arXiv subjects

K. Carvalho Akiba

Publications and source records attributed to K. Carvalho Akiba.

At least 19 recordsLinked to original sources

arXiv2025

Evidence for CP violation in $B^+\to p \bar p K^+$ decays

Three-body $B^+\to p \overline p K^+$ and $B^+\to p \overline p π^+$ decays are studied using a data sample corresponding to an integrated luminosity of 3.0 $fb^{-1}$ collected by the LHCb experiment in proton-proton collisions at center-of-mass energies of $7$ and $8$ TeV. Evidence of CP violation in the $B^+\to p \overline p K^+$ decay is found in regions of the phase space, representing the first measurement of this kind for a final state containing baryons. Measurements of the forward-backward asymmetry of the light meson in the $p\overline p$ rest frame yield $A_{\mathrm{FB}}(p \overline p K^+,~m_{p\overline p}<2.85\mathrm{\,Ge\kern -0.1em V\!/}c^2)=0.495\pm0.012~(\mathrm{stat})\pm0.007~(\mathrm{syst})$ and $A_{\mathrm{FB}}(p\overline p π^+,~m_{p\overline p}<2.85\mathrm{\,Ge\kern -0.1em V\!/}c^2)=-0.409\pm0.033~(\mathrm{stat})\pm0.006~(\mathrm{syst})$. In addition, the branching fraction of the decay $B^+\to\kern 0.1em\overline{\kern -0.1emΛ}(1520)p$ is measured to be $\mathcal{B}(B^+ \to \kern 0.1em\overline{\kern -0.1emΛ}(1520)p)=(3.15\pm0.48~(\mathrm{stat})\pm0.07~(\mathrm{syst})\pm0.26~(\mathrm{BF}))\times 10^{-7}$, where BF denotes the uncertainty on secondary branching fractions.

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arXiv2020

Measurement of psi(2S) meson production in pp collisions at sqrt(s)=7 TeV

The differential cross-section for the inclusive production of psi(2S) mesons in pp collisions at sqrt(s)=7 TeV has been measured with the LHCb detector. The data sample corresponds to an integrated luminosity of 36 pb-1. The psi(2S) mesons are reconstructed in the decay channels psi(2S) -> mu+ mu- and psi(2S) -> J/psi pi+ pi-, with the J/psi meson decaying into two muons. Results are presented both for promptly produced psi(2S) mesons and for those originating from b-hadron decays. In the kinematic range pT(psi(2S)) <= 16 GeV/c and 2 < y(psi(2S)) <= 4.5 we measure 1.44 +- 0.01 +- 0.12+0.2-0.4 mub for prompt psi(2S) production and 0.25 +- 0.01 +- 0.02 mub for psi(2S) from b-hadron decays, where the last uncertainty on the prompt cross-section is due to the unknown psi(2S) polarization. Recent QCD calculations are found to be in good agreement with our measurements. Combining the present result with the LHCb J/psi measurements we determine the inclusive branching fraction B(b -> psi(2S) X) = (2.73 +- 0.06 +- 0.16 +- 0.24) x 10^(-3), where the last uncertainty is due to the B(b -> J/psi X), B(J/psi -> mu+ mu-) and B(psi(2S) -> e+ e-) branching fraction uncertainties. All above results are corrected by an erratum included as an appendix.

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arXiv2019

Physics case for an LHCb Upgrade II - Opportunities in flavour physics, and beyond, in the HL-LHC era

