Publications

Order by: publication date number of citations

• A spectator-model way to transverse-momentum-dependent gluon distribution functions

  Alessandro Bacchetta, Francesco Giovanni Celiberto, Marco Radici, Pieter Taels

  SciPost Phys. Proc. 8, 040 (2022) · published 12 July 2022 | Toggle abstract · pdf

  We present exploratory analyses of the 3D gluon content of the proton via a study of unpolarized and polarized gluon TMDs at twist-2, calculated in a spectator model for the parent nucleon. Our approach embodies a flexible parametrization for the spectator-mass function, suited to describe both moderate and small-$x$ effects. All these studies can serve as a useful guidance in the investigation of the gluon dynamics inside nucleons and nuclei, which constitutes one of the major goals of new-generation colliding machines, as the EIC, the HL-LHC, NICA, and the FPF.

  10 citations

• The muX project

  Frederik Wauters, Andreas Knecht on behalf of the muX collaboration

  SciPost Phys. Proc. 5, 022 (2021) · published 6 September 2021 | Toggle abstract · pdf

  The muX project is conducting a series of muonic X-ray measurements in medium- and high-Z nuclei at PSI, utilizing a high-purity germanium detector array, in-beam muon detectors, and a modern digital data-acquisition system. A novel hydrogen transfer target was developed, enabling measurements with as little as a few micrograms of target material. First measurements with radioactive Cm and Ra targets were conducted, aimed at determining their nuclear charge radii. These serve as important input for upcoming atomic parity violation experiments. The apparatus is also used to perform a feasibility study of an atomic parity violation experiment with the 2s − 1s muonic X-ray transition. In addition, the setup has been made available for a wider range of nuclear, particle, and solid-state physics measurements.

  9 citations

• Laser spectroscopy of light muonic atoms and the nuclear charge radii

  Aldo Antognini, Franz Kottmann, Randolf Pohl

  SciPost Phys. Proc. 5, 021 (2021) · published 6 September 2021 | Toggle abstract · pdf

  The energy levels of hydrogen-like atomic systems are shifted slightly by the complex structure of the nucleus, in particular by the finite size of the nucleus. These energy shifts are vastly magnified in muonic atoms and ions, i.e. the hydrogen-like systems formed by a negative muon and a nucleus. By measuring the 2S-2P energy splitting in muonic hydrogen, muonic deuterium and muonic helium, we have been able to deduce the p, d, 3He and 4He nuclear charge radii to an unprecedented accuracy. These radii provide benchmarks for hadron and nuclear theories, lead to precision tests of bound- state QED in regular atoms and to a better determination of the Rydberg constant.

  9 citations

• Hadronic light-by-light scattering in the anomalous magnetic moment of the muon

  Nils Asmussen, Antoine Gerardin, Andreas Nyffeler, Harvey B. Meyer

  SciPost Phys. Proc. 1, 031 (2019) · published 20 February 2019 | Toggle abstract · pdf

  Hadronic light-by-light scattering in the anomalous magnetic moment of the muon $a_\mu$ is one of two hadronic effects limiting the precision of the Standard Model prediction for this precision observable, and hence the new-physics discovery potential of direct experimental determinations of $a_\mu$. In this contribution, I report on recent progress in the calculation of this effect achieved both via dispersive and lattice QCD methods.

  9 citations

• DELight: A Direct search Experiment for Light dark matter with superfluid helium

  Belina von Krosigk, Klaus Eitel, Christian Enss, Torben Ferber, Loredana Gastaldo, Felix Kahlhoefer, Sebastian Kempf, Markus Klute, Sebastian Lindemann, Marc Schumann, Francesco Toschi, Kathrin Valerius

  SciPost Phys. Proc. 12, 016 (2023) · published 3 July 2023 | Toggle abstract · pdf

  To reach ultra-low detection thresholds necessary to probe unprecedentedly low Dark Matter masses, target material alternatives and novel detector designs are essential. One such target material is superfluid $^4$He which has the potential to probe so far uncharted light Dark Matter parameter space at sub-GeV masses. The new "Direct search Experiment for Light dark matter", DELight, will be using superfluid helium as active target, instrumented with magnetic micro-calorimeters. It is being designed to reach sensitivity to masses well below 100 MeV in Dark Matter-nucleus scattering interactions.

