arXiv subjects

A. Bondar

Publications and source records attributed to A. Bondar.

At least 433 records · Page 24Linked to original sources

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

Measurement of matter-antimatter differences in beauty baryon decays

Differences in the behaviour of matter and antimatter have been observed in $K$ and $B$ meson decays, but not yet in any baryon decay. Such differences are associated with the non-invariance of fundamental interactions under the combined charge-conjugation and parity transformations, known as $C\!P$ violation. Using data from the LHCb experiment at the Large Hadron Collider, a search is made for $C\!P$-violating asymmetries in the decay angle distributions of $Λ^0_b$ baryons decaying to $pπ^-π^+π^-$ and $pπ^-K^+K^-$ final states. These four-body hadronic decays are a promising place to search for sources of $C\!P$ violation both within and beyond the Standard Model of particle physics. We find evidence for $C\!P$ violation in $Λ^0_b$ to $pπ^-π^+π^-$ decays with a statistical significance corresponding to 3.3 standard deviations including systematic uncertainties. This represents the first evidence for $C\!P$ violation in the baryon sector.

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

Search for $CP$ Violation and Measurement of the Branching Fraction in the Decay $D^{0} \to K^0_S K^0_S$

We report a study of the decay $D^0 \to K^0_S K^0_S$ using 921~fb$^{-1}$ of data collected at or near the $Υ(4S)$ and $Υ(5S)$ resonances with the Belle detector at the KEKB asymmetric energy $e^+e^-$ collider. The measured time-integrated $CP$ asymmetry is $ A_{CP}(D^0 \to K^0_S K^0_S) = (-0.02 \pm 1.53 \pm 0.02 \pm 0.17) \%$, and the branching fraction is $\mathcal{B} (D^{0}\rightarrow K_{S}^{0}K_{S}^{0})$ = (1.321 $\pm$ 0.023 $\pm$ 0.036 $\pm$ 0.044) $\times$ 10$^{-4}$, where the first uncertainty is statistical, the second is systematic, and the third is due to the normalization mode ($D^0 \to K_S^0 π^0$). These results are significantly more precise than previous measurements available for this mode. The $A_{CP}$ measurement is consistent with the standard model expectation.

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↗

arXiv2017

Measurement of the $J/ψ$ pair production cross-section in $pp$ collisions at $\sqrt{s} = 13 \,{\mathrm{TeV}}$

The production cross-section of $J/ψ$ pairs is measured using a data sample of $pp$ collisions collected by the LHCb experiment at a centre-of-mass energy of $\sqrt{s} = 13 \,{\mathrm{TeV}}$, corresponding to an integrated luminosity of $279 \pm 11 \,{\mathrm{pb^{-1}}}$. The measurement is performed for $J/ψ$ mesons with a transverse momentum of less than $10 \,{\mathrm{GeV}}/c$ in the rapidity range $2.0<y<4.5$. The production cross-section is measured to be $15.2 \pm 1.0 \pm 0.9 \,{\mathrm{nb}}$. The first uncertainty is statistical, and the second is systematic. The differential cross-sections as functions of several kinematic variables of the $J/ψ$ pair are measured and compared to theoretical predictions.

hep-ex↗

arXiv2017

Observation of charmless baryonic decays $B^0_{(s)} \to p \overline{p} h^+ h^{\prime-}$

Decays of $B^0$ and $B_{s}^0$ mesons to the charmless baryonic final states $p \overline{p} h^+ h^{\prime-}$, where $h$ and $h^\prime$ each denote a kaon or a pion, are searched for using the LHCb detector. The analysis is based on a sample of proton-proton collision data collected at center-of-mass energies of $7$ and $8\,$TeV, corresponding to an integrated luminosity of $3\,$fb$^{-1}$. Four-body charmless baryonic $B_{s}^0$ decays are observed for the first time. The decays $B^0_{s}\to p \overline{p} K^+ K^-$, $B^0_{s}\to p \overline{p} K^\pm π^\mp$, $B^0\to p \overline{p} K^\pm π^\mp$ and $B^0\to p \overline{p} π^+π^-$ are observed with a significance greater than $5$ standard deviations; evidence at $4.1$ standard deviations is found for the $B^0\to p \overline{p} K^+ K^-$ decay and an upper limit is set on the branching fraction for $B^0_{s}\to p \overline{p} π^+ π^-$. Branching fractions in the kinematic region $m(p \overline{p})<2850\,$MeV$/c^2$ are measured relative to the $B^0 \to J/ψ(\to p \overline{p}) K^*(892)^0$ channel.

