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I. A. Koop

Publications and source records attributed to I. A. Koop.

At least 37 records · Page 2Linked to original sources
arXiv2020

Measurement of the $e^+e^- \toπ^+π^- $ process cross section with the SND detector at the VEPP-2000 collider in the energy region $0.525<\sqrt{s}<0.883$ GeV

The cross section of the process $e^+ e^-\toπ^+π^-$ has been measured in the Spherical Neutral Detector (SND) experiment at the VEPP-2000 $e^+e^-$ collider VEPP-2000 in the energy region $525 <\sqrt[]{s} <883$ MeV. The measurement is based on data with an integrated luminosity of about 4.6 pb$^{-1}$. The systematic uncertainty of the cross section determination is 0.8 % at $\sqrt{s}>0.600$ GeV. The $ρ$ meson parameters are obtained as $m_ρ= 775.3\pm 0.5\pm 0.6$ MeV, $Γ_ρ= 145.6\pm 0.6\pm 0.8$ MeV, $B_{ρ\to e^+ e^-}\times B_{ρ\toπ^+π^-} = (4.89\pm 0.02\pm 0.04)\times 10^{-5}$, and the parameters of the $e^+ e^-\toω\toπ^+π^-$ process, suppressed by $G$-parity, as $B_{ω\to e^+ e^-}\times B_{ω\toπ^+π^-}= (1.32\pm 0.06\pm 0.02)\times 10^{-6} $ and $ϕ_{ρω} = 110.7\pm 1.5\pm1.0$ degrees.

hep-ex↗
arXiv2020

Study of dynamics of the process $e^+e^-\to π^+π^-π^0$ in the energy range 1.15--2.00 GeV

The dynamics of the process $ e^+e^- \to π^+π^-π^0 $ is studied in the energy region from 1.15 to 2.00 GeV using data accumulated with the SND detector at the VEPP-2000 $e^+e^-$ collider. The Dalitz plot distribution and $π^+π^-$ mass spectrum are analyzed in a model including the intermediate states $ρ(770)π$, $ρ(1450)π$, and $ωπ^0$. As a result, the energy dependences of the $ρ(770)π$ and $ρ(1450)π$ cross sections and the relative phases between the $ρ(770)π$ amplitude and the $ρ(1450)π$ and $ωπ^0$ amplitudes are obtained. The $ρ(1450)π$ cross section has a peak in the energy region of the $ω(1650)$ resonance (1.55-1.75 GeV). In this energy range the contributions of the $ρ(770)π$ and $ρ(1450)π$ states are of the same order of magnitude. No resonance structure near 1.65 GeV is observed in the $ρ(770)π$ cross section. We conclude that the intermediate state $ρ(1450)π$ gives a significant contribution to the decay of $ω(1650)\toπ^+π^-π^0$, whereas the $ρ(770)π$ mechanism dominates in the decay $ω(1420)\toπ^+π^-π^0$.

hep-ex↗
arXiv2020

Study of the process $e^+e^- \to ηπ^0γ$ in the energy range $\sqrt{s} = \mbox{1.05-2.00}$ GeV with the SND detector

The process $e^+e^-\toηπ^0γ$ is studied in the center-of-mass energy range 1.05-2.00 GeV using data with an integrated luminosity of 94.5 pb$^{-1}$ collected by the SND detector at the VEPP-2000 $e^+e^-$ collider. The $e^+e^-\toηπ^0γ$ cross section is measured for the first time. It is shown that the dominant mechanism of this reaction is the transition through the $ωη$ intermediate state. The measured cross section of the subprocess $e^+e^-\toωη\toηπ^0γ$ is consistent with previous measurements in the $e^+e^-\toπ^+π^-π^0η$ mode. It is found, with a significance of 5.6$σ$, that the process $e^+e^-\toηπ^0γ$ is not completely described by hadronic vector-pseudoscalar intermediate states. The cross section of this missing contribution, which can originate from radiation processes, e. g. $e^+e^-\to a_{0}(1450)γ$, is measured. It is found to be 15-20 pb in the wide energy range from 1.3 to 1.9 GeV.

