Ivan Ovtin

We present the analysis of all KEDR data on the determination of J/ψ and ψ(2S) masses. The data comprise six scans of J/ψ and seven scans of ψ(2S) which were performed at the VEPP-4M e+e− collider in 2002–2008. The beam energy was determined using the resonance depolarization method. The detector and accelerator conditions during scans were very different that increases the reliability of the averaged results. The analysis accounts for partial correlations of systematic uncertainties on the masses. The following mass values were obtained:MJ/ψ=3096.900±0.002±0.006 MeV,Mψ(2S)=3686.099±0.004±0.009 MeV. These results supersede our previous measurements published in 2003 and 2012.

Using the KEDR detector at the VEPP-4M $e^+e^-$ collider, we have measured the values of $R_{\text{uds}}$ and $R$ at seven points of the center-of-mass energy between 3.12 and 3.72 GeV. The total achieved accuracy is about or better than $3.3\%$ at most of energy points with a systematic uncertainty of about $2.1\%$. At the moment it is the most accurate measurement of $R(s)$ in this energy range.

Facility of the extracted beams of electrons and gammas based on the e+e− VEPP-4M collider is described. This installation is designed to test prototype of detectors for HEP projects. Design parameters of the extracted electron beam are the following: intensity is not less than 50 Hz, energy range is from 0.1 GeV to 3.0 GeV and energy resolution is about 2–3%. The gamma energy range is from 0.05 GeV to 4.0 GeV with an accuracy of 0.5% of energy. The designed intensity of the gamma beam is about 1000 Hz.

Using the KEDR detector at the VEPP-4M $e^+e^-$ collider, we have determined the values of $R$ at thirteen points of the center-of-mass energy between 1.84 and 3.05 GeV. The achieved accuracy is about or better than $3.9\%$ at most of the energy points with a systematic uncertainty less than $2.4\%$.

The present work continues a series of the KEDR measurements of the $R$ value that started in 2010 at the VEPP-4M $e^+e^-$ collider. By combining new data with our previous results in this energy range we measured the values of $R_{\text{uds}}$ and $R$ at nine center-of-mass energies between 3.08 and 3.72 GeV. The total accuracy is about or better than $2.6\%$ at most of energy points with a systematic uncertainty of about $1.9\%$. Together with the previous precise $R$ measurement at KEDR in the energy range 1.84-3.05 GeV, it constitutes the most detailed high-precision $R$ measurement near the charmonium production threshold.

In June 2012 we tested a Focusing Aerogel RICH detector prototype based on Digital Photon Counters (DPC) by Philips at the CERN PS T10 beam line with a particle momentum up to 6 GeV/c. The prototype comprises a 20×20 cm2 photon detector with 48×48 DPC pixels. In order to reduce the dark count rate, the photon detector was cooled to −40 °C in addition to disabling individual DPC's microcells. A four layer focusing aerogel radiator with 200 mm focal distance was studied. We obtained a Cherenkov angle resolution of 3.61±0.04 mrad. The mean number of photoelectrons in a ring is 12. Directly measured π/K separation at 6 GeV/c momentum is 3.5σ, μ/π separation is 5.3σ at 1 GeV/c. A comparison with a Monte Carlo simulation is presented as well.

We present our current experience in preparation of focusing aerogels for the Focusing Aerogel RICH detector. Multilayer focusing aerogel tiles have been produced in Novosibirsk by a collaboration of the Budker Institute of Nuclear Physics and Boreskov Institute of Catalysis since 2004. We have obtained 2–3–4-layer blocks with the thickness of 30–45 mm. In 2012, the first samples of focusing blocks with continuous density (refractive index) gradient along thickness were produced. This technology can significantly reduce the contribution from the geometric factor of the radiator thickness to the resolution of the measured Cherenkov angle in the FARICH detector. The special installation was used for automatic control of reagents ratio during the synthesis process. The first samples were tested using the digital radiography method and on the electron beam with the FARICH prototype.

