arXiv subjects

K. Carvalho Akiba

Publications and source records attributed to K. Carvalho Akiba.

At least 91 records · Page 5Linked to original sources

arXiv2014

Differential branching fractions and isospin asymmetries of $B \to K^{(*)}μ^{+}μ^{-}$ decays

The isospin asymmetries of $B \to Kμ^+μ^-$ and $B \to K^{*}μ^+μ^-$ decays and the partial branching fractions of the $B^0 \to K^0μ^+μ^-$, $B^+ \to K^+μ^+μ^-$ and $B^+ \to K^{*+}μ^+μ^-$ decays are measured as functions of the dimuon mass squared, $q^2$. The data used correspond to an integrated luminosity of 3$~$fb$^{-1}$ from proton-proton collisions collected with the LHCb detector at centre-of-mass energies of 7$\,$TeV and 8$\,$TeV in 2011 and 2012, respectively. The isospin asymmetries are both consistent with the Standard Model expectations. The three measured branching fractions, while individually consistent, all favour lower values than their respective Standard Model predictions.

hep-ex↗

arXiv2014

Searches for $Λ^0_{b}$ and $Ξ^{0}_{b}$ decays to $K^0_{\rm S} p π^{-}$ and $K^0_{\rm S}p K^{-}$ final states with first observation of the $Λ^0_{b} \rightarrow K^0_{\rm S}p π^{-}$ decay

A search for previously unobserved decays of beauty baryons to the final states $K^0_{\rm\scriptscriptstyle S} p π^{-}$ and $K^0_{\rm\scriptscriptstyle S}p K^{-}$ is reported. The analysis is based on a data sample corresponding to an integrated luminosity of $1.0\,$fb$^{-1}$ of $pp$ collisions. The $Λ^0_{b} \rightarrow \overline{\kern -0.2em K}^0_{\rm\scriptscriptstyle S}p π^{-}$ decay is observed with a significance of $8.6\,σ$, with branching fraction \begin{eqnarray*} {\cal{B}}(Λ^0_{b} \rightarrow \overline{\kern -0.2em K}^0 p π^{-}) & = & \left(1.26 \pm 0.19 \pm 0.09 \pm 0.34 \pm 0.05 \right) \times 10^{-5} \,, \end{eqnarray*} where the uncertainties are statistical, systematic, from the ratio of fragmentation fractions $f_Λ/f_{d}$, and from the branching fraction of the $B^0 \rightarrow K^0_{\rm\scriptscriptstyle S}π^{+}π^{-}$ normalisation channel, respectively. A first measurement is made of the $CP$ asymmetry, giving \begin{eqnarray*} A_{C/!P} (Λ^0_{b} \rightarrow \overline{\kern -0.2em K}^0 p π^{-}) & = & 0.22 \pm 0.13\mathrm{\,(stat)} \pm 0.03\mathrm{\,(syst)} \, . \end{eqnarray*} No significant signals are seen for $Λ^0_{b} \rightarrow K^0_{\rm\scriptscriptstyle S}p K^{-}$ decays, $Ξ^{0}_{b}$ decays to both the $K^0_{\rm\scriptscriptstyle S}p π^{-}$ and $K^0_{\rm\scriptscriptstyle S}p K^{-}$ final states, and the $Λ^0_{b} \rightarrow D^{-}_{s} (\rightarrow K^0_{\rm\scriptscriptstyle S} K^{-}) p$ decay, and upper limits on their branching fractions are reported.

hep-ex↗

arXiv2014

Measurement of charged particle multiplicities and densities in $pp$ collisions at $\sqrt{s}=7\;$TeV in the forward region

Charged particle multiplicities are studied in proton-proton collisions in the forward region at a centre-of-mass energy of $\sqrt{s} = 7\;$TeV with data collected by the LHCb detector. The forward spectrometer allows access to a kinematic range of $2.0<η<4.8$ in pseudorapidity, momenta down to $2\;$GeV/$c$ and transverse momenta down to $0.2\;$GeV/$c$. The measurements are performed using minimum-bias events with at least one charged particle in the kinematic acceptance. The results are presented as functions of pseudorapidity and transverse momentum and are compared to predictions from several Monte Carlo event generators.

