# NA63 Papers

2023-01-26
08:56
 Precision Measurement of Trident Production in Strong Electromagnetic Fields / Nielsen, Christian F. (Aarhus U.) ; Holtzapple, Robert (Cal. Poly.) ; Lund, Mads M. (Aarhus U.) ; Surrow, Jeppe H. (Aarhus U.) ; Sørensen, Marc B. (Aarhus U.) ; Uggerhøj, Ulrik I. (Aarhus U.) /NA63 Collaboration We demonstrate experimentally that the trident process $e^-\rightarrow e^-e^+e^-$ in a strong external field, with a spatial extension comparable to the effective radiation length, is well understood theoretically. The experiment, conducted at CERN, probes values for the strong field parameter $\chi$ up to 2.4. [...] arXiv:2211.02390.- 2023-02-14 - 5 p. - Published in : Phys. Rev. Lett. 130 (2023) 071601 Fulltext: 2211.02390 - PDF; Publication - PDF;

2021-08-19
06:36
 Experimental verification of the Landau–Lifshitz equation / Nielsen, C F (Aarhus U.) ; Justesen, J B (Aarhus U.) ; Sørensen, A H (Aarhus U.) ; Uggerhøj, U I (Aarhus U.) ; Holtzapple, R (Cal. Poly.) /CERN NA63 Collaboration The Landau–Lifshitz (LL) equation has been proposed as the classical equation to describe the dynamics of a charged particle in a strong electromagnetic field when influenced by radiation reaction. Until recently, there has been no clear experimental verification. [...] 2021 - 8 p. - Published in : New J. Phys. 23 (2021) 085001 Fulltext: PDF;

2018-03-23
11:42
 Measurements and theories of the King–Perkins–Chudakov effect / Thomsen, H D (Aarhus U., ISA) ; Uggerhøj, U I (Aarhus U.) We discuss the available experimental results, based on cosmic rays as well as laboratory measurements, for the King–Perkins–Chudakov (KPC) effect where pairs – when detected close to the creation vertex – suffer a reduced energy loss due to the internal screening of the charges constituting the pair. It is shown that the overall best description of data is obtained from the original theoretical expression by Chudakov based on classical electrodynamics, or the semi-classical extension by Burkhardt. [...] 2011 - 6 p. - Published in : Nucl. Instrum. Methods Phys. Res., B 269 (2011) 1919-1924

2018-03-23
11:41
 Radiation emission as a virtually exact realization of Heisenbergs microscope / Andersen, K K (Aarhus U.) ; Brock, S (Aarhus U. (main)) ; Esberg, J (Aarhus U.) ; Thomsen, H D (Aarhus U.) ; Uggerhøj, U I (Aarhus U.) Through the concept of ‘formation length’, recently observed directly in the radiation emission from ultrarelativistic electrons and an essential component in the interpretation of strong field radiation from electrons penetrating single crystals, we discuss the indeterminacy in the location of radiation emission. The analogy with the indeterminacy in the Heisenberg microscope Gedanken experiment is demonstrated from a number of viewpoints to be almost exact. [...] 2013 - 5 p. - Published in : Nucl. Instrum. Methods Phys. Res., B 315 (2013) 278-282

2018-03-23
11:41
 Vacuum birefringence by Compton backscattering through a strong field / Wistisen, Tobias N (Aarhus U.) ; Uggerhøj, Ulrik I (Aarhus U.) We propose a novel scheme to measure nonlinear effects in electrodynamics arising from QED corrections. Our theoretical starting point is the Heisenberg-Euler-Schwinger effective Lagrangian which predicts that a vacuum with a strong static electromagnetic field turns birefringent. [...] 2013 - 6 p. - Published in : Phys. Rev. D 88 (2013) 053009

