arXiv subjects

C. Betancourt

Publications and source records attributed to C. Betancourt.

At least 415 records · Page 23Linked to original sources

arXiv2018

Measurement of $CP$ violation in $B^0\rightarrow J/ψK^0_\mathrm{S}$ and $B^0\rightarrowψ(2S) K^0_\mathrm{S}$ decays

A measurement is presented of decay-time-dependent $CP$ violation in the decays $B^0\rightarrow J/ψK^0_\mathrm{S}$ and $B^0\rightarrowψ(2S) K^0_\mathrm{S}$, where the $J/ψ$ is reconstructed from two electrons and the $ψ(2S)$ from two muons. The analysis uses a sample of $pp$ collision data recorded with the LHCb experiment at centre-of-mass energies of 7 and 8 TeV, corresponding to an integrated luminosity of 3 $\mathrm{fb}^{-1}$. The $CP$-violation observables are measured to be \begin{equation*} \begin{aligned} C\left(B^0\rightarrow J/ψK^0_\mathrm{S}\right)&=\phantom{+}\,0.12\,\pm\,0.07\pm\,0.02\,, S\left(B^0\rightarrow J/ψK^0_\mathrm{S}\right)&=\phantom{+}\,0.83\,\pm\,0.08\pm\,0.01\,, C\left(B^0\rightarrowψ(2S) K^0_\mathrm{S}\right)&=-\,0.05\,\pm\,0.10\pm\,0.01\,, S\left(B^0\rightarrowψ(2S) K^0_\mathrm{S}\right)&=\phantom{+}\,0.84\,\pm\,0.10\pm\,0.01\,, \end{aligned} \end{equation*} where $C$ describes $CP$ violation in the direct decay, and $S$ describes $CP$ violation in the interference between the amplitudes for the direct decay and for the decay after $B^0$-$\overline{B}^0$ oscillation. The first uncertainties are statistical and the second are systematic. The two sets of results are compatible with the previous LHCb measurement using $B^0\rightarrow J/ψK^0_\mathrm{S}$ decays, where the $J/ψ$ meson was reconstructed from two muons. The averages of all three sets of LHCb results are \begin{equation*} \begin{aligned} C\left(B^0\rightarrow[c\bar{c}]K^0_\mathrm{S}\right)&=-0.017 \pm 0.029\,, S\left(B^0\rightarrow[c\bar{c}]K^0_\mathrm{S}\right)&=\phantom{+}0.760 \pm 0.034\,, \end{aligned} \end{equation*} under the assumption that higher-order contributions to the decay amplitudes are negligible. The uncertainties include statistical and systematic contributions.

hep-ex↗

arXiv2017

Measurement of the $Υ$ polarizations in $pp$ collisions at $\sqrt{s}$=7 and 8TeV

The polarization of the $Υ(1S)$, $Υ(2S)$ and $Υ(3S) $mesons, produced in $pp$ collisions at centre-of-mass energies $\sqrt{s}$=7 and 8TeV, is measured using data samples collected by the LHCb experiment, corresponding to integrated luminosities of 1 and 2fb$^{-1}$, respectively. The measurements are performed in three polarization frames, using $Υ\toμ^+μ^-$ decays in the kinematic region of the transverse momentum $p_{T}(Υ)<30GeV/c$, and rapidity $2.2<y(Υ)<4.5$. No large polarization is observed.

hep-ex↗

arXiv2017

Amplitude analysis of the decay $\overline{B}^0 \to K_{S}^0 π^+ π^-$ and first observation of the CP asymmetry in $\overline{B}^0 \to K^{*}(892)^- π^+$

The time-integrated Dalitz plot of the three-body hadronic charmless decay ${\overline{B}^0 \to K_{\mathrm{\scriptscriptstyle S}}^0 π^+ π^-}$ is studied using a $pp$ collision data sample recorded with the LHCb detector, corresponding to an integrated luminosity of $3.0\;\mathrm{fb}^{-1}$. The decay amplitude is described with an isobar model. Relative contributions of the isobar amplitudes to the ${\overline{B}^0 \to K_{\mathrm{\scriptscriptstyle S}}^0 π^+ π^-}$ decay branching fraction and CP asymmetries of the flavour-specific amplitudes are measured. The CP asymmetry between the conjugate ${\overline{B}^0 \to K^{*}(892)^{-}π^+}$ and ${\overline{B}^0 \to K^{*}(892)^{+}π^-}$ decay rates is determined to be $-0.308 \pm 0.062$.