hep-ex↗
arXiv2020

Measurement of the $e^{+}e^{-}\rightarrowηπ^{+}π^{-}$ cross section with the CMD-3 detector at the VEPP-2000 collider

The cross section of the process $e^{+}e^{-}\rightarrowηπ^{+}π^{-}$ is measured using the data collected with the CMD-$3$ detector at the VEPP-$2000$ collider in the center-of-mass energy range from $1.1$ to $2.0$ GeV. The decay mode $η\rightarrowγγ$ is used for $η$ meson reconstruction in the data sample corresponding to an integrated luminosity of $78.3$ pb$^{-1}$. The energy dependence of the $e^{+}e^{-}\rightarrowηπ^{+}π^{-}$ cross section is fitted within the framework of vector meson dominance in order to extract the $Γ(ρ(1450)\rightarrow{^{+}e^{-}})\mathcal{B}(ρ(1450)\rightarrowηπ^{+}π^{-})$ and the $Γ(ρ(1700)\rightarrow{e^{+}e^{-}})\mathcal{B}(ρ(1700)\rightarrowηπ^{+}π^{-})$ products. Based on conservation of vector current, the analysed data are used to test the relationship between the $e^{+}e^{-}\rightarrowηπ^{+}π^{-}$ cross section and the spectral function in $τ^-\rightarrowηπ^-π^0ν_τ$ decay. The $e^{+}e^{-}\rightarrowηπ^{+}π^{-}$ cross section measured with the CMD-$3$ detector is in good agreement with the previous measurements.

hep-ex↗
arXiv2019

Possibility to investigate P-parity violation in nuclear collisions at facility NICA

A possible experimental setup for measuring the effect of parity violation in the interaction of the polarized proton or deuteron beams with an unpolarized target is discussed. One possibility is investigation of scattering of the proton or deuteron polarized beams on a thick internal target in one of the rings of the NICA collider. In this case, the spin of a circulating particles is transformed into a mode precessing in the horizontal plane using an RF flipper. The effect of parity violation will be studied by measuring the correlation of the interaction cross section of particles and the direction of their spins. In an alternative approach, the flipper transforms the spins of particles into a horizontal plane and the beam is extracted into the channel in a certain phase of the precession. In this more traditional experimental setup, the total cross section of the passage of particles through a dense target is measured, depending on the sign of the helicity of the polarization of the beam.

hep-ex↗
arXiv2019

Search for direct production of the $f_1(1285)$ resonance in $e^+e^-$ collisions

A search for direct production of the $f_1(1285)$ resonance in $e^+e^-$ annihilation is performed with the SND detector at the VEPP-2000 $e^+e^-$ collider. The analysis is based on data with an integrated luminosity of 15.1 pb$^{-1}$ accumulated in the center-of-mass energy range 1.2--1.4 GeV. Two $e^+e^-\to f_1(1285)$ candidate events are found at the peak of the resonance and zero events beyond the resonance. The significance of the $e^+e^-\to f_1(1285)$ signal is $2.5σ$. The cross section at the maximum of the resonance is found to be $σ(e^+e^-\to f_1)=45^{+33}_{-24}$ pb. The corresponding branching fraction $B(f_1(1285)\to e^+e^-)=(5.1^{+3.7}_{-2.7})\times 10^{-9}$. We consider this result as a first indication of the process $e^+e^-\to f_1(1285)$. The measured branching fraction is consistent with the theoretical prediction.

hep-ex↗
arXiv2019

Study of the process $e^+e^-{\to}K^+K^-η$ with the CMD-3 detector at the VEPP-2000 collider

