arXiv subjects

A. Bondar

Publications and source records attributed to A. Bondar.

At least 469 records · Page 26Linked to original sources

arXiv2017

Measurements of prompt charm production cross-sections in $pp$ collisions at $\sqrt{s} = 5\,$TeV

Production cross-sections of prompt charm mesons are measured using data from $pp$ collisions at the LHC at a centre-of-mass energy of $5\,$TeV. The data sample corresponds to an integrated luminosity of $8.60\pm0.33\,$pb$^{-1}$ collected by the LHCb experiment. The production cross-sections of $D^0$, $D^+$, $D_s^+$, and $D^{*+}$ mesons are measured in bins of charm meson transverse momentum, $p_{\text{T}}$, and rapidity, $y$. They cover the rapidity range $2.0<y<4.5$ and transverse momentum ranges $0 < p_{\text{T}} < 10\, \text{GeV}/c$ for $D^0$ and $D^+$ and $1 < p_{\text{T}} < 10\, \text{GeV}/c$ for $D_s^+$ and $D^{*+}$ mesons. The inclusive cross-sections for the four mesons, including charge-conjugate states, within the range of $1 < p_{\text{T}} < 8\, \text{GeV}/c$ are determined to be σ(pp\rightarrow D^0 X) = 1004 \pm 3 \pm 54\,μ\text{b} σ(pp\rightarrow D^+ X) = 402 \pm 2 \pm 30\,μ\text{b} σ(pp\rightarrow D_s^+ X) = 170 \pm 4 \pm 16\,μ\text{b} σ(pp\rightarrow D^{*+} X)= 421 \pm 5 \pm 36\,μ\text{b} where the uncertainties are statistical and systematic, respectively.

hep-ex↗

arXiv2017

Measurement of forward $J/ψ$ production cross-sections in $pp$ collisions at $\sqrt{s}=13$ TeV

The production of $J/ψ$ mesons in proton-proton collisions at a centre-of-mass energy of $\sqrt{s}=13$ TeV is studied with the \lhcb detector. Cross-section measurements are performed as a function of the transverse momentum $p_\mathrm{T}$ and the rapidity $y$ of the $J/ψ$ meson in the region $p_\mathrm{T}<14\mathrm{GeV}/c$ and $2.0<y<4.5$, for both prompt $J/ψ$ mesons and $J/ψ$ mesons from $b$-hadron decays. The production cross-sections integrated over the kinematic coverage are $15.03\pm 0.03\pm 0.94$ $μ$b for prompt $J/ψ$ and $2.25\pm 0.01\pm 0.14$ $μ$b for $J/ψ$ from $b$-hadron decays, assuming zero polarization of the $J/ψ$ meson. The first uncertainties are statistical and the second systematic. The cross-section reported for $J/ψ$ mesons from $b$-hadron decays is used to extrapolate to a total $b\bar{b}$ cross-section. The ratios of the cross-sections with respect to $\sqrt{s}=8$ TeV are also determined.

hep-ex↗

arXiv2017

Search for heavy neutrinos at Belle

We report on a search for heavy neutrinos in B-meson decays. The results are obtained using a data sample that contains 772x10^6 BB-bar pairs collected at the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e- collider. No signal is observed and upper limits are set on mixing of heavy neutrinos with left-handed neutrinos of the Standard Model in the mass range 0.5 - 5.0 GeV/c^2.

hep-ex↗

arXiv2017

Observation of five new narrow $Ω_c^0$ states decaying to $Ξ_c^+ K^-$

The $Ξ_c^+ K^-$ mass spectrum is studied with a sample of $pp$ collision data corresponding to an integrated luminosity of 3.3 fb$^{-1}$, collected by the LHCb experiment. The $Ξ_c^+$ is reconstructed in the decay mode $p K^- π^+$. Five new, narrow excited $Ω_c^0$ states are observed: the $Ω_c(3000)^0$, $Ω_c(3050)^0$, $Ω_c(3066)^0$, $Ω_c(3090)^0$, and $Ω_c(3119)^0$. Measurements of their masses and widths are reported.

hep-ex↗

arXiv2017

Study of cryogenic photomultiplier tubes for the future two-phase cryogenic avalanche detector

