arXiv subjects

C. Bozzi

Publications and source records attributed to C. Bozzi.

At least 145 records · Page 8Linked to original sources

arXiv2018

Angular moments of the decay $Λ_b^0 \rightarrow Λμ^{+} μ^{-}$ at low hadronic recoil

An analysis of the angular distribution of the decay $Λ_b^0 \rightarrow Λμ^{+} μ^{-}$ is presented, using data collected with the LHCb detector between 2011 and 2016 and corresponding to an integrated luminosity of approximately $5\,fb^{-1}$. Angular observables are determined using a moment analysis of the angular distribution at low hadronic recoil, corresponding to the dimuon invariant mass squared range $15 < q^{2} < 20\, GeV^2/c^4$. The full basis of observables is measured for the first time. The lepton-side, hadron-side and combined forward-backward asymmetries of the decay are determined to be \begin{align} A_{FB}^{l} & = -0.39 \pm 0.04\,\rm{stat} \pm 0.01\, \rm{syst}, \nonumber\\ A_{FB}^{h} & = -0.30 \pm 0.05\,\rm{stat} \pm 0.02\, \rm{syst}, \nonumber\\ A_{FB}^{lh} & = +0.25 \pm 0.04\,\rm{stat} \pm 0.01\, \rm{syst}. \nonumber \end{align} The measurements are consistent with Standard Model predictions.

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arXiv2018

Observation of two resonances in the $Λ_b^0 π^\pm$ systems and precise measurement of $Σ_b^\pm$ and $Σ_b^{*\pm}$ properties

The first observation of two structures consistent with resonances in the final states $Λ_b^0 π^-$ and $Λ_b^0 π^+$ is reported using samples of $pp$ collision data collected by the LHCb experiment at $\sqrt{s} = 7$ and $8$ TeV, corresponding to an integrated luminosity of 3 $\mathrm{fb}^{-1}$. The ground states $Σ_b^\pm$ and $Σ_b^{*\pm}$ are also confirmed and their masses and widths are precisely measured.

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arXiv2018

Measurement of $Z\rightarrowτ^+τ^-$ production in proton-proton collisions at $\sqrt{s} = 8$ TeV

A measurement of $Z\rightarrowτ^+τ^-$ production cross-section is presented using data, corresponding to an integrated luminosity of 2 fb$^{-1}$, from $pp$ collisions at $\sqrt{s}=8$ TeV collected by the LHCb experiment. The $τ^+τ^-$ candidates are reconstructed in final states with the first tau lepton decaying leptonically, and the second decaying either leptonically or to one or three charged hadrons. The production cross-section is measured for $Z$ bosons with invariant mass between 60 and 120 GeV/$c^2$, which decay to tau leptons with transverse momenta greater than 20 GeV/$c$ and pseudorapidities between 2.0 and 4.5. The cross-section is determined to be $σ_{pp\rightarrow{}Z\rightarrow{}τ^+τ^-} = 95.8 \pm 2.1 \pm 4.6 \pm 0.2 \pm 1.1 \mathrm{pb}$, where the first uncertainty is statistical, the second is systematic, the third is due to the LHC beam energy uncertainty, and the fourth to the integrated luminosity uncertainty. This result is compatible with NNLO Standard model predictions. The ratio of the cross-sections for $Z\rightarrowτ^+τ^-$ to $Z\rightarrowμ^+μ^-$ ($Z\rightarrow{}e^+e^-$), determined to be $1.01 \pm 0.05$ ($1.02 \pm 0.06$), is consistent with the lepton-universality hypothesis in $Z$ decays.

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arXiv2018

Search for a dimuon resonance in the $Υ$ mass region

A search is performed for a spin-0 boson, $ϕ$, produced in proton-proton collisions at centre-of-mass energies of 7 and 8 TeV, using prompt $ϕ\rightarrowμ^+μ^-$ decays and a data sample corresponding to an integrated luminosity of approximately 3.0 ${\rm fb}^{-1}$ collected with the LHCb detector. No evidence is found for a signal in the mass range from 5.5 to 15 GeV. Upper limits are placed on the product of the production cross-section and the branching fraction into the dimuon final state. The limits are comparable to the best existing over most of the mass region considered and are the first to be set near the $Υ$ resonances.

