arXiv subjects

C. Bozzi

Publications and source records attributed to C. Bozzi.

At least 235 records · Page 13Linked to original sources

arXiv2017

Measurement of the ratio of branching fractions $\mathcal{B}(B_{c}^{+} \to J/ψK^{+})/\mathcal{B}(B_{c}^{+} \to J/ψπ^{+})$

The ratio of branching fractions $R_{K/π} \equiv \mathcal{B}(B_{c}^{+} \to J/ψK^{+})/\mathcal{B}(B_{c}^{+} \to J/ψπ^{+})$ is measured with $pp$ collision data collected by the LHCb experiment at centre-of-mass energies of 7 TeV and 8 TeV, corresponding to an integrated luminosity of 3${\mbox{fb}^{-1}}$. It is found to be $ R_{K/π} = 0.079\pm0.007\pm0.003$, where the first uncertainty is statistical and the second is systematic. This measurement is consistent with the previous LHCb result, while the uncertainties are significantly reduced.

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arXiv2017

Study of the $D^0 p$ amplitude in $Λ_b^0\to D^0 p π^-$ decays

An amplitude analysis of the decay $Λ_b^0\to D^0 p π^-$ is performed in the part of the phase space containing resonances in the $D^0 p$ channel. The study is based on a data sample corresponding to an integrated luminosity of 3.0 fb$^{-1}$ of $pp$ collisions recorded by the LHCb experiment. The spectrum of excited $Λ_c^+$ states that decay into $D^0 p$ is studied. The masses, widths and quantum numbers of the $Λ_c(2880)^+$ and $Λ_c(2940)^+$ resonances are measured. The constraints on the spin and parity for the $Λ_c(2940)^+$ state are obtained for the first time. A near-threshold enhancement in the $D^0 p$ amplitude is investigated and found to be consistent with a new resonance, denoted the $Λ_c(2860)^+$, of spin $3/2$ and positive parity.

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arXiv2017

Measurements of prompt charm production cross-sections in $pp$ collisions at $\sqrt{s} = 5\,$TeV

Production cross-sections of prompt charm mesons are measured using data from $pp$ collisions at the LHC at a centre-of-mass energy of $5\,$TeV. The data sample corresponds to an integrated luminosity of $8.60\pm0.33\,$pb$^{-1}$ collected by the LHCb experiment. The production cross-sections of $D^0$, $D^+$, $D_s^+$, and $D^{*+}$ mesons are measured in bins of charm meson transverse momentum, $p_{\text{T}}$, and rapidity, $y$. They cover the rapidity range $2.0<y<4.5$ and transverse momentum ranges $0 < p_{\text{T}} < 10\, \text{GeV}/c$ for $D^0$ and $D^+$ and $1 < p_{\text{T}} < 10\, \text{GeV}/c$ for $D_s^+$ and $D^{*+}$ mesons. The inclusive cross-sections for the four mesons, including charge-conjugate states, within the range of $1 < p_{\text{T}} < 8\, \text{GeV}/c$ are determined to be σ(pp\rightarrow D^0 X) = 1004 \pm 3 \pm 54\,μ\text{b} σ(pp\rightarrow D^+ X) = 402 \pm 2 \pm 30\,μ\text{b} σ(pp\rightarrow D_s^+ X) = 170 \pm 4 \pm 16\,μ\text{b} σ(pp\rightarrow D^{*+} X)= 421 \pm 5 \pm 36\,μ\text{b} where the uncertainties are statistical and systematic, respectively.