hep-ex↗

arXiv2017

Study of charmonium production in $b$-hadron decays and first evidence for the decay $B_s^0 \rightarrow ϕϕϕ$

Using decays to $ϕ$-meson pairs, the inclusive production of charmonium states in $b$-hadron decays is studied with $pp$ collision data corresponding to an integrated luminosity of $3.0fb^{-1}$, collected by the LHCb experiment at centre-of-mass energies of 7 and 8 TeV. Denoting by $B_C\equiv B(b\to CX)\times B(C\toϕϕ)$ the inclusive branching fraction of a $b$ hadron to a charmonium state $C$ that decays into a pair of $ϕ$ mesons, ratios $R^{C1}_{C2}\equiv B_{C1}/B_{C2}$ are determined as $R^{χ_{c0}}_{η_c(1S)}=0.147\pm0.023\pm0.011$, $R^{χ_{c1}}_{η_c (1S)}=0.073\pm0.016\pm0.006$, $R^{χ_{c2}}_{η_c (1S)}=0.081\pm0.013\pm0.005$, $R^{χ_{c1}}_{χ_{c0}}=0.50\pm0.11\pm0.01$, $R^{χ_{c2}}_{χ_{c0}}=0.56\pm0.10\pm0.01$ and $R^{η_c (2S)}_{η_c(1S)}=0.040\pm0.011\pm0.004$. Here and below the first uncertainties are statistical and the second systematic. Upper limits at $90\%$ confidence level for the inclusive production of $X(3872)$, $X(3915)$ and $χ_{c2}(2P)$ states are obtained as $R^{X(3872)}_{χ_{c1}}<0.34$, $R^{X(3915)}_{χ_{c0}}<0.12$ and $R^{χ_{c2}(2P)}_{χ_{c2}}<0.16$. Differential cross-sections as a function of transverse momentum are measured for the $η_c(1S)$ and $χ_c$ states. The branching fraction of the decay $B_s^0\rightarrowϕϕϕ$ is measured for the first time, $B(B_s^0\toϕϕϕ)=(2.15\pm0.54\pm0.28\pm0.21_{B})\times 10^{-6}$. Here the third uncertainty is due to the branching fraction of the decay $B_s^0\toϕϕ$, which is used for normalization. No evidence for intermediate resonances is seen. A preferentially transverse $ϕ$ polarization is observed. The measurements allow the determination of the ratio of the branching fractions for the $η_c(1S)$ decays to $ϕϕ$ and $p\bar{p}$ as $B(η_c(1S)\toϕϕ)/B(η_c(1S)\to p\bar{p})=1.79\pm0.14\pm0.32$.

hep-ex↗

arXiv2017

Measurement of the tau Michel parameters $\barη$ and $ξκ$ in the radiative leptonic decay $τ^- \rightarrow \ell^- ν_τ \barν_{\ell}γ$

We present a measurement of the Michel parameters of the $τ$ lepton, $\barη$ and $ξκ$, in the radiative leptonic decay $τ^- \rightarrow \ell^- ν_τ \barν_{\ell} γ$ using 711~f$\mathrm{b}^{-1}$ of collision data collected with the Belle detector at the KEKB $e^+e^-$ collider. The Michel parameters are measured in an unbinned maximum likelihood fit to the kinematic distribution of $e^+e^-\rightarrowτ^+τ^-\rightarrow (π^+π^0 \barν_τ)(\ell^-ν_τ\barν_{\ell}γ)$ $(\ell=e$ or $μ)$. The measured values of the Michel parameters are $\barη = -1.3 \pm 1.5 \pm 0.8$ and $ξκ= 0.5 \pm 0.4 \pm 0.2$, where the first error is statistical and the second is systematic. This is the first measurement of these parameters. These results are consistent with the Standard Model predictions within their uncertainties and constrain the coupling constants of the generalized weak interaction.

