arXiv subjects

A. S. Korenchenko

Publications and source records attributed to A. S. Korenchenko.

15 recordsLinked to original sources

arXiv2018

PEN experiment: a precise test of lepton universality

With few open channels and uncomplicated theoretical description, charged pion decays are uniquely sensitive to certain standard model (SM) symmetries, the universality of weak fermion couplings, and to aspects of pion structure and chiral dynamics. We review the current knowledge of the pion electronic decay $π^+ \to e^+ ν_e(γ)$, or $π_{e2(γ)}$, and the resulting limits on non-SM processes. Focusing on the PEN experiment at the Paul Scherrer Institute (PSI), Switzerland, we examine the prospects for further improvement in the near term.

hep-ex↗

arXiv2017

PEN: a low energy test of lepton universality

Allowed charged $π$ meson decays are characterized by simple dynamics, few available decay channels, mainly into leptons, and extremely well controlled radiative and loop corrections. In that sense, pion decays represent a veritable triumph of the standard model (SM) of elementary particles and interactions. This relative theoretical simplicity makes charged pion decays a sensitive means for testing the underlying symmetries and the universality of weak fermion couplings, as well as for studying pion structure and chiral dynamics. Even after considerable recent improvements, experimental precision is lagging far behind that of the theoretical description for pion decays. We review the current state of experimental study of the pion electronic decay $π^+ \to e^+ν_e(γ)$, or $π_{e2(γ)}$, where the $(γ)$ indicates inclusion and explicit treatment of radiative decay events. We briefly review the limits on non-SM processes arising from the present level of experimental precision in $π_{e2(γ)}$ decays. Focusing on the PEN experiment at the Paul Scherrer Institute (PSI), Switzerland, we examine the prospects for further improvement in the near term.

hep-ex↗

arXiv2015

2-D straw detectors with high rate capability

Precise measurement of straw axial coordinate (along the anode wire) with accuracy compatible with straw radial coordinate determination by drift time measurement and increase of straw detector rate capability by using straw cathode readout instead of anode readout are presented.

physics.ins-det↗

arXiv2014

New results in rare allowed muon and pion decays

Simple dynamics, few available decay channels, and highly controlled radiative and loop corrections, make pion and muon decays a sensitive means of exploring details of the underlying symmetries. We review the current status of the rare decays: pi+ -> e+ nu, pi+ -> e+ nu gamma, pi+ -> pi0 e+ nu, and mu+ -> e+ nu nu-bar gamma. For the latter we report new preliminary values for the branching ratio B(E_gamma >10 MeV, theta_(e-gamma) > 30deg) = 4.365 (9)_stat (42)_syst x 10^{-3}, and the decay parameter eta-bar = 0.006 (17)_stat (18)_syst, both in excellent agreement with standard model predictions. We review recent measurements, particularly by the PIBETA and PEN experiments, and near-term prospects for improvement. These and other similar precise low energy studies complement modern collider results materially.

nucl-ex↗

arXiv2013

The use of segmented cathode of a drift tube for designing a track detector with a high rate capability

Detector rate capability is one of the main parameters for designing a new detector for high energy physics due to permanent rise of the beam luminosity of modern accelerators. One of the widely used detectors for particle track reconstruction is a straw detector based on drift tubes. The rate capability of such detectors is limited by the parameters of readout electronics. The traditional method of increasing detector rate capability is increasing their granularity (a number of readout channels) by reducing the straw diameter and/or by dividing the straw anode wire into two parts (for decreasing the rate per readout channel). A new method of designing straw detectors with a high rate capability is presented and tested. The method is based on dividing the straw cathode into parts and independent readout of each part.

physics.ins-det↗

arXiv2012

New studies of allowed pion and muon decays

Building on the rare pion and muon decay results of the PIBETA experiment, the PEN collaboration has undertaken a precise measurement of B_{πe2} = R^π_{e/μ}, the π^+ -> e^+ν(γ) decay branching ratio, at the Paul Scherrer Institute, to reduce the present 40\times experimental precision lag behind theory to ~ 6-7\times. Because of large helicity suppression, R^π_{e/μ} is uniquely sensitive to contributions from non-(V-A) physics, making this decay a particularly suitable subject of study. Even at current precision, the experimental value of B_{πe2} provides the most accurate test of lepton universality available. During runs in 2008-10, PEN has accumulated over 2\times 10^7 π_{e2} events; a comprehensive maximum-likelihood analysis is currently under way. The new data will also lead to improved precision of the earlier PIBETA results on radiative πand μdecays.

hep-ex↗

arXiv2012

Using the cathode surface of straw tube for measuring the track coordinates along the wire

The coordinate detectors based on straw tubes provide a high accuracy of the radial coordinate measurement using the drift time and a small amount of matter in the way of the measured particles. However, the measurement of the coordinate along the wire constitutes a problem. This paper proposes a method for measuring the hit coordinate along the wire with an accuracy better than 1 mm in a straw tube detector using the signals from the cathodes of the detector.

physics.ins-det↗

arXiv2011

Detector with a profile-based cathode and a two-coordinate pad-strip readout system

A detector with a profile-based cathode and a pad-strip cathode readout system is experimentally investigated. Cathode pads arranged along each anode wire are diagonally interconnected and form strips that cross the detector at an angle with respect to the anode wire. Two coordinates from the cathodes and one from the anode wire allow identification of tracks in high multiplicity events with a single detector plane.

