+ anything) final states are reconstructed through the detection of a muon and a $Λ_c^+$ baryon decaying into $pK^-π^+$, and the decays $Λ_b^0\toΛ_c^+π^+π^-μ^-\overlineν$ are used to determine contributions from $Λ_b^0\to Λ_c^{\star+}μ^-\barν$ decays. The measured dependence of the differential decay rate upon the squared four-momentum transfer between the heavy baryons, $q^2$, is compared with expectations from heavy-quark effective theory and from unquenched lattice QCD predictions.

hep-ex↗

arXiv2018

First observation of forward $Z \rightarrow b \bar{b}$ production in $pp$ collisions at $\sqrt{s}=8$ TeV

The decay $Z \rightarrow b \bar{b}$ is reconstructed in $pp$ collision data, corresponding to 2 fb$^{-1}$ of integrated luminosity, collected by the LHCb experiment at a centre-of-mass energy of $\sqrt{s}=8$ TeV. The product of the $Z$ production cross-section and the $Z \rightarrow b \bar{b}$ branching fraction is measured for candidates in the fiducial region defined by two particle-level $b$-quark jets with pseudorapidities in the range $2.2 < η< 4.2$, with transverse momenta $p_{T}>20$ GeV and dijet invariant mass in the range $45 < m_{jj} < 165$ GeV. From a signal yield of $5462 \pm 763$ $Z \rightarrow b \bar{b}$ events, where the uncertainty is statistical, a production cross-section times branching fraction of $332 \pm 46 \pm 59$ pb is obtained, where the first uncertainty is statistical and the second systematic. The measured significance of the signal yield is 6.0 standard deviations. This measurement represents the first observation of the $Z \rightarrow b \bar{b}$ production in the forward region of $pp$ collisions.

hep-ex↗

arXiv2017

Measurement of the $Υ$ polarizations in $pp$ collisions at $\sqrt{s}$=7 and 8TeV

The polarization of the $Υ(1S)$, $Υ(2S)$ and $Υ(3S) $mesons, produced in $pp$ collisions at centre-of-mass energies $\sqrt{s}$=7 and 8TeV, is measured using data samples collected by the LHCb experiment, corresponding to integrated luminosities of 1 and 2fb$^{-1}$, respectively. The measurements are performed in three polarization frames, using $Υ\toμ^+μ^-$ decays in the kinematic region of the transverse momentum $p_{T}(Υ)<30GeV/c$, and rapidity $2.2<y(Υ)<4.5$. No large polarization is observed.

hep-ex↗

arXiv2017

Study of $b\bar{b}$ correlations in high energy proton-proton collisions

Kinematic correlations for pairs of beauty hadrons, produced in high energy proton-proton collisions, are studied. The data sample used was collected with the LHCb experiment at centre-of-mass energies of 7 and 8 TeV and corresponds to an integrated luminosity of 3 fb$^{-1}$. The measurement is performed using inclusive $b\rightarrow J/ψX$ decays in the rapidity range $2<y^{J/ψ}<4.5$. The observed correlations are in good agreement with theoretical predictions.

hep-ex↗

arXiv2017

Measurement of $CP$ observables in $B^\pm \to D^{()} K^\pm$ and $B^\pm \to D^{()} π^\pm$ decays

Measurements of $CP$ observables in $B^\pm \rightarrow D^{(*)} K^\pm$ and $B^\pm \rightarrow D^{(*)} π^\pm$ decays are presented, where $D^{(*)}$ indicates a neutral $D$ or $D^*$ meson that is an admixture of $D^{(*)0}$ and $\bar{D}^{(*)0}$ states. Decays of the $D^*$ meson to the $Dπ^0$ and $Dγ$ final states are partially reconstructed without inclusion of the neutral pion or photon, resulting in distinctive shapes in the $B$ candidate invariant mass distribution. Decays of the $D$ meson are fully reconstructed in the $K^\pm π^\mp$, $K^+ K^-$ and $π^+ π^-$ final states. The analysis uses a sample of charged $B$ mesons produced in $pp$ collisions collected by the LHCb experiment, corresponding to an integrated luminosity of 2.0, 1.0 and 2.0 fb$^{-1}$ taken at centre-of-mass energies of $\sqrt{s}$ = 7, 8 and 13 TeV, respectively. The study of $B^{\pm} \to D^{*} K^{\pm}$ and $B^{\pm} \to D^{*} π^{\pm}$ decays using a partial reconstruction method is the first of its kind, while the measurement of $B^{\pm} \to D K^{\pm}$ and $B^{\pm} \to D π^{\pm}$ decays is an update of previous LHCb measurements. The $B^{\pm} \to D K^{\pm}$ results are the most precise to date.

