arXiv subjects

A. Bondar

Publications and source records attributed to A. Bondar.

At least 289 records · Page 16Linked to original sources

arXiv2019

Study of Three-Nucleon Dynamics in the dp breakup collisions using the WASA detector

Differential cross section for the 1H(d,pp)n breakup reaction at deuteron beam energy of 340 MeV has been measured with the use of WASA detector at COSY-Juelich. The set of proton-proton coincidences registered at Forward Detector has been analysed on dense grid of kinematic variables, giving in total around 5600 data points. The cross section data are compared to theoretical predictions based on the state-of-the-art nucleon-nucleon potentials, combined with three-nucleon force, Coulomb interaction or carried out in a relativistic regime.

nucl-ex↗

arXiv2019

First measurement of charm production in fixed-target configuration at the LHC

The first measurement of heavy-flavour production by the LHCb experiment in its fixed-target mode is presented. The production of $J/ψ$ and $D^0$ mesons is studied with beams of protons of different energies colliding with gaseous targets of helium and argon with nucleon-nucleon centre-of-mass energies of $\sqrt{s_{NN}} = 86.6 $ and $ 110.4$ ${\rm GeV}$, respectively. The $J/ψ$ and $D^0$ (including charge conjugate) production cross sections in $p{\rm He}$ collisions in the rapidity range $[2,4.6]$ are found to be $σ_{J/ψ} = 652 \pm 33$ (stat) $\pm 42$ (syst) nb$/$nucleon and $σ_{D^0} = 80.8 \pm 2.4$ (stat) $\pm 6.3$ (syst) $μ$b$/$nucleon, where the first uncertainty is statistical and the second is systematic. No evidence for a substantial intrinsic charm content of the nucleon is observed in the large Bjorken-$x$ region.

hep-ex↗

arXiv2019

Observation of a new structure near 10.75 GeV in the energy dependence of the $e^+e^-\toΥ(nS)π^+π^-$ ($n=1,2,3$) cross sections

We report a new measurement of the $e^+e^-\toΥ(nS)π^+π^-$ ($n=1,2,3$) cross sections at energies from 10.52 to 11.02 GeV using data collected with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. We observe a new structure in the energy dependence of the cross sections; if described by a Breit-Wigner function its mass and width are found to be $M=(10752.7\pm5.9\,^{+0.7}_{-1.1})\,$MeV/$c^2$ and $Γ=(35.5^{+17.6}_{-11.3}\,^{+3.9}_{-3.3})\,$MeV, where the first error is statistical and the second is systematic. The global significance of the new structure including systematic uncertainty is 5.2 standard deviations. We also find evidence for the $e^+e^-\toΥ(1S)π^+π^-$ process at the energy 10.52 GeV, which is below the $B\bar{B}$ threshold.

hep-ex↗

arXiv2019

A search for $\itΞ^{++}_{cc} \rightarrow D^{+} p K^{-} π^{+}$ decays

A search for the $\itΞ^{++}_{cc}$ baryon through the $\itΞ^{++}_{cc} \rightarrow D^{+} p K^{-} π^{+}$ decay is performed with a data sample corresponding to an integrated luminosity of 1.7 $\mathrm{fb}^{-1}$ recorded by the LHCb experiment in $pp$ collisions at a centre-of-mass energy of 13 TeV. No significant signal is observed in the mass range from the kinematic threshold of the decay to 3800 $\mathrm{MeV}/c^{2}$. An upper limit is set on the ratio of branching fractions $\mathcal{R} = \frac{\mathcal{B}(\itΞ^{++}_{cc} \rightarrow D^{+} p K^{-} π^{+})}{\mathcal{B}(\itΞ^{++}_{cc} \rightarrow Λ^{+}_{c} K^{-} π^{+}π^{+})}$ with $\mathcal{R} < 1.7 \hspace{2pt} (2.1) \times 10^{-2}$ at the 90% (95%) confidence level at the known mass of the $\itΞ^{++}_{cc}$ state.