We report the results of a characterization study of several types of cryogenic photomultipliers manufactured by Hamamatsu Photonics and intended for operation in liquid Ar conditions, namely: compact 2-inch R6041-506MOD tubes, 3-inch R11065-10 and R11065-MOD tubes for operation in liquid Ar and 3-inch R11410-20 tubes originally designed for operation in liquid Xe. These types of PMT are proposed for installation into the future two-phase cryogenic avalanche detector that is developed in the Laboratory of Cosmology and Particle Physics of the Novosibirsk State University jointly with the Budker Institute of Nuclear Physics. Eight R11065 PMTs and seven R11410-20 tubes were tested and all demonstrated excellent performance in liquid Ar in terms of gain and relative single electron efficiency. All 3-inch PMTs showed a maximal gain in liquid Ar above 5x10^6 and relative single electron efficiency higher than 95%. Compact R6041-506MOD tubes have dynode system different from that of the 3-inch photomultipliers and thus their single electron energy resolution and relative efficiency is much worse than that of 3-inch tubes. From 21 2-inch PMTs only 12 tubes were selected with acceptable, i.e. higher than 75%, relative single electron efficiency and the maximal gain higher than 5x10^6. However, these PMTs are very attractive because they are the only compact type of tubes that can operate in liquid Ar.

astro-ph.IM↗

arXiv2017

Measurement of the $τ$ lepton polarization and $R(D^)$ in the decay $\bar{B} \to D^ τ^- \barν_τ$

We report the first measurement of the $τ$ lepton polarization $P_τ(D^*)$ in the decay $\bar{B} \rightarrow D^* τ^- \barν_τ$ as well as a new measurement of the ratio of the branching fractions $R(D^{*}) = \mathcal{B}(\bar {B} \rightarrow D^* τ^- \barν_τ) / \mathcal{B}(\bar{B} \rightarrow D^* \ell^- \barν_\ell)$, where $\ell^-$ denotes an electron or a muon, and the $τ$ is reconstructed in the modes $τ^- \rightarrow π^- ν_τ$ and $τ^- \rightarrow ρ^- ν_τ$. We use the full data sample of $772 \times 10^6$ $B{\bar B}$ pairs recorded with the Belle detector at the KEKB electron-positron collider. Our results, $P_τ(D^*) = -0.38 \pm 0.51 {\rm (stat.)} ^{+0.21}_{-0.16} {\rm (syst.)}$ and $R(D^*) = 0.270 \pm 0.035{\rm (stat.)} ^{+0.028}_{-0.025}{\rm (syst.)}$, are consistent with the theoretical predictions of the Standard Model.

hep-ex↗

arXiv2017

New algorithms for identifying the flavour of $B^0$ mesons using pions and protons

Two new algorithms for use in the analysis of $pp$ collision are developed to identify the flavour of $B^0$ mesons at production using pions and protons from the hadronization process. The algorithms are optimized and calibrated on data, using $B^0 \rightarrow D^- π^+$ decays from $pp$ collision data collected by LHCb at centre-of-mass energies of 7 and 8 TeV. The tagging power of the new pion algorithm is 60 % greater than the previously available one; the algorithm using protons to identify the flavour of a $B^0$ meson is the first of its kind.

hep-ex↗

arXiv2017

Measurements of the S-wave fraction in $B^{0}\rightarrow K^{+}π^{-}μ^{+}μ^{-}$ decays and the $B^{0}\rightarrow K^{\ast}(892)^{0}μ^{+}μ^{-}$ differential branching fraction