hep-ex↗

arXiv2017

First observation of the rare purely baryonic decay $B^0 \to p \bar{p}$

The first observation of the decay of a $B^0$ meson to a purely baryonic final state, $B^0 \to p \bar{p}$, is reported. The proton-proton collision data sample used was collected with the LHCb experiment at center-of-mass energies of 7 and 8 TeV and corresponds to an integrated luminosity of 3.0 fb$^{-1}$. The branching fraction is determined to be $${\cal B}(B^0 \to p \bar{p}) = ( 1.25 \pm 0.27 \pm 0.18 ) \times 10^{-8} ,$$ where the first uncertainty is statistical and the second systematic. The decay mode $B^0 \to p \bar{p}$ is the rarest decay of the $B^0$ meson observed to date. The decay $B_s^0 \to p \bar{p}$ is also investigated. No signal is seen and the upper limit ${\cal B}(B_s^0 \to p \bar{p}) < 1.5 \times 10^{-8}$ at 90% confidence level is set on the branching fraction.

hep-ex↗

arXiv2017

Updated search for long-lived particles decaying to jet pairs

A search is presented for long-lived particles with a mass between 25 and 50 GeV/$c^2$ and a lifetime between 2 and 500 ps, using proton-proton collision data corresponding to an integrated luminosity of 2.0 fb$^{-1}$, collected by the LHCb detector at centre-of-mass energies of 7 and 8 TeV. The particles are assumed to be pair-produced in the decay of a 125 GeV/$c^2$ Standard-Model-like Higgs boson. The experimental signature is a single long-lived particle, identified by a displaced vertex with two associated jets. No excess above background is observed and limits are set on the production cross-section as a function of the mass and lifetime of the long-lived particle.

hep-ex↗

arXiv2017

Measurement of $B^0$, $B^0_s$, $B^+$ and $Λ^0_b$ production asymmetries in 7 and 8 TeV proton-proton collisions

The $B^0$, $B^0_s$, $B^+$ and $Λ^0_b$ hadron production asymmetries are measured using a data sample corresponding to an integrated luminosity of 3.0 fb$^{-1}$, collected by the LHCb experiment in proton-proton collisions at centre-of-mass energies of 7 and 8 TeV. The measurements are performed as a function of transverse momentum and rapidity of the $b$ hadrons within the LHCb detector acceptance. The overall production asymmetries, integrated over transverse momentum and rapidity, are also determined.

hep-ex↗

arXiv2017

Prompt and nonprompt J/$ψ$ production and nuclear modification in $p$Pb collisions at $\sqrt{s_{\text{NN}}}= 8.16$ TeV

The production of J/$ψ$ mesons is studied in proton-lead collisions at the centre-of-mass energy per nucleon pair $\sqrt{s_{\text{NN}}}=8.16$ TeV with the LHCb detector at the LHC. The double differential cross-sections of prompt and nonprompt J/$ψ$ production are measured as functions of the J/$ψ$ transverse momentum and rapidity in the nucleon-nucleon centre-of-mass frame. Forward-to-backward ratios and nuclear modification factors are determined. The results are compared with theoretical calculations based on collinear factorisation using nuclear parton distribution functions, on the colour glass condensate or on coherent energy loss models.

hep-ex↗

arXiv2017

Updated branching fraction measurements of $B^0_{(s)} \to K_{\mathrm{\scriptscriptstyle S}}^0 h^+ h^{\prime -}$ decays