hep-ex↗

arXiv2019

Ion detector for Accelerator Mass Spectrometry based on low-pressure TPC with THGEM readout

A new technique for ion identification in Accelerator Mass Spectrometry (AMS) has been proposed by measuring the ion track ranges using a low-pressure TPC. As a proof of principle, a low-pressure TPC with charge readout using a THGEM multiplier was developed. The tracks of alpha particles from various radioactive sources were successfully recorded in the TPC. The track ranges were measured with a high accuracy, reaching the 2% resolution level. Using these results and the SRIM code simulation, it is shown that the isobaric boron and beryllium ions can be effectively separated at ten sigma level. It is expected that this technique will be applied in the AMS facility in Novosibirsk for dating geological objects, in particular for the geochronology of Cenozoic Era.

physics.ins-det↗

arXiv2019

Measurements of $CP$ asymmetries in charmless four-body $Λ_b$ and $Ξ_b^0$ decays

A search for $CP$ violation in charmless four-body decays of $Λ_b$ and $Ξ_b^0$ baryons with a proton and three charged mesons in the final state is performed. To cancel out production and detection charge-asymmetry effects, the search is carried out by measuring the difference between the $CP$ asymmetries in a charmless decay and in a decay with an intermediate charmed baryon with the same particles in the final state. The data sample used was recorded in 2011 and 2012 with the LHCb detector and corresponds to an integrated luminosity of $3 {\rm fb}^{-1}$. A total of 18 $CP$ asymmetries are considered, either accounting for the full phase space of the decays or exploring specific regions of the decay kinematics. No significant $CP$-violation effect is observed in any of the measurements.

hep-ex↗

arXiv2019

Observation of the $Λ_b^0\rightarrow χ_{c1}(3872)pK^-$ decay

Using proton-proton collision data, collected with the LHCb detector and corresponding to 1.0, 2.0 and 1.9fb$^{-1}$ of integrated luminosity at the centre-of-mass energies of 7, 8, and 13 TeV, respectively, the decay $Λ_b^0\to χ_{c1}(3872)pK^-$ with $χ_{c1}\to J/ψπ^+π^-$ is observed for the first time. The significance of the observed signal is in excess of seven standard deviations. It is found that $(58\pm15)\%$ of the decays proceed via the two-body intermediate state $χ_{c1}(3872)Λ(1520)$. The~branching fraction with respect to that of the $Λ_b\rightarrowψ(2S)p K^{-}$ decay mode, where the $ψ(2S)$~meson is reconstructed in the $J/ψπ^+π^-$ final state, is measured to be: \begin{equation*} \frac{Λ_b^0\toχ_{c1}(3872)pK^-}{Λ_b\toψ(2S)p K^-} \times \frac{\mathcal{B}(χ_{c1} \to J/ψπ^+π^-)}{\mathcal{B}(ψ(2S)\to J/ψπ^+π^-)} = \left(5.4 \pm 1.1 \pm 0.2\right)\times 10^{-2}\,, \end{equation*} where the first uncertainty is statistical and the second is systematic.

hep-ex↗

arXiv2019

Search for the lepton-flavour violating decays $B^+ \to K^+ μ^{\pm} e^{\mp}$

A search for the lepton-flavour violating decays $B^+ \to K^+ μ^{\pm} e^{\mp}$ is performed using a sample of proton-proton collision data, collected with the LHCb experiment at centre-of-mass energies of $7$ and $8~{\rm TeV}$ and corresponding to an integrated luminosity of 3$\rm~fb^{-1}$. No significant signal is observed, and upper limits on the branching fractions are set as $\mathcal{B}(B^+ \to K^+ μ^- e^+) < 7.0~(9.5) \times 10^{-9}$ and $\mathcal{B}(B^+ \to K^+ μ^+ e^-) < 6.4~(8.8) \times 10^{-9}$ at 90 (95) % confidence level. The results improve the current best limits on these decays by more than one order of magnitude.

hep-ex↗

arXiv2019

Observation of $B^0_{(s)} \to J/ψp \overline{p}$ decays and precision measurements of the $B^0_{(s)}$ masses