A measurement of the differential branching fraction of the decay ${B^{0}\rightarrow K^{\ast}(892)^{0}μ^{+}μ^{-}}$ is presented together with a determination of the S-wave fraction of the $K^+π^-$ system in the decay $B^{0}\rightarrow K^{+}π^{-}μ^{+}μ^{-}$. The analysis is based on $pp$-collision data corresponding to an integrated luminosity of 3\,fb$^{-1}$ collected with the LHCb experiment. The measurements are made in bins of the invariant mass squared of the dimuon system, $q^2$. Precise theoretical predictions for the differential branching fraction of $B^{0}\rightarrow K^{\ast}(892)^{0}μ^{+}μ^{-}$ decays are available for the $q^2$ region $1.1<q^2<6.0\,{\rm GeV}^2/c^4$. In this $q^2$ region, for the $K^+π^-$ invariant mass range $796 < m_{Kπ} < 996\,{\rm MeV}/c^2$, the S-wave fraction of the $K^+π^-$ system in $B^{0}\rightarrow K^{+}π^{-}μ^{+}μ^{-}$ decays is found to be \begin{equation*} F_{\rm S} = 0.101\pm0.017({\rm stat})\pm0.009 ({\rm syst}), \end{equation*} and the differential branching fraction of $B^{0}\rightarrow K^{\ast}(892)^{0}μ^{+}μ^{-}$ decays is determined to be \begin{equation*} {\rm d}\mathcal{B}/{\rm d} q^2 = (0.342_{\,-0.017}^{\,+0.017}({\rm stat})\pm{0.009}({\rm syst})\pm0.023({\rm norm}))\times 10^{-7}c^{4}/{\rm GeV}^{2}. \end{equation*} The differential branching fraction measurements presented are the most precise to date and are found to be in agreement with Standard Model predictions.

hep-ex↗

arXiv2017

Observation of $D^0\to ρ^0γ$ and search for $CP$ violation in radiative charm decays

We report the first observation of the radiative charm decay $D^0 \to ρ^0 γ$ and the first search for $CP$ violation in decays $D^0 \to ρ^0 γ$, $ϕγ$, and $\overline{K}{}^{*0} γ$, using a data sample of 943 fb$^{-1}$ collected with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. The branching fraction is measured to be $\mathcal{B}(D^0 \to ρ^0 γ)=(1.77 \pm 0.30 \pm 0.07) \times 10^{-5}$, where the first uncertainty is statistical and the second is systematic. The obtained $CP$ asymmetries, $\mathcal{A}_{CP}(D^0 \to ρ^0 γ)=+0.056 \pm 0.152 \pm 0.006$, $\mathcal{A}_{CP}(D^0 \to ϕγ)=-0.094 \pm 0.066 \pm 0.001$, and $\mathcal{A}_{CP}(D^0 \to \overline{K}{}^{*0} γ)=-0.003 \pm 0.020 \pm 0.000$, are consistent with no $CP$ violation. We also present an improved measurement of the branching fractions $\mathcal{B}(D^0 \to ϕγ)=(2.76 \pm 0.19 \pm 0.10) \times 10^{-5}$ and $\mathcal{B}(D^0 \to \overline{K}{}^{*0} γ)=(4.66 \pm 0.21 \pm 0.21) \times 10^{-4}$.

hep-ex↗

arXiv2017

Measurement of the phase difference between short- and long-distance amplitudes in the $B^{+}\to K^{+}μ^{+}μ^{-}$ decay

A measurement of the phase difference between the short- and long-distance contributions to the $B^{+}\to K^{+}μ^{+}μ^{-}$ decay is performed by analysing the dimuon mass distribution. The analysis is based on $pp$ collision data corresponding to an integrated luminosity of 3 $\rm fb^{-1}$ collected by the LHCb experiment in 2011 and 2012. The long-distance contribution to the $B^{+}\to K^{+}μ^{+}μ^{-}$ decay is modelled as a sum of relativistic Breit--Wigner amplitudes representing different vector meson resonances decaying to muon pairs, each with their own magnitude and phase. The measured phases of the $J/ψ$ and $ψ(2S)$ resonances are such that the interference with the short-distance component in dimuon mass regions far from their pole masses is small. In addition, constraints are placed on the Wilson coefficients, $\mathcal{C}_{9}$ and $\mathcal{C}_{10}$, and the branching fraction of the short-distance component is measured.

hep-ex↗

arXiv2017

Study of $J/ψ$ production in jets

The production of $J/ψ$ mesons in jets is studied in the forward region of proton-proton collisions using data collected with the LHCb detector at a center-of-mass energy of 13 TeV. The fraction of the jet transverse momentum carried by the $J/ψ$ meson, $z \equiv p_{\rm T}(J/ψ)/p_{\rm T}({\rm jet})$, is measured using jets with $p_{\rm T}({\rm jet}) > 20$ GeV in the pseudorapidity range $2.5 < η({\rm jet}) < 4.0$. The observed $z$ distribution for $J/ψ$ mesons produced in $b$-hadron decays is consistent with expectations. However, the results for prompt $J/ψ$ production do not agree with predictions based on fixed-order non-relativistic QCD. This is the first measurement of the $p_{\rm T}$ fraction carried by prompt $J/ψ$ mesons in jets at any experiment.