The process $e^+e^-{\to}K^+K^-η$ has been studied in the center-of-mass energy range from 1.59 to 2.007\,GeV using the data sample of 59.5 pb$^{-1}$, collected with the CMD-3 detector at the VEPP-2000 $e^+e^-$ collider in 2011, 2012 and 2017. The $K^+K^-η$ final state is found to be dominated by the contribution of the $ϕ(1020)η$ intermediate state. The cross section of the process $e^+e^-{\to}ϕ(1020)η$ has been measured with a systematic uncertainty of 5.1$\%$ on the base of 3009 $\pm$ 67 selected events. The obtained cross section has been used to calculate the contribution to the anomalous magnetic moment of the muon: $a_μ^{ϕη}(E<1.8\, {\rm GeV})=(0.321 \pm 0.015_{\rm stat} \pm 0.016_{\rm syst}) \times 10^{-10}$, $a_μ^{ϕη}(E<2.0\, {\rm GeV})=(0.440 \pm 0.015_{\rm stat} \pm 0.022_{\rm syst}) \times 10^{-10}$. From the cross section approximation the $ϕ(1680)$ meson parameters have been determined with better statistical precision, than in previous studies.

hep-ex↗
arXiv2018

Measurement of the $e^+e^- \to π^0γ$ cross section in the energy range 1.075--2 GeV at SND

The process $e^+e^- \to π^0γ$ is studied with the SND detector at the VEPP-2000 $e^+e^-$ collider. Basing on data with an integrated luminosity of 41 pb$^{-1}$ recorded in 2010-2012 we measure the $e^+e^- \to π^0γ$ cross section in the center-of-mass energy range from 1.075 up to 2 GeV. In the range 1.4-2.0 GeV the process $e^+e^- \to π^0γ$ is studied for the first time.

hep-ex↗
arXiv2018

Search for the process $\mathbf{e^+e^- \toη}$

A search for the rare decay $η\rightarrow e^+e^-$ is performed using the inverse process $e^+e^- \rightarrow η$ in the decay mode $η\toπ^0π^0π^0 $. We analyze data with an integrated luminosity of 654 nb$^{-1} $ accumulated at the VEPP-2000 $e^+e^-$ collider with the SND detector at the center-of-mass energy $E=m_ηc ^2\approx 548 $ MeV, and set the upper limit $ {\cal B} (η\rightarrow e^+ e^-) < 7 \times 10^{-7} $ at the 90\% confidence level.

hep-ex↗
arXiv2018

Muon (g-2) Technical Design Report

The Muon (g-2) Experiment, E989 at Fermilab, will measure the muon anomalous magnetic moment a factor-of-four more precisely than was done in E821 at the Brookhaven National Laboratory AGS. The E821 result appears to be greater than the Standard-Model prediction by more than three standard deviations. When combined with expected improvement in the Standard-Model hadronic contributions, E989 should be able to determine definitively whether or not the E821 result is evidence for physics beyond the Standard Model. After a review of the physics motivation and the basic technique, which will use the muon storage ring built at BNL and now relocated to Fermilab, the design of the new experiment is presented. This document was created in partial fulfillment of the requirements necessary to obtain DOE CD-2/3 approval.

physics.ins-det↗
arXiv2017

Measurement of the $e^+e^- \to ηπ^+π^-$ cross section with the SND detector at the VEPP-2000 collider

The $e^+e^- \to ηπ^+π^-$ cross section is measured at the SND detector in the $η$ decay mode $η\to 3π^0$. The analysis is based on the data sample with an integrated luminosity of 32.7 pb$^{-1}$ collected at the VEPP-2000 $e^+e^-$ collider in the center-of-mass energy range $\sqrt{s}=1.075-2.000$ GeV. The data obtained in the $η\to 3π^0$ decay mode are found to be in agreement with the previous SND measurements in the $η\to γγ$ mode. Therefore the measurements in the two modes are combined.

hep-ex↗
arXiv2017

Study of the process $e^+e^- \to K^+K^-$ in the center-of-mass energy range 1010--1060~MeV with the CMD-3 detector

The process $e^+e^- \to K^+K^-$ has been studied using $1.7 \times 10^6$ events from a data sample corresponding to an integrated luminosity of 5.7 pb$^{-1}$ collected with the CMD-3 detector in the center-of-mass energy range 1010--1060 MeV. The cross section measured with an about 2\% systematic uncertainty and it is used to calculate the contribution to the anomalous magnetic moment of the muon $a_μ^{K^+K^-} = (19.33 \pm 0.40) \times 10^{-10}$, and to obtain the $ϕ(1020)$ meson parameters. We consider the relationship between the $e^+e^- \to K^+K^-$ and $e^+e^- \to K^0_SK^0_L$ cross sections and compare it to the theoretical expectations.

