arXiv subjects

A. Cardini

Publications and source records attributed to A. Cardini.

At least 37 records · Page 2Linked to original sources

arXiv2016

Observation of the $B_s^0 \rightarrow J/ψϕϕ$ decay

The $B_s^0 \rightarrow J/ψϕϕ$ decay is observed in $pp$ collision data corresponding to an integrated luminosity of 3 fb$^{-1}$ recorded by the LHCb detector at centre-of-mass energies of 7 TeV and 8 TeV. This is the first observation of this decay channel, with a statistical significance of 15 standard deviations. The mass of the $B_s^0$ meson is measured to be $5367.08\,\pm \,0.38\,\pm\, 0.15$ MeV/c$^2$. The branching fraction ratio $\mathcal{B}(B_s^0 \rightarrow J/ψϕϕ)/\mathcal{B}(B_s^0 \rightarrow J/ψϕ)$ is measured to be $0.0115\,\pm\, 0.0012\, ^{+0.0005}_{-0.0009}$. In both cases, the first uncertainty is statistical and the second is systematic. No evidence for non-resonant $B_s^0 \rightarrow J/ψϕK^+ K^-$ or $B_s^0 \rightarrow J/ψK^+ K^- K^+ K^-$ decays is found.

hep-ex↗

arXiv2016

Studies of the resonance structure in $D^0\to K^0_S K^{\pm}π^{\mp}$ decays

Amplitude models are applied to studies of resonance structure in $D^0\to K^0_S K^- π^+$ and $D^0\to K^0_S K^+ π^-$ decays using $pp$ collision data corresponding to an integrated luminosity of $3.0\,\mathrm{fb}^{-1}$ collected by the LHCb experiment. Relative magnitude and phase information is determined, and coherence factors and related observables are computed for both the whole phase space and a restricted region of $100\,\mathrm{MeV/}c^2$ around the $K^{*}(892)^{\pm}$ resonance. Two formulations for the $Kπ$ $S$-wave are used, both of which give a good description of the data. The ratio of branching fractions $\mathcal{B}(D^0\to K^0_S K^+ π^-)/\mathcal{B}(D^0\to K^0_S K^- π^+)$ is measured to be $0.655\pm0.004\,(\textrm{stat})\pm0.006\,(\textrm{syst})$ over the full phase space and $0.370\pm0.003\, (\textrm{stat})\pm0.012\,(\textrm{syst})$ in the restricted region. A search for $CP$ violation is performed using the amplitude models and no significant effect is found. Predictions from $SU(3)$ flavor symmetry for $K^{*}(892)K$ amplitudes of different charges are compared with the amplitude model results.

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arXiv2016

Measurement of the front-end dead-time of the LHCb muon detector and evaluation of its contribution to the muon detection inefficiency

A method is described which allows to deduce the dead-time of the front-end electronics of the LHCb muon detector from a series of measurements performed at different luminosities at a bunch-crossing rate of 20 MHz. The measured values of the dead-time range from 70 ns to 100 ns. These results allow to estimate the performance of the muon detector at the future bunch-crossing rate of 40 MHz and at higher luminosity.

physics.ins-det↗

arXiv2016

Search for long-lived heavy charged particles using a ring imaging Cherenkov technique at LHCb

A search is performed for heavy long-lived charged particles using 3.0 fb$^{-1}$ of pp collisions collected at $\sqrt{s}$= 7 and 8 TeV with the LHCb detector. The search is mainly based on the response of the ring imaging Cherenkovdetectors to distinguish the heavy, slow-moving particles from muons. No evidence is found for the production of such long-lived states. The results are expressed as limits on the Drell-Yan production of pairs of long-lived particles, with both particles in the LHCb pseudorapidity acceptance, $1.8 < η< 4.9$. The mass-dependent cross-section upper limits are in the range 2-4 fb (at 95\% CL) for masses between 124 and 309 GeV/c$^2$.

hep-ex↗

arXiv2016

Angular analysis of the $B^{0}\rightarrow K^{*0}μ^{+}μ^{-}$ decay using $3\,\mbox{fb}^{-1}$ of integrated luminosity