hep-ex↗

arXiv2017

Observation of $B_{c}^{+} \to J/ψD^{()} K^{()}$ decays

A search for the decays $B_c^+ \to J/ψD^{(*)0} K^+$ and $B_c^+ \to J/ψD^{(*)+} K^{*0}$ is performed with data collected at the LHCb experiment corresponding to an integrated luminosity of 3 fb$^{-1}$. The decays $B_c^+ \to J/ψD^0 K^+$ and $B_c^+ \to J/ψD^{*0} K^+$ are observed for the first time, while first evidence is reported for the $B_c^+ \to J/ψD^{*+} K^{*0}$ and $B_c^+ \to J/ψD^+ K^{*0}$ decays. The branching fractions of these decays are determined relative to the $B_c^+ \to J/ψπ^+$ decay. The $B_c^+$ mass is measured, using the $J/ψD^0 K^+$ final state, to be $6274.28 \pm 1.40 (stat) \pm 0.32 (syst)$ MeV/$c^2$. This is the most precise single measurement of the $B_c^+$ mass to date.

hep-ex↗

arXiv2017

First measurement of $\boldsymbol{T}$-odd moments in $\boldsymbol{D^{0} \rightarrow K_{S}^{0} π^{+} π^{-} π^{0}}$ decays

We report the first measurement of the $T$-odd moments in the decay $D^{0} \rightarrow K_{S}^{0} π^{+} π^{-} π^{0}$ from a data sample corresponding to an integrated luminosity of $966\,{\rm fb}^{-1}$ collected by the Belle experiment at the KEKB asymmetric-energy $e^+ e^-$ collider. From these moments we determine the $CP$-violation-sensitive asymmetry $a_{CP}^{T\text{-odd}} = \left[-0.28 \pm 1.38 ~(\rm{stat.}) ^{+0.23}_{-0.76} ~(\rm{syst.})\right] \times 10^{-3}$, which is consistent with no $CP$ violation. In addition, we perform $a_{CP}^{T\text{-odd}}$ measurements in different regions of the $D^{0} \rightarrow K_{S}^{0} π^{+} π^{-} π^{0}$ phase space; these are also consistent with no $CP$ violation.

hep-ex↗

arXiv2017

Observation of $B_{c}^{+} \rightarrow D^{0} K^{+}$ decays

Using proton-proton collision data corresponding to an integrated luminosity of 3.0 fb$^{-1}$, recorded by the LHCb detector at centre-of-mass energies of 7 and 8 TeV, the $B_{c}^{+} \rightarrow D^{0} K^{+}$ decay is observed with a statistical significance of 5.1 standard deviations. By normalising to $B^{+} \rightarrow \bar{D}^{0} π^{+}$ decays, a measurement of the branching fraction multiplied by the production rates for $B_{c}^{+}$ relative to $B^{+}$ mesons in the LHCb acceptance is obtained, $$ R_{D^{0} K} = \frac{f_{c}}{f_{u}}\times\mathcal{B}(B_{c}^{+} \rightarrow D^{0} K^{+}) = (9.3\,^{+2.8}_{-2.5} \pm 0.6) \times 10^{-7}\,, $$ where the first uncertainty is statistical and the second is systematic. This decay is expected to proceed predominantly through weak annihilation and penguin amplitudes, and is the first $B_{c}^{+}$ decay of this nature to be observed.