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arXiv2018

Observation of the decay $Λ^0_b\rightarrowψ(2S)pπ^-$

The Cabibbo-suppressed decay $Λ^0_b\rightarrowψ(2S)pπ^-$ is observed for the first time using a data sample collected by the LHCb experiment in proton-proton collisions corresponding to 1.0, 2.0 and 1.9fb$^{-1}$ of integrated luminosity at centre-of-mass energies of 7, 8 and 13TeV, respectively. The $ψ(2S)$ mesons are reconstructed in the $μ^+μ^-$ final state. The~branching fraction with respect to that of the $Λ^0_b\rightarrowψ(2S)pK^-$ decay mode is measured to be $$\frac{\mathcal{B}\left(Λ^0_b\rightarrowψ(2S)pπ^- \right)} {\mathcal{B}\left(Λ^0_b\rightarrowψ(2S)pK^-\right)}=\left(11.4 \pm 1.3 \pm 0.2\right)\!\%\,,$$ where the first uncertainty is statistical and the second is systematic. The $ψ(2S)p$ and $ψ(2S)π^-$ mass spectra are investigated and no evidence for exotic resonances is found.

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arXiv2018

Measurement of the CKM angle $γ$ using $B^\pm\to DK^\pm$ with $D\to K_\text{S}^0π^+π^-$, $K_\text{S}^0K^+K^-$ decays

A binned Dalitz plot analysis of $B^\pm \to D K^\pm$ decays, with $D\to K_\text{S}^0π^+π^-$ and $D\to K_\text{S}^0K^+K^-$, is used to perform a measurement of the CP-violating observables $x_{\pm}$ and $y_{\pm}$, which are sensitive to the Cabibbo-Kobayashi-Maskawa angle $γ$. The analysis is performed without assuming any $D$ decay model, through the use of information on the strong-phase variation over the Dalitz plot from the CLEO collaboration. Using a sample of proton-proton collision data collected with the LHCb experiment in 2015 and 2016, and corresponding to an integrated luminosity of 2.0$\,\text{fb}^{-1}$, the values of the CP violation parameters are found to be $x_- = ( 9.0 \pm 1.7 \pm 0.7 \pm 0.4) \times 10^{-2}$, $y_- = ( 2.1 \pm 2.2 \pm 0.5 \pm 1.1) \times 10^{-2}$, $x_+ = (- 7.7 \pm 1.9 \pm 0.7 \pm 0.4) \times 10^{-2}$, and $y_+ = (- 1.0 \pm 1.9 \pm 0.4 \pm 0.9) \times 10^{-2}$. The first uncertainty is statistical, the second is systematic, and the third is due to the uncertainty on the strong-phase measurements. These values are used to obtain $γ= \left(87\,^{+11}_{-12}\right)^\circ$, $r_B = 0.086^{+ 0.013}_{-0.014}$, and $δ_B = (101 \pm 11)^\circ$, where $r_B$ is the ratio between the suppressed and favoured $B$-decay amplitudes and $δ_B$ is the corresponding strong-interaction phase difference. This measurement is combined with the result obtained using 2011 and 2012 data collected with the \lhcb experiment, to give $γ= \left(80\,^{+10}_{\,-9}\right)^\circ$, $r_B = 0.080 \pm 0.011$, and $δ_B = (110 \pm 10)^\circ$.

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arXiv2018

Observation of the decay $\overline{B_s^0} \rightarrow χ_{c2} K^+ K^- $ in the $φ$ mass region

The $\overline{B_s^0} \rightarrow χ_{c2} K^+ K^- $ decay mode is observed and its branching fraction relative to the corresponding $χ_{c1}$ decay mode, in a $\pm 15 \textrm{MeV}/c^2$ window around the $ϕ$ mass, is found to be $\frac{\mathcal{B}(\overline{B_s^0} \rightarrow χ_{c2} K^+ K^-) }{ \mathcal{B}(\overline{B_s^0} \rightarrow χ_{c1} K^+ K^-)} = (17.1 \pm 3.1 \pm 0.4 \pm 0.9)\%,$ where the first uncertainty is statistical, the second systematic and the third due to the knowledge of the branching fractions of radiative $χ_c$ decays. The decay mode $\overline{B_s^0} \rightarrow χ_{c1} K^+ K^- $ allows the $ B_s^0$ mass to be measured as $m(B_s^0) = 5366.83 \pm 0.25 \pm 0.27 \, \textrm{MeV}/c^2,$ where the first uncertainty is statistical and the second systematic. A combination of this result with other LHCb determinations of the $B_s^0$ mass is made.