An angular analysis of the $B^{0}\rightarrow K^{*0}(\rightarrow K^{+}π^{-})μ^{+}μ^{-}$ decay is presented. The dataset corresponds to an integrated luminosity of $3.0\,{\mbox{fb}^{-1}}$ of $pp$ collision data collected at the LHCb experiment. The complete angular information from the decay is used to determine $C\!P$-averaged observables and $C\!P$ asymmetries, taking account of possible contamination from decays with the $K^{+}π^{-}$ system in an S-wave configuration. The angular observables and their correlations are reported in bins of $q^2$, the invariant mass squared of the dimuon system. The observables are determined both from an unbinned maximum likelihood fit and by using the principal moments of the angular distribution. In addition, by fitting for $q^2$-dependent decay amplitudes in the region $1.1<q^{2}<6.0\mathrm{\,Ge\kern -0.1em V}^{2}/c^{4}$, the zero-crossing points of several angular observables are computed. A global fit is performed to the complete set of $C\!P$-averaged observables obtained from the maximum likelihood fit. This fit indicates differences with predictions based on the Standard Model at the level of 3.4 standard deviations. These differences could be explained by contributions from physics beyond the Standard Model, or by an unexpectedly large hadronic effect that is not accounted for in the Standard Model predictions.

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arXiv2016

A model-independent confirmation of the $Z(4430)^-$ state

The decay $B^0\to ψ(2S) K^+π^-$ is analyzed using $\rm 3~fb^{-1}$ of $pp$ collision data collected with the LHCb detector. A model-independent description of the $ψ(2S) π$ mass spectrum is obtained, using as input the $Kπ$ mass spectrum and angular distribution derived directly from data, without requiring a theoretical description of resonance shapes or their interference. The hypothesis that the $ψ(2S)π$ mass spectrum can be described in terms of $Kπ$ reflections alone is rejected with more than 8$σ$ significance. This provides confirmation, in a model-independent way, of the need for an additional resonant component in the mass region of the $Z(4430)^-$ exotic state.

hep-ex↗

arXiv2016

Study of $D^{()+}_{sJ}$ mesons decaying to $D^{+} K^0_{\rm S}$ and $D^{*0} K^+$ final states

A search is performed for $D^{(*)+}_{sJ}$ mesons in the reactions $pp \to D^{*+} K^0_{\rm S} X$ and $pp \to D^{*0} K^+ X$ using data collected at centre-of-mass energies of 7 and 8 TeV with the LHCb detector. For the $D^{*+} K^0_{\rm S}$ final state, the decays $D^{*+} \to D^0 π^+$ with $D^0 \to K^- π^+$ and $D^0 \to K^- π^+ π^+ π^-$ are used. For $D^{*0} K^+$, the decay $D^{*0} \to D^0 π^0$ with $D^0 \to K^- π^+$ is used. A prominent $D_{s1}(2536)^+$ signal is observed in both $D^{*+} K^0_{\rm S}$ and $D^{*0} K^+$ final states. The resonances $D^*_{s1}(2700)^+$ and $D^*_{s3}(2860)^+$ are also observed, yielding information on their properties, including spin-parity assignments. The decay $D^*_{s2}(2573)^+ \to D^{*+} K^0_{\rm S}$ is observed for the first time, at a significance of 6.9 $σ$, and its branching fraction relative to the $D^*_{s2}(2573)^+ \to D^+ K^0_{\rm S}$ decay mode is measured.

hep-ex↗

arXiv2016

Measurement of forward $W$ and $Z$ boson production in $pp$ collisions at $\sqrt{s} = 8\mathrm{\,Te\kern -0.1em V}$

Measurements are presented of electroweak boson production using data from $pp$ collisions at a centre-of-mass energy of $\sqrt{s} = 8\mathrm{\,Te\kern -0.1em V}$. The analysis is based on an integrated luminosity of $2.0\mathrm{\,fb}^{-1}$ recorded with the LHCb detector. The bosons are identified in the $W\rightarrowμν$ and $Z\rightarrowμ^{+}μ^{-}$ decay channels. The cross-sections are measured for muons in the pseudorapidity range $2.0 < η< 4.5$, with transverse momenta $p_{\rm T} > 20{\mathrm{\,Ge\kern -0.1em V\!/}c}$ and, in the case of the $Z$ boson, a dimuon mass within $60 < M_{μ^{+}μ^{-}} < 120{\mathrm{\,Ge\kern -0.1em V\!/}c^{2}}$. The results are \begin{align*} σ_{W^{+}\rightarrowμ^{+}ν} &= 1093.6 \pm 2.1 \pm 7.2 \pm 10.9 \pm 12.7{\rm \,pb} \, , σ_{W^{-}\rightarrowμ^{-}\barν} &= \phantom{0}818.4 \pm 1.9 \pm 5.0 \pm \phantom{0}7.0 \pm \phantom{0}9.5{\rm \,pb} \, , σ_{Z\rightarrowμ^{+}μ^{-}} &= \phantom{00}95.0 \pm 0.3 \pm 0.7 \pm \phantom{0}1.1 \pm \phantom{0}1.1{\rm \,pb} \, , \end{align*} where the first uncertainties are statistical, the second are systematic, the third are due to the knowledge of the LHC beam energy and the fourth are due to the luminosity determination. The evolution of the $W$ and $Z$ boson cross-sections with centre-of-mass energy is studied using previously reported measurements with $1.0\mathrm{\,fb}^{-1}$ of data at $7\mathrm{\,Te\kern -0.1em V}$. Differential distributions are also presented. Results are in good agreement with theoretical predictions at next-to-next-to-leading order in perturbative quantum chromodynamics.