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arXiv2017

Measurement of forward $J/ψ$ production cross-sections in $pp$ collisions at $\sqrt{s}=13$ TeV

The production of $J/ψ$ mesons in proton-proton collisions at a centre-of-mass energy of $\sqrt{s}=13$ TeV is studied with the \lhcb detector. Cross-section measurements are performed as a function of the transverse momentum $p_\mathrm{T}$ and the rapidity $y$ of the $J/ψ$ meson in the region $p_\mathrm{T}<14\mathrm{GeV}/c$ and $2.0<y<4.5$, for both prompt $J/ψ$ mesons and $J/ψ$ mesons from $b$-hadron decays. The production cross-sections integrated over the kinematic coverage are $15.03\pm 0.03\pm 0.94$ $μ$b for prompt $J/ψ$ and $2.25\pm 0.01\pm 0.14$ $μ$b for $J/ψ$ from $b$-hadron decays, assuming zero polarization of the $J/ψ$ meson. The first uncertainties are statistical and the second systematic. The cross-section reported for $J/ψ$ mesons from $b$-hadron decays is used to extrapolate to a total $b\bar{b}$ cross-section. The ratios of the cross-sections with respect to $\sqrt{s}=8$ TeV are also determined.

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arXiv2017

Observation of five new narrow $Ω_c^0$ states decaying to $Ξ_c^+ K^-$

The $Ξ_c^+ K^-$ mass spectrum is studied with a sample of $pp$ collision data corresponding to an integrated luminosity of 3.3 fb$^{-1}$, collected by the LHCb experiment. The $Ξ_c^+$ is reconstructed in the decay mode $p K^- π^+$. Five new, narrow excited $Ω_c^0$ states are observed: the $Ω_c(3000)^0$, $Ω_c(3050)^0$, $Ω_c(3066)^0$, $Ω_c(3090)^0$, and $Ω_c(3119)^0$. Measurements of their masses and widths are reported.

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arXiv2017

New algorithms for identifying the flavour of $B^0$ mesons using pions and protons

Two new algorithms for use in the analysis of $pp$ collision are developed to identify the flavour of $B^0$ mesons at production using pions and protons from the hadronization process. The algorithms are optimized and calibrated on data, using $B^0 \rightarrow D^- π^+$ decays from $pp$ collision data collected by LHCb at centre-of-mass energies of 7 and 8 TeV. The tagging power of the new pion algorithm is 60 % greater than the previously available one; the algorithm using protons to identify the flavour of a $B^0$ meson is the first of its kind.

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arXiv2017

Measurements of the S-wave fraction in $B^{0}\rightarrow K^{+}π^{-}μ^{+}μ^{-}$ decays and the $B^{0}\rightarrow K^{\ast}(892)^{0}μ^{+}μ^{-}$ differential branching fraction

A measurement of the differential branching fraction of the decay ${B^{0}\rightarrow K^{\ast}(892)^{0}μ^{+}μ^{-}}$ is presented together with a determination of the S-wave fraction of the $K^+π^-$ system in the decay $B^{0}\rightarrow K^{+}π^{-}μ^{+}μ^{-}$. The analysis is based on $pp$-collision data corresponding to an integrated luminosity of 3\,fb$^{-1}$ collected with the LHCb experiment. The measurements are made in bins of the invariant mass squared of the dimuon system, $q^2$. Precise theoretical predictions for the differential branching fraction of $B^{0}\rightarrow K^{\ast}(892)^{0}μ^{+}μ^{-}$ decays are available for the $q^2$ region $1.1<q^2<6.0\,{\rm GeV}^2/c^4$. In this $q^2$ region, for the $K^+π^-$ invariant mass range $796 < m_{Kπ} < 996\,{\rm MeV}/c^2$, the S-wave fraction of the $K^+π^-$ system in $B^{0}\rightarrow K^{+}π^{-}μ^{+}μ^{-}$ decays is found to be \begin{equation*} F_{\rm S} = 0.101\pm0.017({\rm stat})\pm0.009 ({\rm syst}), \end{equation*} and the differential branching fraction of $B^{0}\rightarrow K^{\ast}(892)^{0}μ^{+}μ^{-}$ decays is determined to be \begin{equation*} {\rm d}\mathcal{B}/{\rm d} q^2 = (0.342_{\,-0.017}^{\,+0.017}({\rm stat})\pm{0.009}({\rm syst})\pm0.023({\rm norm}))\times 10^{-7}c^{4}/{\rm GeV}^{2}. \end{equation*} The differential branching fraction measurements presented are the most precise to date and are found to be in agreement with Standard Model predictions.

