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V. I. Kravtsov

Publications and source records attributed to V. I. Kravtsov.

At least 19 recordsLinked to original sources
arXiv2026

A search for the dark photon in the OKA experiment

A search for the massless dark photon in the decay $K^{+}\to π^{+}π^{0}\overline{{} γ}$ is performed with the OKA detector exposed to 17.7 GeV/c RF separated secondary beam of the U70 Proton Synchrotron. A high-statistics data sample of the $K^{+}$ decays is used for a missing mass search of the stable massless invisible dark photon ($\overlineγ$) in the final state. In the absence of a statistically valuable signal the upper limit on the branching ratio of the decay $Br<2.0\times10^{-6}$ is obtained with a 90% confidence level based on a realistic matrix element of the process. Currently, it is the best upper limit for this hypothetical decay channel.

hep-ex↗
arXiv2024

The upper limit on the $K^+ \to π^0π^0π^0e^+ν$ decay

A search for the $K^{+} \to π^{0}π^{0}π^{0}e^+ν$ decay is performed by the OKA collaboration. The search is based on $3.65 \times 10^9 ~ K^+$ decays. No signal is observed. The upper limit set is $BR(K^{+} \to π^{0}π^{0}π^{0}e^+ν) < 5.4\times 10^{-8} ~ 90\%$ CL, 65 times lower than the one currently listed by PDG.

hep-ex↗
arXiv2024

Searches for the light invisible axion-like particle in $K^{+}\toπ^{+}π^{0}a$ decay

A high statistics data sample of the $K^{+}$ decays is recorded by the OKA collaboration. A missing mass analysis is performed to search for a light invisible pseudoscalar axion-like particle (ALP) $a$ in the decay $K^{+} \to π^{+} π^{0} a$. No signal is observed, the upper limits for the branching ratio of the decay are calculated. The $90\%$ confidence level upper limit is changing from $2.5\cdot10^{-6}$ to $2\cdot10^{-7}$ for the ALP mass from 0 to 200 MeV/$c^{2}$, except for the region of $π^{0}$ mass, where the upper limit is $4.4\cdot10^{-6}$.

hep-ex↗
arXiv2023

Observation of $K^{+} \to π^{+}π^{0}π^{0}γ$ decay

The $K^{+} \to π^{+}π^{0}π^{0}γ$ decay is observed by the OKA collaboration. The branching ratio is measured to be $(4.1 \pm 0.9(stat) \pm 0.4(syst))\times 10^{-6}$. The branching ratio and $γ$ energy spectrum are consistent with ChPT prediction.

hep-ex↗
arXiv2022

Measurement of T-odd asymmetry in radiative K+ -> pi0 e+ nu gamma decay using OKA detector

The paper presents a measurement of the T-odd correlation in radiation decay \boldmath $K^+ \rightarrow π^{0} e^{+} ν_{e} γ$ performed on the installation of the 101200 candidate events of the investigated decay were identified. Measured correlation $ξ_{πe γ}$ -is a mixed product of moments $e^{+}$, $π^{0}$, $γ$ in the kaon rest system, normalized by $M^{3}_{K}$. To assess the asymmetry of the distribution by $ξ_{πe γ}$ the value used is $A_ξ= \frac {N_{+}-N_{-}} {N_{+}+N_{-}}$, where $N_{+(-)}$ is the number of events with $ξ$ greater than (less than) zero. For the $A_ξ$ asymmetry, the value is obtained $A_ξ = (+0.1 \pm 3.9($stat.$) \pm1.7($syst.$))\times10^{-3}$ or $|A_ξ| < 5.4\times10^{-3} (90\%~ CL)$