The first observation of the decays $B^0_{(s)} \to J/ψp \overline{p}$ is reported, using proton-proton collision data corresponding to an integrated luminosity of $5.2{\text{\,fb}}^{-1}$, collected with the \mbox{LHCb}\xspace detector. These decays are suppressed due to limited available phase space, as well as due to Okubo-Zweig-Iizuka or Cabibbo suppression. The measured branching fractions are \begin{align*} \mathcal{B}(B^0 \to J/ψp \overline{p}) &= (4.51\pm 0.40\; \text{(stat)} \pm 0.44\; \text{(syst)}) \times 10^{-7}, \\ \mathcal{B}(B^0_s \to J/ψp \overline{p}) &= (3.58\pm 0.19\; \text{(stat)} \pm 0.39\; \text{(syst)}) \times 10^{-6}. \end{align*} For the $B^0_s$ meson, the result is much higher than the expected value of $ {\cal O} (10^{-9})$. The small available phase space in these decays also allows for the most precise single measurement of both the $B^0$ mass as ${5279.74 \pm 0.30\; ({\rm stat})\pm 0.10\; ({\rm syst})}$ MeV, and the $B^0_s$ mass as ${5366.85 \pm 0.19\; ({\rm stat})\pm 0.13\; ({\rm syst})}$ MeV.

hep-ex↗

arXiv2019

Measurement of $CP$-violating and mixing-induced observables in $B_s^0 \to ϕγ$ decays

A time-dependent analysis of the $B_s^0 \to ϕγ$ decay rate is performed to determine the $CP$-violating observables $S_{ϕγ}$ and $C_{ϕγ}$, and the mixing-induced observable $\mathcal{A}^Δ_{ϕγ}$. The measurement is based on a sample of $pp$ collision data recorded with the LHCb detector, corresponding to an integrated luminosity of 3 fb$^{-1}$ at center-of-mass energies of 7 and 8 TeV. The measured values are \begin{align*} S_{ϕγ} &= 0.43 \pm 0.30 \pm 0.11, \\ C_{ϕγ} &= 0.11 \pm 0.29 \pm 0.11, \\ \mathcal{A}^Δ_{ϕγ} &= -0.67 \, ^{+0.37}_{-0.41} \pm 0.17, \end{align*} where the first uncertainty is statistical and the second systematic. This is the first measurement of the observables $S$ and $C$ in radiative $B_s^0$ decays. The results are consistent with the Standard Model predictions.

hep-ex↗

arXiv2019

Search for the rare decay $B^{+} \rightarrow μ^{+}μ^{-}μ^{+}ν_{μ}$

A search for the rare leptonic decay $B^{+} \rightarrow μ^{+}μ^{-}μ^{+}ν_{μ}$ is performed using proton-proton collision data corresponding to an integrated luminosity of $4.7$ fb$^{-1}$ collected by the LHCb experiment. The search is carried out in the region where the lowest of the two $μ^{+}μ^{-}$ mass combinations is below $980$MeV/c$^{2}$. The data are consistent with the background-only hypothesis and an upper limit of $1.6 \times 10^{-8}$ at 95% confidence level is set on the branching fraction in the stated kinematic region.

hep-ex↗

arXiv2019

Experimental determination of the isospin of $Λ_c(2765)^+/Σ_c(2765)^+$

We report an experimental determination of the isospin of $Λ_c(2765)^+/Σ_c(2765)^+$ using 980 fb$^{-1}$ data in the $e^+e^-$ annihilation around $\sqrt{s} = 10.6$ GeV collected by the Belle detector located at the KEKB collider. The isospin partners are searched for in the $Σ_c(2455)^{++/0} π^{0}$ channels, and no evidence was obtained. Thus the isospin is determined to be zero, and the particle is established to be a $Λ_c$.