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arXiv2017

Measurement of the phase difference between short- and long-distance amplitudes in the $B^{+}\to K^{+}μ^{+}μ^{-}$ decay

A measurement of the phase difference between the short- and long-distance contributions to the $B^{+}\to K^{+}μ^{+}μ^{-}$ decay is performed by analysing the dimuon mass distribution. The analysis is based on $pp$ collision data corresponding to an integrated luminosity of 3 $\rm fb^{-1}$ collected by the LHCb experiment in 2011 and 2012. The long-distance contribution to the $B^{+}\to K^{+}μ^{+}μ^{-}$ decay is modelled as a sum of relativistic Breit--Wigner amplitudes representing different vector meson resonances decaying to muon pairs, each with their own magnitude and phase. The measured phases of the $J/ψ$ and $ψ(2S)$ resonances are such that the interference with the short-distance component in dimuon mass regions far from their pole masses is small. In addition, constraints are placed on the Wilson coefficients, $\mathcal{C}_{9}$ and $\mathcal{C}_{10}$, and the branching fraction of the short-distance component is measured.

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arXiv2017

Study of $J/ψ$ production in jets

The production of $J/ψ$ mesons in jets is studied in the forward region of proton-proton collisions using data collected with the LHCb detector at a center-of-mass energy of 13 TeV. The fraction of the jet transverse momentum carried by the $J/ψ$ meson, $z \equiv p_{\rm T}(J/ψ)/p_{\rm T}({\rm jet})$, is measured using jets with $p_{\rm T}({\rm jet}) > 20$ GeV in the pseudorapidity range $2.5 < η({\rm jet}) < 4.0$. The observed $z$ distribution for $J/ψ$ mesons produced in $b$-hadron decays is consistent with expectations. However, the results for prompt $J/ψ$ production do not agree with predictions based on fixed-order non-relativistic QCD. This is the first measurement of the $p_{\rm T}$ fraction carried by prompt $J/ψ$ mesons in jets at any experiment.

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arXiv2017

Observation of $B_{c}^{+} \to J/ψD^{()} K^{()}$ decays

A search for the decays $B_c^+ \to J/ψD^{(*)0} K^+$ and $B_c^+ \to J/ψD^{(*)+} K^{*0}$ is performed with data collected at the LHCb experiment corresponding to an integrated luminosity of 3 fb$^{-1}$. The decays $B_c^+ \to J/ψD^0 K^+$ and $B_c^+ \to J/ψD^{*0} K^+$ are observed for the first time, while first evidence is reported for the $B_c^+ \to J/ψD^{*+} K^{*0}$ and $B_c^+ \to J/ψD^+ K^{*0}$ decays. The branching fractions of these decays are determined relative to the $B_c^+ \to J/ψπ^+$ decay. The $B_c^+$ mass is measured, using the $J/ψD^0 K^+$ final state, to be $6274.28 \pm 1.40 (stat) \pm 0.32 (syst)$ MeV/$c^2$. This is the most precise single measurement of the $B_c^+$ mass to date.

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arXiv2017

Observation of $B_{c}^{+} \rightarrow D^{0} K^{+}$ decays

Using proton-proton collision data corresponding to an integrated luminosity of 3.0 fb$^{-1}$, recorded by the LHCb detector at centre-of-mass energies of 7 and 8 TeV, the $B_{c}^{+} \rightarrow D^{0} K^{+}$ decay is observed with a statistical significance of 5.1 standard deviations. By normalising to $B^{+} \rightarrow \bar{D}^{0} π^{+}$ decays, a measurement of the branching fraction multiplied by the production rates for $B_{c}^{+}$ relative to $B^{+}$ mesons in the LHCb acceptance is obtained, $$ R_{D^{0} K} = \frac{f_{c}}{f_{u}}\times\mathcal{B}(B_{c}^{+} \rightarrow D^{0} K^{+}) = (9.3\,^{+2.8}_{-2.5} \pm 0.6) \times 10^{-7}\,, $$ where the first uncertainty is statistical and the second is systematic. This decay is expected to proceed predominantly through weak annihilation and penguin amplitudes, and is the first $B_{c}^{+}$ decay of this nature to be observed.