hep-ex↗

arXiv2017

Search for decays of neutral beauty mesons into four muons

A search for the non-resonant decays $B^0_s \rightarrow μ^{+}μ^{-}μ^{+}μ^{-}$ and $B^0 \rightarrow μ^{+}μ^{-}μ^{+}μ^{-}$ is presented. The measurement is performed using the full Run 1 data set collected in proton-proton collisions by the LHCb experiment at the LHC. The data correspond to integrated luminosities of $1$ and $2~\mathrm{fb}^{-1}$ collected at centre-of-mass energies of $7$ and $8~\mathrm{TeV}$, respectively. No signal is observed and upper limits on the branching fractions of the non-resonant decays at $95\%$ confidence level are determined to be \mathcal{B}(B^0_s \rightarrow μ^{+}μ^{-}μ^{+}μ^{-}) & < 2.5 \times 10^{-9} \mathcal{B}(B^0 \rightarrow μ^{+}μ^{-}μ^{+}μ^{-}) & < 6.9 \times 10^{-10}.

hep-ex↗

arXiv2017

Measurement of the ratio of branching fractions and difference in $CP$ asymmetries of the decays $B^+\to J/ψπ^+$ and $B^+\to J/ψK^+$

The ratio of branching fractions and the difference in $CP$ asymmetries of the decays $B^+\to J/ψπ^+$ and $B^+\to J/ψK^+$ are measured using a data sample of $pp$ collisions collected by the LHCb experiment, corresponding to an integrated luminosity of $3~{{\,\mbox{fb}^{-1}}}$ at centre-of-mass energies of 7 and $8~\mathrm{\,Te\kern -0.1em V}$. The results are \begin{equation*} {\mathcal{B}(B^+\to J/ψπ^+)\over\mathcal{B}(B^+\to J/ψK^+)}=(3.83\pm0.03\pm0.03)\times10^{-2}\,, \end{equation*} \begin{equation*} \mathcal{A}^{CP}(B^+\to J/ψπ^+)-\mathcal{A}^{CP}(B^+\to J/ψK^+)=(1.82\pm0.86\pm0.14)\times10^{-2}, \end{equation*} where the first uncertainties are statistical and the second are systematic. Combining this result with a recent LHCb measurement of $\mathcal{A}^{CP}(B^+\to J/ψK^+)$ provides the most precise estimate to date of $CP$ violation in the decay $B^+\to J/ψπ^+$, \begin{equation*} \mathcal{A}^{CP}(B^+\to J/ψπ^+) =(1.91\pm0.89\pm0.16)\times10^{-2}. \end{equation*}

hep-ex↗

arXiv2017

Observation of the annihilation decay mode $B^{0}\to K^{+}K^{-}$

A search for the $B^{0}\to K^{+}K^{-}$ decay is performed using $pp$-collision data collected by LHCb. The data set corresponds to integrated luminosities of 1 and 2 fb$^{-1}$ at center-of-mass energies of 7 and 8 TeV, respectively. This decay is observed for the first time, with a significance of more than five standard deviations. The analysis also results in an improved measurement of the branching fraction for the $B_s^0\to π^+π^-$ decay. The measured branching fractions are $BR(B^0\to K^+K^-) = (7.80 \pm 1.27 \pm 0.81 \pm 0.21) \times 10^{-8}$ and $BR(B_s^0\toπ^+π^-) = (6.91 \pm 0.54 \pm 0.63 \pm 0.19 \pm 0.40) \times 10^{-7}$. The first uncertainty is statistical, the second is systematic, the third is due to the uncertainty on the $B^0\to K^+π^-$ branching fraction used as a normalization. For the $B_s^0$ mode, the fourth accounts for the uncertainty on the ratio of the probabilities for $b$ quarks to hadronize into $B_s^0$ and $B^0$ mesons.

hep-ex↗

arXiv2017

First experimental study of photon polarization in radiative $B^{0}_{s}$ decays

The polarization of photons produced in radiative $B^{0}_{s}$ decays is studied for the first time. The data are recorded by the LHCb experiment in $pp$ collisions corresponding to an integrated luminosity of 3fb$^{-1}$ at center-of-mass energies of $7$ and $8$TeV. A time-dependent analysis of the $B^{0}_{s} \to ϕγ$ decay rate is conducted to determine the parameter ${\mathcal{A}}^Δ$, which is related to the ratio of right- over left-handed photon polarization amplitudes in $b \to s γ$ transitions. A value of ${\mathcal{A}}^Δ=-0.98^{\,+0.46\,+0.23}_{\,-0.52\,-0.20}$ is measured. This result is consistent with the Standard Model prediction within two standard deviations.

hep-ex↗