The LHCb Upgrade II will fully exploit the flavour-physics opportunities of the HL-LHC, and study additional physics topics that take advantage of the forward acceptance of the LHCb spectrometer. The LHCb Upgrade I will begin operation in 2020. Consolidation will occur, and modest enhancements of the Upgrade I detector will be installed, in Long Shutdown 3 of the LHC (2025) and these are discussed here. The main Upgrade II detector will be installed in long shutdown 4 of the LHC (2030) and will build on the strengths of the current LHCb experiment and the Upgrade I. It will operate at a luminosity up to $ 2 \times 10^{34} \rm cm^{-2}s^{-1}$, ten times that of the Upgrade I detector. New detector components will improve the intrinsic performance of the experiment in certain key areas. An Expression Of Interest proposing Upgrade II was submitted in February 2017. The physics case for the Upgrade II is presented here in more depth. $CP$-violating phases will be measured with precisions unattainable at any other envisaged facility. The experiment will probe $b\to s \ell^+\ell^-$ and $b\to d \ell^+\ell^-$ transitions in both muon and electron decays in modes not accessible at Upgrade I. Minimal flavour violation will be tested with a precision measurement of the ratio of $B(B^0\toμ^+μ^-)/B(B_s^0\to μ^+μ^-)$. Probing charm $CP$ violation at the $10^{-5}$ level may result in its long sought discovery. Major advances in hadron spectroscopy will be possible, which will be powerful probes of low energy QCD. Upgrade II potentially will have the highest sensitivity of all the LHC experiments on the Higgs to charm-quark couplings. Generically, the new physics mass scale probed, for fixed couplings, will almost double compared with the pre-HL-LHC era; this extended reach for flavour physics is similar to that which would be achieved by the HE-LHC proposal for the energy frontier.

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arXiv2018

Differential branching fraction and angular analysis of $Λ^{0}_{b} \rightarrow Λμ^+μ^-$ decays

The differential branching fraction of the rare decay $Λ^{0}_{b} \rightarrow Λμ^+μ^-$ is measured as a function of $q^{2}$, the square of the dimuon invariant mass. The analysis is performed using proton-proton collision data, corresponding to an integrated luminosity of $3.0 \mbox{ fb}^{-1}$, collected by the LHCb experiment. Evidence of signal is observed in the $q^2$ region below the square of the $J/ψ$ mass. Integrating over $15 < q^{2} < 20 \mbox{ GeV}^2/c^4$ the branching fraction is measured as $d\mathcal{B}(Λ^{0}_{b} \rightarrow Λμ^+μ^-)/dq^2 = (1.18 ^{+ 0.09} _{-0.08} \pm 0.03 \pm 0.27) \times 10^{-7} ( \mbox{GeV}^{2}/c^{4})^{-1}$, where the uncertainties are statistical, systematic and due to the normalisation mode, $Λ^{0}_{b} \rightarrow J/ψΛ$, respectively. In the $q^2$ intervals where the signal is observed, angular distributions are studied and the forward-backward asymmetries in the dimuon ($A^{l}_{\rm FB}$) and hadron ($A^{h}_{\rm FB}$) systems are measured for the first time. In the range $15 < q^2 < 20 \mbox{ GeV}^2/c^4$ they are found to be $A^{l}_{\rm FB} = -0.05 \pm 0.09 \mbox{ (stat)} \pm 0.03 \mbox{ (syst)}$ and $A^{h}_{\rm FB} = -0.29 \pm 0.07 \mbox{ (stat)} \pm 0.03 \mbox{ (syst)}$.

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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

Mapping the material in the LHCb vertex locator using secondary hadronic interactions

Precise knowledge of the location of the material in the LHCb vertex locator (VELO) is essential to reducing background in searches for long-lived exotic particles, and in identifying jets that originate from beauty and charm quarks. Secondary interactions of hadrons produced in beam-gas collisions are used to map the location of material in the VELO. Using this material map, along with properties of a reconstructed secondary vertex and its constituent tracks, a $p$-value can be assigned to the hypothesis that the secondary vertex originates from a material interaction. A validation of this procedure is presented using photon conversions to dimuons.

physics.ins-det↗

arXiv2018

The HeRSCheL detector: high-rapidity shower counters for LHCb

The HeRSCheL detector consists of a set of scintillating counters, designed to increase the coverage of the LHCb experiment in the high-rapidity regions on either side of the main spectrometer. The new detector improves the capabilities of LHCb for studies of diffractive interactions, most notably Central Exclusive Production. In this paper the construction, installation, commissioning, and performance of HeRSCheL are presented.