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arXiv2017

Search for decays of neutral beauty mesons into four muons

A search for the non-resonant decays $B^0_s \rightarrow μ^{+}μ^{-}μ^{+}μ^{-}$ and $B^0 \rightarrow μ^{+}μ^{-}μ^{+}μ^{-}$ is presented. The measurement is performed using the full Run 1 data set collected in proton-proton collisions by the LHCb experiment at the LHC. The data correspond to integrated luminosities of $1$ and $2~\mathrm{fb}^{-1}$ collected at centre-of-mass energies of $7$ and $8~\mathrm{TeV}$, respectively. No signal is observed and upper limits on the branching fractions of the non-resonant decays at $95\%$ confidence level are determined to be \mathcal{B}(B^0_s \rightarrow μ^{+}μ^{-}μ^{+}μ^{-}) & < 2.5 \times 10^{-9} \mathcal{B}(B^0 \rightarrow μ^{+}μ^{-}μ^{+}μ^{-}) & < 6.9 \times 10^{-10}.

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arXiv2017

Measurement of the ratio of branching fractions and difference in $CP$ asymmetries of the decays $B^+\to J/ψπ^+$ and $B^+\to J/ψK^+$

The ratio of branching fractions and the difference in $CP$ asymmetries of the decays $B^+\to J/ψπ^+$ and $B^+\to J/ψK^+$ are measured using a data sample of $pp$ collisions collected by the LHCb experiment, corresponding to an integrated luminosity of $3~{{\,\mbox{fb}^{-1}}}$ at centre-of-mass energies of 7 and $8~\mathrm{\,Te\kern -0.1em V}$. The results are \begin{equation*} {\mathcal{B}(B^+\to J/ψπ^+)\over\mathcal{B}(B^+\to J/ψK^+)}=(3.83\pm0.03\pm0.03)\times10^{-2}\,, \end{equation*} \begin{equation*} \mathcal{A}^{CP}(B^+\to J/ψπ^+)-\mathcal{A}^{CP}(B^+\to J/ψK^+)=(1.82\pm0.86\pm0.14)\times10^{-2}, \end{equation*} where the first uncertainties are statistical and the second are systematic. Combining this result with a recent LHCb measurement of $\mathcal{A}^{CP}(B^+\to J/ψK^+)$ provides the most precise estimate to date of $CP$ violation in the decay $B^+\to J/ψπ^+$, \begin{equation*} \mathcal{A}^{CP}(B^+\to J/ψπ^+) =(1.91\pm0.89\pm0.16)\times10^{-2}. \end{equation*}

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arXiv2017

Observation of the annihilation decay mode $B^{0}\to K^{+}K^{-}$

A search for the $B^{0}\to K^{+}K^{-}$ decay is performed using $pp$-collision data collected by LHCb. The data set corresponds to integrated luminosities of 1 and 2 fb$^{-1}$ at center-of-mass energies of 7 and 8 TeV, respectively. This decay is observed for the first time, with a significance of more than five standard deviations. The analysis also results in an improved measurement of the branching fraction for the $B_s^0\to π^+π^-$ decay. The measured branching fractions are $BR(B^0\to K^+K^-) = (7.80 \pm 1.27 \pm 0.81 \pm 0.21) \times 10^{-8}$ and $BR(B_s^0\toπ^+π^-) = (6.91 \pm 0.54 \pm 0.63 \pm 0.19 \pm 0.40) \times 10^{-7}$. The first uncertainty is statistical, the second is systematic, the third is due to the uncertainty on the $B^0\to K^+π^-$ branching fraction used as a normalization. For the $B_s^0$ mode, the fourth accounts for the uncertainty on the ratio of the probabilities for $b$ quarks to hadronize into $B_s^0$ and $B^0$ mesons.

