arXiv subjects

K. Carvalho Akiba

Publications and source records attributed to K. Carvalho Akiba.

At least 73 records · Page 4Linked to original sources

arXiv2014

Observation of $B^0_s \to K^{\pm}K^\mp$ and evidence for $B^0_s \to K^{-}π^+$ decays

Measurements of the branching fractions of $B^0_s \to K^{*\pm}K^\mp$ and $B^0_s \to K^{*\pm}π^\mp$ decays are performed using a data sample corresponding to $1.0 \ {\rm fb}^{-1}$ of proton-proton collision data collected with the LHCb detector at a centre-of-mass energy of $7\mathrm{\,TeV}$, where the $K^{*\pm}$ mesons are reconstructed in the $K^0_{\rm S}π^\pm$ final state. The first observation of the $B^0_s \to K^{*\pm}K^\mp$ decay and the first evidence for the $B^0_s \to K^{*-}π^+$ decay are reported with branching fractions \begin{eqnarray} {\cal B}(B^0_s \to K^{*\pm}K^\mp) & = & (12.7\pm1.9\pm1.9) \times 10^{-6}, \\ {\cal B}(B^0_s \to K^{*-}π^+) & = & ~(3.3\pm1.1\pm0.5) \times 10^{-6}, \end{eqnarray} where the first uncertainties are statistical and the second are systematic. In addition, an upper limit of ${\cal B}(B^0 \to K^{*\pm}K^\mp) < 0.4 \ (0.5) \times 10^{-6}$ is set at $90\,% \ (95\,%)$ confidence level.

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arXiv2014

Measurement of CP asymmetry in $B^0_s \rightarrow D^{\mp}_s K^{\pm}$ decays

We report on measurements of the time-dependent CP violating observables in $B^0_s\rightarrow D^{\mp}_s K^{\pm}$ decays using a dataset corresponding to 1.0 fb$^{-1}$ of pp collisions recorded with the LHCb detector. We find the CP violating observables $C_f=0.53\pm0.25\pm0.04$, $A^{ΔΓ}_f=0.37\pm0.42\pm0.20$, $A^{ΔΓ}_{\bar{f}}=0.20\pm0.41\pm0.20$, $S_f=-1.09\pm0.33\pm0.08$, $S_{\bar{f}}=-0.36\pm0.34\pm0.08$, where the uncertainties are statistical and systematic, respectively. Using these observables together with a recent measurement of the $B^0_s$ mixing phase $-2β_s$ leads to the first extraction of the CKM angle $γ$ from $B^0_s \rightarrow D^{\mp}_s K^{\pm}$ decays, finding $γ$ = (115$_{-43}^{+28}$)$^\circ$ modulo 180$^\circ$ at 68% CL, where the error contains both statistical and systematic uncertainties.

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arXiv2014

Measurement of the B0bar-B0 and Bsbar-Bs production asymmetries in pp collisions at sqrt(s)=7 TeV

The B0bar-B0 and Bsbar-Bs production asymmetries, AP(B0) and AP(Bs), are measured by means of a time-dependent analysis of B0 -> J/ψK*0, B0 -> D- pi+ and Bs -> Ds- pi+ decays, using a data sample corresponding to an integrated luminosity of 1.0 fb^{-1}, collected by LHCb in pp collisions at a centre-of-mass energy of 7 TeV. The measurements are performed as a function of transverse momentum and pseudorapidity of the B0 and Bs mesons within the LHCb acceptance. The production asymmetries, integrated over pT and eta in the range 4 < pT< 30 GeV/c and 2.5<eta<4.5, are determined to be AP(B0) = (-0.35 +/- 0.76 +/- 0.28)% and AP(Bs) = (1.09 +/- 2.61 +/- 0.66)%, where the first uncertainties are statistical and the second systematic.

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arXiv2014

Measurement of the lifetime of the $B_c^+$ meson using the $B_c^+\rightarrow J/ψπ^+$ decay mode

The difference in total widths between the $B_c^+$ and $B^+$ mesons is measured using 3.0fb$^{-1}$ of data collected by the LHCb experiment in 7 and 8 TeV centre-of-mass energy proton-proton collisions at the LHC. Through the study of the time evolution of $B_c^+ \rightarrow J/ψπ^+$ and $B^+\rightarrow J/ψK^+$ decays, the width difference is measured to be $$ ΔΓ\equiv Γ_{B_c^+} - Γ_{B^+} = 4.46 \pm 0.14 \pm 0.07mm^{-1}c,$$ where the first uncertainty is statistical and the second systematic. The known lifetime of the $B^+$ meson is used to convert this to a precise measurement of the $B_c^+$ lifetime, $$τ_{B_c^+} = 513.4 \pm 11.0 \pm 5.7fs,$$ where the first uncertainty is statistical and the second systematic.