physics.ins-det↗

arXiv2016

First observation and amplitude analysis of the $B^{-}\to D^{+}K^{-}π^{-}$ decay

The $B^{-}\to D^{+}K^{-}π^{-}$ decay is observed in a data sample corresponding to $3.0~\rm{fb}^{-1}$ of $pp$ collision data recorded by the LHCb experiment during 2011 and 2012. Its branching fraction is measured to be ${\cal B}(B^{-}\to D^{+}K^{-}π^{-}) = (7.31 \pm 0.19 \pm 0.22 \pm 0.39) \times 10^{-5}$ where the uncertainties are statistical, systematic and from the branching fraction of the normalisation channel $B^{-}\to D^{+}π^{-}π^{-}$, respectively. An amplitude analysis of the resonant structure of the $B^{-}\to D^{+}K^{-}π^{-}$ decay is used to measure the contributions from quasi-two-body $B^{-}\to D_{0}^{*}(2400)^{0}K^{-}$, $B^{-}\to D_{2}^{*}(2460)^{0}K^{-}$, and $B^{-}\to D_{J}^{*}(2760)^{0}K^{-}$ decays, as well as from nonresonant sources. The $D_{J}^{*}(2760)^{0}$ resonance is determined to have spin~1.

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arXiv2016

Search for long-lived heavy charged particles using a ring imaging Cherenkov technique at LHCb

A search is performed for heavy long-lived charged particles using 3.0 fb$^{-1}$ of pp collisions collected at $\sqrt{s}$= 7 and 8 TeV with the LHCb detector. The search is mainly based on the response of the ring imaging Cherenkovdetectors to distinguish the heavy, slow-moving particles from muons. No evidence is found for the production of such long-lived states. The results are expressed as limits on the Drell-Yan production of pairs of long-lived particles, with both particles in the LHCb pseudorapidity acceptance, $1.8 < η< 4.9$. The mass-dependent cross-section upper limits are in the range 2-4 fb (at 95\% CL) for masses between 124 and 309 GeV/c$^2$.

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arXiv2016

First observation of the decay $B_{s}^{0} \to K_{S}^{0} K^{*}(892)^{0}$

A search for $B_{(s)}^{0} \to K_{S}^{0} K^{*}(892)^{0}$ decays is performed using $pp$ collision data, corresponding to an integrated luminosity of $1.0~\text{fb}^{-1}$, collected with the LHCb detector at a centre-of-mass energy of $7~\text{TeV}$. The $B_{s}^{0} \to K_{S}^{0} K^{*}(892)^{0}$ decay is observed for the first time, with a significance of 7.1 standard deviations. The branching fraction is measured to be \begin{equation*} \mathcal{B}(B_{s}^{0} \to \bar{K}^{0} K^{*}(892)^{0}) + \mathcal{B}(B_{s}^{0} \to K^{0} \bar{K}^{*}(892)^{0}) = (16.4 \pm 3.4 \pm 2.3) \times 10^{-6},\\ \end{equation*} where the first uncertainty is statistical and the second is systematic. No evidence is found for the decay $B^{0} \to K_{S}^{0} K^{*}(892)^{0}$ and an upper limit is set on the branching fraction, $\mathcal{B}(B^{0} \to \bar{K}^{0} K^{*}(892)^{0}) + \mathcal{B}(B^{0} \to K^{0} \bar{K}^{*}(892)^{0}) < 0.96 \ \times 10^{-6}, $ at $90\,\% $ confidence level. All results are consistent with Standard Model predictions.

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arXiv2015

Study of $B^{-}\to DK^-π^+π^-$ and $B^-\to Dπ^-π^+π^-$ decays and determination of the CKM angle $γ$

We report a study of the suppressed $B^-\to DK^-π^+π^-$ and favored $B^-\to Dπ^-π^+π^-$ decays, where the neutral $D$ meson is detected through its decays to the $K^{\mp}π^{\pm}$ and CP-even $K^+K^-$ and $π^+π^-$ final states. The measurement is carried out using a proton-proton collision data sample collected by the LHCb experiment, corresponding to an integrated luminosity of 3.0~fb$^{-1}$. We observe the first significant signals in the CP-even final states of the $D$ meson for both the suppressed $B^-\to DK^-π^+π^-$ and favored $B^-\to Dπ^-π^+π^-$ modes, as well as in the doubly Cabibbo-suppressed $D\to K^+π^-$ final state of the $B^-\to Dπ^-π^+π^-$ decay. Evidence for the ADS suppressed decay $B^{-}\to DK^-π^+π^-$, with $D\to K^+π^-$, is also presented. From the observed yields in the $B^-\to DK^-π^+π^-$, $B^-\to Dπ^-π^+π^-$ and their charge conjugate decay modes, we measure the value of the weak phase to be $γ=(74^{+20}_{-19})^{\rm o}$. This is one of the most precise single-measurement determinations of $γ$ to date.