hep-ex↗

arXiv2014

A study of CP violation in $B^\pm \to D K^\pm$ and $B^\pm \to D π^\pm$ decays with $D \to K^0_{\rm S} K^\pm π^\mp$ final states

A first study of CP violation in the decay modes $B^\pm\to [K^0_{\rm S} K^\pm π^\mp]_D h^\pm$ and $B^\pm\to [K^0_{\rm S} K^\mp π^\pm]_D h^\pm$, where $h$ labels a $K$ or $π$ meson and $D$ labels a $D^0$ or $\overline{D}^0$ meson, is performed. The analysis uses the LHCb data set collected in $pp$ collisions, corresponding to an integrated luminosity of 3 fb$^{-1}$. The analysis is sensitive to the CP-violating CKM phase $γ$ through seven observables: one charge asymmetry in each of the four modes and three ratios of the charge-integrated yields. The results are consistent with measurements of $γ$ using other decay modes.

hep-ex↗

arXiv2014

Measurement of D0-D0bar mixing parameters and search for CP violation using D0->K+pi- decays

Measurements of charm mixing parameters from the decay-time-dependent ratio of D0->K+pi- to D0->K-pi+ rates and the charge-conjugate ratio are reported. The analysis uses data, corresponding to 3 fb^{-1} of integrated luminosity, from proton-proton collisions at 7 and 8 TeV center-of-mass energies recorded by the LHCb experiment. In the limit of charge-parity (CP) symmetry, the mixing parameters are determined to be x'^2=(5.5 +- 4.9)x10^{-5}, y'= (4.8 +- 1.0)x10^{-3}, and R_D=(3.568 +- 0.066)x10^{-3}. Allowing for CP violation, the mixing parameters are determined separately for D0 and D0bar mesons yielding A_D = (-0.7 +- 1.9)%, for the direct CP-violating asymmetry, and 0.75 < |q/p|< 1.24 at the 68.3% confidence level, where q and p are parameters that describe the mass eigenstates of the neutral charm mesons in terms of the flavor eigenstates. This is the most precise determination of these parameters from a single experiment and shows no evidence for CP violation.

hep-ex↗

arXiv2014

Measurement of Upsilon production in pp collisions at sqrt{s}=2.76 TeV

The production of Upsilon(1S), Upsilon(2S) and Upsilon(3S) mesons decaying into the dimuon final state is studied with the LHCb detector using a data sample corresponding to an integrated luminosity of 3.3 pb^{-1} collected in proton-proton collisions at a centre-of-mass energy of sqrt{s}=2.76 TeV. The differential production cross-sections times dimuon branching fractions are measured as functions of the Upsilon transverse momentum and rapidity, over the ranges p_T<15 GeV/c and 2.0 Upsilon(1S) X) x B(Upsilon(1S) -> mu+mu-) = 1.111 +/- 0.043 +/- 0.044 nb, sigma(pp -> Upsilon(2S) X) x B(Upsilon(2S) -> mu+mu-) = 0.264 +/- 0.023 +/- 0.011 nb, sigma(pp -> Upsilon(3S) X) x B(Upsilon(3S) -> mu+mu-) = 0.159 +/- 0.020 +/- 0.007 nb, where the first uncertainty is statistical and the second systematic.