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arXiv2018

Measurement of forward top pair production in the dilepton channel in $pp$ collisions at $\sqrt{s}=13$ TeV

Forward top quark pair production is studied in $pp$ collisions in the $μeb$ final state using a data sample corresponding to an integrated luminosity of 1.93 fb$^{-1}$ collected with the LHCb experiment at a centre-of-mass energy of 13 TeV. The cross-section is measured in a fiducial region where both leptons have a transverse momentum greater than 20 GeV and a pseudorapidity between 2.0 and 4.5. The quadrature sum of the azimuthal separation and the difference in pseudorapidities, denoted $ΔR$, between the two leptons must be larger than 0.1. The $b$-jet axis is required to be separated from both leptons by a $ΔR$ of 0.5, and to have a transverse momentum in excess of 20 GeV and a pseudorapidity between 2.2 and 4.2. The cross-section is measured to be $$σ_{t\bar{t}}= 126\pm19\,(\mathrm{stat})\pm16\,(\mathrm{syst})\pm5\,(\mathrm{lumi})\,\,\mathrm{ fb}$$ where the first uncertainty is statistical, the second is systematic, and the third is due to the luminosity determination. The measurement is compatible with the Standard Model prediction.

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arXiv2018

Measurement of the relative rate of prompt $χ_{c0}$, $χ_{c1}$ and $χ_{c2}$ production at $\sqrt{s}=7$TeV

Prompt production of charmonium $χ_{c0}$, $χ_{c1}$ and $χ_{c2}$ mesons is studied using proton-proton collisions at the LHC at a centre-of-mass energy of $\sqrt{s}=7$TeV. The $χ_{c}$ mesons are identified through their decay to $J/ψγ$, with $J/ψ\toμ^+μ^-$ using photons that converted in the detector. A data sample, corresponding to an integrated luminosity of $1.0\mathrm{fb}^{-1}$ collected by the LHCb detector, is used to measure the relative prompt production rate of $χ_{c1}$ and $χ_{c2}$ in the rapidity range $2.0<y<4.5$ as a function of the $J/ψ$ transverse momentum from 3 to 20 GeV$/c$. First evidence for $χ_{c0}$ meson production at a high-energy hadron collider is also presented.

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arXiv2018

Measurement of angular and CP asymmetries in $D^0\toπ^+π^-μ^+μ^-$ and $D^0\to K^+K^-μ^+μ^-$ decays

The first measurements of the forward-backward asymmetry of the dimuon pair ($A_{FB}$), the triple-product asymmetry ($A_{2ϕ}$), and the charge-parity-conjugation asymmetry ($A_{CP}$), in $D^0\toπ^+π^-μ^+μ^-$ and $D^0\to K^+K^-μ^+μ^-$ decays are reported. They are performed using data from proton-proton collisions collected with the LHCb experiment from 2011 to 2016, corresponding to a total integrated luminosity of 5 fb$^{-1}$. The asymmetries are measured to be \begin{align*} A_{FB}(D^0\toπ^+π^-μ^+μ^-) &= (\phantom{-}3.3\pm3.7\pm0.6)\%,\\ A_{2ϕ}(D^0\toπ^+π^-μ^+μ^-)&= (-0.6\pm3.7\pm0.6)\%,\\ A_{CP}(D^0\toπ^+π^-μ^+μ^-) &= (\phantom{-}4.9\pm3.8\pm0.7)\%,\\ A_{FB}(D^0\to K^+K^-μ^+μ^-) &= (0\pm11\pm2)\%,\\ A_{2ϕ}(D^0\to K^+K^-μ^+μ^-)&= (9\pm11\pm1)\%,\\ A_{CP}(D^0\to K^+K^-μ^+μ^-) &= (0\pm11\pm2)\%, \end{align*} where the first uncertainty is statistical and the second systematic. The asymmetries are also measured as a function of the dimuon invariant mass. The results are consistent with the Standard Model predictions.

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arXiv2018

Measurement of the $Ω_c^0$ baryon lifetime

We report a measurement of the lifetime of the $Ω_c^0$ baryon 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 sample consists of about 1000 $Ω_b^-\toΩ_c^0μ^-\barν_μ X$ signal decays, where the $Ω_c^0$ baryon is detected in the $pK^-K^-π^+$ final state and $X$ represents possible additional undetected particles in the decay. The $Ω_c^0$ lifetime is measured to be $τ_{Ω_c^0} = 268\pm24\pm10\pm2$ fs, where the uncertainties are statistical, systematic, and from the uncertainty in the $D^+$ lifetime, respectively. This value is nearly four times larger than, and inconsistent with, the current world-average value.