physics.ins-det↗

arXiv2009

PEN: a sensitive search for non-(V-A) weak processes

A new measurement of $B_{πe2}$, the $π^+ \to e^+ν(γ)$ decay branching ratio, is currently under way at the Paul Scherrer Institute. The present experimental result on $B_{πe2}$ constitutes the most accurate test of lepton universality available. The accuracy, however, still lags behind the theoretical precision by over an order of magnitude. Thanks to the large helicity suppression of $π_{e2}$ decay, the branching ratio is susceptible to significant contributions from new physics, making this decay a particularly suitable subject of study.

hep-ex↗

arXiv2009

PEN experiment: a precise measurement of the pi+ -> e+ nu decay branching fraction

A new measurement of $B_{πe2}$, the $π^+ \to e^+ν(γ)$ decay branching ratio, is currently under way at the Paul Scherrer Institute. The present experimental result on $B_{πe2}$ constitutes the most accurate test of lepton universality available. The accuracy, however, still lags behind the theoretical precision by over an order of magnitude. Because of the large helicity suppression of the $π_{e2}$ decay, its branching ratio is susceptible to significant contributions from new physics, making this decay a particularly suitable subject of study.

hep-ex↗

arXiv2009

New Precise Measurement of the Pion Weak Form Factors in the Pi+ -> e+ nu gamma Decay

We have measured the $π^+\to {\rm e}^+νγ$ branching ratio over a wide region of phase space, based on a total of 65,460 events acquired using the PIBETA detector. Minimum-$χ^2$ fits to the measured $(E_{e^+},E_γ)$ energy distributions result in the weak form factor value of $F_A=0.0119(1)$ with a fixed value of $F_V=0.0259$. An unconstrained fit yields $F_V=0.0258(17)$ and $F_A=0.0117(17)$. In addition, we have measured $a=0.10(6)$ for the dependence of $F_V$ on $q^2$, the ${\rm e}^{+}ν$ pair invariant mass squared, parametrized as $F_V(q^2)=F_V(0)(1+a\cdot q^2)$. The branching ratio for the kinematic region $E_γ> 10 $MeV and $θ_{{\rm e^+}γ} > 40^\circ $ is measured to be $B^{\rm exp}=73.86(54) \times 10^{-8}$. Earlier deviations we reported in the high-$E_γ$/low-$E_{{\rm e}^+}$ kinematic region are resolved, and we find full compatibility with CVC and standard $V$$-$$A$ calculations without a tensor term. We also derive new values for the pion polarizability, $α_E = \rm 2.78(10) \times 10^{-4} fm^3$, and neutral pion lifetime, $τ_{π0} = (8.5 \pm 1.1) \times 10^{-17} $s.

hep-ex↗

arXiv2008

Precise Measurement of pi+ -> e+ nu Branching Ratio

The PEN Collaboration is conducting a new measurement of the pi+ -> e+ nu branching ratio at the Paul Scherrer Institute, with the goal uncertainty of delta B/B(pie2)=5E-4 or lower. At present, the combined accuracy of all published pie2 decay measurements lags behind the theoretical calculation by a factor of 40. In this contribution we report on the PEN detector configuration and its performance during two development runs done in 2007 and 2008.

hep-ex↗

arXiv2004

Precise Measurement of the Pi+ -> Pi0 e+ nu Branching Ratio

Using a large acceptance calorimeter and a stopped pion beam we have made a precise measurement of the rare Pi+ -> Pi0 e+ Nu,(pi_beta) decay branching ratio. We have evaluated the branching ratio by normalizing the number of observed pi_beta decays to the number of observed Pi+ -> e+ Nu, (pi_{e2}) decays. We find the value of Gamma(Pi+ -> Pi0 e+ Nu)/Gamma(total) = [1.036 +/- 0.004(stat.) +/- 0.004(syst.) +/- 0.003(pi_{e2})] x 10^{-8}$, where the first uncertainty is statistical, the second systematic, and the third is the pi_{e2} branching ratio uncertainty. Our result agrees well with the Standard Model prediction.

hep-ex↗

arXiv2003

Precise Measurement of the Pion Axial Form Factor in the Pi+ -> e+ nu gamma Decay

We have studied radiative pion decays Pi+ -> e+ nu gamma in three broad kinematic regions using the PIBETA detector and a stopped pion beam. Based on Dalitz distributions of 42,209 events we have evaluated absolute Pi -> e nu gamma branching ratios in the three regions. Minimum chi^2 fits to the integral and differential (E(e+),E(gamma)) distributions result in the axial-to-vector weak form factor ratio of gamma = F_A/F_V = 0.443(15),or F_A = 0.0115(4) with F_V = 0.0259. However, deviations from Standard Model predictions in the high-E(gamma)/low-E(e+) kinematic region indicate the need for further theoretical and experimental work.

hep-ex↗

arXiv2003

Design, Commissioning and Performance of the PIBETA Detector at PSI

We describe the design, construction and performance of the PIBETA detector built for the precise measurement of the branching ratio of pion beta decay, pi+ -> pi0 e+ nu, at the Paul Scherrer Institute. The central part of the detector is a 240-module spherical pure CsI calorimeter covering 3*pi sr solid angle. The calorimeter is supplemented with an active collimator/beam degrader system, an active segmented plastic target, a pair of low-mass cylindrical wire chambers and a 20-element cylindrical plastic scintillator hodoscope. The whole detector system is housed inside a temperature-controlled lead brick enclosure which in turn is lined with cosmic muon plastic veto counters. Commissioning and calibration data were taken during two three-month beam periods in 1999/2000 with pi+ stopping rates between 1.3*E3 pi+/s and 1.3*E6 pi+/s. We examine the timing, energy and angular detector resolution for photons, positrons and protons in the energy range of 5-150 MeV, as well as the response of the detector to cosmic muons. We illustrate the detector signatures for the assorted rare pion and muon decays and their associated backgrounds.

hep-ex↗