hep-ex↗

arXiv2014

Measurements of $B_c^+$ production and mass with the $B_c^+ \to J/ψπ^+$ decay

Measurements of $B_c^+$ production and mass are performed with the decay mode $B_c^+ \to J/ψπ^+$ using 0.37 fb$^{-1}$ of data collected in $pp$ collisions at $\sqrt{s}=7$ TeV by the LHCb experiment. The ratio of the production cross-section times branching fraction between the $B_c^+ \to J/ψπ^+$ and the $B^+ \to J/ψK^+$ decays is measured to be $(0.68 \pm 0.10\,({\rm stat.}) \pm 0.03\,({\rm syst.}) \pm 0.05\,({\rm lifetime}))$% for $B_c^+$ and $B^+$ mesons with transverse momenta $p_{\rm T}>4 $GeV/$c$ and pseudorapidities $2.5<η<4.5$. The $B_c^+$ mass is directly measured to be $6273.7 \pm 1.3\,({\rm stat.}) \pm 1.6 \,({\rm syst.})$ MeV/$c^2$, and the measured mass difference with respect to the $B^+$ meson is $M(B_c^+)-M(B^+) = 994.6 \pm 1.3\,({\rm stat.}) \pm 0.6\,({\rm syst.})$ MeV/$c^2$.

hep-ex↗

arXiv2014

Study of $J/ψ$ production and cold nuclear matter effects in $p$Pb collisions at $\sqrt{s_{NN}}=5 \mathrm{TeV}$

The production of $J/ψ$ mesons with rapidity $1.5<y<4.0$ or $-5.0<y<-2.5$ and transverse momentum $p_\mathrm{T}<14 \mathrm{GeV}/c$ is studied with the LHCb detector in proton-lead collisions at a nucleon-nucleon centre-of-mass energy $\sqrt{s_{NN}}=5 \mathrm{TeV}$. The analysis is based on a data sample corresponding to an integrated luminosity of about $1.6 \mathrm{nb}^{-1}$. For the first time the nuclear modification factor and forward-backward production ratio are determined separately for prompt $J/ψ$ mesons and $J/ψ$ from $b$-hadron decays. Clear suppression of prompt $J/ψ$ production with respect to proton-proton collisions at large rapidity is observed, while the production of $J/ψ$ from $b$-hadron decays is less suppressed. These results show good agreement with available theoretical predictions. The measurement shows that cold nuclear matter effects are important for interpretations of the related quark-gluon plasma signatures in heavy-ion collisions.

nucl-ex↗

arXiv2014

Measurements of the $B^+$, $B^0$, $B_s^0$ meson and $Λ_b^0$ baryon lifetimes

Measurements of $b$-hadron lifetimes are reported using $pp$ collision data, corresponding to an integrated luminosity of 1.0fb$^{-1}$, collected by the LHCb detector at a centre-of-mass energy of $7$Tev. Using the exclusive decays $B^+\to J/ψK^+$, $B^0\to J/ψK^*(892)^0$, $B^0\to J/ψK^0_{\rm S}$, $Λ_b^0\to J/ψΛ$ and $B^0_s\to J/ψϕ$ the average decay times in these modes are measured to be $τ_{B^+\to J/ψK^+}$ = $1.637 \pm$ 0.004 $\pm$ 0.003 ps, $τ_{B^0\to J/ψK^*(892)^0}$ = $1.524 \pm$ 0.006 $\pm$ 0.004 ps, $τ_{B^0\to J/ψK^0_{\rm S}}$ = $1.499 \pm$ 0.013 $\pm$ 0.005 ps, $τ_{Λ_b^0\to J/ψΛ}$ = $1.415 \pm$ 0.027 $\pm$ 0.006 ps and $τ_{B^0_s\to J/ψϕ}$ = $1.480 \pm$ 0.011 $\pm$ 0.005 ps, where the first uncertainty is statistical and the second is systematic. These represent the most precise lifetime measurements in these decay modes. In addition, ratios of these lifetimes, and the ratio of the decay-width difference, $ΔΓ_d$, to the average width, $Γ_d$, in the $B^0$ system, $ΔΓ_d/Γ_d = -0.044 \pm 0.025 \pm 0.011$, are reported. All quantities are found to be consistent with Standard Model expectations.