Particle identification system based on aerogel threshold Cherenkov counters ASHIPH (Aerogel SHifter PHotomultiplier) was installed in the KEDR detector in 2013. The system consists of 160 counters arranged in two layers and contains 1000 liters of aerogel with refractive index of 1.05 and 160 MCP PMTs with multialkali photocathode. The efficiency of relativistic particles detection was measured. Long-term stability of ASHIPH counters was studied. The main reasons of efficiency degradation are presented.

In June 2012 a FARICH prototype from Philips Digital Photon Counting (PDPC) based on a photon camera with dimensions of 200×200 mm has been tested at CERN. Remarkable particle separation has been achieved with a 4-layer aerogel sample: the π/K separation at a 6 GeV/c momentum is 3.5σ, the μ/π separation is 5.3σ at 1 GeV/c. The analysis of the data has shown that the main contribution to the accuracy of the ring radius measurement comes from aerogel. The development of focusing aerogels is proceeding in two main directions: tuning of production technology of multilayer blocks and development of a new production method with continuous density (refractive index) gradient along the block depth. The beam test was carried out in December 2012–January 2013 at the electron beam test facility at the VEPP-4 M e+e− collider. The goal of this test was to measure different single layer and focusing aerogel samples, both multilayer and gradient. Aerogel samples were tested with a PDPC FARICH prototype. A part of DPC SPADs in each pixel was disabled to form an active area of 1×1 mm2. The collected data proved that gradient aerogel samples focus Cherenkov light.

The work is devoted to the development of the Focusing Aerogel RICH (FARICH). The option of the forward RICH for the SuperB project in Italy is presented. It features an aerogel-NaF radiator and MCP photodetectors. Monte Carlo simulation predicts the π/ K separation at the level better than 3σ from 0.2 to 7 GeV/c, the μ/π separation—from 0.13 to 1.3 GeV/c, and the kaon momentum measurement with an accuracy of about 1% at 1 GeV/c. FARICH for the Super Charm-Tau Factory project in Novosibirsk is proposed. Monte Carlo simulation predicts μ/π separation at the level better than 3σ for a momentum from 0.3 to 1.7 GeV/c. A prototype will be tested on the new electron test beam facility at VEPP-4M collider.

In 2014 the fully installed ASHIPH (Aerogel, SHifter, PHotomultiplier) system began its operation in the KEDR experiment at the VEPP-4 M e+e−-collider. The system contains 1000 liters of aerogel with refractive index n=1.05 in 160 counters that are arranged in two layers. Cherenkov light collection is preformed by means of wavelength shifters (WLS). 160 Micro-Channel Plate (MCP) PMTs with multialkali photocathode are used as photodetectors. Efficiency of relativistic particles detection was measured with e+e−→e+e− events and cosmic muons. Detection efficiency for under-threshold particles was measured with cosmic muons. From these data π/K-separation of 4σ at the momentum 1.2 GeV/c was obtained.

The Super Charm–Tau (SCT) Factory is a proposed electron–positron collider in Novosibirsk with a peak luminosity of 1035cm−1s−1 operating in the energy range between 2and 6 GeV. The interaction region should be equipped by an excellent universal particle detector meeting the requirements of broad physics program of the experiment. Research and development for all detector subsystems is currently underway. Particle identification (PID) system of the detector is required to provide the state-of-the-art level of μ/π separation for the particle momenta up to 1.2GeV∕c. The following options for the PID system are considered in this paper: focusing aerogel ring imaging Cherenkov (FARICH) detector composed of 4-layer aerogel tiles, threshold Cherenkov counters based on aerogel shifter photomultiplier (ASHIPH), and time-of-flight (ToF) detector combined with the time-of-propagation (ToP) approach providing a time resolution better than 30ps. Assessment of the charged particle separation performance for these options based on simulation and prototype tests results is presented.

