arXiv subjects

P. Pakhlov

Publications and source records attributed to P. Pakhlov.

At least 37 records · Page 2Linked to original sources

arXiv2016

Search for $XYZ$ states in $Υ(1S)$ inclusive decays

The branching fractions of the $Υ(1S)$ inclusive decays into final states with a $J/ψ$ or a $ψ(2S)$ are measured with improved precision to be $\BR(Υ(1S)\to J/ψ+ {\rm anything})=(5.25\pm 0.13(\mathrm{stat.})\pm 0.25(\mathrm{syst.}))\times 10^{-4}$ and $\BR(Υ(1S)\to ψ(2S) + {\rm anything})=(1.23\pm 0.17(\mathrm{stat.})\pm 0.11(\mathrm{syst.}))\times 10^{-4}$. The first search for $Υ(1S)$ decays into $XYZ$ states that decay into a $J/ψ$ or a $ψ(2S)$ plus one or two charged tracks yields no significant signals for $XYZ$ states in any of the examined decay modes, and upper limits on their production rates in $Υ(1S)$ inclusive decays are determined.

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arXiv2015

Study of e+e- => B() B()-bar pi+- at sqrt(s)=10.866 GeV

We report the analysis of the three-body e+e- => B B-bar pi, B B*-bar pi, and B* B*-bar pi processes, including the first observation of the Zb+-(10610) =>[B B*-bar+c.c.]+- and Zb+-(10650) => [B*B*-bar]+- transitions. We measure visible cross sections for the three-body production of sigma_vis(e+e- => [B B*-bar+c.c.]+-pi-+=(11.2+-1.0(stat.)+-1.2(syst.)) pb and sigma_vis(e+e- => [B*B*-bar]+-pi-+)=(5.61+-0.73(stat.)+-0.66(syst.)) pb and set a 90% C.L. upper limit of sigma_vis(e+e- => [BB-bar]+-pi-+)<2.1 pb. The results are based on a 121.4 1/fb data sample collected with the Belle detector at a center-of-mass energy near the Y(5S) peak.

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arXiv2015

The Physics of the B Factories

This work is on the Physics of the B Factories. Part A of this book contains a brief description of the SLAC and KEK B Factories as well as their detectors, BaBar and Belle, and data taking related issues. Part B discusses tools and methods used by the experiments in order to obtain results. The results themselves can be found in Part C. Please note that version 3 on the archive is the auxiliary version of the Physics of the B Factories book. This uses the notation alpha, beta, gamma for the angles of the Unitarity Triangle. The nominal version uses the notation phi_1, phi_2 and phi_3. Please cite this work as Eur. Phys. J. C74 (2014) 3026.

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arXiv2015

Measurement of $e^+e^- \to γχ_{cJ}$ via initial state radiation at Belle

The process $e^+e^- \to γχ_{cJ}$ ($J$=1, 2) is studied via initial state radiation using 980 fb$^{-1}$ of data at and around the $Υ(nS)$ ($n$=1, 2, 3, 4, 5) resonances collected with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. No significant signal is observed except from $ψ(2S)$ decays. Upper limits on the cross sections between $\sqrt{s}=3.80$ and $5.56~{\rm GeV}$ are determined at the 90% credibility level, which range from few pb to a few tens of pb. We also set upper limits on the decay rate of the vector charmonium [$ψ(4040$), $ψ(4160)$, and $ψ(4415)$] and charmoniumlike [$Y(4260)$, $Y(4360)$, and $Y(4660)$] states to $γχ_{cJ}$.

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arXiv2015

Charged charmonium-like Z+(4430) from rescattering in conventional B decays

In a previous paper we suggested an explanation for the peak designated as $Z(4430)^+$ in the $ψ^\primeπ^+$ mass spectrum, observed by Belle in ${\bar{\!B}} \to {ψ^\prime} π^+ K$ decays, as an effect of $\bar{\!D}{}^{\,*0}D^{\,+} \to ψ^\primeπ^+$ rescattering in the decays ${\bar{\!B}} \to {D_{s}^{\,\prime -}} {D}$, where the $D_{s}^{\,\prime -}$ is an as-yet unobserved radial excitation of the pseudoscalar ground state $D_{s}^{\,-}$-meson. In this paper, we demonstrate that this hypothesis provides an explanation of the double $Z^+$-like peaking structures, which were studied by LHCb with much higher statistics. While according to our hypothesis, the origin of the peaking structures is purely kinematical, reflecting the presence of a conventional resonance in the hidden intermediate state, the amplitude of the $Z(4430)^+$ peak carries a Breit-Wigner-like complex phase, arising from the intermediate $D_{s}^{\,\prime -}$ resonance. Thus, our hypothesis is entirely consistent with the recent LHCb measurement of the resonant-like amplitude behaviour of the $Z(4430)^+$. We perform a toy fit to the LHCb data, which illustrates that our approach is also consistent with all the observed structure in the LHCb $M({{ψ^\prime}π^+})$ spectrum. We suggest a critical test of our hypothesis that can be performed experimentally.

