arXiv subjects

G. Busetto

Publications and source records attributed to G. Busetto.

At least 127 records · Page 7Linked to original sources

arXiv2014

Measurement of CP violation in $B_s^0 \to ϕϕ$ decays

A measurement of the decay time dependent CP-violating asymmetry in $B_s^0 \to ϕϕ$ decays is presented, along with measurements of the $T$-odd triple-product asymmetries. In this decay channel, the CP-violating weak phase arises from the interference between $B_s^0$-$\bar{B}_s^0$ mixing and the loop-induced decay amplitude. Using a sample of proton-proton collision data corresponding to an integrated luminosity of $3.0\, fb^{-1}$ collected with the LHCb detector, a signal yield of approximately 4000 $B_s^0 \to ϕϕ$ decays is obtained. The CP-violating phase is measured to be ${ϕ_s =-0.17\pm0.15\mathrm{\,(stat)}\pm0.03\mathrm{\,(syst)}}$ rad. The triple-product asymmetries are measured to be ${A_U=-0.003\pm0.017\mathrm{\,(stat)}\pm0.006\mathrm{\,(syst)}}$ and ${A_V=-0.017\pm0.017\mathrm{\,(stat)}\pm0.006\mathrm{\,(syst)}}$. Results are consistent with the hypothesis of CP conservation.

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arXiv2014

Observation of charmonium pairs produced exclusively in $pp$ collisions

A search is performed for the central exclusive production of pairs of charmonia produced in proton-proton collisions. Using data corresponding to an integrated luminosity of $3{\rm\ fb}^{-1}$ collected at centre-of-mass energies of 7 and 8 TeV, $J/ψJ/ψ$ and $J/ψψ(2S)$ pairs are observed, which have been produced in the absence of any other activity inside the LHCb acceptance that is sensitive to charged particles in the pseudorapidity ranges $(-3.5,-1.5)$ and $(1.5,5.0)$. Searches are also performed for pairs of P-wave charmonia and limits are set on their production. The cross-sections for these processes, where the dimeson system has a rapidity between 2.0 and 4.5, are measured to be $$ \begin{array}{rl} σ^{J/ψJ/ψ} &= 58\pm10{(\rm stat)} \pm 6{(\rm syst)} {\rm\ pb} , \\ σ^{J/ψψ(2S)} &= 63 ^{+27}_{-18}{(\rm stat)}\pm 10{(\rm syst)} {\rm\ pb} , \\ σ^{ψ(2S)ψ(2S)} &< 237 {\rm\ pb}, \\ σ^{χ_{c0}χ_{c0}} &< 69 {\rm\ nb}, \\ σ^{χ_{c1}χ_{c1}} &< 45 {\rm\ pb}, \\ σ^{χ_{c2}χ_{c2}} &< 141 {\rm\ pb}, \\ \end{array} $$ where the upper limits are set at the 90% confidence level. The measured $J/ψJ/ψ$ and $J/ψψ(2S)$ cross-sections are consistent with theoretical expectations.

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arXiv2014

Study of the kinematic dependences of $Λ_b^0$ production in $pp$ collisions and a measurement of the $Λ_b^0 \rightarrow Λ_c^+ π^-$ branching fraction

The kinematic dependences of the relative production rates, $f_{Λ_b^0}/f_d$, of $Λ_b^0$ baryons and $\bar{B}^0$ mesons are measured using $Λ_b^0 \rightarrow Λ_c^+ π^-$ and $\bar{B}^0 \rightarrow D^+ π^-$ decays. The measurements use proton-proton collision data, corresponding to an integrated luminosity of 1 fb$^{-1}$ at a centre-of-mass energy of 7 TeV, recorded in the forward region with the LHCb experiment. The relative production rates are observed to depend on the transverse momentum, $p_T$, and pseudorapidity, $η$, of the beauty hadron, in the studied kinematic region $1.5 < p_T < 40$ GeV/$c$ and $2 < η< 5$. Using a previous LHCb measurement of $f_{Λ_b^0}/f_d$ in semileptonic decays, the branching fraction $\mathcal{B}(Λ_b^0 \rightarrow Λ_c^+ π^-) = \Big( 4.30 \pm 0.03 \,\, ^{+0.12}_{-0.11} \pm 0.26 \pm 0.21 \Big) \times 10^{-3}$ is obtained, where the first uncertainty is statistical, the second is systematic, the third is from the previous LHCb measurement of $f_{Λ_b^0}/f_d$ and the fourth is due to the $\bar{B}^0 \rightarrow D^+ π^-$ branching fraction. This is the most precise measurement of a $Λ_b^0$ branching fraction to date.