hep-ex↗

arXiv2017

Study of $b\bar{b}$ correlations in high energy proton-proton collisions

Kinematic correlations for pairs of beauty hadrons, produced in high energy proton-proton collisions, are studied. The data sample used was collected with the LHCb experiment at centre-of-mass energies of 7 and 8 TeV and corresponds to an integrated luminosity of 3 fb$^{-1}$. The measurement is performed using inclusive $b\rightarrow J/ψX$ decays in the rapidity range $2<y^{J/ψ}<4.5$. The observed correlations are in good agreement with theoretical predictions.

hep-ex↗

arXiv2017

$χ_{c1}$ and $χ_{c2}$ resonance parameters with the decays $χ_{c1,c2}\to J/ψμ^+μ^-$

The decays $χ_{c1} \rightarrow J/ψμ^+ μ^-$ and $χ_{c2} \rightarrow J/ψμ^+ μ^-$ are observed and used to study the resonance parameters of the $χ_{c1}$ and $χ_{c2}$ mesons. The masses of these states are measured to be m(χ_{c1}) = 3510.71 \pm 0.04(stat) \pm 0.09(syst)MeV\,, m(χ_{c2}) = 3556.10 \pm 0.06(stat) \pm 0.11(syst)MeV\,, where the knowledge of the momentum scale for charged particles dominates the systematic uncertainty. The momentum-scale uncertainties largely cancel in the mass difference m(χ_{c2}) - m(χ_{c1}) = 45.39 \pm 0.07(stat) \pm 0.03(syst)MeV\,. The natural width of the $χ_{c2}$ meson is measured to be $$Γ(χ_{c2}) = 2.10 \pm 0.20(stat) \pm 0.02(syst)MeV\,.$$ These results are in good agreement with and have comparable precision to the current world averages.

hep-ex↗

arXiv2017

Application of large area SiPMs for the readout of a plastic scintillator based timing detector

In this study an array of eight 6 mm x 6 mm area SiPMs was coupled to the end of a long plastic scintillator counter which was exposed to a 2.5 GeV/c muon beam at the CERN PS. Timing characteristics of bars with dimensions 150 cm x 6 cm x 1 cm and 120 cm x 11 cm x 2.5 cm have been studied. An 8-channel SiPM anode readout ASIC (MUSIC R1) based on a novel low input impedance current conveyor has been used to read out and amplify SiPMs independently and sum the signals at the end. Prospects for applications in large-scale particle physics detectors with timing resolution below 100 ps are provided in light of the results.

physics.ins-det↗

arXiv2017

Measurement of $CP$ observables in $B^\pm \to D^{()} K^\pm$ and $B^\pm \to D^{()} π^\pm$ decays

Measurements of $CP$ observables in $B^\pm \rightarrow D^{(*)} K^\pm$ and $B^\pm \rightarrow D^{(*)} π^\pm$ decays are presented, where $D^{(*)}$ indicates a neutral $D$ or $D^*$ meson that is an admixture of $D^{(*)0}$ and $\bar{D}^{(*)0}$ states. Decays of the $D^*$ meson to the $Dπ^0$ and $Dγ$ final states are partially reconstructed without inclusion of the neutral pion or photon, resulting in distinctive shapes in the $B$ candidate invariant mass distribution. Decays of the $D$ meson are fully reconstructed in the $K^\pm π^\mp$, $K^+ K^-$ and $π^+ π^-$ final states. The analysis uses a sample of charged $B$ mesons produced in $pp$ collisions collected by the LHCb experiment, corresponding to an integrated luminosity of 2.0, 1.0 and 2.0 fb$^{-1}$ taken at centre-of-mass energies of $\sqrt{s}$ = 7, 8 and 13 TeV, respectively. The study of $B^{\pm} \to D^{*} K^{\pm}$ and $B^{\pm} \to D^{*} π^{\pm}$ decays using a partial reconstruction method is the first of its kind, while the measurement of $B^{\pm} \to D K^{\pm}$ and $B^{\pm} \to D π^{\pm}$ decays is an update of previous LHCb measurements. The $B^{\pm} \to D K^{\pm}$ results are the most precise to date.

hep-ex↗

arXiv2017

Measurement of the $B^{\pm}$ production cross-section in pp collisions at $\sqrt{s} =$ 7 and 13 TeV