hep-ph↗

arXiv2015

A scintillator based muon and KLong detector for the Belle II experiment

A new muon and K_Long detector based on scintillators will be used for the endcap and inner barrel regions in the Belle II experiment, currently under construction. The increased luminosity of the e+e- SuperKEKB collider entails challenging detector requirements. We demonstrate that relatively inexpensive polystyrene scintillator stips with wave length shifting fibers ensure a sufficient light yield at the Silcon PhotoMultiplier (SiPM) photodetector, are robust and provide improved physics performance for the Belle II experiment compared to its predecessor, Belle.

physics.ins-det↗

arXiv2014

Search for $B_{s}^{0}\rightarrowγγ$ and a measurement of the branching fraction for $B_{s}^{0}\rightarrowϕγ$

We search for the decay $B_{s}^{0}\rightarrowγγ$ and measure the branching fraction for $B_{s}^{0}\rightarrowϕγ$ using 121.4~$\textrm{fb}^{-1}$ of data collected at the $Υ(\mathrm{5}S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^{+}e^{-}$ collider. The $B_{s}^{0}\rightarrowϕγ$ branching fraction is measured to be $(3.6 \pm 0.5 (\mathrm{stat.}) \pm 0.3 (\mathrm{syst.}) \pm 0.6 (f_{s})) \times 10^{-5}$, where $f_{s}$ is the fraction of $B_{s}^{(*)}\bar{B}_{s}^{(*)}$ in $b\bar{b}$ events. Our result is in good agreement with the theoretical predictions as well as with a recent measurement from LHCb. We observe no statistically significant signal for the decay $B_{s}^{0}\rightarrowγγ$ and set a $90\%$ confidence-level upper limit on its branching fraction at $ 3.1 \times 10^{-6}$. This constitutes a significant improvement over the previous result.

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arXiv2014

Observation of $e^+e^- \to π^+ π^- π^0 χ_{bJ}$ and search for $X_b \to ωΥ(1S)$ at $\sqrt{s}\sim 10.867$ GeV

The $e^+e^- \to π^+ π^- π^0 χ_{bJ}$ ($J=0,~1,~2$) processes are studied using a 118~fb$^{-1}$ data sample collected at a center-of-mass energy of 10.867 GeV, in the $Υ(10860)$ energy range, with the Belle detector. The $π^+ π^- π^0 χ_{b1}$, $π^+π^-π^0χ_{b2}$, $ωχ_{b1}$ signals and the evidence of $ωχ_{b2}$ are observed for the first time and the cross sections are measured. No significant $π^+π^-π^0χ_{b0}$ or $ωχ_{b0}$ signal is observed and 90\% confidence level upper limits on the cross sections for these two processes are obtained. In the $π^+π^-π^0$ invariant mass spectrum, significant non-$ω$ signals are also observed. We search for the $X(3872)$-like state with a hidden $b\bar{b}$ component (named $X_b$) decaying into $ωΥ(1S)$; no significant signal is observed with a mass between $10.55$ and $10.65$ GeV/$c^2$.

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arXiv2014

Observation of the decay $B^0 \to η' K^*(892)^0$

We report a search for charmless hadronic decays of neutral $B$ mesons to $η' K^{*}(892)^{0}$. The results are based on a 711fb$^{-1}$ data sample that contains $772\times 10^6 B\overline{B}$ pairs, collected at the $Υ(4S)$ resonance with the Belle detector at the KEKB asymmetric energy $e^+e^-$ collider. We observe the decay for the first time with a significance of 5.0 standard deviations and obtain its branching fraction ${\cal B}[B^0\toη' K^{*}(892)^{0}]=[2.6\pm0.7{\rm (stat)}\pm0.2{\rm (syst)}]\times 10^{-6}$. We also measure the $CP$ violating asymmetry as ${\cal A}_{CP}[B^0\toη' K^{*}(892)^{0}]=-0.22\pm0.29{\rm (stat)}\pm0.07{\rm syst}$.

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arXiv2014

Search for CP violation in D^0 -> pi^0 pi^0 decays

We search for CP violation in neutral charm meson decays using a data sample with an integrated luminosity of 966 fb^-1 collected with the Belle detector at the KEKB e+e- asymmetric-energy collider. The asymmetry obtained in the rate of D^0 and D^0-bar decays to the pi^0 pi^0 final state, [-0.03+-0.64(stat)+-0.10(syst)]%, is consistent with no CP violation. This constitutes an order of magnitude improvement over the existing result. We also present an updated measurement of the CP asymmetry in the D^0 -> K_S pi^0 decay: A_{CP}(D^0 -> K_S pi^0) = [-0.21+-0.16(stat)+-0.07(syst)]%.