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arXiv2015

Observation of the $B^0_s\toη'η'$ decay

The first observation of the $B^0_s\toη'η'$ decay is reported. The study is based on a sample of proton-proton collisions corresponding to $3.0$ ${\rm fb^{-1}}$ of integrated luminosity collected with the LHCb detector. The significance of the signal is $6.4$ standard deviations. The branching fraction is measured to be $[3.31 \pm 0.64\,{\rm (stat)} \pm 0.28\,{\rm (syst)} \pm 0.12\,{\rm (norm)}]\times10^{-5}$, where the third uncertainty comes from the $B^{\pm}\toη' K^{\pm}$ branching fraction that is used as a normalisation. In addition, the charge asymmetries of $B^{\pm}\toη' K^{\pm}$ and $B^{\pm}\toϕK^{\pm}$, which are control channels, are measured to be $(-0.2 \pm1.3)\%$ and $(+1.7\pm1.3)\%$, respectively. All results are consistent with theoretical expectations.

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arXiv2015

Search for the $Λ_b \rightarrow Λη^\prime$ and $Λ_b \rightarrow Λη$ decays with the LHCb detector

A search is performed for the as yet unobserved baryonic $Λ_b \rightarrow Λη^\prime$ and $Λ_b \rightarrow Λη$ decays with 3$fb^{-1}$ of proton-proton collision data recorded by the LHCb experiment. The $B^0 \rightarrow K_S^0 η^\prime$ decay is used as a normalisation channel. No significant signal is observed for the $Λ_b \rightarrow Λη^\prime$ decay. An upper limit is found on the branching fraction of $\mathcal{B}(Λ_b \rightarrow Λη^\prime)<3.1\times10^{-6}$} at 90\% confidence level. Evidence is seen for the presence of the $Λ_b \rightarrow Λη$ decay at the level of $3σ$ significance, with a branching fraction $\mathcal{B}(Λ_b \rightarrow Λη)=(9.3^{+7.3}_{-5.3})\times10^{-6}$}.

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arXiv2015

Observation of the decay $\overline{B}_s^0 \rightarrow ψ(2S) K^+ π^-$

The decay $\overline{B}_s^0 \rightarrow ψ(2S) K^+ π^-$ is observed using a data set corresponding to an integrated luminosity of $3.0fb^{-1}$ collected by the LHCb experiment in $pp$ collisions at centre-of-mass energies of 7 and 8 TeV. The branching fraction relative to the $B^0\rightarrow ψ(2S) K^+ π^-$ decay mode is measured to be \begin{equation} \frac{{\cal B}(\overline{B}^0_s \rightarrow ψ(2S) K^+ π^-)}{{\cal B}(B^0 \rightarrow ψ(2S) K^+ π^-)} = 5.38 \pm 0.36 (stat) \pm 0.22 (syst) \pm 0.31 \, (f_s/f_d) \, \%,\nonumber \end{equation} where $f_s/f_d$ indicates the uncertainty due to the ratio of probabilities for a $b$ quark to hadronise into a $B_s^0$ or $B^0$ meson. Using an amplitude analysis, the fraction of decays proceeding via an intermediate $K^*(892)^0$ meson is measured to be $0.645 \pm 0.049 (stat) \pm 0.049 (syst)$ and its longitudinal polarisation fraction is $0.524 \pm 0.056 (stat) \pm 0.029 (syst)$. The relative branching fraction for this component is determined to be \begin{equation} \frac{{\cal B}(\overline{B}^0_s \rightarrow ψ(2S) K^*(892)^0)}{{\cal B}(B^0 \rightarrow ψ(2S) K^*(892)^0)} = 5.58 \pm 0.57 (stat) \pm 0.40 (syst) \pm 0.32 \, (f_s/f_d) \, \%. \nonumber \end{equation} In addition, the mass splitting between the $B_s^0$ and $B^0$ mesons is measured as \begin{equation} M(B^0_s) - M(B^0) = 87.45 \pm 0.44 (stat) \pm 0.07 (syst) MeV/c^2. \nonumber \end{equation}