The production of $B^{\pm}$ mesons is studied in $pp$ collisions at centre-of-mass energies of 7 and 13 TeV, using $B^{\pm}\rightarrow J/ψK^{\pm}$ decays and data samples corresponding to 1.0 fb$^{-1}$ and 0.3 fb$^{-1}$, respectively. The production cross-sections summed over both charges and integrated over the transverse momentum range $0<p_{\text{T}}< 40$ GeV/$c$ and the rapidity range $2.0<y<4.5$ are measured to be $σ(pp \rightarrow B^{\pm} X, \sqrt{s} = \text{7 TeV}) = 43.0 \pm 0.2 \pm 2.5 \pm 1.7μb,$ $σ(pp \rightarrow B^{\pm} X, \sqrt{s} = \text{13 TeV}) = 86.6 \pm 0.5 \pm 5.4 \pm 3.4μb,$ where the first uncertainties are statistical, the second are systematic, and the third are due to the limited knowledge of the $B^{\pm}\rightarrow J/ψK^{\pm}$ branching fraction. The ratio of the cross-section at 13 TeV to that at 7 TeV is determined to be $2.02\pm0.02\text{(stat)}\pm0.12\text{(syst)}$. Differential cross-sections are also reported as functions of $p_{\text{T}}$ and $y$. All results are in agreement with theoretical calculations based on the state-of-art fixed next-to-leading order quantum chromodynamics.

hep-ex↗

arXiv2017

First observation of the rare purely baryonic decay $B^0 \to p \bar{p}$

The first observation of the decay of a $B^0$ meson to a purely baryonic final state, $B^0 \to p \bar{p}$, is reported. The proton-proton collision data sample used was collected with the LHCb experiment at center-of-mass energies of 7 and 8 TeV and corresponds to an integrated luminosity of 3.0 fb$^{-1}$. The branching fraction is determined to be $${\cal B}(B^0 \to p \bar{p}) = ( 1.25 \pm 0.27 \pm 0.18 ) \times 10^{-8} ,$$ where the first uncertainty is statistical and the second systematic. The decay mode $B^0 \to p \bar{p}$ is the rarest decay of the $B^0$ meson observed to date. The decay $B_s^0 \to p \bar{p}$ is also investigated. No signal is seen and the upper limit ${\cal B}(B_s^0 \to p \bar{p}) < 1.5 \times 10^{-8}$ at 90% confidence level is set on the branching fraction.

hep-ex↗

arXiv2017

Updated search for long-lived particles decaying to jet pairs

A search is presented for long-lived particles with a mass between 25 and 50 GeV/$c^2$ and a lifetime between 2 and 500 ps, using proton-proton collision data corresponding to an integrated luminosity of 2.0 fb$^{-1}$, collected by the LHCb detector at centre-of-mass energies of 7 and 8 TeV. The particles are assumed to be pair-produced in the decay of a 125 GeV/$c^2$ Standard-Model-like Higgs boson. The experimental signature is a single long-lived particle, identified by a displaced vertex with two associated jets. No excess above background is observed and limits are set on the production cross-section as a function of the mass and lifetime of the long-lived particle.

hep-ex↗

arXiv2017

Measurement of $B^0$, $B^0_s$, $B^+$ and $Λ^0_b$ production asymmetries in 7 and 8 TeV proton-proton collisions

The $B^0$, $B^0_s$, $B^+$ and $Λ^0_b$ hadron production asymmetries are measured using a data sample corresponding to an integrated luminosity of 3.0 fb$^{-1}$, collected by the LHCb experiment in proton-proton collisions at centre-of-mass energies of 7 and 8 TeV. The measurements are performed as a function of transverse momentum and rapidity of the $b$ hadrons within the LHCb detector acceptance. The overall production asymmetries, integrated over transverse momentum and rapidity, are also determined.

hep-ex↗

arXiv2017

Prompt and nonprompt J/$ψ$ production and nuclear modification in $p$Pb collisions at $\sqrt{s_{\text{NN}}}= 8.16$ TeV

The production of J/$ψ$ mesons is studied in proton-lead collisions at the centre-of-mass energy per nucleon pair $\sqrt{s_{\text{NN}}}=8.16$ TeV with the LHCb detector at the LHC. The double differential cross-sections of prompt and nonprompt J/$ψ$ production are measured as functions of the J/$ψ$ transverse momentum and rapidity in the nucleon-nucleon centre-of-mass frame. Forward-to-backward ratios and nuclear modification factors are determined. The results are compared with theoretical calculations based on collinear factorisation using nuclear parton distribution functions, on the colour glass condensate or on coherent energy loss models.