Description of mathematical models for fast photo detectors based on microchannel plates (MCP) in three-dimensional formulation is given. The models include calculations of photoelectron collection efficiency in the gap photo cathode—MCP, gain factor of secondary electron cascades in the channels, the particle scattering in the gaps between the plates, taking into account the fringe fields and strong external magnetic fields. Comparisons of numerical and experimental data are given. The dependencies of major device parameters vs. of applied voltage, pore size, and magnetic field magnitude have been studied.

A high performance particle identification (PID) system is essential for the successful realization of the broad physics program at the future Super C-τ Factory in Novosibirsk. The main requirements for the PID system are as follows: good π/K-separation in the entire operational momentum range and good μ∕π-separation in the momentum range from 0.3 to 1.2 GeV/c. The RICH detector based on focusing aerogel radiator (FARICH) and position-sensitive photon detector meets all these requirements. The FARICH method is described, and the beam test results are presented. The FARICH system design outline for the Super C-τ Factory project is presented. Most promising photon detector options are considered.

The Super Charm-Tau Factory is an electron-positron collider project in Novosibirsk with a peak luminosity of 1035 cm−1s−1 operating in the center of mass energy range between 2 and 6 GeV. The physics program of the experiment in general is devoted to the study of charm quark and tau lepton. Conceptual designs of the collider and a universal detector are presented. The dedicated particle identification (PID) system is required to provide the state-of-the-art level of μ/π separation for the particle momenta up to 1.2 GeV/c. The following options for the PID system are considered in this paper: Focusing Aerogel RICH (FARICH) detector composed of 4-layer aerogel tiles, threshold Cherenkov counters based on aerogel and shifter (ASHIPH), Focusing DIRC (FDIRC) counter and time-of-flight (ToF) detector combined with the time-of-propagation (ToP) approach providing a time resolution better than 30 ps. Also the capabilities of particles separation in tracking system are discussed. Comparison of PID approaches with help of parametric simulation is performed.

The ratio of the electron and muon widths of the $J/\psi$ meson has been measured using direct $J/\psi$ decays in the KEDR experiment at the VEPP-4M electron-positron collider. The result $\Gamma_{ee}(J/\psi)/\Gamma_{\mu\mu}(J/\psi)=1.0022\pm0.0044\pm0.0048\ (0.65\%)$ is in good agreement with the lepton universality. The experience collected during this analysis will be used for a $J/\psi$ lepton width determination with up to 1% accuracy.

Particle identification power of modern aerogel RICH detectors strongly depends on optical quality of radiators. It was shown that wavelength dependence of aerogel tile transparency after polishing cannot be described by the standard Hunt formula. The Hunt formula has been modified to describe scattering in a thin layer of silica dust on the surface of aerogel tile. Several procedures of polishing of aerogel tile have been tested. The best result has been achieved while using natural silk tissue. The resulting block has optical smooth surfaces. The measured decrease of aerogel transparency due to surface scattering is about few percent. This result could be used for production of radiators for the Focusing Aerogel RICH detectors.

The Super C- τ (SCT) Factory at Novosibirsk is a project of new colliding beam experiment proposed in Budker Institute of Nuclear Physics. Electron-positron collider based on Crab-Waist technique for operation energy range 2–5 GeV in center of mass is suggested. The luminosity up to 10 35 cm −1 s −1 (in 100 times higher than in operated today experiments in this energy region) is expected. To perform broad experimental program of the project successfully the excellent particle identification (PID) system is needed. A number of options are under consideration. Three of them are described in the paper: Focusing Aerogel RICH (FARICH) detector, threshold Cherenkov counters based on ASHIPH (Aerogel SHifter PHotomultiplier) technique with 6000 litres of aerogel of two refractive indexes and time-of-flight counters with TOP (Time of Propagation) approach with time resolution better than 30 ps. Comparison of PID capabilities with help of parametric simulation is given.