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arXiv2014

QCD and strongly coupled gauge theories: challenges and perspectives

We highlight the progress, current status, and open challenges of QCD-driven physics, in theory and in experiment. We discuss how the strong interaction is intimately connected to a broad sweep of physical problems, in settings ranging from astrophysics and cosmology to strongly-coupled, complex systems in particle and condensed-matter physics, as well as to searches for physics beyond the Standard Model. We also discuss how success in describing the strong interaction impacts other fields, and, in turn, how such subjects can impact studies of the strong interaction. In the course of the work we offer a perspective on the many research streams which flow into and out of QCD, as well as a vision for future developments.

hep-ph↗

arXiv2014

Measurements of the masses and widths of the $Σ_{c}(2455)^{0/++}$ and $Σ_{c}(2520)^{0/++}$ baryons

We present measurements of the masses and decay widths of the baryonic states $Σ_{c}(2455)^{0/++}$ and $Σ_{c}(2520)^{0/++}$ using a data sample corresponding to an integrated luminosity of 711 fb$^{-1}$ collected with the Belle detector at the KEKB $e^{+}e^{-}$ asymmetric-energy collider operating at the $Υ(4S)$ resonance. We report the mass differences with respect to the $Λ_{c}^{+}$ baryon $M(Σ_{c}(2455)^{0})-M(Λ_{c}^{+}) = 167.29\pm0.01\pm0.02$ MeV/$c^{2}$, $M(Σ_{c}(2455)^{++})-M(Λ_{c}^{+}) = 167.51\pm0.01\pm0.02$ MeV/$c^{2}$, $M(Σ_{c}(2520)^{0})-M(Λ_{c}^{+}) = 231.98\pm0.11\pm0.04$ MeV/$c^{2}$, $M(Σ_{c}(2520)^{++})-M(Λ_{c}^{+}) = 231.99\pm0.10\pm0.02$ MeV/$c^{2}$, and the decay widths $Γ(Σ_{c}(2455)^{0}) = 1.76\pm0.04^{+0.09}_{-0.21}$ MeV/$c^{2}$, $Γ(Σ_{c}(2455)^{++}) = 1.84\pm0.04^{+0.07}_{-0.20}$ MeV/$c^{2}$, $Γ(Σ_{c}(2520)^{0}) = 15.41\pm0.41^{+0.20}_{-0.32}$ MeV/$c^{2}$, $Γ(Σ_{c}(2520)^{++}) = 14.77\pm0.25^{+0.18}_{-0.30}$ MeV/$c^{2}$, where the first uncertainties are statistical and the second are systematic. The isospin mass splittings are measured to be $M(Σ_{c}(2455)^{++})-M(Σ_{c}(2455)^{0})=0.22\pm0.01\pm0.01$ MeV/$c^{2}$ and $M(Σ_{c}(2520)^{++})-M(Σ_{c}(2520)^{0})=0.01\pm0.15\pm0.03$ MeV/$c^{2}$. These results are the most precise to date.

hep-ex↗

arXiv2014

Measurements of Branching Fractions of $τ$ Lepton Decays with one or more $K^{0}_{S}$

We report measurements of branching fractions of $τ$ lepton decays to final states with a $K^{0}_{S}$ meson using a 669 fb$^{-1}$ data sample accumulated with the Belle detector at the KEKB asymmetric-energy $e^{+}e^{-}$ collider. The inclusive branching fraction is measured to be $\mathcal{B}(τ^{-} \to K^{0}_{S}\ X^{-} ν_τ)=(9.15 \pm 0.01 \pm 0.15) \times 10^{-3}$, where $X^{-}$ can be anything; the exclusive branching fractions are $\mathcal{B}(τ^{-} \to π^{-} K^{0}_{S} ν_τ) = (4.16 \pm 0.01 \pm 0.08) \times 10^{-3}$, $\mathcal{B}(τ^{-} \to K^{-} K^{0}_{S} ν_τ) = (7.40 \pm 0.07 \pm 0.27) \times 10^{-4}$, $\mathcal{B}(τ^{-} \to π^{-} K^{0}_{S} π^{0} ν_τ) = (1.93 \pm 0.02 \pm 0.07) \times 10^{-3}$, $\mathcal{B}(τ^{-} \to K^{-} K^{0}_{S} π^{0} ν_τ) = (7.48 \pm 0.10 \pm 0.37)\times 10^{-4}$, $\mathcal{B}(τ^{-} \to π^{-} K^{0}_{S} K^{0}_{S} ν_τ) = (2.33 \pm 0.03 \pm 0.09) \times 10^{-4}$, $\mathcal{B}(τ^{-} \to π^{-} K^{0}_{S} K^{0}_{S} π^{0} ν_τ) = (2.00 \pm 0.22 \pm 0.20) \times 10^{-5}$, where the first uncertainty is statistical and the second is systematic. For each mode, the accuracy is improved over that of pre-$B$-factory measurements by a factor ranging from five to ten. In $τ^{-} \to π^{-} K^0_S K^0_S π^{0} ν_τ$ decays, clear signals for the intermediate states $τ^{-} \to π^- f_{1}(1285)ν_τ$ and $τ^{-} \to K^{*-}K^{0}_{S} π^{0} ν_τ$ are observed.