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arXiv2014

Measurement of the CP-violating phase $ϕ_s$ in $\bar{B}^{0}_{s}\to D_{s}^{+}D_{s}^{-}$ decays

We present a measurement of the $CP$-violating weak mixing phase $ϕ_s$ using the decay $\bar{B}^{0}_{s}\to D_{s}^{+}D_{s}^{-}$ in a data sample corresponding to $3.0$ fb$^{-1}$ of integrated luminosity collected with the LHCb detector in $pp$ collisions at centre-of-mass energies of 7 and 8 TeV. An analysis of the time evolution of the system, which does not constrain $|λ|=1$ to allow for the presence of $CP$ violation in decay, yields $ϕ_s = 0.02 \pm 0.17$ (stat) $\pm 0.02$ (syst) rad, $|λ| = 0.91^{+0.18}_{-0.15}$ (stat) $\pm0.02$ (syst). This result is consistent with the Standard Model expectation.

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arXiv2014

Precision measurement of $CP$ violation in $B_s^0 \to J/ψK^+K^-$ decays

The time-dependent $CP$ asymmetry in $B_s^0 \to J/ψK^+K^-$ decays is measured using $pp$ collision data, 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. In a sample of 96 000 $B_s^0 \to J/ψK^+K^-$ decays, the $CP$-violating phase $ϕ_s$ is measured, as well as the decay widths $Γ_{L}$ and $Γ_{H}$ of the light and heavy mass eigenstates of the $B_s^0-\bar{B}_s^0$ system. The values obtained are $ϕ_s = -0.058 \pm 0.049 \pm 0.006$ rad, $Γ_s \equiv (Γ_{L}+Γ_{H})/2 = 0.6603 \pm 0.0027 \pm 0.0015$ps$^{-1}$, and$ΔΓ_s \equiv Γ_{L} - Γ_{H} = 0.0805 \pm 0.0091 \pm 0.0032$ps$^{-1}$, where the first uncertainty is statistical and the second systematic. These are the most precise single measurements of those quantities to date. A combined analysis with $B_s^{0} \to J/ψπ^+π^-$ decays gives $ϕ_s = -0.010 \pm 0.039 $rad. All measurements are in agreement with the Standard Model predictions. For the first time the phase $ϕ_s$ is measured independently for each polarisation state of the $K^+K^- $ system and shows no evidence for polarisation dependence.

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arXiv2014

Study of $η-η^{\prime}$ mixing from measurement of $B^0_{(s)} \rightarrow J/ψη^{(\prime)}$~decay rates

A study of $B^0$~and $B^0_s$ meson decays into $J/ψη$~and $J/ψη^{\prime}$ final states is performed using a data set of proton-proton collisions at centre-of-mass energies of 7 and 8TeV, collected by the LHCb experiment and corresponding to 3.0fb$^{-1}$ of integrated luminosity. The decay $B^0 \rightarrow J/ψη^{\prime}$ is observed for thefirst time. The following ratios of branching fractions are measured: $$ \frac{\mathcal{B}(B^0 \rightarrow J/ψη^{\prime})}{\mathcal{B}(B^0_s \rightarrow J/ψη^{\prime})} = (2.28\pm0.65\,(stat)\,\pm0.10\,(syst)\,\pm0.13\,(f_{s}/f_{d}))\times10^{-2},$$ $$ \frac{\mathcal{B}(B^0 \rightarrow J/ψη)}{\mathcal{B}(B^0_s \rightarrow J/ψη)} = (1.85\pm0.61\,(stat)\,\pm0.09\,(syst)\,\pm0.11\,(f_{s}/f_{d}))\times10^{-2},$$ where the third uncertainty is related to the present knowledge of $f_{s}/f_{d}$, the ratio between the probabilities for a $b$ quark to form a $B^0_s$ or $B^0$ meson. The branching fraction ratios are used to determine the parameters of $η-η^{\prime}$ meson mixing. In addition, the first evidence for the decay $B^0_s \rightarrow ψ(2S) η^{\prime}$ is reported, and the relative branching fraction is measured, $$\frac{\mathcal{B}(B^0_s \rightarrow ψ(2S) η^{\prime})}{\mathcal{B}(B^0_s \rightarrow J/ψη^{\prime})} = (38.7\pm9.0\,(stat)\,\pm1.3\,(syst)\,\pm0.9(\mathcal{B}))\times10^{-2},$$ where the third uncertainty is due to the limited knowledge of the branching fractions of $J/ψ$ and $ψ(2S)$~mesons.