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arXiv2018

Measurement of $C\!P$ asymmetries in two-body $B_{(s)}^{0}$-meson decays to charged pions and kaons

The time-dependent $C\!P$ asymmetries in $B^0\toπ^+π^-$ and $B_s^0\to K^+\!K^-$ decays are measured using a data sample of $pp$ collisions corresponding to an integrated luminosity of 3.0 fb$^{-1}$, collected with the LHCb detector at centre-of-mass energies of 7 and 8 TeV. The same data sample is used to measure the time-integrated $C\!P$ asymmetries in $B^0\to K^+π^-$ and $B_s^0\toπ^+ K^-$ decays. The results are $C_{π^+π^-} = -0.34 \pm 0.06 \pm 0.01$, $S_{π^+π^-} = -0.63 \pm 0.05 \pm 0.01$, $C_{K^+\!K^-} = 0.20 \pm 0.06 \pm 0.02$, $S_{K^+\!K^-} = 0.18 \pm 0.06 \pm 0.02$, $C_{K^+\!K^-}^{ΔΓ} = -0.79 \pm 0.07 \pm 0.10$, $A_{C\!P}^{B^0} = -0.084 \pm 0.004 \pm 0.003$, and $A_{C\!P}^{B_s^0} = 0.213 \pm 0.015 \pm 0.007$, where the first uncertainties are statistical and the second systematic. Evidence for $C\!P$ violation is found in the $B_s^0\to K^+\!K^-$ decay for the first time.

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arXiv2018

Search for CP violation using triple product asymmetries in $Λ^{0}_{b}\to pK^{-}π^{+}π^{-}$, $Λ^{0}_{b}\to pK^{-}K^{+}K^{-}$ and $Ξ^{0}_{b}\to pK^{-}K^{-}π^{+}$ decays

A search for $C$P and $P$ violation using triple-product asymmetries is performed with $Λ^{0}_{b}\to pK^{-}π^{+}π^{-}$, $Λ^{0}_{b}\to pK^{-}K^{+}K^{-}$ and $Ξ^{0}_{b}\to pK^{-}K^{-}π^{+}$ decays. The data sample corresponds to integrated luminosities of 1.0fb$^{-1}$ and 2.0fb$^{-1}$, recorded with the LHCb detector at centre-of-mass energies of 7TeV and 8TeV, respectively. The $CP$- and $P$-violating asymmetries are measured both integrating over all phase space and in specific phase-space regions. No significant deviation from $CP$ or $P$ symmetry is found. The first observation of $Λ^{0}_{b}\to pK^{-}χ_{c0}(1P)(\toπ^{+}π^{-}, K^{+}K^{-})$ decay is also reported.

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arXiv2018

Observation of a new $Ξ_b^-$ resonance

From samples of $pp$ collision data collected by the LHCb experiment at $\sqrt{s}=7$, $8$ and $13$ TeV corresponding to integrated luminosities of 1.0, 2.0 and 1.5 fb$^{-1}$, respectively, a peak in both the $Λ_b^0K^-$ and $Ξ_b^0π^-$ invariant mass spectra is observed. In the quark model, radially and orbitally excited $Ξ_b^-$ resonances with quark content $bds$ are expected. Referring to this peak as $Ξ_b(6227)^-$, the mass and natural width are measured to be $m_{Ξ_{b}(6227)^-}=6226.9\pm2.0\pm0.3\pm0.2$ MeV/$c^2$ and $Γ_{Ξ_b(6227)^-}=18.1\pm5.4\pm1.8$ MeV/$c^2$, where the first uncertainty is statistical, the second is systematic, and the third, on $m_{Ξ_b(6227)^-}$, is due to the knowledge of the $Λ_b^0$ baryon mass. Relative production rates of the ${Ξ_b(6227)^-\toΛ_b^0K^-}$ and ${Ξ_b(6227)^-\toΞ_b^0π^-}$ decays are also reported.

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arXiv2018

Measurement of $D_s^{\pm}$ production asymmetry in $pp$ collisions at $\sqrt{s} =7$ and 8 TeV

The inclusive $D_s^{\pm}$ production asymmetry is measured in $pp$ collisions collected by the LHCb experiment at centre-of-mass energies of $\sqrt{s} =7$ and 8 TeV. Promptly produced $D_s^{\pm}$ mesons are used, which decay as $D_s^{\pm}\toϕπ^{\pm}$, with $ϕ\to K^+K^-$. The measurement is performed in bins of transverse momentum, $p_{\rm T}$, and rapidity, $y$, covering the range $2.5<p_{\rm T}<25.0$ GeV$/c$ and $2.0<y<4.5$. No kinematic dependence is observed. Evidence of nonzero $D_s^{\pm}$ production asymmetry is found with a significance of 3.3 standard deviations.

