Publications

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Mulan: a part-per-million measurement of the muon lifetime and determination of the Fermi constant

R. Carey, T. Gorringe, D.W. Hertzog

SciPost Phys. Proc. 5, 016 (2021) · published 6 September 2021 | · pdf

The part-per-million measurement of the positive muon lifetime and determination of the Fermi constant by the MuLan experiment at the Paul Scherrer Institute is reviewed. The experiment used an innovative, time-structured, surface muon beam and a near-4π, finely-segmented, plastic scintillator positron detector. Two in-vacuum muon stopping targets were used: a ferromagnetic foil with a large internal magnetic field, and a quartz crystal in a moderate external magnetic field. The experiment acquired a dataset of 1.6e12 positive muon decays and obtained a muon lifetime τ_µ = 2 196 980.3(2.2) ps (1.0 ppm) and Fermi constant G_F = 1.166 378 7(6) × 10−5 GeV^−2 (0.5 ppm). The thirty fold improvement in τ_µ has proven valuable for precision measurements in nuclear muon capture and the commensurate improvement in G_F has proven valuable for precision tests of the standard model.

2 citations
Virial expansion coefficients in the unitary Fermi gas

Shimpei Endo

SciPost Phys. Proc. 3, 049 (2020) · published 27 February 2020 | · pdf

Virial expansion is widely used in cold atoms to analyze high temperature strongly correlated many-body systems. As the n-th order virial expansion coefficient can be accurately obtained by exactly solving up to n-body problems, the virial expansion offers a few-body approach to study strongly correlated many-body problems. In particular, the virial expansion has successfully been applied to unitary Fermi gas. We review recent progress of the virial expansion studies in the unitary Fermi gas, in particular the fourth order virial coefficient.

2 citations
Short range nucleon correlations studied with electron and photon probes

I.J. Douglas MacGregor

SciPost Phys. Proc. 3, 010 (2020) · published 24 February 2020 | · pdf

This paper reviews experimental research into two- and three-body nucleon-nucleon interactions, carried out by the University of Glasgow Nuclear Physics research group. A key aim of these studies has been to elucidate the role of short-range nucleon-nucleon correlations (SRC). Studies of photon-induced two- and three-nucleon emission reactions from a range of light nuclei, carried out at the 840 MeV Mainz electron microtron MAMI-B, have provided detailed information on the contributing mechanisms. More recent electron scattering studies at the 6.0 GeV Jefferson Laboratory have probed SRC at high values of Q2 and xB and suggested a connection between SRC and the EMC effect.

2 citations
MEG: Muon to Electron and Gamma

A.M. Baldini, T. Mori

SciPost Phys. Proc. 5, 019 (2021) · published 6 September 2021 | · pdf

The possible existence of the muon to electron and gamma decay predicted by many new physics scenarios is investigated by stopping positive muons in a very thin target and measuring emitted photons and positrons with the best possible resolutions. Photons are measured by a 2.7 ton ultra pure liquid xenon detector while positron trajectories are measured in a specially designed gradient magnetic field by low-mass drift chambers and precisely timed by scintillation counters. A first phase of the experiment (MEG) ended in 2016, and excluded the existence of the decay with branching ratios larger than 4.2x10**(-13) (90% C.L.). This provides approximately 30 times stronger constraints on a variety of new physics models than previous experiments. In the second phase (MEG II), most of the detectors have been upgraded by adopting up-to-date technologies to improve the search sensitivity by another order of magnitude down to O(10**(-19) ). MEG II will pursue new physics beyond the Standard Model complementary to high energy collider experiments with a compatible or even higher sensitivity.

2 citations
Recent results of laser spectroscopy experiments of pionic helium atoms at PSI

M. Hori, H. Aghai-Khozani, A. S\'ot\'er, A. Dax, D. Barna

SciPost Phys. Proc. 5, 026 (2021) · published 6 September 2021 | · pdf

A review of a recent experiment carried out at PSI involving laser spectroscopy of metastable pionic helium ($\pi{\rm ^4He}^+\equiv\pi^{-}+{\rm ^4He}^{2+}+e^-$) atoms is presented. An infrared transition $(n,\ell)=(17,16)$$\rightarrow$$(17,15)$ at a resonance frequency of $\nu\approx 183760$ GHz was detected.

2 citations
MuSun - Muon Capture on the Deuteron

P. Kammel on behalf of the MuSun collaboration

SciPost Phys. Proc. 5, 018 (2021) · published 6 September 2021 | · pdf

The MuSun experiment is a precision measurement of the rate for nuclear muon capture on the deuteron, designed to resolve a long-standing disagreement between experiment and theory, and to determine an important low-energy constant relevant for a variety of weak and strong dynamics. The experiment is based on a novel active target method employing a pure deuterium cryogenic time-projection chamber. The data taking was completed in two main campaigns and the analysis is well advanced. The unique chal- lenges and corresponding strategy of the experiment as well as the status of the analysis are presented.

2 citations
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 | · pdf

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

2 citations
Integrability for Feynman integrals

Florian Loebbert

SciPost Phys. Proc. 14, 008 (2023) · published 23 November 2023 | · pdf

We give a brief overview of the Yangian symmetry of Feynman integrals. After a short introduction to the Yangian and integrability, we motivate the emergence of integrable structures for Feynman integrals via the fishnet limit of AdS/CFT. We discuss the resulting Yangian differential equations for massless fishnets in four dimensions as well as generalizations to massive propagators and generic dimensions. We also comment on the relation to momentum space conformal symmetry and on examples in dimensional regularization. Finally we sketch the recent application to fishnet integrals in two spacetime dimensions and the curious identification of Yangian invariants with period integrals of Calabi-Yau geometries.

2 citations
On the unexpected fate of scientific ideas: An archeology of the Carroll group

Jean-Marc Lévy-Leblond

SciPost Phys. Proc. 14, 006 (2023) · published 23 November 2023 | · pdf

In 1965, I published a paper, exhibiting a hitherto unknown limit of the Lorentz group, which I christened "Carroll group" due to its seemingly paradoxical physical contents. Since I saw it as more curious than relevant, I published it in French in a journal somewhat afar from the mainstream of theoretical physics at that time. It was most gratifying to witness the quite unexpected favour this paper started to enjoy half a century later, so much that a so-called "Carrollian physics" is now developing, with applications in various domains of forefront theoretical physics, such as quantum gravitation, supersymmetry, string theory, etc. I offer this narrative as an example of the very diverse time scales with which scientific ideas may develop — or not.

2 citations
Phenomenological extraction of a universal TMD fragmentation function from single hadron production in $e^+ e^-$ annihilations

M. Boglione, J.O. Gonzalez-Hernandez, A. Simonelli

SciPost Phys. Proc. 8, 139 (2022) · published 14 July 2022 | · pdf

Factorizing the cross section for single hadron production in $e^+e^-$ annihilations, differential in $z_h$, $P_T$ and thrust, is a highly non trivial task. We have devised a factorization scheme that allows us to recast the $e^+e^- \to hX$ cross section in the convolution of a calculable hard coefficient and a universal Transverse Momentum Dependent (TMD) Fragmentation Function (FF). The predictions obtained from our NLO-LL perturbative computation, together with a simple ansatz to model the non-perturbative part of the TMD, are applied to the experimental measurements of the BELLE Collaboration for the phenomenological extraction of this process independent TMD FF.

2 citations

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