Publications

Order by: publication date number of citations

• The mass of the $\pi^+$

  M. Daum , P.-R. Kettle

  SciPost Phys. Proc. 5, 011 (2021) · published 6 September 2021 | Toggle abstract · pdf

  At the Paul Scherrer Institute, the most precise pion mass value was obtained from a precision determination of the muon momentum, $p_{\mu^+}$, in pion decay at rest, $\pi^+ \rightarrow \mu^+ + \nu_{\mu}$. We find $p_{\mu^+} = (29.792\,00 \pm 0.000\,11$ MeV/c and $m_{\pi^+}$ = (139.570\,21 $\pm$ 0.000\,14) MeV/c$^2$. This value is more precise, however, in agreement with the recent compilation of the Particle Data Group for $m_{\pi^-}$. The agreement of $m_{\pi^+}$ with the most precise and recent single measurement, $m_{\pi^-}$ = (139.570\,77 $\pm$ 0.000\,18) MeV/c$^2$ is only fair (2.43 $\sigma$). From our $p_{\mu^+}$ value and using the above mentioned $m_{\pi^-}$ mass and the mass of the muon, $m_{\mu^+} = (105.658\,374\,5 \pm 0.000\,002\,4)$ MeV/c$^2$ we obtain an upper limit for the muon neutrino mass with 90 \%confidence, $m_{\mu_{\nu}} \leq 230$ keV/c$^2$. One also obtains a new quantitative measure of CPT invariance in the pion sector: $(m_{\pi^+} - m_{\pi^-})/m_{\pi}(\mbox{av}) = (-2.9 \pm 2.0)\cdot 10^{-6}$, an improvement by two orders of magnitude.

• The mass of the $\pi^-$

  M. Daum, D. Gotta

  SciPost Phys. Proc. 5, 010 (2021) · published 6 September 2021 | Toggle abstract · pdf

  The most precise values of the mass of the negatively charged pion have been determined from several measurements of X-ray wavelengths for transitions in pionic atoms at PSI. The Particle Data Group gives the average $m_{\pi^-}= (139.570 61 \pm 0.000 24) MeV/c^2$.

  4 citations

• Muonium-Antimuonium Conversion

  Lorenz Willmann, Klaus Jungmann

  SciPost Phys. Proc. 5, 009 (2021) · published 6 September 2021 | Toggle abstract · pdf

  The MACS experiment performed at PSI in the 1990s provided an yet unchallenged upper bound on the probability for a spontaneous conversion of the muonium atom, ${\rm M=}$($\rm{\mu^+e^-}$) , into its antiatom, antimuonium ${\overline{\rm{M}} = }$($\rm{\mu^-e^+})$. It comprises the culmination of a series of measurements at various accelerator laboratories worldwide. The experimental limits on the process have provided input and steering for the further development of a variety of theoretical models beyond the standard theory, in particular for models which address lepton number violating processes and matter-antimatter oscillations. Several models beyond the standard theory could be strongly disfavored. There is interest in a new measurement and improved sensitivity could be reached by exploiting the time evolution of the conversion process, e.g., at intense pulsed muonium sources.

  1 citation

• SINDRUM II

  A. van der Schaaf

  SciPost Phys. Proc. 5, 008 (2021) · published 6 September 2021 | Toggle abstract · pdf

  In 1987 a collaboration including ETHZ - UZH - PSI - RWTH Aachen - Univ. Tbilisi proposed a new search for μe conversion in muonic atoms. The SINDRUM II spectrometer came into operation in the PSI μE1 area in 1989, but a dedicated beam line was delayed until 1998 by technical setbacks.

  2 citations

• The SINDRUM-I Experiment

  Ralph Eichler, Christoph Grab

  SciPost Phys. Proc. 5, 007 (2021) · published 6 September 2021 | Toggle abstract · pdf