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arXiv2014

Measurement of differential production cross section for $Z/γ^*$ bosons in association with jets in $p\bar{p}$ collisions at $\sqrt{s}=1.96$ TeV

Differential cross sections for the production of $Z$ bosons or off-shell photons $γ^*$ in association with jets are measured in proton-antiproton collisions at center-of-mass energy $\sqrt{s}=1.96$ TeV using the full data set collected with the Collider Detector at Fermilab in Tevatron Run II, and corresponding to 9.6 fb$^{-1}$ of integrated luminosity. Results include first measurements at CDF of differential cross sections in events with a $Z/γ^*$ boson and three or more jets, the inclusive cross section for production of $Z/γ^*$ and four or more jets, and cross sections as functions of various angular observables in lower jet-multiplicity final states. Measured cross sections are compared to several theoretical predictions.

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arXiv2014

First measurement of the charge asymmetry in beauty-quark pair production at a hadron collider

The difference in the angular distributions between beauty quarks and antiquarks, referred to as the charge asymmetry, is measured for the first time in $b\bar{b}$ pair production at a hadron collider. The data used correspond to an integrated luminosity of 1.0fb$^{-1}$ collected at 7TeV center-of-mass energy in proton-proton collisions with the LHCb detector. The measurement is performed in three regions of the invariant mass of the $b\bar{b}$ system. The results obtained are: \begin{eqnarray} A_{C}^{b\bar{b}}(40 < M_{b\bar{b}} < 75\,\rm{GeV/c^2}) &=& 0.4 \pm 0.4(\rm{stat}) \pm 0.3(\rm{syst})\%\newline A_{C}^{b\bar{b}}(75 < M_{b\bar{b}} < 105\,\rm{GeV/c^2}) &=& 2.0 \pm 0.9(\rm{stat}) \pm 0.6(\rm{syst})\%\newline A_{C}^{b\bar{b}}(M_{b\bar{b}} > 105\,\rm{GeV/c^2}) &=&1.6 \pm 1.7(\rm{stat}) \pm 0.6(\rm{syst})\% \end{eqnarray} where $A_{C}^{b\bar{b}}$ is defined as the asymmetry in the difference in rapidity between jets formed from the beauty quark and antiquark. The beauty jets are required to satisfy $2<η<4$, $E_{\rm T} > 20$GeV, and have an opening angle in the transverse plane $Δϕ>2.6$rad. These measurements are consistent with the predictions of the Standard Model.

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arXiv2014

Effective lifetime measurements in the $B_{s}^{0} \rightarrow K^{+}K^{-}$, $B^{0} \rightarrow K^{+}π^{-}$ and $B_{s}^{0} \rightarrow π^{+}K^{-}$ decays

Measurements of the effective lifetimes in the $B_{s}^{0} \rightarrow K^{+}K^{-}$, $B^{0} \rightarrow K^{+}π^{-}$ and $B_{s}^{0} \rightarrow π^{+}K^{-}$ decays are presented using $1.0~\mathrm{fb^{-1}}$ of $pp$ collision data collected at a centre-of-mass energy of 7 TeV by the LHCb experiment. The analysis uses a data-driven approach to correct for the decay time acceptance. The measured effective lifetimes are $τ_{B_{s}^{0} \rightarrow K^{+}K^{-}}$ = $1.407~\pm~0.016~\pm~0.007~\mathrm{ps}$, $τ_{B^{0} \rightarrow K^{+}π^{-}}$ = $1.524~\pm~0.011~\pm~0.004~\mathrm{ps}$, $τ_{B_{s}^{0} \rightarrow π^{+}K^{-}}$ = $1.60~\pm~0.06~\pm~0.01~\mathrm{ps}$. This is the most precise determination to date of the effective lifetime in the $B_{s}^{0} \rightarrow K^{+}K^{-}$ decay and provides constraints on contributions from physics beyond the Standard Model to the $B_{s}^{0}$ mixing phase and the width difference $ΔΓ_{s}$.