The charmless three-body decays $B^0_{(s)} \to K_{\mathrm{\scriptscriptstyle S}}^0 h^+ h^{\prime -}$ (where $h^{(\prime)} = π, K$) are analysed using a sample of $pp$ collision data recorded by the LHCb experiment, corresponding to an integrated luminosity of $3\mbox{fb}^{-1}$. The branching fractions are measured relative to that of the $B^0 \to K_{\mathrm{\scriptscriptstyle S}}^0 π^{+} π^{-}$ decay, and are determined to be: \begin{eqnarray*} \frac{{\cal B}(B^0\rightarrow K^0_{\rm S}K^{\pm}π^{\mp})}{{\cal B}(B^0\rightarrow K^0_{\rm S}π^{+}π^{-})} = {} & 0.123 \pm 0.009 \; \mathrm{\,(stat)}\; \pm 0.015 \; \mathrm{\,(syst)}\,, \frac{{\cal B}(B^0\rightarrow K^0_{\rm S}K^{+}K^{-})} {{\cal B}(B^0\rightarrow K^0_{\rm S}π^{+}π^{-})} = {} & 0.549 \pm 0.018 \; \mathrm{\,(stat)}\; \pm 0.033 \; \mathrm{\,(syst)}\,, \frac{{\cal B}(B_{s}^0\rightarrow K^0_{\rm S}π^{+}π^{-})}{{\cal B}(B^0\rightarrow K^0_{\rm S}π^{+}π^{-})} = {} & 0.191 \pm 0.027 \; \mathrm{\,(stat)}\; \pm 0.031 \; \mathrm{\,(syst)}\; \pm 0.011 \; (f_s/f_d) \,, \frac{{\cal B}(B_{s}^0\rightarrow K^0_{\rm S}K^{\pm}π^{\mp})} {{\cal B}(B^0\rightarrow K^0_{\rm S}π^{+}π^{-})} = {} & 1.70\phantom{0} \pm 0.07\phantom{0} \; \mathrm{\,(stat)} \; \pm 0.11\phantom{0} \; \mathrm{\,(syst)}\; \pm 0.10\phantom{0} \; (f_s/f_d) \,, \frac{{\cal B}(B_{s}^0\rightarrow K^0_{\rm S}K^{+}K^{-})}{{\cal B}(B^0\rightarrow K^0_{\rm S}π^{+}π^{-})} \in {} & [0.008 - 0.051] \rm ~at~90\%~confidence~level, \end{eqnarray*} where $f_s/f_d$ represents the ratio of hadronisation fractions of the $B^0_s$ and $B^0$ mesons.

hep-ex↗

arXiv2017

The Electronics, Trigger and Data Acquisition System for the Liquid Argon Time Projection Chamber of the DarkSide-50 Search for Dark Matter

The DarkSide-50 experiment at the Laboratori Nazionali del Gran Sasso is a search for dark matter using a dual phase time projection chamber with 50 kg of low radioactivity argon as target. Light signals from interactions in the argon are detected by a system of 38 photo-multiplier tubes (PMTs), 19 above and 19 below the TPC volume inside the argon cryostat. We describe the electronics which processes the signals from the photo-multipliers, the trigger system which identifies events of interest, and the data-acquisition system which records the data for further analysis. The electronics include resistive voltage dividers on the PMTs, custom pre-amplifiers mounted directly on the PMT voltage dividers in the liquid argon, and custom amplifier/discriminators (at room temperature). After amplification, the PMT signals are digitized in CAEN waveform digitizers, and CAEN logic modules are used to construct the trigger, the data acquisition system for the TPC is based on the Fermilab "artdaq" software. The system has been in operation since early 2014.

physics.ins-det↗

arXiv2017

Observation of $D^0$ meson decays to $π^+π^-μ^+μ^-$ and $K^+K^-μ^+μ^-$ final states

The first observation of the $D^0 \to π^+π^-μ^+μ^-$ and $D^0 \to K^+K^-μ^+μ^-$ decays is reported using a sample of proton-proton collisions collected by LHCb at a center-of-mass energy of 8$\,$TeV, and corresponding to 2$\,$fb$^{-1}$ of integrated luminosity. The corresponding branching fractions are measured using as normalization the decay $D^0 \to K^- π^+[μ^+μ^-]_{ρ^0/ω}$, where the two muons are consistent with coming from the decay of a $ρ^0$ or $ω$ meson. The results are $\mathcal{B}(D^0 \to π^+π^-μ^+μ^-)=(9.64\pm0.48\pm0.51\pm0.97)\times10^{-7}$ and $\mathcal{B}(D^0 \to K^+K^-μ^+μ^-)=( 1.54\pm0.27\pm0.09\pm0.16)\times10^{-7}$, where the uncertainties are statistical, systematic, and due to the limited knowledge of the normalization branching fraction. The dependence of the branching fraction on the dimuon mass is also investigated.

hep-ex↗

arXiv2017

Search for baryon-number-violating $Ξ_b^0$ oscillations

A search for baryon-number-violating $Ξ_b^0$ oscillations is performed with a sample of $pp$ collision data recorded by the LHCb experiment, corresponding to an integrated luminosity of 3 fb$^{-1}$. The baryon number at the moment of production is identified by requiring that the $Ξ_b^0$ come from the decay of a resonance $Ξ_b^{*-} \to Ξ_b^0 π^-$ or $Ξ_b^{\prime-} \to Ξ_b^0 π^-$, and the baryon number at the moment of decay is identified from the final state using the decays $Ξ_b^0 \to Ξ_c^+ π^-, ~ Ξ_c^+ \to p K^- π^+$. No evidence of baryon number violation is found, and an upper limit at the 95% confidence level is set on the oscillation rate of $ω< 0.08$ ps$^{-1}$, where $ω$ is the associated angular frequency.