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arXiv2015

Measurement of the branching fraction ratio $\mathcal{B}(B_c^+ \rightarrow ψ(2S)π^+)/\mathcal{B}(B_c^+ \rightarrow J/ψπ^+)$

Using $pp$ collision data collected by LHCb at center-of-mass energies $\sqrt{s}$ = 7 TeV and 8 TeV, corresponding to an integrated luminosity of 3 fb$^{-1}$, the ratio of the branching fraction of the $B_c^+ \rightarrow ψ(2S)π^+$ decay relative to that of the $B_c^+ \rightarrow J/ψπ^+$ decay is measured to be 0.268 $\pm$ 0.032 (stat) $\pm$ 0.007 (syst) $\pm$ 0.006 (BF). The first uncertainty is statistical, the second is systematic, and the third is due to the uncertainties on the branching fractions of the $J/ψ\rightarrow μ^+μ^-$ and $ψ(2S) \rightarrow μ^+μ^-$ decays. This measurement is consistent with the previous LHCb result, and the statistical uncertainty is halved.

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arXiv2015

Observation of the ${B^0 \to ρ^0 ρ^0}$ decay from an amplitude analysis of ${B^0 \to (π^+π^-)(π^+π^-)}$ decays

Proton-proton collision data recorded in 2011 and 2012 by the \lhcb experiment, co\-rres\-pon\-ding to an integrated luminosity of 3.0\invfb, are a\-na\-lysed to search for the charmless ${B^0 \to ρ^0 ρ^0}$ decay. More than 600 ${\B^0 \to (π^+π^-)(π^+π^-)}$ signal decays are selected and used to perform an amplitude analysis from which the ${B^0 \to ρ^0 ρ^0}$ decay is observed for the first time with 7.1 standard deviations significance. The fraction of ${B^0 \to ρ^0 ρ^0}$ decays yielding a longitudinally polarised final state is measured to be $\fL = 0.745^{+0.048}_{-0.058} ({\rm stat}) \pm 0.034 ({\rm syst})$. The ${B^0 \to ρ^0 ρ^0}$ branching fraction, using the ${\B^0 \to ϕK^*(892)^{0}}$ decay as reference, is also reported as ${\BF(B^0 \to ρ^0 ρ^0) = (0.94 \pm 0.17 ({\rm stat}) \pm 0.09 ({\rm syst}) \pm 0.06 ({\rm BF})) \times 10^{-6}}$.

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arXiv2015

Angular analysis and differential branching fraction of the decay $B^0_s\toϕμ^+μ^-$

An angular analysis and a measurement of the differential branching fraction of the decay $B^0_s\toϕμ^+μ^-$ are presented, using data corresponding to an integrated luminosity of $3.0\, {\rm fb^{-1}}$ of $pp$ collisions recorded by the LHCb experiment at $\sqrt{s} = 7$ and $8\, {\rm TeV}$. Measurements are reported as a function of $q^{2}$, the square of the dimuon invariant mass and results of the angular analysis are found to be consistent with the Standard Model. In the range $1<q^2<6\, {\rm GeV}^{2}/c^{4}$, where precise theoretical calculations are available, the differential branching fraction is found to be more than $3\,σ$ below the Standard Model predictions.

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arXiv2015

Study of $W$ boson production in association with beauty and charm

The associated production of a $W$ boson with a jet originating from either a light parton or heavy-flavor quark is studied in the forward region using proton-proton collisions. The analysis uses data corresponding to integrated luminosities of 1.0 and $2.0\,{\rm fb}^{-1}$ collected with the LHCb detector at center-of-mass energies of 7 and 8 TeV, respectively. The $W$ bosons are reconstructed using the $W\toμν$ decay and muons with a transverse momentum, $p_{\rm T}$, larger than 20 GeV in the pseudorapidity range $2.0<η<4.5$. The partons are reconstructed as jets with $p_{\rm T} > 20$ GeV and $2.2 < η< 4.2$. The sum of the muon and jet momenta must satisfy $p_{\rm T} > 20$ GeV. The fraction of $W+$jet events that originate from beauty and charm quarks is measured, along with the charge asymmetries of the $W\!+\!b$ and $W\!+\!c$ production cross-sections. The ratio of the $W+$jet to $Z+$jet production cross-sections is also measured using the $Z\toμμ$ decay. All results are in agreement with Standard Model predictions.

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