  9 citations

• Exclusive emissions of rho-mesons and the unintegrated gluon distribution

  Andrèe Dafne Bolognino, Francesco Giovanni Celiberto, Dmitry Yu. Ivanov, Alessandro Papa

  SciPost Phys. Proc. 8, 089 (2022) · published 13 July 2022 | Toggle abstract · pdf

  Exclusive emissions of vector mesons in forward directions of rapidity offer us a faultless chance to probe the proton structure at small-$x$. A high-energy factorization formula is established within BFKL, given as the convolution of an impact factor depicting the forward-meson emission and of an unintegrated gluon distribution (UGD) driving the gluon evolution at small-$x$. As a nonperturbative quantity, the UGD is not well known and several models for it exist. We present recent progresses on the study of the exclusive forward $\rho$-meson leptoproduction at HERA and EIC energies, showing how osbervables sensitive to different polarization states of the $\rho$-particle act as discriminators for the existing UGD models.

  7 citations

• muCool: muon cooling for high-brightness μ+ beams

  Aldo Antognini, David Taqqu

  SciPost Phys. Proc. 5, 030 (2021) · published 6 September 2021 | Toggle abstract · pdf

  A number of experiments with muons are limited by the poor phase space quality of the muon beams currently available. The muCool project aims at developing a phase-space cooling method to transform a surface μ+ beam with 4 MeV energy and 1 cm size into a slow muon beam with eV energy and 1 mm size. In this process the phase space is reduced by a factor of 10^9 − 10^10 with efficiencies of 2 · 10^−5 − 2 · 10^−4 . The beam is then re-accelerated to keV-MeV energies. Such a beam opens up new avenues for research in fundamental particle physics with muons and muonium atoms as well as in the field of μSR spectroscopy.

  7 citations

• A no-go theorem for non-standard explanations of the $\tau\to K_S\pi\nu_\tau$ CP asymmetry

  Vincenzo Cirigliano, Andreas Crivellin, Martin Hoferichter

  SciPost Phys. Proc. 1, 007 (2019) · published 18 February 2019 | Toggle abstract · pdf

  A new tensor interaction is the only possibility to explain the $2.8\sigma$ tension observed by the BaBar collaboration in the CP asymmetry in $\tau\to K_S\pi\nu_\tau$ with physics beyond the Standard Model (BSM) realized above the electroweak scale. However, the strong phase generated by the interference between vector and tensor phases is suppressed by at least two orders of magnitude due to Watson's final-state-interaction theorem, and the strength of the CP-violating tensor interaction is strongly constrained by bounds from the neutron electric dipole moment and $D$-$\bar{D}$ mixing. As a result, a confirmation of the tension at Belle II would point to light BSM physics.

  7 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

• Why space could be quantised on a different scale to matter

  Matthew J. Lake

  SciPost Phys. Proc. 4, 014 (2021) · published 13 August 2021 | Toggle abstract · pdf

  The scale of quantum mechanical effects in matter is set by Planck's constant, $\hbar$. This represents the quantisation scale for material objects. In this article, we present a simple argument why the quantisation scale for space, and hence for gravity, may not be equal to $\hbar$. Indeed, assuming a single quantisation scale for both matter and geometry leads to the `worst prediction in physics', namely, the huge difference between the observed and predicted vacuum energies. Conversely, assuming a different quantum of action for geometry, $\beta \ll \hbar$, allows us to recover the observed density of the Universe. Thus, by measuring its present-day expansion, we may in principle determine, empirically, the scale at which the geometric degrees of freedom should be quantised.

  6 citations