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arXiv2018

Observation of the decay $Λ_b^0 \to Λ_c^+ p \overline{p} π^-$

The decay $Λ_b^0 \to Λ_c^+ p \overline{p} π^-$ is observed using $pp$ collision data collected with the LHCb detector at centre-of-mass energies of $\sqrt{s}=$ 7 and 8 TeV, corresponding to an integrated luminosity of 3 $fb^{-1}$. The ratio of branching fractions between $Λ_b^0 \to Λ_c^+ p \overline{p} π^-$ and $Λ_b^0 \to Λ_c^+ π^-$ decays is measured to be \begin{equation*} \frac{\mathcal{B}(Λ_b^0 \to Λ_c^+ p \overline{p}π^-)}{\mathcal{B}(Λ_b^0 \to Λ_c^+ π^-)} = 0.0540 \pm 0.0023 \pm 0.0032. \end{equation*} Two resonant structures are observed in the $ Λ_c^+ π^-$ mass spectrum of the ${Λ_b^0 \to Λ_c^+ p\overline{p} π^-}$ decays, corresponding to the $Σ_c(2455)^0$ and $Σ_c^{*}(2520)^0$ states. The ratios of branching fractions with respect to the decay $Λ_b^0 \to Λ_c^+ p \overline{p} π^-$ are \begin{align*} \frac{\mathcal{B}(Λ_b^0 \to Σ_c^0 p\overline{p})\times\mathcal{B}(Σ_c^0\to Λ_c^+ π^-)}{\mathcal{B}(Λ_b^0 \to Λ_c^+ p \overline{p}π^-)} = 0.089\pm0.015\pm0.006, \frac{\mathcal{B}(Λ_b^0 \to Σ_c^{*0} p\overline{p})\times\mathcal{B}(Σ_c^{*0}\to Λ_c^+ π^-)}{\mathcal{B}(Λ_b^0 \to Λ_c^+ p \overline{p}π^-)} = 0.119\pm0.020\pm0.014. \end{align*} In all of the above results, the first uncertainty is statistical and the second is systematic. The phase space is also examined for the presence of dibaryon resonances. No evidence for such resonances is found.

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arXiv2018

Measurement of $Υ$ production in $pp$ collisions at $\sqrt{s}$= 13 TeV

The production cross-sections of $Υ(1S)$, $Υ(2S)$ and $Υ(3S)$ mesons in proton-proton collisions at $\sqrt{s}$= 13 TeV are measured with a data sample corresponding to an integrated luminosity of $277 \pm 11$ $\rm pb^{-1}$ recorded by the LHCb experiment in 2015. The $Υ$ mesons are reconstructed in the decay mode $Υ\toμ^{+}μ^{-}$. The differential production cross-sections times the dimuon branching fractions are measured as a function of the $Υ$ transverse momentum, $p_{\rm T}$, and rapidity, $y$, over the range $0 < p_{\rm T}< 30$ GeV/c and $2.0 < y < 4.5$. The ratios of the cross-sections with respect to the LHCb measurement at $\sqrt{s}$= 8 TeV are also determined. The measurements are compared with theoretical predictions based on NRQCD.

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arXiv2018

Evidence for the decay $B_{s}^0 \rightarrow \overline{K}{}^{*0}μ^+μ^-$

A search for the decay $B_{s}^0 \rightarrow \overline{K}{}^{*0}μ^+μ^-$ is presented using data sets corresponding to 1.0, 2.0 and 1.6 $\text{fb}^{-1}$ of integrated luminosity collected during $pp$ collisions with the LHCb experiment at centre-of-mass energies of 7, 8 and 13 TeV, respectively. An excess is found over the background-only hypothesis with a significance of 3.4 standard deviations. The branching fraction of the $B_{s}^0 \rightarrow \overline{K}{}^{*0}μ^+μ^-$ decay is determined to be $\mathcal{B}(B_{s}^0 \rightarrow \overline{K}{}^{*0}μ^+μ^-) = [2.9 \pm 1.0~(\text{stat}) \pm 0.2~(\text{syst}) \pm 0.3~(\text{norm})] \times 10^{-8}$, where the first and second uncertainties are statistical and systematic, respectively. The third uncertainty is due to limited knowledge of external parameters used to normalise the branching fraction measurement.

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