hep-ex↗

arXiv2019

Measurement of b-hadron fractions in 13 TeV pp collisions

The production fractions of $\overline{B}_s^0$ and $Λ_b^0$ hadrons, normalized to the sum of $B^-$ and $\overline{B}^0$ fractions, are measured in 13 TeV pp collisions using data collected by the LHCb experiment, corresponding to an integrated luminosity of 1.67/fb. These ratios, averaged over the $b$-hadron transverse momenta from 4 to 25 GeV and pseudorapidity from 2 to 5, are $0.122 \pm 0.006$ for $\overline{B}_s^0$, and $0.259 \pm 0.018$ for $Λ_b^0$, where the uncertainties arise from both statistical and systematic sources. The $Λ_b^0$ ratio depends strongly on transverse momentum, while the $\overline{B}_s^0$ ratio shows a mild dependence. Neither ratio shows variations with pseudorapidity. The measurements are made using semileptonic decays to minimize theoretical uncertainties. In addition, the ratio of $D^+$ to $D^0$ mesons produced in the sum of $\overline{B}^0$ and $B^-$ semileptonic decays is determined as $0.359\pm0.006\pm 0.009$, where the uncertainties are statistical and systematic.

hep-ex↗

arXiv2019

Measurement of $C\!P$ observables in the process $B^0 \to DK^{*0}$ with two- and four-body $D$ decays

Measurements of $C\!P$ observables in $B^0 \to DK^{*0}$ decays are presented, where $D$ represents a superposition of $D^0$ and $\bar{D}^0$ states. The $D$ meson is reconstructed in the two-body final states $K^+π^-$, $π^+ K^-$, $K^+K^-$ and $π^+π^-$, and, for the first time, in the four-body final states $K^+π^-π^+π^-$, $π^+ K^-π^+π^-$ and $π^+π^-π^+π^-$. The analysis uses a sample of neutral $B$ mesons produced in proton-proton collisions, corresponding to an integrated luminosity of 1.0, 2.0 and 1.8 $\rm fb^{-1}$ collected with the LHCb detector at centre-of-mass energies of $\sqrt{s} = $ 7, 8 and 13 TeV, respectively. First observations of the decays $B^0 \to D(π^+ K^-)K^{*0}$ and $B^0 \to D(π^+π^-π^+π^-)K^{*0}$ are obtained. The measured observables are interpreted in terms of the $C\!P$-violating weak phase $γ$.

hep-ex↗

arXiv2019

Measurement of the $CP$-violating phase $ϕ_s$ from $B_{s}^{0}\to J/ψπ^+π^-$ decays in 13 TeV $pp$ collisions

Decays of $B_{s}^{0}$ and $\overline{B}{}_{s}^{0}$ mesons into $J/ψπ^+π^-$ final states are studied in a data sample corresponding to 1.9 fb$^{-1}$ of integrated luminosity collected with the LHCb detector in 13 TeV $pp$ collisions. A time-dependent amplitude analysis is used to determine the final-state resonance contributions, the $CP$-violating phase $ϕ_s=-0.057\pm 0.060\pm 0.011$ rad, the decay-width difference between the heavier mass $B_{s}^{0}$ eigenstate and the $B^{0}$ meson of $-0.050\pm 0.004\pm 0.004$ ps$^{-1}$, and the $CP$-violating parameter $|λ|=1.01_{-0.06}^{+0.08}\pm0.03$, where the first uncertainty is statistical and the second systematic. These results are combined with previous LHCb measurements in the same decay channel using 7 TeV and 8 TeV $pp$ collisions obtaining $ϕ_s =0.002\pm0.044\pm0.012$ rad, and $|λ| =0.949\pm0.036\pm0.019$.