The excellent particle identification (PID) system is needed for the successful execution of the broad experimental program at future Super C-τ Factory (SCTF) in Novosibirsk. The main requirements for the PID system are the following: good π/K-separation in whole operational momentum range and good μ/π-separation in the momentum range from 0.4 up to 1.2 GeV/c. The RICH detector based on focusing aerogel (FARICH) could provide good π/K-separation from 0.4 GeV/c and μ/π-separation in the momentum range from 0.4 up to 1.5 GeV/c. The method FARICH is described, beam test results are presented and the status of multilayer aerogel production is given.

The work concerns the development of aerogel radiators for RICH detectors. Aerogel tiles with a refractive index of 1.05 were tested with a RICH prototype on the electron beam on the VEPP-4M collider. It has been shown that polishing with silk tissue yields good surface quality, the amount of light loss at this surface being about 5–7%. The Cherenkov angle resolution was measured for a tile in two conditions: with a clean exit face and with a polished exit face. The number of photons detected was 13.3 and 12.7 for the clean and polished surfaces, respectively. The Cherenkov angle resolution for the polished surface is 55% worse, which can be explained with the forward scattering on the polished surface. A tile with a crack inside was also tested. The experimental data show that the Cherenkov angle resolution is the same for tracks crossing the crack area and in a crack-free area.

The particle identification system of the KEDR detector is based on aerogel threshold Cherenkov counters ASHIPH (Aerogel, SHifter, PHotomultiplier).The simulation program of the ASHIPH counters was developed on the base of the Geant3.21 package and integrated into the KEDR full detector simulation.

A time-of-flight detector based on microchannel plates (MCP) is under development. The main goal of this work is the creation of a radiation hard large area detector providing 10 ps time resolution in strong magnetic field. The conceptual detector design is described in details.

The product of the electronic width of the ψ(2S) meson and the branching fraction of its decay to the muon pair was measured in the e+e−→ψ(2S)→μ+μ− process using nine data sets corresponding to an integrated luminosity of about 6.5 pb−1 collected with the KEDR detector at the VEPP-4M electron–positron collider:Γee×Bμμ=19.3±0.3±0.5eV. Adding the previous KEDR results on hadronic and leptonic channels, the values of the ψ(2S) electronic width were obtained under two assumptions: either with the assumption of lepton universalityΓee=2.279±0.015±0.042keV or without it, summing up hadronic and three independent leptonic channelsΓee=2.282±0.015±0.042keV.

A time-of-flight detector based on microchannel plates (MCP) is under development. The main goal is the creation of a radiation hard large area detector providing ∼10 ps time resolution for single charged particle in strong magnetic field. Conceptually, the detector consists of Cherenkov radiator covered with semitransparent photocathode followed by a chevron pair of MCPs. The detector design and the status of the development are reported.

Aerogel for different types of Cherenkov detectors is produced by a collaboration of Budker Institute of Nuclear Physics and Boreskov Institute of Catalysis during more than two decades. So far only the production of two sizes was possible in large numbers: 50 × 50 and 115 × 115 mm2. This work is devoted to the development of the production technology of large scale aerogel radiators for use in the Ring-imaging Cherenkov (RICH) detectors. These detectors require additional parameters to be controlled for each aerogel tile during production. Procedures of measurement of the aerogel tiles refractive index, the light scattering length, the upper surface flatness are described.

Abstract The fast scintillation crystals such as pure CsI or LYSO(Ce) today are considered for timing measurements in future colliding beam experiments. The aim of such counters is to determine time of particles arrival with accuracy better than 100 ps. The work is devoted to investigation of influence of Cherenkov radiation on the time resolution of the detectors based on LYSO(Ce) crystals. The results of MC simulation and beam test are presented.