hep-ex↗

arXiv2014

Search for Majorana neutrinos in $B^- \to π^+μ^-μ^-$ decays

A search for heavy Majorana neutrinos produced in the $B^- \to π^+μ^-μ^-$ decay mode is performed using 3 fb$^{-1}$ of integrated luminosity collected with the LHCb detector in $pp$ collisions at center-of-mass energies of 7 TeV and 8 TeV at the LHC. Neutrinos with masses in the range 250-5000 MeV and lifetimes from zero to 1000 ps are probed. In the absence of a signal, upper limits are set on the branching fraction ${\cal{B}}(B^- \to π^+μ^-μ^-)$ as functions of neutrino mass and lifetime. These limits are on the order of $10^{-9}$ for short neutrino lifetimes of 1 ps or less. Limits are also set on the coupling between the muon and a possible fourth-generation neutrino.

hep-ex↗

arXiv2014

Observation of double charm production involving open charm in pp collisions at $\sqrt{s}$=7 TeV

The production of $J/ψ$ mesons accompanied by open charm, and of pairs of open charm hadrons are observed in pp collisions at a centre-of-mass energy of 7 TeV using an integrated luminosity of $355pb^{-1}$ collected with the LHCb detector. Model independent measurements of absolute cross-sections are given together with ratios to the measured $J/ψ$ and open charm cross-sections. The properties of these events are studied and compared to theoretical predictions.

hep-ex↗

arXiv2014

Searches for $B^{0}_{(s)} \rightarrow J/ψ p \overline{p}$ and $B^{+} \to J/ψ p \overline{p} π^{+}$ decays

The results of searches for $B^{0}_{(s)} \rightarrow J/ψ p \overline{p}$ and $B^{+} \to J/ψ p \overline{p} π^{+}$ decays are reported. The analysis is based on a data sample, corresponding to an integrated luminosity of 1.0 fb$^{-1}$ of $pp$ collisions, collected with the LHCb detector. An excess with 2.8$\,σ$ significance is seen for the decay $B^{0}_{s} \to J/ψ p \overline{p}$ and an upper limit on the branching fraction is set at the 90 % confidence level: ${\cal B}(B^{0}_{s} \to J/ψ p \overline{p}) < 4.8 \times 10^{-6}$, which is the first such limit. No significant signals are seen for $B^{0} \to J/ψ p \overline{p}$ and $B^{+} \to J/ψ p \overline{p} π^{+}$ decays, for which the corresponding limits are set: ${\cal{B}}(B^{0} \to J/ψ p \overline{p}) < 5.2 \times 10^{-7}$, which significantly improves the existing limit; and ${\cal{B}}(B^{+} \to J/ψ p \overline{p} π^{+}) < 5.0 \times 10^{-7}$, which is the first limit on this branching fraction.

hep-ex↗

arXiv2014

Measurements of indirect CP asymmetries in $D^0\to K^-K^+$ and $D^0\toπ^-π^+$ decays

A study of indirect CP violation in $D^0$ mesons through the determination of the parameter $A_Γ$ is presented using a data sample of $pp$ collisions, corresponding to an integrated luminosity of 1.0 fb$^{-1}$, collected with the LHCb detector and recorded at the centre-of-mass energy of 7 TeV at the LHC. The parameter $A_Γ$ is the asymmetry of the effective lifetimes measured in decays of $D^0$ and $\bar{D}^0$ mesons to the CP eigenstates $K^-K^+$ and $π^-π^+$. Fits to the data sample yield $A_Γ(KK)=(-0.35\pm0.62\pm0.12)\times 10^{-3}$ and $A_Γ(ππ)=(0.33\pm1.06\pm0.14)\times 10^{-3}$, where the first uncertainties are statistical and the second systematic. The results represent the world's best measurements of these quantities. They show no difference in $A_Γ$ between the two final states and no indication of CP violation.

hep-ex↗

arXiv2014

Measurement of the $B_c^+$ meson lifetime using $B_c^+ \to J\!/\!ψμ^+ ν_μ X$ decays

The lifetime of the $B_c^+$ meson is measured using semileptonic decays having a $J\!/\!ψ$ meson and a muon in the final state. The data, corresponding to an integrated luminosity of $2\mathrm{~fb^{-1}}$, are collected by the LHCb detector in $pp$ collisions at a centre-of-mass energy of $8\,\mathrm{TeV}$. The measured lifetime is $$τ= 509 \pm 8 \pm 12 \mathrm{~fs},$$ where the first uncertainty is statistical and the second is systematic.