hep-ex↗

arXiv2019

Precision measurement of the $Λ_c^+$, $Ξ_c^+$ and $Ξ_c^0$ baryon lifetimes

We report measurements of the lifetimes of the $Λ_c^+$, $Ξ_c^+$ and $Ξ_c^0$ charm baryons using proton-proton collision data at center-of-mass energies of 7 and 8\tev, corresponding to an integrated luminosity of 3.0 fb$^{-1}$, collected by the LHCb experiment. The charm baryons are reconstructed through the decays $Λ_c^+\to pK^-π^+$, $Ξ_c^+\to pK^-π^+$ and $Ξ_c^0\to pK^-K^-π^+$, and originate from semimuonic decays of beauty baryons. The lifetimes are measured relative to that of the $D^+$ meson, and are determined to be \begin{align*} τ_{Λ_c^+} &= 203.5\pm1.0\pm1.3\pm1.4~{\rm fs}, \newline τ_{Ξ_c^+} &= 456.8\pm3.5\pm2.9\pm3.1~{\rm fs}, \newline τ_{Ξ_c^0} &= 154.5\pm1.7\pm1.6\pm1.0~{\rm fs}, \end{align*} where the uncertainties are statistical, systematic, and due to the uncertainty in the $D^+$ lifetime. The measurements are approximately 3--4 times more precise than the current world average values. The $Λ_c^+$ and $Ξ_c^+$ lifetimes are in agreement with previous measurements; however, the $Ξ_c^0$ baryon lifetime is approximately 3.3 standard deviations larger than the world average value.

hep-ex↗

arXiv2019

On the Relation between Interstellar Spectral Features and Reddening

It is well known that interstellar spectral features correlate with color excess E(B$-$V). This suggests that measuring intensities of these features allows one to estimate reddening of stars. The aim of this paper is to check how tight intensities of interstellar diffuse bands (DIBs)are related to the amount of extinction, measured using E(B$-$V). We have measured equivalent widths of the strongest DIBs (centered at $λλ$ 5780.6, 5797.0, 6196.0, 6379.3, 6613.5, and 8620.7 A), as well as of CH (near 4300.3 A) and CH$^+$ (near 4232.5 A) in high resolution, high S/N ratio echelle spectra from several spectrographs. The equivalent widths of the 8620 DIB in noisy spectra were measured using a template, which was constructed using the high quality spectrum of BD+40 4220. DIB relations with the color excess in the range 0.1--2.0 mag were examined. Our careful analysis demonstrates that all the above mentioned interstellar spectral features (except, perhaps, 6379 DIB) do correlate with E(B$-$V) relatively tightly (with the Pearson's correlation coefficient of 0.8+). Moreover, the observed scatter is apparently not caused by measurement errors but is of physical origin. We present several examples where the strength ratios of a DIB/molecule to E(B$-$V) are different than the average.

astro-ph.GA↗

arXiv2019

Near-threshold $D\bar{D}$ spectroscopy and observation of a new charmonium state

Using proton-proton collision data, corresponding to an integrated luminosity of 9$fb^{-1}$, collected with the~LHCb detector between 2011 and 2018, a new narrow charmonium state, the $X(3842)$ resonance, is observed in the decay modes $X(3842)\rightarrow D^0\bar{D}^0$ and $X(3842)\rightarrow D^+D^-$. The mass and the natural width of this state are measured to be \begin{eqnarray*} m_{X(3842)} & = & 3842.71 \pm 0.16 \pm 0.12 MeV/c^2\,, Γ_{X(3842)} & = & 2.79 \pm 0.51 \pm 0.35 MeV\,, \end{eqnarray*} where the first uncertainty is statistical and the~second is systematic. The observed mass and narrow natural width suggest the~interpretation of the new state as the~unobserved spin\nobreakdash-3 $ψ_3\mathrm{\left(1^3D_3\right)}$ charmonium state. In addition, prompt hadroproduction of the $ψ(3770)$~and $χ_{c2}(3930)$ states is observed for the first time, and the parameters of these~states are measured to be \begin{eqnarray*} m_{ψ(3770)} & = & 3778.1 \pm 0.7 \pm 0.6 MeV/c^2\,, m_{χ_{c2}(3930)} & = & 3921.9 \pm 0.6 \pm 0.2 MeV/c^2\,, Γ_{χ_{c2}(3930)} & = &36.6 \pm 1.9 \pm 0.9 MeV\,, \end{eqnarray*} where the first uncertainty is statistical and the~second is systematic.

hep-ex↗