In this paper we investigated Cherenkov radiation component influence on the time of charged particle detection in LYSO(Ce) crystals. Description of the experiment setup and Monte Carlo simulation scheme are given. The scintillation and Cherenkov radiation processes in LYSO(Ce) crystal were simulated and studied experimentally with electron beam at Budker Institute of Nuclear Physics beam test facilities. The results of the measurements and simulation are presented. The effect of particle detection time shift due to Cherenkov radiation was obtained. It amounts of several tens of picoseconds for LYSO(Ce) crystal bar (it has dimensions of 3 × 4 × 50 mm3). Beam test results are in good agreement with calculations.

Since 2004 the KEDR detector at the VEPP-4M collider has taken several data sets in the ψ(2S) region, acquiring total luminosity of about 7 pb -1 , which corresponds to more than 3.5 × 10 6 ψ(2S). We report the preliminary value of Γ ee × Γ μμ /Γ = 19.4 ± 0.4 ± 1.1 eV for ψ(2S).

We report results of experiments performed with the KEDR detector at the VEPP-4M e + e - collider. They include final results for the mass and other parameters of the J/ψ, ψ(2S) and ψ(3770) and J/ψ → γη c branching fraction determination.

The KEDR collaboration has taken data for R measurements at energies 3.1–3.7 GeV. Preliminary results from the analysis of these data are presented.

Recent results from the KEDR detector obtained in the charmonium energy range are reported: high-precision measurement of the J/ψ and ψ(2S) masses, study of their leptonic decays and J/ψ → η c γ decay

We report results of experiments performed with the KEDR detector at the VEPP-4M $e^+e^-$ collider. They include final results for the mass and other parameters of the $J/\psi$, $\psi(2S)$ and $\psi(3770)$ and $J/\psi\to\gamma\eta_c$ branching fraction determination.

The particle identification system of the KEDR detector is based on aerogel threshold Cherenkov counters called ASHIPH counters. The system consists of 160 counters arranged in two layers. An event reconstruction program for the ASHIPH system was developed. The position of each counter relative to the tracking system was determined using cosmic muons and Bhabha events. The geometric efficiency of the ASHIPH system was verified with Bhabha events. The efficiency of relativistic particle detection was measured with cosmic muons. A π/K separation of 4δ in the momentum range 0.95 −1.45 GeV/ c was confirmed. A simulation program for the ASHIPH counters has been developed.