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arXiv2017

First experimental study of photon polarization in radiative $B^{0}_{s}$ decays

The polarization of photons produced in radiative $B^{0}_{s}$ decays is studied for the first time. The data are recorded by the LHCb experiment in $pp$ collisions corresponding to an integrated luminosity of 3fb$^{-1}$ at center-of-mass energies of $7$ and $8$TeV. A time-dependent analysis of the $B^{0}_{s} \to ϕγ$ decay rate is conducted to determine the parameter ${\mathcal{A}}^Δ$, which is related to the ratio of right- over left-handed photon polarization amplitudes in $b \to s γ$ transitions. A value of ${\mathcal{A}}^Δ=-0.98^{\,+0.46\,+0.23}_{\,-0.52\,-0.20}$ is measured. This result is consistent with the Standard Model prediction within two standard deviations.

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arXiv2017

Observation of $B^+\rightarrow J/ψ3π^+ 2π^-$ and $B^+\rightarrow ψ(2S) π^+π^+π^-$ decays

The decays $B^+\rightarrow J/ψ3π^+ 2π^-$ and $B^+\rightarrow ψ(2S) π^+π^+π^-$ are observed for the first time using a data sample corresponding to an integrated luminosity of $3.0fb^{-1}$, collected by the LHCb experiment in proton-proton collisions at the centre-of-mass energies of 7 and 8 TeV. The branching fractions relative to that of $B^+ \rightarrow ψ(2S)K^+$ are measured to be \begin{eqnarray*} \frac {\mathcal{B}\left(B^+\rightarrow J/ψ3π^+ 2π^- \right)} {\mathcal{B}\left(B^+ \rightarrow ψ(2S)K^+ \right)} & = & \left(1.88\pm0.17\pm0.09\right)\times10^{-2}, \frac {\mathcal{B}\left(B^+\rightarrow ψ(2S) π^+π^+π^- \right)} {\mathcal{B}\left(B^+ \rightarrow ψ(2S)K^+ \right)} & = & \left(3.04\pm0.50\pm0.26\right)\times10^{-2}, \end{eqnarray*} where the first uncertainties are statistical and the second are systematic.

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arXiv2017

Observation of the decay $Ξ_b^- \to p K^-K^-$

Decays of the $Ξ_b^-$ and $Ω_b^-$ baryons to the charmless final states $p h^{-}h^{\prime -}$, where $h^{(\prime)}$ denotes a kaon or pion, are searched for with the LHCb detector. The analysis is based on a sample of proton-proton collision data collected at centre-of-mass energies $\sqrt{s} = 7$ and $8 TeV$, corresponding to an integrated luminosity of $3 {\rm fb}^{-1}$. The decay $Ξ_b^- \to p K^-K^-$ is observed with a significance of $8.7$ standard deviations, and evidence at the level of $3.4$ standard deviations is found for the $Ξ_b^- \to p K^-π^-$ decay. Results are reported, relative to the $B^-\to K^+K^-K^-$ normalisation channel, for the products of branching fractions and $b$-hadron production fractions. The branching fractions of $Ξ_b^- \to p K^-π^-$ and $Ξ_b^- \to p π^-π^-$ relative to $Ξ_b^- \to p K^-K^-$ decays are also measured.

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arXiv2017

Measurement of forward $t\overline{t}$, $W+b\overline{b}$ and $W+c\overline{c}$ production in $pp$ collisions at $\sqrt{s}=8$ TeV

The production of $t\overline{t}$, $W+b\overline{b}$ and $W+c\overline{c}$ is studied in the forward region of proton-proton collisions collected at a centre-of-mass energy of 8 TeV by the LHCb experiment, corresponding to an integrated luminosity of 1.98 $\pm$ 0.02 $\mbox{fb}^{-1}$. The $W$ bosons are reconstructed in the decays $W\rightarrow\ellν$, where $\ell$ denotes muon or electron, while the $b$ and $c$ quarks are reconstructed as jets. All measured cross-sections are in agreement with next-to-leading-order Standard Model predictions.

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