hep-ex↗
arXiv2020

Study of $K^+ \rightarrow π^{0} e^{+} νγ$ decay with OKA setup

Results of a study of the $K^+ \rightarrow π^{0} e^{+} νγ$ decay at OKA setup are presented. More than 32000 events of this decay are observed. The differential spectra over the photon energy and the photon-electron opening angle in kaon rest frame are presented. The branching ratios, normalized to that of $K_{e3}$ decay are calculated for different cuts in $E^*_γ$ and $cosΘ^{*}_{eγ}$. In particular, the branching ratio for $E^{*}_γ>30$ MeV and $Θ^{*}_{e γ}>20^{\circ}$ is measured R = $\frac{Br(K^+ \rightarrow π^{0} e^{+} ν_{e} γ) } {Br(K^+ \rightarrow π^{0} e^{+} ν_{e})} $ = =(0.587$\pm$0.010($stat.$)$\pm$0.015($syst.$))$\times10^{-2}$, which is in a good agreement with ChPT $O(p^{4})$ calculations.

hep-ex↗
arXiv2019

Measurement of the $K^+\rightarrow{μ^+}{ν_μ}γ$ decay form factors in the OKA experiment

A precise measurement of the vector and axial-vector form factors difference $F_V-F_A$ in the $K^+\rightarrow{μ^+}{ν_μ}γ$ decay is presented. About 95K events of $K^+\rightarrow{μ^+}{ν_μ}γ$ are selected in the OKA experiment. The result is $F_V-F_A=0.134\pm0.021(stat)\pm0.027(syst)$. Both errors are smaller than in the previous $F_V-F_A$ measurements.

hep-ex↗
arXiv2019

Study of the decay $K^{+}\toπ^{+}π^{-}π^{+}γ$ in the OKA experiment

A high statistics data sample of the decays of $K^+$ mesons to three charged particles was accumulated by the OKA experiment in 2012 and 2013. This allowed to select a clean sample of about 450 events with $K^{+}\toπ^{+}π^{-}π^{+}γ$ decays with the energy of the photon in the kaon rest frame greater than 30 MeV. The measured branching fraction of the $K^{+}\toπ^{+}π^{-}π^{+}γ$, with $E_γ^{*}$ > 30 MeV is $(0.71 \pm 0.05) \times 10^{-5}$. The measured energy spectrum of the decay photon is compared with the prediction of the chiral perturbation theory to O$(p^{4})$. A search for an up-down asymmetry of the photon with respect to the hadronic system decay plane is also performed.

hep-ex↗
arXiv2018

Search for heavy neutrino in $K^{+} \to μ^{+} ν_{H}$ decay

A high statistics data sample of the $K^{+}\toμ^{+}ν_μ$ decay was accumulated by the OKA experiment in 2012. The missing mass analysis was performed to search for the decay channel $K^{+}\toμ^{+}ν_{H}$ with a hypothetic stable heavy neutrino in the final state. The obtained missing mass spectrum does not show peaks which could be attributed to existence of stable heavy neutrinos in the mass range (220 $< m_{ν_{H}} <$ 375) MeV$/c^{2}$. As a result, we obtain upper limits on the branching ratio and on the value of the mixing element $|U_{μH}|^{2}$.

hep-ex↗
arXiv2017

$K_{e3}$ decay studies in OKA experiment

Recent results from OKA setup concerning form factor studies in $K_{e3}$ decay are presented. About 5.25M events are selected for the analysis. The linear and quadratic slopes for the decay formfactor $f_{+}(t)$ are measured: $λ'_{+}=(26.1 \pm 0.35 \pm 0.28 )\times 10^{-3}$, $λ"_{+}=(1.91 \pm 0.19 \pm 0.14)\times 10^{-3}$. The scalar and tensor contributions are compatible with zero. Several alternative parametrizations are tried: the Pole fit parameter is found to be $M_V = 891 \pm 2.0$ MeV ; the parameter of the Dispersive parametrization is measured to be $Λ_+ =(24.58 \pm 0.18) \times 10^{-3}$. The presented results are considered as preliminary.

hep-ex↗
arXiv2008

Performance of a fine-sampling electromagnetic calorimeter prototype in the energy range from 1 to 19 GeV