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arXiv2014

Observation of the $B^{0}_{s}\rightarrow J/ψK_{\rm S}^{0} K^{\pm} π^{\mp}$ decay

Decays of the form $B^{0}_{(s)}\rightarrow J/ψK_{\rm S}^{0} h^+ h^{\left(\prime\right) -}$ ($h^{(\prime)} = K, π$) are searched for in proton-proton collision data corresponding to an integrated luminosity of $1.0 \, {\rm fb}^{-1}$ recorded with the LHCb detector. The first observation of the $B^{0}_{s}\rightarrow J/ψK_{\rm S}^{0} K^{\pm} π^{\mp}$ decay is reported, with significance in excess of 10 standard deviations. The $B^{0}\rightarrow J/ψK_{\rm S}^{0} K^{+} K^{-}$ decay is also observed for the first time. The branching fraction of $B^{0}\rightarrow J/ψK_{\rm S}^{0} π^{+} π^{-}$ is determined, to significantly better precision than previous measurements, using $B^0 \rightarrow J/ψK_{\rm S}^{0}$ as a normalisation channel. Branching fractions and upper limits of the other $B^{0}_{(s)}\rightarrow J/ψK_{\rm S}^{0} h^+ h^{\left(\prime\right) -}$ modes are determined relative to that of the $B^{0}\rightarrow J/ψK_{\rm S}^{0} π^{+} π^{-}$ decay.

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arXiv2014

Measurement of the $Ξ_b^-$ and $Ω_b^-$ baryon lifetimes

Using a data sample of pp collisions corresponding to an integrated luminosity of $3~ \rm fb^{-1}$, the $Ξ_b^-$ and $Ω_b^-$ baryons are reconstructed in the $Ξ_b^- \rightarrow J/ψΞ^-$ and $Ω_b^- \rightarrow J/ψΩ^-$ decay modes and their lifetimes measured to be $τ(Ξ_b^-) = 1.55\, ^{+0.10}_{-0.09}~{\rm(stat)} \pm 0.03\,{\rm(syst)}$ ps, $τ(Ω_b^-) = 1.54\, ^{+0.26}_{-0.21}~{\rm(stat)} \pm 0.05\,{\rm(syst)}$ ps. These are the most precise determinations to date. Both measurements are in good agreement with previous experimental results and with theoretical predictions.

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arXiv2014

First observation of a baryonic $B_c^+$ decay

A baryonic decay of the $B_c^+$ meson, $B_c^+\to J/ψp\overline{p}π^+$, is observed for the first time, with a significance of $7.3$ standard deviations, in $pp$ collision data collected with the LHCb detector and corresponding to an integrated luminosity of $3.0$ fb$^{-1}$ taken at center-of-mass energies of $7$ and $8$ $\mathrm{TeV}$. With the $B_c^+\to J/ψπ^+$ decay as normalization channel, the ratio of branching fractions is measured to be \begin{equation*} \frac{\mathcal{B}(B_c^+\to J/ψp\overline{p}π^+)}{\mathcal{B}(B_c^+\to J/ψπ^+)} = 0.143^{\,+\,0.039}_{\,-\,0.034}\,(\mathrm{stat})\pm0.013\,(\mathrm{syst}). \end{equation*} The mass of the $B_c^+$ meson is determined as $M(B_c^+)=6274.0\pm1.8\,(\mathrm{stat})\pm0.4\,(\mathrm{syst})\,\mathrm{MeV}/c^2$, using the $B_c^+\to J/ψp\overline{p}π^+$ channel.

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arXiv2014

Observation of the $Λ_b^0\rightarrow J/ψp π^-$ decay

The first observation of the Cabibbo-suppressed decay $Λ_b^0\rightarrow J/ψp π^-$ is reported using a data sample of proton-proton collisions at 7 and 8 TeV, corresponding to an integrated luminosity of 3 $\rm fb^{-1}$. A prominent signal is observed and the branching fraction relative to the decay mode $Λ_b^0\rightarrow J/ψp K^-$ is determined to be $$ \frac{{\cal B}(Λ_b^0\rightarrow J/ψp π^-)}{{\cal B}(Λ_b^0\rightarrow J/ψp K^-)}=0.0824\pm0.0025\:(\text{stat})\pm0.0042\:(\text{syst}). $$ A search for direct CP violation is performed. The difference in the CP asymmetries between these two decays is found to be $$ {\cal A}_{CP}(Λ_b^0\rightarrow J/ψp π^-)-{\cal A}_{CP}(Λ_b^0\rightarrow J/ψp K^-)=(+5.7\pm 2.4\:(\text{stat})\pm1.2\:(\text{syst}))\%, $$ which is compatible with CP symmetry at the $2.2σ$ level.

