arXiv subjects

V. N. Frolov

Publications and source records attributed to V. N. Frolov.

28 records · Page 2Linked to original sources

arXiv2020

Improved limits on a hypothetical X(16.7) boson and a dark photon decaying into $e^+e^-$ pairs

The improved results on a direct search for a new X(16.7 MeV) boson which could explain the anomalous excess of $e^+e^-$ pairs observed in the excited 8Be nucleus decays ("Berillium anomaly") are reported. Due to its coupling to electrons, the X boson could be produced in the bremsstrahlung reaction e-Z -> e-ZX by a high-energy beam of electrons incident on active target in the NA64 experiment at the CERN SPS and observed through its subsequent decay into $e^+e^-$ pair. No evidence for such decays was found from the combined analysis of the data samples with total statistics corresponding to 8.4\times 10^{10} electrons on target collected in 2017 and 2018. This allows to set the new limits on the $X$--$e^-$ coupling in the range 1.2 \times 10^{-4} < ε_e < 6.8 \times 10^{-4}, excluding part of the parameter space favored by the Berillium anomaly. We also set new bounds on the mixing strength of photons with dark photons (A') from non-observation of the decay $A' \to e^+e^-$ of the bremsstrahlung A' with a mass below 24 MeV.

hep-ex↗

arXiv2019

Dark matter search in missing energy events with NA64

A search for sub-GeV dark matter production mediated by a new vector boson $A'$, called dark photon, is performed by the NA64 experiment in missing energy events from 100 GeV electron interactions in an active beam dump at the CERN SPS. From the analysis of the data collected in the years 2016, 2017, and 2018 with $2.84\times10^{11}$ electrons on target no evidence of such a process has been found. The most stringent constraints on the $A'$ mixing strength with photons and the parameter space for the scalar and fermionic dark matter in the mass range $\lesssim 0.2$ GeV are derived, thus demonstrating the power of the active beam dump approach for the dark matter search.

hep-ex↗

arXiv2018

Search for a Hypothetical 16.7 MeV Gauge Boson and Dark Photons in the NA64 Experiment at CERN

We report the first results on a direct search for a new 16.7 MeV boson (X) which could explain the anomalous excess of e+e- pairs observed in the excited Be-8 nucleus decays. Due to its coupling to electrons, the X could be produced in the bremsstrahlung reaction e- Z -> e- Z X by a 100 GeV e- beam incident on an active target in the NA64 experiment at the CERN SPS and observed through the subsequent decay into an e+e- pair. With 5.4\times 10^{10} electrons on target, no evidence for such decays was found, allowing to set first limits on the X-e^- coupling in the range 1.3\times 10^{-4} < ε_e < 4.2\times 10^{-4} excluding part of the allowed parameter space. We also set new bounds on the mixing strength of photons with dark photons (A') from non-observation of the decay A'->e+e- of the bremsstrahlung A' with a mass <~ 23 MeV.

hep-ex↗

arXiv2018

Search for vector mediator of Dark Matter production in invisible decay mode

A search is performed for a new sub-GeV vector boson ($A'$) mediated production of Dark Matter ($χ$) in the fixed-target experiment, NA64, at the CERN SPS. The $A'$, called dark photon, could be generated in the reaction $ e^- Z \to e^- Z A'$ of 100 GeV electrons dumped against an active target which is followed by the prompt invisible decay $A' \to χ\overlineχ$. The experimental signature of this process would be an event with an isolated electron and large missing energy in the detector. From the analysis of the data sample collected in 2016 corresponding to $4.3\times10^{10}$ electrons on target no evidence of such a process has been found. New stringent constraints on the $A'$ mixing strength with photons, $10^{-5}\lesssim ε\lesssim 10^{-2}$, for the $A'$ mass range $m_{A'} \lesssim 1$ GeV are derived. For models considering scalar and fermionic thermal Dark Matter interacting with the visible sector through the vector portal the 90% C.L. limits $10^{-11}\lesssim y \lesssim 10^{-6}$ on the dark-matter parameter $y = ε^2 α_D (\frac{m_χ}{m_{A'}})^4 $ are obtained for the dark coupling constant $α_D = 0.5$ and dark-matter masses $0.001 \lesssim m_χ\lesssim 0.5 $ GeV. The lower limits $α_D \gtrsim 10^{-3} $ for pseudo-Dirac Dark Matter in the mass region $m_χ\lesssim 0.05 $ GeV are more stringent than the corresponding bounds from beam dump experiments. The results are obtained by using tree level, exact calculations of the $A'$ production cross-sections, which turn out to be significantly smaller compared to the one obtained in the Weizsäcker-Williams approximation for the mass region $m_{A'} \gtrsim 0.1$ GeV.

hep-ex↗

arXiv2017

Performance of Multiplexed XY Resistive Micromegas detectors in a high intensity beam