2018-03-23
11:41
 Implementation of the LPM effect in the discrete-bremsstrahlung simulation of GEANT3 and GEANT4 / Mangiarotti, A (LIP, Coimbra) ; Ballestrero, S (Witwatersrand U.) ; Sona, P (Florence U.) ; Uggerhoj, Ulrik Ingerslev (Aarhus U.) Experimental data, recently measured at CERN, on the LPM effect have been used to benchmark the description of the discrete bremsstrahlung incorporated into the GEANT 3 and GEANT 4 codes. The limited accuracy of the native versions required a major revision in the framework of the original Migdal theory. [...] 2008 - 7 p. - Published in : Nucl. Instrum. Methods Phys. Res., B 266 (2008) 5013-5019

2018-03-16
08:03
 Experimental evidence of quantum radiation reaction in aligned crystals / Wistisen, Tobias N. (Aarhus U.) ; Di Piazza, Antonino (Heidelberg, Max Planck Inst.) ; Knudsen, Helge V. (Aarhus U.) ; Uggerhøj, Ulrik I. (Aarhus U.) Radiation reaction is the influence of the electromagnetic field emitted by a charged particle on the dynamics of the particle itself. Here we report experimental radiation emission spectra from ultrarelativistic positrons in silicon in a regime where both quantum and radiation-reaction effects dominate the dynamics of the positrons. [...] arXiv:1704.01080.- 2018-02-23 - 14 p. - Published in : Nature Commun. 9 (2018) 795 Fulltext: arXiv:1704.01080 - PDF; s41467-018-03165-4 - PDF;

2016-03-02
14:24
 Measurements of the spectral location of the structured target resonance for ultrarelativistic electrons / CERN NA63 Collaboration 2014 - 6 p. - Published in : Phys. Lett. B 732 (2014) 309-314 Elsevier Open Access article: PDF;

2015-03-25
18:44
 Investigation of classical radiation reaction with aligned crystals / Di Piazza, A. (Heidelberg, Max Planck Inst.) ; Wistisen, Tobias N. (Aarhus U.) ; Uggerhøj, Ulrik I. (Aarhus U.) Classical radiation reaction is the effect of the electromagnetic field emitted by an accelerated electric charge on the motion of the charge itself. The self-consistent underlying classical equation of motion including radiation-reaction effects, the Landau-Lifshitz equation, has never been tested experimentally, in spite of the first theoretical treatments of radiation reaction having been developed more than a century ago. [...] arXiv:1503.05717.- 2017-02-10 - 5 p. - Published in : Phys. Lett. B 765 (2017) 1-5 Article from SCOAP3: PDF; Fulltext: PDF; External link: Preprint

2013-09-24
04:13
 Experimental investigation of the Landau-Pomeranchuk-Migdal effect in low-Z targets / Andersen, K.K. (Aarhus U.) ; Andersen, S.L. (Aarhus U.) ; Esberg, J. (CERN) ; Knudsen, H. (Aarhus U.) ; Mikkelsen, R.E. (Aarhus U.) ; Uggerhøj, U.I. (Aarhus U.) ; Wistisen, T.N. (Aarhus U.) ; Sona, P. (Florence U.) ; Mangiarotti, A. (Sao Paulo U.) ; Ketel, T.J. (Vrije U., Amsterdam) /CERN NA63 Collaboration In the CERN NA63 collaboration we have addressed the question of the potential inadequacy of the commonly used Migdal formulation of the Landau-Pomeranchuk-Migdal (LPM) effect by measuring the photon emission by 20 and 178 GeV electrons in the range 100 MeV - 4 GeV, in targets of LowDensityPolyEthylene (LDPE), C, Al, Ti, Fe, Cu, Mo and, as a reference target, Ta. For each target and energy, a comparison between simulated values based on the LPM suppression of incoherent bremsstrahlung is shown, taking multi-photon effects into account. [...] arXiv:1309.5765.- 2013-10-15 - 8 p. - Published in : Phys. Rev. D 88 (2013) 072007 APS published version, local copy: PDF; Fulltext: PDF; External link: Preprint