Abstract Using the 1.32 $$\hbox {pb}^{-1}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mtext>pb</mml:mtext> <mml:mrow> <mml:mo>-</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> </mml:math> statistics collected at the $$J/\psi $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>J</mml:mi> <mml:mo>/</mml:mo> <mml:mi>ψ</mml:mi> </mml:mrow> </mml:math> peak with the KEDR detector at the VEPP-4M $$e^{+}e^{-\, }$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msup> <mml:mi>e</mml:mi> <mml:mo>+</mml:mo> </mml:msup> <mml:msup> <mml:mi>e</mml:mi> <mml:mrow> <mml:mo>-</mml:mo> <mml:mspace /> </mml:mrow> </mml:msup> </mml:mrow> </mml:math> collider, we measured the branching fractions of $$J/\psi $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>J</mml:mi> <mml:mo>/</mml:mo> <mml:mi>ψ</mml:mi> </mml:mrow> </mml:math> meson decays to the final states 2( $$\pi ^{+}\pi ^{-})\pi ^{0}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msup> <mml:mi>π</mml:mi> <mml:mo>+</mml:mo> </mml:msup> <mml:msup> <mml:mi>π</mml:mi> <mml:mo>-</mml:mo> </mml:msup> <mml:mrow> <mml:mo>)</mml:mo> </mml:mrow> <mml:msup> <mml:mi>π</mml:mi> <mml:mn>0</mml:mn> </mml:msup> </mml:mrow> </mml:math> , $$K^{+}K^{-}\pi ^{+}\pi ^{-}\pi ^{0}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msup> <mml:mi>K</mml:mi> <mml:mo>+</mml:mo> </mml:msup> <mml:msup> <mml:mi>K</mml:mi> <mml:mo>-</mml:mo> </mml:msup> <mml:msup> <mml:mi>π</mml:mi> <mml:mo>+</mml:mo> </mml:msup> <mml:msup> <mml:mi>π</mml:mi> <mml:mo>-</mml:mo> </mml:msup> <mml:msup> <mml:mi>π</mml:mi> <mml:mn>0</mml:mn> </mml:msup> </mml:mrow> </mml:math> , 2( $$\pi ^{+}\pi ^{-})$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msup> <mml:mi>π</mml:mi> <mml:mo>+</mml:mo> </mml:msup> <mml:msup> <mml:mi>π</mml:mi> <mml:mo>-</mml:mo> </mml:msup> <mml:mrow> <mml:mo>)</mml:mo> </mml:mrow> </mml:mrow> </mml:math> and $$K^{+}K^{-}\pi ^{+}\pi ^{-}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msup> <mml:mi>K</mml:mi> <mml:mo>+</mml:mo> </mml:msup> <mml:msup> <mml:mi>K</mml:mi> <mml:mo>-</mml:mo> </mml:msup> <mml:msup> <mml:mi>π</mml:mi> <mml:mo>+</mml:mo> </mml:msup> <mml:msup> <mml:mi>π</mml:mi> <mml:mo>-</mml:mo> </mml:msup> </mml:mrow> </mml:math> . The results obtained for the decays $$J/\psi \rightarrow $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>J</mml:mi> <mml:mo>/</mml:mo> <mml:mi>ψ</mml:mi> <mml:mo>→</mml:mo> </mml:mrow> </mml:math> 2( $$\pi ^{+}\pi ^{-})\pi ^{0}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msup> <mml:mi>π</mml:mi> <mml:mo>+</mml:mo> </mml:msup> <mml:msup> <mml:mi>π</mml:mi> <mml:mo>-</mml:mo> </mml:msup> <mml:mrow> <mml:mo>)</mml:mo> </mml:mrow> <mml:msup> <mml:mi>π</mml:mi> <mml:mn>0</mml:mn> </mml:msup> </mml:mrow> </mml:math> , $$J/\psi \rightarrow K^{+}K^{-}\pi ^{+}\pi ^{-}\pi ^{0}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>J</mml:mi> <mml:mo>/</mml:mo> <mml:mi>ψ</mml:mi> <mml:mo>→</mml:mo> <mml:msup> <mml:mi>K</mml:mi> <mml:mo>+</mml:mo> </mml:msup> <mml:msup> <mml:mi>K</mml:mi> <mml:mo>-</mml:mo> </mml:msup> <mml:msup> <mml:mi>π</mml:mi> <mml:mo>+</mml:mo> </mml:msup> <mml:msup> <mml:mi>π</mml:mi> <mml:mo>-</mml:mo> </mml:msup> <mml:msup> <mml:mi>π</mml:mi> <mml:mn>0</mml:mn> </mml:msup> </mml:mrow> </mml:math> contradict the measurements performed by other groups in the last century, but agree well with recent results of BABAR and BESIII collaborations.

The particle identification system ASHIPH (Aerogel, SHifter, PHotomultiplier) has been working in the KEDR experiment at VEPP-4M collider (Budker INP, Novosibirsk) since 2014. The system consists of 160 counters arranged in two layers and covers the 96% of the solid angle. Two layer system permits to use different approaches for π/K separation. Three such approaches are described. The status of the system is presented. Main system parameters such as BhaBha suppression factor, π/K separation power, relativistic particle detection efficiency were measured with help of cosmic particles and experimental data collected at the peak of J/ψ-meson. π/K separation in the momentum range from 0.95 to 1.45 GeV/c is better than 4 σ. Monte-Carlo simulation procedures are described and results are presented as well.

We review the recent results obtained by the KEDR experiment in the charmonium energy range. They include the measurements of $J/\psi$ meson total and partial widths and exclusive branching fractions, study of $D^+$ and $D^0$ meson masses and R between 1.8 and 7.0 GeV.