hep-ex↗

arXiv2017

Observation of the decay $B_{s}^{0} \to η_{c} ϕ$ and evidence for $B_{s}^{0} \to η_{c} π^{+} π^{-} $

A study of $B^{0}_{s} \to η_{c} ϕ$ and $B^{0}_{s} \to η_{c} π^{+}π^{-}$ decays is performed using $pp$ collision data corresponding to an integrated luminosity of 3.0$\,\rm fb^{-1}$, collected with the LHCb detector in Run~1 of the LHC. The observation of the decay $B^{0}_{s} \to η_{c} ϕ$ is reported, where the $η_{c}$ meson is reconstructed in the $p\bar p$, $K^+K^-π^+π^-$, $π^+π^-π^+π^-$ and $K^+K^-K^+K^-$ decay modes and the $ϕ(1020)$ in the $K^+ K^-$ decay mode. The decay $B^{0}_{s} \to J/ψϕ$ is used as a normalisation channel. Evidence is also reported for the decay $B^{0}_{s} \to η_{c} π^{+}π^{-}$, where the $η_{c}$ meson is reconstructed in the $p\bar p$ decay mode, using the decay $B^{0}_{s} \to J/ψπ^+ π^-$ as a normalisation channel. The measured branching fractions are \begin{eqnarray*} {\mathcal B (B^{0}_{s} \to η_{c} ϕ)} &=& \left(5.01 \pm 0.53 \pm 0.27 \pm 0.63 \right) \times 10^{-4} \,, \nonumber \\ {\mathcal B (B^{0}_{s} \to η_{c} π^+ π^-)} &=& \left(1.76 \pm 0.59 \pm 0.12 \pm 0.29 \right) \times 10^{-4} \,, \end{eqnarray*} where in each case the first uncertainty is statistical, the second systematic and the third uncertainty is due to the limited knowledge of the external branching fractions.

hep-ex↗

arXiv2017

Measurement of matter-antimatter differences in beauty baryon decays

Differences in the behaviour of matter and antimatter have been observed in $K$ and $B$ meson decays, but not yet in any baryon decay. Such differences are associated with the non-invariance of fundamental interactions under the combined charge-conjugation and parity transformations, known as $C\!P$ violation. Using data from the LHCb experiment at the Large Hadron Collider, a search is made for $C\!P$-violating asymmetries in the decay angle distributions of $Λ^0_b$ baryons decaying to $pπ^-π^+π^-$ and $pπ^-K^+K^-$ final states. These four-body hadronic decays are a promising place to search for sources of $C\!P$ violation both within and beyond the Standard Model of particle physics. We find evidence for $C\!P$ violation in $Λ^0_b$ to $pπ^-π^+π^-$ decays with a statistical significance corresponding to 3.3 standard deviations including systematic uncertainties. This represents the first evidence for $C\!P$ violation in the baryon sector.

hep-ex↗

arXiv2017

Improved limit on the branching fraction of the rare decay $K^0_{\scriptscriptstyle S}\toμ^+μ^-$

A search for the decay $K^0_{\scriptscriptstyle S}\toμ^+μ^-$ is performed, based on a data sample of proton-proton collisions corresponding to an integrated luminosity of 3 fb$^{-1}$, collected by the LHCb experiment at centre-of-mass energies of 7 and 8 TeV. The observed yield is consistent with the background-only hypothesis, yielding a limit on the branching fraction of ${\cal B}(K^0_{\scriptscriptstyle S}\toμ^+μ^-) < 0.8~(1.0) \times 10^{-9}$ at $90\%~(95\%)$ confidence level. This result improves the previous upper limit on the branching fraction by an order of magnitude.

hep-ex↗

arXiv2017

Observation of the $B^+ \to D^{*-}K^+π^+$ decay

The $B^+ \to D^{*-}K^+π^+$ decay potentially provides an excellent way to investigate charm meson spectroscopy. The decay is searched for in a sample of proton-proton collision data collected with the LHCb detector at centre-of-mass energies of 7 and 8 TeV, corresponding to an integrated luminosity of $3~{\rm fb}^{-1}$. A clear signal is observed, and the ratio of its branching fraction to that of the $B^+ \to D^{*-}π^+π^+$ normalisation channel is measured to be \begin{equation*} \frac{\mathcal{B}(B^+ \to D^{*-}K^+π^+)}{\mathcal{B}(B^+ \to D^{*-}π^+π^+)} = \left( 6.39 \pm 0.27 \pm 0.48 \right) \times 10^{-2} \, , \end{equation*} where the first uncertainty is statistical and the second is systematic. This is the first observation of the $B^+ \to D^{*-}K^+π^+$ decay.

hep-ex↗