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arXiv2013

Evidence for the suppressed decay B^- -> DK^-, D -> K^+π^-π^0

We report a study of the suppressed decay B^- -> DK^-, D -> K^+π^-π^0, where D denotes either a D^0 or a \bar{D}^0 meson. The decay is sensitive to the CP-violating parameter ϕ_3. Using a data sample of 772 x 10^6 B\bar{B} pairs collected at the Υ(4S) resonance with the Belle detector, we measure the ratio of branching fractions of the above suppressed decay to the favored decay B^- -> DK^-, D -> K^-π^+π^0. Our result is R_{DK} = [1.98 +/- 0.62(stat.) +/- 0.24(syst.)] x 10^{-2}, which indicates the first evidence of the signal for this suppressed decay with a significance of 3.2 standard deviations. We measure the direct CP asymmetry between the suppressed B^- and B^+ decays to be A_{DK} = 0.41 +/- 0.30 (stat.) +/- 0.05 (syst.). We also report measurements for the analogous quantities R_{Dπ} and A_{Dπ} for the decay B^- -> Dπ^-, D -> K^+π^-π^0.

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arXiv2013

Evidence for B_s^0 -> Lambda_c^+ Lambda-bar pi^-

Using 121.4 fb^{-1} of data collected with the Belle detector at the Y(5S) resonance at the KEKB asymmetric-energy e^+e^- collider, we report evidence for the B_s^0 -> Lambda_c^+ Lambda-bar pi^- decay mode with a measured branching fraction (3.6 +- 1.1[stat.] {+0.3 -0.5}[syst.] +- 0.9[Lambda_c^+] +- 0.7[N_{Bs}]) * 10^{-4} and a significance of 4.4 standard deviations. This is the first evidence for a baryonic B_s^0 decay.

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arXiv2013

Precision measurement of charged pion and kaon differential cross sections in electron-positron annihilation at Q = 10.52 GeV

Measurements of inclusive differential cross sections for charged pion and kaon production in electron-positron annihilation have been carried out at a center-of-mass energy of Q = 10.52 GeV. The measurements were performed with the Belle detector at the KEKB electron-positron collider using a data sample containing 113 million e+e- -> qqbar events, where q={u,d,s,c}. We present charge-integrated differential cross sections dσ_h+-/dz for h+- = pi+-, K+- as a function of the relative hadron energy z = 2*E_h / sqrt{s} from 0.2 to 0.98. The combined statistical and systematic uncertainties for pi+- (K+-) are 4% (4%) at z ~ 0.6 and 15% (24%) at z ~ 0.9. The cross sections are the first measurements of the z-dependence of pion and kaon production for z > 0.7 as well as the first precision cross section measurements at a center-of-mass energy far below the Z^0 resonance used by the experiments at LEP and SLC.

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arXiv2013

Antibaryonic dark matter

Assuming existence of (very) heavy fourth generation of quarks and antiquarks we argue that antibaryon composed of the three heavy antiquarks can be light, stable and invisible, hence a good candidate for the Dark matter particle. Such opportunity allows to keep the baryon number conservation for the generation of the visible baryon asymmetry. The dark matter particles traveling through the ordinary matter will annihilate with nucleons inducing proton(neutron)-decay-like events with ~5GeV energy release in outcoming particles.

hep-ph↗

arXiv2013

Search for CP Violation in the Decay $D^+\rightarrow K^0_S K^+$

We search for CP violation in the decay $D^+\rightarrow K^0_S K^+$ using a data sample with an integrated luminosity of 977 fb$^{-1}$ collected with the Belle detector at the KEKB $e^+e^-$ asymmetric-energy collider. No CP violation has been observed and the CP asymmetry in $D^+\rightarrow K^0_S K^+$ decay is measured to be $(-0.25\pm0.28\pm0.14)%$, which is the most sensitive measurement to date. After subtracting CP violation due to $K^0-\bar{K}^0$ mixing, the CP asymmetry in $D^+\rightarrow\bar{K}^0 K^+$ decay is found to be $(+0.08\pm0.28\pm0.14)%$.

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