hep-ex↗

arXiv2017

Measurement of $B^{0}_{s}$ and $D^{-}_{s}$ meson lifetimes

We report on a measurement of the flavor-specific $B^{0}_{s}$ lifetime and of the $D^{-}_{s}$ lifetime using proton-proton collisions at center-of-mass energies of 7 and 8 TeV, collected by the LHCb experiment and corresponding to 3.0 fb$^{-1}$ of integrated luminosity. Approximately 407 000 $B^{0}_{s} \rightarrow D^{(*)-}_{s} μ^{+}ν_μ$ decays are partially reconstructed in the $K^{+}K^{-}π^{-}μ^{+}$ final state. The $B^{0}_{s}$ and $D^{-}_{s}$ natural widths are determined using, as a reference, kinematically similar $B^{0} \rightarrow D^{(*)-}μ^{+}ν_μ$ decays reconstructed in the same final state. The resulting differences between widths of $B^{0}_{s}$ and $B^{0}$ mesons and of $D^{-}_{s}$ and $D^{-}$ mesons are $Δ_Γ(B) =-0.0115 \pm 0.0053 (stat) \pm 0.0041 (syst)$ ps$^{-1}$ and $Δ_Γ(D) = 1.0131 \pm 0.0117 (stat) \pm 0.0065 (syst)$ ps$^{-1}$, respectively. Combined with the known $B^{0}$ and $D^{-}$ lifetimes, these yield the flavor-specific $B^{0}_{s}$ lifetime, $τ^{\rm fs}_{B^{0}_{s}} = 1.547 \pm 0.013 (stat) \pm 0.010 (syst) \pm 0.004 (τ_{B})$ ps and the $D^{-}_{s}$ lifetime, $τ_{D^{-}_{s}} = 0.5064 \pm 0.0030 (stat) \pm 0.0017 (syst) \pm 0.0017 (τ_{D})$ ps The last uncertainties originate from the limited knowledge of the $B^0$ and $D^{-}$ lifetimes. The results improve upon current determinations.

hep-ex↗

arXiv2017

Observation of the doubly charmed baryon $Ξ_{cc}^{++}$

A highly significant structure is observed in the $Λ_c^+K^-π^+π^+$ mass spectrum, where the $Λ_c^+$ baryon is reconstructed in the decay mode $pK^-π^+$. The structure is consistent with originating from a weakly decaying particle, identified as the doubly charmed baryon $Ξ_{cc}^{++}$. The difference between the masses of the $Ξ_{cc}^{++}$ and $Λ_c^+$ states is measured to be $1334.94 \pm 0.72 (\mathrm{stat}) \pm 0.27 (\mathrm{syst}~\mathrm{MeV}/c^2$, and the $Ξ_{cc}^{++}$ mass is then determined to be $3621.40 \pm 0.72 (\mathrm{stat}) \pm 0.27 (\mathrm{syst} \pm 0.14 \, (Λ_c^+)~\mathrm{MeV}/c^2$, where the last uncertainty is due to the limited knowledge of the $Λ_c^+$ mass. The state is observed in a sample of proton-proton collision data collected by the LHCb experiment at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 1.7 $\mathrm{fb}^{-1}$, and confirmed in an additional sample of data collected at 8 TeV.

hep-ex↗

arXiv2017

Study of $η$ and dipion transitions in $Υ(4S)$ decays to lower bottomonia

We study hadronic transitions between bottomonium states using 496 fb$^{-1}$ data collected at the $Υ(4S)$ resonance with the Belle detector at the KEKB asymmetric energy $e^{+}e^{-}$ collider. We measure: ${\cal B}(Υ(4S)\toπ^+π^-Υ(1S))=(8.2\pm 0.5 {\rm(stat.)} \pm 0.4 {\rm(syst.)})\times10^{-5}$, ${\cal B}(Υ(4S)\toπ^+π^-Υ(2S))=(7.9\pm 1.0 {\rm(stat.)} \pm 0.4 {\rm(syst.)})\times10^{-5}$, and ${\cal B}(Υ(4S)\toηΥ(1S))=(1.70\pm 0.23 {\rm(stat.)} \pm 0.08 {\rm(syst.)})\times10^{-4}$. We measure the ratio of branching fractions ${\cal R} = {\cal B}(Υ(4S)\toηΥ(1S))/{\cal B}(Υ(4S)\toπ^+π^-Υ(1S)) = 2.07\pm 0.30 {\rm(stat.)} \pm 0.11 {\rm(syst.)}$. We search for the decay $Υ(1^3D_{1,2})\toηΥ(1S)$, but do not find significant evidence for such a transition. We also measure the initial state radiation production cross sections of the $Υ(2S,3S)$ resonances and we find values compatible with the expected ones. Finally, the analysis of the $Υ(4S)\toπ^+π^-Υ(1S)$ events shows indications for a resonant contribution due to the $f_0(980)$ meson.