We present the performance of multiplexed XY resistive Micromegas detectors tested in the CERN SPS 100 GeV/c electron beam at intensities up to 3.3 $\times$ 10$^5$ e$^- $/(s$\cdot$cm$^2$). So far, all studies with multiplexed Micromegas have only been reported for tests with radioactive sources and cosmic rays. The use of multiplexed modules in high intensity environments was not explored due to the effect of ambiguities in the reconstruction of the hit point caused by the multiplexing feature. At the beam intensities analysed in this work and with a multiplexing factor of 5, more than 50% level of ambiguity is introduced. Our results prove that by using the additional information of cluster size and integrated charge from the signal clusters induced on the XY strips, the ambiguities can be reduced to a level below 2%. The tested detectors are used in the CERN NA64 experiment for tracking the incoming particles bending in a magnetic field in order to reconstruct their momentum. The average hit detection efficiency of each module was found to be $\sim$ 96% at the highest beam intensities. By using four modules a tracking resolution of 1.1% was obtained with $\sim$ 85% combined tracking efficiency.

physics.ins-det↗

arXiv2017

High purity 100 GeV electron identification with synchrotron radiation

In high energy experiments such as active beam dump searches for rare decays and missing energy events, the beam purity is a crucial parameter. In this paper we present a technique to reject heavy charged particle contamination in the 100 GeV electron beam of the H4 beam line at CERN SPS. The method is based on the detection with BGO scintillators of the synchrotron radiation emitted by the electrons passing through a bending dipole magnet. A 100 GeV $π^-$ beam is used to test the method in the NA64 experiment resulting in a suppression factor of $10^{-5}$ while the efficiency for electron detection is $\sim$95%. The spectra and the rejection factors are in very good agreement with the Monte Carlo simulation. The reported suppression factors are significantly better than previously achieved.

physics.ins-det↗

arXiv2016

Search for invisible decays of sub-GeV dark photons in missing-energy events at the CERN SPS

We report on a direct search for sub-GeV dark photons (A') which might be produced in the reaction e^- Z \to e^- Z A' via kinetic mixing with photons by 100 GeV electrons incident on an active target in the NA64 experiment at the CERN SPS. The A's would decay invisibly into dark matter particles resulting in events with large missing energy. No evidence for such decays was found with 2.75\cdot 10^{9} electrons on target. We set new limits on the γ-A' mixing strength and exclude the invisible A' with a mass < 100 MeV as an explanation of the muon g_μ-2 anomaly.

hep-ex↗

arXiv2005

Proper Motions and CCD-photometry of Stars in the Region of the Open Cluster Trumpler 2

The results of the complex study of galactic open cluster Trumpler 2 are presented. In order to obtain the proper motions the positions of 2600 stars up to the limit magnitude B ~ 16.25 mag in the area 80x80 arcmin around the cluster were measured on 6 plates with the maximal epoch difference of 63 years. The root-mean error of the relative proper motions is 4.2 mas/yr. The catalogue of BV magnitudes of all the stars in the investigated area was compiled. Astrometric selection of the cluster members within the region of R<16 arcmin from the center of the cluster was made by means of the W.Sanders method. In that field 192 stars were found to have the individual membership probability greater then 85%, 148 of them are situated within the +/-3sigma_(B-V) band around the main sequence of the cluster. They are considered to be cluster members by two criteria. The U-B ~ B-V diagram plotted for the astrometrical cluster members by the data taken from the Washington catalogue of the UBV photometry in the galactic cluster fields (Hoag et al.1961) made it possible to redefine the value of the color excess E(B-V)=0.40 mag. The superposition of the MS of the cluster with the ZAMS Schmidt-Kaler leads to the coincidence at the value of the apparent distance module (V-Mv)=10.50 which corresponds to the distance r=725 pc. The luminosity and mass functions of the Trumpler 2 were constructed and the value of the slope Gamma=-1.90+/-0.22 was determined. The cluster age of 8.913x10^7 yr was determined. It is shown that the red giant on the late stage of the evolution (st N.1095) belongs to cluster and indicates the brightness variability. The possibility that the number of both known and recently discovered variables are cluster members was considered. Tables 2,3,3A,5 will be only available in the electronic form.

astro-ph↗

arXiv2002

Memberships and CM Diagrams of the Open Cluster NGC 7243

The results of astrometric and photometric investigations of the open cluster NGC 7243 are presented. Proper motions of 2165 stars with root-mean-square error of 1.1 mas/yr were obtained by means of PDS scanning of astrometric plates covering the time interval of 97 years. A total of 211 cluster members down to V=15.5 mag have been identified. V and B magnitudes have been determined for 2118 and 2110 stars respectively. Estimations of mass (348Mo < M < 522Mo), age (t=2.5x10^8 yr), distance (r=698 pc) and reddening (E(B-V)=0.24) of the cluster NGC 7243 have been made.

astro-ph↗

arXiv2002

Proper Motions and CCD-photometry of Stars in the Region of the Open Cluster NGC 1513

The results of astrometric and photometric investigations of the poorly studied open cluster NGC 1513 are presented. The proper motions of 353 stars with the root-mean-square error of 1.9 mas/yr were obtained by means of the automated measuring complex "Fantasy" scanning of 8 astrometric plates covering the time interval of 101 years. A total of 141 astrometric cluster members have been identified. BV CCD-photometry was made for the stars in a square size 17 arcmin x 17 arcmin centered on cluster. 33 stars with the high reliability were considered to be cluster members by two criteria. The estimation of NGC 1513 age is 2.54 E+08 years. Tables 2 and 3 are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/.

astro-ph↗