  SINDRUM-I was the first nearly 4 spectrometer at SIN. It was initially designed to 9 search for the forbidden decay + ! e+e􀀀e+ , but also successfully studied various 10 other processes with high precision. The upper limit obtained for the branching ratio of B!3e = 􀀀 (+ ! e+e􀀀e+ )=􀀀 (+ ! e+e¯ 11  ) < 1.0  10􀀀12(90% CL) from 1988 is still the best. The first statistically significant observation of the rare decay + ! e+e􀀀e+e¯ 12  , achieved in 1985, yielded a branching ratio of B13 !3e2 = (3.40.20.2)10􀀀5. Several 14 othermeasurements of rare decays were undertaken: the first observation of the -decay 15 + !e+ee􀀀e+ resulted in 􀀀 (+ !e+ee􀀀e+ )=􀀀 (+ !+ ) = (3.2  0.5  0.2)  10􀀀9, 16 also still the best measurement; and a determination of the ratio of the weak axial- to 17 vector-form factor FA=FV = (0.7  0.5), resolving an ambiguity. In addition, upper limits 18 for + ! e+ and + ! e+e with subsequent decay ! e+e􀀀 (search for "massless" Goldstone bosons) and 0 !e+e􀀀 19 < 1.3  10􀀀7 were obtained.

  2 citations

• Muon Decay

  W. Fetscher

  SciPost Phys. Proc. 5, 006 (2021) · published 6 September 2021 | Toggle abstract · pdf

  The decay of the muon has been studied at PSI with several precision measurements: The longitudinal polarization PL(E) with the muon decay parameters ξ′, ξ′′, the Time- Reversal Invariance (TRI) conserving transverse polarization PT1(E) with the muon de- cay parameters η, η′′, the TRI violating transverse polarization PT2(E), with α′/A, β′/A and the muon decay asymmetry with Pμξ. The detailed theoretical analysis of all mea- surements of normal and inverse muon decay has led for the first time to a lower limit |g V | > 0.960 ("V − A") and upper limits for nine other possible complex couplings, espe- cially the scalar coupling |g S | < 0.550 which had not been excluded before.

  1 citation

• A theory vade mecum for PSI experiments

  G. Colangelo, F. Hagelstein, A. Signer, P. Stoffer

  SciPost Phys. Proc. 5, 005 (2021) · published 6 September 2021 | Toggle abstract · pdf

  This article gives a compact introduction and overview of the theory underlying the experiments described in the rest of this review.

  2 citations

• UCN, the ultracold neutron source -- neutrons for particle physics

  Bernhard Lauss, Bertrand Blau

  SciPost Phys. Proc. 5, 004 (2021) · published 6 September 2021 | Toggle abstract · pdf

  Ultracold neutrons provide a unique tool for the study of neutron properties. An overview is given of the ultracold neutron (UCN) source at PSI, which produces the highest UCN intensities to fundamental physics experiments by exploiting the high intensity proton beam in combination with the high UCN yield in solid deuterium at a temperature of 5K. We briefly list important fundamental physics results based on measurements with neutrons at PSI.

  15 citations

• The Meson Production Targets in the high energy beamline of HIPA at PSI

  Daniela Kiselev, Pierre-André Duperrex, Sven Jollet, Stefan Joray, Daniel Laube, Davide Reggiani, Raffaello Sobbia, Vadim Talanov

  SciPost Phys. Proc. 5, 003 (2021) · published 6 September 2021 | Toggle abstract · pdf

  Two target stations in the 590 MeV proton beamline of the High Intensity Proton Accelerator (HIPA) at the Paul Scherrer Institut (PSI) produce pions and muons for seven secondary beamlines, leading to several experimental stations. The two target stations are 18m apart. Target M is a graphite target with an effective thickness of 5mm, Target E is a graphite wheel with a thickness of 40 mm or 60 mm. Due to the spreading of the beam in the thick target, a high power collimator system is needed to shape the beam for further transport. The beam is then transported to either the SINQ target, a neutron spallation source, or stopped in the beam dump, where about 450 kW beam power is dissipated. In the following, the targets, collimators and beam dumps are further described.

  6 citations

• The High Intensity Proton Accelerator Facility

  J. Grillenberger, C. Baumgarten, M. Seidel

  SciPost Phys. Proc. 5, 002 (2021) · published 6 September 2021 | Toggle abstract · pdf

  The High Intensity Proton Accelerator Facility at PSI routinely provides a proton beam with up to $1.4\,\rm{MW}$ power at a kinetic energy of $590\,\rm{MeV}$. The beam is used to generate neutrons in spallation targets and pions in meson production targets. The pions decay into muons and neutrinos, with applications focused on condensed matter research and particle physics at the intensity frontier. This section presents the main physics and technology concepts utilized in the facility. It includes beam dynamics, the control of beam losses and activation, power conversion, efficiency aspects, and performance figures, e.g., the availability of the facility.

  23 citations