hep-ex↗

arXiv2017

Cryogenic Characterization of FBK RGB-HD SiPMs

We report on the cryogenic characterization of Red Green Blue - High Density (RGB-HD) SiPMs developed at Fondazione Bruno Kessler (FBK) as part of the DarkSide program of dark matter searches with liquid argon time projection chambers. A dedicated setup was used to measure the primary dark noise, the correlated noise, and the gain of the SiPMs at varying temperatures. A custom-made data acquisition system and analysis software were used to precisely characterize these parameters. We demonstrate that FBK RGB-HD SiPMs with low quenching resistance (RGB-HD-LR$_q$) can be operated from 40 K to 300 K with gains in the range $10^5$ to $10^6$ and noise rates on the order of a few Hz/mm$^2$.

physics.ins-det↗

arXiv2017

First observation of a baryonic $B_s^0$ decay

We report the first observation of a baryonic $B_s^0$ decay, $B_s^0 \to p \kern 0.1em\overline{\kern -0.1emΛ} K^-$, using proton-proton collision data recorded by the LHCb experiment at center-of-mass energies of 7 and 8 TeV, corresponding to an integrated luminosity of $3.0\,\mathrm{fb}^{-1}$. The branching fraction is measured to be $ \mathcal{B}(B_s^0 \to p \kern 0.1em\overline{\kern -0.1emΛ} K^-) + \mathcal{B}(B_s^0 \to \bar{p} ΛK^+) = \left[5.46 \pm 0.61 \pm 0.57 \pm 0.50 (\mathcal{B}) \pm 0.32 (f_s/f_d)\right]\times 10^{-6}, $ where the first uncertainty is statistical and the second systematic, the third uncertainty accounts for the experimental uncertainty on the branching fraction of the $B^0 \to p \kern 0.1em\overline{\kern -0.1emΛ} π^-$ decay used for normalization, and the fourth uncertainty relates to the knowledge of the ratio of $b$-quark hadronization probabilities $f_s/f_d$.

hep-ex↗

arXiv2017

Resonances and $CP$ violation in $B_s^0$ and $\overline{B}_s^0 \to J/ψK^+K^-$ decays in the mass region above the $ϕ(1020)$

The decays of $B_s^0$ and $\overline{B}_s^0$ mesons into the $J/ψK^+K^-$ final state are studied in the $K^+K^-$ mass region above the $ϕ(1020)$ meson in order to determine the resonant substructure and measure the $CP$-violating phase, $ϕ_s$, the decay width, $Γ_s$, and the width difference between light and heavy mass eigenstates, $ΔΓ_s$. A decay-time dependent amplitude analysis is employed. The data sample corresponds to an integrated luminosity of $3{\rm fb}^{-1}$ produced in 7 and 8 Tev $pp$ collisions at the LHC, collected by the LHCb experiment. The measurement determines $ϕ_s = 119\pm107\pm34 {\rm \, mrad}$. A combination with previous LHCb measurements using similar decays into the $J/ψπ^+π^-$ and $J/ψϕ(1020)$ final states gives $ϕ_s=1\pm37 {\rm \,mrad}$, consistent with the Standard Model prediction.