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arXiv2014

Study of $χ_{b}$ meson production in pp collisions at $\sqrt{s}=7$ and 8TeV and observation of the decay $χ_{b}\rightarrow Υ(3S) γ$

A study of $χ_{b}$ meson production at LHCb is performed on proton-proton collision data, corresponding to 3.0fb$^{-1}$ of integrated luminosity collected at centre-of-mass energies $\sqrt{s}=7$ and 8TeV. The fraction of $Υ(nS)$ mesons originating from $χ_{b}$ decays is measured as a function of the $Υ$ transverse momentum in the rapidity range $2.0 < y^Υ < 4.5$. The radiative transition of the $χ_{b}(3P)$ meson to $Υ(3S)$ is observed for the first time. The $χ_{b1}(3P)$ mass is determined to be $$m(χ_{b1}(3P)) = 10\,511.3 \pm 1.7 \pm 2.5 MeV/c^2,$$ where the first uncertainty is statistical and the second is systematic.

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arXiv2014

Measurement of the $B_s^0$ meson lifetime in $D_s^+π^-$ decays

We present a measurement of the ratio of the Bs meson lifetime, in the flavor-specific decay to $D_s^+π^-$, to that of the B0 meson. The pp collision data used correspond to an integrated luminosity of 1/fb, collected with the LHCb detector, at a center-of-mass energy of 7 TeV. Combining our measured value of 1.010 +/- 0.010 +/- 0.008 for this ratio with the known lifetime, we determine the flavor-specific Bs lifetime to be tau(Bs) = 1.535 +/- 0.015 +/- 0.014 ps, where the uncertainties are statistical and systematic, respectively. This is the most precise measurement to date, and is consistent with previous measurements and theoretical predictions.

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arXiv2014

Precision measurement of the mass and lifetime of the $Ξ_b^0$ baryon

Using a proton-proton collision data sample corresponding to an integrated luminosity of 3 fb$^{-1}$ collected by LHCb at center-of-mass energies of 7 and 8 TeV, about 3800 $Ξ_b^0\toΞ_c^+π^-$, $Ξ_c^+\to pK^-π^+$ signal decays are reconstructed. From this sample, the first measurement of the $Ξ_b^0$ baryon lifetime is made, relative to that of the $Λ_b^0$ baryon. The mass differences $M(Ξ_b^0)-M(Λ_b^0)$ and $M(Ξ_c^+)-M(Λ_c^+)$ are also measured with precision more than four times better than the current world averages. The resulting values are $\frac{τ_{Ξ_b^0}}{τ_{Λ_b^0}} = 1.006\pm0.018\pm0.010$, $M(Ξ_b^0) - M(Λ_b^0) = 172.44\pm0.39\pm0.17 MeV/c^2$, $M(Ξ_c^+) - M(Λ_c^+) = 181.51\pm0.14\pm0.10 MeV/c^2$, where the first uncertainty is statistical and the second is systematic. The relative rate of $Ξ_b^0$ to $Λ_b^0$ baryon production is measured to be $\frac{f_{Ξ_b^0}}{f_{Λ_b^0}}\frac{\cal{B}(Ξ_b^0\toΞ_c^+π^-)}{\cal{B}(Λ_b^0\toΛ_c^+π^-)}\frac{\cal{B}(Ξ_c^+\to pK^-π^+)}{\cal{B}(Λ_c^+\to pK^-π^+)} = (1.88\pm0.04\pm0.03)\times10^{-2}$, where the first factor is the ratio of fragmentation fractions, $b\toΞ_b^0$ relative to $b\toΛ_b^0$. Relative production rates as functions of transverse momentum and pseudorapidity are also presented.

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arXiv2014

Measurement of $CP$ asymmetry in $D^0 \rightarrow K^- K^+$ and $D^0 \rightarrow π^- π^+$ decays

Time-integrated $CP$ asymmetries in $D^0$ decays to the final states $K^- K^+$ and $π^- π^+$ are measured using proton-proton collisions corresponding to $3\mathrm{\,fb}^{-1}$ of integrated luminosity collected at centre-of-mass energies of $7\mathrm{\,Te\kern -0.1em V}$ and $8\mathrm{\,Te\kern -0.1em V}$. The $D^0$ mesons are produced in semileptonic $b$-hadron decays, where the charge of the accompanying muon is used to determine the initial flavour of the charm meson. The difference in $CP$ asymmetries between the two final states is measured to be \begin{align} ΔA_{CP} = A_{CP}(K^-K^+)-A_{CP}(π^-π^+) = (+0.14 \pm 0.16\mathrm{\,(stat)} \pm 0.08\mathrm{\,(syst)})\% \ . \nonumber \end{align} A measurement of $A_{CP}(K^-K^+)$ is obtained assuming negligible $CP$ violation in charm mixing and in Cabibbo-favoured $D$ decays. It is found to be \begin{align} A_{CP}(K^-K^+) = (-0.06 \pm 0.15\mathrm{\,(stat)} \pm 0.10\mathrm{\,(syst)}) \% \ ,\nonumber \end{align} where the correlation coefficient between $ΔA_{CP}$ and $A_{CP}(K^-K^+)$ is $ρ=0.28$. By combining these results, the $CP$ asymmetry in the $D^0\rightarrowπ^-π^+$ channel is $A_{CP}(π^-π^+)=(-0.20\pm0.19\mathrm{\,(stat)}\pm0.10\mathrm{\,(syst)})\%$.