hep-ex↗

arXiv2017

Updated branching fraction measurements of $B^0_{(s)} \to K_{\mathrm{\scriptscriptstyle S}}^0 h^+ h^{\prime -}$ decays

The charmless three-body decays $B^0_{(s)} \to K_{\mathrm{\scriptscriptstyle S}}^0 h^+ h^{\prime -}$ (where $h^{(\prime)} = π, K$) are analysed using a sample of $pp$ collision data recorded by the LHCb experiment, corresponding to an integrated luminosity of $3\mbox{fb}^{-1}$. The branching fractions are measured relative to that of the $B^0 \to K_{\mathrm{\scriptscriptstyle S}}^0 π^{+} π^{-}$ decay, and are determined to be: \begin{eqnarray*} \frac{{\cal B}(B^0\rightarrow K^0_{\rm S}K^{\pm}π^{\mp})}{{\cal B}(B^0\rightarrow K^0_{\rm S}π^{+}π^{-})} = {} & 0.123 \pm 0.009 \; \mathrm{\,(stat)}\; \pm 0.015 \; \mathrm{\,(syst)}\,, \frac{{\cal B}(B^0\rightarrow K^0_{\rm S}K^{+}K^{-})} {{\cal B}(B^0\rightarrow K^0_{\rm S}π^{+}π^{-})} = {} & 0.549 \pm 0.018 \; \mathrm{\,(stat)}\; \pm 0.033 \; \mathrm{\,(syst)}\,, \frac{{\cal B}(B_{s}^0\rightarrow K^0_{\rm S}π^{+}π^{-})}{{\cal B}(B^0\rightarrow K^0_{\rm S}π^{+}π^{-})} = {} & 0.191 \pm 0.027 \; \mathrm{\,(stat)}\; \pm 0.031 \; \mathrm{\,(syst)}\; \pm 0.011 \; (f_s/f_d) \,, \frac{{\cal B}(B_{s}^0\rightarrow K^0_{\rm S}K^{\pm}π^{\mp})} {{\cal B}(B^0\rightarrow K^0_{\rm S}π^{+}π^{-})} = {} & 1.70\phantom{0} \pm 0.07\phantom{0} \; \mathrm{\,(stat)} \; \pm 0.11\phantom{0} \; \mathrm{\,(syst)}\; \pm 0.10\phantom{0} \; (f_s/f_d) \,, \frac{{\cal B}(B_{s}^0\rightarrow K^0_{\rm S}K^{+}K^{-})}{{\cal B}(B^0\rightarrow K^0_{\rm S}π^{+}π^{-})} \in {} & [0.008 - 0.051] \rm ~at~90\%~confidence~level, \end{eqnarray*} where $f_s/f_d$ represents the ratio of hadronisation fractions of the $B^0_s$ and $B^0$ mesons.

hep-ex↗

arXiv2017

Observation of $D^0$ meson decays to $π^+π^-μ^+μ^-$ and $K^+K^-μ^+μ^-$ final states

The first observation of the $D^0 \to π^+π^-μ^+μ^-$ and $D^0 \to K^+K^-μ^+μ^-$ decays is reported using a sample of proton-proton collisions collected by LHCb at a center-of-mass energy of 8$\,$TeV, and corresponding to 2$\,$fb$^{-1}$ of integrated luminosity. The corresponding branching fractions are measured using as normalization the decay $D^0 \to K^- π^+[μ^+μ^-]_{ρ^0/ω}$, where the two muons are consistent with coming from the decay of a $ρ^0$ or $ω$ meson. The results are $\mathcal{B}(D^0 \to π^+π^-μ^+μ^-)=(9.64\pm0.48\pm0.51\pm0.97)\times10^{-7}$ and $\mathcal{B}(D^0 \to K^+K^-μ^+μ^-)=( 1.54\pm0.27\pm0.09\pm0.16)\times10^{-7}$, where the uncertainties are statistical, systematic, and due to the limited knowledge of the normalization branching fraction. The dependence of the branching fraction on the dimuon mass is also investigated.