hep-ex↗

arXiv2014

Updated measurements of exclusive $J/ψ$ and $ψ(2S)$ production cross-sections in $pp$ collisions at $\sqrt{s}=7$ TeV

The differential cross-section as a function of rapidity has been measured for the exclusive production of $J/ψ$ and $ψ(2S)$ mesons in proton-proton collisions at $\sqrt{s}=7$ TeV, using data collected by the LHCb experiment, corresponding to an integrated luminosity of 930 pb$^{-1}$. The cross-sections times branching fractions to two muons having pseudorapidities between 2.0 and 4.5 are measured to be $$\begin{array}{rl} σ_{pp\rightarrow J/ψ\rightarrow{μ^+}{μ^-}}(2.0<η_{μ^\pm }<4.5)=&291\pm 7\pm19 {\rm \ pb},\\ σ_{pp\rightarrowψ(2S)\rightarrow{μ^+}{μ^-}}(2.0<η_{μ^\pm}<4.5)=&6.5\pm 0.9\pm 0.4 {\rm \ pb},\end{array}$$ where the first uncertainty is statistical and the second is systematic. The measurements agree with next-to-leading order QCD predictions as well as with models that include saturation effects.

hep-ex↗

arXiv2014

Observation of associated production of a $Z$ boson with a $D$ meson in the~forward region

A search for associated production of a $Z$ boson with an open charm meson is presented using a data sample, corresponding to an integrated luminosity of $1.0\,\mathrm{fb}^{-`}$ of proton--proton collisions at a centre-of-mass energy of 7\,TeV, collected by the LHCb experiment. %% Seven candidate events for associated production of a $Z$ boson with a $D^0$ meson and four candidate events for a $Z$ boson with a $D^+$ meson are observed with a combined significance of 5.1standard deviations. The production cross-sections in the forward region are measured to be $$σ_{Z\rightarrowμ^+μ^-\!,D^0} = 2.50\pm1.12\pm0.22pb$$ $$σ_{Z\rightarrowμ^+μ^-\!,D^+} = 0.44\pm0.23\pm0.03pb,$$ where the first uncertainty is statistical and the second systematic.

hep-ex↗

arXiv2014

Measurement of the flavour-specific CP-violating asymmetry $a_{\rm sl}^s$ in $B_s^0$ decays

The CP-violating asymmetry a_{sl}^s is studied using semileptonic decays of Bs and anti-Bs mesons produced in pp collisions at a centre-of-mass energy of 7 TeV at the LHC, exploiting a data sample corresponding to an integrated luminosity of 1.0/fb. The reconstructed final states are Ds^(+/-)μ^(-/+), with the Ds^(+/-) particle decaying in the ϕπ^(+/-) mode. The Ds^(+/-)μ^{-/+) yields are summed over Bs and anti-Bs initial states, and integrated with respect to decay time. Data-driven methods are used to measure efficiency ratios. We obtain $a_{sl}^s$ = (-0.06 +/- 0.50 +/- 0.36)%, where the first uncertainty is statistical and the second systematic.

hep-ex↗

arXiv2014

Search for the doubly charmed baryon Xi_cc^+

A search for the doubly charmed baryon Xi_cc^+ in the decay mode Xi_cc^+ -> Lambda_c^+ K^- pi^+ is performed with a data sample, corresponding to an integrated luminosity of 0.65/fb, of pp collisions recorded at a centre-of-mass energy of 7 TeV. No significant signal is found in the mass range 3300-3800 MeV/c^2. Upper limits at the 95% confidence level on the ratio of the Xi_cc^+ production cross-section times branching fraction to that of the Lambda_c^+, R, are given as a function of the Xi_cc^+ mass and lifetime. The largest upper limits range from R < 1.5 x 10^-2 for a lifetime of 100 fs to R < 3.9 x 10^-4 for a lifetime of 400 fs.

hep-ex↗