The fine-sampling electromagnetic calorimeter prototype has been experimentally tested using the 1-19 GeV/c tagged beams of negatively charged particles at the U70 accelerator at IHEP, Protvino. The energy resolution measured by electrons is Delta{E}/E=2.8%/\sqrt{E} + 1.3%. The position resolution for electrons is Delta{x}=3.1 + 15.4/sqrt{E} mm in the center of the cell. The lateral non-uniformity of the prototype energy response to electrons and MIPs has turned out to be negligible. Obtained experimental results are in a good agreement with Monte-Carlo simulations.

physics.ins-det↗
arXiv2007

The Comparative Study of the Inclusive $π^0$ Analyzing Power in Reactions p+p(pol)->π^0 + X and π^-+p(pol)->π^0 + X at 50 and 40 Gev/C Respectively

Single-spin asymmetries $A_N$ in reactions p+p(pol)->π^0 + X and π^-+p(pol)->π^0 + X at 50 and 40 GeV/c respectively behave in drastically different ways in function of transverse momentum in the central region. At the same time $A_N$ in the polarized proton fragmentation region of these reactions are practically coinciding. Our new data on the analyzing power at 50 GeV/c in the polarized proton fragmentation region in reaction p+p(pol)->π^0 + X confirm this conclusion with better statistics and coincide with our previous data at 70 GeV/c for the same reaction.

hep-ex↗
arXiv2007

New Polarization Program at U70 (SPASCHARM Project)

The new polarization program SPASCHARM is being prepared in Protvino. The program has two stages. The first stage is dedicated to single-spin asymmetries in the production of miscellaneous light resonances with the use of 34 GeV $π^-$-beam. Inclusive and exclusive reactions will be studied simultaneously. The second stage is dedicated to single-spin and double-spin asymmetries in charmonium production with the use of 70 GeV polarized proton beam which will allow us to understand charmonium hadronic production mechanism and make gluon polarization $Δg(x)$ extraction at large $x$.

hep-ex↗
arXiv2006

Spin physics with light and heavy neutral mesons at Protvino

PROZA-M experiment results as well the proposal of a new spin program with the use of a polarized proton beam are presented. Significant asymmetries were observed in inclusive $π^0$ production. The new program proposes to study a wealth of single- and double-spin observables in various reactions using longitudinally and transversely polarized proton beams at U70. The main goal is to define gluon contribution to nucleon spin by measuring double-spin asymmetry in charmonium production.

hep-ex↗
arXiv2005

Expected Accuracy in a Measurement of the CKM Angle $α$ Using a Dalitz Plot Analysis of $\boldmath B^0 \to ρπ$ Decays in the BTeV Project

A precise measurement of the angle $α$ in the CKM triangle is very important for a complete test of Standard Model. A theoretically clean method to extract $α$ is provided by B$^0 \to ρπ$ decays. Monte Carlo simulations to obtain the BTeV reconstruction efficiency and to estimate the signal to background ratio for these decays were performed. Finally the time-dependent Dalitz plot analysis, using the isospin amplitude formalism for tree and penguin contributions, was carried out. It was shown that in one year of data taking BTeV could achieve an accuracy on $α$ better than 5$^{\circ}$.

hep-ex↗
arXiv2005

Spin physics program in the U70 polarized proton beam

A possibility to accelerate a high intensity polarized proton beam up to 70 GeV at the IHEP accelerator, extract it from the main ring and deliver to several experimental setups is being studied now. We propose to study a wealth of single- and double-spin observables in various reactions using longitudinally and transverserly polarized proton beams at U70. The proposed measurements can be done at the existing detectors as well as require to create a few new experimental setups at U70.

hep-ex↗
arXiv2005

Design and performance of LED calibration system prototype for the lead tungstate crystal calorimeter

A highly stable monitoring system based on blue and red light emitting diodes coupled to a distribution network comprised of optical fibers has been developed for an electromagnetic calorimeter that uses lead tungstate crystals readout with photomultiplier tubes. We report of the system prototype design and on the results of laboratory tests. Stability better than 0.1% (r.m.s.) has been achieved during one week of prototype operation.

physics.ins-det↗