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arXiv2014

Measurement of the CKM angle γusing B^\pm --> D K^\pm with D-->K_Sπ^+π^-, K_SK^+K^- decays

A binned Dalitz plot analysis of $B^\pm \to D K^\pm$ decays, with $D \to K_S π^+π^-$ and $D \to K_S K^+ K^-$, is performed to measure the \CP-violating observables $x_{\pm}$ and $y_{\pm}$, which are sensitive to the Cabibbo-Kobayashi-Maskawa angle $γ$. The analysis exploits a sample of proton-proton collision data corresponding to 3.0\invfb collected by the LHCb experiment. Measurements from CLEO-c of the variation of the strong-interaction phase of the $D$ decay over the Dalitz plot are used as inputs. The values of the parameters are found to be $x_+ = (-7.7 \pm 2.4 \pm 1.0 \pm 0.4)\times 10^{-2}$, $x_- = (2.5 \pm 2.5 \pm 1.0 \pm 0.5) \times 10^{-2}$, $y_+ = (-2.2 \pm 2.5 \pm 0.4 \pm 1.0)\times 10^{-2}$, and $y_- = (7.5 \pm 2.9 \pm 0.5 \pm 1.4) \times 10^{-2}$. The first, second, and third uncertainties are the statistical, the experimental systematic, and that associated with the precision of the strong-phase parameters. These are the most precise measurements of these observables and correspond to $γ= (62^{\,+15}_{\,-14})^\circ$, with a second solution at $γ\to γ+ 180^\circ$, and $r_B = 0.080^{+ 0.019}_{-0.021}$, where $r_B$ is the ratio between the suppressed and favoured $B$ decay amplitudes.

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arXiv2014

Search for $CP$ violation using $T$-odd correlations in $D^0 \to K^+K^-π^+π^-$ decays

A search for $CP$ violation using $T$-odd correlations is performed using the four-body $D^0 \to K^+K^-π^+π^-$ decay, selected from semileptonic $B$ decays. The data sample corresponds to integrated luminosities of $1.0\,\text{fb}^{-1}$ and $2.0\,\text{fb}^{-1}$ recorded at the centre-of-mass energies of 7 TeV and 8 TeV, respectively. The $CP$-violating asymmetry $a_{CP}^{T\text{-odd}}$ is measured to be $(0.18\pm 0.29\text{(stat)}\pm 0.04\text{(syst)})\%$. Searches for $CP$ violation in different regions of phase space of the four-body decay, and as a function of the $D^0$ decay time, are also presented. No significant deviation from the $CP$ conservation hypothesis is found.

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arXiv2014

First observations of the rare decays $B^+-> K^+π^+π^-μ^+μ^-$ and $B^+->ϕK^+μ^+μ^-$

First observations of the rare decays $B^+\rightarrow K^+π^+π^-μ^+μ^-$ and $B^+\rightarrow ϕK^+μ^+μ^-$ are presented using data corresponding to an integrated luminosity of $3.0\,{fb}^{-1}$, collected by the LHCb experiment at centre-of-mass energies of $7$ and $8\mathrm{\,TeV}$. The branching fractions of the decays are \begin{eqnarray*} \mathcal{B}(B^+\rightarrow K^+π^+π^-μ^+μ^-) &=& (4.36\,^{+0.29}_{-0.27}\,\mathrm{(stat)}\pm 0.21\,\mathrm{(syst)}\pm0.18\,\mathrm{(norm)})\times10^{-7},\\ \mathcal{B}(B^+\rightarrowϕK^+μ^+μ^-) &=& (0.82 \,^{+0.19}_{-0.17}\,\mathrm{(stat)}\,^{+0.10}_{-0.04}\,\mathrm{(syst)}\pm0.27\,\mathrm{(norm)}) \times10^{-7},\end{eqnarray*} where the uncertainties are statistical, systematic, and due to the uncertainty on the branching fractions of the normalisation modes. A measurement of the differential branching fraction in bins of the invariant mass squared of the dimuon system is also presented for the decay $B^+\rightarrow K^+π^+π^-μ^{+}μ^{-}$.

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arXiv2014

Measurement of $C\!P$ asymmetries in the decays $B^0 \rightarrow K^{*0} μ^+ μ^-$ and $B^+ \rightarrow K^{+} μ^+ μ^-$

The direct $C\!P$ asymmetries of the decays $B^0 \rightarrow K^{*0} μ^+ μ^-$ and $B^+ \rightarrow K^{+} μ^+ μ^-$ are measured using $pp$ collision data corresponding to an integrated luminosity of 3.0$\mbox{fb}^{-1}$ collected with the LHCb detector. The respective control modes $B^0 \rightarrow J/ψK^{*0}$ and $B^+ \rightarrow J/ψK^{+}$ are used to account for detection and production asymmetries. The measurements are made in several intervals of $μ^+ μ^-$ invariant mass squared, with the $ϕ(1020)$ and charmonium resonance regions excluded. Under the hypothesis of zero $C\!P$ asymmetry in the control modes, the average values of the asymmetries are \begin{align} {\cal A}_{C\!P}(B^0 \rightarrow K^{*0} μ^+ μ^-) &= -0.035 \pm 0.024 \pm 0.003, \cr {\cal A}_{C\!P}(B^+ \rightarrow K^{+} μ^+ μ^-) &= \phantom{-}0.012 \pm 0.017 \pm 0.001, \end{align} where the first uncertainties are statistical and the second are due to systematic effects. Both measurements are consistent with the Standard Model prediction of small $C\!P$ asymmetry in these decays.

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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

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

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

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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