hep-ex↗

arXiv2016

Search for the lepton-flavour violating decay $D^0 \to e^\pmμ^\mp$

A search for the lepton-flavour violating decay $D^0 \to e^\pm μ^\mp$ is made with a dataset corresponding to an integrated luminosity of 3.0 fb$^{-1}$ of proton-proton collisions at centre-of-mass energies of $7$ TeV and $8$ TeV, collected by the LHCb experiment. Candidate $D^0$ mesons are selected using the decay $D^{*+} \to D^0 π^+$ and the $D^0 \to e^\pm μ^\mp$ branching fraction is measured using the decay mode $D^0 \to K^-π^+$ as a normalisation channel. No significant excess of $D^0 \to e^\pm μ^\mp$ candidates over the expected background is seen, and a limit is set on the branching fraction, $\mathcal{B}(D^0 \to e^\pm μ^\mp) < 1.3 \times 10^{-8}$, at 90 % confidence level. This is an order of magnitude lower than the previous limit and it further constrains the parameter space in some leptoquark models and in supersymmetric models with R-parity violation.

hep-ex↗

arXiv2016

Study of the production of $Λ_b^0$ and $\overline{B}^0$ hadrons in $pp$ collisions and first measurement of the $Λ_b^0\rightarrow J/ψpK^-$ branching fraction

The product of the $Λ_b^0$ ($\overline{B}^0$) differential production cross-section and the branching fraction of the decay $Λ_b^0\rightarrow J/ψpK^-$ ($\overline{B}^0\rightarrow J/ψ\overline{K}^*(892)^0$) is measured as a function of the beauty hadron transverse momentum, $p_{\rm T}$, and rapidity, $y$. The kinematic region of the measurements is $p_{\rm T}<20~{\rm GeV}/c$ and $2.0<y<4.5$. The measurements use a data sample corresponding to an integrated luminosity of $3~{\rm fb}^{-1}$ collected by the LHCb detector in $pp$ collisions at centre-of-mass energies $\sqrt{s}=7~{\rm TeV}$ in 2011 and $\sqrt{s}=8~{\rm TeV}$ in 2012. Based on previous LHCb results of the fragmentation fraction ratio, $f_{Λ_B^0}/f_d$, the branching fraction of the decay $Λ_b^0\rightarrow J/ψpK^-$ is measured to be \begin{equation*} \mathcal{B}(Λ_b^0\rightarrow J/ψpK^-)= (3.17\pm0.04\pm0.07\pm0.34^{+0.45}_{-0.28})\times10^{-4}, \end{equation*} where the first uncertainty is statistical, the second is systematic, the third is due to the uncertainty on the branching fraction of the decay $\overline{B}^0\rightarrow J/ψ\overline{K}^*(892)^0$, and the fourth is due to the knowledge of $f_{Λ_b^0}/f_d$. The sum of the asymmetries in the production and decay between $Λ_b^0$ and $\overlineΛ_b^0$ is also measured as a function of $p_{\rm T}$ and $y$. The previously published branching fraction of $Λ_b^0\rightarrow J/ψpπ^-$, relative to that of $Λ_b^0\rightarrow J/ψpK^-$, is updated. The branching fractions of $Λ_b^0\rightarrow P_c^+(\rightarrow J/ψp)K^-$ are determined.