hep-ex↗
arXiv2017

Correction of magnetic optics and beam trajectory using LOCO based algorithm with expanded experimental data sets

Precise beam based measurement and correction of magnetic optics is essential for the successful operation of accelerators. The LOCO algorithm is a proven and reliable tool, which in some situations can be improved by using a broader class of experimental data. The standard data sets for LOCO include the closed orbit responses to dipole corrector variation, dispersion, and betatron tunes. This paper discusses the benefits from augmenting the data with four additional classes of experimental data: the beam shape measured with beam profile monitors; responses of closed orbit bumps to focusing field variations; betatron tune responses to focusing field variations; BPM-to-BPM betatron phase advances and beta functions in BPMs from turn-by-turn coordinates of kicked beam. All of the described features were implemented in the Sixdsimulation software that was used to correct the optics of the VEPP-2000 collider, the VEPP-5 injector booster ring, and the FAST linac.

physics.acc-ph↗
arXiv2016

Study of the Process $e^+e^-\to π^+π^-π^+π^-$ IN THE C.M. Energy Range 920--1060 MeV with the CMD-3 Detector

A cross section of the process $e^+e^- \to \pipi\pipi$ has been measured using 6798$\pm$93 signal events from a data sample corresponding to an integrated luminosity of 9.8 pb$^{-1}$ collected with the CMD-3 detector in the center-of-mass energy range 920--1060 MeV. The measured cross section exhibits an interference pattern of the $ϕ(1020)\to\pipi\pipi$ decay with a non-resonant process $e^+e^- \to \pipi\pipi$, from which we obtain the branching fraction of the doubly suppressed decays (by G-parity and OZI rule): $\BR(ϕ\to\pipi\pipi) = (6.5\pm2.7\pm1.6)\times 10^{-6}$.

hep-ex↗
arXiv2016

Updated measurement of the $e^+e^- \to ωπ^0 \to π^0π^0γ$ cross section with the SND detector

We analyze a 37 pb$^{-1}$ data sample collected with the SND detector at the VEPP-2000 $e^+e^-$ collider in the center-of-mass energy range 1.05--2.00 GeV and present an updated measurement of the $e^+e^- \to ωπ^0 \to π^0π^0γ$ cross section. In particular, we correct the mistake in radiative correction calculation made in our previous measurement based on a part of the data. The measured cross section is fitted with the vector meson dominance model with three $ρ$-like states and used to test the conserved vector current hypothesis in the $τ^-\toωπ^-ν_τ$ decay.

hep-ex↗
arXiv2016

Measurement of the $\mathbf{e^+e^-\to K^+K^-}$ cross section in the energy range $\mathbf{\sqrt{s}=1.05-2.0}$ GeV

The $e^+e^-\to K^+K^-$ cross section is measured in the center-of-mass energy range $1.05-2.00$ GeV at the SND detector. The measurement is based on data with an integrated luminosity of 35 pb$^{-1}$ collected at the VEPP-2000 $e^+e^-$-collider. The obtained results are consistent with the previous most accurate data obtained in the BABAR experiment and have a comparable accuracy.

hep-ex↗
arXiv2016

Study of the process $e^+e^-\toωηπ^0$ in the energy range $\sqrt{s} <2$ GeV with the SND detector

The process $e^+e^-\toωηπ^0$ is studied in the energy range $1.45-2.00$ GeV using data with an integrated luminosity of 33 pb$^{-1}$ accumulated by the SND detector at the $e^+e^-$ collider VEPP-2000. The $e^+e^-\toωηπ^0$ cross section is measured for the first time. The cross section has a threshold near 1.75 GeV. Its value is about 2 nb in the energy range $1.8-2.0$ GeV. The dominant intermediate state for the process $e^+e^- \to ωηπ^0$ is found to be $ωa_0(980)$.

hep-ex↗