hep-ex↗

arXiv2017

Search for baryon-number-violating $Ξ_b^0$ oscillations

A search for baryon-number-violating $Ξ_b^0$ oscillations is performed with a sample of $pp$ collision data recorded by the LHCb experiment, corresponding to an integrated luminosity of 3 fb$^{-1}$. The baryon number at the moment of production is identified by requiring that the $Ξ_b^0$ come from the decay of a resonance $Ξ_b^{*-} \to Ξ_b^0 π^-$ or $Ξ_b^{\prime-} \to Ξ_b^0 π^-$, and the baryon number at the moment of decay is identified from the final state using the decays $Ξ_b^0 \to Ξ_c^+ π^-, ~ Ξ_c^+ \to p K^- π^+$. No evidence of baryon number violation is found, and an upper limit at the 95% confidence level is set on the oscillation rate of $ω< 0.08$ ps$^{-1}$, where $ω$ is the associated angular frequency.

hep-ex↗

arXiv2017

Observation of the decay $B_{s}^{0} \to η_{c} ϕ$ and evidence for $B_{s}^{0} \to η_{c} π^{+} π^{-} $

A study of $B^{0}_{s} \to η_{c} ϕ$ and $B^{0}_{s} \to η_{c} π^{+}π^{-}$ decays is performed using $pp$ collision data corresponding to an integrated luminosity of 3.0$\,\rm fb^{-1}$, collected with the LHCb detector in Run~1 of the LHC. The observation of the decay $B^{0}_{s} \to η_{c} ϕ$ is reported, where the $η_{c}$ meson is reconstructed in the $p\bar p$, $K^+K^-π^+π^-$, $π^+π^-π^+π^-$ and $K^+K^-K^+K^-$ decay modes and the $ϕ(1020)$ in the $K^+ K^-$ decay mode. The decay $B^{0}_{s} \to J/ψϕ$ is used as a normalisation channel. Evidence is also reported for the decay $B^{0}_{s} \to η_{c} π^{+}π^{-}$, where the $η_{c}$ meson is reconstructed in the $p\bar p$ decay mode, using the decay $B^{0}_{s} \to J/ψπ^+ π^-$ as a normalisation channel. The measured branching fractions are \begin{eqnarray*} {\mathcal B (B^{0}_{s} \to η_{c} ϕ)} &=& \left(5.01 \pm 0.53 \pm 0.27 \pm 0.63 \right) \times 10^{-4} \,, \nonumber \\ {\mathcal B (B^{0}_{s} \to η_{c} π^+ π^-)} &=& \left(1.76 \pm 0.59 \pm 0.12 \pm 0.29 \right) \times 10^{-4} \,, \end{eqnarray*} where in each case the first uncertainty is statistical, the second systematic and the third uncertainty is due to the limited knowledge of the external branching fractions.

hep-ex↗

arXiv2017

Improved limit on the branching fraction of the rare decay $K^0_{\scriptscriptstyle S}\toμ^+μ^-$

A search for the decay $K^0_{\scriptscriptstyle S}\toμ^+μ^-$ is performed, based on a data sample of proton-proton collisions corresponding to an integrated luminosity of 3 fb$^{-1}$, collected by the LHCb experiment at centre-of-mass energies of 7 and 8 TeV. The observed yield is consistent with the background-only hypothesis, yielding a limit on the branching fraction of ${\cal B}(K^0_{\scriptscriptstyle S}\toμ^+μ^-) < 0.8~(1.0) \times 10^{-9}$ at $90\%~(95\%)$ confidence level. This result improves the previous upper limit on the branching fraction by an order of magnitude.

hep-ex↗

arXiv2017

Observation of the $B^+ \to D^{*-}K^+π^+$ decay

The $B^+ \to D^{*-}K^+π^+$ decay potentially provides an excellent way to investigate charm meson spectroscopy. The decay is searched for in a sample of proton-proton collision data collected with the LHCb detector at centre-of-mass energies of 7 and 8 TeV, corresponding to an integrated luminosity of $3~{\rm fb}^{-1}$. A clear signal is observed, and the ratio of its branching fraction to that of the $B^+ \to D^{*-}π^+π^+$ normalisation channel is measured to be \begin{equation*} \frac{\mathcal{B}(B^+ \to D^{*-}K^+π^+)}{\mathcal{B}(B^+ \to D^{*-}π^+π^+)} = \left( 6.39 \pm 0.27 \pm 0.48 \right) \times 10^{-2} \, , \end{equation*} where the first uncertainty is statistical and the second is systematic. This is the first observation of the $B^+ \to D^{*-}K^+π^+$ decay.

hep-ex↗