hep-ex↗

arXiv2016

First observation of the decay $B_{s}^{0} \to K_{S}^{0} K^{*}(892)^{0}$

A search for $B_{(s)}^{0} \to K_{S}^{0} K^{*}(892)^{0}$ decays is performed using $pp$ collision data, corresponding to an integrated luminosity of $1.0~\text{fb}^{-1}$, collected with the LHCb detector at a centre-of-mass energy of $7~\text{TeV}$. The $B_{s}^{0} \to K_{S}^{0} K^{*}(892)^{0}$ decay is observed for the first time, with a significance of 7.1 standard deviations. The branching fraction is measured to be \begin{equation*} \mathcal{B}(B_{s}^{0} \to \bar{K}^{0} K^{*}(892)^{0}) + \mathcal{B}(B_{s}^{0} \to K^{0} \bar{K}^{*}(892)^{0}) = (16.4 \pm 3.4 \pm 2.3) \times 10^{-6},\\ \end{equation*} where the first uncertainty is statistical and the second is systematic. No evidence is found for the decay $B^{0} \to K_{S}^{0} K^{*}(892)^{0}$ and an upper limit is set on the branching fraction, $\mathcal{B}(B^{0} \to \bar{K}^{0} K^{*}(892)^{0}) + \mathcal{B}(B^{0} \to K^{0} \bar{K}^{*}(892)^{0}) < 0.96 \ \times 10^{-6}, $ at $90\,\% $ confidence level. All results are consistent with Standard Model predictions.

hep-ex↗

arXiv2015

Study of $B^{-}\to DK^-π^+π^-$ and $B^-\to Dπ^-π^+π^-$ decays and determination of the CKM angle $γ$

We report a study of the suppressed $B^-\to DK^-π^+π^-$ and favored $B^-\to Dπ^-π^+π^-$ decays, where the neutral $D$ meson is detected through its decays to the $K^{\mp}π^{\pm}$ and CP-even $K^+K^-$ and $π^+π^-$ final states. The measurement is carried out using a proton-proton collision data sample collected by the LHCb experiment, corresponding to an integrated luminosity of 3.0~fb$^{-1}$. We observe the first significant signals in the CP-even final states of the $D$ meson for both the suppressed $B^-\to DK^-π^+π^-$ and favored $B^-\to Dπ^-π^+π^-$ modes, as well as in the doubly Cabibbo-suppressed $D\to K^+π^-$ final state of the $B^-\to Dπ^-π^+π^-$ decay. Evidence for the ADS suppressed decay $B^{-}\to DK^-π^+π^-$, with $D\to K^+π^-$, is also presented. From the observed yields in the $B^-\to DK^-π^+π^-$, $B^-\to Dπ^-π^+π^-$ and their charge conjugate decay modes, we measure the value of the weak phase to be $γ=(74^{+20}_{-19})^{\rm o}$. This is one of the most precise single-measurement determinations of $γ$ to date.

hep-ex↗

arXiv2015

Measurement of the forward-backward asymmetry in $Z/γ^{\ast} \rightarrow μ^{+}μ^{-}$ decays and determination of the effective weak mixing angle

The forward-backward charge asymmetry for the process $q\bar{q} \rightarrow Z/γ^{\ast} \rightarrow μ^{+}μ^{-}$ is measured as a function of the invariant mass of the dimuon system. Measurements are performed using proton proton collision data collected with the LHCb detector at $\sqrt{s} = 7$ and 8\tev, corresponding to integrated luminosities of $1$fb$^{-1}$ and $2$fb$^{-1}$ respectively. Within the Standard Model the results constrain the effective electroweak mixing angle to be $$sin^{2}θ_{W}^{eff} = 0.23142 \pm 0.00073 \pm 0.00052 \pm 0.00056 $$ where the first uncertainty is statistical, the second systematic and the third theoretical. This result is in agreement with the current world average, and is one of the most precise determinations at hadron colliders to date.

hep-ex↗

arXiv2015

Forward production of $Υ$ mesons in $pp$ collisions at $\sqrt{s}=7$ and 8TeV

The production of $Υ$ mesons in $pp$ collisions at $\sqrt=7$ and $8\,\mathrm{TeV}$ is studied with the LHCb detector using data samples corresponding to an integrated luminosity of $1\,\mathrm{fb}^{-1}$ and $2\,\mathrm{fb}^{-1}$ respectively. The production cross-sections and ratios of cross-sections are measured as functions of the meson transverse momentum $p_T$ and rapidity $y$, for $p_T<30\,\mathrm{GeV}/c$} and $2.0<y<4.5$.