hep-ex↗

arXiv2017

Observation of the suppressed decay $Λ^{0}_{b}\rightarrow pπ^{-}μ^{+}μ^{-}$

The suppressed decay $Λ^{0}_{b}\rightarrow pπ^{-}μ^{+}μ^{-}$, excluding the $J/ψ$ and $ψ(2S)\rightarrow μ^{+}μ^{-}$ resonances, is observed for the first time with a significance of 5.5 standard deviations. The analysis is performed with proton-proton collision data corresponding to an integrated luminosity of $3\mathrm{fb}^{-1}$ collected with the LHCb experiment. The $Λ^{0}_{b}\rightarrow pπ^{-}μ^{+}μ^{-}$ branching fraction is measured relative to the $Λ^{0}_{b}\rightarrow J/ψ(\rightarrow μ^{+}μ^{-})pπ^{-}$ branching fraction giving \begin{align} \nonumber \frac{\mathcal{B}(Λ^{0}_{b}\rightarrow pπ^{-}μ^{+}μ^{-})}{\mathcal{B}({Λ^{0}_{b}\rightarrow J/ψ(\rightarrow μ^{+}μ^{-})pπ^{-}})} &= 0.044\pm0.012\pm0.007, \end{align} where the first uncertainty is statistical and the second is systematic. This is the first observation of a $b\rightarrow d$ transition in a baryonic decay.

hep-ex↗

arXiv2017

Test of lepton universality with $B^{0} \rightarrow K^{*0}\ell^{+}\ell^{-}$ decays

A test of lepton universality, performed by measuring the ratio of the branching fractions of the $B^{0} \rightarrow K^{*0}μ^{+}μ^{-}$ and $B^{0} \rightarrow K^{*0}e^{+}e^{-}$ decays, $R_{K^{*0}}$, is presented. The $K^{*0}$ meson is reconstructed in the final state $K^{+}π^{-}$, which is required to have an invariant mass within 100$\mathrm{\,MeV}c^2$ of the known $K^{*}(892)^{0}$ mass. The analysis is performed using proton-proton collision data, corresponding to an integrated luminosity of about 3$\mathrm{\,fb}^{-1}$, collected by the LHCb experiment at centre-of-mass energies of 7 and 8$\mathrm{\,TeV}$. The ratio is measured in two regions of the dilepton invariant mass squared, $q^{2}$, to be \begin{eqnarray*} R_{K^{*0}} = \begin{cases} 0.66~^{+~0.11}_{-~0.07}\mathrm{\,(stat)} \pm 0.03\mathrm{\,(syst)} & \textrm{for } 0.045 < q^{2} < 1.1~\mathrm{\,GeV^2}c^4 \, , \\ 0.69~^{+~0.11}_{-~0.07}\mathrm{\,(stat)} \pm 0.05\mathrm{\,(syst)} & \textrm{for } 1.1\phantom{00} < q^{2} < 6.0~\mathrm{\,GeV^2}c^4 \, . \end{cases} \end{eqnarray*} The corresponding 95.4\% confidence level intervals are $[0.52, 0.89]$ and $[0.53, 0.94]$. The results, which represent the most precise measurements of $R_{K^{*0}}$ to date, are compatible with the Standard Model expectations at the level of 2.1--2.3 and 2.4--2.5 standard deviations in the two $q^{2}$ regions, respectively.

hep-ex↗

arXiv2017

Search for long-lived scalar particles in $B^+ \to K^+ χ(μ^+μ^-)$ decays

A search for a long-lived scalar particle $χ$ is performed, looking for the decay ${B^+ \to K^+ χ}$ with ${χ\to μ^+μ^-}$ in $pp$ collision data corresponding to an integrated luminosity of $3\, {\rm fb}^{-1}$, collected by the LHCb experiment at centre-of-mass energies of $\sqrt{s}=7$ and 8$\,$TeV. This new scalar particle, predicted by Hidden Sector models, is assumed to have a narrow width. The signal would manifest itself as an excess in the dimuon invariant mass distribution over the Standard Model background. No significant excess is observed in the accessible ranges of mass ${250 < m(χ) < 4700\,\rm MeV/c^2}$ and lifetime ${0.1 < τ(χ) < 1000\,\rm ps}$. Upper limits on the branching fraction $\mathcal{B}(B^+ \to K^+ χ(μ^+μ^-))$ at 95% confidence level are set as a function of $m(χ)$ and $τ(χ)$, varying between $2\times10^{-10}$ and $10^{-7}$. These are the most stringent limits to date. The limits are interpreted in the context of a model with a light inflaton particle.

hep-ex↗