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arXiv2014

Studies of high-transverse momentum jet substructure and top quarks produced in 1.96 TeV proton-antiproton collisions

Results of a study of the substructure of the highest transverse momentum (pT) jets observed by the CDF collaboration are presented. Events containing at least one jet with pT > 400 GeV/c in a sample corresponding to an integrated luminosity of 5.95 inverse fb, collected in 1.96 TeV proton-antiproton collisions at the Fermilab Tevatron collider, are selected. A study of the jet mass, angularity, and planar-flow distributions is presented, and the measurements are compared with predictions of perturbative quantum chromodynamics. A search for boosted top-quark production is also described, leading to a 95% confidence level upper limit of 38 fb on the production cross section of top quarks with pT > 400 GeV/c.

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arXiv2014

Measurement of the ratio of $B_c^+$ branching fractions to $J/ψπ^+$ and $J/ψμ^+ν_μ$

The first measurement that relates semileptonic and hadronic decay rates of the $B_c^+$ meson is performed using proton-proton collision data corresponding to 1.0 fb$^{-1}$ of integrated luminosity collected with the LHCb detector. The measured value of the ratio of branching fractions, ${\cal B}(B_c^+ \to J/ψπ^+)/{\cal B}(B_c^+\to J/ψμ^+ν_μ)=0.0469 \pm 0.0028 (stat.) \pm 0.0046 (syst.)$, is at the lower end of available theoretical predictions.

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arXiv2014

Measurement of the resonant and CP components in $\overline{B}^0\rightarrow J/ψπ^+π^-$ decays

The resonant structure of the reaction $\overline{B}^0\rightarrow J/ψπ^+π^-$ is studied using data from 3 fb$^{-1}$ of integrated luminosity collected by the LHCb experiment, one-third at 7 Tev center-of-mass energy and the remainder at 8 Tev. The invariant mass of the $π^+π^-$ pair and three decay angular distributions are used to determine the fractions of the resonant and non-resonant components. Six interfering $π^+π^-$ states: $ρ(770)$, $f_0(500)$, $f_2(1270)$, $ρ(1450)$, $ω(782)$ and $ρ(1700)$ are required to give a good description of invariant mass spectra and decay angular distributions. The positive and negative CP fractions of each of the resonant final states are determined. The $f_0(980)$ meson is not seen and the upper limit on its presence, compared with the observed $f_0(500)$ rate, is inconsistent with a model of tetraquark substructure for these scalar mesons at the eight standard deviation level. In the $q\overline{q}$ model, the absolute value of the mixing angle between the $f_0(980)$ and the $f_0(500)$ scalar mesons is limited to be less than $17^{\circ}$ at 90% confidence level.

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arXiv2014

Study of orbitally excited $B$ mesons and evidence for a new $Bπ$ resonance

Using the full CDF Run II data sample, we report evidence for a new resonance, which we refer to as $B(5970)$, found simultaneously in the $B^0π^+$ and $B^+π^-$ mass distributions with a significance of 4.4 standard deviations. We further report the first study of resonances consistent with orbitally excited $B^{+}$ mesons and an updated measurement of the properties of orbitally excited $B^0$ and $B_s^0$ mesons. We measure the masses and widths of all states, as well as the relative production rates of $B_1$, $B_2^*$, and $B(5970)$ states and the branching fraction of the $B_{s2}^{*0}$ state to either $B^{*+} K^-$ and $B^{+} K^-$. Furthermore, we measure the production rates of the orbitally excited $B^{0,+}$ states relative to the $B^{0,+}$ ground state. The masses of the new $B(5970)$ resonances are $5978\pm5(\textrm{stat})\pm12(\textrm{syst}) \textrm{ MeV/c}^{2}$ for the neutral state and $5961\pm5(\textrm{stat})\pm12(\textrm{syst}) \textrm{ MeV/c}^{2}$ for the charged state, assuming that the resonance decays into $Bπ$ final states. The properties of the orbitally excited and the new $B(5970)^{0,+}$ states are compatible with isospin symmetry.

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