hep-ex↗

arXiv2015

Observation of the $B^0_s\toη'η'$ decay

The first observation of the $B^0_s\toη'η'$ decay is reported. The study is based on a sample of proton-proton collisions corresponding to $3.0$ ${\rm fb^{-1}}$ of integrated luminosity collected with the LHCb detector. The significance of the signal is $6.4$ standard deviations. The branching fraction is measured to be $[3.31 \pm 0.64\,{\rm (stat)} \pm 0.28\,{\rm (syst)} \pm 0.12\,{\rm (norm)}]\times10^{-5}$, where the third uncertainty comes from the $B^{\pm}\toη' K^{\pm}$ branching fraction that is used as a normalisation. In addition, the charge asymmetries of $B^{\pm}\toη' K^{\pm}$ and $B^{\pm}\toϕK^{\pm}$, which are control channels, are measured to be $(-0.2 \pm1.3)\%$ and $(+1.7\pm1.3)\%$, respectively. All results are consistent with theoretical expectations.

hep-ex↗

arXiv2015

Measurement of ${C\!P}$ violation parameters and polarisation fractions in ${B_s^0\to J/ψ\overline{K}^{*0}}$ decays

The first measurement of ${C\!P}$ asymmetries in the decay ${B_s^0\to J/ψ\overline{K}^{*}(892)^{0}}$ and an updated measurement of its branching fraction and polarisation fractions are presented. The results are obtained using data corresponding to an integrated luminosity of $3.0\,fb^{-1}$ of proton-proton collisions recorded with the LHCb detector at centre-of-mass energies of $7$ and $8\,\mathrm{TeV}$. Together with constraints from ${B^0\to J/ψρ^0}$, the results are used to constrain additional contributions due to penguin diagrams in the ${C\!P}$-violating phase ${ϕ_{s}}$, measured through ${B_s^0}$ decays to charmonium.

hep-ex↗

arXiv2015

Search for the $Λ_b \rightarrow Λη^\prime$ and $Λ_b \rightarrow Λη$ decays with the LHCb detector

A search is performed for the as yet unobserved baryonic $Λ_b \rightarrow Λη^\prime$ and $Λ_b \rightarrow Λη$ decays with 3$fb^{-1}$ of proton-proton collision data recorded by the LHCb experiment. The $B^0 \rightarrow K_S^0 η^\prime$ decay is used as a normalisation channel. No significant signal is observed for the $Λ_b \rightarrow Λη^\prime$ decay. An upper limit is found on the branching fraction of $\mathcal{B}(Λ_b \rightarrow Λη^\prime)<3.1\times10^{-6}$} at 90\% confidence level. Evidence is seen for the presence of the $Λ_b \rightarrow Λη$ decay at the level of $3σ$ significance, with a branching fraction $\mathcal{B}(Λ_b \rightarrow Λη)=(9.3^{+7.3}_{-5.3})\times10^{-6}$}.

hep-ex↗

arXiv2015

Observation of the decay $\overline{B}_s^0 \rightarrow ψ(2S) K^+ π^-$

The decay $\overline{B}_s^0 \rightarrow ψ(2S) K^+ π^-$ is observed using a data set corresponding to an integrated luminosity of $3.0fb^{-1}$ collected by the LHCb experiment in $pp$ collisions at centre-of-mass energies of 7 and 8 TeV. The branching fraction relative to the $B^0\rightarrow ψ(2S) K^+ π^-$ decay mode is measured to be \begin{equation} \frac{{\cal B}(\overline{B}^0_s \rightarrow ψ(2S) K^+ π^-)}{{\cal B}(B^0 \rightarrow ψ(2S) K^+ π^-)} = 5.38 \pm 0.36 (stat) \pm 0.22 (syst) \pm 0.31 \, (f_s/f_d) \, \%,\nonumber \end{equation} where $f_s/f_d$ indicates the uncertainty due to the ratio of probabilities for a $b$ quark to hadronise into a $B_s^0$ or $B^0$ meson. Using an amplitude analysis, the fraction of decays proceeding via an intermediate $K^*(892)^0$ meson is measured to be $0.645 \pm 0.049 (stat) \pm 0.049 (syst)$ and its longitudinal polarisation fraction is $0.524 \pm 0.056 (stat) \pm 0.029 (syst)$. The relative branching fraction for this component is determined to be \begin{equation} \frac{{\cal B}(\overline{B}^0_s \rightarrow ψ(2S) K^*(892)^0)}{{\cal B}(B^0 \rightarrow ψ(2S) K^*(892)^0)} = 5.58 \pm 0.57 (stat) \pm 0.40 (syst) \pm 0.32 \, (f_s/f_d) \, \%. \nonumber \end{equation} In addition, the mass splitting between the $B_s^0$ and $B^0$ mesons is measured as \begin{equation} M(B^0_s) - M(B^0) = 87.45 \pm 0.44 (stat) \pm 0.07 (syst) MeV/c^2. \nonumber \end{equation}

hep-ex↗